Gluon helicity from global analysis of experimental data and lattice QCD Ioffe time distributions
Joseph Karpie, R. M. Whitehill, Wally Melnitchouk, Christopher Monahan, Kostas Orginos, Jian-Wei Qiu, D.G. Richards, N. Sato, Savvas Zafeiropoulos
Abstract
We perform a new global analysis of spin-dependent parton distribution functions with the inclusion of Ioffe time pseudodistributions computed in lattice QCD (LQCD), which are directly sensitive to the gluon helicity distribution, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi mathvariant="normal">Δ</a:mi><a:mi>g</a:mi></a:math>. These lattice data have an analogous relationship to parton distributions as do experimental cross sections, and can be readily included in global analyses. We focus in particular on the constraining capability of current LQCD data on the sign of <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:mi mathvariant="normal">Δ</d:mi><d:mi>g</d:mi></d:math> at intermediate parton momentum fractions <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>x</g:mi></g:math>, which was recently brought into question by analysis of data in the absence of parton positivity constraints. We find that present LQCD data cannot discriminate between positive and negative <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mi mathvariant="normal">Δ</i:mi><i:mi>g</i:mi></i:math> solutions, although significant changes in the solutions for both the gluon and quark sectors are observed. Published by the American Physical Society 2024