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First Monte Carlo global analysis of nucleon transversity with lattice QCD constraints

Huey-Wen Lin, W. Melnitchouk, Alexei Prokudin, N. Sato, H. Shows

TL;DR

This report reports on the first global QCD analysis of the quark transversity distributions in the nucleon from semi-inclusive deep-inelastic scattering (SIDIS), using a new Monte Carlo method based on nested sampling and constraints on the isovector tensor charge g_{T} from lattice QCD.

Abstract

We report on the first global QCD analysis of the quark transversity distributions in the nucleon from semi-inclusive deep-inelastic scattering (SIDIS), using a new Monte Carlo method based on nested sampling and constraints on the isovector tensor charge $g_T$ from lattice QCD. A simultaneous fit to the available SIDIS Collins asymmetry data is compatible with $g_T$ values extracted from a comprehensive reanalysis of existing lattice simulations, in contrast to previous analyses which found significantly smaller $g_T$ values. The contributions to the nucleon tensor charge from $u$ and $d$ quarks are found to be $δu = 0.3(2)$ and $δd = -0.7(2)$ at a scale $Q^2 = 2$ GeV$^2$.

First Monte Carlo global analysis of nucleon transversity with lattice QCD constraints

TL;DR

This report reports on the first global QCD analysis of the quark transversity distributions in the nucleon from semi-inclusive deep-inelastic scattering (SIDIS), using a new Monte Carlo method based on nested sampling and constraints on the isovector tensor charge g_{T} from lattice QCD.

Abstract

We report on the first global QCD analysis of the quark transversity distributions in the nucleon from semi-inclusive deep-inelastic scattering (SIDIS), using a new Monte Carlo method based on nested sampling and constraints on the isovector tensor charge from lattice QCD. A simultaneous fit to the available SIDIS Collins asymmetry data is compatible with values extracted from a comprehensive reanalysis of existing lattice simulations, in contrast to previous analyses which found significantly smaller values. The contributions to the nucleon tensor charge from and quarks are found to be and at a scale GeV.

Paper Structure

This paper contains 9 equations, 3 figures.

Figures (3)

  • Figure 1: Comparison of the full SIDIS$+$lattice fit with the $\pi^+$ (filled circles) and $\pi^-$ (open circles) Collins asymmetries $A_{UT}^{\sin(\phi_h+\phi_s)}$ from HERMES Airapetian:2010ds and COMPASS Adolph:2014zbaAlekseev:2008aa (in percent), as a function of $x$, $z$ and $P_{h\perp}$ (in GeV).
  • Figure 2: Transversity PDFs $h_1^{u,d}$ and favored $zH_{\rm 1 (fav)}^{\perp (1)}$ and unfavored $zH_{\rm 1 (unf)}^{\perp (1)}$ Collins FFs for the SIDIS$+$lattice fit (red and blue bands) at $Q^2=2$ GeV$^2$, compared with the SIDIS-only fit uncertainties (yellow bands). The range of direct experimental constraints is indicated by the horizontal dashed lines.
  • Figure 3: (a) Contour plot of $\delta u$ and $\delta d$ samples from the MC analysis, for the SIDIS only (blue) and SIDIS+lattice (red) analysis. The expectation values and $1\sigma$ uncertainties for both fits are indicated by the respective error bars. (b) Normalized yields for the isovector tensor charge $g_T$, for the SIDIS-only (yellow histograms) and SIDIS+lattice (red histograms) MC analyses.