16 research outputs found
Single Top Production at the Next Generation Linear e+e- Colliders
Present limits on the top mass from LEP1 and Tevatron point to a top quark
that is considerably heavier than the vector boson in the standard model.
Hence, e+e- colliders with \sqrt{s} \simeq 300 GeV (the c.m. energy foreseen at
the first phase of the Next Linear e+e- Collider) could be well below the
energy threshold for real top-pair production. We argue that, if this is the
case, single top production through the process e+e- --> t\bar{b}W-
(\bar{t}bW+), where t\bar{b} (\bar{t}b) are produced mainly by means of a
virtual W, becomes the dominant top production mechanism. Total cross sections
and kinematical distributions are evaluated and numerical results are given in
ranges of m_t and \sqrts{s} where single top production can be of relevance.
The relative importance of virtual-W and virtual-t contributions to the process
is discussed.Comment: 20 pages, LaTeX + feynman.tex, 10 compressed (tar.Z) postscript
figures included in a separate uuencoded file, revised version of Rome1
Preprint n.979 (1993), Dec 29, 1993. (In this revised version -- accepted for
publication on Zeit. fur Phys.C in Jan 24, 1994 -- some sentences and 3 new
refs. have been added with respect to the first one
Singe Top Production at LEP 200
We present exact tree level cross sections for the single top production
process at LEP~200. The
results reproduce roughly those obtained earlier by using the equivalent real
photon approximation and we confirm the observation that detecting a top
heavier than half the c.m.~energy is not feasible at LEP~200. The calculation
has been performed by a new automatic Feynman amplitude generator MadGraph
which produces HELAS code for the helicity amplitudes.Comment: 7 pages, 4 postscript figure
PYTHIA 6.4 Physics and Manual
The PYTHIA program can be used to generate high-energy-physics `events', i.e.
sets of outgoing particles produced in the interactions between two incoming
particles. The objective is to provide as accurate as possible a representation
of event properties in a wide range of reactions, within and beyond the
Standard Model, with emphasis on those where strong interactions play a role,
directly or indirectly, and therefore multihadronic final states are produced.
The physics is then not understood well enough to give an exact description;
instead the program has to be based on a combination of analytical results and
various QCD-based models. This physics input is summarized here, for areas such
as hard subprocesses, initial- and final-state parton showers, underlying
events and beam remnants, fragmentation and decays, and much more. Furthermore,
extensive information is provided on all program elements: subroutines and
functions, switches and parameters, and particle and process data. This should
allow the user to tailor the generation task to the topics of interest.Comment: 576 pages, no figures, uses JHEP3.cls. The code and further
information may be found on the PYTHIA web page:
http://www.thep.lu.se/~torbjorn/Pythia.html Changes in version 2: Mistakenly
deleted section heading for "Physics Processes" reinserted, affecting section
numbering. Minor updates to take into account referee comments and new colour
reconnection option
Nonclassical Orthogonal Polynomials and Corresponding Quadratures
We construct nonclassical orthogonal polynomials and calculate abscissas and weights of Gaussian quadrature for arbitrary weight and interval. The program is written by Mathematica and it works if moment integrals are given analytically. The result is a FORTRAN subroutine ready to utilize the quadrature