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Register a new userPrecision Global Determination of the $Bto X_sgamma$ Decay Rate
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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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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.
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.
We present the new parton distribution functions (PDFs) from the CTEQ-TEA collaboration, obtained using a wide variety of high-precision Large Hadron Collider (LHC) data, in addition to the combined HERA I+II deep-inelastic scattering data set, along with the data sets present in the CT14 global QCD analysis. New LHC measurements in single-inclusive jet production with the full rapidity coverage, as well as production of Drell-Yan pairs, top-quark pairs, and high-$p_T$ $Z$ bosons, are included to achieve the greatest sensitivity to the PDFs. The parton distributions are determined at NLO and NNLO, with each of these PDFs accompanied by error sets determined using the Hessian method. Fast PDF survey techniques, based on the Hessian representation and the Lagrange Multiplier method, are used to quantify the preference of each data set to quantities such as $alpha_s(m_Z)$, and the gluon and strange quark distributions. We designate the main resulting PDF set as CT18. The ATLAS 7 TeV precision $W/Z$ data are not included in CT18, due to their tension with other data sets in the global fit. Alternate PDF sets are generated including the ATLAS precision 7 TeV $W/Z$ data (CT18A), a new scale choice for low-$x$ DIS data (CT18X), or all of the above with a slightly higher choice for the charm mass (CT18Z). Theoretical calculations of standard candle cross sections at the LHC (such as the $gg$ fusion Higgs boson cross section) are presented.
We report a high-precision calculation of the Standard Model electroweak radiative corrections in the $Kto pi e^+ u(gamma)$ decay as a part of the combined theory effort to understand the existing anomaly in the determinations of $V_{us}$. Our new analysis features a chiral resummation of the large infrared-singular terms in the radiative corrections and a well-under-control strong interaction uncertainty based on the most recent lattice QCD inputs. While being consistent with the current state-of-the-art results obtained from chiral perturbation theory, we reduce the existing theory uncertainty from $10^{-3}$ to $10^{-4}$. Our result suggests that the Standard Model electroweak effects cannot account for the $V_{us}$ anomaly.
After improving the knowledge about residua of the semileptonic form factor at its first two poles we show that $f_+^{Dpi}(q^2)$ is not saturated when compared with the experimental data. To fill the difference we approximate the rest of discontinuity by an effective pole and show that the data can be described very well with the position of the effective pole larger than the next excitation in the spectrum of $D^ast$ state. The results of fits with experimental data also suggest the validity of superconvergence which in the pole models translates to a vanishing of the sum of residua of the form factor at all poles. A similar discussion in the case of $Bto pi ell u_ell$ leads to the possibility of extracting $vert V_{ub}vert$, the error of which appears to be dominated by $g_{B^ast Bpi}$, which can be nowadays computed on the lattice. In evaluating the residua of the form factors at their nearest pole we needed the vector meson decay constants $f_{D^ast}$ and $f_{B^ast}$, which we computed by using the numerical simulations of QCD on the lattice with $N_{rm f}=2$ dynamical quarks. We obtain, $f_{D^ast}/f_D=1.208(27)$ and $f_{B^ast}/f_B=1.051(17)$.
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