Elliptic Flow in Ultrarelativistic Collisions with Polarized Deuterons.

Predictions are made for elliptic flow in collisions of polarized deuterons with a heavy nucleus. It is shown that the eccentricity of the initial fireball, evaluated with respect to the deuteron polarization axis perpendicular to the beam direction, has a substantial magnitude for collisions of highest multiplicity. Within the Glauber approach we obtain ∼7% for the deuteron states with spin projection 0, and ∼-3% for spin projection ±1. We propose to measure the elliptic flow coefficient as the second order harmonic coefficient in the azimuthal distribution of produced charged hadrons with respect to the fixed polarization axis. Collective expansion yields a value of the order of 1% for this quantity, as compared to zero in the absence of polarization and/or collectivity. Such a vivid rotational symmetry breaking could be measured with the current experimental accuracy of the relativistic heavy-ion experiments. The effect has a fundamental significance for understanding the nature of dynamics in small systems, as its experimental confirmation would prove the presence of the shape-flow transmutation mechanism, typical of hydrodynamic expansion or rescattering in the later stages of the fireball evolution.

Signatures of α clustering in light nuclei from relativistic nuclear collisions.

We argue that relativistic nuclear collisions may provide experimental evidence of α clustering in light nuclei. A light α-clustered nucleus has a large intrinsic deformation. When collided against a heavy nucleus at very high energies, this deformation transforms into the deformation of the fireball in the transverse plane. The subsequent collective evolution of the fireball leads to harmonic flow reflecting the deformation of the initial shape, which can be measured with standard methods of relativistic heavy-ion collisions. We illustrate the feasibility of the idea by modeling the (12)C-(208)Pb collisions and point out that very significant quantitative and qualitative differences between the α-clustered and uniform (12)C nucleus occur in such quantities as the triangular flow, its event-by-event fluctuations, or the correlations of the elliptic and triangular flows. The proposal offers a possibility of studying low-energy nuclear structure phenomena with "snapshots" made with relativistic heavy-ion collisions.

Mass hierarchy in identified particle distributions in proton-lead collisions.

We study the mass dependence for identified particle average transverse momentum and harmonic flow coefficients in proton-lead (p-Pb) collisions, recently measured at the LHC. The collective mechanism in the p-Pb system predicts a specific mass ordering in these observables: the growth of the average transverse momentum with the particle mass and a mass splitting of the elliptic flow coefficient, i.e., smaller differential elliptic flow of protons than pions for p(T)<2 GeV. This provides an opportunity to distinguish between the collective scenario and the mechanism based on the initial gluon dynamics in the evolution of the p-Pb system.

Charge conservation and the shape of the ridge of two-particle correlations in relativistic heavy-ion collisions.

We demonstrate that, in the framework of the event-by-event hydrodynamics followed by statistical hadronization, the proper charge conservation in the mechanism of hadron production provides the crucial nonflow component and leads to agreement with the two-dimensional two-particle correlation data in relative azimuthal angle and pseudorapidity at soft transverse momenta (p(T)<2 GeV). The falloff of the same-side ridge in relative pseudorapidity follows from the fact that a pair of particles with balanced charges is emitted from the same fluid element, whose collective velocity collimates the momenta of the pair. We reproduce basic experimental features of the two-dimensional correlation function, such as the dependence on the relative charge and centrality, as well as the related charge balance functions and the harmonic flow coefficients as functions of the relative pseudorapidity.

Uniform description of soft observables in heavy-ion collisions at sqrt sNN =200 GeV.

We investigate the hydrodynamic evolution of the system formed in ultrarelativistic heavy-ion collisions and find that an appropriate choice of the initial condition, specifically a simple two-dimensional Gaussian profile for the transverse energy, in conjunction with a realistic equation of state, leads to a uniform description of soft observables measured at the relativistic heavy-ion collider. In particular, the transverse-momentum spectra, the elliptic-flow, and the Hanbury-Brown-Twiss correlation radii, including the ratio Rout/Rside as well as the dependence of the radii on the azimuthal angle, are all properly described.