The nuclear theory group at VECC is engaged in exploring nuclear dynamics at energies extending from low to extreme relativistic energies. At a microscopic level, an effective Nucleon - Nucleon interaction is used to investigate nuclear processes such as proton and alpha-decay rates and also nuclear properties like nuclear equation of state. Cross sections of photonuclear reactions and neutron induced reactions are calculated. Fission dynamics of hot and rotating compound nuclei are studied extensively using Langevin equations. Neutron multiplicities and evaporation residue cross-sections from fusion-fission reactions are systematically investigated in order to find the magnitude of nuclear dissipation. At intermediate energies nuclear multi- fragmentation becomes the dominant process for which statistical methods are exploited. Nuclear properties such as symmetry energy are being investigated by comparing the predictions of the statistical model with experimental data.
A new state of matter called quark gluon plasma (QGP), that existed shortly after the Big Bang may be created by colliding heavy ions at ultra-relativistic energies. QGP is believed to be the most perfect fluid ever discovered. Members of the theory division, VECC, are actively engaged in dynamical modelling of relativistic heavy ion collisions to understand the important issues like, initial conditions, thermalisation, equation of state, transport properties etc. Effects of viscosity on several experimentally measured quantities like elliptic flow and transverse momentum distribution of hadrons and photons are investigated by evolving heavy ion collisions in space and time using relativistic hydrodynamics. Works on the systematic of photon and dilepton productions in ultra-relativistic heavy ion collisions including Hanbury Brown Twiss intensity interferometry with electromagnetically interacting particles are being pursued rigorously. The elliptic flow of the matter produced in nuclear collisions at relativistic energies probed by real photons and lepton pairs are shown to be an effective technique for the detection of QGP. In addition, the role of heavy quarks in probing the properties of QGP is examined in detail. Investigation of hadronic properties in hot and dense matter using effective theories of strong interaction constitutes another important sphere of activity in the theory division. In particular, the spectral properties of light vector mesons, nucleons and pions are evaluated at non-zero temperature and baryon density using thermal field theory and its effects on the photon and dilepton spectra are investigated.
Dynamical and statistical models of nuclear fission:
Langevin equations are employed to study the dissipative dynamics of highly excited compound nuclei undergoing fission. A microscopic model of nuclear dissipation is developed.
The statistical model is used to study systematic features of fission including photo-fission cross-section.
Dissipative fluid dynamics in relativistic heavy ion collisions:
Space-time evolution of a dissipative fluid modeling a strongly coupled quark-gluon plasma and undergoing boost-invariant longitudinal and arbitrary transverse expansion is formulated from Israel-Stewart’s formal theory of 2nd order dissipative fluid dynamics. A computer code AZHYDRO-KOLKATA is developed to solve these equations to study the fluid properties.
Quark Gluon Plasma diagnostic: J/psi suppression in nuclear medium:
J/psi suppression in nuclear collisions at SPS (Ecm~18 AGeV) and RHIC (Ecm~200 AGeV) energies is studied and its role as a quark gluon plasma diagnostic evaluated.
Thermal Radiations from Relativistic Heavy Ion Collisions:
Radiation of thermal single photons and dileptons from relativistic heavy ion collisions at SPS (Ecm ~18 AGeV), RHIC (Ecm~200 AGeV), and LHC (Ecm~5500 AGeV) energies and their role as a signature of quark-hadron phase transition is studied.
The intensity interferometry of thermal photons is studied with a view to get information about the evolution of the system formed in such collisions.
Electromagnetic Radiations from Quark Gluon Plasma due to Passage of Jets:
Suppression of particles having large transverse momenta due to the energy loss suffered partons during their passage through quark gluon plasma, known as jet-quenching is one of the most spectacular observations at RHIC energies. First studies of radiation of high energy photons and large mass dileptons due to the passage of high energy partons through quark gluon partons are performed.
Elliptic Flow of Thermal Photons and Thermal Dileptons in Relativistic Heavy Ion Collisions:
Elliptic flow of hadrons radiated from relativistic heavy ion collisions are considered to be a most reliable confirmation of the formation of a hot and dense system very early in the collision. However, the hadrons themselves leave the system at the time of freeze-out. First studies of the elliptic flow of thermal photons and dileptons are performed with a view to get direct information about the evolution of the elliptic flow and the flow of the quark gluon plasma stage of the system.
Parton Cascade Model for Relativistic Heavy Ion Collisions:
A description of the relativistic heavy ion collision is attempted in terms of scattering, radiating, and fusing partonic cascades, based on perturbative quantum chromodynamics. Energy densities, Debye screening lengths, and radiation of pre-equilibrium photons from such studies is performed.
Stochastic Processes:
The perturbed angular correlation between the two gamma rays is investigated in terms of the transport properties of the environment. The role of stochastic resonance in information transmission through noisy channel is being studied. Application of the coherent stochastic resonance phenomenon to separate different sizes of large DNA molecules is under investigation.
Properties of nuclear matter and nuclear processes in finite nuclei
Mean field calculations are made for the properties of nuclear matter. Microscopic calculations of nuclear potentials are also made to extract the particle and cluster radioactivity lifetimes of finite nuclei.
The liquid drop mass formula is extended to estimate the binding energies of hyperons and also to predict the existence of bound hypernuclei near the drip lines.
Propagation of partons through quark gluon plasma and jet quenching
Medium modification of production of hadrons in relativistic heavy ion collisions due to propagation of quarks and gluons through quark gluon plasma undergoing multiple collisions and radiating gluons before fragmenting is studied to understand the phenomenon of jet quenching.
Nuclear multifragmentation in intermediate energy heavy-ion collisions
Thermo-dynamical models based on both canonical and grand canonical ensembles are being developed in order to study multifragmentation in intermediate energy heavy ion collision. The model is also suitably extended for the projectile fragmentation reactions (peripheral collisions). These models are used to study the systematic features of multi-fragmentation like mass and charge distribution, isotopic distribution, multiplicity of intermediate mass fragments and others. Isospin dependence is also being investigated.