Impact of CLAS and COMPASS data on Polarized Parton Densities and Higher Twist

TL;DR

The study analyzes world inclusive polarized DIS data, incorporating CLAS and COMPASS measurements to reassess polarized parton densities and higher-twist corrections. CLAS data robustly constrain higher-twist contributions to g1, tightening HT and reducing uncertainties in the polarized densities without substantially shifting central values, while COMPASS data mainly affect the strange quark density and leave HT largely intact due to the high Q^2. The fits admit three viable gluon-polarization scenarios (positive, negative, and oscillating in x) with small magnitudes, all compatible with DeltaG/G measurements, and HT effects are essential for interpreting g1 at small x. Overall, the work highlights the complementary roles of low- and high-Q^2 data in disentangling parton spins and nonperturbative corrections in nucleon structure.

Abstract

We have re-analyzed the world data on inclusive polarized DIS including the very precise CLAS proton and deuteron data, as well as the latest COMPASS data on the asymmetry $A_1^d$, and have studied the impact of these data on polarized parton densities and higher twist effects. We demonstrate that the low $Q^2$ CLAS data improve essentially our knowledge of higher twist corrections to the spin structure function $g_1$, while the large $Q^2$ COMPASS data influence mainly the strange quark density. In our new analysis we find that a negative polarized gluon density, or one that changes sign as a function of x, cannot be ruled out from the present DIS data.

Figures (13)

• Figure 1: Effect of CLAS data on the higher twist values.
• Figure 2: Impact of CLAS data on the uncertainties for NLO($\rm \overline{MS}$) polarized quark and gluon densities.
• Figure 3: Comparison between the higher twist values corresponding to 5 and 7 $x$-bins.
• Figure 4: Comparison between polarized NLO($\rm \overline{MS}$) LSS'06 strange quark and gluon densities corresponding to fits of the data using 5 and 7 $x$-bins for higher twist.
• Figure 5: Comparison of our NLO($\rm \overline{MS}$) results for $A^d_1$ (a) and $g^d_1$ (b) corresponding to $\Delta G > 0$ and $\Delta G < 0$ with the new COMPASS data at measured $x$ and $Q^2$ values. Error bars represent the total (statistical and systematic) errors.