Effect of color reconnection on forward-backward multiplicity and mean transverse momentum correlation

Abstract

Color reconnection (CR) mechanism in PYTHIA model has been reported to be essential to describe the flow-like collective effect observed in high multiplicity p+p and p+Pb collisions. In this work, we test this mechanism towards explaining the Forward-Backward multiplicity correlation (bcor) measurements in p+p collisions at the LHC energies. Out of the three different CR schemes implemented in PYTHIA, (a) MPI based CR (default mechanism), (b) QCD based CR and (c) Gluon moved CR, we found that the QCD based CR scheme describes relatively better the ALICE measurements of bcor in p+p collisions at √ s = 0.9 and 7 TeV. In addition, we have tuned the parameters of the default CR mechanism in PYTHIA to describe simultaneously the measured charged particle multiplicity pseudo-rapidity (η) distribution and bcor. We found that an average number of multipartonic interactions ( NMPI ) between 2.5 to 3 and CR range between 0.9 to 2.5 best describes the experimental data. Finally, we have presented a study using PYTHIA events for p+p collisions at √ s = 7 TeV which shows that the strength of Forward-Backward mean transverse momentum correlation (b

Energy and system size dependence of strongly intensive fluctuation measures in heavy-ion collisions at FAIR energies

“…For 0%-8% central Be-Be collisions at 150A GeV, Σ values for the three pairs of variables have been observed to increase with increasing η sep [5,8]. These observations appear to be consistent with the predictions of EPOS-1.99 model [5] and quark-gluon string model for pp interactions at LHC energies [61]. Some energy dependence of N p ,…”

“…The study of forward-backward correlations permits to decouple the short-range correlations (SRC) from the long-range-correlations (LRC) [61][62][63]. The SRC are expected to arise due to the decays of resonances or clusters, jet or mini-jet induced correlations.…”

“…The SRC are expected to arise due to the decays of resonances or clusters, jet or mini-jet induced correlations. Contributions from SRC are confined to a pseudorapidity region of ∼two units, whereas, LRC, which are envisaged to extend over a rather longer range (> two units of η), originate from the fluctuations associated with the particle emitting sources, such as strings, clusters, cut pomerons, mini-jets, etc [61][62][63][64][65]. Therefore, in order to look for the forward-backward correlations, not only the selection of pseudorapidity window of proper width is important but their separation from each other in η space is equally important.…”

Forward-backward multiplicity and momentum correlations in $pp$ collisions at LHC energies

“…Furthermore, PYTHIA 8 tune A2 fails to describe the N ch dependency of SRC and LRC components as measured by ATLAS experiment in pp collisions at √ s = 13 TeV [18]. Recent studies in PYTHIA with default color reconnection (CR) scheme [56] fail to explain the ALICE data, though somewhat better agreement is found with tuned CR scheme [60]. While PYTHIA with default CR scheme remains unsuccessful in explaining the LHC data in terms of long-range correlations [61], EPOS3 with hydrodynamical evolution of particles offers better agreement to the LHC data [40,43] in small systems (pp/pA).…”