Detecting The Neutral Top-pion At The High Energy Linear Colliders

The Standard Model (SM) is a pillar of success as low energy effective theory. No experimental deviations from the SM have yet been found. However, the SM can not explain dynamics responsible for the generation of mass. Furthermore, the scalar sector suffers from the problems of triviality and unnaturalness. So, people think there may be new physics beyond the Standard Model. The technicolor (TC) theory is one of the important promising candidates of new physics. In this paper, we introduce the topcolor-assisted technicolor theory(TC2), which is a popular theory in new physics at present. In the framework of TC2 models, we study the process of the neutral top-pion (Π_t~0) production.Firstly, we study a flavor-changing top-pion production process e~+e~-→tcΠ_t~0. The studies show that, with high centre of mass energy in TESLA collider, the production cross section of e~+e~-→tcΠ_t~0 is at the order of magnitude 0.1 fb in most parameter regions of TC2 model and a few tens events of top-pion can be produced each year. The resonance effect can enhance the cross section to a few fb when top-pion mass is small. With clean background, the top-pion events can possibly be detected at TESLA collider. On the other hand, we find that there exists a narrow peak near m_t — m_c in the toppion-charm invariant mass distribution which could be clearly detected. In addition, we investigate a process of the associated production of Π_t~0 with a pair of fermions's process: e~+e~-→ ffΠ_t~0 (f= u, d, c, s, t, b, e, μ, t) at future linear e~+e~- colliders. The largest cross section of the process e~+e-→ f'f'Π_t~0(f'= u,d.c, s,μ,τ) could only reach the level of 0.01fb. So, we can hardly detect top-pions through these process. For the process of e~+e~-→ e~+e~-Π_t~0, e~+e~-→ttΠ_t~0 and e~+e~-→ bbΠ_t~0, these cross section are at the order of magnitude of a few fb for the favorable parameters and a few hundreds of events of top-pion can be produced each year. We also find that the resonance effect enhance the cross section of the process of e~+e~-→ e~+e~-Π_t~0, and e~+e~-→ bbΠ_t~0, to a few fb and there is a narrow peak in the process of e~+e~-→e~+e~-Π_t~0 when M_Π = 350 GeV, which could be clear detected. Therefore, these processes of top-pion production provide us a unique way to detect neutral top-pion events and test TC2 model.Finally, we consider a neutral top-pion production process e~-r → e~Π_t~0 at er colliders . Our results show that the production cross section of e~-r→ e~-Π_t~0 can reach the level of several tens fb, and over 10~3 neutral top-pion events can be produced in the planned e~+e~- linear colliders each year. On the other hand, the cross section of e~-r→e~-Π_t~0 is about one order of magnitude larger than those of some similar processes in SM and MSSM(i.e., e~-r→e~-H in SM and e~-r→ e~-H~0(A~0,h~0)...