Séminaires des Doctorants 2017 (Dernière session) : H. Hassan & R. Hosokawa

Tuesday 27 Jun 2017, 10:00 → 11:00 Europe/Paris

Hadi Hassan: ---------------------------------------------------------------------------- Title: Modeling and measuring the b-jet nuclear modification factor in pPb at √s = 5.02 TeV Abstract: During head-on lead-lead collisions at the LHC, a hot and dense medium of deconfined quarks and gluons is created (Quark Gluon Plasma). This QGP is conjectured to be the state of matter prevailing in the early Universe a few micro seconds after the Big Bang and may still exist in the core of neutron stars. One of the most striking signatures of QGP formation is the jet suppression observed in heavy ion collisions which is interpreted as the energy loss of the initial parton at the origin of the jet while travelling through the QGP medium, the so called jet quenching phenomenon. In the last two decades, many theoretical developments of the theory of jet quenching have been formulated within pQCD. Additionally, testing the mass dependence of the parton energy loss remains an important step towards a comprehensive understanding of jet quenching. Such mass dependence can be studied experimentally by tagging heavy quark jets in the very demanding environment of heavy-ion collisions. In this seminar, I will present a new approach for the study of partonic energy loss which is the synchrotron radiation energy loss. I will also present the ALICE measurement of b-jet production in p-Pb collisions using an impact parameter based tagger. Ritsuya Hosokawa: ---------------------------------------------------------------------------- Title: Measurements of charged jet spectra in pp and PbPb collisions at √sNN = 5.02 TeV with the ALICE experiment at the LHC Abstract: Jets, originating from hard scattered partons at the early stage of heavy-ion collisions, are well esta- blished probes to study the properties of QGP, a deconfined state of QCD. The ALICE calorimeter trigger has been designed to select interactions whose final state includes high transverse momentum jets and photons/electrons. During the LHC Long Shutdown 1, the ALICE calorimetry was upgraded with the Di-jet Calorimeter (DCal), a second arm sitting back-to-back in azimuth to the ElectroMagnetic Calorimeter (EM- Cal) and surrounding the PHOton Spectrometer (PHOS). Taking advantage of this two-arm setup, we have developed and commissioned a new L1 jet trigger algorithm for Run 2 Pb-Pb data taking, aggregating DCal and PHOS regions to estimate the event energy density and thereby correct EMCal jet patches from soft background contamination, and vice versa. This new approach (a.k.a. median mode), besides providing uniform trigger efficiency across event centralities, makes the calorimeter jet trigger more self-consistent (using energy measurements only). The large data sample of pp and Pb-Pb collisions collected by the ALICE experiment in 2015, was used to precisely measure the charged jet nuclear modification factor (RAA) and its centrality dependence, which in turn might help to quantify the partonic energy loss mechanism description within pQCD. In order to extend the study of jet quenching at larger jet resolution parameter and maximize in-medium path length, high-pT hadron triggers recoil jets are also analyzed. The measurement of the semi-inclusive distribution of charged jets recoiling back-to-back from a high-pT charged hadron in Pb-Pb collisions will be presented.