Elliptic flow of hadrons observed at relativistic heavy ion collision experiments at relativistic heavy ion collider (RHIC) and large hadron collider (LHC) provides us an important signature of possible deconfinement transition from the hadronic phase to partonic phase. However, hadronization processes of deconfined partons back into final hadrons are found to play a vital role in the observed hadronic flow. In the present work, we use a coalescence mechanism also known as recombination (ReCo) to combine quarks into hadrons. To get there, we have used the Boltzmann transport equation in relaxation time approximation to transport the quarks into equilibration and finally to freeze-out the surface, before coalescence takes place. A Boltzmann-Gibbs blast wave (BGBW) function is taken as an equilibrium function to get the final distribution and a power-like function to describe the initial distributions of partons produced in heavy ion collisions. In the present work, we try to estimate the elliptic flow of identified hadrons such as <math id="M2"><mi>π</mi></math>, <math id="M3"><mi>K</mi></math>, and <math id="M4"><mi>p</mi></math>, produced in Pb+Pb collisions at <math id="M5"><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>2.76</mn><mtext> </mtext><mtext>TeV</mtext></math> at the LHC for different centralities. The elliptic flow (<math id="M6"><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math>) of identified hadrons seems to be described quite well in the available <math id="M7"><msub><mrow><mi>p</mi></mrow><mrow><mtext>T</mtext></mrow></msub></math> range. After the evolution of quarks until freeze-out time has been calculated using BTE-RTA, the approach used in this paper consists of combining two or more quarks to explain the produced hadrons at intermediate momenta regions. The formalism is found to describe the elliptic flow of hadrons produced in Pb+Pb collisions to a large extent.

India

Raghunath Sahoo

Mohammed Younus

Sushanta Tripathy

Swatantra Kumar Tiwari

Elliptic Flow of Hadrons via Quark Coalescence Mechanism Using the Boltzmann Transport Equation for Pb+Pb Collision at

Transport coefficients serve as important probes in characterizing the QCD matter created in high-energy heavy-ion collisions. Thermal and electrical conductivities as transport coefficients have special significance in studying the time evolution of the created matter. We have adopted a color string percolation approach for the estimation of thermal conductivity (<math><mi>κ</mi></math>), electrical conductivity (<math><msub><mi>σ</mi><mrow><mi>el</mi></mrow></msub></math>), and their ratio, which is popularly known as the Wiedemann-Franz law in condensed matter physics. The ratio <math><mrow><mi>κ</mi><mo>/</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>el</mi></mrow></msub><mi>T</mi></mrow></math>, which is also known as the Lorenz number (<math><mi>L</mi></math>), is studied as a function of temperature and is compared with various theoretical calculations. We observe that the thermal conductivity for a hot QCD medium is almost temperature independent in the present formalism and matches with the results obtained in an ideal equation of state for quark-gluon plasma with a fixed coupling constant (<math><msub><mi>α</mi><mi>s</mi></msub></math>). The obtained Lorenz number is compared with the Stefan-Boltzmann limit for an ideal gas. We observe that a hot QCD medium with color degrees of freedom behaves like a free electron gas.

Pragati Sahoo

Wiedemann-Franz law for hot QCD matter in a color string percolation scenario

In this work, we have studied the isothermal compressibility (<math><msub><mi>κ</mi><mi>T</mi></msub></math>) as a function of temperature, baryon chemical potential, and center-of-mass energy (<math><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt></math>) using hadron resonance gas (HRG) and excluded-volume hadron resonance gas (EV-HRG) models. A mass cut-off dependence of isothermal compressibility has been studied for a physical resonance gas. Further, we study the effect of heavier resonances (<math><mrow><mo>&gt;</mo><mn>2</mn><mspace width="0.16em"></mspace><mi>GeV</mi></mrow></math>) on the isothermal compressibility by considering the Hagedorn mass spectrum, <math><mrow><mi>ρ</mi><mrow><mo>(</mo><mi>m</mi><mo>)</mo></mrow><mo>∼</mo><mrow><mo>exp</mo><mo>(</mo><mi>b</mi><mi>m</mi><mo>)</mo></mrow><mo>/</mo><msup><mrow><mo>(</mo><msup><mi>m</mi><mn>2</mn></msup><mo>+</mo><msubsup><mi>m</mi><mn>0</mn><mn>2</mn></msubsup><mo>)</mo></mrow><mrow><mn>5</mn><mo>/</mo><mn>4</mn></mrow></msup></mrow></math>. Here the parameters <math><mi>b</mi></math> and <math><msub><mi>m</mi><mn>0</mn></msub></math> are extracted after comparing the results of recent lattice QCD simulations at finite baryonic chemical potential. We find a significant difference between the results obtained in EV-HRG and HRG models at higher temperatures. The inclusion of the Hagedorn mass spectrum in the partition function for hadron gas has a large effect at a higher temperature. A higher mass cut-off in the Hagedorn mass spectrum takes the isothermal compressibility to a minimum value, which occurs near the Hagedorn temperature (<math><msub><mi>T</mi><mi>H</mi></msub></math>). We show explicitly that at the future low-energy accelerator facilities like FAIR (CBM), Darmstadt, and NICA, Dubna, the created matter would have higher compressibility compared to the high-energy facilities like the Relativistic Heavy Ion Collider and Large Hadron Collider.

Arvind Khuntia

Pramod Sharma

CERN

Tapan K. Nayak

Effect of Hagedorn states on isothermal compressibility of hadronic matter formed in heavy-ion collisions: From NICA to LHC energies

The hypothesis of limiting fragmentation (LF), or, as it has been otherwise recently called, longitudinal scaling, is an interesting phenomena in the high-energy multiparticle production process. This paper discusses different regions of phase space and their importance in hadron production, giving special emphasis on the fragmentation region. Although it was conjectured as a universal phenomenon in high-energy physics, with the advent of higher center-of-mass energies, it has become prudent to analyze and understand the validity of such a hypothesis in view of the increasing inelastic nucleon-nucleon cross section (<math><msub><mi>σ</mi><mi>in</mi></msub></math>). In this work, we revisit the phenomenon of limiting fragmentation for nucleus-nucleus (<math><mi>A</mi></math>+<math><mi>A</mi></math>) collisions in the pseudorapidity distribution of charged particles at various energies. We use energy-dependent <math><msub><mi>σ</mi><mi>in</mi></msub></math> to transform the charged-particle pseudorapidity distributions (<math><mrow><mi>d</mi><msubsup><mi>N</mi><mi>ch</mi><mrow><mi>A</mi><mi>A</mi></mrow></msubsup><mo>/</mo><mi>d</mi><mi>η</mi></mrow></math>) into differential cross section per unit pseudorapidity (<math><mrow><mi>d</mi><msup><mi>σ</mi><mrow><mi>A</mi><mi>A</mi></mrow></msup><mo>/</mo><mi>d</mi><mi>η</mi></mrow></math>) of charged particles and study the phenomenon of LF. We find that in <math><mrow><mi>d</mi><msup><mi>σ</mi><mrow><mi>A</mi><mi>A</mi></mrow></msup><mo>/</mo><mi>d</mi><mi>η</mi></mrow></math> LF seems to be violated at Large Hadron Collider (LHC) energies while considering the energy-dependent <math><msub><mi>σ</mi><mi>in</mi></msub></math>. We also perform a similar study using the A Multi-Phase Transport model with a string melting scenario and also find that LF is violated at LHC energies.

Pooja Pareek

Limiting fragmentation in high-energy nuclear collisions at the CERN Large Hadron Collider

Recently, transport coefficients, viz., shear viscosity, electrical conductivity, etc., of strongly interacting matter produced in heavy-ion collisions have drawn considerable interest. We study the normalized electrical conductivity (<math><mrow><msub><mrow><mi>σ</mi></mrow><mrow><mi>el</mi></mrow></msub><mo>/</mo><mi>T</mi></mrow></math>) of hot QCD matter as a function of temperature (T) using the color string percolation model (CSPM). We also study the temperature dependence of shear viscosity and its ratio with electrical conductivity for the QCD matter. We compare CSPM estimations with various existing results and lattice QCD predictions with (<math><mrow><mn>2</mn><mo>+</mo><mn>1</mn></mrow></math>) dynamical flavors. We find that <math><mrow><msub><mrow><mi>σ</mi></mrow><mrow><mi>el</mi></mrow></msub><mo>/</mo><mi>T</mi></mrow></math> in CSPM has a very weak dependence on the temperature. We compare CSPM results with those obtained in the Boltzmann approach to multiparton scatterings model. A good agreement is found between CSPM results and predictions of the Boltzmann approach to multiparton scatterings with a fixed strong coupling constant.