Study On Charged Top-pion Production At LHC

Although the Standard Model (SM) of particle physics has been tested by a great many experime-nt in an extreme precision since its foundation. However, the Higgs boson has not yet been discovered.Furthermore, models with an elementary scalar field suffer from some theoretical problems such as thehierarchy problem, and the elementary Higgs models provide no dynamical explanation for the electro-weak symmetry breaking. Analysis in many aspects tends to agree the existence of new physics beyondthe SM. On the other hand, technicolor (TC) theory proposed a scheme for the dynamical electroweaksymmetry breaking (EWSB), and topcolor (TopC) can produce a large top mass, then the Topcolor–Assisted Technicolor Model (TC2Model) emerged as a version of TC theory constructed by combin-ing the technicolor and topcolor (TC), with the prediction on the existence of the pseudo-scalar tripletparticles, top-pions (Π±,0t), which is a distinct signal for the new physics.The Large Hadron Collidr (LHC) is constructed for the purpose of probing the Higgs boson in theSM and new physics beyond the SM, and many theories say there exist new physics at LHC. ATLASand CMS are two general purpose detectors at the LHC. High-precision devices of the detectors andhighly active scheme of data processing are crucial precondition for the data acquisition and analysis,and the design of the event selection scheme must be made by combining with the feature of the signaland the background. It’s one of the most complicated tasks to measure the parameters of the hardonjets in the data processing at LHC.The parton distribution functions (PDFs) are essential inputs required to make theoreticalpredictions for the LHC and other hadron scattering facilities. They are extracted from a comprehen- sive global analysis of hard-scattering data in some factorized scheme in the framework of perturbativeQCD. The heavy quark distribution function are closely related to the gluon collinear splitting.We start with a discussion of the production of Π±tcb, and then study the production anddetection ofΠ~±_tat LHC and Tevatron systematically, where the mass ofΠ~±_tis in the region of100GeV to600GeV. We have analyzed four methods:(1) by counting the total number of events through the total cross section of single charged top-pion production. This method is only practicable for the lepton-decaying signals of top-pion while thehadron jet signals are hardly to distinct from the large QCD background. At LHC, the total productioncross section can range from sevaral to thousands pb depending on the mass of top-pion and the contri-bution fromΠ~±_tproduction in final state excluding top quark is larger than the case including top.(2) by counting the number of the cb→Π*t→c/t+bevents, whose background is cleanbecause it is a flavor changing process. The total production cross section can reach range from102~105fbwith a cut on the transverse momentum pT≥20GeVand the pseudo-rapidity|η|≤2.5for the final state particles at LHC depending on the mass of the top-pion while can onlyrange from103~103fbat Tevatron.(3) by counting the number of the Πt+x(x=t,c,b,g)events. It seems unpractical to tagthis kind of events because of the background, although the cross sections can reach sevaral to thou-sands pb at LHC even with a cut on the transverse momentum pT≥20GeVand the pseudo-rapidity|η|≤2.5for the final state particles, while105~10pbwithout cut at tevatron.(4) by counting the number of the Πt+x+x(x=t,c,b,g)events which can yield hadronic4jets.At Tevatron, the Π±tcbproduction is mainly through the gg-fusion processes while the Π±ttbmainlythrough the qq annilation; at LHC, both are mainly through gg-fusion and the number of the Π~±_ttb events is larger than the Π±tcbevents, although the Π±ttbproduction cross section is smaller. Theresults show σ (pp→Π t+x+x+X)>σ(pp→Π t+x+X)>σ(pp→Π t+X).There mayexist two cases for the detection:(a)4jets are detected, and then it can be treated as a candidate events if theqq are not in pair, that is, with zero total transeverse momentum.(b)3jet (+EmissT)are detected, and wecalculate the cross section of Π±tc(t)bproduction with a cut on the transverse momentumpT(c/t,b)≥80GeV,pT(Π t)≥160GeV,and the pseudo-rapidity|η (c/t,Πt)|≤2.5for the finalstate particles for the threshold of detector and under which condition events includieng at least three jetscan be detected, whose background is realatively clean,and the cross section can reach tens to thousands fbfor Π±tcband Π±ttb, respectively. Obviously, our results can provide a lower bound for the theoreticalprediction.We look with special favor on the method (2) and (4), however, they need to be tried out. Generallyspeaking, our results would provide some worthful references for the detection, and, for the determinationof the parameter space for the other two Higgs doublet models.