Improved determination of $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ flavor asymmetry in the proton by data from the BONuS experiment at JLAB and using an approach by Brodsky, Hoyer, Peterson, and Sakai

The experimental data taken from both Drell-Yan and deep-inelastic scattering experiments suggest a sign change in $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ flavor asymmetry in the proton at large values of momentum fraction $x$. In this work, we present a phenomenological study of $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ flavor asymmetry. First, we extract the $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ distribution using the more recent data from the BONuS experiment at Jefferson Lab on the ratio of neutron to proton structure functions, $F_2^n/F_2^p$, and show that it undergoes a sign change and becomes negative at large values of momentum fraction $x$, as expected. The stability and reliability of our obtained results are examined by including target mass corrections as well as higher twist terms which are particularly important in the large-$x$ region at low $Q^2$. Then, we calculate the $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ distribution using the Brodsky-Hoyer-Peterson-Sakai model and show that if one chooses a mass for the down quark smaller than the one for the up quark it leads to a better description for the Fermilab E866 data. To prove this claim, we determine the masses of down and up sea quarks by fitting to the available and up-to-date experimental data for the $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ distribution. In this respect, unlike the previous theoretical studies, we have shown that this distribution has a sign change at $x>0.3$ after evolution to the scale of available experimental data.

Figure 1

A comparison between HERMES Collaboration [41] and Fermilab E866 [43] collaboration data for the $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ and the NNLO theoretical predictions of JR14 [7], NNPDF3.0 [8], MMHT14 [9], and CT14 [10] PDFs at $Q^2=54$ ${\mathrm{GeV}}^2$.

Figure 2

The $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ flavor asymmetry as a function of $x$. The results obtained by the NNLO JR14 parametrization [7] and the CLAS data [73] related to the three lower cuts on the range of final-state invariant mass $W^{*}$. A detailed explanation is given in the text.

Figure 3

As in Fig. 2 but obtained from the LO CT14 parametrization [10] using the CLAS data [73]. The plot is related to the three lower cuts on the range of final-state invariant mass $W^{*}$.

Figure 4

The $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ asymmetry considering the TMC and HT corrections.

Figure 5

A comparison between the experimental data from the HERMES [41] and E866 [43] experiments and the theoretical results obtained for $\overline{d}\left(x\right)-\overline{u}\left(x\right)$ in four situations, using the BHPS model with masses listed in Table 1.

Figure 6

$\overline{d}\left(x\right)/\overline{u}\left(x\right)$ versus $x$ obtained in four situations, using the BHPS model with masses listed in Table 1.