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, and Yong Zhao ( ${LP}^{3}$ Collaboration)

Phys. Rev. Lett. 121, 242003 – Published 14 December 2018

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 $P_{z} \in {2.2, 2.6, 3.0} GeV$ 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, $Δ \bar{u} (x) > Δ \bar{d} (x)$ .

Received 29 August 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.242003

Physics Subject Headings (PhySH)

Lattice QCD Nuclear spin & parity Nucleon distribution Quantum chromodynamics

Particles & FieldsNuclear Physics

Authors & Affiliations

Huey-Wen Lin^1,2, Jiunn-Wei Chen^3,4, Xiangdong Ji^5,6, Luchang Jin^7,8, Ruizi Li¹, Yu-Sheng Liu^9,*, Yi-Bo Yang^1,10,†, Jian-Hui Zhang¹¹, and Yong Zhao⁴ ( ${LP}^{3}$ Collaboration)

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