1,701 research outputs found
Minijets and Transverse Energy Flow in High Energy Collisions
We study the distribution of jets and transverse energy flow in high energyhadron-hadron or nucleus-nucleus collisions. In the minijet region correlationsand coherence effects can be taken into account in a description, where theparton flux is described by non-integrated structure functions. In a ``naive''calculation based on integrated structure functions, the cross section blows upfor small pT, which makes it necessary to introduce a soft cutoff. In ourapproach we find a dynamical suppression at low pT, which makes it possible toextrapolate to higher energies and make more reliable predictions for RHIC andLHC
Initial-state parton shower kinematics for NLO event generators
We are developing a consistent method to combine tree-level event generators
for hadron collision interactions with those including one additional QCD
radiation from the initial-state partons, based on the limited leading-log
(LLL) subtraction method, aiming at an application to NLO event generators. In
this method, a boundary between non-radiative and radiative processes
necessarily appears at the factorization scale (mu_F). The radiation effects
are simulated using a parton shower (PS) in non-radiative processes. It is
therefore crucial in our method to apply a PS which well reproduces the
radiation activities evaluated from the matrix-element (ME) calculations for
radiative processes. The PS activity depends on the applied kinematics model.
In this paper we introduce two models for our simple initial-state leading-log
PS: a model similar to the "old" PYTHIA-PS and a p_T-prefixed model motivated
by ME calculations. PS simulations employing these models are tested using
W-boson production at LHC as an example. Both simulations show a smooth
matching to the LLL-subtracted W + 1 jet simulation in the p_T distribution of
W bosons, and the summed p_T spectra are stable against a variation of mu_F,
despite that the p_T-prefixed PS results in an apparently harder p_T spectrum.Comment: 10 pages, 6 figures; minor changes in the abstract and the text
according to the comments from the refere
Matching NLO QCD computations with PYTHIA using MC@NLO
We present the matching between a next-to-leading order computation in QCD
and the PYTHIA parton shower Monte Carlo, according to the MC@NLO formalism. We
study the case of initial-state radiation, and consider in particular single
vector boson hadroproduction.Comment: 16 pages, 10 figures. Several comments and two figures have been
adde
Search for Chargino and Neutralino Production at sqrt(s) = 192-209 GeV at LEP
Approximately 438 pb-1 of e+e- data from the OPAL detector, taken with the
LEP collider running at centre-of-mass energies of 192-209 Gev, are analyzed to
search for evidence of chargino pair production, e+e- -> tilde chi^+_1 tilde
chi^-_1, or neutralino associated production, e+e- -> tilde chi^0_2 tilde
chi^0_1. Limits are set at the 95% confidence level on the product of the
cross-section for the process e+e- -> tilde chi^+_1 tilde chi^-_1 and its
branching ratios to topologies containing jets and missing energy, of jest with
a lepton and missing energy, and on the product of the cross-section for e+e-
-> tilde chi^0_2 tilde chi^0_1 and its branching ratio to jets. R-parity
conservation is assumed throughout this paper. When these results are
interpreted in the context of the Constrained Minimal Supersymmetric Standard
Model, limits are also set on the masses of the tilde chi^+-_1, tilde chi^0_1
and tilde chi^0_2, and regions of the parameter space of the model are ruled
out. Nearly model-independent limits are also set at the 95% confidence level
on sigma(e+e- -> tilde chi^+_1 tilde chi^-_1) with the assumption that each
chargino decays via a W boson, and on sigma(e+e- -> tilde chi^0_2 tilde
chi^0_1) with the tilde chi^0_2 assumed to decay via a Z^0.Comment: 33 pages, 13 figures, Submitted to Eur Phys J.
Recommended from our members
Assessing the discordance rate between local and central HER2 testing in women with locally determined HER2-negative breast cancer.
BackgroundThe importance of human epidermal growth factor receptor 2 (HER2) as a prognostic and predictive marker in invasive breast cancer is well established. Accurate assessment of HER2 status is essential to determine optimal treatment options.MethodsBreast cancer tumor tissue samples from the VIRGO observational cohort tissue substudy that were locally HER2-negative were retested centrally with both US Food and Drug Administration (FDA)-approved immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) assays, using FDA-approved assay cutoffs; results were compared.ResultsOf the 552 unique patient samples centrally retested with local HER2-negative results recorded, tumor samples from 22 (4.0%) patients were determined to be HER2-positive (95% confidence interval [CI] = 2.5%-5.7%). Of these, 18 had been tested locally by only one testing methodology; 15 of 18 were HER2-positive after the central retesting, based on the testing methodology not performed locally. Compared with the 530 patients with centrally confirmed HER2-negative tumors, the 22 patients with centrally determined HER2-positive tumors were younger (median age 56.5 versus 60.0 years) and more likely to have ER/PR-negative tumors (27.3% versus 22.3%). These patients also had shorter median progression-free survival (6.4 months [95% CI = 3.8-15.9 months] versus 9.1 months [95% CI = 8.3-10.3 months]) and overall survival (25.9 months [95% CI = 13.8-not estimable] versus 27.9 months [95% CI = 25.0-32.9 months]).ConclusionsThis study highlights the limitations of employing just one HER2 testing methodology in current clinical practice. It identifies a cohort of patients who did not receive potentially efficacious therapy because their tumor HER2-positivity was not determined by the test initially used. Because of inherent limitations in testing methodologies, it is inadvisable to rely on a single test to rule out potential benefit from HER2-targeted therapy
Gluon Distribution Functions in the kT-factorization Approach
At small x, the effects of finite transverse momenta of partons inside a
hadron become increasingly important, especially in analyses of jets and
heavy-quark production. These effects can be systematically accounted for in a
formalism based on kT-factorization and unintegrated distribution functions. We
present results for the unintegrated distribution function, together with the
corresponding integrated one, obtained within the framework of the Linked
Dipole Chain model. Comparisons are made to results obtained within other
approaches
- …