Nucleon participants or quark participants?

Abstract

We show that centrality dependence of charged particle pseudorapidity density at midrapidity in Au+Au collisions at RHIC is well described as proportional to We show that centrality dependence of charged particle pseudorapidity density at midrapidity in Au+Au collisions at RHIC is well described as proportional to the number of participating constituent quarks. In this approach there is no need for an additional contribution from hard processes usually considered in the models based on the number of the nucleon participants.Comment: 3 pages, 4 figures, latex, version accepted for publication in Phys.Rev.

Azimuthal Anisotropy inU+UandAu+AuCollisions at RHIC

“…[30] with a smaller diffuseness and smaller deformation parameter β 2 in combination with the same Glauber model, reduces the downturn in central U+U collisions somewhat but introduces a mismatch between the U+U and Au+Au curves with the Au+Au curves higher while v 2 {4}/ε 2 {4} for U+U still exhibits a downturn (not shown). In the inset of the figure, we show the result for a new Glauber calculation using contituent quarks as participants [18,19] and the new set of parameters [30]. This estimate for ε 2 leads to a seemingly more natural behavior for v 2 /ε 2 with the drop in the highest multiplicity collisions almost entirely gone.…”

“…Both U+U and Au+Au follow a similar trend for v2/ε2 and a turn-over is observed in central collisions. The inset shows the same quantity but with the eccentricity calculated in a constituent quark Glauber model [18,19] with the Woods-Saxon parameters proposed in Ref. [30].…”

“…Those samples can then be used to study other topics like the path-length dependence of jet-quenching [9], or the extent to which three-particle charge-dependent correlations [12,13] can be attributed to local parity violation [14] or background effects [15]. We also investigate two models that do not include any explicit dependence on N bin ; one based on gluon saturation [16,17] and the other based on the number of participating constituent quarks [18,19].…”

“…This indicates that the variation in multiplicity between tip-tip collisions and body-body collisions is smaller than anticipated if multiplicity has a significant contribution proportional to N bin . Given this failure, we investigate two alternatives with no explicit N bin dependence: a constituent-quark Glauber model (Glauber-CQ) [18,19] and the IP-Glasma model [17] based on gluon saturation [16]. The Glauber-CQ model neglects N bin and counts the number of participating constitutent quarks N CQ with each nucleon being treated as three constituent quarks distributed according to ρ = ρ 0 exp(−ar) with a = 4.27 fm−1 [19].…”

Transverse momentum distribution and elliptic flow of charged hadrons in $$U+U$$ U + U collisions at $$\sqrt{s_{NN}}=193$$ s NN = 193 GeV using HYDJET++

“…The constituent quark model is also proposed to describe the experimental observation on v 2 in U + U collisions [26,27]. In this article we want to study the U + U collision at √ s N N = 193 GeV in body-body and tip-tip configurations by modifying HYDJET++ model which uses PYTHIA type initial condition for hard part and Glauber type initial condition for soft part.…”