Search for long-lived heavy charged particles using a ring imaging Cherenkov technique at LHCb

A search is performed for heavy long-lived charged particles using 3.0 [Formula: see text] of proton-proton collisions collected at [Formula: see text][Formula: see text] 7 and 8  TeV with the LHCb detector. The search is mainly based on the response of the ring imaging Cherenkov detectors to distinguish the heavy, slow-moving particles from muons. No evidence is found for the production of such long-lived states. The results are expressed as limits on the Drell-Yan production of pairs of long-lived particles, with both particles in the LHCb pseudorapidity acceptance, [Formula: see text]. The mass-dependent cross-section upper limits are in the range 2-4 fb (at 95 % CL) for masses between 14 and 309 [Formula: see text].

Search for Hidden-Sector Bosons in B(0)→K(*0)μ(+)μ(-) Decays

A search is presented for hidden-sector bosons, χ, produced in the decay B(0)→K*(892)(0)χ, with K*(892)(0)→K(+)π(-) and χ→μ(+)μ(-). The search is performed using pp-collision data corresponding to 3.0  fb(-1) collected with the LHCb detector. No significant signal is observed in the accessible mass range 214≤m(χ)≤4350  MeV, and upper limits are placed on the branching fraction product B(B(0)→K*(892)(0)χ)×B(χ→μ(+)μ(-)) as a function of the mass and lifetime of the χ boson. These limits are of the order of 10(-9) for χ lifetimes less than 100 ps over most of the m(χ) range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.

First observation of top quark production in the forward region

Top quark production in the forward region in proton-proton collisions is observed for the first time. The W+b final state with W→μν is reconstructed using muons with a transverse momentum, p_{T}, larger than 25 GeV in the pseudorapidity range 2.0<η<4.5. The b jets are required to have 50<p_{T}<100  GeV and 2.2<η<4.2, while the transverse component of the sum of the muon and b-jet momenta must satisfy p_{T}>20  GeV. The results are based on data corresponding to integrated luminosities of 1.0 and 2.0  fb^{-1} collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross sections in the fiducial region are σ(top)[7  TeV]=239±53(stat)±33(syst)±24(theory)  fb,σ(top)[8  TeV]=289±43(stat)±40(syst)±29(theory)  fb.These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order standard model predictions.

Measurement of the ratio of branching fractions B(B[over ¯]^{0}→D^{*+}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]^{0}→D^{*+}μ^{-}ν[over ¯]_{μ})

The branching fraction ratio R(D^{*})≡B(B[over ¯]^{0}→D^{*+}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]^{0}→D^{*+}μ^{-}ν[over ¯]_{μ}) is measured using a sample of proton-proton collision data corresponding to 3.0  fb^{-1} of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ^{-}→μ^{-}ν[over ¯]_{μ}ν_{τ}. The semitauonic decay is sensitive to contributions from non-standard-model particles that preferentially couple to the third generation of fermions, in particular, Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate B[over ¯]^{0} decays gives R(D^{*})=0.336±0.027(stat)±0.030(syst). This result, which is the first measurement of this quantity at a hadron collider, is 2.1 standard deviations larger than the value expected from lepton universality in the standard model.

Observation of J/ψp Resonances Consistent with Pentaquark States in Λ_{b}^{0}→J/ψK^{-}p Decays

Observations of exotic structures in the J/ψp channel, which we refer to as charmonium-pentaquark states, in Λ_{b}^{0}→J/ψK^{-}p decays are presented. The data sample corresponds to an integrated luminosity of 3 fb^{-1} acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis of the three-body final state reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the J/ψp mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of 4380±8±29 MeV and a width of 205±18±86 MeV, while the second is narrower, with a mass of 4449.8±1.7±2.5 MeV and a width of 39±5±19 MeV. The preferred J^{P} assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.

Observation of the B(s)(0)→η'η' Decay

The first observation of the B(s)(0)→η'η' decay is reported. The study is based on a sample of proton-proton collisions corresponding to 3.0  fb(-1) of integrated luminosity collected with the LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be [3.31±0.64(stat)±0.28(syst)±0.12(norm)]×10(-5), where the third uncertainty comes from the B(±)→η'K(±) branching fraction that is used as a normalization. In addition, the charge asymmetries of B(±)→η'K(±) and B(±)→ϕK(±), which are control channels, are measured to be (-0.2±1.3)% and (+1.7±1.3)%, respectively. All results are consistent with theoretical expectations.

Measurement of CP Violation in B0→J/ψK{S}^{0} Decays

Measurements are presented of the CP violation observables S and C in the decays of B(0) and Bover ¯]0 mesons to the J/ψK(S)(0) final state. The data sample corresponds to an integrated luminosity of 3.0  fb(-1) collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, and contains a total of 41 560 selected B^{0} and B[over ¯]^{0} decays. The analysis of the time evolution of these decays yields S=0.731±0.035(stat)±0.020(syst) and C=-0.038±0.032(stat)±0.005(syst). In the standard model, S equals sin(2β) to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.

Search for long-lived particles decaying to jet pairs

A search is presented for long-lived particles with a mass between 25 and 50 [Formula: see text] and a lifetime between 1 and 200[Formula: see text] in a sample of proton-proton collisions at a centre-of-mass energy of [Formula: see text] TeV, corresponding to an integrated luminosity of 0.62 [Formula: see text], collected by the LHCb detector. The particles are assumed to be pair-produced by the decay of a standard model-like Higgs boson. The experimental signature of the long-lived particle is a displaced vertex with two associated jets. No excess above the background is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime.

Measurement of Bc+ Production in Proton-Proton Collisions at √[s]=8 TeV

Production of Bc+ mesons in proton-proton collisions at a center-of-mass energy of 8 TeV is studied with data corresponding to an integrated luminosity of 2.0  fb-1 recorded by the LHCb experiment. The ratio of production cross sections times branching fractions between the Bc+→J/ψπ+ and B+→J/ψK+ decays is measured as a function of transverse momentum and rapidity in the regions 0<pT<20  GeV/c and 2.0<y<4.5. The ratio in this kinematic range is measured to be (0.683±0.018±0.009)%, where the first uncertainty is statistical and the second systematic.

Observation of two new Ξ(b)(-) baryon resonances

Two structures are observed close to the kinematic threshold in the Ξ(b)(0)π(-) mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0  fb(-1), recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content bds are expected in this mass region: the spin-parity J(P)=(1/2)(+) and J(P)=(3/2)(+) states, denoted Ξ(b)('-) and Ξ(b)(*-). Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be m(Ξ(b)('-))-m(Ξ(b)(0))-m(π(-))=3.653±0.018±0.006  MeV/c(2), m(Ξ(b)(*-))-m(Ξ(b)(0))-m(π(-))=23.96±0.12±0.06  MeV/c(2), Γ(Ξ(b)(*-))=1.65±0.31±0.10  MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of Γ(Ξ(b)('-))<0.08  MeV at 95% confidence level. Relative production rates of these states are also reported.

Precision measurement of CP violation in B(S)(0)→J/ΨK+K- decays

The time-dependent CP asymmetry in B(s)(0)→J/ψK+K- decays is measured using pp collision data, corresponding to an integrated luminosity of 3.0  fb-1, collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. In a sample of 96,000 B(s)(0)→J/ψK+K- decays, the CP-violating phase ϕs is measured, as well as the decay widths ΓL and ΓH of the light and heavy mass eigenstates of the B(s)(0)-B[over ¯]s0 system. The values obtained are ϕs=-0.058±0.049±0.006  rad, Γs≡(ΓL+ΓH)/2=0.6603±0.0027±0.0015  ps-1, and ΔΓs≡ΓL-ΓH=0.0805±0.0091±0.0032  ps-1, where the first uncertainty is statistical and the second, systematic. These are the most precise single measurements of those quantities to date. A combined analysis with Bs0→J/ψπ+π- decays gives ϕs=-0.010±0.039  rad. All measurements are in agreement with the standard model predictions. For the first time, the phase ϕs is measured independently for each polarization state of the K+K- system and shows no evidence for polarization dependence.

Measurement of the semileptonic CP asymmetry in B0-B[over ¯]0 mixing

The semileptonic CP asymmetry in B0-B[over ¯]0 mixing, a(sl)(d), is measured in proton-proton collision data, corresponding to an integrated luminosity of 3.0  fb-1, recorded by the LHCb experiment. Semileptonic B0 decays are reconstructed in the inclusive final states D-μ+ and D*-μ+, where the D- meson decays into the K+π-π- final state and the D*- meson into the D[over ¯]0(→K+π-)π- final state. The asymmetry between the numbers of D(*)-μ+ and D(*)+μ- decays is measured as a function of the decay time of the B0 mesons. The CP asymmetry is measured to be a(sl)(d)=(-0.02±0.19±0.30)%, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of a(sl)(d) to date and is consistent with the prediction from the standard model.

Precision measurement of the mass and lifetime of the Ξb⁻ baryon

We report on measurements of the mass and lifetime of the Ξ(b)⁻ baryon using about 1800 Ξ(b)⁻ decays reconstructed in a proton-proton collision data set corresponding to an integrated luminosity of 3.0  fb⁻¹ collected by the LHCb experiment. The decays are reconstructed in the Ξ(b)⁻→Ξ(c)⁰π⁻, Ξ(c)⁰→pK⁻K⁻π⁺ channel and the mass and lifetime are measured using the Λ(b)⁰→Λ(c)⁺π⁻ mode as a reference. We measure M(Ξ(b)⁻)-M(Λ(b)⁰)=178.36±0.46±0.16  MeV/c², (τ(Ξ(b)⁻)/τ(Λ(b)⁰)=1.089±0.026±0.011, where the uncertainties are statistical and systematic, respectively. These results lead to a factor of 2 better precision on the Ξ(b)⁻ mass and lifetime compared to previous best measurements, and are consistent with theoretical expectations.

Measurement of the CP-violating phase ϕs in Bs(0)→Ds(+)Ds(-) decays

We present a measurement of the CP-violating weak mixing phase ϕs using the decay Bs(0)→Ds(+)Ds(-) in a data sample corresponding to 3.0 fb(-1) of integrated luminosity collected with the LHCb detector in pp collisions at center-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not use the constraint |λ|=1 to allow for the presence of CP violation in decay, yields ϕs=0.02±0.17(stat)±0.02(syst)  rad, |λ|=0.91(-0.15)(+0.18)(stat)±0.02(syst). This result is consistent with the standard model expectation.