Forward-backward multiplicity correlations in pp collisions at s $$ \sqrt{s} $$ = 0.9, 2.76 and 7 TeV

Abstract

The strength of forward-backward (FB) multiplicity correlations is measured by the ALICE detector in proton-proton (pp) collisions at √ s = 0.9, 2.76 and 7 TeV. The measurement is performed in the central pseudorapidity region (|η| < 0.8) for the transverse momentum p T > 0.3 GeV/c. Two separate pseudorapidity windows of width (δη) ranging from 0.2 to 0.8 are chosen symmetrically around η = 0. The multiplicity correlation strength (b corr) is studied as a function of the pseudorapidity gap (η gap) between the two windows as well as the width of these windows. The correlation strength is found to decrease with increasing η gap and shows a non-linear increase with δη. A sizable increase of the correlation strength with the collision energy, which cannot be explained exclusively by the increase of the mean multiplicity inside the windows, is observed. The correlation coefficient is also measured for multiplicities in different configurations of two azimuthal sectors selected within the symmetric FB η-windows. Two different contributions, the short-range (SR) and the long-range (LR), are observed. The energy dependence of b corr is found to be weak for the SR component while it is strong for the LR component. Moreover, the correlation coefficient is studied for particles belonging to various transverse momentum intervals chosen to have the same mean multiplicity. Both SR and LR contributions to b corr are found to increase with p T in this case. Results are compared to PYTHIA and PHOJET event generators and to a string-based phenomenological model. The observed dependencies of b corr add new constraints on phenomenological models.

Partial correlation analysis method in ultrarelativistic heavy-ion collisions

“…Early investigations of pp and pp collisions [19][20][21][22][23][24][25] and nuclear collisions [26,27] were followed by the studies of ultra-relativistic heavy-ion and pp reactions at RHIC [2,28] and at the LHC [29][30][31][32][33][34][35]. Numerous physical models and theoretical methods have been invented in attempts to understand the mechanisms behind the generation of long-range correlations [3,12,17,18,.…”

Long-range correlation studies at the SPS energies in MC model with string fusion

“…There is an alternative definition on long-range correlation coefficient [38]: b corr = n B n F − n B n F n 2 F − n F 2 . The definitions are equivalent in case of linear correlation functions, and both of them are used in theoretical and experimental studies [39,40,41,42].…”

Strongly Intensive Observables in the Model with String Fusion

“…In the case of charge symmetry, which is a very good approximation for mid-rapidity region at LHC collision energies, these charge-wise strongly intensive observables are expressed through the string pair correlation functions for particles of the same and opposite signs, Λ same (∆η) and Λ opp (∆η). We get information about these two functions from the ALICE data on the FB correlations [13,14] and the balance function [15], using the relations (11) and (34). Finally, using these two-particle correlation functions of a string, we calculate the charge-wise strongly intensive observables Σ(n…”