6,142 research outputs found
MCPLOTS: a particle physics resource based on volunteer computing
The mcplots.cern.ch web site (MCPLOTS) provides a simple online repository of
plots made with high-energy-physics event generators, comparing them to a wide
variety of experimental data. The repository is based on the HEPDATA online
database of experimental results and on the RIVET Monte Carlo analysis tool.
The repository is continually updated and relies on computing power donated by
volunteers, via the LHC@HOME platform.Comment: 30 page
Physics at a gamma gamma, e gamma and e-e- Option for a Linear Collider
This report presents a review of the studies made in the working group on
gamma gamma and e gamma physics" of the ECFA/DESY workshop on linear collider
physics. It reports on several new physics studies, in particular s-channel
Higgs production. A summary of R&D activities for the interaction region is
presented. The merits of e-e- collisions are briefly recalled.Comment: 10 pages, 20 figures. Proceedings of the ECFA/DESY study on Physics
and Detectors at a Linear Collider. The wor reported in this talk was done by
members of the gamma gamma and e gamma physics working group of the Extended
ECFA/DESY Stud
Recommended from our members
Measurements of μμ pairs from open heavy flavor and Drell-Yan in p+p collisions at s =200 GeV
PHENIX reports differential cross sections of μμ pairs from semileptonic heavy-flavor decays and the Drell-Yan production mechanism measured in p+p collisions at s=200 GeV at forward and backward rapidity (1.2<|η|<2.2). The μμ pairs from cc, bb, and Drell-Yan are separated using a template fit to unlike- and like-sign muon pair spectra in mass and pT. The azimuthal opening angle correlation between the muons from cc and bb decays and the pair-pT distributions are compared to distributions generated using pythia and powheg models, which both include next-to-leading order processes. The measured distributions for pairs from cc are consistent with pythia calculations. The cc data present narrower azimuthal correlations and softer pT distributions compared to distributions generated from powheg. The bb data are well described by both models. The extrapolated total cross section for bottom production is 3.75±0.24(stat)±0.500.35(syst)±0.45(global) [μb], which is consistent with previous measurements at the Relativistic Heavy Ion Collider in the same system at the same collision energy and is approximately a factor of 2 higher than the central value calculated with theoretical models. The measured Drell-Yan cross section is in good agreement with next-to-leading-order quantum-chromodynamics calculations
Improving NLO-parton shower matched simulations with higher order matrix elements
In recent times the algorithms for the simulation of hadronic collisions have
been subject to two substantial improvements: the inclusion, within parton
showering, of exact higher order tree level matrix elements (MEPS) and,
separately, next-to-leading order corrections (NLOPS). In this work we examine
the key criteria to be met in merging the two approaches in such a way that the
accuracy of both is preserved, in the framework of the POWHEG approach to
NLOPS. We then ask to what extent these requirements may be fulfilled using
existing simulations, without modifications. The result of this study is a
pragmatic proposal for merging MEPS and NLOPS events to yield much improved
MENLOPS event samples. We apply this method to W boson and top quark pair
production. In both cases results for distributions within the remit of the NLO
calculations exhibit no discernible changes with respect to the pure NLOPS
prediction; conversely, those sensitive to the distribution of multiple hard
jets assume, exactly, the form of the corresponding MEPS results.Comment: 38 pages, 17 figures. v2: added citations and brief discussion of
related works, MENLOPS prescription localized in a subsection. v3: cited 4
more MEPS works in introduction
Measurement of the top quark mass using the matrix element technique in dilepton final states
We present a measurement of the top quark mass in pp¯ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. The data were collected by the D0 experiment corresponding to an integrated luminosity of 9.7  fb−1. The matrix element technique is applied to tt¯ events in the final state containing leptons (electrons or muons) with high transverse momenta and at least two jets. The calibration of the jet energy scale determined in the lepton+jets final state of tt¯ decays is applied to jet energies. This correction provides a substantial reduction in systematic uncertainties. We obtain a top quark mass of mt=173.93±1.84  GeV
Diffusion in a Granular Fluid - Simulation
The linear response description for impurity diffusion in a granular fluid
undergoing homogeneous cooling is developed in the preceeding paper. The
formally exact Einstein and Green-Kubo expressions for the self-diffusion
coefficient are evaluated there from an approximation to the velocity
autocorrelation function. These results are compared here to those from
molecular dynamics simulations over a wide range of density and inelasticity,
for the particular case of self-diffusion. It is found that the approximate
theory is in good agreement with simulation data up to moderate densities and
degrees of inelasticity. At higher density, the effects of inelasticity are
stronger, leading to a significant enhancement of the diffusion coefficient
over its value for elastic collisions. Possible explanations associated with an
unstable long wavelength shear mode are explored, including the effects of
strong fluctuations and mode coupling
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