arXiv subjects
Publications and source records attributed to Philip Bechtle.
We show that presently available precision data are in good agreement with supersymmetry at a mass scale below 1 TeV. Using a SUSY point close to the best fit to present data, we give a projection of the capabilities of the LHC to constrain SUSY models and their parameters as function of the accumulated luminosity.
The LEP collaborations ALEPH, DELPHI, L3 and OPAL have searched for the neutral Higgs bosons which are predicted within the framework of the Minimal Supersymmetric Standard Model (MSSM). The data of the four collaborations are statistically combined and show no signicant excess of events which would indicate the production of Higgs bosons. The search results are thus used to set upper bounds on the cross sections of various Higgs-like event topologies and limits on MSSM benchmark models, including CP-conserving and CP-violating scenarios. Here, the limits on the model parameters of the CP-violating benchmark scenario CPX and derivates of this scenario are shown.
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.
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.
We present the results of a realistic global fit of the Lagrangian parameters of the Minimal Supersymmetric Standard Model to simulated data from ILC and LHC with realistic estimates of the observable uncertainties. Higher order radiative corrections are accounted for where ever 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 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.