Multiplicity distribution and source deformation in full-overlap U+U collisions

Physical Review C - Nuclear Physics

Volumn 72, Issue 3, 2005, Pages

  Kuhlman, Anthony ^a   Heinz, Ulrich ^a  

^a OHIO STATE UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 28844446606     PISSN: 05562813     EISSN: 1089490X     Source Type: Journal    
DOI: 10.1103/PhysRevC.72.037901     Document Type: Article

References (14)

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3. E. Iancu and R. Venugopalan, in Quark-Gluon Plasma 3, edited by, R. C. Hwa, and, X.-N. Wang, (World Scientific, Singapore, 2004), p. 249.
4. T. Hirano and Y. Nara, Nucl. Phys. NUPABL 0375-9474 10.1016/j.nuclphysa. 2004.08.003 A743, 305 (2004).
5. B. B. Back (PHOBOS Collaboration), Phys. Rev. Lett. PRLTAO 0031-9007 10.1103/PhysRevLett.89.222301 89, 222301 (2002).
6. P. F. Kolb and U. Heinz, in Quark-Gluon Plasma 3, edited by, R. C. Hwa, and, X.-N. Wang, (World Scientific, Singapore, 2004), p. 634.
7. D. Kharzeev and M. Nardi, Phys. Lett. PYLBAJ 0370-2693 10.1016/S0370-2693(01)00457-9 B507, 121 (2001).
8. Our calculations neglect event-by-event fluctuations of the number of spectators in collisions of given impact parameter b and orientations Ω1,Ω2. We leave this for a more detailed Monte Carlo simulation when U+U collisions become available.
9. Note that the qualitative difference between the shapes of the double-hump “ideal case†and the single-peak multiplicity distribution for the realistic situation shown in Fig. 3 is due to the contamination from slightly off-angle, off-center U+U collisions near the low end of the distribution of spectator nucleons, which is calculated from the initial distributions of nucleons in the two colliding nuclei. It is thus independent of how we parametrize the distribution of produced particles in Eqs. (1) and (3), which need not necessarily reflect the nucleon density (i.e., the baryon number distribution of the colliding nuclei) but could instead depend on their low-momentum gluon density distribution [4]. Replacing Eqs. (1) and (3) by a CGC-motivated distribution (as given, for example, in Refs. [4, 7, 10]) would require an adjustment of the normalization contant Îs in Eqs. (1) and (3) to maintain the agreement between model and Au+Au collision data in Fig. 1 and thus might lead to slightly different predictions for the total charged multiplicity produced in full-overlap U+U collisions (resulting in a horizontal shift of the curves in Fig. 3). It would not affect, however, the different shapes of the two multiplicity distributions shown in Fig. 3.
10. D. Kharzeev, E. Levin, and M. Nardi, Phys. Rev. C PRVCAN 0556-2813 10.1103/PhysRevC.71.054903 71, 054903 (2005).
11. P. F. Kolb, U. Heinz, P. Huovinen, K. J. Eskola, and K. Tuominen, Nucl. Phys. NUPABL 0375-9474 10.1016/S0375-9474(01)01114-9 A696, 197 (2001).
12. This statement remains true even in view of recently pointed out intricacies [13, 14] of interpreting elliptic flow data for v2(pâ¥) of different hadronic species that result from the late hadronic redistribution of the total momentum anisotropy generated during the early hydrodynamic evolution. Although we expect the additional gain in initial energy and entropy density in full-overlap U+U collisions to significantly improve the chances for ideal fluid dynamical evolution and early saturation of the total momentum anisotropy Îμp=〈〈Txx- TyyâŒâŒ/〈〈 Txx+TyyâŒâŒ [2], the redistribution of this momentum anisotropy over the different hadron species and over transverse momentum reflects an intricate interplay between thermal and (radial) collective motion, which is sensitive to the equation of state and chemical composition (as well as to nonideal fluid effects caused, e.g., by a large hadronic viscosity) during the late hadronic stage of the collision [13, 14]. These issues are independent of the initial energy and entropy density and beyond the scope of the present Brief Report.
13. N. Borghini and J. Y. Ollitrault, nucl-th/0506045.
14. T. Hirano and M. Gyulassy, nucl-th/0506049.