998 research outputs found
Jetting Through The Primordial Universe
Collisions of heavy ion nuclei at relativistic speeds (close to the speed of
light) creates a high temperature and very dense form of matter, now known to
consist of de-confined quarks and gluons, named the quark gluon plasma (QGP).
In this thesis, Run1 experimental data from pp and heavy ion collisions at the
CERN LHC is analyzed with the CMS detector. The pp jet cross section is
compared with next to leading order theoretical calculations supplemented with
non perturbative corrections for three different jet radii highlighting better
comparisons for larger radii jets. Measurement of the jet yield followed by the
nuclear modification factors in proton-lead at 5.02 TeV and lead-lead
collisions at 2.76 TeV are presented. A new data driven technique is introduced
to estimate and correct for the fake jet contribution in PbPb for low
transverse momenta jets. The nuclear modification factors studied in this
thesis show jet quenching to be attributed to final state effects, have a
strong correlation to the event centrality, a weak inverse correlation to the
jet transverse momenta and an apparent independence on the jet radii in the
kinematic range studied. These measurements are compared with leading
theoretical model calculations and other experimental results at the LHC
leading to unanimous agreement on the qualitative nature of jet quenching. This
thesis also features novel updates to the Monte Carlo heavy ion event generator
JEWEL (Jet Evolution With Energy Loss) including the boson-jet production
channels and also background subtraction techniques to reduce the effect of the
thermal background. Keeping track of these jet-medium recoils in JEWEL due to
the background subtraction techniques significantly improves its descriptions
of several jet structure and sub-structure measurements at the LHC. [Shortened
abstract]Comment: PhD Thesis: Defended on June 6th 2017 at Rutgers University, New
Brunswick. Advised by Prof. Sevil Salur. Includes material from 1707.01539,
1609.05383, 1608.03099, 1601.02001 and 1510.0337
Medium response in JEWEL and its impact on jet shape observables in heavy ion collisions
Realistic modeling of medium-jet interactions in heavy ion collisions is
becoming increasingly important to successfully predict jet structure and shape
observables. In JEWEL, all partons belonging to the parton showers initiated by
hard scattered partons undergo collisions with thermal partons from the medium,
leading to both elastic and radiative energy loss. The recoiling medium partons
carry away energy and momentum from the jet. Since the thermal component of
these recoils' momenta is part of the soft background activity, comparison with
data requires the implementation of a subtraction procedure. We present two
independent procedures through which background subtraction can be performed
and discuss the impact of the medium recoil on jet shape observables. Keeping
track of the medium response significantly improves the JEWEL description of
jet shape measurements.Comment: 23 pages, 16 figure
Medium Recoils and background subtraction in JEWEL
\textsc{Jewel} is a fully dynamical event generator for jet evolution in a
dense QCD medium, which has been validated for multiple jet and jet-like
observables. Jet constituents (partons) undergo collisions with thermal partons
from the medium, leading to both elastic and radiative energy loss. The
recoiling medium scattering centers carry away energy and momentum from the
jet. Keeping track of these recoils is essential for the description of
intra-jet observables. Since the thermal component of the recoils is part of
the soft background activity, comparison with data on jet observables requires
the implementation of a background subtraction procedure. We will show two
independent procedures through which background subtraction can be performed
and discuss the impact of the medium recoil on jet shape observables and
jet-background correlations. Keeping track of the medium recoil significantly
improves the \textsc{Jewel} description of jet shape measurements.Comment: Proceedings for talk given at HP 2016 at Wuhan Chin
Simulating V+jet processes in heavy ion collisions with JEWEL
Processes in which a jet recoils against an electroweak boson complement
studies of jet quenching in heavy ion collisions at the LHC. As the boson does
not interact strongly it escapes the dense medium unmodified and thus provides
a more direct access to the hard scattering kinematics than can be obtained in
di-jet events. First measurements of jet modification in these processes are
now available from the LHC experiments and will improve greatly with better
statistics in the future. We present an extension of JEWEL to boson-jet
processes. JEWEL is a dynamical framework for jet evolution in a dense
background based on perturbative QCD, that is in agreement with a large variety
of jet observables. We also obtain a good description of the CMS and ATLAS data
for y+jet and Z+jet processes at 2.76 TeV and 5.02 TeV.Comment: 8 pages, v2: version to be publishe
Identifying Heavy-Flavor Jets Using Vectors of Locally Aggregated Descriptors
Jets of collimated particles serve a multitude of purposes in high energy
collisions. Recently, studies of jet interaction with the quark-gluon plasma
(QGP) created in high energy heavy ion collisions are of growing interest,
particularly towards understanding partonic energy loss in the QGP medium and
its related modifications of the jet shower and fragmentation. Since the QGP is
a colored medium, the extent of jet quenching and consequently, the transport
properties of the medium are expected to be sensitive to fundamental properties
of the jets such as the flavor of the parton that initiates the jet.
Identifying the jet flavor enables an extraction of the mass dependence in
jet-QGP interactions. We present a novel approach to tagging heavy-flavor jets
at collider experiments utilizing the information contained within jet
constituents via the \texttt{JetVLAD} model architecture. We show the
performance of this model in proton-proton collisions at center of mass energy
GeV as characterized by common metrics and showcase its
ability to extract high purity heavy-flavor jet sample at various jet momenta
and realistic production cross-sections including a brief discussion on the
impact of out-of-time pile-up. Such studies open new opportunities for future
high purity heavy-flavor measurements at jet energies accessible at current and
future collider experiments.Comment: 18 pages, 6 figures and 3 tables. Accepted by JINS
Resolving the Scales of the Quark-Gluon Plasma with Energy Correlators
Jets provide us with ideal probes of the quark-gluon plasma (QGP) produced in
heavy-ion collisions, since its dynamics at its different scales is imprinted
into the multi-scale substructure of the final state jets. We present a new
approach to jet substructure in heavy-ion collisions based on the study of
correlation functions of energy flow operators. By analysing the two-point
correlator of an in-medium quark jet, we demonstrate that the spectra of
correlation functions robustly identify the scales defined by the properties of
the QGP, particularly those associated with the onset of colour coherence.Comment: 5 pages, 4 lovely figure
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