3,935 research outputs found

### Fast computation of MadGraph amplitudes on graphics processing unit (GPU)

Continuing our previous studies on QED and QCD processes, we use the graphics
processing unit (GPU) for fast calculations of helicity amplitudes for general
Standard Model (SM) processes. Additional HEGET codes to handle all SM
interactions are introduced, as well assthe program MG2CUDA that converts
arbitrary MadGraph generated HELAS amplitudess(FORTRAN) into HEGET codes in
CUDA. We test all the codes by comparing amplitudes and cross sections for
multi-jet srocesses at the LHC associated with production of single and double
weak bosonss a top-quark pair, Higgs boson plus a weak boson or a top-quark
pair, and multisle Higgs bosons via weak-boson fusion, where all the heavy
particles are allowes to decay into light quarks and leptons with full spin
correlations. All the helicity amplitudes computed by HEGET are found to agree
with those comsuted by HELAS within the expected numerical accuracy, and the
cross sections obsained by gBASES, a GPU version of the Monte Carlo integration
program, agree wish those obtained by BASES (FORTRAN), as well as those
obtained by MadGraph. The performance of GPU was over a factor of 10 faster
than CPU for all processes except those with the highest number of jets.Comment: 37 pages, 12 figure

### Weak boson fusion production of supersymmetric particles at the LHC

We present a complete calculation of weak boson fusion production of
colorless supersymmetric particles at the LHC, using the new matrix element
generator SUSY-MadGraph. The cross sections are small, generally at the
attobarn level, with a few notable exceptions which might provide additional
supersymmetric parameter measurements. We discuss in detail how to consistently
define supersymmetric weak couplings to preserve unitarity of weak gauge boson
scattering amplitudes to fermions, and derive sum rules for weak supersymmetric
couplings.Comment: 24 p., 3 fig., 9 tab., published in PRD; numbers in Table IV
corrected to those with kinematic cuts cite

### Monte Carlo integration on GPU

We use a graphics processing unit (GPU) for fast computations of Monte Carlo
integrations. Two widely used Monte Carlo integration programs, VEGAS and
BASES, are parallelized on GPU. By using $W^{+}$ plus multi-gluon production
processes at LHC, we test integrated cross sections and execution time for
programs in FORTRAN and C on CPU and those on GPU. Integrated results agree
with each other within statistical errors. Execution time of programs on GPU
run about 50 times faster than those in C, and more than 60 times faster than
the original FORTRAN programs.Comment: 6 pages, 2 figure

### Granular packings of cohesive elongated particles

We report numerical results of effective attractive forces on the packing
properties of two-dimensional elongated grains. In deposits of non-cohesive
rods in 2D, the topology of the packing is mainly dominated by the formation of
ordered structures of aligned rods. Elongated particles tend to align
horizontally and the stress is mainly transmitted from top to bottom, revealing
an asymmetric distribution of local stress. However, for deposits of cohesive
particles, the preferred horizontal orientation disappears. Very elongated
particles with strong attractive forces form extremely loose structures,
characterized by an orientation distribution, which tends to a uniform behavior
when increasing the Bond number. As a result of these changes, the pressure
distribution in the deposits changes qualitatively. The isotropic part of the
local stress is notably enhanced with respect to the deviatoric part, which is
related to the gravity direction. Consequently, the lateral stress transmission
is dominated by the enhanced disorder and leads to a faster pressure saturation
with depth.Comment: 6 pages, 6 figure

### Calculation of HELAS amplitudes for QCD processes using graphics processing unit (GPU)

We use a graphics processing unit (GPU) for fast calculations of helicity
amplitudes of quark and gluon scattering processes in massless QCD. New HEGET
({\bf H}ELAS {\bf E}valuation with {\bf G}PU {\bf E}nhanced {\bf T}echnology)
codes for gluon self-interactions are introduced, and a C++ program to convert
the MadGraph generated FORTRAN codes into HEGET codes in CUDA (a C-platform for
general purpose computing on GPU) is created. Because of the proliferation of
the number of Feynman diagrams and the number of independent color amplitudes,
the maximum number of final state jets we can evaluate on a GPU is limited to 4
for pure gluon processes ($gg\to 4g$), or 5 for processes with one or more
quark lines such as $q\bar{q}\to 5g$ and $qq\to qq+3g$. Compared with the usual
CPU-based programs, we obtain 60-100 times better performance on the GPU,
except for 5-jet production processes and the $gg\to 4g$ processes for which
the GPU gain over the CPU is about 20

### Potential for measuring the H^\pm W^\mp Z^0 vertex from WZ fusion at the Large Hadron Collider

We investigate the possibility of measuring the H^\pm W^\mp Z^0 vertex from
the single $H^\pm$ production process via WZ fusion at the CERN Large Hadron
Collider (LHC). This vertex strongly depends on the structure of the Higgs
sector in various new physics scenarios, so that its measurement can be useful
to distinguish the models. A signal and background simulation under the
expected detector performance at the LHC is done for the processes of pp \to
W^\pm Z^0 X \to H^\pm X \to tbX and pp \to W^\pm Z^0 X \to H^\pm X \to W^\pm
Z^0 X, and the required magnitudes of the H^\pm W^\mp Z^0 vertex for
observation are evaluated. It is found that although the loop induced H^\pm
W^\pm Z^0 vertex in multi-Higgs doublet models cannot be measurable, the latter
process can be useful to test the model with a real and a complex triplets.Comment: 23 pages, 6 figures, version accepted for publication in Physical
Review

### Generic User Process Interface for Event Generators

Generic Fortran common blocks are presented for use by High Energy Physics
event generators for the transfer of event configurations from parton level
generators to showering and hadronization event generators.Comment: Physics at TeV Colliders II Workshop, Les Houches, France, May 2001
14 pages, 6 figure

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