Long and Short Range Correlations: A Signature of String Fusion

Abstract

The study of backward-forward and forward-forward correlations in collisions of two nuclei at high energies allow us to distinguish between the fusion of strings produced in the collision into new strings of higher color and the possibility of the fusion of produced hadrons into clusters. The results for AB collisions at the CERN Super Proton Synchrotron (SPS) and the Brookhaven Relativistic Heavy Ion Collider (RHIC) are discussed. PACS numbers: 25.75.+r, 12.38.Mh, 13.85.Ni, 24.85.+p In the last few years many efforts have been made in the search for the quark-gluon plasma [1]. One of the main points in this search is to know how the quarkgluon plasma (QGP) can be reached in the framework of the usual models of hadronic interactions [2 -4]. In these models, strings or Pomerons are exchanged between the projectile and target. The number of strings grows with the energy and with the number of nucleons of the participant nuclei. Recently, using this kind of model, two different ways to reach the QGP have been proposed.In one of them [5,6], elaborated in the framework of the vENUS model [4], the strings produced in a nucleusnucleus collision break, forming resonances and particles, which, whenever they come closer than a given radius, fuse, forming a cluster. Afterwards, this cluster decays into resonances and particles isotropically.The critical radius is fixed by comparison to the data at gszz = 19. 4 GeV. The distribution in the number of clusters as a function of the volume size is peaked at small values of the volume, as it was expected, but the probability of obtaining clusters of large volume is not negligible.In the other proposal [7,8], the strings produced in a nucleus-nucleus collision fuse if they overlap in impact parameter space, forming a new string which has a higher color charge at its ends, corresponding to the summation of the color charges located at the ends of the original strings. Then the new strings break into hadrons according to their higher color. As a result, heavy flavor is produced more efficiently and there is a reduction of the total multiplicity [9]. New strings, like the ones proposed in Refs. [7,8], have also been found[10]by studying the diffractive process y(02) + quark X + quark. In a determined kinematic range, the leading diagram is a typical triple Pomeron diagram, but the Pomeron corresponding to the discontinuity through the X system is formed by two coupled ladders of gluons, instead of one ladder as with the other two Pomerons. In the first approach, the fusion of resonances does not modify the distribution in the number of strings. There-fore there is no variation in the long range correlations. A measurement of such correlations is the backward-forward dispersion DsF = (nsnF) -(ns)(nF), (I) where ns (nF) is the number of particles in a backward (forward) rapidity range. Indeed, in any model based on a superposition of independent exchanges (Pomerons or strings), in such a way that distinct "elementary" exchanges are statistically independent, is easy to show that the...

Long range forward–backward correlations and the color glass condensate

“…As a final comment, let us recall the result for forward-backward correlations in a different framework: string models which allow for some kind of collectivity [31]- [33] e.g. a non-thermal phase transition like percolation.…”

Long range forward–backward rapidity correlations in proton–proton collisions at LHC

“…Models that can explain, in a straight forward manner, long range F-B correlations are models that introduce extended objects in rapidity as colour flux tubes [9] or strings [10].…”

Long-range rapidity correlations between mean transverse momenta in the model with string fusion

“…The study of the correlations between observables in two separated rapidity windows (the so called long-range forward-backward correlations) has been proposed [1] as a signature of the string fusion and percolation phenomenon [2][3][4][5], which is one of the collectivity effects in ultrarelativistic heavy ion collisions. Later it was realized [6][7][8][9][10][11] that the investigations of the forward-backward correlations between intensive observables, such e.g.…”