Narrow Results

Extensions of the blast-wave model for the description of noncentral collisions are reviewed and the physics behind them is explained and illustrated. It is shown how the second-order anisotropy in expansion velocity together with the anisotropy in the shape or the density profile of the fireball determine the elliptic flow of the produced hadrons. Ambiguities and limitations of the models are discussed and different models are compared among themselves and with example data. It is concluded that model results should always be compared to $v_2(p_t)$ from several identified species in order to receive meaningful results about the freeze-out stage of the fireball and that even such a comparison may not be conclusive as the models may not be able to reproduce all relevant data.

Large elliptic flow at RHIC seems to indicate that ideal hydrodynamics provides a good description of Au–Au collisions, at least at the maximum RHIC energy. The medium formed has been interpreted as a nearly perfect (low-viscosity) liquid, and connections have been made to gravitation through string theory. Recently, claimed observations of large flow fluctuations comparable to participant eccentricity fluctuations seem to confirm the ideal hydro scenario. However, determination of the azimuth quadrupole with 2D angular autocorrelations, which accurately distinguish "flow" (quadrupole) from "nonflow" (minijets), contradicts conventional interpretations. Centrality trends may depend only on the initial parton geometry, and methods used to isolate flow fluctuations are sensitive instead mainly to minijet correlations. The results presented in this paper suggest that the azimuth quadrupole may be a manifestation of gluonic multipole radiation.

We have argued that the azimuthal symmetry and asymmetry components in Fourier expansion of particle momentum azimuthal distribution, v_n(n = 0,1,2,…), should be calculated as an average of cos(nϕ) first over particles in an event and then over events (eventwise average) rather than "an average over all particles in all events" (particlewise average). In case of large centrality (multiplicity) bin the particlewise average is not accurate because the influence (fluctuation) of particle multiplicity was not taken into account.

The momentum dependence of the medium modifications on nucleon–nucleon elastic cross sections is investigated with the microscopic transport model UrQMD. The semi-peripheral Au+Au collision at the beam energy E_b = 400A MeV is adopted as an example. It is found that uncertainties of the momentum dependence on medium modifications of cross sections visibly influence the yield and collective flow distributions of free nucleons. In these observables, the elliptic flow is sensitively dependent on detailed forms of the momentum dependence. However, it is weakly influenced by the splitting effect of the neutron–neutron and proton–proton cross sections.

It is known that the presence of background magnetic field in cosmic plasma distorts the acoustic peaks in CMBR. This primarily results from different types of waves in the plasma with velocities depending on the angle between the magnetic field and the wave vector. We consider the consequences of these effects in relativistic heavy-ion collisions where very strong magnetic fields arise during early stages of the plasma evolution. We show that flow coefficients can be significantly affected by these effects when the magnetic field remains strong during early stages due to strong induced fields in the conducting plasma. In particular, the presence of magnetic field can lead to enhancement in the elliptic flow coefficient v₂.

We carry out hydrodynamical simulation of the evolution of fluid in relativistic heavy-ion collisions with random initial fluctuations. The time evolution of power spectrum of momentum anisotropies shows very strong correspondence with the physics of cosmic microwave anisotropies as was earlier predicted by us. In particular, our results demonstrate suppression of superhorizon fluctuations and the correspondence between the location of the first peak in the power spectrum of momentum anisotropies and the length scale of fluctuations and expected freeze-out time-scale (more precisely, the sound horizon size at freeze-out).

The difference in elliptic flow between protons and antiprotons, produced in ${}^{197}\mathrm{\text{Au}}+{}^{197}\mathrm{\text{Au}}$ collisions at center-of-mass energies $\sqrt{s_{NN}}=5\text{–}12\mathrm{\text{GeV}}$, is studied within a modified version of the ultra-relativistic quantum molecular dynamics (UrQMD) model. Two different model scenarios are compared: the cascade mode and the mean field mode which includes potential interactions for both formed and pre-formed hadrons. The model results for the elliptic flow of protons and the relative elliptic flow difference between protons and antiprotons obtained from the mean field mode agree with the available experimental data, while the elliptic flow difference is near zero for the cascade mode. Our results show that the elliptic flow splitting, observed for particles and antiparticles, can be explained by the inclusion of proper hadronic interactions. In addition, the difference in elliptic flow between protons and antiprotons depends on the centrality and the rapidity window. With smaller centrality and/or rapidity acceptance, the observed elliptic flow splitting is more sensitive to the beam energy, indicating a strong net baryon density dependence of the effect. We propose to confirm this splitting at the upcoming experiments from Beam Energy Scan (BES) Phase-II at Relativistic Heavy Ion Collider (RHIC), the Compressed Baryonic Matter (CBM) at Facility for Antiproton and Ion Research (FAIR), High Intensity heavy ion Accelerator Facility (HIAF) and Nuclotron-based Ion Collider fAcility (NICA).

The elliptic flows of identified hadrons in Au + Au collisions at are systematically investigated within the framework of quark (re)combination/coalescence. The results indicate that the quark combination mechanism can describe self-consistently the elliptic flows of various hadrons from low to intermediate p_T range.

We describe azimuth structure commonly associated with elliptic and directed flow in the context of 2D angular autocorrelations for the purpose of precise separation of so-called nonflow (mainly minijets) from flow. We extend the Fourier-transform description of azimuth structure to include power spectra and autocorrelations related by the Wiener–Khintchine theorem. We analyze several examples of conventional flow analysis in that context and question the relevance of reaction plane estimation to flow analysis. We introduce the 2D angular autocorrelation with examples from data analysis and describe a simulation exercise which demonstrates precise separation of flow and nonflow using the 2D autocorrelation method. We show that an alternative correlation measure based on Pearson's normalized covariance provides a more intuitive measure of azimuth structure.

We present a method of measuring the elliptic flow (v₂) of nonphotonic electrons from heavy flavor quark decays using the STAR detector at RHIC in Au + Au collisions at . Inclusive electrons are identified in the p_T range 0.5–4 GeV/c at mid-rapidity -1 < η < 0 by the STAR time projection chamber (TPC) and time-of-flight detector. Photonic e⁺e^- pairs with characteristic low invariant mass are reconstructed in the TPC and their v₂ is measured using the standard event plane method by subtracting the combinatorial background in the dN/dΔϕ distributions in each p_T bin. The nonphotonic electron v₂ and its propagated error can be derived from the inclusive and photonic electron v₂. We estimate the necessary statistics and errors of nonphotonic electron v₂ for a more recent RHIC run.

The elliptic flow in collisions of neutron-rich heavy-ion systems at intermediate energies emerges as an observable sensitive to the strength of the symmetry energy at supra-saturation densities. First results obtained by comparing ratios or differences of neutron and hydrogen flows with predictions of transport models favor a moderately soft to linear density dependence, consistent with ab initio nuclear-matter theories. Comprehensive data sets of high accuracy can be expected to improve our knowledge of the equation of state of asymmetric nuclear matter.

Fluid dynamical description of elementary particle collisions has a long history dating back to the works of Landau and Fermi. Nevertheless, it is during the last 10–15 years when fluid dynamics has become the standard tool to describe the evolution of matter created in ultrarelativistic heavy-ion collisions. In this paper, I briefly describe the hydrodynamical models, what we have learned when analyzing the RHIC and LHC data using these models, and what the latest developments and challenges are.

Elliptic flow parameter, v₂ is considered as a sensitive probe for early dynamics of the heavy-ion collision. In this work, we have discussed the effect of detector efficiency, procedure of centrality determination, effect of resonance decay and the procedure to correct event plane resolution on the measured v₂ by standard event plane method within the framework of a transport model. The measured value of v₂ depends on the efficiency in particle number counting by the detector. The effect of centrality determination is found to be negligible. The new method of event plane resolution correction for wide centrality bin yields results in v₂ values closer to the true value of the v₂. The contributions from the resonance decay seems to decrease the value of v₂ of π and K within the Ultra relativistic Quantum Molecular Dynamics (UrQMD) model based calculation. We also propose a procedure to correct for an event bias effect on v₂ arising while comparing the minimum bias collision centrality v₂ values for different multi-strange hadrons. Finally, we have presented a model based confirmation of the recently proposed relation between v₂ obtained using event plane method and scalar product method to the true value of v₂.

The nuclear suppression factor $R_{AA}$ and elliptic flow ${\nu }_2$ are calculated by considering the effects of shear viscosity to the entropy density ratio $\eta /s$, using the viscose hydrodynamics at the first- and second-orders of approximation and considering temperature dependent coupling ${\alpha }_s(T)$. It is shown that the second-order viscose hydrodynamics (varying shear viscosity to entropy ratio) with averaged value of $4\pi \eta /s=1.5\pm 0.1$ gives the best results of $R_{AA}$ and ${\nu }_2$ in comparison to the experimental data.

We study the effect of in-medium mass-shift on transverse-momentum spectrum and elliptic anisotropy of $\varphi$ meson. It is found that the mass-shift enhances the $\varphi$ yields and suppresses the elliptic flow $v_2$ in large momentum region, and the effects increase with the increasing mass-shift. The effects are various for different sources and decrease with the increasing collision energy. We further study the effects for parts of all $\varphi$ meson with mass-shift, and the effects decrease with the decreasing probability of $\varphi$ meson with mass-shift. A possible method to detect the mass-shift of $\varphi$ meson via transverse-momentum spectrum and $v_2$ is proposed.

We study the impact of the in-medium mass splitting between bosons and anti-bosons on their spectra and elliptic flow. The in-medium mass splitting may cause a separation in the transverse momentum spectra, as well as a division in the elliptic flow between bosons and anti-bosons. The magnitude of this effect becomes greater as the in-medium mass splitting increases. With the increasing rapidity, the splitting effect of the spectra increases and the splitting effect of the elliptic flow decreases. These phenomena may provide a way to differentiate whether the influences on boson and anti-boson in the medium are consistent.

The relativistic heavy ion collisions experiments are working on the different energies. In this paper we will study elliptic flow variation with pseudo rapidity at for charge pions and photons using HIJING event generator models. Elliptic flow is a signal in search of quark gluon plasma.

The relativistic heavy ion collisions are the experiment which is working on the different energies 200 and 62.4 GeV. In this paper we will study elliptic flow variation with Impact Parameter at above mentioned energies using HIJING event generator models. Elliptic flow is a signal in search of quark gluon plasma.

Heavy-flavour hadrons are effective probes to study the Quark-Gluon Plasma (QGP) formed in ultra-relativistic heavy-ion collisions. The ALICE Collaboration measured the D-mesons (D⁰, D${}^{+}$, D*${}^{+}$ and D${}_{\mathrm{\text{s}}}^{+}$) production in Pb–Pb collisions at $\sqrt{s_{\mathrm{\text{NN}}}}$ = 5.02 TeV. The in-medium energy loss can be studied by means of the nuclear modification factor ($R_{\mathrm{\text{AA}}}$). The comparison between the D${}_{\mathrm{\text{s}}}^{+}$ and the non-strange D-meson $R_{\mathrm{\text{AA}}}$ can help to study the hadronisation mechanism of the charm quark in the QGP. In semi-central collisions the measurement of the D-meson elliptic flow, $v_2$, at low $p_{\mathrm{\text{T}}}$ allows to investigate the participation of the heavy quarks in the collective expansion of the system while at high $p_{\mathrm{\text{T}}}$ it constrains the path-length dependence of the energy loss. Furthermore the Event-Shape Engineering (ESE) technique is used to measure D-meson elliptic flow in order to study the coupling of the charm quarks to the light quarks of the underlying medium.