Study of high-transverse-monontum lepton productoin in ep collisions

我们利用德国DESY建造的e-p对撞机HERA研究了电子-质子散射中具有高横向能量的轻子的产生。与标准模型的预测相比，截面上的任何偏差都可能意味着新现象的产生，比如超对称粒子的产生。特别是，当我们开始这个项目时，一个实验报告了高能μ子产生的轻微过剩，因此迫切需要更高统计量的进一步搜索。在利用HERA ZEUS探测器采集的数据进行实验搜索的同时，还进行了基础理论研究，以了解对新现象的敏感性。从2002年开始，计划对HERA进行升级，以获得更高的亮度，并能够在碰撞中使用纵向极化电子。研究了极化对超对称粒子产生的影响，发现超对称粒子的横截面增大了一倍。为了从双光子过程中估计稀有背景，研制了一种新的蒙特卡罗发生器。对高动量μ子和τ子进行了搜索，发现它与W玻色子衰变的产生是一致的。高动量电子和中微子的产生也符合标准的中性和带电电流相互作用。根据这些结果，我们设定了超对称粒子、轻夸克和激发态费米子的质量/耦合极限。

We have studied productions of leptons with high transverse-energy in electron-proton scatterings with the e-p collider HERA built at DESY in Germany. Any deviation in the cross sections compared with the predictions of the standard model could imply new phenomena such as the production of supersymmetric particles. Especially, when we started the project, an experiment reported a slight excess of high energy muon production so that further searches with the higher statistics were urgently awaited.In parallel to experimental searches with the data taken by ZEUS detector at HERA, basic theoretical studies were performed in order to understand sensitivity to new phenomena. It is planned to upgrade the HERA to get higher luminosity and to enable to use longitudinally polarized electron in the collision since 2002. The effect of the polarization in the production of supersymmetric particles are studied and found that the cross section is doubled.In order to estimate the rare background from the two-photon processes, a new Monte Carlo generator was developed.Searches for high momentum muons and taus were performed and found that it is consistent to the production from W boson decays. High momentum electron and neutrino productions were also consistent with the standard neutral- and charged- current interactions. From these results we set limit in the mass/coupling of supersymmetric particles, leptoquarks and excited fermions.