The transverse polarization of $$\Lambda $$ hyperons in $$e^+e^-\rightarrow \Lambda ^\uparrow h X$$ processes within TMD factorization

We investigate the transverse polarization of the $$\Lambda $$ Λ hyperon in the processes $$e^+e^-\rightarrow \Lambda ^\uparrow \pi ^\pm X$$ e + e - → Λ ↑ π ± X and $$e^+e^-\rightarrow \Lambda ^\uparrow K^\pm X$$ e + e - → Λ ↑ K ± X within the framework of the transverse momentum dependent (TMD) factorization. The transverse polarization is contributed by the convolution of the transversely polarizing fragmentation function (PFF) $$D_{1T}^\perp $$ D 1 T ⊥ of the lambda hyperon and the unpolarized fragmentation function $$D_1$$ D 1 of pion/kaon. We adopt the spectator diquark model result for $$D_{1T}^{\perp }$$ D 1 T ⊥ to numerically estimate the transverse polarization in $$e^+e^-\rightarrow \Lambda ^\uparrow h X$$ e + e - → Λ ↑ h X process at the kinematical region of Belle Collaboration. To implement the TMD evolution formalism of the fragmentation functions, we apply two different parametrizations on the nonperturbative Sudakov form factors associated with the fragmentation functions of the $$\Lambda $$ Λ , pion and kaon. It is found that our prediction on the polarization in the $$\Lambda \pi ^+$$ Λ π + production and $${\bar{\Lambda }} \pi ^-$$ Λ ¯ π - is consistent with the recent Belle measurement in size and sign, while the model predictions on the polarizations in $$\Lambda \pi ^-$$ Λ π - and $$\Lambda K^\pm $$ Λ K ± productions show strong disagreement with the Belle data. The reason for the discrepancies is discussed and possible approaches to improve the calculation in the future are also discussed.

Factorization of e+e− → H X cross section, differential in zh, PT and thrust, in the 2-jet limit

Factorizing the cross section for single hadron production in e+e− annihilations is a highly non trivial task when the transverse momentum of the outgoing hadron with respect to the thrust axis is taken into account. We work in a scheme that allows to factorize the e+e−→ H X cross section as a convolution of a calculable hard coefficient and a Transverse Momentum Dependent (TMD) fragmentation function. The result, differential in zh, PT and thrust, will be given to all orders in perturbation theory and explicitly computed to Next to Leading Order (NLO) and Next to Leading Log (NLL) accuracy. The predictions obtained from our computation, applying the simplest and most natural ansatz to model the non-perturbative part of the TMD, are in exceptional agreement with the experimental measurements of the BELLE Collaboration. The factorization scheme we propose relates the TMD parton densities defined in 1-hadron and 2-hadron processes, restoring the possi- bility to perform global phenomenological studies of TMD physics including experimental data from semi-inclusive deep inelastic scattering, Drell-Yan processes, e+e−→ H1H2X and e+e−→ H X annihilations.

Joint thrust and TMD resummation in electron-positron and electron-proton collisions

We present the framework for obtaining precise predictions for the transverse momentum of hadrons with respect to the thrust axis in e+e− collisions. This will enable a precise extraction of transverse momentum dependent (TMD) fragmentation functions from a recent measurement by the Belle Collaboration. Our analysis takes into account, for the first time, the nontrivial interplay between the hadron transverse momentum and the cut on the thrust event shape. To this end, we identify three different kinematic regions, derive the corresponding factorization theorems within Soft Collinear Effective Theory, and present all ingredients needed for the joint resummation of the transverse momentum and thrust spectrum at NNLL accuracy. One kinematic region can give rise to non-global logarithms (NGLs), and we describe how to include the leading NGLs. We also discuss alternative measurements in e+e− collisions that can be used to access the TMD fragmentation function. Finally, by using crossing symmetry, we obtain a new way to constrain TMD parton distributions, by measuring the displacement of the thrust axis in ep collisions.

QCD resummation on single hadron transverse momentum distribution with the thrust axis

We derive the transverse momentum dependent (TMD) factorization and resummation formula of the unpolarized transverse momentum distribution (jT) for the single hadron production with the thrust axis in an electron-positron collision. Two different kinematic regions are considered, including small transverse momentum limit jT « Q, and joint transverse momentum and threshold limit jT « Q(1 − zh) « Q, where Q and zh are the hard scattering energy and the observed hadron momentum fraction. Using effective theory methods, we resum logarithms ln(Q/jT) and ln(1 − zh) to all orders. In the end, we present the differential cross sections and Gaussian widths calculated for the inclusive charged pion production and find that our results are consistent with the measurements reported by the Belle collaboration.

Probing lepton universality with (semi)-leptonic B decays

The most recent measurements of the observables R_{D^{(*)}}RD(*) are in tension with the Standard Model offering hints of New Physics in b\rightarrow c \ell \bar{\nu}_{\ell}b→cℓν‾ℓ transitions. Motivated by these results, in this work we present an analysis on their b\rightarrow u \ell \bar{\nu}_{\ell}b→uℓν‾ℓ counterparts (for \ell=e, ~\mu, ~\tauℓ=e,μ,τ). Our study has three main objectives. Firstly, using ratios of branching fractions, we assess the effects of beyond the Standard Model scalar and pseudoscalar particles in leptonic and semileptonic BB decays (B^-\rightarrow \ell^- \bar{\nu}_{\ell}B−→ℓ−ν‾ℓ, \bar{B}\rightarrow \pi \ell \bar{\nu}_{\ell}B‾→πℓν‾ℓ and \bar{B}\rightarrow \rho \ell \bar{\nu}_{\ell}B‾→ρℓν‾ℓ). Here a key role is played by the leptonic BB processes, which are highly sensitive to new pseudoscalar interactions. In particular, we take advantage of the most recent measurement of the branching fraction of the channel B^-\rightarrow \mu^-\bar{\nu}_{\mu}B−→μ−ν‾μ by the Belle collaboration. Secondly, we extract the CKM matrix element |V_{ub}||Vub| while accounting simultaneously for New Physics contributions. Finally, we provide predictions for the branching fractions of yet unmeasured leptonic and semileptonic BB decays.

Exclusive open-charm near-threshold cross sections in a coupled-channel approach

Data on 7 open-charm channels collected by the Belle Collaboration are analyzed simultaneously using a unitary approach based on a coupled channel model in a wide energy range $ \sqrt s $ = 3.7 − 4.7 GeV. The resulting fit provides a remarkably good overall description of the line shapes in all studied channels. Parameters of 5 vector charmonium resonances are extracted from the fit. It is demonstrated, that this approach could be used account for all exclusive channels and thus solve the long-term problem of the charmonium spectra near threshold.

X, Y, Z Search at Belle II

Search for exotics has increased importance since the observation of the X(3872), 13 years ago, announced by the Belle Collaboration. The observation of pentaquark states by LHCb, and the Z-charged states observed at Belle and BES III have raised even more the attention to the field. Presently several states are observed that do not fit potential models, and looking for them in different production mechanisms and search for their decay modes it is important, as well as to do precise measurement of their mass, width, lineshape. We shortly report in this note about the plan in searching for exotics at Belle II at KEK (Tsukuba, Japan), that just ended the Phase-II running period, and show the first re-discovery results using 5 pb−1 integrated luminosity.

THE INCLUSIVE SEMI-LEPTONIC $\bar B \to X_s \mu^+ \mu^-$ AND LEPTONIC $\bar{B}_s \rightarrow \mu^+ \mu^-$ DECAYS IN THE PRESENCE OF A LIGHT STABILIZED RADION IN RANDALL–SUNDRUM MODEL

The Belle collaboration has reported [Formula: see text] for the inclusive decay [Formula: see text]. Recently, the LHCb and the CMS collaboration has released the combined limit [Formula: see text]. The standard model results of the [Formula: see text] and [Formula: see text] are found to be within the 1σ of the experimental result. Taking a conservative viewpoint, we use these decays to constrain the braneworld Randall–Sundrum model. The stabilized radion in the Randall–Sundrum model, which is an electro-weak singlet, can cause the flavor changing neutral current (FCNC) b →s transition at the oneloop level. We investigate the possible impact of a stabilized radion on the above two decays and obtain the possible constraints on the radion vev 〈ϕ〉 for an ultra-light radion.

INCLUSIVE PRODUCTION OF FOUR CHARM HADRONS AT B-FACTORIES

Measurements by the Belle Collaboration of the exclusive J/ψ + ηc and inclusive [Formula: see text] productions in e+e- annihilation differ substantially from theoretical predictions based on the nonrelativistic QCD factorization approach. In order to test if such a discrepancy is originated from the large perturbative corrections to the hard-scattering amplitude, we study inclusive production of four charm hadrons in e+e- annihilation at B factories.

QCD

In this talk I review recent experimental and theoretical results in QCD. Since the topic is too vast to cover within given time constraints I choose to highlight some of the subjects that I find particularly exciting. On the experimental side I focus on measurements made at the Tevatron. Specifically jet production rates, and the cross section for B meson production. In addition I discuss an interesting measurement made by the Belle collaboration of double exclusive charmonium production. On the theory side I quickly review recent advances in computing hadronic cross sections at subleading order in perturbation theory. I then move on to soft-collinear effective theory. After a lightning review of the formalism I discuss recently published results on color-suppressed B → D decays.