高能e+e-对撞机上top介子辅助的b夸克对产生

在顶色辅助的人工色模型下计算了高能e^ e^-对撞机上top介子辅助的b夸克对产生过程e^ e^-→bb^-π^0t的产生截面．发现在一定的参数范围内，这个过程的产生截面大于lOfb，比标准模型下标量Higgs粒子辅助的b夸克对产生过程大许多，与最小超对称模型下标量和赝标量Higgs粒子h^0，H^0，A^0的相应产生截面大致相当．人工色理论的信息可能在下一代正负电子对撞实验中探测到．     

TC2模型中的TC介子对e+e-→(t-)c过程的贡献

计算了Topcolor辅助的人工色模型中的赝标哥尔斯通玻色子对超高能正负电子对撞机上的e+e-→(t-)((c-)t)过程的修正. 发现在质心能量为(s)=200GeV时新物理对该过程的修正结果比标准模型的结果高出约1个量级. 如果选取质心能量为(s)=500GeV得到的结果为σ(e+e-→(t-)c)～10-37cm2.     

顶色辅助的多标度人工色理论中的PGB′s对顶夸克产生的修正

在顶色辅助的多标度人工色模型框架下,计算了赝标哥尔斯通玻色子(TC介子,Top介子)对Tevatron上qq→tt顶夸克对产生的单圈修正.计算表明此修正主要来自Top介子,在适当的参数范围内,PGB′s对顶夸克对树图级产生截面的单圈修正可达17%.     

高能e+e－对撞机上top介子辅助的b夸克对产生

在顶色辅助的人工色模型下计算了高能e⁺e^－对撞机上top介子辅助的b夸克对产生过程e⁺e^－→bbπ0t的产生截面.发现在一定的参数范围内,这个过程的产生截面大于10fb,比标准模型下标量Higgs粒子辅助的b夸克对产生过程大许多,与最小超对称模型下标量和赝标量Higgs粒子h⁰,H⁰,A⁰的相应产生截面大致相当.人工色理论的信息可能在下一代正负电子对撞实验中探测到.     

顶色辅助的多标度人工色理论中的PGB＇s对顶夸克产生的修正

在顶色辅助的多标度人工色模型框架下,计算了赝标哥尔斯通玻色子(TC介子,Top介子)对Tevatron上qq→tt顶夸克对产生的单圈修正.计算表明此修正主要来自Top介子,在适当的参数范围内,PGB＇s对顶夸克对树图级产生截面的单圈修正可达17％.     

TC2模型下底夸克对产生的研究

在顶色辅助的technicolor模型下, 计算了来自赝标哥得斯通玻色子和新规范玻色子对e⁺e^－→bb的截面贡献. 发现由technipions和新规范玻色子产生截面的修正足够小以至于可以忽略, 在合理的参数范围内, top pions起主要作用, 在质心能量√s=500GeV, 修正的最大值可以达到43%; 在√s=1500GeV, 最大的相对修正却只有3.1%. 这为我们在下一代直线对撞机实验中探测顶色辅助的technicolor模型下(TC2模型)提供了可行的方法.     

顶色辅助的人工色模型下顶夸克极化效应的研究

在顶色辅助的人工色(TC2)理论下, 在强子对撞机上研究了顶夸克-反顶夸克对的产生过程中顶夸克的极化效应, 在计算过程中, 运用了MRS set A'部分子分布函数和螺旋度投影算符的方法. 研究结果表明: 在Tevatron上顶夸克的极化效应太小不可探测; 参数选取得当, 该效应在LHC上可以探测到, 其值可达16%. 因此, 顶夸克的极化效应提供了一种切实可行的检验顶色辅助的人工色模型的方法.     

OGTC模型中PGBs对γγ→bb过程的Yukawa修正

计算了一代人工色(One Generation Technicolor,简称OGTC)模型中的赝标哥尔斯通玻色子(Pseudo-Goldstone Bosons,简称PGBs)对γγ→bb过程的Yukawa修正.发现在一定的参数范围内,PGBs对γγ→bb散射截面的修正超过10%;而PGBs对过程e⁺e^－→γγ→bb的相对修正,在laser back-scattering photons模式下最大可达－51%,在beamstrahlung photons模式下最大只有－17.9%;这些修正比标准模型和超对称模型下相应粒子的贡献大许多,将为在下一代高能光子碰撞实验上寻找人工色理论的信息提供参考.     

最轻的中性TC介子P0和μ+μ－对撞机

在顶色辅助的多标度人工色(TOPCMTC)模型框架下,讨论了最轻的中性TC介子P⁰在μ⁺μ^－对撞机(FMC)上的s道共振产生.计算结果表明:其有效产生截面非常大,至少比标准模型中的Higgs粒子h⁰的产生截面大一个量级.因此,FMC可以用来探测TC介子的存在进而检验人工色理论.     

TOPCMTC模型中π介子与W±规范玻色子在LHC上的辅助产生

在顶色辅助多标度人工色(TOPCMTC)模型下计算了大动量强子对撞机(LHC)上π介子与W±规范玻色子辅助产生过程pp→bb→W±π的产生截面.发现这个产生截面与最小超对称模型下pp→bb→W±H的相应结果大致相当.在一定的参数范围内,这个过程的产生截面能够达到几十个甚至一百多个fb.W±π的信息可能在LHC上被探测到.     

SUSY QCD Impact on Top-Pair Production Associated with a Z0-Boson at a Photon-Photon Collider

The top-pair production in association with a Z⁰-boson at a photon-photon collider is an important process in probing the coupling between top-quarks and vector boson and discovering the signature of possible new physics. We describe the impact of the complete supersymmetric QCD (SQCD) next-to-leading order (NLO)radiative corrections on this process at a polarized or unpolarized photon collider, and make a comparison between the effects of the SQCD and the standard model (SM) QCD. We investigate the dependence of the lowest-order (LO) and QCD NLO corrected cross sections in both the SM and minimal supersymmetric standard model (MSSM) on colliding energy s^1/2 in different polarized photon collision modes. The LO, SM NLO, and SQCD NLO corrected distributions of the invariantmass of t\bar{t}-pair and the transverse momenta of final Z⁰-boson are presented. Our numerical results show that the pure SQCD effects in γγ→t\bar{t}z⁰ process can be more significant in the + + polarized photon collision mode than in other collision modes, and the relative SQCD radiative correction in unpolarized photon collision mode varies from 32.09\% to -1.89\% when s^1/2 goes up from 500 GeV to 1.5 TeV.     

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.     

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⁺ Π_t^-Π_t⁰. 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 Π_t⁰ → t\bar{c} is the best channel to detect theneutral 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.     

Research of bb Production in the Topcolor Assisted Technicolor Model

In the framework of topcolor assisted technicolor (TC2) model, we calculate the contributions of cross section from the pseudo Goldstone bosons and new gauge bosons to e⁺e^－ →bb. We find that, within reasonable ranges of the parameters, the corrections arising from technipions and new gauge bosons are negligibly small; and the top pions afford dominate contribution, the maxim cross section corrections can reach 43% with the c.m. energy √s=500GeV; whereas in case of √s=1500GeV, the maxim cross section relative corrections is only 3.1%. It might open a window to detect topcolor assisted technicolor model in the experiment of next generation linear collider.     

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.     

Calculation of Total Cross Section for γγ→γZ Scattering at High Energy

The total cross sections of γγ→γZ process for γγ c.m.s. energy 91.2—2000GeV are presented. W loop contribution is dominating when γγ c.m.s. energy is larger than 140GeV. The total cross section has a maximum, 220 fb(|cosθ|33cm^－2·s^－1 in which case more than 6000 events for γγ→γZ would be observable. In principle this process provides a test of the non-abelian nature of the standard model, especially the anomalous triple and quartic W-boson vertices.     

Improved search for a Higgs boson produced in association with Z → l+ l- in pp collisions sqrt[s] = 1.96 TeV

We search for the standard model Higgs boson produced with a Z boson in 4.1 fb(-1) of integrated luminosity collected with the CDF II detector at the Tevatron. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the Z boson to electrons or muons, we set 95% credibility level upper limits on the ZH production cross section multiplied by the H → bb branching ratio. Improved analysis methods enhance signal sensitivity by 20% relative to previous searches. At a Higgs boson mass of 115 GeV/c2 we set a limit of 5.9 times the standard model cross section.     

Sum rules for light-by-light scattering

We derive a set of sum rules for the light-by-light scattering and fusion: γγ→all, and verify them in lowest order QED calculations. A prominent implication of these sum rules is the superconvergence of the helicity-difference total cross section for photon fusion, which in the hadron sector reveals an intricate cancellation between the pseudoscalar and tensor mesons. An experimental verification of superconvergence of the polarized photon fusion into hadrons is called for, but will only be possible at e+ e- and γγ colliders with both beams polarized. We also show how the sum rules can be used to measure various contributions to the low-energy light-by-light scattering.     

Open charm production in diffractive ep collisions

The cross section for the diffractive reactionγ + p → cc + p with a real or virtual photon is calculated in the nonperturbative two-gluon exchange model of Landshoff and Nachtmann. Numerical predictions are given for cross sections and spectra at typical HERA values of c.m. energy and photon virtuality. The contribution of charm to the diffractive structure function is evaluated and found to be rather small in the model, and the ratio between the production rates for bb and cc is tiny.     

What can be discovered in the γγ→ωω reaction

It is shown that the considerable resonance type enhancement due to the one-pion exchange is to be observed in the cross section of the γγ→ωω reaction near its threshold. The possible one-pion exchange part in the γγ→ρ⁰ω reaction is discussed, too.