Search

Abstract The rare decay B ¯ $$ \overline{B} $$ → X s γ 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 7γ in the effective weak Hamiltonian. One of the three leading contributions, Q 1 q − Q 7 γ $$ {Q}_1^q-{Q}_{7\gamma } $$ , 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 B ¯ $$ \overline{B} $$ → X s γ total rate and CP asymmetry.

Abstract Employing the systematic framework of soft-collinear effective theory (SCET) we perform an improved calculation of the leading-power contributions to the double radiative B d,s -meson decay amplitudes in the heavy quark expansion by including the perturbative resummation of enhanced logarithms of m b /ΛQCD at the next-to-leading-logarithmic accuracy. We then construct the QCD factorization formulae for the subleading power contributions arising from the energetic photon radiation off the constituent light-flavour quark of the bottom meson at tree level. Furthermore, we explore the factorization properties of the subleading power correction from the effective SCET current at O α s 0 $$ \mathcal{O}\left({\alpha}_s^0\right) $$ by virtue of the operator identities due to the classical equations of motion. The higher-twist contributions to the B d,s → γγ helicity form factors from the two-particle and three-particle bottom-meson distribution amplitudes are evaluated with the perturbative factorization technique, up to the twist-six accuracy. In addition, the subleading power weak-annihilation contributions from both the current-current and QCD penguin operators are taken into account at the one-loop accuracy. We proceed to apply the operator-production-expansion-controlled dispersion relation for estimating the power-suppressed soft contributions to the double radiative B d,s -meson decay form factors, which cannot be factorized into the light-cone distribution amplitudes of the heavy-meson and the resolved photon as well as the hard-scattering kernel calculable in perturbation theory canonically. Phenomenological explorations of the radiative B d,s → γγ decay observables in the presence of the neutral-meson mixing, including the CP-averaged branching fractions, the polarization fractions and the time-dependent CP asymmetries, are carried out subsequently with an emphasis on the numerical impacts of the newly computed ingredients together with the theory uncertainties from the shape parameters of the HQET bottom-meson distribution amplitudes.

Abstrac We present a first, detailed study of diffractive dijet photoproduction at the recently approved electron-ion collider (EIC) at BNL. Apart from establishing the kinematic reaches for various beam types, energies and kinematic cuts, we make precise predictions at next-to-leading order (NLO) of QCD in the most important kinematic variables. We show that the EIC will provide new and more precise information on the diffractive parton density functions (PDFs) in the pomeron than previously obtained at HERA, illuminate the still disputed mechanism of global vs. only resolved-photon factorization breaking, and provide access to a completely new quantity, i.e. nuclear diffractive PDFs.

Abstract We revisit QCD calculations of radiative heavy meson decay form factors by including the subleading power corrections from the twist-two photon distribution amplitude at next-to-leading-order in α s with the method of the light-cone sum rules (LCSR). The desired hard-collinear factorization formula for the vacuum-to-photon correlation function with the interpolating currents for two heavy mesons is constructed with the operator- product-expansion technique in the presence of evanescent operators. Applying the back- ground field approach, the higher twist corrections from both the two-particle and three- particle photon distribution amplitudes are further computed in the LCSR framework at leading-order in QCD, up to the twist-four accuracy. Combining the leading power “point- like” photon contribution at tree level and the subleading power resolved photon corrections from the newly derived LCSR, we update theory predictions for the nonperturbative couplings describing the electromagnetic decay processes of the heavy mesons H ∗± → H ± γ, H ∗0 → H 0 γ, H s ∗ ± $$ {H_s^{\ast}}^{\pm } $$ → H s ± $$ {H}_s^{\pm } $$ γ (with H = D, B). Furthermore, we perform an exploratory comparisons of our sum rule computations of the heavy-meson magnetic couplings with the previous determinations based upon different QCD approaches and phenomenological models.

Abstract Applying the method of light-cone sum rules with photon distribution amplitudes, we compute the subleading-power correction to the radiative leptonic B → γℓν decay from the twist-two hadronic photon contribution at next-to-leading order in QCD; and further evaluate the higher-twist “resolved photon” corrections at leading order in α s , up to twist-four accuracy. QCD factorization for the vacuum-to-photon correlation function with an interpolating current for the B-meson is established explicitly at leading power in Λ/m b employing the evanescent operator approach. Resummation of the parametrically large logarithms of m b 2/Λ2 entering the hard function of the leading-twist factorization formula is achieved by solving the QCD evolution equation for the light-ray tensor operator at two loops. The leading-twist hadronic photon effect turns out to preserve the symmetry relation between the two B → γ form factors due to the helicity conservation, however, the higher-twist hadronic photon corrections can yield symmetry-breaking effect already at tree level in QCD. Using the conformal expansion of photon distribution amplitudes with the non-perturbative parameters estimated from QCD sum rules, the twist-two hadronic photon contribution can give rise to approximately 30% correction to the leading-power “direct photon” effect computed from the perturbative QCD factorization approach. In contrast, the subleading-power corrections from the higher-twist two-particle and three-particle photon distribution amplitudes are estimated to be of O3∼5% $$ \mathcal{O}\left(3\sim 5\%\right) $$ with the light-cone sum rule approach. We further predict the partial branching fractions of B → γℓν with a photon-energy cut E γ ≥ E cut, which are of interest for determining the inverse moment of the leading-twist B-meson distribution amplitude thanks to the forthcoming high-luminosity Belle II experiment at KEK.