Significance of the Fragmentation Region in Ultrarelativistic Heavy-Ion Collisions

Abstract

We present measurements of the pseudorapidity distribution of primary charged particles produced in Au+Au collisions at three energies, sqrt[s(NN)]=19.6, 130, and 200 GeV, for a range of collision centrali-ties. The distribution narrows for more central collisions and excess particles are produced at high pseudorapidity in peripheral collisions. For a given centrality, however, the distributions are found to scale with energy according to the "limiting fragmentation" hypothesis. The universal fragmentation region described by this scaling grows in pseudorapidity with increasing collision energy, extending well away from the beam rapidity and covering more than half of the pseudorapidity range over which particles are produced. This approach to a universal limiting curve appears to be a dominant feature of the pseudorapidity distribution and therefore of the total particle production in these collisions.

Holographic phase diagram of quark-gluon plasma formed in heavy-ion collisions

“…In figure 2, we plot the dependence of entropy bound (2.45) on the energy together with the curve schematically representing the realistic curve that fits the experimental data [76]. It can be seen that by changing the coefficient M, we can avoid the conflict only for energy up to some E max .…”

“…It can be seen that by changing the coefficient M, we can avoid the conflict only for energy up to some E max . We chose the overall coefficient of the numerical plot to fit the RHIC data [76], which are indicated by dots in figure 2.…”

CMS Physics Technical Design Report: Addendum on High Density QCD with Heavy Ions

“…On the one hand, several measurements [141][142][143] have given evidence for the existence of an extended longitudinal scaling (also called "limiting fragmentation" [144]) region close to beam rapidity, which increases with √ s N N (figure 1.20-left). On the other hand, measurements in the forward region can be used to study baryon density effects on particle production, essentially changing the chemistry of the produced quark-gluon system [145,146].…”

“…The shape of the dN ch /dη distribution for charged particles is extrapolated from the highest RHIC energy to the LHC energy using the longitudinal scaling behaviour observed at RHIC (see e.g. figure 1.20 left) [141]. A value of dN /dη = 3000 is used as default charged particle density at η = 0 in central PbPb events, corresponding to a total multiplicity of ∼26 000 hadrons.…”

“…Measurements at RHIC suggest that the initial state described by the concept of parton saturation is directly reflected in the multiplicity of produced hadrons and their phase-space distribution. These global features of multiparticle production, measured by PHOBOS and others [64,68,147,159], exhibit great simplicity, such as factorisation into separate dependencies on energy and collision geometry as well as the general feature of extended longitudinal scaling over a large fraction of the rapidity range [141,142]. In CMS, the high tracking efficiency and low rate of fake tracks, together with a large calorimetric coverage, provide a precise measurement of global event characteristics, event by event.…”