Simulation studies of R-2(Delta eta, Delta phi) and P-2(Delta eta, Delta phi) correlation functions in pp collisions with the PYTHIA and HERWIG models

Abstract

We report studies of charge-independent (CI) and charge-dependent (CD) two-particle differential-number correlation functions, R-2 (Delta eta, Delta phi), and transverse momentum (p(T)) correlation functions, P-2 (Delta eta, Delta phi), of charged particles in root s = 2.76 TeV pp collisions with the PYTHIA and HERWIG models. Model predictions are presented for inclusive charged hadrons (h(+/-)), as well as pions (pi(+/-)), kaons (K-+/-), and (anti-) protons ((p) over bar /p) in the ranges 0.2 < pT <= 2.0 GeV/c, 2.0 < p(T) <= 5.0 GeV/c, and 5.0 < p(T) <= 30.0 GeV/c, with full azimuthal coverage in the range vertical bar eta vertical bar < 1.0. We compare the model predictions for the strength and shape of the R-2 and P-2 correlators as these pertain to recent measurements by the ALICE collaboration. The R-2 and P-2 correlation functions estimated with PYTHIA and HERWIG exhibit qualitatively similar near-side and away-side correlation structures but feature important differences. Our analysis indicates that comparative studies of R-2 and P-2 correlation functions would provide valuable insight towards the understanding of particle production in pp collisions, and by extension, should also be useful in studies of heavy-ion collisions. Comparison of the eta. dependence of R-2 and P-2 could contribute, in particular, to a better understanding and modeling of the angular ordering of particles produced by hadronization in jets, as well as a better description of jet fragmentation functions of identified species at low momentum fraction (z).