4,517 research outputs found
Reconstructed Jets at RHIC
To precisely measure jets over a large background such as pile up in high
luminosity p+p collisions at LHC, a new generation of jet reconstruction
algorithms is developed. These algorithms are also applicable to reconstruct
jets in the heavy ion environment where large event multiplicities are
produced. Energy loss in the medium created in heavy ion collisions are already
observed indirectly via inclusive hadron distributions and di-hadron
correlations. Jets can be used to study this energy loss in detail with reduced
biases. We review the latest results on jet-medium interactions as seen in A+A
collisions at RHIC, focusing on the recent progress on jet reconstruction in
heavy ion collisions.Comment: Proceedings for the 26th Winter Workshop on Nuclear Dynamic
Strange hadrons as dense matter probes
The spectra of strange hadrons have been measured in detail as a function of
centrality for a variety of collision systems and energies at RHIC. Recent
results are presented and compared to those measured at the SPS. The effects of
the system size on strange particle production and kinematics are examined. I
place specific emphasis on comparing A-A to pp production and discuss how
strangeness can be used to probe the dense matter produced in heavy-ion
collisions.Comment: Proceedings of the Strange Quark Matter Conference 200
Resonance production in heavy ion collisions
Recent results of resonance production from RHIC at
200 GeV and SPS at 17 GeV are presented and discussed in
terms of the evolution and freeze-out conditions of a hot and dense fireball
medium. Yields and spectra are compared with thermal model predictions at
chemical freeze-out. Deviations in the low transverse momentum region of the
resonance spectrum of the hadronic decay channel, suggest a strongly
interaction hadronic phase between chemical and kinetic freeze-out. Microscopic
models including resonance rescattering and regeneration are able to describe
the trend of the data. The magnitude of the regeneration cross sections for
different inverse decay channels are discussed. Model calculations which
include elastic hadronic interactions between chemical freeze-out and thermal
freeze-out based on the K(892)/K and (1520)/ ratios suggest a
time between two freeze-outs surfaces of 4 fm/c. The difference
in momentum distributions and yields for the (1020) resonance
reconstructed from the leptonic and hadronic decay channels at SPS energy are
discussed taking into account the impact of a hadronic phase and possible
medium modifications.Comment: 8 pages, 4 figures, conference proceedings (SQM2004
What do we learn from Resonance Production in Heavy Ion Collisions?
Resonances with their short life time and strong coupling to the dense and
hot medium are suggested as a signature of the early stage of the fireball
created in a heavy ion collision \cite{rap00,lut01,lut02}. The comparison of
resonances with different lifetimes and quark contents may give information
about time evolution and density and temperature of during the expanding of
fireball medium. Resonances in elementary reactions have been measured since
1960. Resonance production in elementary collisions compared with heavy ion
collisions where we expect to create a hot and dense medium may show the direct
of influence of the medium on the resonances. This paper shows a selection of
the recent resonance measurements from SPS and RHIC heavy ion colliders.Comment: 10 pages, 8 figures, HotQuarks 2004 conference proceeding
Jet Reconstruction in Heavy Ion Collisions
We examine the problem of jet reconstruction at heavy-ion colliders using
jet-area-based background subtraction tools as provided by FastJet. We use
Monte Carlo simulations with and without quenching to study the performance of
several jet algorithms, including the option of filtering, under conditions
corresponding to RHIC and LHC collisions. We find that most standard algorithms
perform well, though the anti-kt and filtered Cambridge/Aachen algorithms have
clear advantages in terms of the reconstructed transverse-momentum offset and
dispersion.Comment: 31 pages, 17 figure
Resonance Production
Recent results on rho(770)^0, K(892)^*0, f_0(980), phi(1020), Delta(1232)^++,
and Lambda(1520) production in A+A and p+p collisions at SPS and RHIC energies
are presented. These resonances are measured via their hadronic decay channels
and used as a sensitive tool to examine the collision dynamics in the hadronic
medium through their decay and regeneration. The modification of resonance
mass, width, and shape due to phase space and dynamical effects are discussed.Comment: 8 pages, 10 figures, proceedings of the Quark Matter 2004, in
Oakland, California, to be published in Journal of Physics G: Nuclear and
Particle Physic
Future Experiments in Relativistic Heavy Ion Collisions
The measurements at RHIC have revealed a new state of matter, which needs to
be further characterized in order to better understand its implications for the
early evolution of the universe and QCD. I will show that, in the near future,
complementary key measurements can be performed at RHIC, LHC, and FAIR. I will
focus on results than can be obtained using identified particles, a probe which
has been the basis for this conference over the past three decades. The
sophisticated detectors, built and planned, for all three accelerator
facilities enable us to measure leptons, photons, muons as well as hadrons and
resonances of all flavors almost equally well, which makes these experiments
unprecedented precision tools for the comprehensive understanding of the
physics of the early universe.Comment: 10 pages, 4 figures, Proceedings for Summary Talk at SQM 2007,
Levoca, Slovakia, June 24-29, 200
Jet coherence in QCD media: the antenna radiation spectrum
We study the radiation of a highly energetic partonic antenna in a colored
state traversing a dense QCD medium. Resumming multiple scatterings of all
involved constituents with the medium we derive the general gluon spectrum
which encompasses both longitudinal color coherence between scattering centers
in the medium, responsible for the well known Landau-Pomeranchuk-Migdal (LPM)
effect, and transverse color coherence between partons inside a jet, leading,
in vacuum, to angular ordering of the parton shower. We discuss shortly the
onset of transverse decoherence which is reached in opaque media. In this
regime, the spectrum consists of independent radiation off the antenna
constituents.Comment: 15 pages, 2 figures, paper shortened and partly rewritten, references
added, results unchange
An effective theory for jet propagation in dense QCD matter: jet broadening and medium-induced bremsstrahlung
Two effects, jet broadening and gluon bremsstrahlung induced by the
propagation of a highly energetic quark in dense QCD matter, are reconsidered
from effective theory point of view. We modify the standard Soft Collinear
Effective Theory (SCET) Lagrangian to include Glauber modes, which are needed
to implement the interactions between the medium and the collinear fields. We
derive the Feynman rules for this Lagrangian and show that it is invariant
under soft and collinear gauge transformations. We find that the newly
constructed theory SCET recovers exactly the general result for the
transverse momentum broadening of jets. In the limit where the radiated gluons
are significantly less energetic than the parent quark, we obtain a jet
energy-loss kernel identical to the one discussed in the reaction operator
approach to parton propagation in matter. In the framework of SCET we
present results for the fully-differential bremsstrahlung spectrum for both the
incoherent and the Landau-Pomeranchunk-Migdal suppressed regimes beyond the
soft-gluon approximation. Gauge invariance of the physics results is
demonstrated explicitly by performing the calculations in both the light-cone
and covariant gauges. We also show how the process-dependent
medium-induced radiative corrections factorize from the jet production cross
section on the example of the quark jets considered here.Comment: 52 pages, 15 pdf figures, as published in JHE
The effective action of D6-branes in N=1 type IIA orientifolds
We use a Kaluza-Klein reduction to compute the low-energy effective action
for the massless modes of a spacetime-filling D6-brane wrapped on a special
Lagrangian 3-cycle of a type IIA Calabi-Yau orientifold. The modifications to
the characteristic data of the N=1 bulk orientifold theory in the presence of a
D6-brane are analysed by studying the underlying Type IIA supergravity coupled
to the brane worldvolume in the democratic formulation and performing a
detailed dualisation procedure. The N=1 chiral coordinates are found to be in
agreement with expectations from mirror symmetry. We work out the Kahler
potential for the chiral superfields as well as the gauge kinetic functions for
the bulk and the brane gauge multiplets including the kinetic mixing between
the two. The scalar potential resulting from the dualisation procedure can be
formally interpreted in terms of a superpotential. Finally, the gauging of the
Peccei-Quinn shift symmetries of the complex structure multiplets reproduces
the D-term potential enforcing the calibration condition for special Lagrangian
3-cycles.Comment: 48 pages, v2: typos corrected, references adde
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