3,411 research outputs found
New Signatures of Squarks
When the gluino is light and long lived, missing energy is a poor signature
for both squarks and gluinos. Instead, production in and
collisions characteristically results in events with jets.
Methods are proposed for deciding whether an observed excess of 4-jet events is
due to production. The recent report by ALEPH of observation of 14
4-jet events when 7 were expected is discussed.Comment: 12/22/95 version (put on net 1/1/96) elaborates remarks on squarks as
possible source of ALEPH 4-jet excess and adds a ref. latex, 10 pages
(including 1 figure), uufile
Light, long-lived and secluded: can gluinos be driven out from LEP1 data ?
We briefly report about a possible settlement of the still ongoing dispute
concerning the existence of SUSY signals in 4jet events at LEP1. We base our
arguments on a simple selection strategy exploiting secondary vertex tagging
and kinematical constraints, which could allow one to access or exclude gluino
events for a broad range of masses and lifetimes.Comment: 10 pages, LaTeX, 3 PostScript figures embedded with epsfig. Complete
ps paper and figures available also at ftp://ftae3.ugr.es/pub/rmt/ugrft70.p
Possible manifestation of heavy stable colored particles in cosmology and cosmic rays
We discuss the cosmological implications as well as possible observability of
massive, stable, colored particles which often appear in the discussion of
physics beyond the standard model. We argue that if their masses are more than
a few hundred GeV and if they saturate the halo density and/or occur with
closure density of the universe, they are ruled out by the present WIMP search
experiments as well as the searches for anomalous heavy isotopes of ordinary
nuclei. We then comment on the possibility that these particles as well as the
monopoles could be responsible for the ultra high energy cosmic rays with
energy eV and point out that their low inelasticity argues
against this.Comment: 9 pages; UMD-PP-98-1
Group independent color decomposition of next-to-leading order matrix elements for e^+ e^- \to four partons
We present the next-to-leading order partonic cross sections involving an
electroweak vector boson and four massless partons (quarks, gluons or long
living gluinos) in a general gauge theory with a simple Lie Group. The vector
boson couples to a massless lepton pair and a quark-antiquark pair. The cross
sections are given in terms of group independent kinematical functions
multiplying the eigenvalues of the Casimir operators of the Lie group. This
kind of color decomposition is required for the calculation of O()
corrections to the group independent kinematical functions in the four-jet
production cross sections in electron-positron annihilation. The knowledge of
these corrections facilitates the simultaneous precision meaurement of the
strong coupling and the color charge factors using the four-jet LEP or SLC data
as well as the test whether these data favour or exclude the existence of a
light gluino.Comment: 11 pages, elsart styl
A General Approach To Photon Radiation Off Fermions
Soft or collinear photon emission potentially poses numerical problems in the
phase-space integration of radiative processes. In this paper, a general
subtraction formalism is presented that removes such singularities from the
integrand of the numerical integration and adds back the analytically
integrated contributions that have been subtracted. The method is a
generalization of the dipole formalism of Catani and Seymour, which was
formulated for NLO QCD processes with massless unpolarized particles. The
presented formalism allows for arbitrary mass and helicity configurations in
processes with charged fermions and any other neutral particles. Particular
attention is paid to the limit of small fermion masses, in which collinear
singularities cause potentially large corrections. The actual application and
the efficiency of the formalism are demonstrated by the discussion of photonic
corrections to the processes \gamma \gamma --> t \bar t (\gamma), e^- \gamma
--> e^- \gamma (\gamma), and \mu^+ \mu^- --> \nu_e \bar\nu_e (\gamma).Comment: 51 pages, latex; two sentences dropped (in Sections 3.2 and 4.2); to
appear in Nucl. Phys.
Electroweak baryogenesis and the Higgs and stop masses
In this talk we review the actual situation concerning electroweak phase
transition and baryogenesis in the minimal supersymmetric extension of the
Standard Model. A strong enough phase transition requires light Higgs and stop
eigenstates. For a Higgs mass in the range 110--115 GeV, there is a stop window
in the range 105--165 GeV. If the Higgs is heavier than 115 GeV, stronger
constrains are imposed on the space of supersymmetric parameters. A
baryon-to-entropy ratio is generated by the chargino sector provided that the
parameter has a CP-violating phase larger than 0.04.Comment: 10 pages, 6 figures, uses espcrc2.sty. Contribution to the
conferences: Strong Electroweak Matter, Centre de Physique Theorique,
Universite de Marseille, Marseilles (France), June 14-17, 2000; and, Thirty
years of supersymmetry, Theoretical Physics Institute, School of Physics and
Astronomy, Minneapolis, Minnesota (USA), October 16-27, 200
Galaxies Correlating with Ultra-high Energy Cosmic Rays
The Pierre Auger Observatory reports that 20 of the 27 highest energy cosmic
rays have arrival directions within 3.2 deg of a nearby galaxy in the
Veron-Cetty & Veron Catalog of Quasars and Active Galactic Nuclei (12th Ed.),
with ~5 of the correlations expected by chance. In this paper we examine the
correlated galaxies to gain insight into the possible UHECR sources. We find
that 14 of the 21 correlated VCV galaxies are AGNs and we determine their
bolometric luminosities. The remaining 7 are primarily star-forming galaxies.
The bolometric luminosities of the correlated AGNs are all greater than 5 x
10^{42} erg/s, which may explain the absence of UHECRs from the Virgo region in
spite of the large number of VCV galaxies in Virgo, since most of the VCV
galaxies in the Virgo region are low luminosity AGNs. Interestingly, the
bolometric luminosities of most of the AGNs are significantly lower than
required to satisfy the minimum condition for UHECR acceleration in a
continuous jet. If a UHECR-AGN correlation is substantiated with further
statistics, our results lend support to the recently proposed ``giant AGN
flare" mechanism for UHECR acceleration.Comment: 13 pages, 3 figures, to be submitted to Ap
SUSYGEN 2.2 - A Monte Carlo Event Generator for MSSM Sparticle Production at e+ e- Colliders
SUSYGEN is a Monte Carlo program designed for computing distributions and
generating events for MSSM sparticle production in e+ e- collisions. The
Supersymmetric (SUSY) mass spectrum may either be supplied by the user, or can
alternatively be calculated in two different models of SUSY Breaking: gravity
mediated supersymmetry breaking (SUGRA), and gauge mediated supersymmetry
breaking (GMSB). The program incorporates the most important production
processes and decay modes, including the full set of R-parity violating decays,
and the decays to the gravitino in GMSB models. Initial state radiation
corrections take into account pT/pL effects in the Structure Function
formalism, and an optimised hadronisation interface to JETSET 7.4 including
final state radiation is also provided.Comment: 68 pages, 8 figures. Submitted to Comp. Phys. Commu
Charm production in antiproton-nucleus collisions at the and the thresholds
We discuss the production of charmonium states in antiproton-nucleus
collisions at the threshold. It is explained that measurements in collisions will allow to get new information about the strengths of the
inelastic interaction, on the production of and
in charmonium-nucleon interactions and for the first time about
nondiagonal transitions . The inelastic -nucleon
cross section is extracted from the comparison of hadron-nucleus collisions
with hadron-nucleon collisions. We extract the total nucleon cross
section from photon-nucleon collisions by accounting for the color transparency
phenomenon within the frame of the GVDM (Generalized Vector meson Dominance
Model). We evaluate also within the GVDM the inelastic -nucleon cross
section as well as the cross section for the nondiagonal transitions.
Predictions for the ratio of to yields in antiproton-nucleus
scatterings close to the threshold of production for different nuclear
targets are presented.Comment: 13 pages, 10 figures, typos corrected, some discussion adde
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