Extrapolation of Multiplicity distribution in p+p(\bar(p)) collisions to LHC energies

TL;DR

This paper extrapolates charged particle multiplicity and pseudorapidity distributions in proton-proton collisions to LHC energies, compares models with existing data, and predicts distributions at higher energies.

Contribution

It introduces a method to extrapolate multiplicity distributions to LHC energies using existing data and compares model predictions with these extrapolations.

Findings

Logarithmic dependence of <N_ch> on s is favored at midrapidity.

Extrapolated pseudorapidity distributions match basic features of existing data.

PYTHIA and PHOJET models underestimate charged particle densities at LHC energies.

Abstract

The multiplicity (N_ch) and pseudorapidity distribution (dN_ch/d\eta) of primary charged particles in p+p collisions at Large Hadron Collider (LHC) energies of \sqrt(s) = 10 and 14 TeV are obtained from extrapolation of existing measurements at lower \sqrt(s). These distributions are then compared to calculations from PYTHIA and PHOJET models. The existing \sqrt(s) measurements are unable to distinguish between a logarithmic and power law dependence of the average charged particle multiplicity (<N_ch>) on \sqrt(s), and their extrapolation to energies accessible at LHC give very different values. Assuming a reasonably good description of inclusive charged particle multiplicity distributions by Negative Binomial Distributions (NBD) at lower \sqrt(s) to hold for LHC energies, we observe that the logarithmic \sqrt(s) dependence of <N_ch> are favored by the models at midrapidity. The dN_ch/d\eta versus \eta for the existing measurements are found to be reasonably well described by a function with three parameters which accounts for the basic features of the distribution, height at midrapidity, central rapidity plateau and the higher rapidity fall-off. Extrapolation of these parameters as a function of \sqrt(s) is used to predict the pseudorapidity distributions of charged particles at LHC energies. dN_ch/d\eta calculations from PYTHIA and PHOJET models are found to be lower compared to those obtained from the extrapolated dN_ch/d\eta versus \eta distributions for a broad \eta range.