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

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.)

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 D meson decays at hadron colliders

The search for CP violation in charmed meson decays represents an important test of the Standard Model and hence a promising sector where to look for New Physics. In this paper, the first observation of D0 mixing with a significance of more than 5 standard deviations performed by a single experiment is presented. The measured mixing parameters are: RD = (3.52±0.15)×10−3, y = (7.2±2.4)×10−3, x2 = (−0.09±0.13)×10−3. Furthermore, the recent measurements of the difference between the CP asymmetries of the D0 → K+K− and D0 → π+π− decays (ΔACP ) are discussed

Differential branching fraction and angular analysis of Λb0→Λμ+μ−\Lambda^{0}_{b} \rightarrow \Lambda \mu^+\mu^- decays

The differential branching fraction of the rare decay $\Lambda^{0}_{b} \rightarrow \Lambda \mu^+\mu^-$ is measured as a function of $q^{2}$, the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of 3.0 \mbox{ fb}^{-1}, collected by the LHCb experiment. Evidence of signal is observed in the $q^2$ region below the square of the $J/\psi$ mass. Integrating over 15 < q^{2} < 20 \mbox{ GeV}^2/c^4 the branching fraction is measured as d\mathcal{B}(\Lambda^{0}_{b} \rightarrow \Lambda \mu^+\mu^-)/dq^2 = (1.18 ^{+ 0.09} _{-0.08} \pm 0.03 \pm 0.27) \times 10^{-7} ( \mbox{GeV}^{2}/c^{4})^{-1}, where the uncertainties are statistical, systematic and due to the normalisation mode, $\Lambda^{0}_{b} \rightarrow J/\psi \Lambda$, respectively. In the $q^2$ intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon ($A^{l}_{\rm FB}$) and hadron ($A^{h}_{\rm FB}$) systems are measured for the first time. In the range 15 < q^2 < 20 \mbox{ GeV}^2/c^4 they are found to be A^{l}_{\rm FB} = -0.05 \pm 0.09 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)} and A^{h}_{\rm FB} = -0.29 \pm 0.07 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)}.Comment: 27 pages, 10 figures, Erratum adde

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

Study of B−→DK−π+π−B^{-}\to DK^-\pi^+\pi^- and B−→Dπ−π+π−B^-\to D\pi^-\pi^+\pi^- decays and determination of the CKM angle γ\gamma

We report a study of the suppressed $B^-\to DK^-\pi^+\pi^-$ and favored $B^-\to D\pi^-\pi^+\pi^-$ decays, where the neutral $D$ meson is detected through its decays to the $K^{\mp}\pi^{\pm}$ and CP-even $K^+K^-$ and $\pi^+\pi^-$ final states. The measurement is carried out using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 3.0~fb$^{-1}$. We observe the first significant signals in the CP-even final states of the $D$ meson for both the suppressed $B^-\to DK^-\pi^+\pi^-$ and favored $B^-\to D\pi^-\pi^+\pi^-$ modes, as well as in the doubly Cabibbo-suppressed $D\to K^+\pi^-$ final state of the $B^-\to D\pi^-\pi^+\pi^-$ decay. Evidence for the ADS suppressed decay $B^{-}\to DK^-\pi^+\pi^-$, with $D\to K^+\pi^-$, is also presented. From the observed yields in the $B^-\to DK^-\pi^+\pi^-$, $B^-\to D\pi^-\pi^+\pi^-$ and their charge conjugate decay modes, we measure the value of the weak phase to be $\gamma=(74^{+20}_{-19})^{\rm o}$. This is one of the most precise single-measurement determinations of $\gamma$ to date.Comment: 22 pages, 9 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-2015-020.htm

Measurements of the branching fractions of B+→ppK+ decays

The branching fractions of the decay B+ → pp̄K+ for different intermediate states are measured using data, corresponding to an integrated luminosity of 1.0 fb-1, collected by the LHCb experiment. The total branching fraction, its charmless component Mpp̄ < 2.85 GeV/c2 and the branching fractions via the resonant cc̄ states η c(1S) and ψ(2S) relative to the decay via a J/ψ intermediate state are [Equation not available: see fulltext.] Upper limits on the B + branching fractions into the η c(2S) meson and into the charmonium-like states X(3872) and X(3915) are also obtained