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

We report a measurement of the angular distributions of Drell-Yan dimuons produced using an $800\mathrm{GeV}/c$ proton beam on a hydrogen target. The polar and azimuthal angular distribution parameters have been extracted over the kinematic range $4.5<m_{\mu \mu }<15\mathrm{GeV}/c^2$ (excluding the ${\rm Y}$ resonance region), $0<p_T<4\mathrm{GeV}/c$, 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 $\cos 2\varphi$ 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 need to include QCD effects before reliable information on the Boer-Mulders function can be extracted. The validity of the Lam-Tung relation in $p+p$ Drell-Yan data is also tested.

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 $800\mathrm{GeV}/c$. The vertical error bars include the statistical uncertainties only.

Figure 2

Parameter $\nu$ vs $p_T$ in the Collins-Soper frame for the $p+p$ and $p+d$ Drell-Yan data. The solid curve and the dotted curve are calculations [23] 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 $800\mathrm{GeV}/c$. The vertical error bars correspond to the statistical uncertainties only.