Azimuthal collimation of long range rapidity correlations by strong color fields in high multiplicity hadron-hadron collisions

Abstract

The azimuthal collimation of di-hadrons with large rapidity separations in high multiplicity p+p collisions at the LHC is described in the Color Glass Condensate (CGC) effective theory [1] by N_c^2 suppressed multi-ladder QCD diagrams that are enhanced α_S^(-8) due to gluon saturation in hadron wavefunctions. We show that quantitative computations in the CGC framework are in good agreement with data from the CMS experiment on per trigger di-hadron yields and predict further systematics of these yields with varying trigger pT and charged hadron multiplicity. Radial flow generated by re-scattering is strongly limited by the structure of the p+p di-hadron correlations. In contrast, radial flow explains the systematics of identical measurements in heavy ion collisions.

Figures (5)

• Figure 1: Representative back-to-back (left) and Glasma graphs (right) in perturbative QCD.
• Figure 2: Associated yield for four different initial saturation scales representing different centralities. The blue circles (red squares) represent the softer (harder) $D_1(z)$ ($D_2(z))$ fragmentation functions. Dashed lines connect computed points to guide the eye. Data points are from the CMS collaboration CMS-PAS-HIN-11-006.
• Figure 3: Associated yield for central $p+p$ ($Q_0^2=0.6$ GeV$^2$) collisions using soft (hard) $D_1(z)$-blue circles ($D_2(z)$-red squares) fragmentation functions. Dashed lines connect computed points to guide the eye. The black squares are the vailable CMS data CMS-PAS-HIN-11-006 for the $N\geq 110$ multiplicity bin of $pp$ collisions at $\sqrt{s}=7$ TeV. The middle and bottom figures are predictions for the labeled associated $p_T$ windows.
• Figure 4: Effect of transverse flow on the intrinsic $pp$ correlation using the hard $D_2(z)$ fragmentation function. Boosts from bottom to top: $\beta=0,0.1,0.2,0.25,0.3$.
• Figure 5: Computations of the associated per trigger yield in Pb Pb collisions at $\sqrt{s}=2.76$ TeV using $Q_0^2=0.9$ GeV$^2$ in the fundamental representation compared to the CMS data CMS-PAS-HIN-11-006. The curves shown, with the $D_2(z)$ fragmentation function, are for transverse boosts of $\beta=0, 0.65, 0.85$. At large flow velocities, the intrinsic angular correlation is entirely washed out.