351 research outputs found
Parton distributions for LO generators
We present a study of the results obtained combining LO partonic matrix
elements with either LO or NLO partons distributions. These are compared to the
best prediction using NLO for both matrix elements and parton distributions.
The aim is to determine which parton distributions are most appropriate to use
in those cases where only LO matrix elements are available, e.g. as in many
Monte Carlo generators. Both LO and NLO parton distributions have flaws,
sometimes serious, for some processes, so a modified optimal LO set is
suggested. We investigate a wide variety of process, and the LO* pdf works at
least as well as, and often better than, both LO and NLO pdfs in nearly all
cases.The LO* pdf set is now available in the LHAPDF package
An Iterative Rejection Sampling Method
In the note we consider an iterative generalisation of the rejection sampling
method. In high energy physics, this sampling is frequently used for event
generation, i.e. preparation of phase space points distributed according to a
matrix element squared for a scattering process. In many realistic
cases is a complicated multi-dimensional function, so, the standard von
Neumann procedure has quite low efficiency, even if an error reducing
technique, like VEGAS, is applied. As a result of that, many of the
calculations go to ``waste''. The considered iterative modification of the
procedure can extract more ``unweighted'' events, i.e. distributed according to
. In several simple examples we show practical benefits of the technique
and obtain more events than the standard von Neumann method, without any extra
calculations of
Room-temperature InAs0.89Sb0.11 photodetectors for CO detection at 4.6 mu m. .
An InAs0.89Sb0.11 photovoltaic detector that operates at room temperature in the 2.5-5 mu m mid-infrared wavelength region is reported. The photodiode has an extended spectral response compared with other currently available III-V room-temperature detectors. In order to accommodate the large lattice mismatch between the InAs0.89Sb0.11 active region and the InAs substrate, a buffer layer with an intermediate composition was introduced into the structure. In this way, we obtained room-temperature photodiodes with a cutoff wavelength near 5 mu m, a peak responsivity of 0.8 A/W, and a detectivity of 1.26 x 10(9) cm Hz(1/2)/W. These devices could be effectively used as the basis of an optical sensor for the environmental monitoring of carbon monoxide at 4.6 mu m, or as a replacement for PbSe photoconductors. (C) 2000 American Institute of Physics. [S0003-6951(00)02332-9]
LCG MCDB -- a Knowledgebase of Monte Carlo Simulated Events
In this paper we report on LCG Monte Carlo Data Base (MCDB) and software
which has been developed to operate MCDB. The main purpose of the LCG MCDB
project is to provide a storage and documentation system for sophisticated
event samples simulated for the LHC collaborations by experts. In many cases,
the modern Monte Carlo simulation of physical processes requires expert
knowledge in Monte Carlo generators or significant amount of CPU time to
produce the events. MCDB is a knowledgebase mainly dedicated to accumulate
simulated events of this type. The main motivation behind LCG MCDB is to make
the sophisticated MC event samples available for various physical groups. All
the data from MCDB is accessible in several convenient ways. LCG MCDB is being
developed within the CERN LCG Application Area Simulation project
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