Searcharxiv⌕ Search

arXiv subjects

H. Fraas

Publications and source records attributed to H. Fraas.

At least 55 records · Page 3Linked to original sources
arXiv2000

Neutralino Production with Polarized Beams in Extended Supersymmetric Models

We discuss associated neutralino production e^+ e^- --> \tildeχ^0_1 \tildeχ^0_2 with both beams polarized in the MSSM, NMSSM and an E_6 model. It is shown that neutralinos with a large singlino component can be produced at a high luminosity linear collider in a broad parameter range. Polarization effects in the extended models are compared over the whole parameter space where the lightest neutralino is mainly a singlino. We explain the complete different behavior of these models in some parameter regions, which may help to identify the respective supersymmetric model.

hep-ph↗
arXiv2000

Exploiting Spin Correlations in Neutralino Production and Decay with Polarized e^- and e^+ Beams

We study the production process e^+ e^- -> chi^0_1 chi^0_2 and the subsequent decay chi^0_2 -> chi^0_1 l^+ l^- with polarized e^+ and e^- beams, including the spin correlations between production and decay. We work out the advantages of polarizing both beams. We study in detail the angular distribution and the forward--backward asymmetry of the decay lepton as well as the opening angle distribution between the decay leptons. We investigate the dependence on the masses of tilde{e}_L and tilde{e}_R and on the mixing character of the neutralinos. In particular we study the dependence on the gaugino mass parameter M_1.

hep-ph↗
arXiv2000

Possible Test of the GUT Relation between $M_1$ and $M_2$ in Electron-Photon Scattering

We investigate associated production of selectrons and the lightest neutralino (LSP) in the process e^- + gamma --> neutralino_1 + selectron_{L/R} with the selectron subsequently decaying into an electron and the LSP. Total cross sections and various polarization asymmetries are calculated for photons produced by Compton backscattering of a polarized laser beam at an $e^+e^-$ linear collider with CMS energy $\sqrt{s_{ee}}=500$ GeV and with polarized beams. The total cross section and in particular the polarization asymmetries show a characteristic dependence on the gaugino mass parameter $M_1$. Therefore this process is suitable for testing the GUT relation $M_1=M_2\cdot{5/3}\tan^2θ_W $.

hep-ph↗
arXiv1999

Selectron Mass Effects in Neutralino Production

We study the possibility to measure the masses of the selectrons in neutralino production at an e^+ e^- linear collider with polarized beams. The cross sections and polarization asymmetries of neutralinos with gaugino character strongly depend on the masses of the exchanged selectrons. If the usual GUT relations of the selectron masses in the MSSM are relaxed large effects are possible especially in the polarization asymmetries. These can be used to determine the masses of both selectrons.

hep-ph↗
arXiv1999

Polarization and Spin Effects in Neutralino Production and Decay in Supersymmetric Models

We study polarization and spin correlation effects in the MSSM and in extended supersymmetric models at an e^+e^- linear collider with polarized beams. The production of light neutralinos e^+ e^- --> \tildeχ^0_1 \tildeχ^0_2 and the subsequent decay \tildeχ^0_2 --> \tildeχ^0_1 e^+ e^- including full spin correlations is compared in three supersymmetric models: MSSM, NMSSM and an E_6-inspired model with an additional U(1)' gauge group. It is shown that polarization and spin effects can lead to a complete different behavior of these models. Finally, the dependence of the cross section and the decay angular distribution on the gaugino mass parameter M_1 for polarized beams is briefly outlined.

hep-ph↗
arXiv1999

Polarization and Spin Effects in Neutralino Production and Decay

We study the production of neutralinos e^+ e^- ->chi^0_i χ^0_j with polarized beams and the subsequent decays chi^0_i -> chi^0_k l^+ l^- and chi^0_j -> chi^0_l l^+ l^-, including the complete spin correlations between production and decay. We present analytical formulae for the differential cross section of the combined process of production and decay of neutralinos. We also allow for complex couplings. The spin correlations have a strong influence on the decay angular distributions and the corresponding forward-backward asymmetries. They are very sensitive to the SUSY parameters and depend strongly on the beam polarizations. We present numerical results for the cross section and the electron forward-backward asymmetry for e^+ e^- -> chi^0_1 chi^0_2, chi^0_2 -> chi^0_1 e^+ e^-. We study the dependence on the parameter M' for various mass splittings between tilde{e}_L and tilde{e}_R and different beam polarizations.

hep-ph↗
arXiv1999

Constraining the Sneutrino Mass in Chargino Production and Decay with Polarized Beams

Production and decay of gaugino-like charginos are crucially determined by sneutrino exchange. Therefore we study the pair production of charginos e^+ e^- -> chi^+_1 chi^-_1 with polarized beams and the subsequent decay chi^-_1 -> chi^0_1 e^- nu_e, including the complete spin correlations between production and decay. The spin correlations have strong influence on the decay angular distribution and on the corresponding forward-backward asymmetry. We show for two representative scenarios for sqrt{s}=270 GeV and for sqrt{s}=500 GeV that forward-backward asymmetries for polarized beams are an important tool for constraining the sneutrino mass m_{tilde{nu}_e}.

hep-ph↗
arXiv1998

Spin Correlations in Production and Subsequent Decay of Neutralinos

We study the process e^{-} e^{+} -> chi^0_1 chi^0_2 with the subsequent decay chi^0_2 -> chi^0_1 l^{+} l^{-} taking into account the complete spin correlations. We give the analytical formulae for the differential cross section and present numerical results for the lepton angular distribution and the distribution of the opening angle between the outgoing leptons for the LEP2 energy of sqrt{s}=193 GeV and for sqrt{s}=500 GeV. We examine three representative mixing scenarios in the MSSM and also study the influence of the common scalar mass parameter m_0 on the shape of the distributions. For the lepton angular distribution the effect of the spin correlations amounts to up to 20% for lower energies. We find that the opening angle distribution is suitable for distinguishing between higgsino-like and gaugino-like neutralinos. The shape of the lepton angular distribution is very sensitive to the mixing in the gaugino sector and to the value of m_0. For higher energies it is also suitable for distinguishing between higgsino-like and gaugino-like neutralino.

hep-ph↗
arXiv1998

Spin Correlations in Production and Decay of Charginos

We study the production of charginos e^+ e^- -> chi^+_i chi^-_j, (i,j=1,2) with polarized beams and the subsequent decays chi^+_i -> chi^0_k ell^+ nu and chi^-_j -> chi^0_l ell^- nu, (k,l=1,...,4), including the complete spin correlations between production and decay. Analytical formulae are presented for the joint spin-density matrix of the charginos, for the chargino decay matrix and for the differential cross section of the combined processes of production and decays. We present numerical results for pair production of the lighter chargino with unpolarized beams and the leptonic decay of chi^+_1 into the lightest neutralino chi^0_1. The lepton angular distribution and the forward-backward asymmetry are studied in four representative scenarios for sqrt{s}=192 GeV and sqrt{s}=200 GeV.

hep-ph↗
arXiv1998

Spin Effects in Neutralino Production in $e^+e^-$ Annihilation with polarized beams

We study the process e^+ e^- -> chi^0_1 chi^0_2 and the subsequent decay chi^0_2 -> chi^0_1 l^{+} l^{-}$ with polarized beams, including the complete spin correlations of chi^0_2$. We present numerical results for the lepton energy and angular distributions, and for the distribution of the opening angle between the leptons for sqrt{s}=500 GeV. The effects of spin correlations are important in the lepton angular distribution, especially for gaugino-like neutralinos. The opening angle distribution is particularly suitable for distinguishing between higgsino- and gaugino-like neutralinos. The polarized cross sections and lepton angular distributions are very sensitive to the mixing of the neutralinos.

hep-ph↗
arXiv1997

Angular and Energy Distribution in Neutralino Production and Decay with complete Spin Correlations

We study the process e^{-}e^{+} \to \tildeχ^0_1\tildeχ^0_2 with the subsequent decay \tildeχ^0_2 \to \tildeχ^0_1 \ell^{+}\ell^{-} taking into account the complete spin correlations between production and decay. We present numerical results for the lepton angular distribution and the distribution of the opening angle between the outgoing leptons for \sqrt{s}=182 GeV. We examine representative mixing scenarios in the MSSM and study the influence of the common scalar mass parameter m_0. For the lepton angular distribution the effect of the spin correlations amounts to up to 20%. The shape of the lepton angular distribution is very sensitive to the mixing in the gaugino sector and to the value of m_0. We find that the opening angle distribution is suitable for distinguishing between Higgsino-like and gaugino-like neutralinos.

hep-ph↗
arXiv1997

Production of neutralinos in superstring-inspired E_6 models

We study the neutralino mass spectra and production cross sections at an e^+e^- linear collider in superstring-inspired E_6 models. These models are characterized by the existence of new neutral gauge bosons and singlet Higgs fields which also lead to an extended neutralino sector compared to the Minimal Supersymmetric Standard Model (MSSM) or the Next-To-Minimal Supersymmetric Standard Model (NMSSM). For different E_6 models we develop scenarios with new light exotic neutralinos which may offer important possibilities to distinguish between the models.

hep-ph↗
arXiv1997

Chargino-Sneutrino Production in Electron-Photon Collisions

We study the production of charginos and sneutrinos in electron-photon collisions within the minimal supersymmetric standard model (MSSM). The high energy photons can be generated by Compton backscattering of intense laser pulses off one of the beams of the Next Linear Collider (NLC). This process could offer a significant opportunity to identify sneutrinos, which exclusively decay invisibly into a neutrino and the LSP, since the cross sections are two orders of magnitude higher than for the radiative production of invisible sneutrinos. For three scenarios of gaugino-higgsino mixing the cross sections and polarization asymmetries are computed and the resulting signatures are compared with the SM background.

hep-ph↗
arXiv1996

Searches For New Physics

Review of prospects for discovery of new physics signals at LEP2. The areas covered include SUSY, exotic fermions, BESS models, leptoquarks, virtual effects and CP violating observables.

hep-ph↗
arXiv1995

Neutralinos and Higgs Bosons in the Next-To-Minimal Supersymmetric Standard Model

The purpose of this paper is to present a complete and consistent list of the Feynman rules for the vertices of neutralinos and Higgs bosons in the Next-To-Minimal Supersymmetric Standard Model (NMSSM), which does not yet exist in the literature. The Feynman rules are derived from the full expression for the Lagrangian and the mass matrices of the neutralinos and Higgs bosons in the NMSSM. Some crucial differences between the vertex functions of the NMSSM and the Minimal Supersymmetric Standard Model (MSSM) are discussed.

hep-ph↗
arXiv1995

Production and Decay of Neutralinos in the Next-To-Minimal Supersymmetric Standard Model

Within the framework of the Next-To-Minimal Supersymmetric Standard Model (NMSSM) we study neutralino production $e^+e^- \longrightarrow \tildeχ^0_i \tildeχ^0_j$ ($i,j=1,\ldots ,5$) at center-of-mass energies between 100 and 600 GeV and the decays of the heavier neutralinos into the LSP plus a fermion pair, a photon or a Higgs boson. For representative gaugino/higgsino mixing scenarios, where the light neutralinos have significant singlet components, we find some striking differences between the NMSSM and the minimal supersymmetric model. Since in the NMSSM neutralino and Higgs sector are strongly correlated, the decay of the second lightest neutralino into a Higgs boson and the LSP often is kinematically possible and even dominant in a large parameter region of typical NMSSM scenarios. Also, the decay rates into final states with a photon may be enhanced.

hep-ph↗
arXiv1995

Mass Bounds for the Neutral Higgs Bosons in the Next-To-Minimal Supersymmetric Standard Model

In the Next--To--Minimal Supersymmetric Standard Model (NMSSM), the Higgs and neutralino/chargino sectors are strongly correlated by four common parameters at tree level. Therefore we analyze the experimental data from both the search for Higgs bosons as well as for neutralinos and charginos at LEP 100 in order to constrain the parameter space and the masses of the neutral Higgs particles in the NMSSM. We find that small singlet vacuum expectation values are ruled out, but a massless neutral Higgs scalar and pseudoscalar is not excluded for most of the parameter space of the NMSSM. Improved limits from the neutralino/chargino search at LEP 200, however, may lead to nonvanishing lower Higgs mass bounds.

hep-ph↗