Two particle unitarity for helicity amplitudes with particles of arbitrary spin

The two particle unitarity contribution to the double spectral function of the scattering amplitude for any 2 → 2 process is explicitly calculated for the case of arbitrary spins of the initial, intermediate and final particles. A closed, simple result is obtained which is a generalization of the Mandelstam result for spinless particles. The results should be of value in calculations of the contribution of the exchange of pairs of high spin particles to the nucleon-nucleon force.     

Elastic antiproton-proton photoproduction between threshold and 4.8 GeV

The cross section for the process $\text{γ}\text{p}\text{→}\text{p}\text{pp}$ has been measured from threshold up to 4.8 GeV using a tagged photon beam and a multiparticle spectrometer which detected all final state particles. The production cross section rises rapidly from threshold to a constant value of 35 nb. No evidence is found in the mass spectra for the production of narrow meson resonances decaying into $\text{p}\text{p}$.     

The pomeron-particle total cross section and diffractive production of showers at very high energies

The experimental data of ISR and NAL for the process pp → pX are used for the determination of the pomeron-particle total cross section and the triple-pomeron vertex. Estimates of the cross sections of the diffractive production of one and several showers of particles are given. It is shown that at s ～ 10³ GeV² the cross section of all inelastic diffractive processes is ～ 6 mb and grows with energy. A theoretical estimate of the amplitude of pomeron-pomeron scattering is given.     

Production of the new gauge boson BH via e-γ collision in the littlest Higgs model

The lightest new gauge boson BH with mass of hundreds GeV is predicted in the littlest Higgs model. BH should be accessible in the planned ILC and the observation of such particle can strongly support the littlest Higgs model. The realization of γγ and e-γ collisions would open a wider window to probe BH. Inthis paper, we study the new gauge boson BH production processes e-γ→ e-γBH and e-γ→e-ZBH at the ILC. Our results show that the production cross section of the process e-γ→ e-ZBH is less than 0.1 fb in most parameter spaces allowed by the electroweak precision data while the cross section of the process e-γ→ e-γBH can be over one fb in the favorable parameter spaces. With the high luminosity, the enough typical signals could be produced via e-γ→ e-γBH. Because the final electron and photon beams can be easily identified and the signal can be easily distinguished from the backgrounds produced by Z and H decaying, e-γ→e-γBH is a promising process to probe BH.     

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.     

T invariance and polarization effects in the reactions p+3He → π++4He and π++4He → p+3He

On the basis of T invariance, it is established that the dependence of the effective cross section for a binary reaction of the a+b → c+d type on the polarization vectors of primary particles a and b determines completely the polarization vectors and spin correlations for the same particles in the inverse reaction c+d → a+b induced by collisions between unpolarized primary particles c and d. By using the formalism of helicity amplitudes, polarization effects are studied in the process p+³He → π⁺+⁴He and in the inverse process π⁺+⁴He → p+³He. It is shown that, in the reaction π⁺+⁴He → p+³He, the spins of the final-state particles (proton and ³He nucleus) are strongly correlated. An expression for the correlation tensor is obtained for arbitrary values of the (p, ³He) emission angle.     

Production of Charged Higgs Bosons from Left-Right Twin Higgs Model at TeV Energy e-γ Colliders

The left-right twin Higgs (LRTH) model predicts the existence of three additional Higgs bosons: one neutral Higgs ø⁰ and a pair of charged Higgs bosons ø^±. In this paper, we study two pair production processes of these new particles at the next generation eγ colliders, i.e., e^-γ → e^-ø⁺ø^-, ande^-γ→ ν_Rø^-ø⁰. We find that the production cross section of the process e^-γ →e^-ø⁺ø^- are at the level of several tens fb, the production cross section of the process e^-γ→ν_Rø^-ø⁰ can reach 0.35 fb with the reasonable parameter values. As long as the charged Higgs bosons are not too heavy, we conclude that these processes might be used to test for the left-right twin Higgs model in future high-energy linear collider experiments.     

Proton Compton effect in the Δ(1232) energy region

The proton Compton effectγ+p→γ+p in theΔ (1232) energy region has been thoroughly studied. At the Bonn 500 MeV synchrotron differential cross sections were measured covering a large range of the CM scattering angle (50°≦θ_γ≦130°) and an energy range from 240 to 440 MeV (LAB energy of the primary photon). A contribution to the counting rate from the competing process ofπ ⁰ photoproduction was strongly suppressed by detecting both particles in the final state and by a proper choice of the endpoint energy of the gamma ray beam. The remaining contribution was monitored experimentally. The measured data were complemented by cross sections at 0° which were computed from the totalγ p cross sections with an input from a multipole analysis of single pion photoproduction. Preliminary results of this experiment have been published in Lett. Nuovo Cimento. In the meantime the experimental data were reanalyzed. The final data presented here are larger than the preliminary ones by about 15%.     

Inclusive production at large transverse momentum in QCD

We calculate the cross section for the process quark + quark → quark (with large transverse momentum) + anything, up to order g⁶ in the cross section and in the leading-logarithm approximation. The result is suggestive of a simple ansatz for the calculation of the asymptotic behaviour of cross sections for the production of particles or jets with large transverse momenta.     

Wγ production and limits on anomalous WWγ couplings in pp collisions at sqrt[s] = 1.96 TeV

We measure the cross section and the difference in rapidities between photons and charged leptons for inclusive W(→lν) + γ production in eγ and μγ final states. Using data corresponding to an integrated luminosity of 4.2 fb(-1) collected with the D0 detector at the Fermilab Tevatron Collider, the measured cross section times branching fraction for the process pp → Wγ + X → lνγ + X and the distribution of the charge-signed photon-lepton rapidity difference are found to be in agreement with the standard model. These results provide the most stringent limits on anomalous WWγ couplings for data from hadron colliders: -0.4<Δκ(γ)<0.4 and -0.08<λ(γ)<0.07 at the 95% C.L.     

Electroproduction of neutral pions at energies above the resonance region

The reaction e p→e'pπ⁰ has been measured at W=2.55 GeV a fixed electron scattering angle of 10.3°. Two magnetic spectrometers and a lead glass hodoscope were used to detect all four final state particles. Electroproduction cross sections in the t range ?0.15 to ?1.4 (GeV/c)² at q² = ?0.22, ?0.55 and ?0.85 (GeV/c)² are presented. Above |t|=0.6 (GeV/c)² the cross sections are considerably smaller than those for photoproduction.     

Stokes parameters of γ-quanta in the e+ + e− → Z + γ reaction

A general analysis is made of the polarization properties of γ-quanta in the e⁺ + e^? → Z + γ reaction. Besides the standard mechanism of this reaction; which is determined by the eeZ interaction (neutral weak currents), the possible anomalous magnetic moment χ of the Z boson is also taken into account. A linear contribution in χ. to the differential cross section of the e⁺ + e^? → Z + γ process (with unpolarized particles in the initial and final states) leads to CP-odd asymmetry of the angular distribution of γ-quanta relative to the substitution cos Θ→?cos Θ, where Θ is the angle of emission of the γ-quantum relative to the electron. Measurement of this asymmetry with an accuracy of the order of 1% makes it possible to get a “sense” of the contribution of the magnetic moment of a Z boson of the order of 10^?3 GeV^?1.     

关于光子对撞机上底夸克对产生的研究

计算了顶色辅助人工色模型对光子对撞机上底夸克对产生过程的Yukawa 修正.发现在合理的参数范围内,赝标量Goldstone 玻色子引起的相对修正与树图水平相比有3.17% 到5.90% 的压低.该结果明显地大于标准模型、双Higgs 二重态模型和最小超对称模型中的相应贡献. 这样的修正对于正在设计中的国际直线对撞机上检验标准模型和探索新物理是很有意义的. 关键词： 顶色辅助人工色模型 光子对撞机 散射截面     

ILC上Z玻色子与荷电top-pion对联合产生过程的研究

在国际直线对撞机(ILC)上顶色辅助的人工色(TC2)模型下对Z玻色子与荷电top-pion对联合产生过程e⁺e^- → Zπ_t⁺π_t^-进行了研究. 计算了过程e⁺e^- → Zπ_t⁺π_t^-的产生截面, 发现在TC2模型所允许的参数空间范围之内该过程的截面最大可达到1 fb. 考虑到荷电top-pion的主要的衰变模式π_t⁺ → tb, 发现该截面在ILC能产生很可观的事例数.     

Debye等离子体中高能H++H碰撞激发过程的研究

利用碰撞参数玻恩近似方法研究了Debye 等离子体环境中高能H⁺+H的碰撞激发过程, 研究了不同Debye 半径下氢原子1s → 2p 的激发耦合相互作用矩阵元、入射粒子能量为160 keV/u 的激发电子跃迁概率以及入射粒子能量范围为100–1000 keV/u 的碰撞激发截面. 结果表明: 随着屏蔽效应的增强, 激发截面减小. 根据激发截面的公式以及计算结果详细分析了引起激发截面减少的原因. 入射粒子与激发电子之间的屏蔽相互作用势和靶的电子结构(波函数和能级) 对激发截面都有很重要的影响. 关键词： 等离子体 碰撞参数玻恩近似方法 碰撞激发截面     

Duality for the reggeon-reggeon amplitude: A study through quasi-three-body reactions

We consider reactions of the type ab→cdR in the double-Regge region. The cross sections are proportional to the reggeon-reggeon forward amplitude in the resonance region. Using semi-local duality the cross sections can be written in terms of the relevant triple-Regge couplings which are already known from reggeon-particle scattering, i.e. from analysing data on reactions of the type ab→cR. We compare the predictions of pp→pp (?, f) π^?p→π^?p (?, f) with data at 12, 24 and 205 GeV/c and find encouraging results. We suggest a series of cross sections, the measurement of which will provide a definite test of the duality hypothesis for reggeon-reggeon scattering.     

Top—Higgs and the Process e^＋e^— → vvtt

We discuss the contributions of the top-Higgs ht^0 proedicted by topcolor-assisted technicolor (TC2) models to the process e^ e^-→vvtt.We find that the contributions are very large.For mht=400 GeV and ε=0.01,the production cross section of this process can reach 11.2fb,which may be detected in the future high energy e^ e^- collider experiments.The process e^ e^-→vvtt can be used to test experimentally the signal of TC2 models.     

Spurious nature of certain unitarity corrections to the isobar model for three hadron final states

Various methods of implementing unitarity corrections to the isobar model for three hadron final states are discussed, and it is explained why some lead to spurious effects because insufficient attention is paid to analyticity. Recent calculations of unitarity corrections in the processes A1 → πππ and πN → ππN are shown to contain spuriously large effects. This may explain why fits to the first process were worsened when these corrections were included.     

Semiclassical approach for multiparticle production in scalar theories

We propose a semiclassical approach to calculate multiparticle cross sections in scalar theories, which have been strongly argued to have the exponential form exp(λ⁻¹ F(λn, ϵ)) in the regime λ → 0, λn, ϵ = fixed, where λ is the scalar coupling, n is the number of produced particles, and ϵ is the kinetic energy per final particle. The formalism is based on singular solutions to the field equation, which satisfy certain boundary and extremizing conditions. At low multiplicities and small kinetic energies per final particle we reproduce in the framework of this formalism the main perturbative results. We also obtain a lower bound on the tree-level cross section in the ultra-relativistic regime.     

Photoproduction of π+ mesons on polarized protons

The asymmetry of the cross sections for the photoproduction of π⁺ mesons on polarized protons γ + p↑ → π⁺ + n has been studied in the four-momentum transfer range 0.1 ? |t| ? 1.25 (GeV/c)² for photon energies of 2.5, 3.4 and 5.0 GeV. The measurements were carried out on a polarized butanol target. Both particles in the final state were detected: the pion by a magnetic spectrometer, the recoil nucleon in a scintillation counter matrix. The asymmetry was found to be negative with values around ?0.4.