434 research outputs found
Colour connection structure of (supersymmetric) QCD () processes
The colour connection structure of QCD () processes is discussed, with
emphasis on its application to the supersymmetric 2 parton 2 sparton
processes, which are currently being implemented in the HERWIG Monte Carlo
event generator. The procedure described by Marchesini and Webber is found to
be inadequate, and a new method is proposed. However, this alteration is
unlikely to significantly affect the theoretical predictions for soft gluon
radiation. A complete list of supersymmetric QCD matrix elements and
their colour decompositions is presented.Comment: 12 pages, 4 figures, LaTeX2
The processes and at the Next Linear Collider in the Minimal Supersymmetric Standard Model
The complete matrix elements for and
are computed at tree-level within the Minimal
Supersymmetric Standard Model. Rates of interest to phenomenological analyses
at the Next Linear Collider are given. In particular, we analyse: (i)
pair production followed by the top decays into and final states; (ii) signals in which and . Top and Higgs finite width
effects are included as well as all those due to the irreducible backgrounds.Comment: 34 pages, latex, epsfig, 15 postscript figures bitmapped at 1000dpi,
complete paper including high resolution plots available at
ftp://axpa.hep.phy.cam.ac.uk/moretti/cavendish_9701 and at
http://www.hep.phy.cam.ac.uk/theory/papers
Regge-cascade hadronization
We argue that the evolution of coloured partons into colour-singlet hadrons
has approximate factorization into an extended parton-shower phase and a
colour-singlet resonance--pole phase. The amplitude for the conversion of
colour connected partons into hadrons necessarily resembles Regge-pole
amplitudes since qq-bar resonance amplitudes and Regge-pole amplitudes are
related by duality. A `Regge-cascade' factorization property of the N-point
Veneziano amplitude provides further justification of this protocol. This
latter factorization property, in turn, allows the construction of general
multi-hadron amplitudes in amplitude-squared factorized form from (1->2) link
amplitudes. We suggest an algorithm with cascade-decay configuration, ordered
in the transverse momentum, suitable for Monte-Carlo simulation. We make a
simple implementation of this procedure in Herwig++, obtaining some improvement
to the description of the event-shape distributions at LEP.Comment: 10 pages, 9 figure
Heavy charged Higgs boson production at next generation colliders
We assess the potential of future electron-positron linear colliders
operating in the mode in detecting charged Higgs bosons with mass
around and larger than the top quark mass, using Compton back-scattered photons
from laser light. We compare the pair production mode, , to a variety of channels involving only one charged Higgs scalar in
the final state, such as the tree-level processes ( and ) and
( and ) as well as the loop-induced channel . We show that, when the charged Higgs boson mass is smaller than or
comparable to half the collider energy, \sqrt s_{ee}\gsim 2M_{H^\pm}, single
production cross sections are of the same size as the pair production rate,
whereas, for charged Higgs boson masses larger than , all
processes are heavily suppressed. In general, production cross sections of
charged Higgs bosons via scatterings are smaller than those
induced at an collider and the latter represents a better option to
produce and analyse such particles.Comment: 18 pages, latex, 9 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
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