268 research outputs found

### Tau Polarizations in the Three-body Slepton Decays with Stau as the NLSP

In the gauge-mediated supersymmetry breaking models with scalar tau as the
next-to-lightest supersymmetric particle, a scalar lepton may decay dominantly
into its superpartner, tau lepton, and the lightest scalar tau particle. We
give detailed formulas for the three-body decay amplitudes and the polarization
asymmetry of the outgoing tau lepton . We find that the tau polarizations are
sensitive to the model parameters such as the stau mixing angle, the neutralino
to slepton mass ratio and the neutralino mixing effect.Comment: 13 pages, 5 figures, RevTe

### A Non-supersymmetric Interpretation of the CDF e+e-\gamma\gamma + missing E_T Event

The \eegg event reported recently by the CDF Collaboration has been
interpreted as a signal of supersymmetry in several recent papers. In this
article, we report on an alternative non-supersymmetric interpretation of the
event using an extension of the standard model which contains new physics at
the electroweak scale that does not effect the existing precision electroweak
data. We extend the standard model by including an extra sequential generation
of fermions, heavy right-handed neutrinos for all generations and an extra
singly charged SU(2)-singlet Higgs boson. We discuss possible ways to
discriminate this from the standard supersymemtric interpretations.Comment: 7 pages, Latex, no figure

### Measuring the SUSY Breaking Scale at the LHC in the Slepton NLSP Scenario of GMSB Models

We report a study on the measurement of the SUSY breaking scale sqrt(F) in
the framework of gauge-mediated supersymmetry breaking (GMSB) models at the
LHC. The work is focused on the GMSB scenario where a stau is the
next-to-lightest SUSY particle (NLSP) and decays into a gravitino with lifetime
c*tau_NLSP in the range 0.5 m to 1 km. We study the identification of
long-lived sleptons using the momentum and time of flight measurements in the
muon chambers of the ATLAS experiment. A realistic evaluation of the
statistical and systematic uncertainties on the measurement of the slepton mass
and lifetime is performed, based on a detailed simulation of the detector
response. Accessible range and precision on sqrt(F) achievable with a counting
method are assessed. Many features of our analysis can be extended to the study
of different theoretical frameworks with similar signatures at the LHC.Comment: 28 pages, 12 figures (18 eps files). Revised version v2(published in
JHEP): Some important corrections and additions to v

### Scalar Top Quark as the Next-to-Lightest Supersymmetric Particle

We study phenomenologically the scenario in which the scalar top quark is
lighter than any other standard supersymmetric partner and also lighter than
the top quark, so that it decays to the gravitino via stop -> W^+ b G. In this
case, scalar top quark events would seem to be very difficult to separate from
top quark pair production. However, we show that, even at a hadron collider, it
is possible to distinguish these two reactions. We show also that the
longitudinal polarization of the final $W^+$ gives insight into the scalar top
and wino/Higgsino mixing parameters.Comment: 18 pages, LaTeX, 7 figures, minor typographical correction

### Determining the Mass for a Light Gravitino

Gauge mediated supersymmetry breaking scenarios with an ultra-light gravitino
of mass m_{3/2}=1-10 eV are very interesting, since there is no cosmological
gravitino problem. We propose a new experimental determination of the gravitino
mass for such an ultra-light gravitino, by measuring a branching ratio of two
decay modes of sleptons.Comment: 9 pages, 12 figure

### Aspects of GMSB Phenomenology at TeV Colliders

The status of two on-going studies concerning important aspects of the
phenomenology of gauge-mediated supersymmetry breaking (GMSB) models at TeV
colliders is reported. The first study deals with the characteristics of the
light Higgs boson spectrum allowed by the (minimal and non-minimal) GMSB
framework. Today's most accurate GMSB model generation and two-loop
Feynman-diagrammatic calculation of m_h have been combined. The Higgs masses
are shown in dependence of various model parameters at the messenger and
electroweak scales. In the minimal model, an upper limit on m_h of about 124
GeV is found for m_t = 175 GeV. The second study is focused on the measurement
of the fundamental SUSY breaking scale sqrt(F) at the LHC in the GMSB scenario
where a stau is the next-to-lightest SUSY particle (NLSP) and decays into a
gravitino with c*tau_NLSP in the range 0.5 m to 1 km. This implies the
measurement of mass and lifetime of long lived sleptons. The identification is
performed by determining the time of flight in the ATLAS muon chambers.
Accessible range and precision on sqrt(F) achievable with a counting method are
assessed.Comment: 22 pages, 9 figures (12 eps files). Report of the GMSB SUSY Working
Group, Workshop "Physics at TeV Colliders", Les Houches, 7-18 June 1999.
Revised version v3: A few typos correcte

### Supersymmetric Scenarios with Dominant Radiative Neutralino Decay

The radiative decay of the next-to-lightest neutralino into a lightest
neutralino and a photon is analyzed in the MSSM. We find that significant
regions of the supersymmetric parameter space with large radiative BR's (up to
about 100%) do exist. The radiative channel turns out to be enhanced when the
neutralino tree-level decays are suppressed either "kinematically" or
"dynamically". In general, in the regions allowed by LEP data and not
characterized by asymptotic values of the SuSy parameters, the radiative
enhancement requires tan beta ~= 1 and/or M_1 ~= M_2, and negative values of
\mu. We present typical specific scenarios where these "necessary" conditions
are fulfilled, relaxing the usual relation M_1=(5/3)*tan^2(th_W)*M_2. The
influence of varying the stop masses and mixing angle when the radiative decay
is enhanced is also considered. Some phenomenological consequences of the above
picture are discussed.Comment: 32 pages, LaTeX file + 23 figures embedded with epsf.sty. In this
revised version, Eq.(3) plus some related notations and text passages have
been changed. Minor error corrected in Fig.12(a). The numerical analysis and
the conclusions of the paper are not affected. (Includes the erratum to
appear in Phys. Rev. D.) Source and ps files are also available at
ftp://hpteo.roma1.infn.it/pub/preprints/ambr-mele/Rome1-1148/ or at
http://feynman.physics.lsa.umich.edu/~ambros/Physics.html#1

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