Study Of The New Physics Effect Related To Top Quark At Hadron Collider

The standard model(SM) of elementary particle has been extensively tested by the precise experimental data during the past 40 years. However, with the development of experimental and teoretical researches, it has been found that the SM still has some problems. Therefore, the exploration of new physics beyond the SM becomes one of the most inportant tasks in current particle physics. Due to the top quark with mass at electroweak scale, it is believed that top quark plays a special roles in the element particles zoo and will help us not only to understand the mechanism of electroweak symmetry breaking (EWSB) but also to explore the new physics signals.Recently, the top quark forward-backward asymmetry has been measured by the CDF and D0 collaborations at the Tevatron, which is a proton-antiproton collider at Fermi Lab. The result shows there is a more than 2σdiscrepancy between experimental value(AFB(exp)= 19 .6±6.9%) and theoretical value(AFB(SM)= 5 .0±1.5%). This deviation probably indicates the existence of new physics beyond the SM and has been studied in many new physics models in details. In our work, we examine the contribution to top quark AFB in the minimal supersymmetric model without R-parity (RPV-MSSM) and the third-generation enhanced left-right model (LR model). We find that under the constrains from the t t production rate and the t t invariant mass distribution, the LR model can enhance AFB to 12% in most part of the parameter space, which is slightly below the 1σbound. Nevertheless, for the RPV-MSSM, only in a narrow part of the parameter space, the AFB can be enhaced to within the 2σregionBesides the possible new physics signal manifesting in the top quark forward-backward asymmetry, the top quark flavor changing neutral current(FCNC) can be also served as the smoking gun for new physics. Due to the copious top quark production events at the large hadron collider(LHC), it provides an great opportunity for us to search the top quark FCNC sigmals. In this work, we havre studied the top quark FCNC production processes at LHC. The results show that, in contrast to the R parity conserving case, the production processes gg→tc, cg→t, cg→tγand cg→tZ except cg→th can reach the 3σsensitivity at LHC in the RPV-MSSM. These signals can be used as a compass to testify the RPV-MSSM and discriminate the different new physics models at LHC.