Measurement of the EMC effect in the deuteron

We determined the structure function ratio $R_{\mathrm{EMC}}^d=F_2^d/(F_2^n+F_2^p)$ from recently published $F_2^n/F_2^d$ data taken by the BONuS experiment using CLAS at Jefferson Lab. This ratio deviates from unity, with a slope $d{R}_{\mathrm{EMC}}^d/dx=-0.10\pm 0.05$ in the range of Bjorken $x$ from 0.35 to 0.7, for invariant mass $W>1.4$ GeV and $Q^2>1{\mathrm{GeV}}^2$. The observed EMC effect for these kinematics is consistent with conventional nuclear physics models that include off-shell corrections, as well as with empirical analyses that find the EMC effect proportional to the probability of short-range nucleon-nucleon correlations.

Figure 1

BONuS data for $F_2^n/F_2^d$ vs Bjorken $x$ taken with a 5.26-GeV beam. Only data for $Q^2\ge 1{\mathrm{GeV}}^2$ are shown. The red points ($W>1.4$ GeV) are used in this analysis. Error bars are statistical only. Each spectrum is shifted upward by 1.0 from the set below it.

Figure 2

The deuteron EMC ratio $R_{\mathrm{EMC}}^d=F_2^d/(F_2^n+F_2^p)$ as extracted from the BONuS data. Total systematic uncertainties are shown as a band arbitrarily positioned at 0.91 (blue). The yellow band shows the CJ12 [49] limits expected from their nuclear models. The black points are the combined 4- and 5-GeV data, whereas the red points are the 4-GeV data alone. The dashed blue line shows the calculations of Ref. [36]. The solid line (black) is the fit to the black points for $0.35<x<0.7$.

Figure 3

EMC slopes per isoscalar nucleon, $-d{R}_{\mathrm{IMC}}^A/dx$, vs the relative probability with respect to the deuteron of short-range correlations, $R_{2N}(A/d)$. Fits assume that ($d{R}_{\mathrm{IMC}}^A/dx)/(R_{2N}(A/d)$) is constant. The red points are from Ref. [13]. The blue points are from Ref. [20] and are corrected for isospin and for $x$ normalized to a maximum of $x=A$. Their uncertainties are the same as for the red points.