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Premomoy Ghosh

Publications and source records attributed to Premomoy Ghosh.

17 recordsLinked to original sources

Forward-backward multiplicity and momentum correlations in pp and pPb collisions at the LHC energies

Correlations and fluctuations between produced particles in an ultra-relativistic nuclear collision remain one of the successor to understand the basics of the particle production mechanism. More differential tools like Forward-Backward (FB) correlations between particles from two different phase-space further strengthened our cognizance. We have studied the strength of FB correlations in terms of charged particle multiplicity and summed transverse momentum for proton-proton ($pp$) and proton-lead ($pPb$) collisions at the centre-of-mass energies $\sqrt{s}$ = 13 TeV and $\sqrt{s_{\rm NN}}$ = 5.02 TeV respectively for the EPOS3 simulated events with hydrodynamical evolution of produced particles. Furthermore, the correlation strengths are separately obtained for the particles coming from the core and the corona. FB correlation strengths are examined as a function of psedorapidity gap ($η_{gap}$), psedorapidity window-width ($δη$), centre-of-mass energy ($\sqrt{s}$), minimum transverse momentum ($p_{Tmin}$) and different multiplicity classes following standard kinematical cuts used by the ALICE and the ATLAS experiments at the LHC for all three EPOS3 event samples. EPOS3 model shows a similar trend of FB multiplicity and momentum correlation strengths for both $pp$ \& $pPb$ systems, though the correlation strengths are found to be larger for $pPb$ system than $pp$ system. Moreover, $δη$-weighted average of FB correlation strengths as a function of different center-of-mass energies for $pp$ collisions delineates a tendency of saturation at very high energies.

hep-ph

Forward-backward multiplicity and momentum correlations in $pp$ collisions at LHC energies

Charged-particle multiplicity and summed values of the transverse momentum ($p_{\rm T}$) have been utilized for estimating forward-backward (FB) correlation strength for EPOS3 simulated proton-proton ($pp$) events with and without hydrodynamical evolution of particles at center-of-mass energies $\sqrt{s}$ = 0.9, 2.76, and 7 TeV for different pseudorapidity window width ($δη$) and gap ($η_{gap}$) between the FB windows. We have studied the variation of FB correlation strength with $η_{gap}$, $δη$, $\sqrt{s}$, $p_{\rm T}$ cuts and multiplicity classes. Results are compared with the corresponding ALICE and ATLAS data. EPOS3 model qualitatively reproduces the overall variation of correlation strength of the LHC data. However, quantitative agreement is better for $pp$ events, generated using EPOS3 with hydrodynamical evolution of particles, with ATLAS data.

hep-ph

Finite size effect on thermodynamics of hadron gas in high-multiplicity events of proton-proton collisions at the LHC

Multiple Reflection Expansion (MRE) formalism has been applied to hadron resonance gas (HRG) model to study the finite-size effect on thermodynamics of small systems of hadron gas at the chemical freeze-out temperature in high-multiplicity events of proton-proton (pp) colisions at the LHC. Comparison with larger systems of heavy-ion (AA) collisions helps in undersanding the usefulness of the effect on small systems. Thermodynamic properties of these systems at the chemical freeze-out, with and without system-size effect, are contrasted with those for infinite hadronic phase of strongly interacting matter at ideal thermodynamic limit, as provided by LQCD calculations. On introduction of finite size effect, the small hadronic systems produced in high-multiplicity pp events, unlike those in AA collisions, remain away from ideal thermodynamic limit. Knudsen number estimations validate the findings.

hep-ph

Anomalous features of particle production in high-multiplicity events of pp collisions at the LHC energies

Prevalent models of multi-particle production in relativistic pp collisions at pre-LHC energies, fail to provide convincing explanations to certain significant features of the final-state charged particles in high-multiplicity pp events at the LHC. This article presents a study, contrasting those features, usually interpreted as collective behaviour of particle production in relativistic heavy-ion collisions, in the framework of hydrodynamic EPOS3 model, emphasizing quantitative comparison between the data and the model-based simulation in the same kinematic ranges, for better cognizance of the data. The work reveals quantitative mismatch between the data and the model.

hep-ph

Centrality dependent long-range angular correlations of intermediate-pT D-mesons and charged particles in pPb collisions at the LHC energy

The high-multiplicity events of pPb collisions at $\sqrt s_{NN}$ = 5.02 TeV at the LHC exhibit unforeseen collective behaviour. One of the possible explanations to the collectivity could be the formation of thermalized partonic matter, like the one formed in relativistic nucleus-nucleus collisions and is described by the hydrodynamic models. This article presents a study on the centrality dependent long-range 2 < $|Δη|$ < 4 two-particle azimuthal correlations of D-mesons and charged particles in pPb collisions at $\sqrt s_{NN}$ = 5.02 TeV. The study has been conducted on the events, generated with the EPOS3 hydrodynamic code that reproduces most of the features of the pPb data at the LHC energy. There appears a ridge-like structure in the long-range two-particle angular correlations of D-mesons, in the intermediate pT -range, and charged particles in the simulated high-multiplicity pPb events.

hep-ph

The $η/s$ of the LQCD-EoS complied hadron gas of different sizes approach common minimum near the crossover temperature

We study the temperature dependence of the ratio of the shear viscosity to entropy density for the LQCD-contrasted hadron resonance gas of different finite system-sizes, which may represent the final state hadronic matter, formed in systems of ultra-relativistic collisions. The transport coefficient reaches the lowest common value, for the systems of different sizes of thermalized hadron gas, near the critical temperature $T_{c}$ of the QCD crossover.

hep-ph

van der Waals hadron resonance gas and QCD phase diagram

Taking into account the recently developed van der Waals (VDW) like equation of state (EoS) for grand canonical ensemble of fermions, the temperature dependent profiles of normalized entropy density ($s /T^3$) and the ratio of shear viscosity and entropy density ($η/ s$) for hadron resonance gas have been evaluated. The VDW parameters, corresponding to interactions between (anti)baryons, have been obtained by contrasting lattice EoS for QCD matter at finite chemical potentials ($μ_{B}$) and for $T \le$ 160 MeV. The temperature and chemical potential dependent study of $s /T^3$ and $η/s$ for hadron gas, by signalling onsets of first order phase transition and crossover in the hadronic phase of QCD matter, helps in understanding the QCD phase diagram in the ($T, μ_{B}$) - plane. An estimation of probable location of critical point matches predictions from other recent studies.

hep-ph

Thermalization in small system of hadron gas and high-multiplicity pp events

We study the system-size dependence of Knudsen number, a measure of degree of thermalization, for hadron resonance gas that follows the Lattice-QCD equation of state at zero chemical potential. A comparison between Knudsen numbers for the AuAu collisions at RHIC and the hadron gas of size similar to the size of high-multiplicity pp events at LHC, reassures the applicability of hydrodynamics in interpreting the features of particle production in high-multiplicity pp events.

hep-ph

Indication of change of phase in high-multiplicity proton-proton events at LHC in String Percolation Model

We analyze high multiplicity proton-proton ($pp$) collision data in the framework of the String Percolation Model (SPM) that has been successful in describing several phenomena of multiparticle production, including the signatures of recent discovery of strongly interacting partonic matter, the Quark Gluon Plasma (QGP), in relativistic heavy-ion collisions. Our study in terms of the ratio of shear viscosity and entropy density ($η/s$) and the (LQCD) predicted signature of QCD change of phase, in terms of effective number of degrees of freedom ($ε/T^4$), reiterates the possibility of strongly interacting collective medium in these events.

nucl-th

Collectivity in high-multiplicity events of proton-proton collisions in the framework of String Percolation

We analyze high multiplicity proton-proton ($pp$) collision data at the energies $\sqrt{s}=900$ GeV, $2.76$ TeV and $7$ TeV in the framework of the String Percolation Model (SPM) in terms of the ratio of shear viscosity and entropy density ($η/s$) showing that the model allows the formation of strongly interacting collective medium in the high energy and high multiplicity events in p-p collisions.

hep-ph

Do we see change of phase in proton-proton collisions at the Large Hadron Collider?

High multiplicity events in proton-proton collisions at the Large Hadron Collider exhibit features resembling those found in relativistic nuclear collisions, indicating formation of medium of similar nature. Analyzing the proton-proton collision data, we find a clear signal of occurrence of change in phase between thermalized partonic matter and hadronic one as has been predicted by the lattice quantum chromodynamics.

hep-ph

Indication of transverse radial flow in high-multiplicity proton-proton collisions at the Large Hadron Collider

We analyze the measured spectra of $π^\pm$, $K^\pm$, $p$($\bar p$) in $pp$ collisions at $\sqrt {s}$ = 0.9, 2.76 and 7 TeV, in the light of blast-wave model to extract the transverse radial flow velocity and kinetic temperature at freeze-out for the system formed in $pp$ collisions. The dependency of the blast-wave parameters on average charged particle multiplicity of event sample or the `centrality' of collisions has been studied and compared with results of similar analysis in nucleus-nucleus ($AA$) and proton-nucleus ($pA$) collisions. We analyze the spectra of $K_{s}^0$, $Λ$($\bar Λ$) and $Ξ^-$ also to see the dependence of blast-wave description on the species of produced particles. Within the framework of the blast-wave model, the study reveals indication of collective behavior for high-multiplicity events in $pp$ collisions at LHC. Strong transverse radial flow in high multiplicity $pp$ collisions and its comparison with that in $pA$ and $AA$ collisions match with predictions from a very recent theoretical work [Shuryak and Zahed 2013 arXiv:1301.4470] that addresses the conditions for applicability of hydrodynamics in $pp$ and $pA$ collisions.

hep-ph

Multiplicity distributions in the forward rapidity region in proton-proton collisions at the Large Hadron Collider

Measured multiplicity distributions of primary charged particles produced in the forward rapidity region of the $proton-proton$ ($pp$) collisions at the centre-of-mass energy, $\sqrt {s}$ = 7 TeV at the Large Hadron Collider (LHC) have been analyzed in terms of the Negative Binomial Distribution (NBD) function. Like the multiplicity distributions in the mid-rapidity region for the $pp$ collisions at $\sqrt {s}$ = 7 TeV, the distributions for the minimum bias events in the forward region also are better described with the superposition of two-NBDs, as proposed by a two-component model of particle production from two processes, the "$soft$" and the "$hard$". However, the multiplicity distribution for the "hard-QCD" events in a large pseudorapidity window does not oblige the two-component model.

hep-ph

Analysis of multiplicity distributions in proton-proton collisions at LHC up to $\sqrt {s}$ = 7 TeV in quantum statistical approach

Proton-proton collisions at new high energies ($\sqrt {s}=$2.36 and 7 TeV) at LHC resulted into a greater mean multiplicities ($ $) of charged particles in the mid-rapidity region than estimated $< n >$s by different models and event generators. Another significant observation in multiplicity data is a change in slope in the distribution of primary charged hadrons in pseudorapidity intervals $|η|<2.4$ at $\sqrt{s} = 7$ TeV. These new observations merit further studies. We consider a two-component model of particle production to analyze the multiplicity distributions of charged hadrons from the proton-proton collisions at centre-of-mass energies $\sqrt{s} = 0.9$ TeV, $\sqrt{s} = 2.36$ TeV and $\sqrt{s} = 7$ TeV in pseudorapidity intervals $|η|$ of increasing width around the centre-of-mass pseudorapidity $η_{cm} =0$. The model, based on quantum statistical formalism, considers one chaotic and another coherent source of particle productions. The LHC data has been found to be consistent with characteristic features of the model. The analysis provides a reasonable explanation to the observed change in slope in the distribution and suggests a possible reason for underestimations of mean multiplicities by the event generators. In addition, an interesting revelation is the deviation from a scaling law, involving information entropy in quantum statistical viewpoint, derived as a function of chaotic multiplicity obtained from the two-component model.

hep-ph

Two-component model in quantum statistical framework compared with multiplicity distributions in proton-proton collisions at energies up to $\sqrt {s}$ = 7 TeV

Proton-proton collisions at new high energies ($\sqrt {s} =$ 2.36 and 7 TeV) at LHC resulted into greater mean multiplicities ($ $) of charged particles in the mid-rapidity region than estimated ones by different models and event generators. Another significant observation in multiplicity data is the change in slope in the distribution of primary charged hadrons in symmetric pseudorapidity interval $|η|<$2.4. The change is most prominent with data at $\sqrt{s} = 7$ TeV. These new observations merit further studies. We consider a two-component model of particle production to analyze multiplicity distributions of charged hadrons from proton-proton collisions at centre-of-mass energies $\sqrt{s} = $ 0.9, 2.36 and 7 TeV in symmetric pseudorapidity intervals $|η|$ of increasing width around the centre-of-mass pseudorapidity $η_{cm} = 0$. The model, based on quantum statistical (QS) formalism, describes multiplicity distribution by convolution of a Negative Binomial Distribution (NBD), representing a chaotic component, and a Poisson Distribution (PD), representing a coherent component of particle productions. The behaviour of characteristic parameters of the model is followed by the LHC data, while a scaling law, involving information entropy in quantum statistical viewpoint and derived as a function of chaotic multiplicity obtained from the two-component model, is not obeyed by the data, satisfactorily. An attempt to match the measured multiplicity distributions and suggested convolutions with values of characteristic parameters extracted from the data confirms disagreement between the data and the model.

hep-ph

Negative binomial multiplicity distribution in proton-proton collisions in limited pseudorapidity intervals at LHC up to sqrt (s) = 7 TeV and the clan model

Experiments at the Large Hadron Collider (LHC) have measured multiplicity distributions in proton-proton collisions at a new domain of center-of-mass energy ($\sqrt {s}$) in limited pseudorapidity intervals. We analyze multiplicity distribution data of proton-proton collisions at LHC energies as measured by the Compact Muon Solenoid (CMS) experiment in terms of characteristic parameters of the Negative Binomial Distribution (NBD) function that has played a significant role in describing multiplicity distribution data of particle production in high energy physics experiments, in the pre-LHC energy-range, in various kinds of collisions for a wide range of collision energy and for different kinematic ranges. Beside a single NBD, we apply the formalism of weighted superposition of two NBDs to examine if the multiplicity distribution data of CMS could be better explained. The weighted superposition of two NBDs indeed explain the distribution data better at the highest available LHC energy and in large interval of phase space. The two-NBD formalism further reveals that the energy invariance of the multiplicity distribution of the "soft" component of particle production in hadronic collisions is valid at LHC also, as it is at RHIC and Tevatron. We analyze the data further in terms of clan parameters in the framework of the two-NBD model.

hep-ph

Saturation of product's exoticity in compound nuclear reactions and its role in the production of new n-deficient nuclei with radioactive projectiles

Representation in terms of a new parameter, exoticity, a measure of n-deficiency or p-richness, clearly brings out the saturation tendency of the product's maximum exoticity in a compound nuclear reaction as the compound nucleus is made more and more exotic using radioactive projectile (RIBs). The effect of this saturation on the production of new proton-rich species with RIBs over a wide Z-range has been discussed.

nucl-th