Wang Xue-Lei

Study on Charged Top-Pion Decay Processes*

In the framework of top-color assisted technicolor(TC2) theory, we study the four decay processes of charged top-pion, i.e., Π+t → tb, Π+t → cb, Π+t → Wγ, Π+t → WZ, the decay branching ratio of these modes are calculated. The results show that the main decay channels of charged top-pion are the tree level modes: Π+t → tb̄ and Π+t → cb̄. Light Π+t is easier to be detected than heavy one at future coliders. So, the study provides us some useful information to search for charged top-pion. PACS number(s): 12.60Nz, 14.80.Mz, 12.15.LK, 14.65.Ha This work is supported by the National Natural Science Foundation of China(10175017), the Excellent Youth Foundation of Henan Scientific Committee(02120000300), the Henan Innovation Project for University Prominent Research Talents(2002kycx009). E-mail:wangxuelei@263.netIn the framework of top-color assisted technicolor (TC2) theory, we study the four decay processes of charged top-pion, i.e., . The decay branching ratio of these modes are calculated. The results show that the main decay channels of charged top-pion are the tree level modes: and . Light is easier to be detected than heavy one at future coliders. So, the study provides us with some useful informations to search for charged top-pion.

Single Production of Vector-Like Top Quark in the Littlest Higgs Model at TeV Energy e−γ Colliders

The new colored vector-like heavy fermion T is a crucial prediction in little Higgs models, which plays a key role in breaking the electroweak symmetry. The littlest Higgs model is the most economical one among various little Higgs models. In the context of the littlest Higgs model, we study single production of the new heavy vector-like quark via eγ collisions and discuss the possibility of detecting this new particle in the TeV energy ee collider(LC). We find that the production cross section can vary in a wide range(10 − 10fb) in most parameter spaces. For the favorable parameter spaces, the possible signals of the vector-like top quark T can be easily detected via eγ collisions in future LC experiment with √ s = 3TeV and £ = 500fb. PACS number(s): 12.60.Cn, 14.70.Pw, 14.65.Ha ∗E-mail:hnxxlyb2000@sina.comThe existence of a new coloured vector-like heavy fermion T is a crucial prediction in little Higgs models, which play a key role in breaking the electroweak symmetry. The littlest Higgs model is the most economical one among various little Higgs models. In the context of the littlest Higgs model, we study single production of the new heavy vector-like quark and discuss the possibility of detecting this new particle in the future LC experiment. It is found that the production cross section is in the range of 1.7×10−3−30 fb at TeV energy electron–photon collider with (s)1/2 = 3 TeV and a yearly integrated luminosity of £ = 500 fb−1.

Single Production of Charged Top-Pions at High Energy Linear e+e- Colliders*

The dominant decay modes of charged top-pions are or . We consider the single production of charged top-pions in association with a top quark via e+e- annihilation and calculate the production cross section of the processes at the leading order. We find that it can reach 1.2 fb with reasonable parameter values. The charged top-pions may be detected via the channel in the future high energy e+e- colliders.

Detecting Toppion via a Flavor-Changing Single Top QuarkProduction Process*

In the framework of topcolor-assisted technicolor (TC2) theory, we study a flavor changing single top quarkproduction process pp(pp) →Ⅱ0t → tc(tc) at upgraded Tevatron and LHC. The results show that with the flavor changingcoupling of neutral toppion to top and charm quark, toppion provides a large te-channel resonance effect. The signal ofsingle top production could be detected at LHC. Otherwise, the narrow peak in the invariant mass distribution could beclearly detected both at upgraded Tevatron and LHC. Therefore, such single top production process provides a uniqueway to test TC2 model via the detection of tc-channel neutral toppion contribution.

Single Production of Top Quark via e− γ Collision in Left-Right Twin Higgs Model

In the context of the left-right twin Higgs (LRTH) model, we fist study single production of the standard model (SM) top quark via e−γ collisions. We find that the corrections of the LRTH model to the cross section of the process e− γ → νeb might be observed only for f ≤ 750 GeV and the heavy top quark mass scale M ≥ 500 GeV in future high energy linear e+e− collider (LC) experiment with the center-of-mass (CM) energy √s = 500 GeV and a yearly integrated luminosity of £ = 100 fb−1. We also consider single production of the heavy top quark T via e−γ collisions. Our numerical results show that the possible signals of the heavy top quark T might be observed via the decay channel T → +b → tb in future LC experiment with √s = 3 TeV and £ = 500 fb−1.

Single Charged Top-Pion Production at the Next Generation e+e− Colliders

The single charged top-pion production processes e+e−→tΠt− and e+e−→W+Πt− are studied in the framework of top-color-assisted technicolor (TC2) model. Our studies show that the cross section σ(e+e−→tΠt−) reaches the level of tens of fb and σ(e+e−→W+Πt−) reaches the level of a few fb. With the yearly integrated luminosity of £~500 fb−1 expected at the planned colliders, one could collect thousands of charged top-pion of events via the process e+e−→tΠt− and hundreds of events via the process e+e−→W+Πt−. The flavor changing decay mode Π−t→b is the best channel to detect charged top-pion due to the clean SM background. With a large number of events and the clean background, the charged top-pion should be observable at the planned colliders. Therefore, our studies in this paper can help us to search for charged top-pion, and furthermore, to test the TC2 model.

NLO Corrections of HTCΠ0 and Π+Π− Pair Production at ILC in TC2 Model

As well known, if the Higgs boson were not observed at LHC, the technicolor model would be the most favorable candidate responsible for the symmetry breaking. To overcome some defects in the previous model, some extended versions have been proposed. In the TC2 model typical signature is existence of heavy HTC and technipion Π. A direct proof of validity of the model is to produce them at accelerator. Thus we study the production rates of e+e− → HTCΠ0 and e+e− → Π+Π− at ILC in the topcolor-assisted technicolor (TC2) model. In fact, there is a flood of models belonging to new physics, which can result in products with characteristics similar to HTC + Π of the TC2 model. Therefore to distinguish this model from others one may need to investigate some details by calculating the cross section to NLO. We indeed find that the NLO corrections are significant, namely the ratio δ = (σNLO – σLO)/σLO in e+e− → HTCΠ0 exceeds 100% within a plausible parameter space.As well known, if the Higgs boson were not observed at LHC, the technicolor model would be the most favorable candidate responsible for the symmetry breaking. To overcome some defects in the previous model, some extended versions have been proposed. In the TC2 model typical signature is existence of heavy HTC and technipion Π. A direct proof of validity of the model is to produce them at accelerator. Thus we study the production rates of ee → HTCΠ and ee → ΠΠ at ILC in the topcolor-assisted technicolor (TC2) model. In fact, there is a flood of models belonging to new physics which can result in products with characteristics similar to HTC + Π of the TC2 model. Therefore to distinguish this model from others one may need to investigate some details by calculating the cross section to NLO. We indeed find that the NLO corrections are significant, namely the ratio δ ≡ (σNLO − σLO)/σLO in ee → HTCΠ exceeds 100% within a plausible parameter space.

Single Production of Charged Gauge Boson WH− from Left-Right Twin Higgs Model in Association with Top Quark at LHC

The twin Higgs mechanism has recently been proposed to solve the little hierarchy problem. In the context of the left-right twin Higgs (LRTH) model, we discuss single production of the new charged gauge boson WH−, which is predicted by the left-right twin Higgs model, in association with top quark at the CERN Large Hadron Collider (LHC). It is found that, for a typical nonzero value of mass mixing parameter M = 150 GeV in the LRTH model, the production cross section is in the range of 3 × 10-2 ~ 6.07 × 103 fb at the LHC. As long as the WH− is not too heavy, the possible signatures of the heavy charged gauge boson might be detected at the LHC experiments.

Charged Top-Pion Production Associated with a Gluon Jet at the LHC

The charged top-pions have been predicted by the topcolour-assisted technicolour (TC2) model and the observation of the charged top-pions can be regarded as the robust evidence of the model. We study the charged top-pion and gluon associated production at the LHC, i.e., pp ↠ g ∏t+. The cross section of this process can reach tens of pb, even hundreds ofpb, and there will be enough g∏t+ events produced at the LHC. Because the g∏t+ production is a flavour-changing (FC) process, the SM background can be greatly depressed. Furthermore, there exists an FC decay mode c for the charged top-pions, and such decay mode can provide us with the typical signals to detect the charged top-pions. Therefore, it is hopeful to find the charged top-pions via the g∏t+ production at the LHC.

Production of Neutral Top-Pion Associated with a Gauge Boson at LHC

In this paper, we study the production of the neutral top-pion (Π0t) associated with a gauge boson at the LHC, i.e. pp→Πt0V (V = g,W,Z,γ). The cross section of pp→Πt0g is at the level of 102 pb in the most parameter space. Such a process with the flavor-changing decay mode Πt0→t might provide viable signatures to detect Π0t at the LHC. The cross sections of other processes pp→Πt0W(Z,γ) are too small to detect Π0t, which open a window to distinguish the Higgs boson in the SM or MSSM from Π0t.