Model-Independent Evidence for J/ψp Contributions to Λ_{b}^{0}→J/ψpK^{-} Decays

The data sample of Λ_{b}^{0}→J/ψpK^{-} decays acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3  fb^{-1}, is inspected for the presence of J/ψp or J/ψK^{-} contributions with minimal assumptions about K^{-}p contributions. It is demonstrated at more than nine standard deviations that Λ_{b}^{0}→J/ψpK^{-} decays cannot be described with K^{-}p contributions alone, and that J/ψp contributions play a dominant role in this incompatibility. These model-independent results support the previously obtained model-dependent evidence for P_{c}^{+}→J/ψp charmonium-pentaquark states in the same data sample.

A precise measurement of the [Formula: see text] meson oscillation frequency

The oscillation frequency, [Formula: see text], of [Formula: see text] mesons is measured using semileptonic decays with a [Formula: see text] or [Formula: see text] meson in the final state. The data sample corresponds to 3.0[Formula: see text] of pp collisions, collected by the LHCb experiment at centre-of-mass energies [Formula: see text] = 7 and 8[Formula: see text]. A combination of the two decay modes gives [Formula: see text], where the first uncertainty is statistical and the second is systematic. This is the most precise single measurement of this parameter. It is consistent with the current world average and has similar precision.

First Observation of D^{0}-D[over ¯]^{0} Oscillations in D^{0}→K^{+}π^{-}π^{+}π^{-} Decays and Measurement of the Associated Coherence Parameters

Charm meson oscillations are observed in a time-dependent analysis of the ratio of D^{0}→K^{+}π^{-}π^{+}π^{-} to D^{0}→K^{-}π^{+}π^{-}π^{+} decay rates, using data corresponding to an integrated luminosity of 3.0  fb^{-1} recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favored amplitudes r_{D}^{K3π} and the product of the coherence factor R_{D}^{K3π} and a charm mixing parameter y_{K3π}^{'}. The constraints measured are r_{D}^{K3π}=(5.67±0.12)×10^{-2}, which is the most precise determination to date, and R_{D}^{K3π}y_{K3π}^{'}=(0.3±1.8)×10^{-3}, which provides useful input for determinations of the CP-violating phase γ in B^{±}→DK^{±}, D→K^{∓}π^{±}π^{∓}π^{±} decays. The analysis also gives the most precise measurement of the D^{0}→K^{+}π^{-}π^{+}π^{-} branching fraction, and the first observation of D^{0}-D[over ¯]^{0} oscillations in this decay mode, with a significance of 8.2 standard deviations.

Search for Violations of Lorentz Invariance and CPT Symmetry in B_{(s)}^{0} Mixing

Violations of CPT symmetry and Lorentz invariance are searched for by studying interference effects in B^{0} mixing and in B_{s}^{0} mixing. Samples of B^{0}→J/ψK_{S}^{0} and B_{s}^{0}→J/ψK^{+}K^{-} decays are recorded by the LHCb detector in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3  fb^{-1}. No periodic variations of the particle-antiparticle mass differences are found, consistent with Lorentz invariance and CPT symmetry. Results are expressed in terms of the standard model extension parameter Δa_{μ} with precisions of O(10^{-15}) and O(10^{-14})  GeV for the B^{0} and B_{s}^{0} systems, respectively. With no assumption on Lorentz (non)invariance, the CPT-violating parameter z in the B_{s}^{0} system is measured for the first time and found to be Re(z)=-0.022±0.033±0.005 and Im(z)=0.004±0.011±0.002, where the first uncertainties are statistical and the second systematic.

Measurement of the Difference of Time-Integrated CP Asymmetries in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} Decays

A search for CP violation in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays is performed using pp collision data, corresponding to an integrated luminosity of 3  fb^{-1}, collected using the LHCb detector at center-of-mass energies of 7 and 8 TeV. The flavor of the charm meson is inferred from the charge of the pion in D^{*+}→D^{0}π^{+} and D^{*-}→D[over ¯]^{0}π^{-} decays. The difference between the CP asymmetries in D^{0}→K^{-}K^{+} and D^{0}→π^{-}π^{+} decays, ΔA_{CP}≡A_{CP}(K^{-}K^{+})-A_{CP}(π^{-}π^{+}), is measured to be [-0.10±0.08(stat)±0.03(syst)]%. This is the most precise measurement of a time-integrated CP asymmetry in the charm sector from a single experiment.

Observation of B_{s}^{0}→D[over ¯]^{0}K_{S}^{0} and Evidence for B_{s}^{0}→D[over ¯]^{*}^{0}K_{S}^{0} Decays

The first observation of the B_{s}^{0}→D[over ¯]^{0}K_{S}^{0} decay mode and evidence for the B_{s}^{0}→D[over ¯]^{*0}K_{S}^{0} decay mode are reported. The data sample corresponds to an integrated luminosity of 3.0  fb^{-1} collected in pp collisions by LHCb at center-of-mass energies of 7 and 8 TeV. The branching fractions are measured to be B(B_{s}^{0}→D[over ¯]^{0}K[over ¯]^{0})=[4.3±0.5(stat)±0.3(syst)±0.3(frag)±0.6(norm)]×10^{-4},B(B_{s}^{0}→D[over ¯]^{*0}K[over ¯]^{0})=[2.8±1.0(stat)±0.3(syst)±0.2(frag)±0.4(norm)]×10^{-4},where the uncertainties are due to contributions coming from statistical precision, systematic effects, and the precision of two external inputs, the ratio f_{s}/f_{d} and the branching fraction of B^{0}→D[over ¯]^{0}K_{S}^{0}, which is used as a calibration channel.

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].

Evidence for the Strangeness-Changing Weak Decay Ξ_{b}^{-}→Λ_{b}^{0}π^{-}

Using a pp collision data sample corresponding to an integrated luminosity of 3.0  fb^{-1}, collected by the LHCb detector, we present the first search for the strangeness-changing weak decay Ξ_{b}^{-}→Λ_{b}^{0}π^{-}. No b hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported. The relative rate is measured to be f_{Ξ_{b}^{-}}/f_{Λ_{b}^{0}}B(Ξ_{b}^{-}→Λ_{b}^{0}π^{-})=(5.7±1.8_{-0.9}^{+0.8})×10^{-4},where f_{Ξ_{b}^{-}} and f_{Λ_{b}^{0}} are the b→Ξ_{b}^{-} and b→Λ_{b}^{0} fragmentation fractions, and B(Ξ_{b}^{-}→Λ_{b}^{0}π^{-}) is the branching fraction. Assuming f_{Ξ_{b}^{-}}/f_{Λ_{b}^{0}} is bounded between 0.1 and 0.3, the branching fraction B(Ξ_{b}^{-}→Λ_{b}^{0}π^{-}) would lie in the range from (0.57±0.21)% to (0.19±0.07)%.

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.