Bedangadas
Mohanty

One of the major goals of the heavy-ion collision program is to explore the QCD phase diagram. Finite temperature lattice QCD calculations at zero baryon chemical potential suggest a crossover above a critical temperature ~ 170–190 MeV from a system with hadronic degrees of freedom to a system where the relevant degrees of freedom are quarks and gluons. Several QCD based calculations find the quark-hadron phase transition to be first order at large baryon chemical potential. The point in the QCD phase plane (T vs muB) where the first order phase transition ends is the QCD critical point (CP). Attempts are being made to locate the CP both experimentally and theoretically. Current theoretical calculations are highly uncertain about the location of the CP. Lattice QCD calculations at finite muB face numerical challenges in computing. The experimental plan is to vary the center of mass energy of heavy-ion collisions to scan the phase plane and, at each energy, search for signatures of the CP that could survive the time evolution of the system.

Publications Related to QCD Phase Diagram

• Setting the Scale of the Phase Diagram of QCD: Science 332 (2011) 1525-1528
• Experimental Paper on QCD Critical Point Search - STAR - I: Physical Review Letters 105 (2010) 022302
• Experimental Paper on QCD Critical Point Search - STAR - II: Physical Review Letters 112 (2014) 032302
• Experimental Paper on first Order Phase Transition - STAR - III: Physical Review Letters 112 (2014) 162301
• Experimental Paper on possible Chiral Symmetry Restoration (indirect) - STAR - IV: Physical Review Letters 113 (2014) 052302
• Experimental Paper non-monotonic variation of v3 with beam energy (indirect) - STAR - V: Physical Review Letters 116 (2016) 112302
• Experimental Paper on possible Chiral Magentic Wave (indirect) - STAR - VI: Physical Review Letters 114 (2015) 252302
• Experimental Paper that led to approval of RHIC Beam Energy Scan Program Phase - I: Physical Review C 81 (2010) 024911
• Experimental Proposal for Beam Energy Scan Program at RHIC (Editor): SN0493: Experimental Study of the QCD Phase Diagram & Search for the Critical Point: Selected Arguments for the Run-10 Beam Energy Scan
• Experimental White Paper on Beam Energy Scan Program at RHIC (Editor): SN0598: Studying the Phase Diagram of QCD Matter at RHIC
• Experimental Technique for Critical Point Search - I: Journal of Physics G 40 (2013) 105104
• Experimental Technique for Critical Point Search - II: Journal of Physics G 37 (2010) 094061
• Experimental Technique for Critical Point Search - III: Journal of Physics G 40 (2013) 055103
• Baseline for Critical Point Search (HRG) - I: Physics Letters B 726 (2013) 691-696
• Baseline for Critical Point Search - II: Nucl.Phys. A947 (2016) 248-259
• Baseline for Critical Point Search - mixed cumulants (HRG) - III: Physical Review C 94 (2016) 054906
• Baseline for Critical Point Search - mixed cumulants (urQMD) - IV: arXiv:1610.07580
• Review of Status of QCD Phase Diagram (Invited Review): New Journal of Physics 13 (2011) 065031
• Invited Talk at the biggest Nuclear Physics Conference - INPC: EPJ Web Conf. 66 (2014) 04022
• Invited Talk at the biggest QCD Phase Diagram Conference (CPOD): PoS CPOD2013 (2013) 001
• Plenary Talk at biggest conference in heavy-ion Quark Matter: Journal of Physics G 38 (2011) 124023
• Summary talk of QCD Phase Diagram at Quark Matter (Biggest Conference in our field): Nuclear Physics A 830 (2009) 899C-907C

For our purposes here, we take the QGP to be a (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes.

Signature: Strangeness Enhancement and Phi-meson Production

Several possible mechanisms of φ meson production in nucleus–nucleus collisions have been reported in the literature. Some of these are supported by the experimental data which is not true with others. In a QGP, thermal s and ¯s quarks can be produced by gluon–gluon interactions. These interactions could occur very rapidly and the s-quark abundance would equilibrate. During hadronization, the s and ¯s quarks from the plasma coalesce to form φ mesons. Production by this process is not suppressed as per the OZI (Okubo–Zweig–Izuka) rule. This, coupled with large abundances of strange quarks in the plasma, may lead to a dramatic increase in the production of φ mesons and other strange hadrons relative to non-QGP p + p collisions. Alternative ideas of canonical suppression of strangeness in small systems as a source of strangeness enhancement in high energy heavy-ion collisions have been proposed for other strange hadrons (e.g. Λ, Ξ and Ω). The strangeness conservation laws require the production of an ¯s -quark for each s-quark in the strong interaction. The main argument in such canonical models is that the energy and space–time extensions in smaller systems may not be sufficiently large. This leads to a suppression of strange hadron production in small collision systems. These statistical models fit the data reasonably well. According to these models, strangeness enhancement in nucleus–nucleus collisions, relative to p + p collisions, should increase with the strange quark content of the hadrons. This enhancement is predicted to decrease with increasing beam energy. So far, discriminating between the two scenarios (strange hadron enhancement being due to dense partonic medium formed in heavy-ion collisions or due to canonical suppression of their production in p + p collisions) using the available experimental data has been, to some extent, ambiguous. Enhancement of φ(s¯s) production (zero net strangeness) in Cu + Cu and Au + Au relative to p + p collisions would clearly indicate the formation of a dense partonic medium in these collisions. This would then rule out canonical suppression effects being the most likely cause for the observed enhancement in other strange hadrons in high energy heavy-ion collisions.

Publications on phi-meson production and strangeness enhancement

• Experimental Data Paper - STAR - I: Physics Letters B 673 (2009) 183-191
• Experimental Data Paper - STAR - II: Physical Review C 79 (2009) 064903
• Phenomenological Studies: Physical Review C 87 (2013) 014903 (Work done with a PhD student)
• phi meson production as a probe of QCD phase diagram - Invited Plenary Talk at Strange Quark Matter: Journal of Physics G 36 (2009) 064022
• A review paper on phi meson production in heavy-ion collisions: Adv.High Energy Phys. 2015 (2015) 197930
• A review paper on results from LHC heavy-ion collisions: Adv.High Energy Phys. 2013 (2013) 761474

Partons from the colliding nuclei that undergo a hard scattering in the initial stage of the collision provide colored probes for the colored bulk matter that may be formed in the collision's wake. It was Bjorken who first suggested that partons traversing bulk partonic matter might undergo significant energy loss, with observable consequences on the parton's subsequent fragmentation into hadrons. More recent theoretical studies have demonstrated that the elastic parton scattering contribution to energy loss first contemplated by Bjorken is likely to be quite small, but that gluon radiation induced by passage through the matter may be quite sizable. Such induced gluon radiation would be manifested by a significant softening and broadening of the jets resulting from the fragmentation of partons that traverse substantial lengths of matter containing a high density of partons – a phenomenon called "jet quenching".

Publications on jet-quenching and jet-medium interactions

• Experimental paper on establishing the baseline from pp collisions and pQCD - STAR - I: Physics Letters B 637 (2006) 161-169 (Work done with a PhD student)
• Experimental paper on establishing the baseline from d+Au collisions - STAR - II: Physical Review C 76 (2007) 054903
• Experimental paper on nuclear modification factor - STAR - III: Physics Letters B 655 (2007) 104-113
• Experimental paper on nuclear modification factor - STAR - IV: Physical Review Letters 97 (2006) 152301
• New idea of search for color charge dependence of energy loss: arXiv: 0705.0953
• Experimental technique paper to use relativistic rise for high pT particle identification: Nucl. Instrum. Meth. A 614 (2010) 28-33
• Plenary talk (at the biggest conference in our field) in Quark Matter: Journal of Physics G 35 (2008) 104006

The concept of quark recombination was introduced to describe hadron production in the forward region in p+p collisions. At forward rapidity, this mechanism allows a fast quark resulting from a hard parton scattering to recombine with a slow anti-quark, which could be one in the original sea of the incident hadron, or one excited by a gluon. If a QGP is formed in relativistic heavy ion collisions, then one might expect recombination of a different sort, namely, coalescence of the abundant thermal partons, to provide another important hadron production mechanism, active over a wide range of rapidity and transverse momentum. In particular, at moderate pT values (above the realm of hydrodynamics applicability), this hadron production "from below" (recombination of lower pT partons from the thermal bath) has been predicted to be competitive with production "from above" (fragmentation of higher pT scattered partons). It has been suggested that the need for substantial recombination to explain observed hadron yields and flow may be taken as a signature of QGP formation.

This picture leads to clear predicted effects on baryon and meson production rates, with the former depending on the spectrum of thermal constituent quarks and antiquarks at roughly one-third the baryon pT , and the latter determined by the spectrum at one-half the meson pT . Indeed, the recombination model was recently re-introduced in the RHIC context, precisely to explain an anomalous abundance of baryons vs. mesons observed at moderate pT values. If the observed (saturated) hadronic elliptic flow values in this momentum range result from coalescence of collectively flowing constituent quarks, then one can expect a similarly simple baryon vs. meson relationship: the baryon (meson) flow would be 3 (2) times the quark flow at roughly one-third (one-half) the baryon pT.

Publications on Partonic Collectivity

• Experimental data paper - STAR - I: Physical Review Letters 116 (2016) 062301 (PhD thesis work of a student)
• Experimental data paper - STAR - II: Physical Review C 93 (2016) 014907 (PhD thesis work of a student)
• Experimental data paper - STAR - III: Physical Review C 92 (2016) 021903 (Part of PhD thesis work of a student)
• Experimental data paper - STAR - IV: Physical Review Letters 110 (2013) 142301 (PhD thesis work of a student)
• Experimental data paper - STAR - V: Physical Review C 88 (2013) 014902 (PhD thesis work of a student)
• Experimental data paper - STAR - VI: Physical Review Letters 99 (2007) 112301
• Phenomenological Model study: Physical Review C 82 (2010) 054908 (PhD thesis work of a student)
• Method paper on collectivity: Int.J.Mod.Phys. E24 (2015) no.04, 1550027

In very high-energy hadronic and/or nuclear collisions highly excited states are produced and subsequently decay toward vacuum via incoherent multi-particle emission. Due to the approximate SUR(2)×SUL(2) chiral symmetry of strong interactions, there exists a continuum of nearly degenerate low-energy (pseudo-vacuum) states. These correspond to collective excitations where the chiral quark condensate is rotated from its vacuum orientationinchiral space and can be seen as semi-classical configurations of the pion field. An interesting possibility is that the decay of highly excited states produced in high-energy collisions may proceed via one of these collective states characterized by a disoriented chiral condensate (DCC). The latter would subsequently decay toward ordinary vacuum through coherent emission of low-momentum pions. Due to the semi-classical nature of the corresponding emission process, this may lead to specific signatures, such as anomalously large event-by-event fluctuations of the charged-to-neutral ratio of produced pions. If the space–time region where this happens is large enough the phenomenon might be experimentally observable, thereby providing an interesting opportunity to study the chiral structure of QCD.

Although very speculative, the idea that a DCC may form in high-energy collisions is quite appealing. Since it has been proposed inthe early 1990s it has attracted a lot of interest and has generated an intense theoretical and experimental activity. One of the main motivations—beyond its appealing simplicity—has probably been the existence of exotic, so-called Centauro events reported in the cosmic-ray literature, where clusters consisting of almost exclusively charged pions and no neutrals have been observed. The DCC would indeed provide a simple explanation for such phenomenon.

Publications related to DCC (my PhD work)

• 1. Review of theory and experimental status of DCC (Invited Review): Physics Reports 414 (2005) 263-358
• 2. Experimental data paper on DCC Search - WA98 - I: Physical Review C 64 (2001) 011901
• 3. Experimental data paper on DCC Search - WA98 - II: Physical Review C 67 (2003) 044901
• 4. Experimental Techniques for DCC Search - I: Physics Letters B 449 (1999) 109-113
• 5. Experimental Techniques for DCC Search - II: Physics Letters B 461 (1999) 142-148
• 6. Experimental Techniques for DCC Search - III: Physical Review C 66 (2002) 044901
• 7. Experimental Techniques for DCC Search - IV: International Journal of Modern Physics A 18 (2003) 1067
• 8. Limitations and Possibilities of finding DCC in heavy-ion collisions: International Journal of Modern Physics A 19 (2004) 1453-1474
• 9. Quark Matter (Highest Conference in our Field) Plenary Talk: Nuclear Physics A 715 (2003) 339-348

Prior to the experiments at RHIC and LHC, the expectation for the high temperature states of quarks and gluons to be created in nuclear collisions was that of a weakly coupled system (due to asymptotic freedom) that would behave like an ideal gas and expand isotropically. The first results on the azimuthal angle anisotropy measurements of the produced particles in the collisions proved that this view was wrong. The measurements were found to be close to those obtained from an ideal hydrodynamics, indicating the formation of a strongly coupled system (a small value of shear viscosity to entropy density ratio, η/s). Little later it was realized that AdS/CFT calculations could be used to calculate the η/s for a strongly coupled system, in a regime where standard kinetic theory was known to break down. These calculations suggested a lower bound to η/s = 1/4π, providing a theoretical basis for the argument that excitations cannot be localized to a precision smaller than their thermal wavelength. However this conjecture of a lower bound to η/s has been debated in literature. For example this bound could be violated for a system of nonrelativistic gas by increasing the number of species in the fluid while keeping the dynamics independent of the species type. Detailed studies of several string theory based models suggest that in a wide class of models such a bound is conceivable but with models including fundamental matter leads to corrections which results in violation of this lower bound. However all these does not take away the important question that can one extend the AdS/CFT methods to do quantitative phenomenology relevant to physics at RHIC and LHC. This led to the push in the theory community to develop a proper framework for relativistic viscous hydrodynamics. When first results from relativistic viscous hydrodynamics calculations started to be compared to experimental data, it was realized that the extracted η/s values depend on the choice of initial condition in the calculations. Specifically the importance of fluctuations in the initial geometric configurations of the nucleons in the colliding nuclei was discovered. The initial state of a nuclear collision was found not to be a smooth density, but the one that varied from one collision to other. Further inspired from the multi-pole analysis procedures used of looking at anisotropies in the cosmic microwave background spectrum, it was realized that high order components of azimuthal anisotropy could better constrain the values of η/s. The current estimates of the shear viscosity to entropy density ratio for QGP at the transition temperature is between (1 – 2)/4π.

Publications related to flow and viscous hydrodynamics

• Event-by-Event hydrodynamic simulations at RHIC and higher harmonics: Physical Review C 87 (2013) 034907 (PhD thesis work of a student and work of a RA)
• Viscous hydrodynamics with Glauber and CGC initial conditions at LHC: Journal of Physics G 40 (2013) 065103 (PhD thesis work of a student)
• Data versus viscous hydrodynamics calculations at RHIC: Physical Review C 86 (2012) 014902 (PhD thesis work of a student)
• Elliptic flow of thermal dileptons: Physical Review C 85 (2012) 031903 (PhD thesis work of a student)
• Energy Dependence of elliptic flow in heavy-ion collision models: Physical Review C 82 (2010) 054908 (PhD thesis work of a student)
• Predictions of Elliptic flow in U+U collisions at RHIC: Physics Letters B 679 (2009) 440-444 (Work done with a RA)
• Experimental data - elliptic flow at RHIC - STAR-I: Physical Review C 88 (2013) 014902 (PhD thesis work of a student)
• Experimental data - elliptic flow at RHIC - STAR - II: Physical Review C 86 (2012) 054908
• Experimental data - elliptic flow in Cu+Cu collisions - STAR - III: Physical Review C 81 (2010) 044902

High energy heavy-ion collisions form a system whose constituents undertake various type of interactions during different times of evolution of the system. Many resonances have been observed in these collisions - f2(1270), Rho0(770), Delta++
(1232),f0(980), K*(892)0±, Sigma*(1385),Lambda (1520) and phi(1020) with life times of 1.1 fm/c, 1.3 fm/c, 1.6 fm/c, 2.6 fm/c, 4 fm/c, 5.5 fm/c, 12.6 fm/c and 44 fm/c, respectively. Resonances are very good probes of the dynamics of the system formed in heavy ion collisions as they cover from the very early time scales to close to the freeze-out of the system.

In the hadronic phase of the system formed in heavy-ion collisions, two important temperature or time scales comes into picture. One is the chemical freeze-out, where the inelastic collision among the constituents are expected to cease and the other is the later kinetic freeze-out when the distance scales among the constituents are larger than the mean free path due to which all (elastic) interactions cease. If resonances decay before kinetic freeze-out then they will be subject to hadronic re-scattering of the daughter particles which will alter their momentum distributions. This would lead to loss in the reconstruction of the parent resonance. The amount of loss could depend on the life time of hadronic phase (specifically the time between chemical and kinetic freeze-out), resonance daughter particle hadronic interaction cross section, particle density in the medium and the resonance phase space distributions. On the other hand after chemical freeze-out pseudo-elastic interactions could regenerate resonances in the medium leading to enhancement in their yields.

Publications related to Resonances

• 1. Experimental paper on varity of resonance production in d+Au collisions - STAR - I: Physical Review C 78 (2008) 044906 (PhD thesis work of a student)
• 2. Experimental paper on K* production - STAR - II: Physical Review C 84 (2011) 034909 (PhD thesis work of a student)
• 3. Experimental paper on K* and phi production - ALICE - I: Physical Review C 91 (2015) 024609 (PhD thesis work of a student)
• 4. Experimental paper on phi-meson production - STAR - III: Physical Review C 79 (2009) 064903
• 5. Experimental paper on phi-meson production - STAR - IV: Physics Letters B 673 (2009) 183-191
• 6. Experimental paper on Sigma and Cascade production - ALICE - II: Eur.Phys.J. C75 (2015) no.1, 1
• 7. Phenomenology Paper: Int.J.Mod.Phys. E24 (2015) 1550041
• 8. Experimental paper on K* and phi production - ALICE - III: Physical Review C 95 (2017) 064606 (PhD thesis work of a student)

As a result of ultrarelativistic collision between two heavy ions, a fireball is expected to form that rapidly thermalizes as well as expands and hence cools. As the inter-particle distance grows with time, the particles cease to interact after sometime and free stream to the detector. The surface of last scattering is the freeze-out surface. Since scattering could be both elastic (where particle identities do not change) as well as inelastic (where particle identities change), it is possible to have two distinct freeze-outs namely chemical freeze-out (CFO) where inelastic collisions cease, and thermal/kinetic freeze-out (KFO) where elastic collisions cease and the particle mean free path becomes higher than the system size, which forbids the elastic collision of the constituents in the system. While the CFO surface is determined by analysing the measured hadron yields, the KFO surface can be determined by studying the data of transverse momentum (pT ) distribution of produced particles. In general, freeze-out could be a complicated process involving duration in time and a hierarchy where different types of particles and reactions switch-off at different times. This leads to the concept of "differential freeze-out" . From kinetic arguments, it is expected that reactions with lower cross-sections switch-off at higher densities/temperature or earlier in time compared to reactions with higher cross-sections. Hence, the chemical freeze-out, which corresponds to inelastic reactions occurs earlier in time compared to the kinetic freeze-out, which corresponds to elastic reactions. In accordance with the above discussions, one can think of strange or charmed particles decoupling from the system earlier than the lighter hadrons. A series of freeze-outs could be thought of corresponding to particular reaction channels. Further the freeze-out properties are extracted by confronting data to models. These models make various assumptions, starting from treating hadrons to be non-interacting, point particles to those with inlcusion of only replusive interactions (excluded volume effects) to those with including both repulsive and attractive interactions. Some only fit the particle yields to extract the freeze-out dynamics and some also study the particle spectra. We have looked at all these various aspects. Such models commonly called as Hadron Resonance Gas (HRG) models can also be used to extract transport coefficients and understand fluctuations in conserved quantities in stringly interacting systems. We have studied these aspects also. Another interesting problem is that light nuclei have been observed in high energy heavy-ion experiments. The binding energy of these nuclei are of the order of few MeV, however the estimated freeze-out temperature are of the order of 100 MeV. So the question is how are nuclei formed.

Publications related to Freeze-out dynamics, Hadron Resonance Gas Models and Nuclei Production

• 1. Measurement of elliptic flow of light nuclei at 200, 62.4, 39, 27, 19.6, 11.5 and 7.7 GeV at BNL Relativistic Heavy Ion Collider - STAR experimental paper: Physical Review C 94 (2016) 034908 (Phd thesis work of a student)
• 2. Freeze-out parameters in Heavy-Ion Collisions at AGS, SPS, RHIC and LHC Energies: Adv. High Energy Physics 2015 (2015) 349013 (Review paper)
• 3. Production of light nuclei and anti-nuclei in pp and Pb-Pb collisions at energies available at the CERN Large Hadron Collider - ALICE experiment: Physical Review C 93 (2016) 024917 (IRC)
• 4. Freezeout hypersurface at energies available at the CERN Large Hadron Collider from particle spectra: Flavor and centrality dependence: Physical Review C 92 (2015) 024917 (work done with RA)
• 5. Production of light nuclei in heavy ion collisions within multiple freeze-out scenario: Physical Review C 90 (2014) 034908 (work done with RA)
• 6. Freeze-out conditions in proton-proton collisions at the highest energies available at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider : Physical Review C 95 (2017), 014912 (work done with PhD students and RA)
• 7. Correlations of conserved number mixed susceptibilities in a hadron resonance gas model : Physical Review C 94 (2016) 054906 (work done with collaborators in BARC)
• 8. Bulk viscosity for pion and nucleon thermal fluctuation in the hadron resonance gas model : Physical Review C 94 (2016) 045208 (work done with RAs)
• 9. Contrasting Freezeouts in Large Versus Small Systems : Journal of Physics G 44 (2017) 105106 (work done with RAs)
• 10. Finite size effect of hadronic matter on its transport coefficients : Journal of Physics G 45 (2018) 075101 (work done with RA and Collaborator at IIT Bhilai)
• 11. A Review of Elliptic Flow of Light Nuclei in Heavy-Ion Collisions at RHIC and LHC Energies: Adv. High Energy Physics 2017 (2017) 1248563 (Review paper)
• 12. Freezeout systematics due to the hadron spectrum : Physical Review C 96 (2017) 054907 (work done with collaborators, PhD student and RA)
• 13. Criticality in a Hadron Resonance Gas model with the van der Waals interaction : Physical Review C 97 (2018) 015201 (work done with RA)
• 14. Interacting hadron resonance gas model in the K -matrix formalism : Physical Review C 97 (2018) 055208 (work done with PhD student and RA)
• 15. Role of new resonance states on fluctuations and correlations of conserved charges in hadron resonance gas model : Int.J.Mod.Phys. E27 (2018) 18500808 (work done with PhD student and RA)

The Indian group comprising of Universities of Jammu, Panjab, Rajasthan, Instititue of Physics, Bhubaneswar, Variable Energy Cyclotron Centre and Indian Institute of Technology, Bombay were responsible for building a photon multiplicity detector (PMD) for measurent of inclusive photons produced in high energy heavy-ion collisions at SPS, RHIC and LHC facilities. This detector was a preshower detector which gave the inclusive photon multiplicity event-by-event and the spatial distribution of the photons. USing this information and in conjunction with other detectors in the experiment one could study the particle production in heavy-ion collisions, azimuthal anisotropy of the photon production, and fluctuations and correlations (DCC-type). The detector was scintillator pad based in SPS and proportional counter gas based for RHIC and LHC.

I was heavily involved in the analysis of the data taken by PMD in all the three facilities. While PMD data analysis formed partb of my PhD work in WA98 experiment at SPS, the analysis of data taken by PMD in STAR experiment at RHIC and ALICE experiment in LHC were part of the PhD thesis of my students. I also contributed heavily to the technical design reports of PMD in STAR and ALICE. The entire chapter on test detector analysis and physics simulations were my work. I was also the person responsible to implement PMD in GEANT framework of the experiments at STAR and ALICE. In addition I contributed to testing of the detector and its design, building and installation.

Contribution to PMD in terms of Physics

• 1. Event-by-Event fluctuation measurements at SPS : Physical Review C 65 (2002) 054912
• 2. Localised charged neutral fluctuations in 158 A GeV Pb+Pb Collisions: Physical Review C 64 (2001) 011901 (R)
• 3. Centrality dependence of charged neutral in 158 A GeV Pb+Pb collisions: Physical Review C 67 (2003) 044901
• 4. Azimuthal Anisotropy measurements: European Journal of Physics C 41 (2005) 287-296

• 5. Multiplicity and Pseudorapidity distribution, Limiting Fragmentation : Physical Review Letters 95 (2005) 062301
• 6. Details of inclusive photon production: Physical Review C 73 (2006) 034906
• 7. Energy and system size study of inclusive photon production: Nuclear Physics A 832 (2010) 134-147
• 8. The STAR PMD : Nuclear Instrumentation and Methods A 499 (2003) 751-761

• 9. PMD technical Document : CERN-ALICE-INT-1999-16
• 10. PMD part in ALICE Experiment at the CERN LHC : JINST 3 (2008) S08002
• 11. ALICE Physics Performance - I : Journal of Physics G 30 (2004) 1517-1763
• 12. Detector for ALICE PMD: Nuclear Instrumentation and Methods A 488 (2002) 131-143
• 13. ALICE Physics Performance - II : Journal of Physics G 32 (2006) 1295-2040
• 14. Inclusive photon production at forward rapidity in proton-proton collisions at 0.9, 2.76 and 7 TeV : ALICE PMD first paper Eur.Phys.J. C75 (2015) no.4, 146 (Phd work of my student - first time unfolding technique was used in PMD)

• Highest conference in India in our field: ICPAQGP 2005: Journal of Physics Conf. Series 50 (2006) 319-322
• Highest conference in our field worldwide: Quark Matter 2006 : Nuclear Physics A 774 (2006) 481-484
• Highest conference in our field worldwide: Quark Matter 2002: Nuclear Physics A 715 (2003) 339-348
• Highest Conference in India in our field: ICPAQGP 2001: Pramana 60 (2003) 613-626

With some initial seed grant from NISER and financial support from SERB/DST we started building a detector laboratory at NISER. To start with we decided to concentrate on making gas based detectors with some application of this R&D to high energy heavy-ion collision experiments. We tried to fabricate proportional counter, Resistive Plate CHamber and Gas Electron Multipliers in the laboratory. We also tried to understand the charecteristics of gas based detectors through some simulations.

Publications under this category (selected)

• A simple technique for gamma ray and cosmic ray spectroscopy using plastic scintillators: Nucl.Instrum.Meth. A824 (2016) 606-608 (Work done with summer students)
• Characteristics of GEM detector prototype: Nucl.Instrum.Meth. A824 (2016) 501-503
• Design and fabrication of a data logger for atmospheric pressure, temperature, and relative humidity for gas filled detector development: RD51-NOTE-2015-004
• Detailed 3D simulation of the GEM-based detector: J.Phys.Conf.Ser. 759 (2016) 012071

Given that Dark Matter consitutes a large fraction (~27%) of our Universe and the candidates that constitute the matter has not yet been discovered, we decided to contribute to this physics. NISER defended a proposal and joined the SuperCDMS experiment. This experiment looks for direct search for dark matter candidates. NISER also is part of MINER experiment, which essentially looks at the background contributions for Dark Matter experiments.

Publications

• Background Studies for the MINER Coherent Neutrino Scattering Reactor Experiment : arXiv:1609.02066

I like to interpreat heavy-ion collision data, for which I construct simple models, use already established models and try to extract information which can be connected to basic physics. In addition I also like to propose new measurements, techniques and methods. The following are some of the selected work which I enjoyed a lot while working on them.

Publications under this category (selected)

• Does the data at AGS, SPS, RHIC provide any indication or a first order phase transition (la Van Hove): Physical Review C 68 (2003) 021901
• Can we get access to the speed of sound in the medium formed in heavy-ion collisions: Physical Review C 68 (2003) 064903
• What is the reason behind longitudinal scaling of various observables: Physical Review C 83 (2011) 054902
• How about doing dilepton interferometry: Physical Review C 84 (2011) 024903 and Lepton interferometry: Physical Review C 70 (2004) 054901
• How about measuring dilepton flow: Physical Review C 85 (2012) 031903
• Understanding the anti-proton to proton ratio in high energy collisions: Physical Review C 82 (2010) 044902
• What do we learn looking at width of rapidity distribution: Physical Review C 71 (2005) 047901
• Nparticipants, Ncollisions what about Quark Participants: Physical Review C 70 (2004) 027901
• How does fluctuations evolve with time in heavy-ion collisions : Physical Review C 67 (2003) 024904
• How to get a handle on initial state in heavy-ion collisions : Physics Letters B 754 (2016) 144-150
• How to disentangle different initial state confirgurations in U+U collisions : Physical Review C 91 (2015) 054903
• What to expect from asymmetric heavy-ion collisions viz-viz elliptic and triangular flow : Physical Review C 84 (2011) 067901
• Bulk Viscosity of QCD matter : Physical Review C 94 (2016) 045208
• Random walk model in heavy-ion collisions : Pramana 82 (2014) no.5, 893-905