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Register a new userInclusive $Bto X_sgamma$ and $Bto X_sell^+ell^-$ at the B factories
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John Walsh
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I report here recent measurements of observables from the inclusive decays $Bto X_sgamma$ and $Bto X_sell^+ell^-$. Included are measurements of the branching fractions and CP asymmetries for both channels, as well as the forward-backward lepton asymmetry in inclusive $Bto X_sell^+ell^-$ decays, which is the first measurement of this quantity.
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In this article, I review the recent results for inclusive and exclusive measurements for $bto sgamma$ and $bto dgamma$ decays from $B$ factories Belle and Babar. I describe the measurement of branching fraction and direct CP violating asymmetry for inclusive $Bto X_sgamma$ decay. For results of $bto dgamma$ process, I introduce the measurement of branching fraction of exclusive $bto dgamma$ modes, the first measurement for CP asymmetry of $bto dgamma$ process using $Btorhogamma$ mode, and semi-inclusive measurement for $Bto X_dgamma$.
The rare decay $bar Bto X_sgamma$ is an important probe of physics beyond the standard model. The largest uncertainty on the total rate and the CP asymmetry arises from resolved photon contributions. These appear first at order $1/m_b$ and are related to operators other than $Q_{7gamma}$ in the effective weak Hamiltonian. One of the three leading contributions, $Q^q_1-Q_{7gamma}$, is described by a non-local function whose moments are related to HQET parameters. We use recent progress in our knowledge of these parameters to reevaluate the resolved photon contribution to $bar Bto X_sgamma$ total rate and CP asymmetry.
We report on the measurement of inclusive charmless semileptonic B decays $B to X_{u} ell u$. The analysis makes use of hadronic tagging and is performed on the full data set of the Belle experiment comprising 772 million $Bbar{B}$ pairs. In the proceedings, the preliminary results of measurements of partial branching fractions and the CKM matrix element $|V_{ub}|$ are presented.
$bto stau^+tau^-$ measurements are highly motivated for addressing lepton-flavor-universality (LFU)-violating puzzles such as $R_{K^{(ast)}}$ anomalies. The anomalies of $R_{D^{(*)}}$ and $R_{J/psi}$ further strengthen their necessity and importance, given that the LFU-violating hints from both involve the third-generation leptons directly. $Z$ factories at the future $e^-e^+$ colliders stand at a great position to conduct such measurements because of their relatively high production rates and reconstruction efficiencies for $B$ mesons at the $Z$ pole. To fully explore this potential, we pursue a dedicated sensitivity study in four $bto stau^+tau^-$ benchmark channels, namely $B^0to K^{ast 0} tau^+ tau^-$, $B_stophi tau^+ tau^-$, $B^+ to K^+ tau^+ tau^- $ and $B_s to tau^+ tau^-$, at the future $Z$ factories. We develop a fully tracker-based scheme for reconstructing the signal $B$ mesons and introduce a semi-quantitative method for estimating their major backgrounds. The simulations indicate that branching ratios of the first three channels can be measured with a precision $sim mathcal O(10^{-7} - 10^{-6})$ and that of $B_s to tau^+ tau^-$ with a precision $sim mathcal O(10^{-5})$ at Tera-$Z$. The impacts of luminosity and tracker resolution on the expected sensitivities are explored. The interpretations of these results in effective field theory are also presented.
We perform the first global fit to inclusive $Bto X_sgamma$ measurements using a model-independent treatment of the nonperturbative $b$-quark distribution function, with next-to-next-to-leading logarithmic resummation and $mathcal{O}(alpha_s^2)$ fixed-order contributions. The normalization of the $Bto X_sgamma$ decay rate, given by $lvert C_7^{rm incl} V_{tb} V_{ts}^*rvert^2$, is sensitive to physics beyond the Standard Model (SM). We determine $lvert C_7^{rm incl} V_{tb} V_{ts}^* rvert = (14.77 pm 0.51_{rm fit} pm 0.59_{rm theory} pm 0.08_{rm param})times 10^{-3}$, in good agreement with the SM prediction, and the $b$-quark mass $m_b^{1S} = (4.750 pm 0.027_{rm fit} pm 0.033_{rm theory} pm 0.003_{rm param}),mathrm{GeV}$. Our results suggest that the uncertainties in the extracted $Bto X_sgamma$ rate have been underestimated by up to a factor of two, leaving more room for beyond-SM contributions.
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