Narrow Results

The experimental data on the capture and evaporation residue cross-sections obtained in the ⁴⁸Ca+²⁰⁸Pb reaction were analyzed in the framework of the dynamical model based on the dinuclear system concept and advanced statistical method to clarify the reaction mechanism. The experimental excitation function of the capture reactions was decomposed into contributions of the fusion–fission, quasifission and fast-fission processes. Total evaporation residues and ones after neutron emission were only calculated and compared with the available experimental data.

The difference between intensity interferometry and measurements of two-particle momentum correlations in heavy-ion collisions is discussed. These approaches are generally used to estimate the time-space scale of fireballs produced in heavy-ion collisions. It is inferred that the C(q_inv) function will increase with the decrease of q_inv for both bosons and fermions, if q_inv does not approach zero.

Net proton rapidity distributions are calculated, reproduce very well data obtained at AGS, SPS, RHIC and predict results for the LHC experiment.¹ Presence of non-ideal plasma effects due to strongly coupled plasma in the early stage of relativistic heavy-ion collisions is investigated in the framework of non-conventional statistical mechanics.

It is established that a strong magnetic field is generated along with quark–gluon plasma in heavy-ion collision. This unique scenario offers an opportunity to study and analyze the impact of the magnetic field on the evolution of the plasma. We calculate the dilepton yield from quark–gluon plasma in a magnetic environment by considering a suitably modified magnetized effective quark mass (MEQM). Further, we study the dilepton yield for different values of magnetic field and different values of chemical potential with MEQM. The results obtained are very encouraging and we compare it with recently reported theoretical results.

I review recent applications of the open quantum system framework in the understanding of quarkonium suppression in heavy-ion collisions, which has been used as a probe of the quark–gluon plasma for decades. The derivation of the Lindblad equations for quarkonium in both the quantum Brownian motion and the quantum optical limits and their semiclassical counterparts is explained. The hierarchy of time scales assumed in the derivation is justified from the separation of energy scales in nonrelativistic effective field theories of QCD. Physical implications of the open quantum system approach are also discussed. Finally, I list some open questions for future studies.

We review the properties of the parametric coupling model and analyze its results when considering neutron star observations and heavy-ion collision experiments, specially those concerning the isospin characteristics of symmetric and asymmetric nuclear matter. By the end of the analysis, we are able to constrain the free parameters to a very small range of acceptable values.

The relativistic parametric coupling model is used here to describe global static properties of nuclear matter and neutron stars. Using recent observational data related to neutron star properties and experimental results of heavy-ion collisions, we review some properties of the effective model and we impose this way new constraints on its coupling constants. Then we analyze the consequences on already known parameters of nuclear matter, i.e., the compression modulus, the effective nucleon mass and the maximum neutron star mass predicted by integrating the Tolman–Oppenheimer–Volkoff equations. We make use of recent data on flow analysis to constrain the parameters of the theory and to achieve this goal, and have explored the parametric coupling model in a wide range of parameters. Our predictions for the compression modulus of nuclear matter and for the maximum mass of neutron stars are in good agreement with the observational data.

Symmetric nuclear matter, described by the linear Walecka model, is considered in conformally flat space-time. The dependence of the critical parameters of liquid-gas phase transition on magnitude of the conformal step-like factor is investigated.

An attempt is made to study multifractal specific heat from F_q, modified G_q and Takagi moments, which can provide some interesting information about event-by-event fluctuations in heavy-ion collisions at high energies. It is an established fact that constancy of the specific heat (CSH) of solids and gases helps explain thermodynamical behavior of intermittency and multifractality in A–A collisions at different projectile energies. It is worthmentioning that the present paper deals with multifractal specific heat, c, extracted from F_q, modified G_q and Takagi moments for the experimental as well as FRITIOF generated data on 14.5A GeV/c²⁸Si-nucleus interactions. The results obtained using the three approaches are compared for both the data sets. The observed power law behavior reflects self-similar property of the multiparticle production process. The common feature of the multifractal specific heat obtained using the three approaches is that there is no systematic variation in its value for different orders of the moments. Furthermore, the value of c is found to be different for both the data sets and no strong target mass dependence is observed in any of the cases. A noteworthy observation is that a non-zero finite value of the multifractal specific heat may be considered a good signal for the presence of multifractality in the relativistic charged particle multiplicity distribution.

This paper reports the results of an investigation regarding occurrence of second-order phase transition in 14.5A GeV/c²⁸Si-nucleus interactions using the method of scaled factorial moments. Incidentally, the value of the universal scaling exponent, ν, for our experimental data is found to be 1.224±0.068, which is quite close to its critical value 1.304. An attempt is also made to search for the evidence of phase transition in terms of Levy index, μ, using scaled factorial moments as well as Takagi moments for both experimental and FRITIOF generated data sets. Average value of μ, calculated from F_q moments, turns out to be more than unity but is less than unity when estimated in terms of Takagi moments for both the data sets. Thus the analyses carried out in terms of F_q and Takagi moments reveal the occurrence of nonthermal and thermal phase transitions, respectively.

This paper presents the results of an investigation pertaining to multifractal structure, degree of multifractality and occurrence of deconfinement phase transition. These results are obtained by carrying out analysis of generalized dimensions and Levy index involving relativistic charged particles produced on 14.5A GeV/c²⁸Si-nucleus collisions following Takagi's approach. The values of Levy index, μ, generalized fractal dimensions, D_q and degree of multifractality, β_q, for different orders of moments are calculated in terms of Takagi moments for the experimental, FRITIOF, HIJING and random Monte Carlo (MC-RAND) generated events. The values of multifractal specific heats for all the above data sets are extracted using generalized dimensions, D_q. The analysis also shows small variations in the degree of multifractality for the experimental, FRITIOF and HIJING simulated events. However, the degree of multifractality is quite larger for the random Monte Carlo ²⁸Si-nucleus generated events at 14.5A GeV/c. Furthermore, the analyses of multifractal specific heat and Levy index in terms of Takagi moments support the presence of multifractality and occurrence of deconfinement phase transition in the experimental and simulated data sets, but for the uncorrelated Monte Carlo simulated events, occurrence of nonthermal phase transition is revealed.

Collisions of bare heavy nuclei implemented by means of merging-beam technique are suggested for the study of remarkable phenomena appearing in very strong fields created when distance between the nuclear surfaces approaches zero. Suggested here is to build a collider with two beams of actinide nuclei merging within a common straight section. Principal parameters of this collider are outlined.

A study of eccentricity (ε_n) fluctuations and its possible impact on final state momentum anisotropy (υ_n) for symmetric collisions are presented in the framework of Glauber model. Effect of fluctuations of nucleon's position on the initial geometry has been studied using a new method, where the difference between oppositely moving spectators is taken as a measurement of eccentricity fluctuations. This study shows that higher harmonics (n = 3, 4 and 5) of eccentricity are less sensitive to fluctuations in transverse plane compared to the 2nd harmonic. Position fluctuations in transverse plane will increase ε₂ and hence possibly υ₂ for the most central nucleus–nucleus collisions. For semi-central and peripheral collisions, the fluctuations have opposite effect, it decreases the eccentricity ε₂. The fluctuation of initial geometry can be studied in collider experiments by studying the spectator distribution on the both sides of the beam.

The lattice QCD data of pressure and the energy density have been used to extract the hadronic radius parameter of the excluded volume hadron resonance gas (EVHRG) model. The equation of state can be described well with the extracted radius parameter $R_h=0.15$ fm. Specific heat is also calculated in the EVHRG model. Further, two new universal descriptions of chemical freeze-out parameters have been introduced based on pressure and specific heat, respectively. It is shown that the chemical freeze-out parameters obtained at various $\sqrt{s_{NN}}$ in ideal hadron resonance gas (HRG) model approximately correspond to $P/T^4=0.88$ and $C_V/T^3=47$, respectively. These two quantities are important to describe the thermodynamic properties of the hadronic matter created in heavy-ion collision experiment. The sensitivity of universal chemical freeze-out lines on repulsive interaction is also studied. It has been observed that the behaviors of chemical freeze-out lines for $P/T^4$ and $C_V/T^3$ in EVHRG model remain similar to ideal HRG model for the best fit value of hadronic radii.

Correlation among singly charged particles emitted in the forward and backward pseudo-rapidity cones is measured in ${}^{16}$O-Ag/Br and ${}^{32}$S-Ag/Br interactions at an incident energy of $200$ GeV/nucleon. Event-by-event fluctuations in the charged particle multiplicities and their pseudo-rapidity values are also investigated in terms of some known statistical measures. Evidences of short-ranged particle correlation and cluster formation in the pseudo-rapidity space are found from our analysis. A microscopic transport model based on the Ultra-relativistic Quantum Molecular Dynamics could not match the experimental results. The differences between experimental observation and corresponding simulation could neither be accounted for even when a Bose–Einstein type of correlation effect is implemented into the simulated data.

The masses of open bottom mesons ($B$($B^{+}$,$B^0$), $\bar{B}$($B^{-}$,$\overline{B^0}$), $B_s$(${B_s}^0$, $\overline{{B_s}^0}$)) and upsilon states ($\mathrm{{\rm Y}}(1S)$, $\mathrm{{\rm Y}}(2S)$, $\mathrm{{\rm Y}}(3S)$, $\mathrm{{\rm Y}}(4S)$ and $\mathrm{{\rm Y}}(1D)$) are investigated in the isospin asymmetric strange hadronic medium at finite temperature in the presence of strong magnetic fields using a chiral effective Lagrangian approach. Here the chiral SU(3) Lagrangian is generalized to include the bottom sector to incorporate the interactions of the open bottom mesons with the magnetized medium. At finite temperature, the number density and scalar density of baryons are expressed in terms of thermal distribution functions. For charged baryons, the magnetic field introduces contribution from Landau energy levels. The masses of the open bottom mesons get modified through their interactions with the baryons and the scalar mesons, which undergo modifications in a magnetized medium. The charged $B^{+}$, $B^{-}$ mesons have additional positive mass shifts due to Landau quantization in the presence of the magnetic field. The medium mass shift of the upsilon states originates from the modification of the gluon condensates simulated by the variation of dilaton field ($\chi$) and a quark mass term in the magnetized medium. The open bottom mesons and upsilon states experience a mass drop in the magnetized medium. The masses of these mesons initially increase with a rise in temperature, and beyond a high value of temperature, their masses are observed to drop. When the temperature is below 90MeV, the in-medium masses of the mesons increase with an increase in the magnetic field. However, at high temperatures (T > 90 MeV), the masses are observed to drop with an increase in the magnetic field. These in-medium modifications can have observable effects in asymmetric heavy-ion collisions experiments.

Polarization has opened a new physics chapter in relativistic heavy-ion collisions. Since the first prediction and experimental observation of global spin polarization, a lot of progress has been made in understanding its features, both at experimental and theoretical levels. In this paper, we give an overview on the recent advances in this field. The covered topics include a review of measurements of global and local spin polarization of hyperons and the global spin alignment of vector meson’s. We account for the basic theoretical framework to describe spin polarization in a relativistic fluid such as the Quark–Gluon Plasma, including statistical quantum field theory and local thermodynamic equilibrium, spin hydrodynamics, relativistic kinetic theory with spin and coalescence models.

The total and the partial charge-changing cross-sections of ${}^{28}$Si fragmentation on C, CH₂ and H targets at the intermediate and high energies of 500–800AMeV are investigated using CR-39 plastic nuclear track detector. The total charge-changing cross-sections for H target are calculated based on the results of C and CH₂ targets. It is found that the total charge-changing cross-sections for fragmentation of ${}^{28}$Si on C, CH₂ and H targets are independent on the beam energy but increase with the mass of the targets in our studied energies, and are consistent with the predictions of Bradt–Peters semi-empirical formula and NUCFRG2 simulation codes. The partial cross-sections for projectile fragment production are independent on the beam energy in our present studied energies and show a significant odd–even staggering effect. The partial cross-sections for projectile fragment production are also compared with different predicted models, such as Cummings, Nilsen, EPAX2, EPAX3 and FRACS. Only the FRACS model reproduces a significant odd–even staggering effect, while its strength is weaker than the experimental data. Generally, these models can reproduce the experimental data of ${}^{28}$Si on the CH₂ target well compared with the C target.

This paper reports a study on multidimensional fractal behavior of pions emitted in ¹⁶O-AgBr interactions at 2.1 and 60 AGeV by dividing the full bin range into different sub-bin ranges. Analysis is performed in (X_η - X_ϕ) space following two-dimensional factorial moment methodology using the concept of Hurst exponent, which takes into account the anisotropy of phase space. Different scaling behavior is observed in different bins at two different energies. The data show a positive evidence of change of fluctuation pattern from self-similarity to self-affinity with increase of energy. Multifractal dimensions have been calculated in each case and it is observed that pions at both energies exhibit multifractal behavior.

The nucleon-nucleon interaction is investigated by using the ImQMD model with the three sets of parameters IQ1, IQ2 and IQ3 in which the corresponding incompressibility coefficients of nuclear matter are different. Fusion excitation function and the charge distribution of fragments are calculated for reaction systems ⁴⁰Ca+⁴⁰Ca at different incident energies. It is found that obvious differences in the charge distribution were observed at the energy region 10-25AMeV by adopting the three sets of parameters, while the results were close to each other at energy region of 30-45A MeV for the reaction system. It indicates that the Fermi energy region is a sensitive energy region to explore the N-N interaction. The fragment multiplicity spectrum for ²³⁸U+¹⁹⁷Au at 15A MeV are reproduced by the ImQMD model with the set of parameter IQ3. It is concluded that charge distribution of the fragments and the fragment multiplicity spectrum are good observables for studying N-N interaction, and IQ3 is a suitable set of parameters for the ImQMD model.