Searches for rare Bs0 and B 0 decays into four muons

Searches for rare Bs0 and B0 decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. Direct decays and decays via light scalar and J/ψ resonances are considered. No evidence for the six decays searched for is found and upper limits at the 95% confidence level on their branching fractions ranging between 1.8 × 10−10 and 2.6 × 10−9 are set. [Figure not available: see fulltext.

Searches for rare B-s(0) and B-0 decays into four muons

Searches for rare B-s(0) and B-0 decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). Direct decays and decays via light scalar and J/psi resonances are considered. No evidence for the six decays searched for is found and upper limits at the 95% confidence level on their branching fractions ranging between 1.8 x 10(-10) and 2.6 x 10(-9) are set

Measurement of the photon polarization in Λb→Λγ\Lambda_b \to \Lambda \gamma decays

The photon polarization in $b \to s \gamma$ transitions is measured for the first time in radiative b-baryon decays exploiting the unique spin structure of $\Lambda_b \to \Lambda \gamma$ decays. A data sample corresponding to an integrated luminosity of $6\;fb^{-1}$ collected by the LHCb experiment in $pp$ collisions at a center-of-mass energy of $13\;TeV$ is used. The photon polarization is measured to be $\alpha_{\gamma}= 0.82^{\,+\,0.17\,+\,0.04}_{\,-\,0.26\,-\,0.13}$, where the first uncertainty is statistical and the second systematic. This result is in agreement with the Standard Model prediction and previous measurements in b-meson decays. Charge-parity breaking effects are studied for the first time in this observable and found to be consistent with $CP$ symmetry.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2021-030.html (LHCb public pages

Observation of the Decay Λ0b→Λ+cτ−¯ν

The first observation of the semileptonic b-baryon decay Λb0→Λc+τ-ν¯τ, with a significance of 6.1σ, is reported using a data sample corresponding to 3 fb-1 of integrated luminosity, collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV at the LHC. The τ- lepton is reconstructed in the hadronic decay to three charged pions. The ratio K=B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+π-π+π-) is measured to be 2.46±0.27±0.40, where the first uncertainty is statistical and the second systematic. The branching fraction B(Λb0→Λc+τ-ν¯τ)=(1.50±0.16±0.25±0.23)% is obtained, where the third uncertainty is from the external branching fraction of the normalization channel Λb0→Λc+π-π+π-. The ratio of semileptonic branching fractions R(Λc+)B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+μ-ν¯μ) is derived to be 0.242±0.026±0.040±0.059, where the external branching fraction uncertainty from the channel Λb0→Λc+μ-ν¯μ contributes to the last term. This result is in agreement with the standard model prediction

Observation of the B0→¯D*0K+π− and B0s→¯D*0K−π+ decays

The first observations of B0→D¯∗(2007)0K+π- and Bs0→D¯∗(2007)0K-π+ decays are presented, and their branching fractions relative to that of the B0→D¯∗(2007)0π+π- decay are reported. These modes can potentially be used to investigate the spectroscopy of charm and charm-strange resonances and to determine the angle γ of the Cabibbo-Kobayashi-Maskawa unitarity triangle. It is also important to understand them as a source of potential background in determinations of γ from B+→DK+ and B0→DK+π- decays. The analysis is based on a sample corresponding to an integrated luminosity of 5.4 fb-1 of proton-proton collision data at 13 TeV center-of-mass energy recorded with the LHCb detector. The D¯∗(2007)0 mesons are fully reconstructed in the D¯0π0 and D¯0γ channels with the D¯0→K+π- decay. A novel weighting method is used to subtract background while simultaneously applying an event-by-event efficiency correction to account for resonant structures in the decays

A study of CP violation in the decays B±→[K+K-π+π-]Dh± (h= K, π) and B±→[π+π-π+π-]Dh±

The first study of CP violation in the decay mode B±→[K+K-π+π-]Dh± , with h= K, π , is presented, exploiting a data sample of proton–proton collisions collected by the LHCb experiment that corresponds to an integrated luminosity of 9 \,fb - 1 . The analysis is performed in bins of phase space, which are optimised for sensitivity to local CP asymmetries. CP -violating observables that are sensitive to the angle γ of the Unitarity Triangle are determined. The analysis requires external information on charm-decay parameters, which are currently taken from an amplitude analysis of LHCb data, but can be updated in the future when direct measurements become available. Measurements are also performed of phase-space integrated observables for B±→[K+K-π+π-]Dh± and B±→[π+π-π+π-]Dh± decays

Search for D∗(2007)0→μ+μ− in B−→π−μ+μ− decays

The very rare D*(2007)(0) -> mu(+)mu(-) decay is searched for by analysing B- -> pi(-)mu(+)mu(-) decays. The analysis uses a sample of beauty mesons produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb(-1). The signal signature corresponds to simultaneous peaks in the mu(+)mu(-) and pi(-)mu(+)mu(-) invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at B(D*(2007)(0) -> mu(+)mu(-)) < 2.6x10(-8) at 90% confidence level. This is the first limit on the branching fraction of D*(2007)(0) -> mu(+)mu(-) decays and the most stringent limit on D*(2007)(0) decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays

Open charm production and asymmetry in ppNe collisions at sNN=\sqrt{s_{\scriptscriptstyle\rm NN}} = 68.5 GeV

A measurement of $D^0$ meson production by the LHCb experiment in its fixed-target configuration is presented. The production of $D^0$ mesons is studied with a beam of 2.5 TeV protons colliding on a gaseous neon target at rest, corresponding to a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{\rm NN}}$ = 68.5 GeV. The $D^0$ and ${\overline D^0}$ production cross-section in $p$Ne collisions in the centre-of-mass rapidity range $y^{\star}\in [-2.29, 0]$ is found to be $\sigma_{D^{0}}^{y^\star \in [-2.29, 0]} = 48.2 \pm 0.3 \pm 4.5 \,\mu\textrm{b/nucleon}$ where the first uncertainty is statistical and the second is systematic. The $D^0-{\overline D^0}$ production asymmetry is also evaluated and suggests a negative trend at large negative $y^{\star}$. The considered models do not account precisely for all the features observed in the LHCb data, but theoretical predictions including 1$\%$ intrinsic charm and 10$\%$ recombination contributions better describe the data than the other models considered.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-015.html (LHCb public pages). arXiv admin note: text overlap with arXiv:1810.0790