Decisive test of color coherence in proton-nucleus collisions at the LHC

Understand

Proton-nucleus collisions (p+A) at LHC energies provide a rigorous test of the Color Glass Condensate (CGC), a model proposed to describe the high energy limit of Quantum Chromodynamics.

• In the CGC the average multiplicity of charged particles at midrapidity in p+A collisions depends logarithmically on the number of participants, $N_{part}$.
• In contrast, the Wounded Nucleon Model (WNM) of independent nucleon-nucleon scatterings, verified at RHIC energies, predicts that multiplicity in p+A depends linearly on $N_{part}$.
• We argue that for the first time, the dependence of mean multiplicity on $N_{part}$ in p+A collisions at LHC energies can single out a model of particle production, thus offering a stringent test of the CGC and the WNM.