Anisotropic escape mechanism and elliptic flow of bottomonia

Abstract

We study the role of anisotropic escape in generating the elliptic flow of bottomonia produced in ultrarelativistic heavy-ion collisions. We implement temperature-dependent decay widths for the various bottomonium states, to calculate their survival probability when traversing through the anisotropic hot medium formed in non-central collisions. We employ the recently developed 3+1d quasiparticle anisotropic hydrodynamic simulation to model the space-time evolution of the quark-gluon plasma. We provide a quantitative prediction for transverse momentum dependence of bottomonium elliptic flow and nuclear modification factor for Pb + Pb collisions in √ sNN = 2.76 TeV at the Large Hadron Collider.arXiv:1809.06235v2 [hep-ph]

Measurement of ϒ(1S) Elliptic Flow at Forward Rapidity in Pb-Pb Collisions at sN<

“…The results are compatible with 0 and with the small positive values predicted by the available theoretical models within uncertainties. The BBJS model calculations consider only the path-length dependent dissociation of initially created bottomonia inside the QGP medium [52]. The TAMU model incorporates in addition a regeneration component originating from the recombination of (partially) thermalized bottom quarks [36].…”

“…This observation, coupled to the different measured centrality and p T dependence of the ϒð1SÞ and J=ψ suppression in Pb-Pb collisions at the LHC [17,35], can be interpreted within the models used for comparison as a sign that unlike ϒð1SÞ, J=ψ production has a significant regeneration component. [52], while the magenta band denotes the TAMU model calculations [36]. Error bars (open boxes) represent the statistical (systematic) uncertainties.…”

Anisotropic Flow in the Few Collisions Regime: Application to Bottomonia

“…Setting now the average number of collisions per bottomonium to 1-which is physically absurd since none is surviving, but gives an upper limit on the signal-and taking both eccentricities to be equal to 0.5, we show in Figure 1 the transverse momentum dependence of these anisotropic flow coefficients. In comparison to more elaborate computations [7,8], both v 2 and v 4 grow over the whole momentum range: in contrast to those models, we have no mechanism to "protect" the bottomonia from destruction, like the competition between their formation time-there is none in our model-and the time scale for the drop of the disassociation cross section, which we take to be constant.…”

“…Starting from the initial distributions (3), we can compute the anisotropic flow coefficients v 2 and v 4 of bottomonia for the case of a collision kernel (7) estimated with the free-streaming distributions. At a given transverse momentum (or, strictly speaking, transverse velocity, since this is the relevant kinematic quantity in the Boltzmann equation), we find…”

“…We further assume that the bottomonia are so few in the system that they do not scatter with themselves, but only on the massless partners, in such a way that such encounters always lead to their dissociation. That is, the final state bottomonia are those that escaped the fireball, and their flow thus results from an anisotropic escape mechanism [7]. Disregarding the possible reformation of bottomonia, we thus consider as collision term in their evolution equation…”