Search for the Lepton-Flavor-Violating Decays Bs0 →τ±μâ' and B0 →τ±μâ'

Results are reported from a search for the rare decays Bs0→τ±μâ' and B0→τ±μâ', where the τ lepton is reconstructed in the channel τ-→π-π+π-ντ. These processes are effectively forbidden in the standard model, but they can potentially occur at detectable rates in models of new physics that can induce lepton-flavor-violating decays. The search is based on a data sample corresponding to 3 fb-1 of proton-proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected τ neutrino, the Bs0 and B0 signal regions are highly overlapping. Assuming no contribution from B0→τ±μâ', the upper limit B(Bs0→τ±μâ')<4.2×10-5 is obtained at 95% confidence level. If no contribution from Bs0→τ±μâ' is assumed, a limit of B(B0→τ±μâ')<1.4×10-5 is obtained at 95% confidence level. These results represent the first limit on B(Bs0→τ±μâ') and the most stringent limit on B(B0→τ±μâ')

Measurement of psi (2S) production cross-sections in proton-proton collisions at v s=7 and 13 TeV

The cross-sections of ψ(2S) meson production in proton-proton collisions at √ s = 13 TeV are measured with a data sample collected by the LHCb detector corresponding to an integrated luminosity of 275 pb−1. The production cross-sections for prompt ψ(2S) mesons and those for ψ(2S) mesons from b-hadron decays (ψ(2S)-from-b) are determined as functions of the transverse momentum, pT, and the rapidity, y, of the ψ(2S) meson in the kinematic range 2 < pT < 20 GeV/c and 2.0 < y < 4.5. The production cross-sections integrated over this kinematic region are σ(prompt ψ(2S), 13 TeV) = 1.430 ± 0.005 (stat) ± 0.099 (syst) μb, σ(ψ(2S)-from-b, 13 TeV) = 0.426 ± 0.002 (stat) ± 0.030 (syst) μb. A new measurement of ψ(2S) production cross-sections in pp collisions at √ s = 7 TeV is also performed using data collected in 2011, corresponding to an integrated luminosity of 614 pb−1. The integrated production cross-sections in the kinematic range 3.5 < pT < 14 GeV/c and 2.0 < y < 4.5 are σ(prompt ψ(2S),7 TeV) = 0.471 ± 0.001 (stat) ± 0.025 (syst) μb, σ(ψ(2S)-from-b,7 TeV) = 0.126 ± 0.001 (stat) ± 0.008 (syst) μb. All results show reasonable agreement with theoretical calculations

Measurement of the Mass Difference Between Neutral Charm-Meson Eigenstates

We report a measurement of the mass difference between neutral charm-meson eigenstates using a novel approach that enhances sensitivity to this parameter. We use 2.3 × 10 6 D 0 → K 0 S π + π − decays reconstructed in proton-proton collisions collected by the LHCb experiment in 2011 and 2012. Allowing for C P violation in mixing and in the interference between mixing and decay, we measure the C P -averaged normalized mass difference x C P = [ 2.7 ± 1.6 ( stat ) ± 0.4 ( syst ) ] × 10 − 3 and the C P -violating parameter Δ x = [ − 0.53 ± 0.70 ( stat ) ± 0.22 ( syst ) ] × 10 − 3 . The results are consistent with C P symmetry. These determinations are the most precise from a single experiment and, combined with current world-average results, yield the first evidence that the masses of the neutral charm-meson eigenstates differ

Measurement of charged hadron production in Z-tagged jets in proton-proton collisions at s√=8 TeV

The production of charged hadrons within jets recoiling against a Z boson is measured in proton-proton collision data at ffiffi s p ¼ 8 TeV recorded by the LHCb experiment. The charged-hadron structure of the jet is studied longitudinally and transverse to the jet axis for jets with transverse momentum pT > 20 GeV and in the pseudorapidity range 2.5 < η < 4. These are the first measurements of jet hadronization at these forward rapidities and also the first where the jet is produced in association with a Z boson. In contrast to previous hadronization measurements at the Large Hadron Collider, which are dominated by gluon jets, these measurements probe predominantly light-quark jets which are found to be more longitudinally and transversely collimated with respect to the jet axis when compared to the previous gluon dominated measurements. Therefore, these results provide valuable information on differences between quarks and gluons regarding nonperturbative hadronization dynamics

Measurement of the mass and production rate of Xi(-)(b)( )baryons

The first measurement of the production rate of Ξ − b baryons in p p collisions relative to that of Λ 0 b baryons is reported, using data samples collected by the LHCb experiment, and corresponding to integrated luminosities of 1, 2 and 1.6     fb − 1 at √ s = 7 , 8 and 13 TeV, respectively. In the kinematic region 2 < η < 6 and p T < 20     GeV / c , we measure f Ξ − b f Λ 0 b B ( Ξ − b → J / ψ Ξ − ) B ( Λ 0 b → J / ψ Λ ) = ( 10.8 ± 0.9 ± 0.8 ) × 10 − 2 [ √ s = 7 , 8     TeV ], f Ξ − b f Λ 0 b B ( Ξ − b → J / ψ Ξ − ) B ( Λ 0 b → J / ψ Λ ) = ( 13.1 ± 1.1 ± 1.0 ) × 10 − 2 [ √ s = 13     TeV ], where f Ξ − b and f Λ 0 b are the fragmentation fractions of b quarks into Ξ − b and Λ 0 b baryons, respectively; B represents branching fractions; and the uncertainties are due to statistical and experimental systematic sources. The values of f Ξ − b / f Λ 0 b are obtained by invoking SU(3) symmetry in the Ξ − b → J / ψ Ξ − and Λ 0 b → J / ψ Λ decays. Production asymmetries between Ξ − b and ¯ Ξ + b baryons are also reported. The mass of the Ξ − b baryon is also measured relative to that of the Λ 0 b baryon, from which it is found that m ( Ξ − b ) = 5796.70 ± 0.39 ± 0.15 ± 0.17     MeV / c 2 , where the last uncertainty is due to the precision on the known Λ 0 b mass. This result represents the most precise determination of the Ξ − b mass

Measurement of CP violation in the Bs0→ϕϕ decay and search for the B 0 → ϕϕ decay

A measurement of the time-dependent CP-violating asymmetry in B0s → φφ decays is presented. Using a sample of proton-proton collision data corresponding to an integrated luminosity of 5.0 fb−1 collected by the LHCb experiment at centre-of-mass energies √ s = 7 TeV in 2011, 8 TeV in 2012 and 13 TeV in 2015 and 2016, a signal yield of around 9000 B0 s → φφ decays is obtained. The CP-violating phase φ sss¯ s is measured to be −0.073 ± 0.115(stat) ± 0.027(syst) rad, under the assumption it is independent of the helicity of the φφ decay. In addition, the CP-violating phases of the transverse polarisations under the assumption of CP conservation of the longitudinal phase are measured. The helicity-independent direct CP-violation parameter is also measured, and is found to be |λ| = 0.99 ± 0.05(stat) ± 0.01(syst). In addition, T-odd triple-product asymmetries are measured. The results obtained are consistent with the hypothesis of CP conservation in ¯b → ss¯ ss¯ transitions. Finally, a limit on the branching fraction of the B0 → φφ decay is determined to be B(B0 → φφ) < 2.7 × 10−8 at 90 % confidence level

Amplitude analysis of B± → π±K+K− decays

The first amplitude analysis of the B± → π ±K+K− decay is reported based on a data sample corresponding to an integrated luminosity of 3.0 fb−1 of pp collisions recorded in 2011 and 2012 with the LHCb detector. The data are found to be best described by a coherent sum of five resonant structures plus a nonresonant component and a contribution from ππ ↔ KK S-wave rescattering. The dominant contributions in the π ±K∓ and K+K− systems are the nonresonant and the B± → ρ(1450)0π ± amplitudes, respectively, with fit fractions around 30%. For the rescattering contribution, a sizeable fit fraction is observed. This component has the largest CP asymmetry reported to date for a single amplitude of (−66 ± 4 ± 2)%, where the first uncertainty is statistical and the second systematic. No significant CP violation is observed in the other contributions

Measurement of the CP-violating phase ϕs from Bs0→J/ψπ+π− decays in 13 TeV pp collisions

Decays of B0s and B0s mesons into J/ψ π+π− final states are studied in a data sample corresponding to 1.9 fb−1 of integrated luminosity collected with the LHCb detector in 13 TeV pp collisions. A time-dependent amplitude analysis is used to determine the final-state resonance contributions, the CP-violating phase φs = −0.057 ± 0.060 ± 0.011 rad, the decay-width difference between the heavier mass B0 s eigenstate and the B0 meson of −0.050 ± 0.004 ± 0.004 ps−1, and the CP-violating parameter |λ| = 1.01+0.08 −0.06 ± 0.03, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV pp collisions obtaining φs = 0.002 ± 0.044 ± 0.012 rad, and |λ| = 0.949 ± 0.036 ± 0.019

Determination of quantum numbers for several excited charmed mesons observed in B- -> D*(+)pi(-) pi(-) decays

A four-body amplitude analysis of the B−→D*+π−π− decay is performed, where fractions and relative phases of the various resonances contributing to the decay are measured. Several quasi-model-independent analyses are performed aimed at searching for the presence of new states and establishing the quantum numbers of previously observed charmed meson resonances. In particular the resonance parameters and quantum numbers are determined for the D1(2420), D1(2430), D0(2550), D∗1(2600), D2(2740) and D∗3(2750) states. The mixing between the D1(2420) and D1(2430) resonances is studied and the mixing parameters are measured. The dataset corresponds to an integrated luminosity of 4.7  fb−1, collected in proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV with the LHCb detector

Search for the doubly charmed baryon Ω+cc

A search for the doubly charmed baryon Ω+ cc with the decay mode Ω+ cc → Ξ+ c K−π+ is performed using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4 fb−1 . No significant signal is observed within the invariant mass range of 3.6 to 4.0 GeV/c2. Upper limits are set on the ratio R of the production cross-section times the total branching fraction of the Ω+ cc → Ξ+ c K−π+ decay with respect to the Ξ++ cc → Λ+ c K−π+π+ decay. Upper limits at 95% credibility level for R in the range 0.005 to 0.11 are obtained for different hypotheses on the Ω+ cc mass and lifetime in the rapidity range from 2.0 to 4.5 and transverse momentum range from 4 to 15 GeV/c