The automatic computation for SUSY processes

We have constructed a system for the automatic computation of cross-sections for the processes of the SUSY QED by the extension of the GRACE system including a Majorana fermion. The system has also been applied to another model including Majorana fermions, MSSM, by the definition of the model file.Comment: total 4 page

Is a high PTP_T muon of the e+p→μ+Xe^+p \to \mu^+ X event observed at HERA a signature of the stop?

We investigate the $e^+p \to \mu^+ X$ event with high transverse momenta observed at HERA (H1) and show that this event could be interpreted as a signature of the single production of the scalar top quark in a supersymmetric model with $R$-parity breaking interactions. The event topology of the H1 event is rather characteristic and in fact it can be simulated by our specific scenario if we reasonably choose our model parameters to be ({\romannumeral 1}) $m_{{\widetilde{d}},{\widetilde{b}}, {\widetilde{\nu}}}$ ${{\stackrel{>}{\sim}}}$ $1$TeV [$0.8$TeV] for ${\lambda'_{131}}$ $=$ $0.1$ [$0.05$] and ({\romannumeral 2}) $m_{{\widetilde{W}}_{1}}$ ${{\stackrel{<}{\sim}}}$ $150$GeV, $100$GeV ${{\stackrel{<}{\sim}}}$ $m_{{\widetilde{t}}_1}$ ${{\stackrel{<}{\sim}}}$ $200$GeV and ${\lambda'_{131}}$ ${{\stackrel{>}{\sim}}}$ $0.05$.Comment: 8 pages, LaTeX, 4 figures (included in a separate .uu file

Single scalar top production with polarized beams in ep collisions at HERA

From the point of view of the R-parity breaking supersymmetric model, we propose a scalar top (stop) search with longitudinally polarized electron (e-) and positron(e+) beams which will soon be available at the upgraded HERA. Fully polarized e- or e+ beams could produce the stop two times as much as unpolarized beams, while they increase background events due to the process of the standard model by about 30% in comparison with unpolarized ones. We show that right-handed e+ beams at HERA is efficient to produce the stop in the model. With 1 fb**(-1) of integrated luminosity we estimate reach in the coupling constant lambda'(131) for masses of the stop in the range 160-400 GeV. We can set a 95% confidence-level exclusion limit for lambda'(131) > 0.01-0.05 in the stop mass range of 240-280 GeV if no singal of the stop is observed. We also point out that y(=Q**2/sx) distributions of e+ coming from the stop shows the different behavior from those of the standard model.Comment: 12 pages, 6 eps figure

Single Sbottom/Scharm Production at HERA in an R-Parity Breaking Supersymmetric Model

We investigate the production process of the single scalar bottom quark (sbottom) and scalar charm quark (scharm) at HERA. The sbottom and scharm could be produced via an R-parity breaking interactions $\lambda'_{123} \neq 0$ in the Minimal Supersymmetric Standard Model (MSSM). These processes give a slight excess in the invariant mass $M_{eq}$ distribution of the high $Q^2$ deep inelastic scattering for sufficiently heavy gauginos and the scalar top (stop). For the light gauginos and stop, it is shown that the tagging of $b/c$-quarks and charged leptons with high transverse energies will be indispensable to search for the processes.Comment: 11 pages, 4 figures Added reference