arXiv subjects

S. Hesselbach

Publications and source records attributed to S. Hesselbach.

At least 37 records · Page 2Linked to original sources

arXiv2006

Les Houches "Physics at TeV Colliders 2005'' Beyond the Standard Model working group: summary report

The work contained herein constitutes a report of the "Beyond the Standard Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. We present reviews of current topics as well as original research carried out for the workshop. Supersymmetric and non-supersymmetric models are studied, as well as computational tools designed in order to facilitate their phenomenology.

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arXiv2005

CP-odd observables in neutralino production with transverse e+ and e- beam polarization

We consider neutralino production and decay e^+e^ --> chi^0_i chi^0_j, chi^0_j --> chi^0_1 f \bar{f} at a linear collider with transverse e^+ and e^- beam polarization. We propose CP asymmetries by means of the azimuthal distribution of the produced neutralinos and of that of the final leptons, while taking also into account the subsequent decays of the neutralinos. We include the complete spin correlations between production and decay. Our framework is the Minimal Supersymmetric Standard Model with complex parameters. In a numerical study we show that there are good prospects to observe these CP asymmetries at the International Linear Collider and estimate the accuracy expected for the determination of the phases in the neutralino sector.

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arXiv2005

Supersymmetry Parameter Analysis: SPA Convention and Project

High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e+e- linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.

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arXiv2005

Identifying the NMSSM by the interplay of LHC and ILC

The interplay between the LHC and the $e^+ e^-$ International Linear Collider (ILC) with $\sqrt{s}=500$ GeV might be crucial for the discrimination between the minimal and next-to-minimal supersymmetric standard model. We present an NMSSM scenario, where the light neutralinos have a significant singlino component, that cannot be distinguished from the MSSM by cross sections and mass measurements. Mass and mixing state predictions for the heavier neutralinos from the ILC analysis at different energy stages and comparison with observation at the LHC, lead to clear identification of the particle character and identify the underlying supersymmetric model.

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arXiv2005

The role of polarized positrons and electrons in revealing fundamental interactions at the Linear Collider

The proposed International Linear Collider (ILC) is well-suited for discovering physics beyond the Standard Model and for precisely unraveling the structure of the underlying physics. The physics return can be maximized by the use of polarized beams. This report shows the paramount role of polarized beams and summarizes the benefits obtained from polarizing the positron beam, as well as the electron beam. The physics case for this option is illustrated explicitly by analyzing reference reactions in different physics scenarios. The results show that positron polarization, combined with the clean experimental environment provided by the linear collider, allows to improve strongly the potential of searches for new particles and the identification of their dynamics, which opens the road to resolve shortcomings of the Standard Model. The report also presents an overview of possible designs for polarizing both beams at the ILC, as well as for measuring their polarization.

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arXiv2005

Distinguishing between MSSM and NMSSM by combined LHC and ILC analyses

We show that the interplay between the LHC and the e^+ e^- International Linear Collider (ILC) with sqrt{s}=500 GeV might be crucial for the discrimination between the minimal and next-to-minimal supersymmetric standard model. We present an NMSSM scenario that cannot be distinguished from the MSSM by cross sections and mass measurements if only the light neutralinos and the lightest chargino are kinematically accessible, even if one of the neutralinos has a significant singlino component. Mass predictions for the heavier neutralinos from the ILC analysis and their observation at the LHC lead to an identification of the neutralino mixing character and the underlying supersymmetric model in a combined LHC/ILC analysis. In our numerical example we include errors in the mass measurements and use standard methods of supersymmetric parameter determination.

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arXiv2004

Standard Model and Beyond

We first discuss the basic features of electroweak 1-loop corrections in the Standard Model. We also give a short and elementary review on Higgs boson searches, grand unification, supersymmetry and extra dimensions.

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arXiv2004

A T-odd asymmetry in neutralino production and decay

We study CP-violating effects in neutralino production and subsequent decay within the Minimal Supersymmetric Standard Model with complex parameters M_1 and mu. The observable we propose is a T-odd asymmetry based on a triple product in neutralino production e^+ e^- -> tilde{chi}^0_i tilde{chi}^0_2, i = 1,...,4, with subsequent leptonic three-body decay tilde{chi}^0_2 -> tilde{chi}^0_1 l^+ l^-, l = e, mu, at an e^+ e^- linear collider with sqrt{s} = 500 GeV and polarised beams. We provide compact analytical formulae for the cross section and the T-odd asymmetry taking into account the complete spin correlations between production and decay. We give numerical predictions for the cross section and the T-odd asymmetry. The asymmetry can go up to 10 %.

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arXiv2004

Effects of CP phases on the Phenomenology of SUSY Particles

We review our recent studies on the effects of CP-violating supersymmetric (SUSY) parameters on the phenomenology of neutralinos, charginos and third generation squarks. The CP-even branching ratios of the squarks show a pronounced dependence on the phases of A_t, A_b, mu and M_1 in a large region of the supersymmetric parameter space, which can be used to get information on these phases. In addition we have studied CP-odd observables, like asymmetries based on triple product correlations. In neutralino and chargino production with subsequent three-body decays these asymmetries can be as large as 20%.

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arXiv2004

Effects of CP-violating phases in supersymmetry

Recent studies about the impact of the CP-violating complex parameters in supersymmetry on the decays of third generation squarks and about T-odd asymmetries in neutralino and chargino production and decay are reviewed. The CP-even branching ratios of the third generation squarks show a pronounced dependence on the phases of A_t, A_b, mu and M_1 in a large region of the supersymmetric parameter space. This could have important implications for stop and sbottom searches and the MSSM parameter determination in future collider experiments. We have estimated the expected accuracy in the determination of the parameters by global fits of measured masses, decay branching ratios and production cross sections. We have found that the parameter A_t can be determined with an error of 2 - 3%, whereas the error on A_b is likely to be of the order of 50 - 100%. In addition we have studied CP-odd observables, like asymmetries based on triple product correlations, which are necessary to unambiguously establish CP violation. We have analysed these asymmetries in neutralino and chargino production with subsequent three-body decays at the International Linear Collider with longitudinally polarised beams in the MSSM with complex parameters M_1 and mu. The asymmetries, which appear already at tree-level because of spin correlation between production and decay, can be as large as 20% and will therefore be an important tool for the search for CP-violating effects in supersymmetry.

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arXiv2004

Impact of CP phases on the search for top and bottom squarks

We study the decays of top squarks (~t_{1,2}) and bottom squarks (~b_{1,2}) in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters A_t, A_b, mu and M_1. We show that including the corresponding phases strongly affects the branching ratios of ~t_{1,2} and ~b_{1,2} decays in a large domain of the MSSM parameter space. This could have an important impact on the search for ~t_{1,2} and ~b_{1,2} and the determination of the underlying MSSM parameters at future colliders.

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arXiv2004

CP Violation in Supersymmetry

A review about some recent studies on the determination of the CP-violating complex parameters in supersymmetry at an e^+ e^- linear collider is presented. CP-even observables, like masses, cross sections and branching ratios, can have a strong dependence on the supersymmetric phases. However, CP-odd observables, like asymmetries based on triple product correlations, are necessary to unambiguously establish CP violation. In the chargino and neutralino sector these asymmetries can be as large as 30 % and will therefore be an important tool for the search for CP-violating effects in supersymmetry.

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arXiv2004

Physics Possibilities at a Linear Collider

We review some recent studies about the parameter determination of top quarks, W bosons, Higgs bosons, supersymmetric particles and in the ADD model of extra dimensions at a linear collider.

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arXiv2004

Top Squarks and Bottom Squarks in the MSSM with Complex Parameters

We present a phenomenological study of top squarks (~t_1,2) and bottom squarks (~b_1,2) in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters A_t, A_b, μand M_1. In particular we focus on the CP phase dependence of the branching ratios of (~t_1,2) and (~b_1,2) decays. We give the formulae of the two-body decay widths and present numerical results. We find that the effect of the phases on the (~t_1,2) and (~b_1,2) decays can be quite significant in a large region of the MSSM parameter space. This could have important implications for (~t_1,2) and (~b_1,2) searches and the MSSM parameter determination in future collider experiments. We have also estimated the accuracy expected in the determination of the parameters of ~t_i and ~b_i by a global fit of the measured masses, decay branching ratios and production cross sections at e^+ e^- linear colliders with polarized beams. Analysing two scenarios, we find that the fundamental parameters apart from A_t and A_b can be determined with errors of 1% to 2%, assuming an integrated luminosity of 1 ab^-1 and a sufficiently large c.m.s. energy to produce also the heavier ~t_2 and ~b_2 states. The parameter A_t can be determined with an error of 2 - 3%, whereas the error on A_b is likely to be of the order of 50%.

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arXiv2003

Impact of CP phases on SUSY particle production and decays

We report on the results of a phenomenological study of top squarks (stop_{1,2}) and bottom squarks (sbottom_{1,2}) in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters A_t, A_b, mu and M_1. In particular we focus on the CP phase dependence of the branching ratios of stop_{1,2} and sbottom_{1,2} decays. We find that the effect of the phases on the stop_{1,2} and sbottom_{1,2} decays can be quite significant in a large region of the MSSM parameter space. We also study a CP asymmetry in sfermion decays.

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arXiv2003

New Ideas on SUSY Searches at Future Linear Colliders

Several results obtained within the SUSY group of the ECFA/DESY linear collider study are presented: (i) a possibility to determine tan beta and the trilinear couplings A_f via polarisation in sfermion decays, (ii) the impact of complex MSSM parameters on the third generation sfermion decays, (iii) determination of CP violation in the complex MSSM via T-odd asymmetries in neutralino production and decay, and (iv) an analysis of the chargino and neutralino mass parameters at one-loop level.

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arXiv2003

Impact of SUSY CP Phases on Stop and Sbottom Decays in the MSSM

We study the decays of top squarks and bottom squarks in the Minimal Supersymmetric Standard Model with complex parameters A_t, A_b and mu. In a large region of the supersymmetric parameter space the branching ratios of stop_1 and sbottom_1 show a pronounced phase dependence. This could have an important impact on the search for stop_1 and sbottom_1 at a future linear collider and on the determination of the supersymmetric parameters.

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arXiv2003

Impact of CP phases on stop and sbottom searches

We study the decays of top squarks (stop_{1,2}) and bottom squarks (sbottom_{1,2}) in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters A_t, A_b, mu and M_1. We show that including the corresponding phases substantially affects the branching ratios of stop_{1,2} and sbottom_{1,2} decays in a large domain of the MSSM parameter space. We find that the branching ratios can easily change by a factor of 2 and more when varying the phases. This could have an important impact on the search for stop_{1,2} and sbottom_{1,2} and the determination of the MSSM parameters at future colliders.

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