Measurement of Angular Distributions of Drell-Yan Dimuons in $p + p$ Interactions at 800 GeV/c

TL;DR

A measurement of the angular distributions of Drell-Yan dimuons produced using an 800 GeV/c proton beam on a hydrogen target indicates the need to include QCD effects before reliable information on the Boer-Mulders function can be extracted.

Abstract

We report a measurement of the angular distributions of Drell-Yan dimuons produced using an 800 GeV/c proton beam on a hydrogen target. The polar and azimuthal angular distribution parameters have been extracted over the kinematic range $4.5 < m_{μμ} < 15$ GeV/c$^2$ (excluding the $Υ$ resonance region), $0 < p_T < 4 $ GeV/c, and $0 < x_F < 0.8$. The $p+p$ angular distributions are similar to those of $p+d$, and both data sets are compared with models which attribute the $\cos 2 φ$ distribution either to the presence of the transverse-momentum-dependent Boer-Mulders structure function $h_1^\perp$ or to QCD effects. The data indicate the presence of both mechanisms. The validity of the Lam-Tung relation in $p+p$ Drell-Yan is also tested.

Figures (3)

• Figure 1: Parameters $\lambda, \mu, \nu$ and $2\nu - (1-\lambda)$ vs. $p_T$ in the Collins-Soper frame. Solid squares (open circles) are for E866 $p+p$ ($p+d$) at 800 GeV/c. The vertical error bars include the statistical uncertainties only.
• Figure 2: (color online). Parameter $\nu$ vs. $p_T$ in the Collins-Soper frame for the $p+p$ and $p+d$ Drell-Yan data. The solid and dotted curves are calculations zhang08 for $p+p$ and $p+d$, respectively, using parametrizations based on a fit to the $p+d$ data. The dot-dashed curve is the contribution from the QCD process (Eq. 2).
• Figure 3: Parameter $\nu$ vs. $m_{\mu\mu}$, $x_F$, $x_1$, and $x_2$ in the Collins-Soper frame for $p+p$ (solid squares) and $p+d$ (open circles) at 800 GeV/c. The vertical error bars correspond to the statistical uncertainties only.