1,394 research outputs found
Heavy-to-light ratios as a test of medium-induced energy loss at RHIC and the LHC
The ratio of nuclear modification factors of high- heavy-flavored mesons
tolight-flavored hadrons (heavy-to-light ratio) is shown to be a sensitive tool
to test medium-induced energy loss at RHIC and LHC energies. Heavy-to-light
ratios of mesons at RHIC in the region GeV, and of and
mesons at the LHC in the region GeV, are proposed for such a test.
Finally, the different contributions to the nuclear modification factor for
electrons at RHIC are analyzed. Preliminary PHENIX and STAR data are compatible
with radiative energy loss provided the contribution of electrons from beauty
decays is small compared to that from charm.Comment: 5 pages, latex, 4 eps figs included using graphicx; to appear in the
proceedings of 18th International Conference on Ultrarelativistic
Nucleus-Nucleus Collisions: Quark Matter 2005 (QM 2005), Budapest, Hungary,
4-9 Aug 200
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
How sensitive are high-pt electron spectra at RHIC to heavy quark energy loss?
In nucleus-nucleus collisions, high-pt electron spectra depend on the medium
modified fragmentation of their massive quark parents, thus giving novel access
to the predicted mass hierarchy of parton energy loss. Here we calculate these
spectra in a model, which supplements the perturbative QCD factorization
formalism with parton energy loss. In general, we find - within large errors -
rough agreement between theory and data on the single inclusive electron
spectrum in pp, its nuclear modification factor, and its azimuthal anisotropy.
However, the nuclear modification factor depends on the relative contribution
of charm and bottom production, which we find to be affected by large
perturbative uncertainties. In order for electron measurements to provide a
significantly more stringent test of the expected mass hierarchy, one must then
disentangle the b- and c-decay contributions, for instance by reconstructing
the displaced decay vertices.Comment: 9 pages RevTex, 4 eps-figures, asci-file containing numerical tables
of results include
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
Prospects for the Measurement of the Higgs Yukawa Couplings to b and c quarks, and muons at CLIC
The investigation of the properties of the Higgs boson, especially a test of
the predicted linear dependence of the branching ratios on the mass of the
final state is going to be an integral part of the physics program at colliders
at the energy frontier for the foreseeable future. The large Higgs boson
production cross section at a 3TeV CLIC machine allows for a precision
measurement of the Higgs branching ratios. The cross section times branching
ratio of the decays H->bb, H->cc and H->{\mu}{\mu} of a Standard Model Higgs
boson with a mass of 120 GeV can be measured with a statistical uncertainty of
0.23%, 3.1% and 15%, respectively, assuming an integrated luminosity of 2 ab-1.Comment: 6 pages, 4 figure
NLO predictions for t-channel production of single top and fourth generation quarks at hadron colliders
We present updated NLO predictions for the electroweak t-channel production
of heavy quarks at the Tevatron and at the LHC. We consider production of
single top and fourth generation t' starting from both 2 to 2 and 2 to 3 Born
processes. Predictions for tb' and t'b' cross sections at NLO are also given
for the first time. A thorough study of the theoretical uncertainties coming
from parton distribution functions, renormalisation and factorisation scale
dependence and heavy quark masses is performed.Comment: 25 pages, 8 figure
Next-to-leading-order predictions for D^{*+-} plus jet photoproduction at DESY HERA
We study the photoproduction of a D^{*+-} meson in association with a hadron
jet at next-to-leading order in the parton model of QCD with non-perturbative
fragmentation functions extracted from LEP1 data of e^+e^- annihilation. The
transverse-momentum and rapidity distributions recently measured at DESY HERA
in various kinematic ranges nicely agree with our theoretical predictions. This
provides a useful test of the universality and the scaling violations of the
fragmentation functions predicted by the factorization theorem. These
comparisons also illustrate the significance of the charm component in the
resolved photon. This is elaborated by investigating the cross-section
distributions in x_obs^gamma and cos(theta^*).Comment: 20 pages, 10 figure
Heavy-flavour production in Pb-Pb collisions at the LHC, measured with the ALICE detector
We present the first results from the ALICE experiment on the nuclear
modification factors for heavy-flavour hadron production in Pb-Pb collisions at
sqrt{s_NN}=2.76 TeV. Using proton-proton and lead-lead collision samples at
sqrt{s}=7 TeV and sqrt{s_NN}=2.76 TeV, respectively, nuclear modification
factors R_AA(pt) were measured for D mesons at central rapidity (via displaced
decay vertex reconstruction), and for electrons and muons, at central and
forward rapidity, respectively.Comment: 8 pages, 5 figures, plenary talk at Quark Matter 2011, Annecy, Franc
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
Measurement of Jets and Jet Suppression in sqrt(s_NN)=2.76 TeV Lead-Lead Collisions with the ATLAS detector at the LHC
The first results of single jet observables in Pb+Pb collisions at
sqrt(s_NN)=2.76 TeV measured with the ATLAS detector at the LHC are presented.
Full jets are reconstructed with the anti-kt algorithm with R= 0.2 and 0.4,
using an event-by-event subtraction procedure to correct for the effects of the
underlying event including elliptic flow. The geometrically-scaled ratio of jet
yields in central and peripheral events,Rcp, indicates a clear suppression of
jets with ET >100 GeV. The transverse and longitudinal distributions of jet
fragments is also presented. We find little no substantial change to the
fragmentation properties and no significant change in the level of suppression
when moving to the larger jet definition.Comment: 5 pages, 6 figures, proceedings for Quark Matter 2011, Annecy,
France, May 23-28, 201
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