arXiv subjects

A. Kokulu

Publications and source records attributed to A. Kokulu.

5 recordsLinked to original sources

arXiv2019

$B \rightarrow T$ transition form factors in light-cone sum rules

We present a new calculation of the semileptonic tree-level and flavor-changing neutral current form factors describing $B$-meson transitions to tensor mesons $T=D_2^*,K_2^*,a_2,f_2$ ($J^{P}=2^{+}$). We employ the QCD Light-Cone Sum Rules approach with $B$-meson distribution amplitudes. We go beyond the leading-twist accuracy and provide analytically, for the first time, higher-twist corrections for the two-particle contributions up to twist four terms. We observe that the impact of higher twist terms to the sum rules is noticeable. We study the phenomenological implications of our results on the radiative ${B} \to K_2^{*}γ$ and semileptonic ${B} \to D_2^* \ell {\bar ν}_\ell$, ${B} \to K_2^{*}\ell^+\ell^-$ decays.

hep-ph↗

arXiv2019

The Belle II Physics Book

We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB $e^+e^-$ collider. Belle II collected its first collisions in 2018, and is expected to operate for the next decade. It is anticipated to collect 50/ab of collision data over its lifetime. This book is the outcome of a joint effort of Belle II collaborators and theorists through the Belle II theory interface platform (B2TiP), an effort that commenced in 2014. The aim of B2TiP was to elucidate the potential impacts of the Belle II program, which includes a wide scope of physics topics: B physics, charm, tau, quarkonium, electroweak precision measurements and dark sector searches. It is composed of nine working groups (WGs), which are coordinated by teams of theorist and experimentalists conveners: Semileptonic and leptonic B decays, Radiative and Electroweak penguins, phi_1 and phi_2 (time-dependent CP violation) measurements, phi_3 measurements, Charmless hadronic B decay, Charm, Quarkonium(like), tau and low-multiplicity processes, new physics and global fit analyses. This book highlights "golden- and silver-channels", i.e. those that would have the highest potential impact in the field. Theorists scrutinised the role of those measurements and estimated the respective theoretical uncertainties, achievable now as well as prospects for the future. Experimentalists investigated the expected improvements with the large dataset expected from Belle II, taking into account improved performance from the upgraded detector.

hep-ex↗

arXiv2016

Improved analysis of the (O_7, O_7) contribution to $\bar{B} \rightarrow X_s γγ$ at $O(α_s)$

The present study is devoted for an improved analysis of the self-interference contribution of the electromagnetic dipole operator O_7 to the double differential decay width $dΓ/(ds_1 ds_2)$ for the inclusive $\bar{B} \to X_s γγ$ process, where the kinematical variables s_1 and s_2 are defined as s_i=(p_b - q_i)^2/m_b^2 with p_b, q_1, q_2 being the momenta of the b-quark and two photons. This calculation completes the NLL QCD prediction of the numerically important self-interference contribution of O_7 by keeping the full dependence on the strange-quark mass m_s, which is introduced to control possible collinear configurations of one of the photons with the strange quark. Our results are given for exact m_s, in contrast to an earlier work where only logarithmic and constant terms in m_s were retained. This improved NLL result for the (O_7, O_7)-interference contribution shows that finite m_s effects are only sizable near the kinematical endpoints of the spectrum $dΓ/(ds_1 ds_2)$. At the level of the branching ratio, in the phase-space region considered in this paper, it is observed that $Br[\bar{B} \to X_s γγ]$ does not develop a sizable m_s dependence: the impact on this branching ratio is less than 5% when m_s is varied between 400-600 MeV. For the same phase-space region finite strange quark mass effects for the branching ratio are less than 7%.

hep-ph↗

arXiv2016

(O_8, O_8) contribution to $\bar{B} \to X_s γγ$ at O(α_s)

In this analysis, we present the contribution associated with the chromomagnetic dipole operator O_8 to the double differential decay width dΓ/(ds_1 ds_2) for the inclusive process $\bar{B} \to X_s γγ$. The kinematical variables s_1 and s_2 are defined as s_i=(p_b - q_i)^2/m_b^2, where p_b, q_1, q_2 are the momenta of b-quark and two photons. This contribution (taken at tree level) is of order α_s, like the recently calculated QCD corrections to the contribution of the operator O_7. In order to regulate possible collinear singularities of one of the photons with the strange quark, we introduce a non zero mass m_s for the strange quark. Our results are obtained for exact m_s, which we interpret as a constituent mass being varied between 400 and 600 MeV. Numerically it turns out that the effect of the (O_8, O_8) contribution to the branching ratio of $\bar{B} \to X_s γγ$ does not exceed +0.1 % for any kinematically allowed value of our physical cutoff parameter c, confirming the expected suppression of this contribution relative to the QCD corrections to dΓ_{77}/(ds_1 ds_2).

hep-ph↗

arXiv2011

NLL QCD contribution of the Electromagnetic Dipole operator to B-> X_s gamma gamma

We calculate the set of O(alpha_s) corrections to the double differential decay width dGamma_77/(ds_1*ds_2) for the process B -> X_s gamma gamma originating from diagrams involving the electromagnetic dipole operator O_7. The kinematical variables s_1 and s_2 are defined as s_i=(p_b - q_i)^2/m_b^2, where p_b, q_1, q_2 are the momenta of b-quark and two photons. While the (renormalized) virtual corrections are worked exactly for a certain range of s_1 and s_2, we retain in the gluon bremsstrahlung process only the leading power w.r.t. the (normalized) hadronic mass s_3=(p_b-q_1-q_2)^2/m_b^2 in the underlying triple differential decay width dGamma_77/(ds_1*ds_2*ds_3). The double differential decay width, based on this approximation is free of infrared- and collinear singularities when combining virtual- and bremsstrahlung corrections. The corresponding results are obtained analytically. When retaining all powers in s_3, the sum of virtual- and bremstrahlung corrections contains uncanceled 1/epsilon singularities (which are due to collinear photon emission from the s-quark) and other concepts, which go beyond perturbation theory, like parton fragmentation functions of a quark or a gluon into a photon, are needed which is beyond the scope of our paper.

hep-ph↗