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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 0 b 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 first observation of the B 0 s → D ¯ 0 K 0 S decay mode and evidence for the B 0 s → D ¯* 0 K 0 S 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.
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 ¯ 0 π – decays. The difference between the CP asymmetries in D 0 → K – K + and D 0 → π – π + decays, Δ A 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.
Violations of CPT symmetry and Lorentz invariance are searched for by studying interference effects in B 0 mixing and in B 0 s mixing. Samples of B 0 → J/ψK 0 S and B 0 s → 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 0 s systems, respectively. With no assumption on Lorentz (non)invariance, the CPT -violating parameter z in the B 0 s system is measured for the first time and found to be R e(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.
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 K3π D and the product of the coherence factor R K3π D and a charm mixing parameter y' K3π . The constraints measured are r K3π D = (5.67 ± 0.12) × 10 –2 , which is the most precise determination to date, and R K3π D y'K 3π = (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 ¯ 0 oscillations in this decay mode, with a significance of 8.2 standard deviations.
The CP asymmetry in the mixing of B 0 s and B¯ 0 s mesons is measured in proton-proton collision data corresponding to an integrated luminosity of 3.0 fb -1 , recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV. Semileptonic B 0 s and B¯ 0 s decays are studied in the inclusive mode D ∓ s μ ± ν (–) μ X with the D ∓ s mesons reconstructed in the K + K – π ∓ final state. Correcting the observed charge asymmetry for detection and background effects, the CP asymmetry is found to be a s sl = (0.39 ± 0.26 ± 0.20)%, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of a s sl to date. It is consistent with the prediction from the standard model and will constrain new models of particle physics.
The data sample of Λ 0 b → 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 0 b → 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 full amplitude analysis of Λ 0 b →J/ψpπ – decays is performed with a data sample acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb –1 . A significantly better description of the data is achieved when, in addition to the previously observed nucleon excitations N→pπ – , either the P c (4380) + and P c (4450) + →J/ψp states, previously observed in Λ 0 b →J/ψpK – decays, or the Z c (4200) – →J/ψπ – state, previously reported in B 0 →J/ψK + π – decays, or all three, are included in the amplitude models. The data support a model containing all three exotic states, with a significance of more than three standard deviations. Within uncertainties, the data are consistent with the P c (4380) + and P c (4450) + production rates expected from their previous observation taking account of Cabibbo suppression.
The CP violation observables S and C in the decay channel B 0 →D + D – are determined from a sample of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 3 fb –1 . The observable S describes CP violation in the interference between mixing and the decay amplitude, and C parametrizes direct CP violation in the decay. The following values are obtained from a flavor-tagged, decay-time-dependent analysis: S = –0.54 +0.17 –0.16 (stat)±0.05(syst), C = 0.26 +0.18 –0.17 (stat)±0.02(syst). These values provide evidence for CP violation at a significance level of 4.0 standard deviations. The phase shift due to higher-order standard model corrections is constrained to a small value of ΔΦ = –0.16 +0.19 –0.21 rad.
The polarization of photons produced in radiative B 0 s decays is studied for the first time. The data are recorded by the LHCb experiment in pp collisions corresponding to an integrated luminosity of 3 fb –1 at center-of-mass energies of 7 and 8 TeV. A time-dependent analysis of the B 0 s →Φγ decay rate is conducted to determine the parameter A Δ , which is related to the ratio of right- over left-handed photon polarization amplitudes in b→sγ transitions. A value of A Δ = –0.98 +0.46 –0.52 +0.23 –0.20 is measured. This result is consistent with the standard model prediction within 2 standard deviations.
The first full amplitude analysis of B + → J/ψϕK + with J/ψ → μ + μ - , ϕ → K + K - decays is performed with a data sample of 3 fb -1 of pp collision data collected at $\sqrt{s}$ =7 and 8 TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into ϕK + , and four J/ψϕ structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed X(4140) state.
Measurements of the cross section for producing b quarks in the reaction pp→bbX are reported in 7 and 13 TeV collisions at the LHC as a function of the pseudorapidity η in the range 2 < η < 5 covered by the acceptance of the LHCb experiment. The measurements are done using semileptonic decays of b-flavored hadrons decaying into a ground-state charmed hadron in association with a muon. The cross sections in the covered η range are 72.0±0.3±6.8 and 154.3±1.5±14.3 μb for 7 and 13 TeV. The ratio is 2.14±0.02±0.13, where the quoted uncertainties are statistical and systematic, respectively. The agreement with theoretical expectation is good at 7 TeV, but differs somewhat at 13 TeV. The measured ratio of cross sections is larger at lower η than the model prediction.
A search for the B 0 → K + K - decay is performed using pp -collision data collected by LHCb. The data set corresponds to integrated luminosities of 1.0 and 2.0 fb -1 at center-of-mass energies of 7 and 8 TeV, respectively. This decay is observed for the first time, with a significance of more than 5 standard deviations. The analysis also results in an improved measurement of the branching fraction for the $B^{0}_{s}$ → π + π - decay. The measured branching fractions are $\mathcal{B}$(B 0 → K + K - ) = (7.80 ± 1.27 ± 0.81 ± 0.21) × 10 -8 and $\mathcal{B}$(B$^{0}_{s}$ → π + π - ) = (6.91 ± 0.54 ± 0.63 ± 0.19 ± 0.40) × 10 -7 . The first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the B 0 → K + π - branching fraction used as a normalization. For the $B^{0}_{s}$ mode, the fourth accounts for the uncertainty on the ratio of the probabilities for b quarks to hadronize into $B^{0}_{s}$ and $B^0$ mesons.
The $\Xi{^+_c}$$K^-$ mass spectrum is studied with a sample of $pp$ collision data corresponding to an integrated luminosity of 3.3 fb -1 , collected by the LHCb experiment. The $\Xi{^+_c}$ is reconstructed in the decay mode $pK^-$$π^+$. Five new, narrow excited $Ω_c^0$ states are observed: the $Ω_c$(3000)$^0$, $Ω_c$(3050)$^0$, $Ω_c$(3066)$^0$, $Ω_c$(3090)$^0$, and $Ω_c$(3119)$^0$. Measurements of their masses and widths are reported.
A search for the rare decays $B^0_s$→$μ$ + $μ$ - and B 0 →$μ$ + $μ$ - is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4 fb -1 . An excess of $B^0_s$→$μ$ + $μ$ - decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be $B$($μ$ + $μ$ - )=(3.0 ± $0.6^{+0.3}_{-0.2}$) × 10 -9 , where the first uncertainty is statistical and the second systematic. The first measurement of the $B^0_s$→$μ$ + $μ$ - effective lifetime, τ($B^0_s$→($μ$ + $μ$ - ) = 2.04 ± 0.44 ± 0.05 ps, is reported. No significant excess of B 0 →($μ$ + $μ$ - decays is found, and a 95% confidence level upper limit, $B$(B 0 →($μ$ + $μ$ - ) < 3.4 × 10 -10 , is determined. All results are in agreement with the standard model expectations.
The production of $J/ψ$ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the $J/ψ$ meson, $z$($J/ψ$)≡$p$ T ($J/ψ$)/$p$ T (jet), is measured using jets with $p$ T (jet) > 20 GeV in the pseudorapidity range 2.5 < $η$(jet) < 4.0. The observed $z$($J/ψ$) distribution for $J/ψ$ mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt $J/ψ$ production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the $p$ T fraction carried by prompt $J/ψ$ mesons in jets at any experiment.
A search for the rare decays $B^0_s$→$τ$ + $τ$ - and $B$ 0 →$τ$ + $τ$ - is performed using proton-proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 fb -1 collected in 2011 and 2012. The $τ$ leptons are reconstructed through the decay $τ$ - →$π$ - $π$ + $π$ - $ν$ $τ$ . Assuming no contribution from B 0 →$τ$ + $τ$ - decays, an upper limit is set on the branching fraction $B$($B^0_s$→$τ$ + $τ$ - ) < 6.8×10-3 at the 95% confidence level. If instead no contribution from $B^0_s$→$τ$ + $τ$ - decays is assumed, the limit is $B$($B$ 0 →$τ$ + $τ$ - ) < 2.1×10 -3 at the 95% confidence level. These results correspond to the first direct limit on $B$($B^0_s$→$τ$+$τ$-) and the world's best limit on $B$($B$ 0 →$τ$ + $τ$ - ).
Asymmetries in the time-dependent rates of D 0 →K + K - and D 0 →$π$ + $π$ - decays are measured in a $pp$ collision data sample collected with the LHCb detector during LHC Run 1, corresponding to an integrated luminosity of 3 fb -1 . The asymmetries in effective decay widths between $D$ 0 and $\bar{D}$ 0 decays, sensitive to indirect $CP$ violation, are measured to be A $Γ$ (K + K - ) = (-0.30 ± 0.32 ± 0.10) × 10 -3 and A $Γ$ ($π$ + $π$ - ) = (0.46 ± 0.58 ± 0.12) × 10 -3 , where the first uncertainty is statistical and the second systematic. These measurements show no evidence for $CP$ violation and improve on the precision of the previous best measurements by nearly a factor of two.