Measurement of the proton spin structure at long distances

Abstract

Measuring the spin structure of protons and neutrons tests our understanding of how they arise from quarks and gluons, the fundamental building blocks of nuclear matter. At long distances the coupling constant of the strong interaction becomes large, requiring non-perturbative methods to calculate quantum chromodynamics processes, such as lattice gauge theory or effective field theories. Here we report proton spin structure measurements from scattering a polarized electron beam off polarized protons. The spin-dependent cross-sections were measured at large distances, corresponding to the region of low momentum transfer squared between 0.012 and 1.0 GeV${}^2$. This kinematic range provides unique tests of chiral effective field theory predictions. Our results show that a complete description of the nucleon spin remains elusive, and call for further theoretical works, e.g. in lattice quantum chromodynamics. Finally, our data extrapolated to the photon point agree with the Gerasimov-Drell-Hearn sum rule, a fundamental prediction of quantum field theory that relates the anomalous magnetic moment of the proton to its integrated spin-dependent cross-sections.

arXiv commentPublished version. 10 pages, 5 figures. 20 pages of supplementary material (data tables and a figure)

References in corpus (35)

• Measurements of the Proton and Deuteron Spin Structure Functions g1 and g2
• QCD Constrains on the Shape of Polarized Quark and Gluon Distributions
• Global analysis of proton elastic form factor data with two-photon exchange corrections
• Chiral Perturbation Theory and Baryon Properties
• The QCD Running Coupling
• Dispersion relations in real and virtual Compton scattering
• A percent-level determination of the nucleon axial coupling from Quantum Chromodynamics
• Nucleon structure functions from lattice operator product expansion
• Spin Structure of the Nucleon - Status and Recent Results
• Virtual Compton Scattering and Generalized Polarizabilities of the Proton
• Measurement of the $x$- and $Q^2$-Dependence of the Asymmetry $A_1$ on the Nucleon
• The Spin Structure of the Nucleon
• Experimental determination of the evolution of the Bjorken integral at low Q^2
• The Q^2 evolution of the generalized Gerasimov-Drell-Hearn integral for the neutron using a He-3 target
• Spin structure of the nucleon at low energies
• Q^2 Evolution of the Neutron Spin Structure Moments using a He-3 Target
• Generalized Sum Rules for Spin-Dependent Structure Functions of the Nucleon
• Experimental study of isovector spin sum rules
• Generalized Drell-Hearn-Gerasimov Sum Rule at Order {\cal O}(p^4) in Chiral Perturbation Theory
• New insights into the spin structure of the nucleon
• Burkhardt-Cottingham sum rule and forward spin polarizabilities in Heavy Baryon Chiral Perturbation Theory
• Towards the nucleon hadronic tensor from lattice QCD
• Determination of the Proton Spin Structure Functions for 0.05 < Q^2 < 5 GeV^2 using CLAS
• Gold-plated moments of nucleon structure functions in baryon chiral perturbation theory
• Chiral Perturbation Theory: Introduction and Recent Results in the One-Nucleon Sector
• Novel analysis of chiral loop effects in the generalized Gerasimov-Drell-Hearn sum rule
• Measurement of the Generalized Forward Spin Polarizabilities of the Neutron
• Precise Determination of the Deuteron Spin Structure at Low to Moderate $Q^2$ with CLAS and Extraction of the Neutron Contribution
• Nucleon spin structure at low momentum transfers
• The Nucleon Spin Polarizability at Order $\mathcal{O}(p^4$) in Chiral Perturbation Theory
• Small Momentum Evolution of the Extended Drell--Hearn--Gerasimov Sum Rule
• Measurement of the Q^2 Dependence of the Deuteron Spin Structure Function g_1 and its Moments at Low Q^2 with CLAS
• Forward doubly-virtual Compton scattering off the nucleon in chiral perturbation theory: II. Spin polarizabilities and moments of polarized structure functions
• Measurement of the 3He Spin-Structure Functions and of Neutron (3He) Spin-Dependent Sum Rules at 0.035<Q^2<0.24 GeV^2
• Generalized polarizabilities of the nucleon in baryon chiral perturbation theory

Cited by in corpus (12)

• The Present and Future of QCD
• Measurement of the Bjorken Sum at very low $Q^2$
• Radiative corrections to semileptonic beta decays: Progress and challenges
• Measured proton electromagnetic structure deviates from theoretical predictions
• Evaluation of Bjorken polarised sum rule with a renormalon-motivated approach
• Interpolating between small- and large-$g$ expansions using Bayesian Model Mixing
• Resonant contributions to polarized proton structure functions
• Single-pion contribution to the Gerasimov--Drell--Hearn sum rule and related integrals
• The polarized photon distribution function
• Measurement of the nucleon spin structure functions for 0.01<$Q^2$<1 GeV${}^2$ using CLAS
• The Gerasimov-Drell-Hearn sum-rule with nuclear targets
• Coupled-channel contributions to the GDH sum rule from the Jülich-Bonn approach