Measurement of CPCP-violating and mixing-induced observables in Bs0→ϕγB_s^0 \to \phi\gamma decays

International audienceA time-dependent analysis of the Bs0→ϕγ decay rate is performed to determine the CP -violating observables Sϕγ and Cϕγ and the mixing-induced observable AϕγΔ. The measurement is based on a sample of pp collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3  fb-1 at center-of-mass energies of 7 and 8 TeV. The measured values are Sϕγ=0.43±0.30±0.11, Cϕγ=0.11±0.29±0.11, and AϕγΔ=-0.67-0.41+0.37±0.17, where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables S and C in radiative Bs0 decays. The results are consistent with the standard model predictions

Observation of Several Sources of CPCP Violation in B+→π+π+π−B^+ \to \pi^+ \pi^+ \pi^- Decays

International audienceObservations are reported of different sources of CP violation from an amplitude analysis of B+→π+π+π- decays, based on a data sample corresponding to an integrated luminosity of 3  fb-1 of pp collisions recorded with the LHCb detector. A large CP asymmetry is observed in the decay amplitude involving the tensor f2(1270) resonance, and in addition significant CP violation is found in the π+π-S wave at low invariant mass. The presence of CP violation related to interference between the π+π-S wave and the P wave B+→ρ(770)0π+ amplitude is also established; this causes large local asymmetries but cancels when integrated over the phase space of the decay. The results provide both qualitative and quantitative new insights into CP -violation effects in hadronic B decays

Measurement of CP violation in the Bs0→ϕϕ {B}_s^0\to \phi \phi decay and search for the B0→ϕϕB^0\rightarrow \phi\phi decay

International audienceA measurement of the time-dependent CP-violating asymmetry in ${B}_s^0\to \phi \phi$ 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 $\sqrt{s}$ = 7 TeV in 2011, 8 TeV in 2012 and 13 TeV in 2015 and 2016, a signal yield of around 9000 ${B}_s^0\to \phi \phi$ decays is obtained. The CP-violating phase ${\phi}_s^{s\overline{s}s}$ 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 $\overline{b}\to \overline{s}s\overline{s}s$ transitions. Finally, a limit on the branching fraction of the B$^{0}$ → ϕϕ decay is determined to be $\mathcal{B}\left({B}^0\to \phi \phi \right)<2.7\times {10}^{-8}$ at 90 % confidence level

Amplitude analysis of the B+→π+π+π−B^+ \rightarrow \pi^+\pi^+\pi^- decay

International audienceThe results of an amplitude analysis of the charmless three-body decay B+→π+π+π-, in which CP-violation effects are taken into account, are reported. The analysis is based on a data sample corresponding to an integrated luminosity of 3  fb-1 of pp collisions recorded with the LHCb detector. The most challenging aspect of the analysis is the description of the behavior of the π+π-  S-wave contribution, which is achieved by using three complementary approaches based on the isobar model, the K-matrix formalism, and a quasi-model-independent procedure. Additional resonant contributions for all three methods are described using a common isobar model, and include the ρ(770)0, ω(782) and ρ(1450)0 resonances in the π+π- P-wave, the f2(1270) resonance in the π+π- D-wave, and the ρ3(1690)0 resonance in the π+π- F-wave. Significant CP-violation effects are observed in both S- and D-waves, as well as in the interference between the S- and P-waves. The results from all three approaches agree and provide new insight into the dynamics and the origin of CP-violation effects in B+→π+π+π- decays

Search for the lepton-flavour-violating decays Bs0→τ±μ∓B^{0}_{s}\to\tau^{\pm}\mu^{\mp} and B0→τ±μ∓B^{0}\to\tau^{\pm}\mu^{\mp}

International audienceResults are reported from a search for the rare decays Bs0→τ±μ∓ and B0→τ±μ∓, 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±μ∓, the upper limit B(Bs0→τ±μ∓)<4.2×10-5 is obtained at 95% confidence level. If no contribution from Bs0→τ±μ∓ is assumed, a limit of B(B0→τ±μ∓)<1.4×10-5 is obtained at 95% confidence level. These results represent the first limit on B(Bs0→τ±μ∓) and the most stringent limit on B(B0→τ±μ∓)

Measurement of the Λb0→J/ψΛ\Lambda^0_b\rightarrow J/\psi\Lambda angular distribution and the Λb0\Lambda^0_b polarisation in pppp collisions

International audienceThis paper presents an analysis of the ${\Lambda}_b^0$→ J/ψΛ angular distribution and the transverse production polarisation of ${\Lambda}_b^0$ baryons in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb$^{−1}$, collected with the LHCb experiment. The polarisation is determined in a fiducial region of ${\Lambda}_b^0$ transverse momentum and pseudorapidity of 1 < p$_{T}$< 20 GeV/c and 2 < η < 5, respectively. The data are consistent with ${\Lambda}_b^0$ baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the Λ → pπ$^{−}$ decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES III collaboration.[graphic not available: see fulltext

Measurement of the electron reconstruction efficiency at LHCb

International audienceThe single electron track-reconstruction efficiency is determined using a sample corresponding to $1.3~\mathrm{fb}^{-1}$of $pp$ collision data recorded with the LHCb detector in 2017. This measurement exploits $B^+\to J/\psi (e^+e^-)K^+$ decays, where one of the electrons is fully reconstructed and paired with the kaon, while the other electron is reconstructed using only the information of the vertex detector. Despite this partial reconstruction, kinematic and geometric constraints allow the $B^+$-meson mass to be reconstructed and the signal to be well separated from backgrounds. This in turn allows the electron reconstruction efficiency to be measured by matching the partial track segment found in the vertex detector to tracks found by LHCb's regular reconstruction algorithms. The agreement between data and simulation is evaluated, and corrections are derived for simulated electrons in bins of kinematics. The presented method allows LHCb to measure branching fractions involving single electrons with a an electron reconstruction systematic uncertainty below $1\%$

Precision measurement of the Bc+B_{c}^{+} meson mass

International audienceA precision measurement of the ${B}_c^{+}$ meson mass is performed using proton- proton collision data collected with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9.0 fb$^{−1}$. The ${B}_c^{+}$ mesons are reconstructed via the decays ${B}_c^{+}$→ J/ψπ$^{+}$, ${B}_c^{+}$→ J/ψπ$^{+}$π$^{−}$π$^{+}$, ${B}_c^{+}\to J/\psi p\overline{p}{\pi}^{+}$, ${B}_c^{+}\to J/\psi {D}_s^{+}$, ${B}_c^{+}$→ J/ψ D$^{0}$K$^{+}$ and ${B}_c^{+}\to {B}_s^0{\pi}^{+}$. Combining the results of the individual decay channels, the ${B}_c^{+}$ mass is measured to be 6274.47 ± 0.27 (stat) ± 0.17 (syst) MeV/c$^{2}$. This is the most precise measurement of the ${B}_c^{+}$ mass to date. The difference between the ${B}_c^{+}$ and ${B}_s^0$ meson masses is measured to be 907.75 ± 0.37 (stat) ± 0.27 (syst) MeV/c.[graphic not available: see fulltext