Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userReevaluating Uncertainties in $bar Bto X_sgamma$ Decay
103
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
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.
We investigate the possibility of explaining the enhancement in semileptonic decays of $bar B to D^{(*)} tau bar u$, the anomalies induced by $bto smu^+mu^-$ in $bar Bto (K, K^*, phi)mu^+mu^-$ and violation of lepton universality in $R_K = Br(bar Bto K mu^+mu^-)/Br(bar Bto K e^+e^-)$ within the framework of R-parity violating (RPV) MSSM. Exchange of down type right-handed squark coupled to quarks and leptons yield interactions which are similar to leptoquark induced interactions that have been proposed to explain the $bar B to D^{(*)} tau bar u$ by tree level interactions and $bto s mu^+mu^-$ anomalies by loop induced interactions, simultaneously. However, the Yukawa couplings in such theories have severe constraints from other rare processes in $B$ and $D$ decays. Although this interaction can provide a viable solution to $R(D^{(*)})$ anomaly, we show that with the severe constraint from $bar B to K u bar u$, it is impossible to solve the anomalies in $bto s mu^+mu^-$ process simultaneously.
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.
In the absence of direct evidence for New Physics at present LHC energies, the focus is set on the anomalies and discrepancies recently observed in rare $b to sellell$ transitions which can be interpreted as indirect hints. Global fits have shown that an economical New Physics solution can simultaneously alleviate the tensions in the various channels and can lead to a significant improvement in the description of the data. Alternative explanations within the Standard Model for part of the observed anomalies have been proposed in terms of (unexpectedly large) hadronic effects at low dilepton invariant mass and attributing tensions in protected observables to statistical fluctuations or experimental errors. We review the treatment of hadronic uncertainties in this kinematic regime for one of the most important channels, $B to K^*mu^+mu^-$, in a pedagogical way. We provide detailed arguments showing that factorisable power corrections cannot account for the observed anomalies and that an explanation through long-distance charm contributions is disfavoured. Some optimized observables at very low dilepton invariant mass are shown to be protected against contributions from the semileptonic coefficient $C_9$ (including any associated long-distance charm effects), enhancing their sensitivity to New Physics contributions to other Wilson coefficients. Finally, we discuss how the recent measurement of $Q_5$ by Belle (and in the future by LHCb and Belle-II) may provide a robust cross-check of our arguments.
We comprehensively study the charged-Higgs contributions to the leptonic $B^-_q to ell bar u$ ($q=u,c$) and semileptonic $bar B to X_q ell bar u$ ($X_u=pi, rho; X_c=D,D^*$) decays in the type-III two-Higgs-doublet model (2HDM). We employ the Cheng-Sher ansatz to suppress the tree-level flavor-changing neutral currents (FCNCs) in the quark sector. When the strict constraints from the $Delta B=2$ and $bto s gamma$ processes are considered, parameters $chi^u_{tq}$ from the quark couplings and $chi^ell_ell$ from the lepton couplings dictate the leptonic and semileptonic $B$ decays. It is found that when the measured $B^-_uto tau bar u$ and indirect bound of $B^-_c to tau bar u$ obtained by LEP1 data are taken into account, $R(D)$ and $R(pi)$ can have broadly allowed ranges; however, the values of $R(rho)$ and $R(D^*)$ are limited to approximately the standard model (SM) results. We also find that the same behaviors also occur in the $tau$-lepton polarizations and forward-backward asymmetries ($A^{X_q,tau}_{FB}$) of the semileptonic decays, with the exception of $A^{D^*,tau}_{FB}$, for which the deviation from the SM due to the charged-Higgs effect is still sizable. In addition, the $q^2$-dependent $A^{pi,tau}_{FB}$ and $A^{D,tau}_{FB}$ can be very sensitive to the charged-Higgs effects and have completely different shapes from the SM.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
