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Register a new userForward-backward multiplicity fluctuations in ultra-relativistic nuclear collisions with wounded quarks and fluctuating strings
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We analyze a generic model where wounded quarks are amended with strings in which both end-point positions fluctuate in spatial rapidity. With the assumption that the strings emit particles independently of one another and with a uniform distribution in rapidity, we are able to analyze the model semi-analytically, which allows for its detailed understanding. Using as a constraint the one-body string emission functions obtained from the experimental data for collisions at $sqrt{s_{NN}}=200$ GeV, we explore the two-body correlations for various scenarios of string fluctuations. We find that the popular measures used to quantify the longitudinal fluctuations are limited with upper and lower bounds and assume close values for the most likely models of the end-point distributions, which may explain why various approaches yield here very similar results.
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Multiplicity distributions of hadrons produced in central nucleus-nucleus collisions are studied within the hadron-resonance gas model in the large volume limit. In the canonical ensemble conservation of three charges (baryon number, electric charge, and strangeness) is enforced. In addition, in the micro-canonical ensemble energy conservation is included. An analytical method is used to account for resonance decays. Multiplicity distributions and scaled variances for negatively charged hadrons are presented along the chemical freeze-out line of central Pb+Pb (Au+Au) collisions from SIS to LHC energies. Predictions obtained within different statistical ensembles are compared with preliminary NA49 experimental results on central Pb+Pb collisions in the SPS energy range. The measured fluctuations are significantly narrower than a Poisson reference distribution, and clearly favor expectations for the micro-canonical ensemble.
While string models describe initial state radiation in ultra-relativistic nuclear collisions well, they mainly differ in their end-point positions of the strings in spatial rapidity. We present a generic model where wounded constituents are amended with strings whose both end-point positions fluctuate and analyze semi-analytically various scenarios of string-end-point fluctuations. In particular we constrain the different cases to experimental data on rapidity spectra from collisions at $sqrt{s_{rm NN}}=200$~GeV, and explore their respective two-body correlations, which allows to partially discriminate the possible solutions.
In high energy heavy ion collisions, the directed flow of particles is conventionally measured with respect to that of the projectile spectators, which is defined as positive $x$ direction. But it is not known if the spectators deflect in the outward direction or inward -- toward the center line of the collision. In this Letter we discuss how the measurements of the directed flow at mid-rapidity, especially in asymmetric collision such as Cu+Au, can be used to answer this question. We show that the existing data strongly favor the case that the spectators, in the ultrarelativistic collisions, on average deflect outwards.
Estimates for elliptic flow in collisions of polarized light nuclei with spin $jge1$ with a heavy nucleus are presented. In such collisions the azimuthal symmetry is broken via polarization of the wave function of the light nucleus, resulting in nonzero one-body elliptic flow coefficient evaluated relative to the polarization axis. Our estimates involve experimentally well known features of light nuclei, such as their quadrupole moment and the charge radius, yielding the one-body elliptic flow coefficient in the range from 1% for collisions with the deuteron to 5% for for collisions with $^{10}$B nucleus. Prospects of addressing the issue in the upcoming fixed-target experiment at the Large Hadron Collider are discussed.
In heavy-ion ({it A-A}) collisions, the correlations among the particles produced across wide range in rapidity, probe the early stages of the reaction. The analyses of forward-backward multiplicity correlations in these collisions are complicated by several effects, which are absent or minimized in hadron-hadron collisions. This includes effects, such as the centrality selection in the {it A-A} collisions, which interfere with the measurement of the dynamical correlations. A method, which takes into account the fluctuations in centrality selection, has been utilized to determine the forward-backward correlation strength {$b_{rm corr}$} in {itA-A} collisions. This method has been validated by using the HIJING event generator in case of Au-Au collisions at $sqrt{s_{NN}}$= 200 GeV and Pb-Pb collisions at $sqrt{s_{NN}}$= 2.76 TeV. It is shown that the effect of impact parameter fluctuations is to be considered properly in order to obtain meaningful results.
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