44,826 research outputs found
Angular Structure of Jet Quenching Within a Hybrid Strong/Weak Coupling Model
Within the context of a hybrid strong/weak coupling model of jet quenching,
we study the modification of the angular distribution of the energy within jets
in heavy ion collisions, as partons within jet showers lose energy and get
kicked as they traverse the strongly coupled plasma produced in the collision.
To describe the dynamics transverse to the jet axis, we add the effects of
transverse momentum broadening into our hybrid construction, introducing a
parameter that governs its magnitude. We show that,
because of the quenching of the energy of partons within a jet, even when
the jets that survive with some specified energy in the final state
are narrower than jets with that energy in proton-proton collisions. For this
reason, many standard observables are rather insensitive to . We propose a
new differential jet shape ratio observable in which the effects of transverse
momentum broadening are apparent. We also analyze the response of the medium to
the passage of the jet through it, noting that the momentum lost by the jet
appears as the momentum of a wake in the medium. After freezeout this wake
becomes soft particles with a broad angular distribution but with net momentum
in the jet direction. We show that the particles coming from the response of
the medium to the momentum and energy deposited in it leads to a correlation
between the momentum of soft particles well separated from the jet in angle
with the direction of the jet momentum, and find qualitative but not
quantitative agreement with experimental data on observables designed to
extract such a correlation. By confronting the results that we obtain upon
introducing transverse momentum broadening and the response of the medium to
the jet with available jet data, we highlight the importance of these processes
for understanding the internal, soft, angular structure of high energy jets.Comment: 62 pages, 14 figure
Clan structure analysis and QCD parton showers in multiparticle dynamics. An intriguing dialog between theory and experiment
This paper contains a review of the main results of a search of regularities
in collective variables properties in multiparticle dynamics, regularities
which can be considered as manifestations of the original simplicity suggested
by QCD. The method is based on a continuous dialog between experiment and
theory. The paper follows the development of this research line, from its
beginnings in the seventies to the current state of the art, discussing how it
produced both sound interpretations of the most relevant experimental facts and
intriguing perspectives for new physics signals in the TeV energy domain.Comment: 118 pages, 48 figures; table of contents fixed for hyperre
Supersymmetry in the shadow of photini
Additional neutral gauge fermions -- "photini" -- arise in string
compactifications as superpartners of U(1) gauge fields. Unlike their vector
counterparts, the photini can acquire weak-scale masses from soft SUSY breaking
and lead to observable signatures at the LHC through mass mixing with the bino.
In this work we investigate the collider consequences of adding photini to the
neutralino sector of the MSSM. Relatively large mixing of one or more photini
with the bino can lead to prompt decays of the lightest ordinary supersymmetric
particle; these extra cascades transfer most of the energy of SUSY decay chains
into Standard Model particles, diminishing the power of missing energy as an
experimental handle for signal discrimination. We demonstrate that the missing
energy in SUSY events with photini is reduced dramatically for supersymmetric
spectra with MSSM neutralinos near the weak scale, and study the effects on
limits set by the leading hadronic SUSY searches at ATLAS and CMS. We find that
in the presence of even one light photino the limits on squark masses from
hadronic searches can be reduced by 400 GeV, with comparable (though more
modest) reduction of gluino mass limits. We also consider potential discovery
channels such as dilepton and multilepton searches, which remain sensitive to
SUSY spectra with photini and can provide an unexpected route to the discovery
of supersymmetry. Although presented in the context of photini, our results
apply in general to theories in which additional light neutral fermions mix
with MSSM gauginos.Comment: 23 pages, 8 figures, references adde
Theoretical Overview Quark Matter '04
The much wider transverse-momentum range accessible in heavy-ion collisions
at RHIC and at the LHC allows us to disentangle the dynamics of partonic
equilibration from the dynamics of delayed hadronization. This provides a novel
tool for testing the equilibration mechanisms underlying QCD thermodynamics.
Here, I argue, on the basis of simple formation-time arguments, why this is so,
and I review recent theoretical developments in this context.Comment: 12 pages, Latex, 3 eps figures, invited introductory talk at Quark
Matter 2004, Oakland, January 11-17, 200
Oscillatory relaxation of zonal flows in a multi-species stellarator plasma
The low frequency oscillatory relaxation of zonal potential perturbations is
studied numerically in the TJ-II stellarator (where it was experimentally
detected for the first time). It is studied in full global gyrokinetic
simulations of multi-species plasmas. The oscillation frequency obtained is
compared with predictions based on single-species simulations using simplified
analytical relations. It is shown that the frequency of this oscillation for a
multi-species plasma can be accurately obtained from single-species
calculations using extrapolation formulas. The damping of the oscillation and
the influence of the different inter-species collisions is studied in detail.
It is concluded that taking into account multiple kinetic ions and electrons
with impurity concentrations realistic for TJ-II plasmas allows to account for
the values of frequency and damping rate in zonal flows relaxations observed
experimentally.Comment: 11 figures, 22 page
Higgs, di-Higgs and tri-Higgs production via SUSY processes at the LHC with 14 TeV
We have systematically investigated the production of a Higgs boson with a
mass of about GeV in the decays of supersymmetric particles within the
phenomenological MSSM (pMSSM). We find regions of parameter space that are
consistent with all world data and that predict a sizeable rate of anomalous
Higgs, di-Higgs and even tri-Higgs events at the 14 TeV LHC. All relevant SUSY
production processes are investigated. We find that Higgs bosons can be
produced in a large variety of SUSY processes, resulting in a large range of
different detector signatures containing missing transverse momentum. Such
Higgs events are outstanding signatures for new physics already for the early
14 TeV LHC data. SUSY processes are also important to interprete deviations
found in upcoming Standard Model Higgs and di-Higgs production measurements.Comment: Version submitted to JHE
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