KNO scaling of fluctuations in pp and pA, and eccentricities in heavy-ion collisions

TL;DR

This paper investigates multiplicity fluctuations in high-energy pp, pA, and AA collisions, demonstrating the importance of KNO scaling and fluctuations in understanding particle production and eccentricities in heavy-ion collisions.

Contribution

It shows that KNO scaling applies to fluctuations in various collision systems and highlights the role of fluctuations in eccentricity moments in heavy-ion collisions.

Findings

KNO fluctuations are crucial for reproducing multiplicity distributions in p+p, d+Au, and p+Pb collisions.

Particle production fluctuations significantly increase eccentricity moments like epsilon_3.

Deviations from KNO scaling are predicted for p+Pb collisions at the LHC.

Abstract

Multiplicity fluctuations at midrapidity in p+p collisions at high energies are described by a negative binomial distribution and exhibit approximate Koba-Nielsen-Olesen (KNO) scaling. We find that these KNO fluctuations are important also for reproducing the multiplicity distribution in d+Au collisions observed at RHIC, adding to the Glauber fluctuations of the number of binary collisions or participants. We predict that the multiplicity distribution in p+Pb collisions at the LHC also deviates little from the KNO scaling function. Finally, we analyze various moments of the eccentricity of the particle production zone in A+A collisions at RHIC and LHC and find that particle production fluctuations increase fluctuation dominated moments such as the triangularity epsilon_3 substantially.