Speaker
Description
One of the most exciting and puzzling observations in ultrarelativistic
p+A reactions is the fairly large harmonic flow (such as v2(pT) and
v3(pT) coefficients). On one hand, the flow seems to be consistent with
hydrodynamic simulations [1], suggesting a high degree of thermalization
even in such very small collision systems. On the other hand, several
non-thermal mechanisms can also generate azimuthal correlations. For
example, there are inherent angular correlations in multi-gluon
production in QCD [2]. Anisotropic escape from the collision zone is yet
another non-thermal mechanism that results in flow anisotropy [3].
Intrinsic space-momentum correlations in quantum mechanics also lead to
significant harmonic flow [4]. Unlike hydrodynamic evolution, where
momentum anisotropies need time to be generated by pressure gradients,
the quantum anisotropies are inherent at the initial condition to
hydrodynamics. (Such correlations, therefore, are also very different
from pre-flow generated during thermalization.) They arise because of
the Heisenberg uncertainty relation that prohibits perfect simultaneous
localization in both momentum and coordinate space. This kind of
anisotropy, therefore, has two main features: it gets more pronounced
the smaller the system size, but it vanishes in the infinite temperature
("classical") limit.
Up to now these quantum anisotropies have only been calculated for
nonrelativistic particles, which is unfortunate because the results lose
their validity for transverse momenta exceeding the particle mass (pT >~
m), right where anisotropies start to become really significant and
interesting [4]. I will present new results from a calculation for
relativistic particles, and show that intrinsic quantum anisotropies are
indeed significant at pT ~ 1-2 GeV. I will also discuss how the
intrinsic anisotropies are affected by the subsequent expansion dynamics
of the system.
[1] P. Bozek and W. Broniowski, Phys. Rev. C 88, 014903 (2013)
[2] A. Dumitru, L. McLerran and V. Skokov, Phys. Lett. B 743, 134 (2015)
[3] L. He, T. Edmonds, Z. W. Lin, F. Liu, D. Molnar and F. Wang,
Phys. Lett. B 753, 506 (2016)
[4] D. Molnar, F. Wang and C. H. Greene, arXiv:1404.4119 [nucl-th]
| List of tracks | Small systems (pA) |
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