Quark Matter 2018

May 13 – 19, 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

Forward di-hadron back-to-back correlations in p+A collisions at RHIC and the LHC

May 16, 2018, 6:30 PM
20m
Sala Volpi, 1st Floor (Palazzo del Casinò)

Sala Volpi, 1st Floor

Palazzo del Casinò

Parallel Talk Initial state physics and approach to equilibrium

Speaker

Cyrille Marquet (CPHT - Ecole Polytechnique)

Description

The suppression of the away-side peak in azimuthal correlations of forward di-hadrons in d+Au vs. p+p collisions observed at RHIC remains one of the most striking experimental evidences supporting the saturation regime of quantum chromodynamics. Within the Color Glass Condensate (CGC) framework, we improve the state-of-the-art description of this observable, by deriving a cross section for the production of hadron pairs in the back-to-back limit. In this configuration, the cross section is manifestly factorized into a dilute component, the projectile proton, described by standard collinear parton distribution functions, and a dense counterpart, the saturated nuclear target, which is described by means of transverse-momentum-dependent gluon distributions, whose small-x evolution we obtain by solving the running-coupling Balitsky-Kovchegov equation. This formalism has proven able to accurately capture the suppression of the away-side peak observed in RHIC data.

Starting from this approach, then, we argue that the forward two-particle correlation function measured by the LHCb Collaboration in central p+Pb collisions at $\sqrt{s}=5.02$ TeV is amenable to a CGC description. In particular, we show that the away-side peak observed at LHCb can be decomposed into a double-ridge structure - whose origin is not our concern - and a di-jet structure, whose away-side peak is sensitive to parton saturation effects. We show that our formalism correctly describes the away-side peak measured at LHCb in p+Pb collisions, and we make predictions upcoming p+p data at 5 TeV. Comparing our results in p+p to LHCb data, the observation made at RHIC is replicated: We predict a visible suppression of the away-side peak in forward p+Pb collisions at LHC energies. This finding, if confirmed in experiment, would end up providing the best evidence in favor of QCD saturation in LHC data.

Centralised submission by Collaboration Presenter name already specified Theory

Primary author

Cyrille Marquet (CPHT - Ecole Polytechnique)

Co-author

Giuliano Giacalone (Université Paris-Saclay)