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Study on transient photocurrent induced by energy level defect of schottky diode irradiated by high power pulsed laser. Sci Rep 2023; 13:14487. [PMID: 37660183 PMCID: PMC10475039 DOI: 10.1038/s41598-023-40983-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Accepted: 08/19/2023] [Indexed: 09/04/2023] Open
Abstract
The transient photocurrent is one of the key parameters of the spatial radiation effect of photoelectric devices, and the energy level defect affects the transient photocurrent. In this paper, by studying the deep level transient spectrum of a self-designed Schottky diode, the defect properties of the interface region of the anode metal AlCu and Si caused by high-temperature annealing at 150 ℃, 200 ℃ and 300 ℃ for 1200 h have been quantitatively analyzed. The study shows that the defect is located at the position of + 0.41 eV on the valence band, the concentration is 2.8 [Formula: see text] 1013/cm2, and the capture cross section is [Formula: see text] = 8.5 [Formula: see text] 1017. The impurity energy level mainly comes from the diffusion of Al atom in anode metal. We found that the defect did not cause the electrical performance degradation and obvious morphology change of the device, but the transient photocurrent increased significantly. The reason is that the high temperature treatment results in a growth in the density of states at the interface between AlCu-Si. The more mismatched dislocations and recombination center increased the reverse current of the heterojunction. The above view is proved by the TCAD simulation test.
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Azimuthal Correlations within Exclusive Dijets with Large Momentum Transfer in Photon-Lead Collisions. PHYSICAL REVIEW LETTERS 2023; 131:051901. [PMID: 37595238 DOI: 10.1103/physrevlett.131.051901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 11/11/2022] [Accepted: 02/15/2023] [Indexed: 08/20/2023]
Abstract
The structure of nucleons is multidimensional and depends on the transverse momenta, spatial geometry, and polarization of the constituent partons. Such a structure can be studied using high-energy photons produced in ultraperipheral heavy-ion collisions. The first measurement of the azimuthal angular correlations of exclusively produced events with two jets in photon-lead interactions at large momentum transfer is presented, a process that is considered to be sensitive to the underlying nuclear gluon polarization. This study uses a data sample of ultraperipheral lead-lead collisions at sqrt[s_{NN}]=5.02 TeV, corresponding to an integrated luminosity of 0.38 nb^{-1}, collected with the CMS experiment at the LHC. The measured second harmonic of the correlation between the sum and difference of the two jet transverse momentum vectors is found to be positive, and rising, as the dijet transverse momentum increases. A well-tuned model that has been successful at describing a wide range of proton scattering data from the HERA experiments fails to describe the observed correlations, suggesting the presence of gluon polarization effects.
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Hemodynamics of acute decompensated heart failure in patients with very low NP levels. Eur Heart J 2022. [DOI: 10.1093/eurheartj/ehac544.812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Abstract
Background/Introduction
Natriuretic Peptides are hormones secreted by the heart in response to cardiomyocyte stretch. The principal biological action of NP is natriuresis, diuresis and vasodilation. These are salutary effects in acute decompensated heart failure (ADHF). Some patients admitted with ADHF have very low NP levels. It is unknown if this is due to a defect in biosynthesis or inadequate stimulation.
Purpose
We analyzed data from the National heart Lung and Blood institute sponsored ESCAPE trial which included patients admitted with acute decompensated heart failure who underwent hemodynamic assessment with pulmonary artery catheters at admission and after diuresis. Our aim was to evaluate if there were characteristic hemodynamic findings among patients with very low NP levels at admission which differed from those who had elevated NP levels at admission.
Methods
We performed a secondary analysis of the ESCAPE Trial. We defined very low BNP as patients with BNP level at admission <50 pg/mL. We then compared baseline characteristics between the groups. Continuous groups were compared using X-square test, and Categorical variables were compared using Wilcoxon-signed-Rank-Sum test. We compared groups by Demographic, Anthropometric, Laboratory, and Functional status. We then performed propensity matching on Age, Sex, and BMI and then compared groups.
Results
25/351 patients had very low BNP (<50pg/mL). Patients in the low BNP group had higher BMI than those with elevated BNP (35.8 vs. 28.9 p<0.001). The cohort with low BNP was younger. (50.2 vs. 56.4 p=0.029). In propensity matched cohorts of Age, Sex, BMI. Cardiac output was elevated in the low BNP cohort. (5.2 vs. 3.9 p=0.011). However, Cardiac Index was similar between the groups (2.2 vs. 2.0 p=0.244). Patients in the Low NP group had lower pulmonary capillary wedge pressure (PCWP) compared to those with elevated BNP. (16.5 vs. 25.4 p=0.023). The groups had similar RA pressures (11.5 vs. 13.0 p=0.515). The calculated transmural pressure (PCWP – RA pressure) was lower in the low NP group. There was a reduction in BNP levels at discharge among the group with elevated BNP at admission (1072.6 (baseline) 798.8 (discharge)) In the low BNP group there was an increase in BNP at time of discharge (20.2 (baseline) to 172.7 (discharge)). In follow-up, the low BNP group had reduction in BNP compared to their discharge levels. The group with elevated BNP had elevated BNP at follow-up in 3 and 6 months. Length of stay was shorter in the Low BNP group (6.2 vs. 8.8, p=0.052).
Conclusion(s)
In this secondary analysis of the ESCAPE trial, we find that those patients admitted with ADHF who have unexpectedly low BNP have lower transmural pressures at baseline compared to those who have elevated BNP levels. This suggests that there may not be adequate stimulus for cardiac wall distention and release of BNP.
Funding Acknowledgement
Type of funding sources: None.
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First Search for Exclusive Diphoton Production at High Mass with Tagged Protons in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2022; 129:011801. [PMID: 35841572 DOI: 10.1103/physrevlett.129.011801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 05/09/2022] [Accepted: 05/16/2022] [Indexed: 06/15/2023]
Abstract
A search for exclusive two-photon production via photon exchange in proton-proton collisions, pp→pγγp with intact protons, is presented. The data correspond to an integrated luminosity of 9.4 fb^{-1} collected in 2016 using the CMS and TOTEM detectors at a center-of-mass energy of 13 TeV at the LHC. Events are selected with a diphoton invariant mass above 350 GeV and with both protons intact in the final state, to reduce backgrounds from strong interactions. The events of interest are those where the invariant mass and rapidity calculated from the momentum losses of the forward-moving protons match the mass and rapidity of the central, two-photon system. No events are found that satisfy this condition. Interpreting this result in an effective dimension-8 extension of the standard model, the first limits are set on the two anomalous four-photon coupling parameters. If the other parameter is constrained to its standard model value, the limits at 95% confidence level are |ζ_{1}|<2.9×10^{-13} GeV^{-4} and |ζ_{2}|<6.0×10^{-13} GeV^{-4}.
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Using Z Boson Events to Study Parton-Medium Interactions in Pb-Pb Collisions. PHYSICAL REVIEW LETTERS 2022; 128:122301. [PMID: 35394329 DOI: 10.1103/physrevlett.128.122301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2021] [Revised: 01/16/2022] [Accepted: 02/25/2022] [Indexed: 06/14/2023]
Abstract
The spectra measurements of charged hadrons produced in the shower of a parton originating in the same hard scattering with a leptonically decaying Z boson are reported in lead-lead nuclei (Pb-Pb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Both Pb-Pb and pp data sets are recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of 1.7 nb^{-1} and 320 pb^{-1}, respectively. Hadronic collision data with one reconstructed Z boson candidate with the transverse momentum p_{T}>30 GeV/c are analyzed. The Z boson constrains the initial energy and direction of the associated parton. In heavy ion events, azimuthal angular distributions of charged hadrons with respect to the direction of a Z boson are sensitive to modifications of the in-medium parton shower and medium response. compared to reference data from pp interactions, the results for central Pb-Pb collisions indicate a modification of the angular correlations. The measurements of the fragmentation functions and p_{T} spectra of charged particles in Z boson events, which are sensitive to medium modifications of the parton shower longitudinal structure, are also reported. Significant modifications in central Pb-Pb events compared to the pp reference data are also found for these observables.
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Evidence for X(3872) in Pb-Pb Collisions and Studies of its Prompt Production at sqrt[s_{NN}]=5.02 TeV. PHYSICAL REVIEW LETTERS 2022; 128:032001. [PMID: 35119878 DOI: 10.1103/physrevlett.128.032001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Revised: 09/02/2021] [Accepted: 12/22/2021] [Indexed: 06/14/2023]
Abstract
The first evidence for X(3872) production in relativistic heavy ion collisions is reported. The X(3872) production is studied in lead-lead (Pb-Pb) collisions at a center-of-mass energy of sqrt[s_{NN}]=5.02 TeV per nucleon pair, using the decay chain X(3872)→J/ψπ^{+}π^{-}→μ^{+}μ^{-}π^{+}π^{-}. The data were recorded with the CMS detector in 2018 and correspond to an integrated luminosity of 1.7 nb^{-1}. The measurement is performed in the rapidity and transverse momentum ranges |y|<1.6 and 15<p_{T}<50 GeV/c. The significance of the inclusive X(3872) signal is 4.2 standard deviations. The prompt X(3872) to ψ2S yield ratio is found to be ρ^{Pb-Pb}=1.08±0.49(stat)±0.52(syst), to be compared with typical values of 0.1 for pp collisions. This result provides a unique experimental input to theoretical models of the X(3872) production mechanism, and of the nature of this exotic state.
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Artapilosines A and B, Unusual Phenanthrene Derivatives Related to Aporphine Alkaloids from Artabotrys pilosus. JOURNAL OF NATURAL PRODUCTS 2021; 84:3117-3121. [PMID: 34812640 DOI: 10.1021/acs.jnatprod.1c00896] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Two unusual phenanthrene derivatives related to aporphine alkaloids, artapilosines A (1) and B (2), as well as two biogenetically related known aporphine alkaloids, (-)-anonaine (3) and (-)-N-acetylanonaine (4), were separated and purified from Artabotrys pilosus. Artapilosine A (1) is the first compound representative of a new class of phenanthrene derivatives having an unprecedented carbon skeleton, in which the six-membered nitrogen-containing heterocyclic structure in a typical aporphine alkaloid was substituted with a unique five-membered carbocyclic ring. This is the first report of the formation of a carbon-carbon bond between C-5 and C-6a in 1 with the loss of the nitrogen atom N-6 in the classic aporphine alkaloid. Artapilosine B (2) is a novel phenanthrene derivative having a hydroxyethyl as a substituent on the phenanthrene ring. Their chemical structures as well as absolute configurations were determined based on analysis of spectroscopic data. Additionally, the potential anti-HIV activities of all isolates 1-4 were appraised. Artapilosines A (1) and B (2) showed notable anti-HIV reverse transcriptase affects, with EC50 values of 20.93 and 125.29 nM, respectively. These results suggested that the discovery of these novel phenanthrene derivatives from A. pilosus with remarkable anti-HIV effects could be essentially important for the researching and developing of new anti-HIV agents.
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Observation of Forward Neutron Multiplicity Dependence of Dimuon Acoplanarity in Ultraperipheral Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV. PHYSICAL REVIEW LETTERS 2021; 127:122001. [PMID: 34597080 DOI: 10.1103/physrevlett.127.122001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 04/20/2021] [Accepted: 07/21/2021] [Indexed: 06/13/2023]
Abstract
The first measurement of the dependence of γγ→μ^{+}μ^{-} production on the multiplicity of neutrons emitted very close to the beam direction in ultraperipheral heavy ion collisions is reported. Data for lead-lead interactions at sqrt[s_{NN}]=5.02 TeV, with an integrated luminosity of approximately 1.5 nb^{-1}, are collected using the CMS detector at the LHC. The azimuthal correlations between the two muons in the invariant mass region 8<m_{μμ}<60 GeV are extracted for events including 0, 1, or at least 2 neutrons detected in the forward pseudorapidity range |η|>8.3. The back-to-back correlation structure from leading-order photon-photon scattering is found to be significantly broader for events with a larger number of emitted neutrons from each nucleus, corresponding to interactions with a smaller impact parameter. This observation provides a data-driven demonstration that the average transverse momentum of photons emitted from relativistic heavy ions has an impact parameter dependence. These results provide new constraints on models of photon-induced interactions in ultraperipheral collisions. They also provide a baseline to search for possible final-state effects on lepton pairs caused by traversing a quark-gluon plasma produced in hadronic heavy ion collisions.
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Constraints on the Initial State of Pb-Pb Collisions via Measurements of Z-Boson Yields and Azimuthal Anisotropy at sqrt[s_{NN}]=5.02 TeV. PHYSICAL REVIEW LETTERS 2021; 127:102002. [PMID: 34533355 DOI: 10.1103/physrevlett.127.102002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 06/17/2021] [Accepted: 07/27/2021] [Indexed: 06/13/2023]
Abstract
The CMS experiment at the LHC has measured the differential cross sections of Z bosons decaying to pairs of leptons, as functions of transverse momentum and rapidity, in lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The measured Z boson elliptic azimuthal anisotropy coefficient is compatible with zero, showing that Z bosons do not experience significant final-state interactions in the medium produced in the collision. Yields of Z bosons are compared to Glauber model predictions and are found to deviate from these expectations in peripheral collisions, indicating the presence of initial collision geometry and centrality selection effects. The precision of the measurement allows, for the first time, for a data-driven determination of the nucleon-nucleon integrated luminosity as a function of lead-lead centrality, thereby eliminating the need for its estimation based on a Glauber model.
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10
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Evidence for Top Quark Production in Nucleus-Nucleus Collisions. PHYSICAL REVIEW LETTERS 2020; 125:222001. [PMID: 33315428 DOI: 10.1103/physrevlett.125.222001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 10/07/2020] [Indexed: 06/12/2023]
Abstract
Ultrarelativistic heavy ion collisions recreate in the laboratory the thermodynamical conditions prevailing in the early universe up to 10^{-6} sec, thereby allowing the study of the quark-gluon plasma (QGP), a state of quantum chromodynamics (QCD) matter with deconfined partons. The top quark, the heaviest elementary particle known, is accessible in nucleus-nucleus collisions at the CERN LHC, and constitutes a novel probe of the QGP. Here, we report the first evidence for the production of top quarks in nucleus-nucleus collisions, using lead-lead collision data at a nucleon-nucleon center-of-mass energy of 5.02 TeV recorded by the CMS experiment. Two methods are used to measure the cross section for top quark pair production (σ_{tt[over ¯]}) via the selection of charged leptons (electrons or muons) and bottom quarks. One method relies on the leptonic information alone, and the second one exploits, in addition, the presence of bottom quarks. The measured cross sections, σ_{tt[over ¯]}=2.54_{-0.74}^{+0.84} and 2.03_{-0.64}^{+0.71} μb, respectively, are compatible with expectations from scaled proton-proton data and QCD predictions.
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Observation of the B_{s}^{0}→X(3872)ϕ Decay. PHYSICAL REVIEW LETTERS 2020; 125:152001. [PMID: 33095627 DOI: 10.1103/physrevlett.125.152001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2020] [Revised: 06/22/2020] [Accepted: 08/27/2020] [Indexed: 06/11/2023]
Abstract
Using a data sample of proton-proton collisions at sqrt[s]=13 TeV, corresponding to an integrated luminosity of 140 fb^{-1} collected by the CMS experiment in 2016-2018, the B_{s}^{0}→X(3872)ϕ decay is observed. Decays into J/ψπ^{+}π^{-} and K^{+}K^{-} are used to reconstruct, respectively, the X(3872) and ϕ. The ratio of the product of branching fractions B[B_{s}^{0}→X(3872)ϕ]B[X(3872)→J/ψπ^{+}π^{-}] to the product B[B_{s}^{0}→ψ(2S)ϕ]B[ψ(2S)→J/ψπ^{+}π^{-}] is measured to be [2.21±0.29(stat)±0.17(syst)]%. The ratio B[B_{s}^{0}→X(3872)ϕ]/B[B^{0}→X(3872)K^{0}] is found to be consistent with one, while the ratio B[B_{s}^{0}→X(3872)ϕ]/B[B^{+}→X(3872)K^{+}] is two times smaller. This suggests a difference in the production dynamics of the X(3872) in B^{0} and B_{s}^{0} meson decays compared to B^{+}. The reported observation may shed new light on the nature of the X(3872) particle.
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Observation of the Production of Three Massive Gauge Bosons at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2020; 125:151802. [PMID: 33095594 DOI: 10.1103/physrevlett.125.151802] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Accepted: 08/24/2020] [Indexed: 06/11/2023]
Abstract
The first observation is reported of the combined production of three massive gauge bosons (VVV with V=W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV. The analysis is based on a data sample recorded by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 137 fb^{-1}. The searches for individual WWW, WWZ, WZZ, and ZZZ production are performed in final states with three, four, five, and six leptons (electrons or muons), or with two same-sign leptons plus one or two jets. The observed (expected) significance of the combined VVV production signal is 5.7 (5.9) standard deviations and the corresponding measured cross section relative to the standard model prediction is 1.02_{-0.23}^{+0.26}. The significances of the individual WWW and WWZ production are 3.3 and 3.4 standard deviations, respectively. Measured production cross sections for the individual triboson processes are also reported.
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Studies of Charm Quark Diffusion inside Jets Using Pb-Pb and pp Collisions at sqrt[s_{NN}]=5.02 TeV. PHYSICAL REVIEW LETTERS 2020; 125:102001. [PMID: 32955327 DOI: 10.1103/physrevlett.125.102001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 05/28/2020] [Accepted: 08/05/2020] [Indexed: 06/11/2023]
Abstract
The first study of charm quark diffusion with respect to the jet axis in heavy ion collisions is presented. The measurement is performed using jets with p_{T}^{jet}>60 GeV/c and D^{0} mesons with p_{T}^{D}>4 GeV/c in lead-lead (Pb-Pb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of sqrt[s_{NN}]=5.02 TeV, recorded by the CMS detector at the LHC. The radial distribution of D^{0} mesons with respect to the jet axis is sensitive to the production mechanisms of the meson, as well as to the energy loss and diffusion processes undergone by its parent parton inside the strongly interacting medium produced in Pb-Pb collisions. When compared to Monte Carlo event generators, the radial distribution in pp collisions is found to be well described by pythia, while the slope of the distribution predicted by sherpa is steeper than that of the data. In Pb-Pb collisions, compared to the pp results, the D^{0} meson distribution for 4<p_{T}^{D}<20 GeV/c hints at a larger distance on average with respect to the jet axis, reflecting a diffusion of charm quarks in the medium created in heavy ion collisions. At higher p_{T}^{D}, the Pb-Pb and pp radial distributions are found to be similar.
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Measurements of tt[over ¯]H Production and the CP Structure of the Yukawa Interaction between the Higgs Boson and Top Quark in the Diphoton Decay Channel. PHYSICAL REVIEW LETTERS 2020; 125:061801. [PMID: 32845700 DOI: 10.1103/physrevlett.125.061801] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Accepted: 06/19/2020] [Indexed: 06/11/2023]
Abstract
The first observation of the tt[over ¯]H process in a single Higgs boson decay channel with the full reconstruction of the final state (H→γγ) is presented, with a significance of 6.6 standard deviations (σ). The CP structure of Higgs boson couplings to fermions is measured, resulting in an exclusion of the pure CP-odd structure of the top Yukawa coupling at 3.2σ. The measurements are based on a sample of proton-proton collisions at a center-of-mass energy sqrt[s]=13 TeV collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb^{-1}. The cross section times branching fraction of the tt[over ¯]H process is measured to be σ_{tt[over ¯]H}B_{γγ}=1.56_{-0.32}^{+0.34} fb, which is compatible with the standard model prediction of 1.13_{-0.11}^{+0.08} fb. The fractional contribution of the CP-odd component is measured to be f_{CP}^{Htt}=0.00±0.33.
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Measurement of the Jet Mass Distribution and Top Quark Mass in Hadronic Decays of Boosted Top Quarks in pp Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2020; 124:202001. [PMID: 32501048 DOI: 10.1103/physrevlett.124.202001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2019] [Revised: 03/25/2020] [Accepted: 05/01/2020] [Indexed: 06/11/2023]
Abstract
A measurement is reported of the jet mass distribution in hadronic decays of boosted top quarks produced in pp collisions at sqrt[s]=13 TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 35.9 fb^{-1}. The measurement is performed in the lepton+jets channel of tt[over ¯] events, where the lepton is an electron or muon. The products of the hadronic top quark decay t→bW→bqq[over ¯]^{'} are reconstructed as a single jet with transverse momentum larger than 400 GeV. The tt[over ¯] cross section as a function of the jet mass is unfolded at the particle level and used to extract a value of the top quark mass of 172.6±2.5 GeV. A novel jet reconstruction technique is used for the first time at the LHC, which improves the precision by a factor of 3 relative to an earlier measurement. This highlights the potential of measurements using boosted top quarks, where the new technique will enable future precision measurements.
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Constraints on the χ_{c1} versus χ_{c2} Polarizations in Proton-Proton Collisions at sqrt[s]=8 TeV. PHYSICAL REVIEW LETTERS 2020; 124:162002. [PMID: 32383915 DOI: 10.1103/physrevlett.124.162002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Revised: 01/25/2020] [Accepted: 03/26/2020] [Indexed: 06/11/2023]
Abstract
The polarizations of promptly produced χ_{c1} and χ_{c2} mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at sqrt[s]=8 TeV. The χ_{c} states are reconstructed via their radiative decays χ_{c}→J/ψγ, with the photons being measured through conversions to e^{+}e^{-}, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_{c2} to χ_{c1} yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ→μ^{+}μ^{-} decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.
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Search for a Narrow Resonance Lighter than 200 GeV Decaying to a Pair of Muons in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2020; 124:131802. [PMID: 32302170 DOI: 10.1103/physrevlett.124.131802] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Accepted: 02/24/2020] [Indexed: 06/11/2023]
Abstract
A search is presented for a narrow resonance decaying to a pair of oppositely charged muons using sqrt[s]=13 TeV proton-proton collision data recorded at the LHC. In the 45-75 and 110-200 GeV resonance mass ranges, the search is based on conventional triggering and event reconstruction techniques. In the 11.5-45 GeV mass range, the search uses data collected with dimuon triggers with low transverse momentum thresholds, recorded at high rate by storing a reduced amount of trigger-level information. The data correspond to integrated luminosities of 137 and 96.6 fb^{-1} for conventional and high-rate triggering, respectively. No significant resonant peaks are observed in the probed mass ranges. The search sets the most stringent constraints to date on a dark photon in the ∼30-75 and 110-200 GeV mass ranges.
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Search for Supersymmetry with a Compressed Mass Spectrum in Events with a Soft τ Lepton, a Highly Energetic Jet, and Large Missing Transverse Momentum in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2020; 124:041803. [PMID: 32058742 DOI: 10.1103/physrevlett.124.041803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Indexed: 06/10/2023]
Abstract
The first search for supersymmetry in events with an experimental signature of one soft, hadronically decaying τ lepton, one energetic jet from initial-state radiation, and large transverse momentum imbalance is presented. These event signatures are consistent with direct or indirect production of scalar τ leptons (τ[over ˜]) in supersymmetric models that exhibit coannihilation between the τ[over ˜] and the lightest neutralino (χ[over ˜]_{1}^{0}), and that could generate the observed relic density of dark matter. The data correspond to an integrated luminosity of 77.2 fb^{-1} of proton-proton collisions at sqrt[s]=13 TeV collected with the CMS detector at the LHC in 2016 and 2017. The results are interpreted in a supersymmetric scenario with a small mass difference (Δm) between the chargino (χ[over ˜]_{1}^{±}) or next-to-lightest neutralino (χ[over ˜]_{2}^{0}), and the χ[over ˜]_{1}^{0}. The mass of the τ[over ˜] is assumed to be the average of the χ[over ˜]_{1}^{±} and χ[over ˜]_{1}^{0} masses. The data are consistent with standard model background predictions. Upper limits at 95% confidence level are set on the sum of the χ[over ˜]_{1}^{±}, χ[over ˜]_{2}^{0}, and τ[over ˜] production cross sections for Δm(χ[over ˜]_{1}^{±},χ[over ˜]_{1}^{0})=50 GeV, resulting in a lower limit of 290 GeV on the mass of the χ[over ˜]_{1}^{±}, which is the most stringent to date and surpasses the bounds from the LEP experiments.
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Search for Physics beyond the Standard Model in Events with Overlapping Photons and Jets. PHYSICAL REVIEW LETTERS 2019; 123:241801. [PMID: 31922872 DOI: 10.1103/physrevlett.123.241801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2019] [Revised: 10/23/2019] [Indexed: 06/10/2023]
Abstract
Results are reported from a search for new particles that decay into a photon and two gluons, in events with jets. Novel jet substructure techniques are developed that allow photons to be identified in an environment densely populated with hadrons. The analyzed proton-proton collision data were collected by the CMS experiment at the LHC, in 2016 at sqrt[s]=13 TeV, and correspond to an integrated luminosity of 35.9 fb^{-1}. The spectra of total transverse hadronic energy of candidate events are examined for deviations from the standard model predictions. No statistically significant excess is observed over the expected background. The first cross section limits on new physics processes resulting in such events are set. The results are interpreted as upper limits on the rate of gluino pair production, utilizing a simplified stealth supersymmetry model. The excluded gluino masses extend up to 1.7 TeV, for a neutralino mass of 200 GeV and exceed previous mass constraints set by analyses targeting events with isolated photons.
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Search for Low-Mass Quark-Antiquark Resonances Produced in Association with a Photon at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2019; 123:231803. [PMID: 31868480 DOI: 10.1103/physrevlett.123.231803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 10/12/2019] [Indexed: 06/10/2023]
Abstract
A search for narrow low-mass resonances decaying to quark-antiquark pairs is presented. The search is based on proton-proton collision events collected at 13 TeV by the CMS detector at the CERN LHC. The data sample corresponds to an integrated luminosity of 35.9 fb^{-1}, recorded in 2016. The search considers the case where the resonance has high transverse momentum due to initial-state radiation of a hard photon. To study this process, the decay products of the resonance are reconstructed as a single large-radius jet with two-pronged substructure. The signal would be identified as a localized excess in the jet invariant mass spectrum. No evidence for such a resonance is observed in the mass range 10 to 125 GeV. Upper limits at the 95% confidence level are set on the coupling strength of resonances decaying to quark pairs. The results obtained with this photon trigger strategy provide the first direct constraints on quark-antiquark resonance masses below 50 GeV obtained at a hadron collider.
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21
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Search for a Light Charged Higgs Boson Decaying to a W Boson and a CP-Odd Higgs Boson in Final States with eμμ or μμμ in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2019; 123:131802. [PMID: 31697516 DOI: 10.1103/physrevlett.123.131802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2019] [Revised: 07/19/2019] [Indexed: 06/10/2023]
Abstract
A search for a light charged Higgs boson (H^{+}) decaying to a W boson and a CP-odd Higgs boson (A) in final states with eμμ or μμμ is performed using data from pp collisions at sqrt[s]=13 TeV, recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb^{-1}. In this search, it is assumed that the H^{+} boson is produced in decays of top quarks, and the A boson decays to two oppositely charged muons. The presence of signals for H^{+} boson masses between 100 and 160 GeV and A boson masses between 15 and 75 GeV is investigated. No evidence for the production of the H^{+} boson is found. Upper limits at 95% confidence level are obtained on the combined branching fraction for the decay chain, t→bH^{+}→bW^{+}A→bW^{+}μ^{+}μ^{-}, of 1.9×10^{-6} to 8.6×10^{-6}, depending on the masses of the H^{+} and A bosons. These are the first limits for these decay modes of the H^{+} and A bosons.
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22
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Studies of Beauty Suppression via Nonprompt D^{0} Mesons in Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV. PHYSICAL REVIEW LETTERS 2019; 123:022001. [PMID: 31386524 DOI: 10.1103/physrevlett.123.022001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 02/27/2019] [Indexed: 06/10/2023]
Abstract
The transverse momentum spectra of D^{0} mesons from b hadron decays are measured at midrapidity (|y|<1) in pp and Pb-Pb collisions at a nucleon-nucleon center of mass energy of 5.02 TeV with the CMS detector at the LHC. The D^{0} mesons from b hadron decays are distinguished from prompt D^{0} mesons by their decay topologies. In Pb-Pb collisions, the B→D^{0} yield is found to be suppressed in the measured p_{T} range from 2 to 100 GeV/c as compared to pp collisions. The suppression is weaker than that of prompt D^{0} mesons and charged hadrons for p_{T} around 10 GeV/c. While theoretical calculations incorporating partonic energy loss in the quark-gluon plasma can successfully describe the measured B→D^{0} suppression at higher p_{T}, the data show an indication of larger suppression than the model predictions in the range of 2<p_{T}<5 GeV/c.
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23
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Jet Shapes of Isolated Photon-Tagged Jets in Pb-Pb and pp Collisions at sqrt[s_{NN}]=5.02 TeV. PHYSICAL REVIEW LETTERS 2019; 122:152001. [PMID: 31050516 DOI: 10.1103/physrevlett.122.152001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2018] [Indexed: 06/09/2023]
Abstract
The modification of jet shapes in Pb-Pb collisions, relative to those in pp collisions, is studied for jets associated with an isolated photon. The data were collected with the CMS detector at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Jet shapes are constructed from charged particles with track transverse momenta (p_{T}) above 1 GeV/c in annuli around the axes of jets with p_{T}^{jet}>30 GeV/c associated with an isolated photon with p_{T}^{γ}>60 GeV/c. The jet shape distributions are consistent between peripheral Pb-Pb and pp collisions, but are modified for more central Pb-Pb collisions. In these central Pb-Pb events, a larger fraction of the jet momentum is observed at larger distances from the jet axis compared to pp, reflecting the interaction between the partonic medium created in heavy ion collisions and the traversing partons.
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24
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Search for W Boson Decays to Three Charged Pions. PHYSICAL REVIEW LETTERS 2019; 122:151802. [PMID: 31050519 DOI: 10.1103/physrevlett.122.151802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Indexed: 06/09/2023]
Abstract
For the first time, a search for the rare decay of the W boson to three charged pions has been performed. Proton-proton collision data recorded by the CMS experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 77.3 fb^{-1}, have been analyzed. No significant excess is observed above the background expectation. An upper limit of 1.01×10^{-6} is set at 95% confidence level on the branching fraction of the W boson to three charged pions. This provides a strong motivation for theoretical calculations of this branching fraction.
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25
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Observation of Single Top Quark Production in Association with a Z Boson in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2019; 122:132003. [PMID: 31012605 DOI: 10.1103/physrevlett.122.132003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 02/27/2019] [Indexed: 06/09/2023]
Abstract
The observation of single top quark production in association with a Z boson and a quark (tZq) is reported. Events from proton-proton collisions at a center-of-mass energy of 13 TeV containing three charged leptons (either electrons or muons) and at least two jets are analyzed. The data were collected with the CMS detector in 2016 and 2017 and correspond to an integrated luminosity of 77.4fb^{-1}. The increased integrated luminosity, a multivariate lepton identification, and a redesigned analysis strategy improve significantly the sensitivity of the analysis compared to previous searches for tZq production. The tZq signal is observed with a significance well over 5 standard deviations. The measured tZq production cross section is σ(pp→tZq→tℓ^{+}ℓ^{-}q)=111±13(stat)_{-9}^{+11}(syst) fb, for dilepton invariant masses above 30 GeV, in agreement with the standard model expectation.
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26
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Observation of Two Excited B_{c}^{+} States and Measurement of the B_{c}^{+}(2S) Mass in pp Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2019; 122:132001. [PMID: 31012626 DOI: 10.1103/physrevlett.122.132001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 02/18/2019] [Indexed: 06/09/2023]
Abstract
Signals consistent with the B_{c}^{+}(2S) and B_{c}^{*+}(2S) states are observed in proton-proton collisions at sqrt[s]=13 TeV, in an event sample corresponding to an integrated luminosity of 143 fb^{-1}, collected by the CMS experiment during the 2015-2018 LHC running periods. These excited b[over ¯]c states are observed in the B_{c}^{+}π^{+}π^{-} invariant mass spectrum, with the ground state B_{c}^{+} reconstructed through its decay to J/ψπ^{+}. The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1±1.5(stat)±0.7(syst) MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B_{c}^{+}(2S) meson is measured to be 6871.0±1.2(stat)±0.8(syst)±0.8(B_{c}^{+}) MeV, where the last term corresponds to the uncertainty in the world-average B_{c}^{+} mass.
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27
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Combination of Searches for Higgs Boson Pair Production in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2019; 122:121803. [PMID: 30978057 DOI: 10.1103/physrevlett.122.121803] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Indexed: 06/09/2023]
Abstract
This Letter describes a search for Higgs boson pair production using the combined results from four final states: bbγγ, bbττ, bbbb, and bbVV, where V represents a W or Z boson. The search is performed using data collected in 2016 by the CMS experiment from LHC proton-proton collisions at sqrt[s]=13 TeV, corresponding to an integrated luminosity of 35.9 fb^{-1}. Limits are set on the Higgs boson pair production cross section. A 95% confidence level observed (expected) upper limit on the nonresonant production cross section is set at 22.2 (12.8) times the standard model value. A search for narrow resonances decaying to Higgs boson pairs is also performed in the mass range 250-3000 GeV. No evidence for a signal is observed, and upper limits are set on the resonance production cross section.
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28
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Search for Narrow Hγ Resonances in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2019; 122:081804. [PMID: 30932612 DOI: 10.1103/physrevlett.122.081804] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 11/15/2018] [Indexed: 06/09/2023]
Abstract
A search for heavy, narrow resonances decaying to a Higgs boson and a photon (Hγ) has been performed in proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb^{-1} collected with the CMS detector at the LHC in 2016. Events containing a photon and a Lorentz-boosted hadronically decaying Higgs boson reconstructed as a single, large-radius jet are considered, and the γ+jet invariant mass spectrum is analyzed for the presence of narrow resonances. To increase the sensitivity of the search, events are categorized depending on whether or not the large-radius jet can be identified as a result of the merging of two jets originating from b quarks. Results in both categories are found to agree with the predictions of the standard model. Upper limits on the production rate of Hγ resonances are set as a function of their mass in the range of 720-3250 GeV, representing the most stringent constraints to date.
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29
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Search for the Higgs Boson Decaying to Two Muons in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2019; 122:021801. [PMID: 30720313 DOI: 10.1103/physrevlett.122.021801] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Revised: 10/28/2018] [Indexed: 06/09/2023]
Abstract
A search for the Higgs boson decaying to two oppositely charged muons is presented using data recorded by the CMS experiment at the CERN LHC in 2016 at a center-of-mass energy sqrt[s]=13 TeV, corresponding to an integrated luminosity of 35.9 fb^{-1}. Data are found to be compatible with the predicted background. For a Higgs boson with a mass of 125.09 GeV, the 95% confidence level observed (background-only expected) upper limit on the production cross section times the branching fraction to a pair of muons is found to be 3.0 (2.5) times the standard model expectation. In combination with data recorded at center-of-mass energies sqrt[s]=7 and 8 TeV, the background-only expected upper limit improves to 2.2 times the standard model value with a standard model expected significance of 1.0 standard deviation. The corresponding observed upper limit is 2.9 with an observed significance of 0.9 standard deviation. This corresponds to an observed upper limit on the standard model Higgs boson branching fraction to muons of 6.4×10^{-4} and to an observed signal strength of 1.0±1.0(stat)±0.1(syst).
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30
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Search for Dark Matter Particles Produced in Association with a Top Quark Pair at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2019; 122:011803. [PMID: 31012697 DOI: 10.1103/physrevlett.122.011803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Indexed: 06/09/2023]
Abstract
A search is performed for dark matter particles produced in association with a top quark pair in proton-proton collisions at sqrt[s]=13 TeV. The data correspond to an integrated luminosity of 35.9 fb^{-1} recorded by the CMS detector at the LHC. No significant excess over the standard model expectation is observed. The results are interpreted using simplified models of dark matter production via spin-0 mediators that couple to dark matter particles and to standard model quarks, providing constraints on the coupling strength between the mediator and the quarks. These are the most stringent collider limits to date for scalar mediators, and the most stringent for pseudoscalar mediators at low masses.
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31
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Observation of Medium-Induced Modifications of Jet Fragmentation in Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV Using Isolated Photon-Tagged Jets. PHYSICAL REVIEW LETTERS 2018; 121:242301. [PMID: 30608764 DOI: 10.1103/physrevlett.121.242301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Revised: 10/16/2018] [Indexed: 06/09/2023]
Abstract
Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in pp and Pb-Pb collisions. The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Fragmentation functions are obtained for jets with p_{T}^{jet}>30 GeV/c in events containing an isolated photon with p_{T}^{γ}>60 GeV/c, using charged tracks with transverse momentum p_{T}^{trk}>1 GeV/c in a cone around the jet axis. The association with an isolated photon constrains the initial p_{T} and azimuthal angle of the parton whose shower produced the jet. For central Pb-Pb collisions, modifications of the jet fragmentation functions are observed when compared to those measured in pp collisions, while no significant differences are found in the 50% most peripheral collisions. Jets in central Pb-Pb events show an excess (depletion) of low (high) p_{T} particles, with a transition around 3 GeV/c. This measurement shows for the first time the in-medium shower modifications of partons (quark dominated) with well-defined initial kinematics. It constitutes a new well-controlled reference for testing theoretical models of the parton passage through the quark-gluon plasma.
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32
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Search for Leptoquarks Coupled to Third-Generation Quarks in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2018; 121:241802. [PMID: 30608761 DOI: 10.1103/physrevlett.121.241802] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Indexed: 06/09/2023]
Abstract
Three of the most significant measured deviations from standard model predictions, the enhanced decay rate for B→D^{(*)}τν, hints of lepton universality violation in B→K^{(*)}ℓℓ decays, and the anomalous magnetic moment of the muon, can be explained by the existence of leptoquarks (LQs) with large couplings to third-generation quarks and masses at the TeV scale. The existence of these states can be probed at the LHC in high energy proton-proton collisions. A novel search is presented for pair production of LQs coupled to a top quark and a muon using data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb^{-1}, recorded by the CMS experiment. No deviation from the standard model prediction has been observed and scalar LQs decaying exclusively into tμ are excluded up to masses of 1420 GeV. The results of this search are combined with those from previous searches for LQ decays into tτ and bν, which excluded scalar LQs below masses of 900 and 1080 GeV. Vector LQs are excluded up to masses of 1190 GeV for all possible combinations of branching fractions to tμ, tτ and bν. With this analysis, all relevant couplings of LQs with an electric charge of -1/3 to third-generation quarks are probed for the first time.
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33
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Evidence for the Associated Production of a Single Top Quark and a Photon in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2018; 121:221802. [PMID: 30547617 DOI: 10.1103/physrevlett.121.221802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Indexed: 06/09/2023]
Abstract
The first evidence of events consistent with the production of a single top quark in association with a photon is reported. The analysis is based on proton-proton collisions at sqrt[s]=13 TeV and recorded by the CMS experiment in 2016, corresponding to an integrated luminosity of 35.9 fb^{-1}. Events are selected by requiring the presence of a muon (μ), a photon (γ), an imbalance in transverse momentum from an undetected neutrino (ν), and at least two jets (j) of which exactly one is identified as associated with the hadronization of a b quark. A multivariate discriminant based on topological and kinematic event properties is employed to separate signal from background processes. An excess above the background-only hypothesis is observed, with a significance of 4.4 standard deviations. A fiducial cross section is measured for isolated photons with transverse momentum greater than 25 GeV in the central region of the detector. The measured product of the cross section and branching fraction is σ(pp→tγj)B(t→μνb)=115±17(stat)±30(syst) fb, which is consistent with the standard model prediction.
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34
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Observation of the Z→ψℓ^{+}ℓ^{-} Decay in pp Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2018; 121:141801. [PMID: 30339440 DOI: 10.1103/physrevlett.121.141801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Indexed: 06/08/2023]
Abstract
This Letter presents the observation of the rare Z boson decay Z→ψℓ^{+}ℓ^{-}. Here, ψ represents contributions from direct J/ψ and ψ(2S)→J/ψX, ℓ^{+}ℓ^{-} is a pair of electrons or muons, and the J/ψ meson is detected via its decay to μ^{+}μ^{-}. The sample of proton-proton collision data, collected by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, corresponds to an integrated luminosity of 35.9 fb^{-1}. The signal is observed with a significance in excess of 5 standard deviations. After subtraction of the ψ(2S)→J/ψX contribution, the ratio of the branching fraction of the exclusive decay Z→J/ψℓ^{+}ℓ^{-} to the decay Z→μ^{+}μ^{-}μ^{+}μ^{-} within a fiducial phase space is measured to be B(Z→J/ψℓ^{+}ℓ^{-})/B(Z→μ^{+}μ^{-}μ^{+}μ^{-})=0.67±0.18(stat)±0.05(syst).
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35
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Search for Pair-Produced Resonances Each Decaying into at Least Four Quarks in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2018; 121:141802. [PMID: 30339442 DOI: 10.1103/physrevlett.121.141802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Indexed: 06/08/2023]
Abstract
This Letter presents the results of a search for pair-produced particles of masses above 100 GeV that each decay into at least four quarks. Using data collected by the CMS experiment at the LHC in 2015-2016, corresponding to an integrated luminosity of 38.2 fb^{-1}, reconstructed particles are clustered into two large jets of similar mass, each consistent with four-parton substructure. No statistically significant excess of data over the background prediction is observed in the distribution of average jet mass. Pair-produced squarks with dominant hadronic R-parity-violating decays into four quarks and with masses between 0.10 and 0.72 TeV are excluded at 95% confidence level. Similarly, pair-produced gluinos that decay into five quarks are also excluded with masses between 0.10 and 1.41 TeV at 95% confidence level. These are the first constraints that have been placed on pair-produced particles with masses below 400 GeV that decay into four or five quarks, bridging a significant gap in the coverage of R-parity-violating supersymmetry parameter space.
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36
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Observation of Higgs Boson Decay to Bottom Quarks. PHYSICAL REVIEW LETTERS 2018; 121:121801. [PMID: 30296133 DOI: 10.1103/physrevlett.121.121801] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Indexed: 06/08/2023]
Abstract
The observation of the standard model (SM) Higgs boson decay to a pair of bottom quarks is presented. The main contribution to this result is from processes in which Higgs bosons are produced in association with a W or Z boson (VH), and are searched for in final states including 0, 1, or 2 charged leptons and two identified bottom quark jets. The results from the measurement of these processes in a data sample recorded by the CMS experiment in 2017, comprising 41.3 fb^{-1} of proton-proton collisions at sqrt[s]=13 TeV, are described. When combined with previous VH measurements using data collected at sqrt[s]=7, 8, and 13 TeV, an excess of events is observed at m_{H}=125 GeV with a significance of 4.8 standard deviations, where the expectation for the SM Higgs boson is 4.9. The corresponding measured signal strength is 1.01±0.22. The combination of this result with searches by the CMS experiment for H→bb[over ¯] in other production processes yields an observed (expected) significance of 5.6 (5.5) standard deviations and a signal strength of 1.04±0.20.
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37
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Observation of the χ_{b1}(3P) and χ_{b2}(3P) and Measurement of their Masses. PHYSICAL REVIEW LETTERS 2018; 121:092002. [PMID: 30230889 DOI: 10.1103/physrevlett.121.092002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Revised: 07/08/2018] [Indexed: 06/08/2023]
Abstract
The χ_{b1}(3P) and χ_{b2}(3P) states are observed through their ϒ(3S)γ decays, using an event sample of proton-proton collisions collected by the CMS experiment at the CERN LHC. The data were collected at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 80.0 fb^{-1}. The ϒ(3S) mesons are identified through their dimuon decay channel, while the low-energy photons are detected after converting to e^{+}e^{-} pairs in the silicon tracker, leading to a χ_{b}(3P) mass resolution of 2.2 MeV. This is the first time that the J=1 and 2 states are well resolved and their masses individually measured: 10513.42±0.41(stat)±0.18(syst) MeV and 10524.02±0.57(stat)±0.18(syst) MeV; they are determined with respect to the world-average value of the ϒ(3S) mass, which has an uncertainty of 0.5 MeV. The mass splitting is measured to be 10.60±0.64(stat)±0.17(syst) MeV.
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38
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Elliptic Flow of Charm and Strange Hadrons in High-Multiplicity p+Pb Collisions at sqrt[s_{NN}]=8.16 TeV. PHYSICAL REVIEW LETTERS 2018; 121:082301. [PMID: 30192601 DOI: 10.1103/physrevlett.121.082301] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Revised: 07/22/2018] [Indexed: 06/08/2023]
Abstract
The elliptic azimuthal anisotropy coefficient (v_{2}) is measured for charm (D^{0}) and strange (K_{S}^{0}, Λ, Ξ^{-}, and Ω^{-}) hadrons, using a data sample of p+Pb collisions collected by the CMS experiment, at a nucleon-nucleon center-of-mass energy of sqrt[s_{NN}]=8.16 TeV. A significant positive v_{2} signal from long-range azimuthal correlations is observed for all particle species in high-multiplicity p+Pb collisions. The measurement represents the first observation of possible long-range collectivity for open heavy flavor hadrons in small systems. The results suggest that charm quarks have a smaller v_{2} than the lighter quarks, probably reflecting a weaker collective behavior. This effect is not seen in the larger PbPb collision system at sqrt[s_{NN}]=5.02 TeV, also presented.
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39
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Constraining Gluon Distributions in Nuclei Using Dijets in Proton-Proton and Proton-Lead Collisions at sqrt[s_{NN}]=5.02 TeV. PHYSICAL REVIEW LETTERS 2018; 121:062002. [PMID: 30141647 DOI: 10.1103/physrevlett.121.062002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2018] [Indexed: 06/08/2023]
Abstract
The pseudorapidity distributions of dijets as functions of their average transverse momentum (p_{T}^{ave}) are measured in proton-lead (pPb) and proton-proton (pp) collisions. The data samples were collected by the CMS experiment at the CERN LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. A significant modification of the pPb spectra with respect to the pp spectra is observed in all p_{T}^{ave} intervals investigated. The ratios of the pPb and pp distributions are compared to next-to-leading order perturbative quantum chromodynamics calculations with unbound nucleon and nuclear parton distribution functions (PDFs). These results give the first evidence that the gluon PDF at large Bjorken x in lead ions is strongly suppressed with respect to the PDF in unbound nucleons.
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Search for Physics Beyond the Standard Model in Events with High-Momentum Higgs Bosons and Missing Transverse Momentum in Proton-Proton Collisions at 13 TeV. PHYSICAL REVIEW LETTERS 2018; 120:241801. [PMID: 29956995 DOI: 10.1103/physrevlett.120.241801] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Indexed: 06/08/2023]
Abstract
A search for physics beyond the standard model in events with one or more high-momentum Higgs bosons, H, decaying to pairs of b quarks in association with missing transverse momentum is presented. The data, corresponding to an integrated luminosity of 35.9 fb^{-1}, were collected with the CMS detector at the LHC in proton-proton collisions at the center-of-mass energy sqrt[s]=13 TeV. The analysis utilizes a new b quark tagging technique based on jet substructure to identify jets from H→bb[over ¯]. Events are categorized by the multiplicity of H-tagged jets, jet mass, and the missing transverse momentum. No significant deviation from standard model expectations is observed. In the context of supersymmetry (SUSY), limits on the cross sections of pair-produced gluinos are set, assuming that gluinos decay to quark pairs, H (or Z), and the lightest SUSY particle, LSP, through an intermediate next-to-lightest SUSY particle, NLSP. With large mass splitting between the NLSP and LSP, and 100% NLSP branching fraction to H, the lower limit on the gluino mass is found to be 2010 GeV.
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Observation of tt[over ¯]H Production. PHYSICAL REVIEW LETTERS 2018; 120:231801. [PMID: 29932697 DOI: 10.1103/physrevlett.120.231801] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2018] [Revised: 05/01/2018] [Indexed: 06/08/2023]
Abstract
The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of sqrt[s]=7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9 fb^{-1}, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26_{-0.26}^{+0.31}.
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Search for Heavy Neutral Leptons in Events with Three Charged Leptons in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2018; 120:221801. [PMID: 29906166 DOI: 10.1103/physrevlett.120.221801] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2018] [Indexed: 06/08/2023]
Abstract
A search for a heavy neutral lepton N of Majorana nature decaying into a W boson and a charged lepton is performed using the CMS detector at the LHC. The targeted signature consists of three prompt charged leptons in any flavor combination of electrons and muons. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV, with an integrated luminosity of 35.9 fb^{-1}. The search is performed in the N mass range between 1 GeV and 1.2 TeV. The data are found to be consistent with the expected standard model background. Upper limits are set on the values of |V_{eN}|^{2} and |V_{μN}|^{2}, where V_{ℓN} is the matrix element describing the mixing of N with the standard model neutrino of flavor ℓ. These are the first direct limits for N masses above 500 GeV and the first limits obtained at a hadron collider for N masses below 40 GeV.
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Measurement of Prompt D^{0} Meson Azimuthal Anisotropy in Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV. PHYSICAL REVIEW LETTERS 2018; 120:202301. [PMID: 29864330 DOI: 10.1103/physrevlett.120.202301] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2017] [Revised: 03/06/2018] [Indexed: 06/08/2023]
Abstract
The prompt D^{0} meson azimuthal anisotropy coefficients, v_{2} and v_{3}, are measured at midrapidity (|y|<1.0) in Pb-Pb collisions at a center-of-mass energy sqrt[s_{NN}]=5.02 TeV per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum (p_{T}) range of 1 to 40 GeV/c, for central and midcentral collisions. The v_{2} coefficient is found to be positive throughout the p_{T} range studied. The first measurement of the prompt D^{0} meson v_{3} coefficient is performed, and values up to 0.07 are observed for p_{T} around 4 GeV/c. Compared to measurements of charged particles, a similar p_{T} dependence, but smaller magnitude for p_{T}<6 GeV/c, is found for prompt D^{0} meson v_{2} and v_{3} coefficients. The results are consistent with the presence of collective motion of charm quarks at low p_{T} and a path length dependence of charm quark energy loss at high p_{T}, thereby providing new constraints on the theoretical description of the interactions between charm quarks and the quark-gluon plasma.
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Search for the X(5568) State Decaying into B_{s}^{0}π^{±} in Proton-Proton Collisions at sqrt[s]=8 TeV. PHYSICAL REVIEW LETTERS 2018; 120:202005. [PMID: 29864318 DOI: 10.1103/physrevlett.120.202005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2017] [Revised: 02/19/2018] [Indexed: 06/08/2023]
Abstract
A search for resonancelike structures in the B_{s}^{0}π^{±} invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at sqrt[s]=8 TeV, corresponding to an integrated luminosity of 19.7 fb^{-1}. The B_{s}^{0} mesons are reconstructed in the decay chain B_{s}^{0}→J/ψϕ, with J/ψ→μ^{+}μ^{-} and ϕ→K^{+}K^{-}. The B_{s}^{0}π^{±} invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed B_{s}^{0} and π^{±} candidates. Upper limits are set on the relative production rates of the X(5568) and B_{s}^{0} states times the branching fraction of the decay X(5568)^{±}→B_{s}^{0}π^{±}. In addition, upper limits are obtained as a function of the mass and the natural width of possible exotic states decaying into B_{s}^{0}π^{±}.
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Search for Narrow Resonances in the b-Tagged Dijet Mass Spectrum in Proton-Proton Collisions at sqrt[s]=8 TeV. PHYSICAL REVIEW LETTERS 2018; 120:201801. [PMID: 29864370 DOI: 10.1103/physrevlett.120.201801] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Indexed: 06/08/2023]
Abstract
A search for narrow resonances decaying to bottom quark-antiquark pairs is presented, using a data sample of proton-proton collisions at sqrt[s]=8 TeV corresponding to an integrated luminosity of 19.7 fb^{-1}. The search is extended to masses lower than those reached in typical searches for resonances decaying into jet pairs at the LHC, by taking advantage of triggers that identify jets originating from bottom quarks. No significant excess of events is observed above the background predictions. Limits are set on the product of cross section and branching fraction to bottom quarks for spin 0, 1, and 2 resonances in the mass range of 325-1200 GeV. These results improve on the limits for resonances decaying into jet pairs in the 325-500 GeV mass range.
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Measurement of the Splitting Function in pp and Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV. PHYSICAL REVIEW LETTERS 2018; 120:142302. [PMID: 29694107 DOI: 10.1103/physrevlett.120.142302] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Indexed: 06/08/2023]
Abstract
Data from heavy ion collisions suggest that the evolution of a parton shower is modified by interactions with the color charges in the dense partonic medium created in these collisions, but it is not known where in the shower evolution the modifications occur. The momentum ratio of the two leading partons, resolved as subjets, provides information about the parton shower evolution. This substructure observable, known as the splitting function, reflects the process of a parton splitting into two other partons and has been measured for jets with transverse momentum between 140 and 500 GeV, in pp and PbPb collisions at a center-of-mass energy of 5.02 TeV per nucleon pair. In central PbPb collisions, the splitting function indicates a more unbalanced momentum ratio, compared to peripheral PbPb and pp collisions.. The measurements are compared to various predictions from event generators and analytical calculations.
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Suppression of Excited ϒ States Relative to the Ground State in Pb-Pb Collisions at sqrt[s]_{NN}=5.02 TeV. PHYSICAL REVIEW LETTERS 2018; 120:142301. [PMID: 29694144 DOI: 10.1103/physrevlett.120.142301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 01/16/2018] [Indexed: 06/08/2023]
Abstract
The relative yields of ϒ mesons produced in pp and Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV and reconstructed via the dimuon decay channel are measured using data collected by the CMS experiment. Double ratios are formed by comparing the yields of the excited states, ϒ(2S) and ϒ(3S), to the ground state, ϒ(1S), in both Pb-Pb and pp collisions at the same center-of-mass energy. The double ratios, [ϒ(nS)/ϒ(1S)]_{Pb-Pb}/[ϒ(nS)/ϒ(1S)]_{pp}, are measured to be 0.308±0.055(stat)±0.019(syst) for the ϒ(2S) and less than 0.26 at 95% confidence level for the ϒ(3S). No significant ϒ(3S) signal is found in the Pb-Pb data. The double ratios are studied as a function of collision centrality, as well as ϒ transverse momentum and rapidity. No significant dependencies are observed.
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Observation of Correlated Azimuthal Anisotropy Fourier Harmonics in pp and p+Pb Collisions at the LHC. PHYSICAL REVIEW LETTERS 2018; 120:092301. [PMID: 29547300 DOI: 10.1103/physrevlett.120.092301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 12/06/2017] [Indexed: 06/08/2023]
Abstract
The azimuthal anisotropy Fourier coefficients (v_{n}) in 8.16 TeV p+Pb data are extracted via long-range two-particle correlations as a function of the event multiplicity and compared to corresponding results in pp and PbPb collisions. Using a four-particle cumulant technique, v_{n} correlations are measured for the first time in pp and p+Pb collisions. The v_{2} and v_{4} coefficients are found to be positively correlated in all collision systems. For high-multiplicity p+Pb collisions, an anticorrelation of v_{2} and v_{3} is observed, with a similar correlation strength as in PbPb data at the same multiplicity. The new correlation results strengthen the case for a common origin of the collectivity seen in p+Pb and PbPb collisions in the measured multiplicity range.
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Observation of Top Quark Production in Proton-Nucleus Collisions. PHYSICAL REVIEW LETTERS 2017; 119:242001. [PMID: 29286735 DOI: 10.1103/physrevlett.119.242001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2017] [Indexed: 06/07/2023]
Abstract
The first observation of top quark production in proton-nucleus collisions is reported using proton-lead data collected by the CMS experiment at the CERN LHC at a nucleon-nucleon center-of-mass energy of sqrt[s_{NN}]=8.16 TeV. The measurement is performed using events with exactly one isolated electron or muon candidate and at least four jets. The data sample corresponds to an integrated luminosity of 174 nb^{-1}. The significance of the tt[over ¯] signal against the background-only hypothesis is above 5 standard deviations. The measured cross section is σ_{tt[over ¯]}=45±8 nb, consistent with predictions from perturbative quantum chromodynamics.
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Search for Evidence of the Type-III Seesaw Mechanism in Multilepton Final States in Proton-Proton Collisions at sqrt[s]=13 TeV. PHYSICAL REVIEW LETTERS 2017; 119:221802. [PMID: 29286783 DOI: 10.1103/physrevlett.119.221802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2017] [Indexed: 06/07/2023]
Abstract
A search for a signal consistent with the type-III seesaw mechanism in events with three or more electrons or muons is presented. The data sample consists of proton-proton collisions at sqrt[s]=13 TeV collected by the CMS experiment at the LHC in 2016 and corresponds to an integrated luminosity of 35.9 fb^{-1}. Selection criteria based on the number of leptons and the invariant mass of oppositely charged lepton pairs are used to distinguish the signal from the standard model background. The observations are consistent with the expectations from standard model processes. The results are used to place limits on the production of heavy fermions of the type-III seesaw model as a function of the branching ratio to each lepton flavor. In the scenario of equal branching fractions to each lepton flavor, heavy fermions with masses below 840 GeV are excluded. This is the most sensitive probe to date of the type-III seesaw mechanism.
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