2020/08/10 by Nicole Lewis, Lewis, Nicole
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High-Energy Particle Collisions Research #Nuclear Experiment (nucl-ex) #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.2008.04283
openalex publication_date 2020/08/10 · openalex created_date 2022/07/26 · openalex updated_date 2026/07/28
Experimental observations of strikingly large transverse single-spin\nasymmetries (TSSAs) opened a window into quark and gluon dynamics present in\nhadronic collisions, revealing large spin-momentum correlations within nucleons\nand in the process of forming hadrons. Though originally measured in lower\nenergy fixed target experiments, they have been found to persist in collisions\nwith momentum transfer well into the perturbative regime of quantum\nchromodynamics (QCD) and yet their origin remains poorly understood. TSSA\nmeasurements have allowed for the development of both transverse momentum\ndependent and collinear twist-3 descriptions of nonperturbative spin-momentum\ncorrelations for both initial- and final-state effects. Results are presented\nfor the TSSAs of direct photons, neutral pions, and eta mesons in the\npseudorapidity range |\η|<0.35 from p^ uparrow+p collisions with\n\√(s) = 200 GeV at PHENIX. As hadrons, \π0 and \η mesons are\nsensitive to both initial- and final-state effects. At midrapidity, \π0 and\n\η measurements are sensitive to the dynamics of gluons along with a mix of\nquark flavors. These results are a factor of three increase in statistical\nprecision and extend to higher transverse momentum when compared with previous\nPHENIX measurements in this kinematic region. Because direct photon production\ndoes not include hadronization, the direct photon TSSA is only sensitive to\nspin-momentum correlations in the proton. The kinematics of this result in\nparticular make the direct photon TSSA a clean probe of gluon dynamics in the\ntransversely polarized proton. All three of these asymmetries will help\nconstrain the twist-3 trigluon collinear correlation function as well as the\ngluon Sivers function, improving our knowledge of spin-dependent gluon dynamics\nin QCD.\n