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S. Hesselbach

Publications and source records attributed to S. Hesselbach.

49 records · Page 3Linked to original sources
arXiv2002

Sfermion Precision Measurements at a Linear Collider

At future e+- e- linear colliders, the event rates and clean signals of scalar fermion production - in particular for the scalar leptons - allow very precise measurements of their masses and couplings and the determination of their quantum numbers. Various methods are proposed for extracting these parameters from the data at the sfermion thresholds and in the continuum. At the same time, NLO radiative corrections and non-zero width effects have been calculated in order to match the experimental accuracy. The substantial mixing expected for the third generation sfermions opens up additional opportunities. Techniques are presented for determining potential CP-violating phases and for extracting tan(beta) from the stau sector, in particular at high values. The consequences of possible large mass differences in the stop and sbottom system are explored in dedicated analyses.

hep-ph↗
arXiv2002

Singlino-dominated Neutralinos in Extended Supersymmetric Models

We adopt the SUSY benchmark scenario SPS 1a in supersymmetric models where the Higgs sector is extended by singlet superfields. We consider light neutralinos with dominant singlino character whose couplings are generally suppressed. The cross sections for direct production of the singlino-dominated neutralinos can be of the order of several fb for singlet vevs of some TeV. Hence even exotic neutralinos which are not the LSP and are omitted in the decay chains of the other supersymmetric particles may be visible at a high luminosity linear e^+e^- collider. If, however, the LSP is singlino-dominated the decay width of the NLSP can be very small and displaced vertices exist for large singlet vacuum expectation values.

hep-ph↗
arXiv2002

Testing radiative neutrino mass generation via R-parity violation at the Tevatron

An R-parity violating SUSY model with lepton-number violating couplings $λ'_{i33}$, i=2,3 can generate a neutrino mass spectrum that explains the recent results from neutrino oscillation experiments. These R-parity violating couplings lead to a clean signal with at least one isolated lepton and at least three tagged $b$ jets that is accessible in chargino and neutralino production at the Tevatron collider. This signature can be probed at $3 σ$ up to $m_{1/2} = 230$ GeV (320 GeV) with an integrated luminosity of $2 fb^{-1}$ ($30 fb^{-1}$).

hep-ph↗
arXiv2001

Production of singlino dominated neutralinos in extended supersymmetric models

Neutralinos with a large singlino component may appear in extended supersymmetric models with additional singlet Higgs fields. Since singlinos do not couple to (s)fermions and gauge bosons, the cross sections for the production of singlino dominated neutralinos are generally small. Within the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and an E_6 inspired model we study neutralino production e^+ e^- --> neutralino_1 neutralino_2 (neutralino_1,2 neutralino_3) with a singlino dominated neutralino_2 (neutralino_3). It is shown that neutralinos with a singlino contribution up to 99 % can be produced with a cross section larger than 1 fb and may therefore be detected at a high luminosity e^+ e^- linear collider even if they are not the LSP.

hep-ph↗
arXiv2001

Neutralinos in E_6 inspired supersymmetric U(1)' models

The neutralino sector in E_6 inspired supersymmetric models with extra neutral gauge bosons and singlet Higgs fields contains additional gaugino and singlino states compared to the MSSM. We discuss the neutralino mixing in rank 5 and rank 6 models and analyze the supersymmetric parameter space where the light neutralinos have mainly singlino or MSSM character. The neutralino character, resonance effects of the new gauge bosons and, assuming mSUGRA-type RGEs, different selectron masses lead to significant differences between the MSSM and the extended models in neutralino production at an e^+e^- linear collider. Beam polarization may improve the signatures to distinguish between the models. In an appendix, we present the mass terms of the gauge bosons, charginos and sfermions which show a significant different mass spectrum than in the MSSM and give all relevant neutralino couplings.

hep-ph↗
arXiv2000

Displaced Vertices in Extended Supersymmetric Models

In extended supersymmetric models with additional singlet Higgs fields displaced vertices could be observed if the decay width of the next-to-lightest supersymmetric particle becomes very small due to a singlino dominated LSP. We study the supersymmetric parameter space where displaced vertices of the second lightest neutralino exist in the NMSSM and an E6 inspired model. For a mass difference between LSP and NLSP of more than 10 GeV the singlet vacuum expectation value has to be at least of the order of 100 TeV in order to obtain a lightest neutralino with a singlino component large enough for displaced vertices.

hep-ph↗
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↗
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↗
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

Neutralino mass bounds at the upgraded LEP collider

Assuming that no supersymmetric signature will be found at the upgraded LEP collider we derive lower bounds on the masses of the four neutralinos $\tildeχ_i^0$ in the Minimal Supersymmetric Standard Model (MSSM). We consider the recently published results from the search for the light chargino $\tildeχ^\pm_1$ and the next-to-lightest neutralino $\tildeχ^0_2$ at LEP1.5 and study the consequences of possible future lower $\tildeχ^\pm_1$ and $\tildeχ^0_2$ mass limits between 65 and 95 GeV. For a chargino mass bound of 66.8 GeV at LEP1.5, a massless neutralino is not excluded for $\tanβ< 1.2$. If either $\tanβ> 2.3$ or the gluino mass $m_{\tilde{g}} > 160$ GeV, we find $m_{\tildeχ_1^0} > 28$ GeV. A possible chargino bound $m_{\tildeχ_1^\pm} > 95$ GeV at LEP2 would raise this bound to 31 GeV (for all $\tanβ$) or 44 GeV ($\tanβ> 2$).

hep-ph↗