Recent LHCb results related to the measurement of the CKM phase γ

Using data collected during 2011 at a center-of-mass energy of 7 TeV LHCb selected samples of B± → Dh± and Hb → h+h− decays. Using these samples the measurement of the full set of partial widths and CP asymmetries of B± → Dh± decays has been performed. From the analysis of the selected charmless charged two-body hadronic B decays LHCb measured the direct CP asymmetries ACP (B0 → Kπ) and ACP (B0 s → πK), the branching ratios BR(B0 → K+K−) and BR(B0 s → π+π−) and the time-dependent CP asymmetries of B0 → π+π− and B0 s → K+K− decays

CP violation in B hadron decays at LHCb

LHCb is one of the four major experiments operating at the Large Hadron Collider, and is specifically dedicated to the measurement of CP violation and rare decays in the beauty and charm quark sectors. In this report we present some of the latest and most relevant CP violation measurements in B hadron decays, performed by LHCb using the data sample collected during 2011 and 2012

Measurements of ACP (B0 → K+π−) and ACP (Bs → π+K−) at LHCb

The LHCb experiment is designed to perform flavour physics measurements at the Large Hadron Collider. Using data collected during the 2010 run, we reconstruct a sample of Hb → h+h− decays, where Hb can be either a B0 meson, a B0s meson or a Λb baryon, while h and h' stand for π, K or p. We provide preliminary values of the direct CP asymmetries of the neutral B0 and B0s mesons ACP (B0 → K+π−) = −0.074 ± 0.033(stat.) ± 0.008(syst.) and ACP (B0s → π+K−) = 0.15 ± 0.19(stat.) ± 0.02(syst.)

Particle identification for charmless two-body B decays at LHCb

Due to the possibility to produce $B^0$, $B_s^0$ and $\lambda_b$ hadrons in the proton-proton collisions at the LHC, the mass peaks of many two-body $B$ decays overlap. For this reason, the particle identification capabilities of the LHCb detector will play a crucial role in the measurements related to these decay modes. In this document we propose a method for combining different observables provided by the LHCb particle identification system into a single generalized discriminating variable, useful when performing the statistical separation of the various channels in event-by-event fits

Invariant mass line shape of B -> PP decays at LHCb

The family of B meson decays into pairs of charmless charged pseudo-scalar mesons comprises many different channels. In order to disentagle the overlapped mass peaks of the various decay modes, an accurate description of the invariant mass distribution of each mode is required. In particular, the invariant mass parameterization must take into account the effect of QED final state radiation, which leads to the presence of a long tail on the lower side of the mass peak. In this document we propose a new parameterization based on a complete QED calculation of the photon emission rate and we compare it to a simpler one based on phenomenological arguments. Furthermore, we show how the shape of the invariant mass distributions under the pi+pi- mass hypothesis, for every decay mode of interest, can be described very precisely by means of analytical calculations

Observation of two new Ξb−\Xi_b^- baryon resonances

Two structures are observed close to the kinematic threshold in the $\Xi_b^0 \pi^-$ mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content $bds$ are expected in this mass region: the spin-parity $J^P = \frac{1}{2}^+$ and $J^P=\frac{3}{2}^+$ states, denoted $\Xi_b^{\prime -}$ and $\Xi_b^{*-}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(\Xi_b^{\prime -}) - m(\Xi_b^0) - m(\pi^{-}) = 3.653 \pm 0.018 \pm 0.006$ MeV$/c^2$, $m(\Xi_b^{*-}) - m(\Xi_b^0) - m(\pi^{-}) = 23.96 \pm 0.12 \pm 0.06$ MeV$/c^2$, $\Gamma(\Xi_b^{*-}) = 1.65 \pm 0.31 \pm 0.10$ MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of $\Gamma(\Xi_b^{\prime -}) < 0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.Comment: 17 pages, 2 figure

Search for CP violation in D+→ϕπ+ and D+s→K0Sπ+ decays

A search for CP violation in D + → ϕπ + decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fb−1 at a centre of mass energy of 7 TeV. The CP -violating asymmetry is measured to be (−0.04 ± 0.14 ± 0.14)% for candidates with K − K + mass within 20 MeV/c 2 of the ϕ meson mass. A search for a CP -violating asymmetry that varies across the ϕ mass region of the D + → K − K + π + Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the D+s→K0Sπ+ decay is measured to be (0.61 ± 0.83 ± 0.14)%

Measurement of the mass and lifetime of the Ωb−\Omega_b^- baryon

A proton-proton collision data sample, corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at $\sqrt{s}=7$ and 8 TeV, is used to reconstruct $63\pm9$ $\Omega_b^-\to\Omega_c^0\pi^-$, $\Omega_c^0\to pK^-K^-\pi^+$ decays. Using the $\Xi_b^-\to\Xi_c^0\pi^-$, $\Xi_c^0\to pK^-K^-\pi^+$ decay mode for calibration, the lifetime ratio and absolute lifetime of the $\Omega_b^-$ baryon are measured to be \begin{align*} \frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\ \tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the uncertainties are statistical, systematic and from the calibration mode (for $\tau_{\Omega_b^-}$ only). A measurement is also made of the mass difference, $m_{\Omega_b^-}-m_{\Xi_b^-}$, and the corresponding $\Omega_b^-$ mass, which yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5~{\rm MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2. \end{align*} These results are consistent with previous measurements.Comment: 11 pages, 5 figures, All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-008.htm

Differential branching fraction and angular analysis of the decay B0→K∗0μ+μ−

The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions

Observation of associated production of a ZZ boson with a DD meson in the~forward region

A search for associated production of a $Z$ boson with an open charm meson is presented using a data sample, corresponding to an integrated luminosity of $1.0\,\mathrm{fb}^{-`}$ of proton--proton collisions at a centre-of-mass energy of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for associated production of a $Z$ boson with a $D^0$ meson and four candidate events for a $Z$ boson with a $D^+$ meson are observed with a combined significance of 5.1standard deviations. The production cross-sections in the forward region are measured to be $$\sigma_{Z\rightarrow\mu^+\mu^-\!,D^0} = 2.50\pm1.12\pm0.22pb$$ $$\sigma_{Z\rightarrow\mu^+\mu^-\!,D^+} = 0.44\pm0.23\pm0.03pb,$$ where the first uncertainty is statistical and the second systematic.Comment: 18 pages, 2 figure