Narrow Results

Using our recently developed one parameter quasiparticle model, we analyze more recent (refined) results of (2+1)-flavor quark–gluon plasma (QGP) in lattice simulation of quantum chromodynamics (QCD) by various groups [S. Borsanyi et al., arXiv:1007.2580v2; A. Bazavov et al., Phys. Rev. D80 (2009) 014504; T. Umeda et al., arXiv:1011.2548v1; C. DeTar et al., Phys. Rev. D81 (2010) 114504]. We got a remarkable good fit to lattice thermodynamics of [S. Borsanyi et al., arXiv:1007.2580v2] and reasonable good fit to [A. Bazavov et al., Phys. Rev. D80 (2009) 014504] by adjusting single parameter of the model which may be related QCD scale parameter. The same model also fits the lattice results of [S. Borsanyi et al., arXiv:1007.2580v2] on (2+1+1)-flavor QGP. Further, we extend our model for above system with zero chemical potential to nonzero chemical potential and predict quark density without any new parameters which may be compared with future lattice data.

It is shown that de-confinement can be achieved in high multiplicity nonjet $\bar{p}p$ collisions at $\sqrt{s}=1.8$TeV Fermi National Accelerator Laboratory (FNAL- E735) experiment. Previously, the evidence for de-confinement was demonstrated by the constant freeze out energy density in high multiplicity events. In this paper, we use the same but analyze the transverse momentum spectrum in the framework of the clustering of color sources. This frame work naturally predicts the reduction in the charged particle multiplicity with respect to the value expected from the number of independent strings. The charged particle pseudorapidity densities in the range $7.0\le 〈d{N}_c/d\eta 〉\le 26.0$ are considered. Results are presented for both thermodynamic and transport properties. The initial temperature and energy density are obtained from the data via the color reduction factor $F(\xi )$ and the associated string density parameter $\xi$. The Bjorken ideal fluid description of the $QGP$, when modified by the color reduction factor and the trace anomaly $\mathrm{\Delta }$ is in remarkable agreement with the lattice quantum chromo dynamics (LQCD) simulations. The energy density $(\epsilon /T^4)\sim 11.5$ for $〈d{N}_c/d\eta 〉\sim 25.0$ is close to the value for 0–10% central events in Au+Au collisions at $\sqrt{s_{NN}}=200$GeV. The shear viscosity to entropy density ratio ($\eta /s$) is $\sim$0.2 at the transition temperature of 167MeV. The result for the trace anomaly $\mathrm{\Delta }$ is in excellent agreement with LQCD simulations. These results confirm our earlier observation that the de-confined state of matter was created in high multiplicity events in $\bar{p}p$ collisions at $\sqrt{s}=1.8$TeV.

In the nearly 20 years that have elapsed since its discovery, the gauge-gravity correspondence has become established as an efficient tool to explore the physics of a large class of strongly-coupled field theories. A brief overview is given here of its formulation and a few of its applications, emphasizing attempts to emulate aspects of the strong-coupling regime of quantum chromodynamics (QCD). To the extent possible, the presentation is self-contained, and does not presuppose knowledge of string theory.

In this work, we review what we consider are some of the most relevant results of heavy-ion physics at the Large Hadron Collider (LHC). This paper is not intended to cover all the many important results of the experiments, instead we present a brief overview of the current status on the characterization of the hot and dense Quantum-Chromo Dynamics (QCD) medium produced in the heavy-ion collisions. Recent exciting results which are still under debate are discussed too, leading to intriguing questions like whether we have a real or fake Quark-Gulon Plasma (QGP) formation in small systems.

Heavy flavor production is a sensitive probe of the initial gluon density in the nucleon and is modified by the entire evolution of the hot quark and gluon medium created in high-energy nucleus–nucleus collisions. Besides, it is a process that can be calculated by perturbative QCD because of their large mass. The PHENIX experiment at RHIC studied the heavy flavor productions for a broad momentum and rapidity ranges using single leptons from the semileptonic decay of charm and bottom hadrons, and dileptons from $J/\psi$ decays in $p+p$, $p+$A, and Au$+$Au collisions at $\sqrt{s_{NN}}$$=$200GeV. In these proceedings, the recent experimental results in $p+p$, Au$+$Au, and the small collision systems are presented and the heavy flavor productions and their modifications are discussed.

We have attempted to build a parametric-based simplified and analytical model to map the interaction of quarks and gluons in the presence of magnetic field, which has been constrained by quark condensate and thermodynamical quantities like pressure, energy density, etc., obtained from the calculation of lattice quantum chromodynamics (QCDs). To fulfill that mapping, we have assumed a parametric temperature and magnetic field-dependent degeneracy factor, average energy, momentum and velocity of quarks and gluons. Implementing this QCD interaction in calculation of transport coefficient at finite magnetic field, we have noticed that magnetic field and interaction both are two dominating sources, for which the values of transport coefficients can be reduced. Though the methodology is not so robust, but with the help of its simple parametric expressions, one can get a quick rough estimation of any phenomenological quantity, influenced by temperature and magnetic field-dependent QCD interaction.

In this paper, a detailed study of the multiplicities of charged particles produced in $p$–$p$ collisions, at $\sqrt{s}=13$TeV, has been carried out. Analysis of UrQMD generated events along pseudo–rapidity ($\eta$), azimuthal angle ($\varphi$) and $\eta$-$\varphi$ phase spaces is made with the help of scaled factorial moment method. The results have also been compared with the UrQMD events with finite impact parameter ($b$) and minimum bias (MB) conditions. From the intermittency exponent (${\alpha }_q$), the anomalous fractal dimension $d_q$ is derived and the variations of $d_q$ with order $q$ are investigated. The observed intermittent fluctuations are manifested by various parameters such as anomalous fractal dimension $d_q$, degree of multifractality ($r$), critical exponent ($\nu$), Levy index ($\mu$) and multifractal specific heat. In the framework of Ginzburg–Landau theory, the second-order phase transition in the light of scaled factorial moment method has also been carried out to search for the quark-hadron phase transition. It is observed that the intermittent type of fluctuations are strong enough in $\eta$-$\varphi$ space compared to the one-dimensional $\eta$ space and $\varphi$ space. The data reflects the signature of multifractality in $\varphi$ space and $\eta$-$\varphi$ space. Whereas in case of $\eta$ space, it shows the evidence of monofractality. It is also interesting to note that the values of critical exponents for all impact parameters indicate the apparent existence of quark hadron phase transition except for MB events. However, no such behaviour is observed in $\varphi$ space. From the knowledge of generalized fractal dimension $D_q$, multifractal specific heat is derived from scale factorial moment analysis in case of one-dimensional $\eta$ space, $\varphi$ space and two-dimensional $\eta$-$\varphi$ space.

The two-dimensional intermittency and its self-affine nature are investigated for p–p collisions at $\sqrt{s}=13$TeV in the two-dimensional anisotropic $(\eta -\varphi )$ space. The UrQMD model has been employed to generate and accumulate the p–p collisions data. Our investigation is made in the framework of scaled factorial moment (SFM) method. The concept of Hurst exponent $H$ is incorporated to bring a qualitative comparison between the UrQMD generated minimum bias (MB) events and the events at a particular impact parameter $b=0.4$ fm. The variation of the fractal strength with the variation of $H$ as well as with the variation of the order of the moment $q$ has been analyzed. Also, the nonlinearity in the variation of SFM with that of $H$ has been accompanied in this paper. It is observed that the fractal strength and the intermittent type of fluctuations are found to be much stronger in the region with $H<1$ compared to the region with $H>1$ and the self-affine nature in the fluctuations increases as $H$ deviates from unity.

The properties of quark–gluon plasma (QGP) have been studied considering it as fractal fluid where configuration space shows a noninteger dimension. The fractal dimension for the QGP droplet is suggested. The thermodynamic properties like radial distribution function, packing fraction, excess entropy and susceptibility are studied. The viscosity of the QGP phase has also been investigated and fluid is found to behave like a superfluid. Some interesting observations are made.

In this paper, we propose to measure the effect of the background field on the coupling constant through the process of photon annihilation into lepton pairs and a real photon in ultraperipheral collisions of relativistic heavy ion. In our study, the coupling constant after being corrected by background field has a significant impact on cross-section compared to the uncorrected one.