Multiplicity dependence of the freezeout parameters in high energy hadron-hadron collisions

We examined the transverse momentum(pT)spectra of various identified particles,encompassing both light-flavored and strange hadrons(π++π−,K++K−,p+p¯,ϕ,K0s,Λ+Λ¯,Ξ−+Ξ¯+,andΩ−+Ω¯+),across different multiplicity classes in proton-proton collisions(p-p)at a center-of-mass energy of s√=7 TeV.Utilizing the Tsallis and Hagedorn models,parameters relevant to the bulk properties of nuclear matter were extracted.Both models exhibit good agreement with experimental data.In our analyses,we observed a consistent decrease in the effective temperature(T)for the Tsallis model and the kinetic or thermal freeze-out temperature(T0)for the Hagedorn model,as we transitioned from higher multiplicity(class-I)to lower multiplicity(class-X).This trend is attributed to the diminished energy transfer in higher multiplicity classes.Additionally,we observed that the transverse flow velocity(βT)experiences a decline from class-I to class-X.The normalization constant,which represents the multiplicity of produced particles,was observed to decrease as we moved toward higher multiplicity classes.While the effective and kinetic freeze-out temperatures,as well as the transverse flow velocity,show a mild dependency on multiplicity for lighter particles,this dependency becomes more pronounced for heavier particles.The multiplicity parameter for heavier particles was observed to be smaller than that of lighter particles,indicating a greater abundance of lighter hadrons compared to heavier ones.Various particle species were observed to undergo decoupling from the fireball at distinct temperatures:lighter particles exhibit lower temperatures,while heavier ones show higher temperatures,thereby supporting the concept of multiple freeze-out scenarios.Moreover,we identified a positive correlation between the kinetic freeze-out temperature and transverse flow velocity,a scenario where particles experience stronger collective motion at a higher freeze-out temperature.The reason for this positive correlation is that,as the multiplicity increases,more energy is transferred into the system.This increased energy causes greater excitation and pressure within the system,leading to a quick expansion.

Dependence of thermodynamic quantities at freeze-out on pseudorapidity and collision energy in p-p collisions at LHC energies

The transverse momentum distributions of charged hadrons produced in proton-proton collisions at center-of-mass energies(√s)of 0.9 TeV and 2.36 TeV,as measured by the CMS detector at the Large Hadron Collider(LHC),have been analyzed within various pseudorapidity classes utilizing the thermodynamically consistent Tsallis distribution.The fitting procedure resulted in the key parameters,namely,effective temperature(T),non-extensivity parameter(q),and kinetic freezeout volume(V).Additionally,the mean transverse momentum(<pT>)and initial temperature(T_(i))of the particle source are determined through the fit function and string percolation method,respectively.An alternative method is employed to calculate the kinetic freezeout temperature(T_(0))and transverse flow velocity(β_(T))from T.Furthermore,thermodynamic quantities at the freezeout,including energy density(ε),particle density(n),entropy density(s),pressure(P),and squared speed of sound(C_(s)^(2)),are computed using the extracted T and q.It is also observed that,with a decrease in pseudorapidity,all thermodynamic quantities except V and q increase.This trend is attributed to greater energy transfer along the mid pseudorapidity.q increases towards higher values of pseudorapidity,indicating that particles close to the beam axis are far from equilibrium.Meanwhile,V remains nearly independent of pseudorapidity.The excitation function of these parameters(q)shows a direct(inverse)correlation with collision energy.The ε,n,s,and P show a strong dependence on collision energies at low pseudorapidities.Explicit verification of the thermodynamic inequality ε≥3P suggests the formation of a highly dense droplet-like Quark-Gluon Plasma(QGP).Additionally,the inequality T_(i)>T>T_(0)is explicitly confirmed,aligning with the evolution of the produced fireball.

Comparative analysis of jet and underlying event properties across various models as a function of charged particle multiplicity at 7 TeV

In this study,a comprehensive analysis of jets and underlying events as a function of charged particle multiplicity in proton-proton(pp)collisions at a center-of-mass energy of √s=7 TeV is conducted.Various Monte Carlo(MC)event generators,including Pythia8.308,EPOS 1.99,EPOSLHC,EPOS4_(Hydro),and EPOS4_(noHydro),are employed to predict particle production.The predictions from these models are compared with experimental data from the CMS collaboration.The charged particles are categorized into those associated with underlying events and those linked to jets,and the analysis is restricted to charged particles with|η|<2.4 and p_T>0.25 GeV/c.By comparing the MC predictions with CMS data,we find that EPOS4_(Hydro),EPOSLHC,and Pythia8 consistently reproduce the experimental results for all charged particles,underlying events,intrajets,and leading charged particles.For charged jet rates with p_T^(ch.jet)>5 GeV/c,EPOS4_(Hydro)and Pythia8 perform exceptionally well.In the case of charged jet rates with p_T^(ch.jet)→30 GeV/c,EPOSLHC reproduces satisfactorily good results,whereas EPOS4 Hydro exhibits good agreement with the data at higher charged particle multiplicities compared to the other models.This can be attributed to the conversion of energy into flow when"Hydro=on"leading to an increase in multiplicity.The EPOSLHC model describes the data better owing to the new collective flow effects,correlated flow treatment,and parameterization compared to EPOS 1.99.However,the examination of the jet p_T spectrum and normalized charged p_T density reveals that EPOS4_(Hydro),EPOS4_(noHydro),and EPOSLHC exhibit good agreement with the experimental results,whereas Pythia8 and EPOS 1.99 do not perform as well owing to the lack of correlated flow treatment.