13 Elliptic Flow in Relativistic Heavy-Ion Collisions
185
13.3 Summary
The elliptic flow (v 2 ) measured from two-particle correlations is larger than that from
multi-particle correlations. This can be because of either non-flow effects or fluctuations. The dependence of v 2 on p T is well described by hydrodynamical models. The
mass ordering of v 2 at low p T follows the predictions of hydrodynamical models.
RHIC and LHC data agree with VISHNU predictions and yielded η/s = 0.16 and
0.20 at
√ s NN = 200 GeV and 2.76 TeV energies, respectively. The v 2 scales with the
number of constituent quarks, n q , within ∼10% at the RHIC energies, above p T /n q
∼ 0.6 GeV/c indicating hadron production via coalescence of constituent quarks.
However, pions deviates from this which may be due to large contribution from resonance decay. There are deviations in the NCQ scaling at the level of 20% at the LHC
energies. The v 2 fluctuations are well described by fKNL-CGC and IP-Glasma models. The v 2 versus η
= η − y beam follows linear scaling behaviour. The v 2 versus p T
for different collision centralities follows universal curve if v 2 and p T are properly
scaled for collision geometry and mean p T changes, respectively. It is observed that
v 2 increases with increase in energy due to increase in mean p T .
Acknowledgements Financial assistance from the Department of Science & Technology and University Grants Commission is gratefully acknowledged.
References
1. E.V. Shuryak, Quantum chromodynamics and the theory of superdense matter. Phys. Rep. 61,
71–158 (1980)
2. S. Borsanyi et al., The QCD equation of state with dynamical quarks. JHEP 11, 077 (2010)
3. L. Kumar, D. Keane, Experimental studies of the quantum chromodynamics phase diagram at
the STAR experiment. Pramana 84, 773–786 (2015)
4. U. Heinz, M. Jacob, Evidence for a new state of matter: an assessment of the results from the
CERN lead beam program nucl-th/0002042, pp. 1–7
5. J.Y. Ollitrault, Anisotropy as a signature of transverse collective flow. Phys. Rev. D 46, 229–245
(1992)
6. U. Heinz, R. Snellings, Collective flow and viscosity in relativistic heavy-ion collisions. Ann.
Rev. Nucl. Part. Sci. 63, 123 (2013)
7. C. Gale, S. Jeon, B. Schenke, Hydrodynamic modelling of heavy-ion collisions. Int. J. Mod.
Phys. A 28, 1340011 (2013)
8. P. Huovinen, Hydrodynamics at RHIC and LHC: what have we learned? Int. J. Mod. Phys. E
22, 1330029 (2013)
9. R.S. Bhalerao, (AEPSHEP 2012), Relativistic heavy-ion collisions, in Proceedings on 1st AsiaEurope-Pacific School of High-Energy Physics TIFR-TH-14-11, arXiv:1404.3294 [nucl-th]
10. R. Snellings, Elliptic flow: a brief review. New. J. Phys. 13, 055008 (2011)
11. J.Y. Ollitrault, Relativistic hydrodynamics for heavy-ion collisions. Eur. J. Phys. 29, 275–302
(2008)
12. J. Admas et al., STAR Collaboration, Experimental and theoretical challenges in the search for
the quark-gluon plasma: the STAR Collaboration’s critical assessment of the evidence from
RHIC collisions. Nucl. Phys. A 757, 102–183 (2005)
185
13.3 Summary
The elliptic flow (v 2 ) measured from two-particle correlations is larger than that from
multi-particle correlations. This can be because of either non-flow effects or fluctuations. The dependence of v 2 on p T is well described by hydrodynamical models. The
mass ordering of v 2 at low p T follows the predictions of hydrodynamical models.
RHIC and LHC data agree with VISHNU predictions and yielded η/s = 0.16 and
0.20 at
√ s NN = 200 GeV and 2.76 TeV energies, respectively. The v 2 scales with the
number of constituent quarks, n q , within ∼10% at the RHIC energies, above p T /n q
∼ 0.6 GeV/c indicating hadron production via coalescence of constituent quarks.
However, pions deviates from this which may be due to large contribution from resonance decay. There are deviations in the NCQ scaling at the level of 20% at the LHC
energies. The v 2 fluctuations are well described by fKNL-CGC and IP-Glasma models. The v 2 versus η
= η − y beam follows linear scaling behaviour. The v 2 versus p T
for different collision centralities follows universal curve if v 2 and p T are properly
scaled for collision geometry and mean p T changes, respectively. It is observed that
v 2 increases with increase in energy due to increase in mean p T .
Acknowledgements Financial assistance from the Department of Science & Technology and University Grants Commission is gratefully acknowledged.
References
1. E.V. Shuryak, Quantum chromodynamics and the theory of superdense matter. Phys. Rep. 61,
71–158 (1980)
2. S. Borsanyi et al., The QCD equation of state with dynamical quarks. JHEP 11, 077 (2010)
3. L. Kumar, D. Keane, Experimental studies of the quantum chromodynamics phase diagram at
the STAR experiment. Pramana 84, 773–786 (2015)
4. U. Heinz, M. Jacob, Evidence for a new state of matter: an assessment of the results from the
CERN lead beam program nucl-th/0002042, pp. 1–7
5. J.Y. Ollitrault, Anisotropy as a signature of transverse collective flow. Phys. Rev. D 46, 229–245
(1992)
6. U. Heinz, R. Snellings, Collective flow and viscosity in relativistic heavy-ion collisions. Ann.
Rev. Nucl. Part. Sci. 63, 123 (2013)
7. C. Gale, S. Jeon, B. Schenke, Hydrodynamic modelling of heavy-ion collisions. Int. J. Mod.
Phys. A 28, 1340011 (2013)
8. P. Huovinen, Hydrodynamics at RHIC and LHC: what have we learned? Int. J. Mod. Phys. E
22, 1330029 (2013)
9. R.S. Bhalerao, (AEPSHEP 2012), Relativistic heavy-ion collisions, in Proceedings on 1st AsiaEurope-Pacific School of High-Energy Physics TIFR-TH-14-11, arXiv:1404.3294 [nucl-th]
10. R. Snellings, Elliptic flow: a brief review. New. J. Phys. 13, 055008 (2011)
11. J.Y. Ollitrault, Relativistic hydrodynamics for heavy-ion collisions. Eur. J. Phys. 29, 275–302
(2008)
12. J. Admas et al., STAR Collaboration, Experimental and theoretical challenges in the search for
the quark-gluon plasma: the STAR Collaboration’s critical assessment of the evidence from
RHIC collisions. Nucl. Phys. A 757, 102–183 (2005)