Collinear factorization in wide-angle hadron pair production in e+e− annihilation

Abstract

We compute the inclusive unpolarized dihadron production cross section in the far from backto-back region of e + e − annihilation in leading order pQCD using existing fragmentation function fits and standard collinear factorization, focusing on the large transverse momentum region where transverse momentum is comparable to the hard scale (the center-of-mass energy). We compare with standard transverse-momentum-dependent (TMD) fragmentation function-based predictions intended for the small transverse momentum region with the aim of testing the expectation that the two types of calculation roughly coincide at intermediate transverse momentum. We find significant tension, within the intermediate transverse momentum region, between calculations done with existing non-perturbative TMD fragmentation functions and collinear factorization calculations if the center-of-mass energy is not extremely large. We argue that e + e − measurements are ideal for resolving this tension and exploring the large-to-small transverse momentum transition, given the typically larger hard scales ( 10 GeV) of the process as compared with similar scenarios that arise in semi-inclusive deep inelastic scattering and fixed-

Parton distributions and lattice-QCD calculations: Toward 3D structure

“…A current challenge is that calculations done with existing collinear parton distribution and fragmentation functions produce significant tension with data in the Y -term region of transverse momentum (Bacchetta et al, 2019b;Gonzalez-Hernandez et al, 2018;Moffat et al, 2019;Wang et al, 2019a). Work is needed to understand and resolve this tension.…”

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

“…(2.3) neglects the power corrections from the ratios j 2 T /Q 2 , which is small in the kinematic j T Q region we consider. Nevertheless, in the region of j T ∼ Q one can include such power corrections from the fixed-order calculations [60]. This is usually referred to as the Y -term in the CSS formalism [28,29].…”

Recent Developments in $x$-dependent Structure Calculations

“…Most obviously, nonperturbative calculations of more complicated quantities, such as generalised parton distributions and transverse momentumdependent distributions (TMDs), will be particularly important in the electron-ion collider era. Lattice QCD will also be able to directly calculate higher twist effects and Ioffe time matrix elements at unphysical pion masses or kinematics, both of which will help limn the limits of the collinear factorisation paradigm itself [6,8]. In short, a precision era will bring a wealth of opportunities for lattice calculations of hadron structure.…”