Moments of the nucleon transverse quark spin densities using lattice QCD
Constantia Alexandrou, Simone Bacchio, Martha Constantinou, P. Dimopoulos, Jacob Finkenrath, R. Frezzotti, Kyriakos Hadjiyiannakou, K. Jansen, Bartosz Kostrzewa, Giannis Koutsou, Gregoris Spanoudes, Carsten Urbach
Abstract
We present the first calculation of the Mellin moments of the transverse quark spin densities in the nucleon using lattice QCD simulations with physical values of the pion mass and in the continuum limit. Specifically, we use three ${N}_{f}=2+1+1$ twisted mass fermion gauge ensembles each at different lattice spacings. The densities are extracted from the unpolarized and transversity generalized form factors. The first moment of transversely polarized quarks in an unpolarized nucleon shows an interesting distortion, which can be traced back to the sharp falloff of the transversity generalized form factor ${\overline{B}}_{Tn0}({Q}^{2})$. The isovector tensor anomalous magnetic moment is determined to be ${\ensuremath{\kappa}}_{T}=1.051(94)$, which confirms a negative and large Boer-Mulders function, ${h}_{1}^{\ensuremath{\perp}}$, in the nucleon.