2,046 research outputs found
Jet Trimming
Initial state radiation, multiple interactions, and event pileup can
contaminate jets and degrade event reconstruction. Here we introduce a
procedure, jet trimming, designed to mitigate these sources of contamination in
jets initiated by light partons. This procedure is complimentary to existing
methods developed for boosted heavy particles. We find that jet trimming can
achieve significant improvements in event reconstruction, especially at high
energy/luminosity hadron colliders like the LHC.Comment: 20 pages, 11 figures, 3 tables - Minor changes to text/figure
RR Lyrae variables in the globular cluster M3 (NGC5272). I. BVI CCD photometry
New BVI CCD photometry is presented for 60 RR Lyrae variables in the globular
cluster M3. Light curves have been constructed and ephemerides have been
(re)-derived for all of them. Four stars (i.e. V29, V136, V155 and V209),
although recognized as variables, had no previous period determinations. Also,
the period derived for V129 is significantly different from the one published
by Sawyer-Hogg (1973). Light curve parameters, i.e. mean magnitudes, amplitudes
and rise-times, have been derived. The discussion of these results in the
framework of the stellar evolution and pulsation theories will be presented in
a forthcoming paper.Comment: 19 pages, latex, uses mn.sty, 12 encapsulated figures, to be
published in MNRAS, text and figures also available at
http://www.bo.astro.it/bap/BAPhome.html or via anonymous ftp at
ftp://boas3.bo.astro.it/bap/files (bap98-12-textfig.ps
D^* production from e^+e^- to ep collisions in NLO QCD
Fragmentation functions for D mesons, based on the convolution of a
perturbative part, related to the heavy quark perturbative showering, and a
non-perturbative model for its hadronization into the meson, are used to
describe D^* production in e^+e^- and ep collisions. The non-perturbative part
is determined by fitting the e^+e^- data taken by ARGUS and OPAL at 10.6 and
91.2 GeV respectively. When fitting with a non perturbative Peterson
fragmentation function and using next-to-leading evolution for the perturbative
part, we find an epsilon parameter sensibly different from the one commonly
used, which is instead found with a leading order fit. The use of this new
value is shown to increase considerably the cross section for D^* production at
HERA, suggesting a possible reconciliation between the next-to-leading order
theoretical predictions and the experimental data.Comment: 20 pages, LaTeX2e, 8 Postscript figure
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
A note on the fate of the Landau-Yang theorem in non-Abelian gauge theories
Using elementary considerations of Lorentz invariance, Bose symmetry and BRST
invariance, we argue why the decay of a massive color-octet vector state into a
pair of on-shell massless gluons is possible in a non-Abelian SU(N) Yang-Mills
theory, we constrain the form of the amplitude of the process and offer a
simple understanding of these results in terms of effective-action operators.Comment: 7 pages. v2: typos corrected, one reference adde
A Short Review on Jet Identification
Jets can be used to probe the physical properties of the high energy density
matter created in collisions at the Relativistic Heavy Ion Collider (RHIC).
Measurements of strong suppression of inclusive hadron distributions and
di-hadron correlations at high have already provided evidence for
partonic energy loss. However, these measurements suffer from well-known
geometric biases due to the competition of energy loss and fragmentation. These
biases can be avoided if the jets are reconstructed independently of their
fragmentation details - quenched or unquenched. In this paper, we discuss
modern jet reconstruction algorithms (cone and sequential recombination) and
their corresponding background subtraction techniques required by the high
multiplicities of heavy ion collisions. We review recent results from the STAR
experiment at RHIC on direct jet reconstruction in central Au+Au collisions at
GeV.Comment: Proceedings for the invited talk of Hot Quarks 2008, Estes Park, CO
18-23 August 200
Theoretical predictions for charm and bottom production at the LHC
We present predictions for a variety of single-inclusive observables that
stem from the production of charm and bottom quark pairs at the 7 TeV LHC. They
are obtained within the FONLL semi-analytical framework, and with two "Monte
Carlo + NLO" approaches, MC@NLO and POWHEG. Results are given for final states
and acceptance cuts that are as close as possible to those used by experimental
collaborations and, where feasible, are compared to LHC data.Comment: 22 pages, 10 figure
Charmonium Production via Fragmentation at DESY HERA
The cross section for the photoproduction of large-p_T J/psi mesons at HERA
is calculated at next-to-leading order, adopting a perturbative approach to
describe the fragmentation of charm quarks and gluons into J/psi mesons. We
treat the charm quark according to the massless factorization scheme, where it
is assumed to be one of the active flavours inside the proton and the resolved
photon. We present inclusive distributions in transverse momentum and rapidity,
including the contributions due to direct and resolved photons. The importance
of the colour-octet components of the J/psi wave function, which contribute to
the fragmentation process, is emphasized. In addition to prompt J/psi
production, we consider also the production of chi_{cJ} states followed by
radiative decays to J/psi mesons, both in the colour-singlet and colour-octet
channels.Comment: 32 pages (Latex), 12 figures (Postscript
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