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Abstract:

Asymmetries in the time-dependent rates of D0→K+K- and D0→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 D0 and D¯0 decays, sensitive to indirect CP violation, are measured to be AΓ(K+K-)=(-0.30±0.32±0.10)×10^-3 and AΓ(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.

Abstract:

The production cross-section of J/ψ pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of s=13 TeV, corresponding to an integrated luminosity of 279 ±11 pb −1 . The measurement is performed for J/ψ mesons with a transverse momentum of less than 10 GeV/c in the rapidity range 2.0 < y < 4.5. The production cross-section is measured to be 15.2 ± 1.0 ± 0.9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/ψ pair are measured and compared to theoretical predictions.

Abstract:

A search for CP violation in the decay Λb0 → pK−μ+μ− is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb^−1. The Λb0 → pK−μ+μ− decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured, ΔACP ≡ ACP(Λ0b→pK−μ+μ−) − ACP(Λ0b→pK−J/ψ) and a aT-odd/CP, where the latter is based on asymmetries in the angle between the μ+μ− and pK− decay planes. These are measured to be ΔACP = (−3.5 ±5.0(stat) ±0.2(syst))×10^−2, aT-odd/CP = (1.2 ±5.0 (stat) ±0.7 (syst))×10^−2,and no evidence for CP violation is found.

Abstract:

The observation of the decay Ξ b − →J/ψΛK − is reported, using a data sample corresponding to an integrated luminosity of 3fb −1 , collected by the LHCb detector in pp collisions at centre-of-mass energies of 7 and 8TeV. The production rate of Ξ b − baryons detected in the decay Ξ b − →J/ψΛK − is measured relative to that of Λ b 0 baryons using the decay Λ b 0 →J/ψΛ. Integrated over the b-baryon transverse momentum p T < 25GeV/c and rapidity 2.0 < y < 4.5, the measured ratio is [Formula presented][Formula presented] =(4.19±0.29 (stat)±0.15 (syst))×10 −2 , where f Ξ b − and f Λ b 0 are the fragmentation fractions of b→Ξ b − and b→Λ b 0 transitions, and B represents the branching fraction of the corresponding b-baryon decay. The mass difference between Ξ b − and Λ b 0 baryons is measured to be M(Ξ b − )−M(Λ b 0 )=177.08±0.47 (stat)±0.16 (syst)MeV/c 2 .

Abstract:

A search for the rare decays B0s→ τþτ− and B0 → τþτ− 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−ντ. Assuming no contribution from B0 → τþτ− decays, an upper limit is set on the branching fraction B(B0s → τ+τ−) < 6.8 × 10^−3 at the 95% confidence level. If instead no contribution from B0s → τ+τ− decays is assumed, the limit is B(B0 → τþτ−) < 2.1 × 10^−3 at the 95% confidence level. These results correspond to the first direct limit on B(B0s→ τ+τ−) and the world’s best limit on B(B0 → τ+τ−).