Azimuthal collimation of long range rapidity correlations by strong color fields in high multiplicity hadron-hadron collisions (1201.2658v2)

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 \alpha_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.

Azimuthal Collimation of Long Range Rapidity Correlations by Strong Color Fields in High Multiplicity Hadron-Hadron Collisions: An Analysis

This paper conducted by Kevin Dusling and Raju Venugopalan examines the azimuthal collimation of di-hadrons with large rapidity separations in high multiplicity proton-proton (p+p) collisions at the Large Hadron Collider (LHC), using the Color Glass Condensate (CGC) effective theory. The authors explore the dynamics associated with "hot spots" of wee gluon states within each proton, establishing a theoretical framework to interpret the phenomena observed in such collisions.

Theoretical Framework

The CGC effective theory relies on the concept that in high multiplicity p+p collisions, configurations of wee gluons form hot spots in each proton. These hot spots are characterized by high gluon occupancy relative to the QCD fine structure constant $\alpha_S$ and a typical scale $Q_S$, which serves as a dynamical saturation scale. When $Q_S$ exceeds the fundamental QCD scale $\Lambda_{\rm QCD}$, weak coupling techniques allow for the description of highly occupied hadron wavefunctions.

The CGC comprises an effective field theory that shines light on high-density wee parton configurations in a proton, forming the basis of "glasma flux tubes." The theory predicts multiplicity distributions that align well with LHC data, supporting its validity in modeling long-range rapidity correlations in gluons.

Numerical Analysis and Results

Quantitative predictions within the CGC framework are compared to CMS experiment data regarding per trigger di-hadron yields. The analysis revealed that in high multiplicity regions, CGC's prediction aligns closely with observed results, particularly when focusing on large rapidity separations. Radial flow resulting from re-scattering effects is notably limited, contrasting with scenarios in heavy-ion collisions where radial flow dominates.

Key numerical results were derived from expressions for two-gluon correlated glasma distributions as well as single-inclusive gluon distributions. Optimal results were achieved by varying saturation scale parameters in rcBK equation initial conditions, showcasing the role that QCD saturation plays in explaining observed near-side yields in azimuthal collimation.

Implications and Future Directions

The findings extend our understanding of azimuthal correlations in high multiplicity p+p collisions, suggesting substantial contributions from strong gluon saturation effects. For similar measurements in heavy-ion collision systems, radial flow dominated and could differentiate significantly in the presence of high multiplicity proton collisions.

Speculation on future developments includes refining fragmentation functions for forward rapidities as more LHC data becomes available and further investigation into intrinsic QCD correlations that saturate color field dynamics in generating azimuthal collimations. More sophisticated Monte Carlo simulations could provide a deeper dive into the higher-order corrections and impact parameter fluctuations critical for understanding the multiplicity thresholds.

Overall, the paper provides an insightful perspective into gluon saturation dynamics in hadron-hadron collisions and supports a theoretical framework that aligns with empirical data, paving the way for potential advancements in particle physics analyses of collision events at various multiplicity thresholds.