CERN Accelerating science

The major physics goals of the ALICE (A Large Ion Collider Experiment) collaboration at the Large Hadron Collider (LHC) of CERN are to study the properties of a new form of high temperature and high energy density matter, called the quark-gluon plasma (QGP). The QGP had its origin in the Early Universe, within few microseconds of the Big Bang. By colliding proton-proton, Pb-Pb and proton-Pb at the LHC and analysing the data taken during Run-1 and Run-2 (2009 to 2019), the ALICE collaboration has reported the formation of QGP and many interesting results associated with QGP formation. For the precise measurement of the rare phenomena, ALICE has decided to take high statistics data with the increased collision energy of $\sqrt{s_{NN}}$ = 5.5 TeV for Pb-Pb in Run-3 and Run-4, starting from the year 2021. A major upgrade of the ALICE central barrel detectors (ITS and the TPC) are ongoing during Long Shutdown 2 (2019-2020). This thesis is based on the development and implementation of Gas Electron Multiplier (GEM) detector for the ALICE TPC upgrade and study of the particle production in the Pb-Pb collision in Run-3 environment. GEM detectors have proven capabilities in terms of their high gain, good energy resolution, long term stability and low ion backflow. Detailed characteristic study of a triple GEM detector and a quadruple GEM detector, using Ar/CO_{2} 90:10 and 70:30 gas mixtures, have been performed in this research work. The energy spectrum, gain, energy resolution, efficiency, time resolution are measured for both the detectors and the results are compared. The gain comparison study shows that quadruple GEM detector can operate at lower GEM voltages compare to triple GEM detector. Operating with low GEM voltages have the advantage of long term stable operation. The triple GEM detector has better energy resolution compared to the quadruple GEM detector. A method for the spatial uniformity study of the detector has been developed for the first time. The quadruple GEM detector is also tested with the ALICE TPC like electric field (IBF field setting) configuration in the standard field setting. The importance of the electric field in GEM characterization has been studied. The optimum drift field for the maximum electron transfer from the drift region to the transfer region is found to be about 1000 V/cm. A model calculation of time resolution of the GEM detectors using the Garfield software has been performed. The simulation results are compared with different experimental obtained results. TPC upgrade using GEM readout can accomplish high collision rates expected for Run-3 and beyond without any space charge accumulation within the drift volume. A stack of four GEM foils with a special electric field configuration meets the required TPC performances. The production procedure and testing of the new chambers using GEM readouts are discussed in this thesis. The comprehensive study of global observables in heavy-ion collision provides valuable information in QGP characterizations. A simulation based on AMPT model has been performed to obtain multiplicity and momentum distributions, and initial energy density has been extracted for $\sqrt{s_{NN}}$ = 5.5 TeV in Pb-Pb collisions. Detailed results have been reported in the thesis.