Study of hard processes in the ALICE experiment

Jets are collimated sprays of particles resulting from fragmentation of associated hard scattered partons. They are measured in different types of collisions at different energies to test perturbative quantum chromodynamic calculations and are used to study the hard scattering, fragmentation, hadronisation and other properties of partons. These properties studied in simple systems such as proton-proton collisions, serve as a baseline to investigate their modifications by hot and dense nuclear matter created in high energy heavy-ion collisions. This thesis presents analysis of data from minimum bias proton-proton collisions at centre of mass energy of 2.76 and 7 TeV collected using the ALICE detector system at the LHC is presented with jet transverse momenta in range from 20 GeV/c to 100 GeV/c. Reconstruction of the inclusive jet cross-section from charged tracks at midrapidity is done using standard modern anti-k$_T$ and k$_T$ algorithms with underlying event subtraction and correction for detector effects via unfolding and its systematics study for both energies. These results are compared to Monte Carlo predictions from different PYTHIA6 tunes and results from the ATLAS collaboration, observing good agreement. Additionally, next-to-leading order simulations of jet production are presen- ted. They are carried out using POWHEG-Box framework, implementation of POWHEG NLO generator, with parton showering provided by PYTHIA8. These simulations are performed for proton-proton collisions at centre of mass energy of 7 TeV and proton-lead collisions at 5.02 TeV, in order to study jet production cross sections and ratio of jet spectra reconstructed using different resolution parameter, in momentum range matching that of real data analyses. Additionally, the modification of lead parton distribution functions with respect to the one of proton is investigated via extracted Bjorken x variable using the leading di-jet in the event as no significant modification is observed in differential cross section. Parton distribution function’s effect on heavy ions are implemented using nuclear parton distribution functions such as HKN07 and utilising nuclear modification factors provided in EPS09. Jet reconstruction algorithms are provided by the FastJet package.