1,263 research outputs found
SUSY Parameter Measurements with Fittino
This article presents the results of a realistic global fit of the Lagrangian
parameters of the Minimal Supersymmetric Standard Model with no assumptions on
the SUSY breaking mechanism using the fit program Fittino. The fit is performed
using the precision of future mass measurements of superpartners at the LHC and
mass and polarized topological cross-section measurements at the ILC. Higher
order radiative corrections are accounted for wherever possible to date.
Results are obtained for a modified SPS1a MSSM benchmark scenario (general MSSM
without assumptions on the breaking mechanism) and for a specific mSUGRA
scenario. Exploiting a simulated annealing algorithm, a stable result is
obtained without any {\it a priori} assumptions on the fit parameters. Most of
the Lagrangian parameters can be extracted at the percent level or better if
theoretical uncertainties are neglected. Neither LHC nor ILC measurements alone
will be sufficient to obtain a stable result.Comment: 3 pages, presented at the 2005 International Linear Collider Physics
And Detector Workshop, Snowmass, CO, 14.-27. August 200
A DAQ System for Linear Collider TPC Prototypes based on the ALEPH TPC Electronics
Within the international studies of a high energy linear electron positron
collider, several groups are developing and testing prototypes for a Linear
Collider TPC. This detector is planned to be used as a central part in the
tracking system of a detector at such a machine. In this note we describe a DAQ
system, which has been developed for the use in tests of TPC prototypes. It is
based on electronics used at the ALEPH experiment at CERN.Comment: 15 pages, 4 figure
LHC and the Dark Matter Connection
The presentation describes what we might learn about dark matter from LHC data
The race for supersymmetry: using mT2 for discovery
We describe how one may employ a very simple event selection, using only the
kinematic variable mT2, to search for new particles at the LHC. The method is
useful when searching for evidence of models (such as R-parity conserving
supersymmetry) which have a Z2 parity and a weakly-interacting lightest
parity-odd particle. We discuss the kinematic properties which make this
variable an excellent discriminant against the great majority of Standard Model
backgrounds. Monte Carlo simulations suggest that this approach could be used
to discover supersymmetry with somewhat smaller integrated luminosities (or
perhaps lower center-of-mass energies) than would be required for other
comparable analyses.Comment: 8 page
Stau as the Lightest Supersymmetric Particle in R-Parity Violating SUSY Models: Discovery Potential with Early LHC Data
We investigate the discovery potential of the LHC experiments for R-parity
violating supersymmetric models with a stau as the lightest supersymmetric
particle (LSP) in the framework of minimal supergravity. We classify the final
states according to their phenomenology for different R-parity violating decays
of the LSP. We then develop event selection cuts for a specific benchmark
scenario with promising signatures for the first beyond the Standard Model
discoveries at the LHC. For the first time in this model, we perform a detailed
signal over background analysis. We use fast detector simulations to estimate
the discovery significance taking the most important Standard Model backgrounds
into account. Assuming an integrated luminosity of 1 inverse femtobarn at a
center-of-mass energy of 7 TeV, we perform scans in the parameter space around
the benchmark scenario we consider. We then study the feasibility to estimate
the mass of the stau-LSP. We briefly discuss difficulties, which arise in the
identification of hadronic tau decays due to small tau momenta and large
particle multiplicities in our scenarios.Comment: 26 pages, 18 figures, LaTeX; minor changes, final version published
in PR
Fittino, a program for determining MSSM parameters from collider observables using an iterative method
Provided that Supersymmetry (SUSY) is realized, the Large Hadron Collider
(LHC) and the future International Linear Collider (ILC) may provide a wealth
of precise data from SUSY processes. An important task will be to extract the
Lagrangian parameters. On this basis the goal is to uncover the underlying
symmetry breaking mechanism from the measured observables. In order to
determine the SUSY parameters, the program Fittino has been developed. It uses
an iterative fitting technique and a Simulated Annealing algorithm to determine
the SUSY parameters directly from the observables without any a priori
knowledge of the parameters, using all available loop-corrections to masses and
couplings. Simulated Annealing is implemented as a stable and efficient method
for finding the optimal parameter values. The theoretical predictions can be
provided from any program with SUSY Les Houches Accord interface. As fit
result, a set of parameters including the full error matrix and two-dimensional
uncertainty contours are obtained. Pull distributions can automatically be
created and allow an independent cross-check of the fit results and possible
systematic shifts in the parameter determination. A determination of the
importance of the individual observables for the measurement of each parameter
can be performed after the fit. A flexible user interface is implemented,
allowing a wide range of different types of observables and a wide range of
parameters to be used.Comment: 32 pages, 6 figures, accepted by Comp. Phys. Com
Measuring a Light Neutralino Mass at the ILC: Testing the MSSM Neutralino Cold Dark Matter Model
The LEP experiments give a lower bound on the neutralino mass of about 46 GeV
which, however, relies on a supersymmetric grand unification relation. Dropping
this assumption, the experimental lower bound on the neutralino mass vanishes
completely. Recent analyses suggest, however, that in the minimal
supersymmetric standard model (MSSM), a light neutralino dark matter candidate
has a lower bound on its mass of about 7 GeV. In light of this, we investigate
the mass sensitivity at the ILC for very light neutralinos. We study slepton
pair production, followed by the decay of the sleptons to a lepton and the
lightest neutralino. We find that the mass measurement accuracy for a few-GeV
neutralino is around 2 GeV, or even less if the relevant slepton is
sufficiently light. We thus conclude that the ILC can help verify or falsify
the MSSM neutralino cold dark matter model even for very light neutralinos.Comment: 7 pages, 1 figure; references adde
Charge Transfer and Charge Broadening of GEM Structures in High Magnetic Fields
We report on measurements of charge transfer in GEM structures in high
magnetic fields. These were performed in the framework of the R&D work for a
Time Projection Chamber at a future Linear Collider. A small test chamber has
been installed into the aperture of a superconducting magnet with the GEM
structures mounted perpendicular to the B field direction. The charge transfer
is derived from the electrical currents monitored during irradiation with an
Fe source. No severe loss of primary ionisation charge is observed,
but an improved ion feedback suppression is achieved for high magnetic fields.
Additionally, the width of the charge cloud released by individual Fe
photons is measured using a finely segmented strip readout after the triple GEM
structure. Charge widths between 0.3 and 0.5 mm RMS are observed, which
originate from the charge broadening inside the GEM readout. This charge
broadening is only partly suppressed at high magnetic fields.Comment: 11 pages, 9 figure
Determination of MSSM Parameters from LHC and ILC Observables in a Global Fit
We present the results of a realistic global fit of the Lagrangian parameters
of the Minimal Supersymmetric Standard Model assuming universality for the
first and second generation and real parameters. No assumptions on the SUSY
breaking mechanism are made. The fit is performed using the precision of future
mass measurements of superpartners at the LHC and mass and polarized
topological cross-section measurements at the ILC. Higher order radiative
corrections are accounted for whereever possible to date. Results are obtained
for a modified SPS1a MSSM benchmark scenario but they were checked not to
depend critically on this assumption. Exploiting a simulated annealing
algorithm, a stable result is obtained without any a priori assumptions on the
values of the fit parameters. Most of the Lagrangian parameters can be
extracted at the percent level or better if theoretical uncertainties are
neglected. Neither LHC nor ILC measurements alone will be sufficient to obtain
a stable result. The effects of theoretical uncertainties arising from unknown
higher-order corrections and parametric uncertainties are examined
qualitatively. They appear to be relevant and the result motivates further
precision calculations. The obtained parameters at the electroweak scale are
used for a fit of the parameters at high energy scales within the bottom-up
approach. In this way regularities at these scales are explored and the
underlying model can be determined with hardly any theoretical bias. Fits of
high-scale parameters to combined LHC+ILC measurements within the mSUGRA
framework reveal that even tiny distortions in the low-energy mass spectrum
already lead to inacceptable chi^2 values. This does not hold for ``LHC only''
inputs.Comment: 25 pages, 5 figure
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