Hard probes : jets and their kT broadening

Heavy ion collisions at high energies can be used as an interesting way to recreate and study the medium of the quark-gluon plasma (QGP). We particularly investigate the jets produced in hard binary collisions and their interactions with a tentative medium. These jets were obtained numerically from the Monte-Carlo simulations of hard collisions using the KATIE -algorithm [1], where parton momenta within the colliding nucleons were describe by means of unintegrated parton distribution functions (uPDF). We evolved these jets within a medium that contains both, transverse kicks (yielding a broadening in momentum transvers to the jet-axis) as well as medium induced radiation within the MINCAS -algorithm [2] following the works of Blzizot, Iancu, Mehtar-Tani, Domiguez. We produce qualitative results for the decorrelation of dijets. In particular, we study deviations from a transverse momentum broadening that follows a Gaussian distribution. We study jet-pairs produced in hard partonic collisions during the early stages of ultrarelativistic heavy ion collisions. In order to study the ultrarelativistic nuclear collisions, we first describe di-jet production in p - p collisions, where we assume that a QGP-medium is not formed, and later on extend this description to include medium effects. In our study of di-jet observables we focus on distributions of jet-pairs in the transverse plane, orthogonal to the collision axis of the incoming nucleons. In this case the momentum components of the incoming hard partons transverse to the collision axis cannot be neglected, since they contribute considerably to the deviations of pure back-to-back emission of the di-jet pairs. Thus, we describe the di-jet production cross section σ hard using the following factorization formula