4,465 research outputs found
Event generation with SHERPA 1.1
In this paper the current release of the Monte Carlo event generator Sherpa,
version 1.1, is presented. Sherpa is a general-purpose tool for the simulation
of particle collisions at high-energy colliders. It contains a very flexible
tree-level matrix-element generator for the calculation of hard scattering
processes within the Standard Model and various new physics models. The
emission of additional QCD partons off the initial and final states is
described through a parton-shower model. To consistently combine multi-parton
matrix elements with the QCD parton cascades the approach of Catani, Krauss,
Kuhn and Webber is employed. A simple model of multiple interactions is used to
account for underlying events in hadron--hadron collisions. The fragmentation
of partons into primary hadrons is described using a phenomenological
cluster-hadronisation model. A comprehensive library for simulating tau-lepton
and hadron decays is provided. Where available form-factor models and matrix
elements are used, allowing for the inclusion of spin correlations; effects of
virtual and real QED corrections are included using the approach of Yennie,
Frautschi and Suura.Comment: 47 pages, 21 figure
MadEvent: Automatic Event Generation with MadGraph
We present a new multi-channel integration method and its implementation in
the multi-purpose event generator MadEvent, which is based on MadGraph. Given a
process, MadGraph automatically identifies all the relevant subprocesses,
generates both the amplitudes and the mappings needed for an efficient
integration over the phase space, and passes them to MadEvent. As a result, a
process-specific, stand-alone code is produced that allows the user to
calculate cross sections and produce unweighted events in a standard output
format. Several examples are given for processes that are relevant for physics
studies at present and forthcoming colliders.Comment: 11 pages, MadGraph home page at http://madgraph.physics.uiuc.ed
Lifetime statistics of quantum chaos studied by a multiscale analysis
In a series of pump and probe experiments, we study the lifetime statistics
of a quantum chaotic resonator when the number of open channels is greater than
one. Our design embeds a stadium billiard into a two dimensional photonic
crystal realized on a Silicon-on-insulator substrate. We calculate resonances
through a multiscale procedure that combines graph theory, energy landscape
analysis and wavelet transforms. Experimental data is found to follow the
universal predictions arising from random matrix theory with an excellent level
of agreement.Comment: 4 pages, 6 figure
Neutrino mass from higher than d=5 effective operators in SUSY, and its test at the LHC
We discuss neutrino masses from higher than d=5 effective operators in a
supersymmetric framework, where we explicitly demonstrate which operators could
be the leading contribution to neutrino mass in the MSSM and NMSSM. As an
example, we focus on the d=7 operator L L H_u H_u H_d H_u, for which we
systematically derive all tree-level decompositions. We argue that many of
these lead to a linear or inverse see-saw scenario with two extra neutral
fermions, where the lepton number violating term is naturally suppressed by a
heavy mass scale when the extra mediators are integrated out. We choose one
example, for which we discuss possible implementations of the neutrino flavor
structure. In addition, we show that the heavy mediators, in this case SU(2)
doublet fermions, may indeed be observable at the LHC, since they can be
produced by Drell-Yan processes and lead to displaced vertices when they decay.
However, the direct observation of lepton number violating processes is on the
edge at LHC.Comment: 24 pages, 5 figures, 6 table
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