RT Dissertation/Thesis
T1 Energy Loss of Fast Partons in a Colored Medium
A1 Apolinário, Liliana Marisa Cunha
A2 Facultade de Física. Departamento de Física de Partículas, 
K1 quarks
K1 gluons
K1 Jet Quenching
K1 Monte Carlo
AB Through heavy-ion collisions it is possible to form a new state of matter called the quarkgluon plasma. It is characterized by the deconfinement of quarks and guons up to distances muchlarger than those when they are inside a nucleus. However, the lifetime of this plasma is very short,and therefore, one have to rely on hard probes, objects with a large transverse momentum formedat a very early stage of the collision that carry information about the evolution of the producedmedium. The advantage of using these probes is that they can be described by the perturbativeregime of the theory of the strong interactions, the Quantum Choromodynamics, where analyticalcalculations from first principles are possible. By comparing the modifications of the hard probes inheavy-ion collisions with the result form other collisional systems where the energy and density arenot sufficient to form the quark gluon plasma, like proton-proton collisions, one can infer theproperties of the produced medium. The modifications include additional energy loss processesthat are induced by the interactions with medium constituents, a process that is generically knownas Jet Quenching.! This thesis is focused on the jet quenching study to understand how the parton showering(the process by which a highly-energetic particle decreases its energy up to the hadronizationscale) is modified in the presence of a medium. For that, two different approaches were followed: amore analytical one, where theoretical calculations were performed to improve the description ofone of the elementary vertices of the parton branching in the presence of a medium, the gluonradiation off a quark; and a more phenomenological one, where, using a Monte Carlo protonprotonevent generator with medium effects, it was compared the result of several simulatedevents with experimental data of different jet related observables.! The first part led to a fully consistent description of the parton branching, that contains allfinite energy corrections in the approximation of small angle emissions and assuming staticscattering centers (only radiative energy loss was taken into account). In particular, previousmodels of jet quenching were improved to take into account the emission of finite energy gluons,and where all vertex particles are allowed to have Brownian deviations in the transverse planeinstead of having its motion constrained to a straight line.! In the second part, a systematic study was conducted to understand the influence of jetreconstruction and jet quenching phenomena on different jet observables. It was compareddifferent background subtraction methods by using a toy model to simulate the underlying eventcharacteristic of a heavy-ion collision, in which the hard event generated by the Monte Carlo eventgenerator was embedded in. It was possible to conclude that it is necessary an accuratedescription of the jet reconstruction techniques to compare models to data in order to accuratelydescribe the medium properties. Moreover, it was observed that jet quenching approaches basedon soft gluon radiation are not refuted by the experimental data, but a better description can beachieved if the new theoretical developments, like the ones that were calculated in this thesis, areimplemented in the Monte Carlo codes. This would be a natural followup of this work.
YR 2014
FD 2014-02-03
LK http://hdl.handle.net/10347/9788
UL http://hdl.handle.net/10347/9788
LA eng
DS Minerva
RD 3 may 2026