Nuclear parton distributions and the Drell-Yan process

We study the nuclear parton distribution functions on the basis of our recently developed semimicroscopic model, which takes into account a number of nuclear effects including nuclear shadowing, Fermi motion and nuclear binding, nuclear meson-exchange currents, and off-shell corrections to bound nucleon distributions. We discuss in detail the dependencies of nuclear effects on the type of parton distribution (nuclear sea vs valence), as well as on the parton flavor (isospin). We apply the resulting nuclear parton distributions to calculate ratios of cross sections for proton-induced Drell-Yan production off different nuclear targets. We obtain a good agreement on the magnitude, target and projectile $x$, and the dimuon mass dependence of proton-nucleus Drell-Yan process data from the E772 and E866 experiments at Fermilab. We also provide nuclear corrections for the Drell-Yan data from the E605 experiment.

Figure 1

Effective cross section ${\sigma }_0^{+}$ calculated from the normalization condition (42) (see text) as a function of $Q^2$. The phenomenological cross section of Ref. [15] is also shown for comparison.

Figure 2

Different nuclear effects on the $C$-even and $C$-odd combinations of the isoscalar $q_0=u+d$ (top panels) and the isovector $q_1=u-d$ (bottom panels) quark distributions calculated at $Q^2=20{\mathrm{GeV}}^2$. The ratios are between ${}^{184}\mathrm{W}$ and the deuteron ${}^2\mathrm{H}$ (top panels) and between ${}^{184}\mathrm{W}$ and the proton ${}^1\mathrm{H}$ (bottom panels) (see text for details).

Figure 3

The $C$-even and $C$-odd combinations of the isoscalar $q_0=u+d$ (top panels) and the isovector $q_1=u-d$ (bottom panels) quark distributions calculated at a few different $Q^2$. Notations are similar to those in Fig. 2.

Figure 4

Different nuclear effects on the cross section for DY lepton pair production with a fixed invariant mass $Q^2=20{\mathrm{GeV}}^2$ in the collision of $800\mathrm{GeV}/c$ protons with nuclear targets. The top panel shows the ratio of the reaction yields in Eq. (50) between tungsten ${}^{184}\mathrm{W}$ and deuterium ${}^2\mathrm{H}$ targets as a function of $x_T$, while the bottom panel shows the same ratio as a function of $x_B$.

Figure 5

Ratio of the DY reaction cross sections for different nuclei as a function of $x_T$. Data points are from the E772 experiment [43, 57], while the curves represent our predictions with (solid) and without (dashed) the energy loss correction to the projectile quark (see text for details).

Figure 6

Ratio of the DY reaction cross sections for different nuclei (rows) and the bins of dimuon mass $Q$ (columns), as a function of $x_B$. Data points are from the E772 experiment [43, 57], while the curves represent our predictions with (solid) and without (dashed) the energy-loss correction to the projectile quark (see text for details).

Figure 7

Comparison of the ratio of the DY reaction yields in different nuclei from the E866 experiment [44] with our predictions with (solid) and without (dashed) the quark energy loss correction.

Figure 8

Ratio of the DY cross sections in the collisions of $800\mathrm{GeV}$ protons with a ${}^{63}\mathrm{Cu}$ target and an average isoscalar nucleon $N=(p+n)/2$, as a function of $x_T$ for a few values of the invariant mass square $Q^2$. The calculation includes a quark energy loss $E^{\prime }=0.7$ GeV/fm.