Amit Kumar

JETSCAPE is a state-of-the-art simulation framework with capabilities to accommodate physics of each stage of the high-energy heavy-ion collisions. It has been developed to study the properties of quark-gluon plasma (QGP), explore behavior of elementary particles in nuclear medium and discover new physics.
   The figure on left panel represents production of a almond-shaped fireball, a deconfined state of quarks and gluons (quark-gluon plasma) hypothesized to have existed in the early universe. Such collisions are routinely performed in accelerator facilities LHC in Geneva and RHIC in NewYork to produce QGP. The figure in top-center is a schematic block-diagram of JETSCAPE physics software. Each block represents a physics module. The figure in bottom-center panel illustrates three different phases of parton energy loss in expanding quark-gluon plasma. We performed full model calculation for proton-proton collision and nucleus-nucleus collisions and tested model hypothesis against the experimental data. The study demonstrated that there is a significant space-time and energy loss dependence during early stage (high-virtuality) of the parton energy loss. The space-time dependence during early stage played crucial role in simultaneous description of key observables at multiple collision energies.

In this project, we computed transport coefficient q-hat which characterizes the transverse momementum broadening of the parton propagating through hot-dense plasma. It is challenging to determine the temperature dependence of this quantity due to non-perturbative nature of strong-coupling constant. The quantity controls the rate of medium-induced radiative energy loss and hence, plays central role in understanding the modification of the energetic parton traversing the evolving QGP.
   We considered a leading-order process where the energetic quark interact through plasma (box) by exchanging a single gluon and exit the box (Figure left-panel). The plasma in the box was considered to be gluonic and was modeled using pure SU(3) lattice gauge theory. The gluonic fields were represented via 3x3 SU(3) matrix computed using Monte-Carlo sampling of action density dependent probability distribution.
  The operators were computed on 4-dimensional lattice of sizes Nt*Ns^3 = 4x16^3, 6x24^3 and 8x32^3 for temperature range 200 MeV < T < 1000 MeV. We have also extended the calculation to the case of QCD plasma where we used MILC lattice QCD code to evaluate operators.

This project was carried out during my M.Sc. (2013-2015) at Saint Mary's University Halifax, Canada. In this project, we made first attempt to measure the elastic scattering cross section for scattering between exotic unstable nucleus ¹⁰C and proton. The goal of the measurement was to see if three-nucleon (3-body) forces plays an important role in nuclear reaction and test the validity of ab-initio nuclear models.
    We successfully performed the elastic scattering of the unstable nucleus ¹⁰C on a proton target using the ISAC Charged Particle Reaction Spectroscopy Station (IRIS) facility stationed at TRIUMF, Canada. The facility utilizes a novel thin windowless solid H₂ target (~4 Kelvin) which made the reaction study possible with a beam intensity of ∼ 2.5×10 ³ pps. The angular distribution measurement was based on the detection of the protons with the thin Silicon (Si) and Thallium doped Cesium Iodide(CsI:Tl) detectors. We compared the measured cross section with the predictions made by ab initio no core shell model with continuum (NCSMC) based on NN (N3LO) and 3N (N2LO) forces. The results with 3N forces showed significant improvement to the calculation.