Proton Isovector Helicity Distribution on the Lattice at Physical Pion Mass

Huey-Wen Lin; Jiunn-Wei Chen; Xiangdong Ji; Luchang Jin; Ruizi Li; Yu-Sheng Liu; Yi-Bo Yang; Jian-Hui Zhang; Yong Zhao; <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>LP</mi></mrow><mrow><mn>3</mn></mrow></msup></mrow></math> Collaboration

doi:10.1103/PhysRevLett.121.242003

Proton Isovector Helicity Distribution on the Lattice at Physical Pion Mass

Phys Rev Lett. 2018 Dec 14;121(24):242003. doi: 10.1103/PhysRevLett.121.242003.

Authors

Affiliations

¹ Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.
² Department of Computational Mathematics, Michigan State University, East Lansing, Michigan 48824, USA.
³ Department of Physics, Center for Theoretical Physics, and Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei 106, Taiwan.
⁴ Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
⁵ Tsung-Dao Lee Institute and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, 200240, China.
⁶ Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, Maryland 20742, USA.
⁷ Physics Department, University of Connecticut, Storrs, Connecticut 06269-3046, USA.
⁸ RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973, USA.
⁹ Tsung-Dao Lee Institute, Shanghai Jiao-Tong University, Shanghai 200240, China.
¹⁰ Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China.
¹¹ Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany.

PMID: 30608734
DOI: 10.1103/PhysRevLett.121.242003

Abstract

We present a state-of-the-art calculation of the isovector quark-helicity Bjorken-x distribution in the proton using lattice-QCD ensembles at the physical pion mass. We compute quasidistributions at proton momenta P_{z}∈{2.2,2.6,3.0} GeV on the lattice and match them systematically to the physical parton distribution using the large-momentum effective theory. We reach an unprecedented precision through high statistics in simulations, large-momentum proton matrix elements, and control of excited-state contamination. The resulting distribution with combined statistical and systematic errors is in agreement with the latest phenomenological analysis of the spin-dependent experimental data, in particular, Δu[over ¯](x)>Δd[over ¯](x).