9 research outputs found
GR@PPA 2.8: initial-state jet matching for weak boson production processes at hadron collisions
The initial-state jet matching method introduced in our previous studies has
been applied to the event generation of single and production processes
and diboson (, and ) production processes at hadron
collisions in the framework of the GR@PPA event generator. The generated events
reproduce the transverse momentum spectra of weak bosons continuously in the
entire kinematical region. The matrix elements (ME) for hard interactions are
still at the tree level. As in previous versions, the decays of weak bosons are
included in the matrix elements. Therefore, spin correlations and phase-space
effects in the decay of weak bosons are exact at the tree level. The program
package includes custom-made parton shower programs as well as ME-based hard
interaction generators in order to achieve self-consistent jet matching. The
generated events can be passed to general-purpose event generators to make the
simulation proceed down to the hadron level.Comment: 29 pages, 14 figures; minor changes to clarify the discussions, and
corrections of typo
Computational Particle Physics for Event Generators and Data Analysis
High-energy physics data analysis relies heavily on the comparison between
experimental and simulated data as stressed lately by the Higgs search at LHC
and the recent identification of a Higgs-like new boson. The first link in the
full simulation chain is the event generation both for background and for
expected signals. Nowadays event generators are based on the automatic
computation of matrix element or amplitude for each process of interest.
Moreover, recent analysis techniques based on the matrix element likelihood
method assign probabilities for every event to belong to any of a given set of
possible processes. This method originally used for the top mass measurement,
although computing intensive, has shown its power at LHC to extract the new
boson signal from the background.
Serving both needs, the automatic calculation of matrix element is therefore
more than ever of prime importance for particle physics. Initiated in the
eighties, the techniques have matured for the lowest order calculations
(tree-level), but become complex and CPU time consuming when higher order
calculations involving loop diagrams are necessary like for QCD processes at
LHC. New calculation techniques for next-to-leading order (NLO) have surfaced
making possible the generation of processes with many final state particles (up
to 6). If NLO calculations are in many cases under control, although not yet
fully automatic, even higher precision calculations involving processes at
2-loops or more remain a big challenge.
After a short introduction to particle physics and to the related theoretical
framework, we will review some of the computing techniques that have been
developed to make these calculations automatic. The main available packages and
some of the most important applications for simulation and data analysis, in
particular at LHC will also be summarized.Comment: 19 pages, 11 figures, Proceedings of CCP (Conference on Computational
Physics) Oct. 2012, Osaka (Japan) in IOP Journal of Physics: Conference
Serie
Consistent simulation of non-resonant diphoton production at hadron collisions with a custom-made parton shower
We have developed a Monte Carlo event generator for non-resonant diphoton
() production at hadron collisions in the framework of GR@PPA,
which consistently includes additional one-jet production. The jet-matching
method developed for initial-state jet production has been extended to the
final state in order to regularize the final-state QED divergence in the process. A QCD/QED-mixed parton shower (PS) has
been developed to complete the matching. The PS has the capability of enforcing
hard-photon radiation, and small- photon radiations that are not covered
by the PS are supplemented by using a fragmentation function. The generated
events can be passed to general-purpose event generators in order to perform
the simulations down to the hadron level. Thus, we can simulate the isolation
requirements that must be applied in experiments at the hadron level. The
simulation results are in reasonable agreement with the predictions from RESBOS
and DIPHOX. The simulated hadron-level events can be further fed to detector
simulations in order to investigate the detailed performance of experiments.Comment: 23 pages, 15 figure