14 research outputs found
Uncertainties on parton distribution functions from the ZEUS NLO QCD fit to data on deep inelastic scattering
An NLO QCD analysis of the ZEUS data on deep inelastic scattering
together with fixed-target data has been performed from which the gluon and
quark densities of the proton and the value of the strong coupling parameter,
, have been extracted. The study includes a full treatment of
the experimental systematic uncertainties, including point-to-point
correlations. Different ways of incorporating correlated systematic
uncertainties into the fit are discussed and compared.Comment: 8 pages, 1 figure. Invited talk at the Conference on Advanced
Statistical Techniques in Particle Physics, March 18-22 2002, Durham, U
phi puzzle in heavy-ion collisions at 2 AGeV: how many K-from phi decays?
The preliminary experimental data on production in the reaction
Ni(1.93 AGeV) + Ni point to a puzzling high yield which can not be
reproduced with present transport codes. We survey the experimental situation
and present prospects for dedicated measurements of the multiplicities
with the and channels at HADES and FOPI.Comment: talk at Strange Quarks in Matter 2001, Frankfurt Sep. 24 - 29, 200
The High E_T Drop of J/psi to Drell-Yan Ratio from the Statistical c anti-c Coalescence Model
The dependence of the J/psi yield on the transverse energy E_T in heavy ion
collisions is considered within the statistical c anti-c coalescence model. The
model fits the NA50 data for Pb+Pb collisions at the CERN SPS even in the
high-E_T region (E_T > 100 GeV). Here E_T-fluctuations and E_T-losses in the
dimuon event sample naturally create the celebrated drop in the J/psi to
Drell-Yan ratio.Comment: 14 pages, REVTeX, 1 PS-figure. v2: References are corrected and
update
The process in topcolor-assisted technicolor models
In the context of topcolor-assisted technicolor (TC2) models, we consider the
process and calculate the cross section of
this process at leading order.It is shown that the extra U(1) gauge boson
predicted by TC2 models can give significant contributions to the
process , which may be detected
in the future high energy linear collider(LC) experiments.Comment: latex files,9 pages, 3 figure
Present and Future CP Measurements
We review theoretical and experimental results on CP violation summarizing
the discussions in the working group on CP violation at the UK phenomenology
workshop 2000 in Durham.Comment: 104 pages, Latex, to appear in Journal of Physics
A comprehensive description of multiple observables in heavy-ion collisions at SPS
Combining and expanding on work from previous publications, a model for the
evolution of ultrarelativistic heavy-ion collisions at the CERN SPS for 158
AGeV beam energy is presented. Based on the assumption of thermalization and a
parametrization of the space-time expansion of the produced matter, this model
is able to describe a large set of observables including hadronic momentum
spectra, correlations and abundancies, the emission of real photons, dilepton
radiation and the suppression pattern of charmonia. Each of these obervables
provides unique capabilities to study the reaction dynamics and taken together
they form a strong and consistent picture of the evolving system. Based on the
emission of hard photons, we argue that a strongly interacting, hot and dense
system with temperatures above 250 MeV has to be created early in the reaction.
Such a system is bound to be different from hadronic matter and likely to be a
quark-gluon plasma, and we find that this assumption is in line with the
subsequent evolution of the system that is reflected in other observables.Comment: 21 pages, 10 figures, submitted to J. Phys.
Precision Electroweak Tests of the Standard Model
The present status of precision electroweak data is reviewed. These data
include measurements of e+e- -> f+fbar, taken at the Z resonance at LEP, which
are used to determine the mass and width of the Z boson. In addition,
measurements have also been made of the forward-backward asymmetries for
leptons and heavy quarks, and also the final state polarisation of the
tau-lepton. At SLAC, where the electron beam was polarised, measurements were
made of the left-right polarised asymmetry, A_LR, and the left-right
forward-backward asymmetries for b and c quarks.
The mass, MW, and width, GW, of the W boson have been measured at the
Tevatron and at LEP, and the mass of the top quark, Mt, has been measured at
the Tevatron. These data, plus other electroweak data, are used in global
electroweak fits in which various Standard Model parameters are determined. A
comparison is made between the results of the direct measurements of MW and Mt
with the indirect results coming from electroweak radiative corrections. Using
all precision electroweak data fits are also made to determine limits on the
mass of the Higgs boson. The influence on these limits of specific
measurements, particularly those which are somewhat inconsistent with the
Standard Model, is explored. The data are also analysed in terms of the quasi
model-independent epsilon variables.
Finally, the impact on the electroweak fits of the improvements in the
determination of the W-boson and top-quark masses, expected from the Tevatron
Run 2, is examined.Comment: 80 pages, 36 Figures, Late
Dark Matter Candidates: A Ten-Point Test
An extraordinarily rich zoo of non-baryonic Dark Matter candidates has been
proposed over the last three decades. Here we present a 10-point test that a
new particle has to pass, in order to be considered a viable DM candidate: I.)
Does it match the appropriate relic density? II.) Is it {\it cold}? III.) Is it
neutral? IV.) Is it consistent with BBN? V.) Does it leave stellar evolution
unchanged? VI.) Is it compatible with constraints on self-interactions? VII.)
Is it consistent with {\it direct} DM searches? VIII.) Is it compatible with
gamma-ray constraints? IX.) Is it compatible with other astrophysical bounds?
X.) Can it be probed experimentally?Comment: 29 pages, 12 figure