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Register a new userMeasurements of $A_{CP}(B^0rightarrow K^+ pi^-)$ and $A_{CP}(B_srightarrow pi^+ K^-)$ at LHCb
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Stefano Perazzini Stefano Perazzini
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2011
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English
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Stefano Perazzini
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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 $H_brightarrow h^+h^-$ decays, where $H_b$ can be either a $B^0$ meson, a $B_s^0$ meson or a $Lambda_b$ baryon, while $h$ and $h^prime$ stand for $pi$, $K$ or $p$. We provide preliminary values of the direct $mathcal{CP}$ asymmetries of the neutral $B^0$ and $B_s^0$ mesons $A_{CP} (B^0rightarrow K^+pi^-) = -0.074 pm 0.033mathrm{(stat.)} pm 0.008mathrm{(syst.)}$ and $A_{CP}(B_s^0rightarrowpi^+K^-)=0.15 pm 0.19mathrm{(stat.)} pm 0.02mathrm{(syst.)}$.
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Time-dependent $CP$ asymmetries in the decay rates of the singly Cabibbo-suppressed decays $D^0rightarrow K^-K^+$ and $D^0rightarrow pi^-pi^+$ are measured in $pp$ collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb experiment. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial state as $D^0$ or $bar{D}^0$. The asymmetries in effective lifetimes between $D^0$ and $bar{D}^0$ decays, which are sensitive to indirect $CP$ violation, are determined to be begin{align*} A_{Gamma}(K^-K^+) = (-0.134 pm 0.077 ; {}^{+0.026}_{-0.034})% , A_{Gamma}(pi^-pi^+) = (-0.092pm 0.145 ; {}^{+0.025}_{-0.033})% , end{align*} where the first uncertainties are statistical and the second systematic. This result is in agreement with previous measurements and with the hypothesis of no indirect $CP$ violation in $D^0$ decays.
We present updated measurements of branching fractions and CP-violating asymmetries for neutral B meson decays to two-body final states of charged pions and kaons. The results are obtained from a data sample of about 60 million Y(4S) --> B-anti-B decays collected between 1999 and 2001 by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. The sample contains 124^{+16}_{-15} pi-pi, 403+/-24 K-pi, and 0.6^{+8.0}_{-7.4} K-K candidates, from which we measure the following quantities: BF(B0 --> pi+pi-) = (5.4+/-0.7+/-0.4) x 10^{-6}, BF(B0 --> K+pi-) = (17.8+/-1.1+/-0.8) x 10^{-6}, BF(B0 --> K+K-) < 1.1 x 10^{-6} (90% C.L.} A_Kpi = -0.05+/-0.06+/-0.01 [-0.14,+0.05], S_pipi = -0.01+/-0.37+/-0.07 [-0.66,+0.62], C_pipi = -0.02+/-0.29+/-0.07 [-0.54,+0.48], where the errors are statistical and systematic, respectively, and the asymmetry limits correspond to the 90% confidence level. These results are preliminary.
We report measurements of the branching fractions and direct CP asymmetries (A_{CP}) for B->K pi, pi pi and KK decays (but not pi^0 pi^0) based on the final data sample of 772x10^6 B B-bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider. We set a 90% confidence-level upper limit for K^+- K^-+ at 2.0x10^{-7}; all other decays are observed with branching fractions ranging from 10^{-6} to 10^{-5}. In the $B^0/B^0-bar -> K^+-pi^-+ mode, we confirm Belles previously reported large A_{CP} with a value of -0.069 +- 0.014 +- 0.007 and a significance of 4.4 sigma. For all other flavor-specific modes, we find A_{CP} values consistent with zero, including A_{CP}(K^+- pi^0) = +0.043 +- 0.024 +- 0.007 with 1.8 sigma significance. The difference of CP asymmetry between B^+- -> K^+- pi^0 and B^0/B^0-bar -> K^+-pi^-+ is found to be Delta A_{K pi} equiv A_{CP} (K^+ pi^0) - A_{CP}(K^+ pi^-) = +0.112 +- 0.027 +- 0.007 with 4.0 sigma significance. We also calculate the ratios of partial widths for the B-> K pi decays. Using our results, we test the validity of the sum rule A_{CP}(K^+ pi^-) + A_{CP}(K^0pi^+) x Gamma(K^0pi^+)/Gamma(K^+ pi^-)} - A_{CP}(K^+ pi^0)x 2Gamma(K^+ pi^0)/Gamma(K^+ pi^-) - A_{CP}(K^0 pi^0)x 2Gamma(K^0 pi^0)/Gamma(K^+ pi^-) = 0 and obtain a sum of -0.270 +- 0.132 +- 0.060 with 1.9 sigma significance.
In this work, we study the localized $CP$ violation and the branching fraction of the four-body decay $bar{B}^0rightarrow K^-pi^+pi^-pi^+$ by employing a quasi-two-body QCD factorization approach. Considering the interference of $bar{B}^0rightarrow bar{K}_0^*(700)rho^0(770)rightarrow K^-pi^+pi^-pi^+$ and $bar{B}^0rightarrow bar{K}^*(892)f_0(500)rightarrow K^-pi^+pi^-pi^+$ channels, we predict $mathcal{A_{CP}}(bar{B}^0rightarrow K^-pi^+pi^-pi^+)in[0.15,0.28]$ and $mathcal{B}(bar{B}^0rightarrow K^-pi^+pi^-pi^+)in[1.73,5.10]times10^{-7}$, respectively, which shows that this two channels interference mechanism can induce the localized $CP$ violation to this four-body decay. Meanwhile, within the two quark model framework for the scalar mesons $f_0(500)$ and $bar{K}_0^*(700)$, we calculate the direct CP violations and branching fractions of the $bar{B}^0rightarrow bar{K}_0^*(700)rho^0(770)$ and $bar{B}^0rightarrow bar{K}^*(892)f_0(500)$ decays, respectively. The corresponding results are $mathcal{A_{CP}}(bar{B}^0rightarrow bar{K}_0^*(700)rho^0(770)) in [0.20, 0.36]$, $mathcal{A_{CP}}(bar{B}^0rightarrow bar{K}^*(892)f_0(500))in [0.08, 0.12]$, $mathcal{B} (bar{B}^0rightarrow bar{K}_0^*(700)rho^0(770)in [6.76, 18.93]times10^{-8}$ and $mathcal{B} (bar{B}^0rightarrow bar{K}^*(892)f_0(500))in [2.66, 4.80]times10^{-6}$, respectively, indicating the $CP$ violations of these two two-body decays are both positive and the branching fractions are quite different. These studies provide a new way to investigate the aforementioned four-body decay and could be helpful in clarifying the configuration of the structure of light scalar meson.
We investigate a possibility of observing CP asymmetries in the partial widths for the decays B^- -> pi^+ pi^- K^- and B^- -> K^+ K^- K^- produced by the interference of the non-resonant decay amplitude with the resonant amplitudes. The resonant states which subsequently decay into pi^+ pi^- and K^+ K^- or K^- pi^+ are charmonium c(bar) c states with J^P = 0^+, 1^-, 1^+ or the phi(1020) meson. We find that the largest partial width asymmetry comes from the chi_c0 resonance, while the resonances K^*_0(1430) and psi(2S) give a partial width asymmetry of the order 10%.
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