Transverse single-spin asymmetries inp↑p→γXfrom quark-gluon-quark correlations in the proton

Abstract

We analyze the transverse single-spin asymmetry in direct photon production from proton-proton collisions, denoted A γ N , within collinear twist-3 factorization. We provide a calculation of the contribution due to quark-gluon-quark correlations in the unpolarized proton as well as summarize previous studies on those effects in the polarized proton. Both soft-gluon poles and soft-fermion poles are considered. From this complete result we then estimate A γ N , including error bands due to uncertainties in the non-perturbative inputs, at kinematics relevant for planned measurements of this observable at the Relativistic Heavy Ion Collider. We find A γ N can allow for a "clean" extraction of the Qiu-Sterman function, which could lead to a definitive solution to the so-called "sign mismatch" crisis. Since we use the Sivers function extracted from semi-inclusive deep-inelastic scattering to develop our input for the Qiu-Sterman function, this reaction can also make a statement about the process dependence of the Sivers function.

A_N in Single-Inclusive Particle Production from Proton-Proton Collisions

“…[17,21,23,45,46,47,48,49,50,51]. There are a few pieces of A γ N that enter from the side of the incoming protons 2 : (1) the (soft-gluon pole (SGP) chiral-even) QS function, (2) soft-fermion pole (SFP) chiral-even quarkgluon-quark functions, (3) SGP and SFP quark-gluon-quark chiral-odd functions, and (4) SGP 1 In the CT3 framework the Sivers-type (QS) piece, due to the sign mismatch, gives a contribution that is opposite to the data (and in fact small in magnitude) if one uses the Sivers function from SIDIS.…”

“…The natural assumption has been that (1) is dominant, but there is no reason a priori that (2), (3) cannot give a large asymmetry. Therefore, in [51] we analyzed numerically (1), (2), (3) in order to determine what is the main source of A γ N , and we refer the reader to that paper for details on the phenomenology. The results of this study are shown in Fig.…”

Connections between TMDs and collinear twist-3 functions within the context of single-spin asymmetries

“…These identities have not only been routinely used in phenomenology (see, e.g., Refs. [59,60,63,64,65]), but also give important physical interpretations of these functions as being connected to average parton transverse momentum [71]. However, these important connections actually break down within the original CSS formalism discussed in Sec.…”

“…However, since the individual terms in (2.1) add together and cannot be "projected out", one must try to isolate certain pieces through experiments that are only mainly sensitive to a specific function or functions. For example, if one looks at direct photon production, which eliminates the third term in (2.1) since there is no fragmentation, we find such a process is dominated by a quark-gluon-quark PDF, the Qiu-Sterman (QS) function F FT (x, x) [59,60]. The QS function has an important, model-independent relation to the TMD Sivers function [57] f ⊥ 1T (x, k 2 T ) that enters SSAs in processes like semi-inclusive deep-inelastic scattering (SIDIS) and Drell-Yan (DY), which we will cover in Sec.…”

Probing the Anomalous FCNC tqγ Couplings at Large Hadron Electron Collider

“…Search for flavour changing neutral currents in the single top association with a 2 Advances in High Energy Physics photon at the LHC has been studied in [9]. In the same sign top quark production at the LHC the top FCNC couplings have been studied in [10]. The top FCNC couplings at future circular hadron electron colliders have been studied in [11].…”