How to study a gluon jet produced by antiproton—proton colliding beams

We show that at the energies and luminosities soon to be attained with antiproton—proton colliding beams, the cross section for antiquark—quark annihilation, leading to production of a gluon jet in association with a Z⁰ at large angles, is measurable and has a magnitude, energy dependence, and angular dependence which can serve to establish the existence of the gluon and to fix its spin.     

Investigation of rare components of nucleon wave function in antiproton-nucleus interactions

Antiproton-nucleus annihilation at high energies is found to be strongly model-dependent. It is expected to be large and energy-independent in the perturbative QCD, but it falls off at high energies and asymptotically vanishes in the Rossi-Veneziano approach.Antiproton surviving a hard scattering on a bound nucleon changes significantly its properties: its inelastic interaction cross section decreases due to the colour transparency, annihilation cross section is suppressed much stronger yet. The hard scattering cuts off multiparton Fock components of the antiproton and deforms its structure function. As a result the Reggeon-exchange contribution to the antiproton interaction vanishes. Specific predictions are made. It is shown also that the effect of nuclear colour transparency in antiproton charge-exchange quasifree scattering displays itself and can be observed at rather low transferred momenta. It is argued that nuclear colour transparency can exceed unity at high transferred momenta.We are very grateful to C. Guaraldo, M. G. Sapozhnikov, and P. E. Volkovitsky, who initiated this investigation, for fruitful discussions.     

On studying charm in nuclei through antiproton annihilation

We examine the production of open charm in antiproton annihilation on finite nuclei. The enhancement of the subthreshold production cross section, even in a nucleus as light as carbon, should provide a clean signature of the reduction in the masses of these mesons in-medium. We also show that a careful analysis of the D⁺ and D⁻ spectra can yield important information on the cross section for D^±N scattering. Received: 10 June 1999 / Revised version: 13 August 1999     

Atomic processes in antiproton-matter interactions

Atomic processes dominate antiproton stopping in matter at nearly all energies of interest. They significantly influence or determine the antiproton annihilation rate at all energies around or below several MeV. This article discusses what is known about the atomic processes which, through their effect on stopping and annihilation, significantly influence the spatial distribution of antiproton annihilations in a material. For stopping above about 10 eV the processes are antiproton-electron collisions, effective at medium keV through high MeV energies, and elastic collisions with atoms and adiabatic ionization of atoms, effective from medium eV through low keV energies. For annihilation above about 10 eV it is the enhancement of the antiproton annihilation rate due to the antiproton-nucleus Coulomb attraction, effective around and below a few tens of MeV. At about 10 eV and below, the atomic rearrangement/annihilation process determines both the stopping and annihilation rates. Although a fair amount of theoretical and some experimental work relevant to these processes exist, there are a number of energy ranges and material types for which experimental data does not exist and for which the theoretical information is not as well grounded or as accurate as desired. Additional experimental and theoretical work is required for accurate prediction of antiproton stopping and annihilation for energies and materials relevant to antiproton experimentation and application.     

Antiproton-hydrogen scattering at low-eV energies

In the scattering of negative particles other than the electron by atoms at lab-frame energies around 10 eV, an elastic process termed “brickwall scattering” might lead to a high probability for scattering angles around 180°. For an antiproton slowing in hydrogen, this backward scattering would result in the loss of nearly all of its energy in a single collision, since it and a hydrogen atom have nearly the same mass. Such energy loss would have a significant effect on the energy distribution of antiprotons at energies where capture by the protons of hydrogen is possible and might, thereby, affect the capture rate and the distribution of capture states. In the semiclassical treatment of the problem with an adiabatic potential energy, brickwall scattering is indeed present, and with a substantial cross section. However, this model appears to underestimate inelastic processes. Based on calculations for negative muons on hydrogen atoms, these processes appear to occur for about the same impact parameters as brickwall scattering and thus substantially reduce its effect.     

Inclusive production of D and K mesons in e+e− annihilation

We present measurements of the cross section for inclusive D and K meson production in e⁺e^? annihilation in the center of mass energy range 3.6 to 5.8 GeV. D production accounts for most of the increase in the total cross section for hadron production in e⁺e^? annihilation at energies above 4 GeV.     

Photoproduction of πΔ(1236) from protons below 1.1 GeV

A model for the annihilation of electron-positron pairs into hadrons for q² = s > 4 GeV² and up to the highest measured energies is developed. The main ingredients are point-like couplings between three resonances and photons and the high level of opening thresholds that follows from an effective Lagrangian formalism. The model gives an almost constant annihilation cross section, soft pions everywhere and at all energies, high multiplicities and a large absolute cross section. The details of all exclusive channels are also predicted. Other consequences of this point of view concern the discovery of hitherto ignored couplings in low-energy photon initiated reactions. We argue that the energy regime explored by SPEAR is not the asymptopia and we discuss possible further constancy of the cross section in a range of s.     

Double strangeness production in antiproton annihilation on nuclei

The recent data on double strangeness production after antiproton annihilation on nuclei are analyzed within the conventional picture of the reaction, namely annihilation on a single nucleon, followed by rescattering of the products in the nucleus, assumed to proceed in a hadronic phase. General expressions for single and double strangeness are derived within this picture. The relevant parameters are determined, as far as possible, from the single strangeness production yields and are used to predict double strangeness production yields. The later are compared with experiment and found consistent with the conventional picture. However, the data seem to indicate that the strangeness production in the primordial annihilation is different from what it is in nucleon-antinucleon reactions. An estimate of theΞ production rate is also performed. It is shown that the latter is much less sensitive to the rescattering process than in theΛ production case.     

Antiproton production in heavy-ion collisions at subthreshold energies

Within the framework of the Lanzhou quantum molecular dynamics model,the deep subthreshold antiproton production in heavy-ion collisions has been investigated thoroughly.The elastic scattering,annihilation and charge exchange reactions associated with antiproton channels are implemented in the model.The attractive antiproton potential extracted from the G-parity transformation of nucleon selfenergies reduces the threshold energies in meson-baryon and baryon-baryon collisions,and consequently enhances the antiproton yields to some extent.The calculated invariant spectra are consistent with the available experimental data.The primordial antiproton yields increase with the mass number of the colliding system.However,annihilation reactions reduce the antiproton production which becomes independent of the colliding partners.Anti-flow phenomena of antiprotons correlated with the mean field potential and annihilation mechanism is found by comparing them with the proton flows.Possible experiments at the high-intensity heavy-ion accelerator facility(HIAF) in China are discussed.     

Electron-positron annihilation above 2 GeV and the new particles

This paper reviews the experimental and phenomenological aspects of electron-positron annihilation into hadrons at center-of-mass energies above 2 GeV. The behavior of the total cross section for hadron production as a function of energy is described; and the important parameter R - the ratio of this cross section to the muon-pair production cross section - is discussed. Data on charged particle multiplicities, particle production ratios, and single particle inclusive distributions is also summarized. The paper than summarizes our knowledge of the newly discovered ψ particles; and examines the various theories as to their nature and their relation to conventional hadronic physics.     

Low-energy antiproton annihilation in nuclei

The annihilation of 100 MeV antiprotons in atomic nuclei is studied in the frame of an intranuclear cascade model. It is found that the antiproton is annihilated about 1 fm inside the nucleus on the average. The energy released by the annihilation is carried by an average of 5 pions, which cascade throughout the nucleus. About 5% (10%) of the primordial pions are absorbed by the ⁴⁰Ca (¹⁰⁸Ag) target. The pions transfer around 5̃50 MeV (7̃00 MeV) to the nucleons and eject about one-fifth of the nucleons. The pion and proton cross sections are calculated. In particular, the relative transparency of the nucleus to high-energy pions (and not to pions in the Δ-resonance region) gives rise to a peculiar pion emission pattern. The time evolution of the baryon density and of the spectrum of the participant nucleons is investigated. It turns out that the cascade does not generate high energy density.     

Energy dependence of fusion and reaction cross sections in the 9Be + 12C system

Angular distributions of protons, deuterons. tritons and α-particles were measured for the system ⁹Be + ¹²C at lab energies between 12 and 27 MeV. The compound nucleus model with level densities calculated according to the Gilbert-Cameron formula describes satisfactorily the measured proton, deuteron and triton data. In the α-particle spectra contributions from other processes seem to be present. In the analysis the fusion cut-off angular momentum was adjusted at each energy in order to reproduce correctly the proton, deuteron and triton channels. From this analysis the fusion cross section was determined as a function of the energy. The results were compared with fusion and total reaction cross section values calculated from a potential model with the real part of the interaction potential obtained from the double folding procedure of Satchler.     

反质子物理

本文介绍反质子与核子和与原子核碰撞后各种物理现象．它与核子的散射获得的位势是吸引势和吸收型,与核的光学势是强吸收到．湮没后产生众多的介子和重子．以及在高能下湮没产生奇特性粒子、带粲的介子、重子．并探索获得混杂子、在核中存在反质子、其它新粒子的可能性． In this paper several physical phenomena of antiproton-nucleon and antiproton-necleus collision are discussed. The potential obtained from p-N scattering is attraction and absorption type. The optical potential of nucleus is strong absorption type. The annihilation happens after pp collision and thenproduces many kinds of meson, hadron, even produce some exotic particle and charmonium at high energy pp anihilation. Posibilities to find hybrids, antiproton and other particles in nucleus are also explored.     

Large angle cross section and analyzing power for proton-4he elastic scattering between 185 and 500 MeV

The differential cross section for the elastic scattering of protons from ⁴He has been measured for ten proton energies between 185 and 500 MeV in the angular range 144° to 168° in the lab system. The analyzing power has also been measured for seven energies in the same angular range. The differential cross section does not show the marked backward peaking that has been observed at both lower and higher energies. The possible structure in the 180° excitation function suggested for energies around 240 MeV is not observed. The analyzing power is large and negative, and shows strong dependence on both energy and angle.     

基于相对论平均场理论对超重核冷熔合反应截面的研究

在形变约束的相对论平均场理论框架下计算了合成Z=102—118元素的(可能)冷熔合反应中复合核及蒸发一或两个中子剩余核的位能曲面,得到了复合核和剩余核平衡点和鞍点的性质、静态裂变垒高度和冷熔合反应的最佳入射能;利用壳修正和对修正方法计算了平衡点和鞍点的壳修正能、对修正能和微观能.利用由此得到的壳结构信息,用简单的熔合蒸发唯象模型计算了相应反应的冷熔合截面.结果发现,TM1参数提供的结构性质给出了与实验接近的反应截面.     

Sum rules fore + e − annihilation in general electroweak mixing models and extended gauge theories

We derive a lower bound for the integrated cross section for production of weak neutral bosons ine ⁺ e ^? annihilation within general electroweak theories containing an arbitrary number of weak bosons. The low energy parameterC of such theories is expressed in terms of integrals over the weighted cross section fore ⁺ e ^? annihilation at high energies.     

Kaon production in hadronic matter

Subthreshold kaon production has been studied in symmetric nucleus-nucleus collisions as a function of the nucleus mass, beam energy and centrality. In Au+Au collsions at 1 AGeV theK ⁺ multiplicity increases more than linearly with increasing number of participating nucleons. Transport calculations have to assume a soft equation of state in order to reproduce the data. The in-mediumK ^? cross section measured in Ni+Ni collisions is enhanced by about a factor of 7 as compared to the free cross section when using theK ⁺ cross section at equivalent beam energies as a normalization.     

Application of the Second Born Approximation to Excitation of Hydrogen Atoms by Protons and Antiprotons Impact

We present and compare total cross sections for excitation in collisions of protons and antiprotons with hydrogen atoms in the 2s state. Calculations axe performed in the framework of the second Born approximation, in the energy range of 5-1000 keV. We apply the usual approach of the second Born approximation, which approximates the summation raised by retaining few terms, as well as another approach approximates all energies corresponding to the intermediate states to that corresponding to the initial state. The annihilation effect in the case of the antiproton collision is investigated. We compare the results with the previous theoretical calculations.     

Relativistic antihydrogen production

Antihydrogen has recently been produced in collisions of antiprotons with ions. While passing through the Coulomb field of a nucleus an antiproton will create an electron-positron pair. In rare cases the positron is bound by the antiproton and an antihydrogen atom produced. We calculate the production of relativistic antihydrogen atoms by bound-free pair production. The cross section is calculated in the semiclassical approximation (SCA), or equivalently in the plane wave Born approximation (PWBA) using exact Dirac-Coulomb wave functions. We compare our calculations to the equivalent photon approximation (EPA). Received: 19 December 1997 / Published online: 10 March 1998     

The interaction of 538 MeV 56Fe with 238U

Binary coincident fragments from the ⁵⁶Fe+²³⁸U reaction at 538 MeV have been studied. Fragment energies were measured and fragment masses determined by a kinematic method. Three types of event are defined by suitable adjacent limits in the mass versus energy event space. The angular distributions of cross section, energy and mass have determined for each event region and particular attention paid to that part containing possible fissions following complete fusion. The total reaction cross section consists of about 50 % of binary fragmentation channels. The remaining channels correspond to a ternary process of heavy recoil fission.