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Measurements of branching fractions and direct ${it CP}$-violating asymmetries in $B^+ to K^+ pi^0~mbox{and}~pi^+ pi^0$ decays using 2019 and 2020 Belle II data

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 Added by Ching Hua Li
 Publication date 2021
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and research's language is English




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We report measurements of branching fractions ($mathcal B$) and direct ${it CP}$-violating asymmetries ($mathcal A_{it CP}$) for the decays $B^+to K^+pi^0$ and $B^+ to pi^+pi^0$ reconstructed with the Belle II detector in a sample of asymmetric-energy electron-positron collisions at the $Upsilon(4S)$ resonance corresponding to 62.8 $text{fb}^{-1}$ of integrated luminosity. The results are $mathcal{B}(B^+ to K^+pi^0) = [11.9 ^{+1.1}_{-1.0} (rm stat)pm 1.6(rm syst)]times 10^{-6}$, $mathcal{B}(B^+ to pi^+pi^0) = [5.5 ^{+1.0}_{-0.9} (rm stat)pm 0.7(rm syst)]times 10^{-6}$, $mathcal A_{it CP}(B^+ to K^+pi^0) = -0.09 pm 0.09 (rm stat)pm 0.03(rm syst)$, and $mathcal A_{it CP}(B^+ to pi^+pi^0) = -0.04 pm 0.17 (rm stat)pm 0.06(rm syst)$. The results are consistent with previous measurements and show a detector performance comparable with early Belle performance.



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We report updated measurements of branching fractions ($mathcal{B}$) and CP-violating charge asymmetries ($mathcal{A_{rm CP}}$) for charmless $B$ decays at Belle II, which operates on or near the $Upsilon$(4S) resonance at the SuperKEKB asymmetric energy $e^{+}e^{-}$ collider. We use samples of 2019 and 2020 data corresponding to 62.8 fb$^{-1}$ of integrated luminosity. The samples are analysed using two-dimensional fits in $Delta E$ and $M_{it bc}$ to determine signal yields of approximately 568, 103, and 115 decays for the channels $B^0 to K^+pi^-$, $B^+ to K_{rm S}^0pi^+$, and $B^0 to pi^+pi^-$, respectively. Signal yields are corrected for efficiencies determined from simulation and control data samples to obtain branching fractions and CP-violating asymmetries for flavour-specific channels. The results are compatible with known determinations and contribute important information to an early assessment of Belle II detector performance.
136 - Y.-T. Duh , T.-Y. Wu , P. Chang 2012
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.
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 on the first measurement of the direct $CP$-violating asymmetry ($mathcal{A}$) in the charmless decay $B^0 to K^0pi^0$ at Belle II and an updated measurement of its branching fraction ($mathcal{B}$). We use a sample of electron-positron collisions collected in 2019 and 2020 at the $Upsilon(4S)$ resonance and corresponding to $62.8$ $text{fb}^{-1}$ of integrated luminosity. We reconstruct and select about $50$ $B^0 to K_S^0 pi^0$ candidates, and we measure $mathcal{A}_{{K^0pi^0}} = -0.40_{-0.44}^{+0.46} (text{stat}) pm 0.04 (text{syst})$ and $mathcal{B}(B^0 to K^0 pi^0) = [8.5_{-1.6}^{+1.7} (text{stat}) pm 1.2 (text{syst})] times 10^{-6}$. This is the first measurement of $CP$ violation in $B^0 to K^0pi^0$ decays reported by Belle II. The results agree with previous determinations and show a detector performance comparable with the best Belle results.
We report on first measurements of branching fractions~($mathcal{B}$) and CP-violating charge asymmetries~($mathcal{A}$) in charmless $B$ decays at Belle~II. We use a sample of electron-positron collisions collected in 2019 and 2020 at the $Upsilon(4S)$ resonance and corresponding to $34.6$,fb$^{-1}$ of integrated luminosity. We use simulation to determine optimized event selections. The $Delta E$ distributions of the resulting samples, restricted in $M_{rm bc}$, are fit to determine signal yields. Signal yields are corrected for efficiencies determined from simulation and control data samples to obtain branching fractions and CP-violating asymmetries for flavour-specific channels. These are the first measurements in charmless decays reported by Belle~II. Results are compatible with known determinations and show detector performance comparable with the best Belle results offering a reliable basis to assess projections for future reach.
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