Associated production of a neutral top-Higgs with a heavy-quark pair in the γγ collisions at ILC

We have studied the associated production processes of a neutral top-Higgs in the topcolor assisted technicolor model with a pair of heavy quarks in γγ collisions at the International Linear Collider (ILC). We find that the cross section for ttht in γγ collisions is at the level of a few fb with the c.m. energy √s=1000 GeV, which is consistent with the results of the cross section of ttH in the standard model and the cross section of tth in the minimal supersymmetric standard model. It should be clear that hundreds of to thousands of ht per year can be produced at the ILC. This process of γγ→ttht is really interesting in testing the standard model and searching the signs of technicolor.     

Production of Top-Pions Associated with W Boson at Next Generation γγ Colliders

In the context of topcolor-assisted technicolor （TC2） model, we study the charged and neutral top-pions production process γγ →W＋ ∏t-∏t^0. We find that the production cross section is larger than that of the process γγ→ W＋ H-H in the minimal supersymmetric standard model. With reasonable values of the parameters in the TC2 model, the cross section can reach the level of a few fb. Furthermore, the flavor-changing （FC） decay mode ∏t^0 → te^- is the best channel to detect the neutral top-pion due to the clean SM background. With a large number of events and the clean background, the neutral top-pion should be observable at future linear colliders operating in γγ mode at the TeV energy scale.     

Probing the TC2 model via Production of Top Quark Pairs at Tevatron and LHC

The topcolour-assisted technicolour （TC2） model is an interesting dynamical theory among the various new physics models. We cMculate the total tt cross section and the relative correction of the TC2 model to the cross section at Tevatron Run Ⅱ and LHC. At the Tevatron Run Ⅱ, the cross section predicted by the standard model （SM） is consistent with the experimental data, and in most parameter spaces of the TC2 model, the relative correction of the TC2 model to the cross section is too small to be detectable. We find that the tt cross section is more sensitive to the parameters of the TC2 model at the LHC and the relative correction of the TC2 model to the cross section is over 10% in general. Such a value of the relative correction should be large enough to be detectable at the LHC. Therefore, it is promising to find the clue of the TC2 model via the tt production at the LHC.     

Searching for Flavor-Changing Neutral-Current Signals via e＋e-（γγ） →tcht0 in Topcolor-Assisted Technicolor Model

In the context of the top-color-assisted technicolor （TC2） model, the flavor-changing neutral-current （FCNC） interaction induced by the top-higgs （hOt） are predicted at tree level. We study the relevant processes of e＋e-（γγ）→tcht0 at the International Linear Collider （ILC）. It is found that these rare processes production rates can be enhanced significantly in the TC2 model. Especially for the process γγ→tcht0, the total cross section will reach a few fb in the reasonable parameter space. We also calculate the distributions of transverse momenta, pseudo-rapid and invariant mass of the top-higgs. In view of the main decay modes of top-higgs for mho 〈 2mr, we find that there will be several hundreds FCNC events produced at the ILC with annually integral luminosity of 500 fb-1. Due to the clean background, such FCNC signals can possibly be detected at the ILC.     

Charged Top-Pion Production at e^＋e^- and γγ Colliders

We study the charged top-pion in the topcolor assisted technicolor model（TC2）, and calculate the production of charged top-pion at e^＋ e^- and γγ colliders. At an e^＋ e^- collider, charged top-pion can be produced via the processes e^＋e^- → t^bπt^-（^tbπt^＋）. At a γγ collider, it can be produced via the processes γγ →t^bπt^-（t^-bπt^＋）. The cross section can reach to a few of fb depending on the mass of the charged top-pion.     

Top pair production in the littlest Higgs model with T-parity

In the framework of the littlest Higgs model with T-parity, we study the top pair production at the next generation colliders like LHC and ILC. We find that the order O（αs） corrections to the standard model top pair production cross section at LHC can be very small and the magnitude is below 1%. However, the magnitude of corrections to the standard model top pair production rate at ILC may be over 5% for reasonable values＇of the parameters. Besides this, the corrections to the asymmetry ALR（tt） may be more sizable. Therefore, the top pair production at ILC may serve as a probe of the littlest Higgs model with T-parity, especially the asymmetry ALR（tt）.     

Dark-matter pair production at the ILC in the littlest Higgs model with T-parity

In the littlest Higgs model with T-parity, the heavy photon (A_H) is supposed to be a possible dark matter (DM) candidate. The direct proof of the validity of this model is to produce the heavy photon at an accelerator. In this paper, we study the production rate of e~+ e~- → AH AH at the international e~+ e~- linear collider (ILC) in the littlest Higgs model with T-parity, and show the distributions of the transverse momenta of A H . The numerical results indicate that the heavy photon production rate could reach the 10~-1 fb level at some parameter space, so this could be a good chance to observe the heavy photon via the pair production process with high luminosity at the ILC (500 fb~-1). We know that DM is composed of weakly interacting massive particles, so the interactions with standard model particles are weak. How to detect heavy photons at a collider and distinguish them from other DM candidates are discussed in the final section of the paper.     

NLO Corrections of HTC∏^0 and ∏＋∏- 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 ∏. A direct proof of validity of the model is to produce them at accelerator. Thus we study the production rates of e＋e^- → HTC∏^0 and e＋e^- → ∏＋∏- 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 ＋ ∏ 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- →HTC∏^0 exceeds 100% within a plausible parameter space.     

Top-Higgs htO and the Process γγ→ ZZ

In the context of topcolor-assisted technicolor (TC2) models, we calculate the s-channel contributions ofthe top-Higgs htO to the process γγ→ ZZ. We find that, for reasonable ranges of the parameters, htO can give significantcontributions to this process. When the top-Higgs mass approximately equals to the center-of-mass energy √s and thefree parameter e = 0.01, the cross section can reach 161 fb, which may be detected in the γγ collisions based on thefuture e+e- colliders. Thus, the process γγ→ ZZ may be used to probe the top-Higgs and further test TC2 models inγγ collisions.     

Searches for the technicolor signatures via gg→W～(±)π_t～(■) at the Large Hadron Collider

In this paper,we calculate the production of a charged top pion in association with a W boson via gg fusion at CERN's Large Hadron Collider in the context of the topcolor assisted technicolor model.We find that the total cross section of pp→gg→W～(±)π_t～(■) is several dozen femtobarns with reasonable values of the parameters,and the total cross section of pp→W～(±)π_t～(■) can reach a few hundred femtobarns when we consider the sum of the contributions of these two parton subprocesses,gg→W～(±)π_t～(■) and b→W～...     

Near-threshold η production in pp collisions

We study near-threshold η meson production in pp collisions within an effective Lagrangian approach combined with the isobar model, by allowing for the various intermediate nucleon resonances due to the π, η, and ρ-meson exchanges. It is shown that the ρ-meson exchange is the dominant excitation mechanism for these resonances,and the contribution from the N*(1720) is dominant. The total cross section data can be reasonably reproduced,and the anisotropic angular distributions of the emitted η meson are consistent with experimental measurements.Besides, the invariant mass spectra of pp and pη explain the data well at excess energy of 15 Me V, and are basically consistent with the data at excess energy of 40 Me V. However, our model calculations cannot reasonably account for the two-peak structure in the pη distribution at excess energies of 57 and 72 Me V, which suggests that a more complicated mechanism is needed at higher energy region.     

Surface Emission of Quark Gluon Plasma at RHIC and LHC

Within the framework of a factorization model, we study the behaviour of nuclear modification factor in Au Au collisions at RHIC and Pb-Pb collisions at LHC. We find that the nuclear modification factor is inversely proportional to the radius of the quark-gluon plasma and is dominated by the surface emission of hard jets. We predict the nuclear modification factor R^LHC AA - 0.15 in central Pb-Pb collisions at LHC. The study shows that the factorization model can be used to describe the centrality dependence of nuclear modification factor of the high transverse momentum particles produced in heavy ion collisions at both RHIC and LHC.     

Correction of the Littlest Higgs Model to Higgs Production Process e-γ→veW-H in e-γ Collisions

The littlest Higgs model is the most economical one among various little Higgs models. In the context of the littlest Higgs （LH） model, we study the process e-γ → veW^-H and calculate the contributions of the LH model to the cross section of this process. The results show that in most of the parameter spaces preferred by the electroweak precision data, the value of the relative correction is larger than 10%. Such correction to the process e-γ →veW^-H is large enough to be detected via e-γ collisions in the future high energy linear e^＋ e^- collider （ILC） experiment with the c.m. energy √s = 500 GeV and a yearly integrated luminosity ￡ = 100fb^-1, which will give an idea/way to test the model.     

Top Quark Decay t → cb-↑b in Topcolor-Assisted Technicolor Models

The topcolor-assisted technicolor （TC2） model predicts the existence of the top-pions and the CP-even top-Higgs with large flavor-changing couplings to the top quark, which at tree-level can mediate the top quark three-body decay t → cb-↑b. We study this decay, show the dependence of the decay rate on the relevant TC2 parameters and compare the results with the predictions in the minimal supersymmetric model. We find that the decay rate in the TC2 model is much larger than that in the minimal supersymmetric model if the new particles are not too heavy. However, in consideration of the ODF and the LEP experiment limits, the top-pion mass is greater than 340 GeV in a more realistic parameter space, so the decay width of the channel t → cb-↑b intermediated by top-pions will be depressed greatly and difficult to be detected at the future collider. Thus, to observe this channel at the future collider, considering the top-higgs contribution may be the possible way when the masses of the top-pions and the top-higgs are not degenerate.     

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→vebt 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 →Ф^＋b→tbb in future LC experiment with √s = 3 TeV and ￡ = 500 fb^-1.     

Feasibility study of a J/ψ cross section measurement with early CMS data

We report the methods and plans for measuring the differential cross section of J/ψ→μ^＋μ^- production, using data to be collected in the first LHC run by the CMS detector. Making use of the large B-hadron lifetime, we show how to separate the promptly produced J/ψ’s from those coming from B-hadron decays. Since the J/ψ production cross section is expected to be large, the analysis should be viable with relatively small data sets, that will become available early in the startup of the LHC. We also address effects of a non-perfect detector alignment, as well as systematic uncertainties. About 70 thousand J/ψ decays are reconstructed from Monte Carlo data, which corresponds to an integrated luminosity of 3 pb^-1 in 14 TeV collisions, in the range of pT^J/ ψbetween 5 and 40 GeV/c. The precision of the result is limited by systematic uncertainties, and is at the 15% level.     

Radiative Decay Bc → Ds*γ in the Technicolor with a Massless Scalar Doublet Model

Applying perturbative QCD, we study the process Bc → Dsγ in the technicolor with a massless scalar doublet model (TCMLSM). There are mainly two mechanisms contributing to the Bc → D*sγ process. One proceeds through the short distance b → sγ transition and the other through weak annihilation accompanied by a photon emission.We find that, compared with the standard model, the modification of Bc → D*sγ from πρ (the physical pions in the TCMLSM) is so small that can be neglected for the allowed mass ofπρ. The weak-annihilation contribution is found to be about one order larger than that of the electromagnetic penguin diagrams.     

The High Energy γγ→γγ Scattering Cross Sections

Contributions of fermion loops, W-boson loops and their sum to the high energy γγ -- γγ scatteringtotal cross sections (1 cosθ＜ cos30) are calculated by analytical expressions of γγ - γγ scattering amplitude. Thesecontributions may be observed in the future photon linear collider and may be uscd to test standard model. Thecontribution of fermions' loops is a half of that in R.K. Arphlus and M. Neuuman's paper (Phys. Rev. 80 (1950) 380;83 (1951) 776).     

Pair production of right-handed neutrinos in the left-right twin Higgs model at ILC and LHC

In the framework of the left-right twin Higgs model, we study pair production of the right-handed neutrinos at the International Linear Collider (ILC) and the CERN Large Hadron Collider (LHC). Our numerical results show that the production cross section of the process e+e→N N is at the level of several tens fb at the ILC. However, the resonance production cross section can be significantly enhanced to the order of pb. The pair production cross section for the right-handed neutrinos is the level of several h...     

Study of ππ production in two-photon collisions at Belle

We have measured the cross section for π+π- production in two-photon collisions using a data sample with an integrated luminosity of 85.9 fb-1 collected with the Belle detector. The f0(980) resonance is observed as a peak in the energy spectrum of the cross section. We also report preliminary results for γγ→π0π0 with two-photon center-of-mass energies ranging from 0.6 to 4.0 GeV, based on a 95 fb-1 data sample. We find at least four resonant structures including a peak from f0(980). In addition, there is evidence for Xc0 production. We also make a preliminary discussion of the angular dependence and cross section ratio of γγ→π+π- and γγ→π0π0.