Abstract
We perform a new Monte Carlo QCD analysis of pion parton distribution functions, including, for the first time, transverse momentum dependent pion-nucleus Drell-Yan cross sections together with $p_{\rm T}$-integrated Drell-Yan and leading neutron electroproduction data from HERA. We assess the sensitivity of the Monte Carlo fits to kinematic cuts, factorization scale, and parametrization choice, and we discuss the impact of the various datasets on the pion's quark and gluon distributions. This study provides the necessary step towards the simultaneous analysis of collinear and transverse momentum dependent pion distributions and the determination of the pion's three-dimensional structure.
Highlights
The pion is one of the most enigmatic particles in nature, with unresolved questions about its most fundamental properties and behavior
IV we describe the Monte Carlo methodology used to extract the parton distribution functions (PDFs) through Bayesian inference
In addition to the inclusive lepton-pair production cross sections in pion-nucleus scattering in Eqs. (1) and (7), following Ref. [3], we supplement the analysis with data from leading neutron (LN) electroproduction in ep collisions at HERA [6,7] in the very forward region, ep → enX, in order to better constrain the pion PDFs at small values of parton momentum fraction x in the pion
Summary
The pion is one of the most enigmatic particles in nature, with unresolved questions about its most fundamental properties and behavior. The theoretical formalism developed in the 1980s by Collins, Soper and Sterman (CSS) [21] allows one to describe pT-dependent observables within the so-called “W þ Y” framework (where pT is the transverse momentum of the virtual photon relative to the beam axis of the colliding hadrons) In this construction, the “W” term is computed in terms of TMD parton distributions in the region where pT ≪ Q, where Q is the invariant mass of the lepton pair. In regions of large transverse momenta pT ∼ Q, the spectrum is dominated by hard QCD radiation in which the photon recoils from hard radiated partons In such situations, the cross sections can be described by collinear factorization involving collinear PDFs. In practice, the CSS framework has been very successful in applications in collider environments such as W and Z production in large-pT ppand pp collisions at the Tevatron and LHC, respectively.
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