Rapidity and centrality dependence of azimuthal correlations in Deuteron-Gold collisions at RHIC

TL;DR

This paper analyzes how gluon saturation in the Color Glass Condensate impacts azimuthal two-particle correlations in dAu collisions at RHIC. Using $k_T$-factorization with CGC-inspired unintegrated gluon distributions and a saturation scale, it computes single and double inclusive cross sections and calibrates normalization against pp data. The main finding is a quantitative explanation for the suppression of back-to-back correlations in dAu relative to pp, persisting across small and large rapidity separations and exhibiting centrality dependence. The results bolster CGC as a valid descriptor of the nuclear wave function in these collisions and underscore the role of small-x evolution in the observed correlations.

Abstract

We calculate azimuthal correlations in dAu collisions at different rapidities and centralities and argue that experimentally observed depletion of the back-to-back pick can be quantitatively explained by gluon saturation in the Color Glass Condensate of the Gold nucleus.

Figures (5)

• Figure 1: Correlation function at the central rapidity. Kinematic region is $4<p_T <6$, $2<p_A <p_T$ (all momenta are in GeV), $y_T=3.1$, $y_A=3$. Left (right) panel: minbias $pp$ ($dAu$) collisions. Data from Adams:2003im.
• Figure 2: Correlation function at forward rapidities. Kinematic region is $p_T>4$, $1.5<p_A <p_T$ (all momenta are in GeV), $y_T=3.1$, $y_A=3$. Left (right) panel: the minbias $pp$ ($dAu$) collisions. Data from AGordon.
• Figure 3: Correlation function at forward rapidities. Kinematic region is $p_T>2$, $1.5<p_A <p_T$ (all momenta are in GeV), $y_T=3.1$, $y_A=3$. Upper left (right) panel: minbias $pp$ ($dAu$) collisions. Lower left (right) panel: peripheral (central) $dAu$ collisions. Note: centrality of the theoretical calculation may not coincide with the centrality of the data (the former is not yet known at the time of publication). Data from AGordon.
• Figure 4: Effect of fragmentation on the azimuthal correlation function. Solid lines are the same as in Fig. \ref{['fig:cc']}. Dashed lines represent a conservative estimate of the fragmentation effect as discussed in the text.
• Figure 5: Forward-backward correlations. Kinematic region is $p_T >2$, $1<p_A <p_T$ (all momenta are in GeV), $y_T=3$, $y_A=0$. Left (right) panel: minbias $pp$ ($dAu$) collisions. Solid lines: calculations with (\ref{['nlow']}) (exact $2\to 4$ amplitude, no evolution between the trigger and associate particles). Dashed line: calculations with (\ref{['wev']}) (MRK approximation of $2\to 4$ amplitude, includes evolution between the trigger and associate particles). Data from Adams:2006uzBraidot:2009ji (forward $\pi^0$ and midrapidity $h^\pm$).