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(L)(-)) and positron (e(R)(+)) beams which will soon be available at the upgraded HERA. Fully polarized e(-) or ef 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 similar to 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 to 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 signal of the stop is observed. We also point out that y (= Q(2)/sx) distributions of et coming from the stop shows different behavior from those of the standard model.