Calculation of the lowest 1 S resonance state of the H− anion by the stabilization method

By the example of the lowest resonance state of the H^? system, two versions of the stabilization method are considered: with introduction of an external potential into the Hamiltonian and with enlargement of the single-particle function basis. A comparison of the results suggests the possibility of applying these methods to calculating the resonance parameters in many-electron systems.     

Charge transfer in H~ H and H~ He~ collisions at intermediate and high energies using an asymptotic two-state atomic expansion method

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Meson-photon transition form factors and resonance cross-sections in e+e− collisions

Meson-photon-photon transition form factors for S-, P-, and D-wave states are calculated, the meson being treated as a non-relativistic heavy-quark-antiquark pair. The full dependence on both photon virtualities is included. Cross-section formulas for charge-conjugation even mesons with J^p = 0⁻, 0⁺, 1⁺, 2⁺, and 2⁻ in electron-positron collisions are presented and numerical results for LEP energies are given. In particular, we find two-photon event rates for χ_c1, η_c(2S), and η_b(1S) within reach of LEP.With minor modifications to incorporate SU(3)-flavour breaking we estimate rates for 18 light mesons as well, based on the observation that their two-photon decay widths agree remarkably well with measured data. Finally we point out that e⁺e⁻ cross sections for 1⁺ states do not vanish at low Q², the Landau-Yang suppression factors of the two-photon cross sections being compensated by the photon propagators.     

Comparison of π±, K± and p,p production in the central rapidity region in hadron-hadron collisions and in e+e− annihilation

We compare the p_T dependence of pion, kaon and proton production cross sections in the central rapidity region in e⁺e⁻ annihilation events and in proton-proton collisions at ISR energies. We find similarities both in the p_T dependence of cross sections and in the particle composition as a function of p_T, in agreement with the hypothesis of a universal mechanism of particle production.     

Post-collision interactions and the polarization effect in （e, 2e） collisions of helium

A modified distorted-wave Born approximation (DWBA) method is used to calculate the triple differential cross sections (TDCSs) in a coplanar asymmetric geometry for the electron impact single ionization of a He (1s2) atom at intermediate and lower energies. The post-collision interaction and the polarization effect in (e, 2e) collisions of helium are considered in the calculations. The polarization potentials from the damping method and density functional theory (DFT) are compared. Theoretical results are compared with the recent experimental data.     

Observation of e ± in the inelastic e + A interaction

Results of observation and analysis of e ^± appearing in the interaction of 32-GeV positrons with nuclear emulsion have been reported. The angular distributions of particles have been measured in the range of 0°–180°. The energy of particles has been measured in the angular range of 145°–180° and values of the Bjorken variable x _B have been calculated. The distribution in x _B corresponds to values smaller than unity at Q ² > 7.0 (GeV/s)². This means that e ^± with energies lower than 250 MeV cannot be attributed to multinucleon correlations.     

Confined phase of electroweak theory and the e+e− peaks observed in large-Z heavy-ion collisions

We discuss the speculations that the e⁺e⁻ peaks seen in large-Z heavy-ion collisions are evidence for a confined phase of an effective theory similar to strongly-coupled QED. It has been suggested that the observed radiation arises from the decay of nontopological solitons in this confined phase. (In this work we develop a scenario in which a photon condensate is formed in a finite region of space. We show that the existence of such a condensate will lead to the confinement of electrons and positrons.) However, as has been recently pointed out by Peccei, Solà and Wetterich, a new phase of QED requires that the nonlinear effects in the effective Lagrangian for the electromagnetic field become large. We describe how this might come about, within the context of electroweak theory with two Higgs doublets.     

Studies of the gamma-strength function and low energy levels in 65Ga using the (p, γ) average resonance method

The ⁶⁴Zn(p, γ)⁶⁵Ga reaction has been studied in the proton energy ranges E_p = 2.0–2.9 and 3.3–4.3 MeV. Using a three-crystal pair spectrometer, gamma-ray spectra of primary transitions were measured throughout this proton energy interval in steps of about 20 keV. An average gamma ray spectrum for each energy region was formed by adding all the relevant individual spectra after adjustment due to the change of the proton energy. In the excitation energy range 0.0–3.7 MeV 50 levels, of which 20 are new, were observed. The gamma strength function was deduced from the average intensities of the primary gamma-rays. The absolute value of the strength function was found to be 5–10 times smaller than that expected from the extrapolation of the lorentzian shape of the El giant resonance.     

Polarization of Λ0 hyperons in nucleus-nucleus collisions at high energies

The measurement of Λ⁰-hyperon polarization in nucleus-nucleus collisions is considered as one of possible tools to study the phase transition. Fixed target and collider experiments are discussed for the case of λ⁰ production from Au-Au central collisions at $ \sqrt {s_{NN} } $ of about several GeV.     

Production of polarized baryons in polarized and unpolarizede + e − collisions

Polarized and unpolarizede ⁺ e ^? annihilation is considered in lowest order at energies 30–150 GeV taking γ andZ ⁰ exchange in the standardSU(2)×U(1) model into account. The fragmentation of polarized quarks into polarized baryons is described by two kinds of fragmentation functions; the first is based onSU(6) weights and empirical expressions for favoured and disfavoured fragmentation; the second is based upon a Monte Carlo model of the chain decay including helicities of quarks and hadrons. From the cross sections for \(e^ + e^ - \to q\bar q\) and the fragmentation functions we obtain predictions for the baryon polarization as function of the collision energy and of kinematical variables.     

Centrality dependences of the pseudorapidity distributions of charged particles in Au+Au collisions at RHIC energies

By employing the Glauber model, we give the centrality dependences of the numbers of participants and binary nucleon-nucleon collisions in nucleus-nucleus collisions. By taking into account the energy loss of the participants in their multiple collisions, we then present the pseudorapidity distributions of charged particles in nucleus-nucleus collisions as a function of beam energy and impact parameter. Finally, we analyze the centrality dependence of the pseudorapidity of the charged particles in Au＋Au collisions at energies from √SNN=19.6 to 200 GeV. The theoretical results are in good agreement with the experimental observations of the RHIC-PHOBOS collaboration.     

Scaling multiplicities of h-p collisions toe + e −→π±+... by the Fermi-Landau law

The similarity of rapidity distributions of hadrons frompp and $\bar p$ p withe ⁺ e ^?→π^±+... implies a scaling forE _cm, reflecting the quark-quark interaction of particle production by $\bar p$ /p+p. This scaling relates the meson multiplicity fromh+p→m $\bar m$ +... to the Fermi-Landau law $n_{ch} = a\sqrt {E_{cm} } $ fore ⁺ e ^? collisions, without free-parameters, threshold energy being taken into account including the mass of quarks constituent of the projectile and the target, the coefficient behaves like bremsstrahlung a～1/m ².     

Single-particle resonance states of 122Zr in relativistic mean-field theory combined with real stabilization method

Single-particle resonance states of ¹²²Zr are studied in the real stabilization method within the framework of relativistic mean field theory. Two efficient methods are adopted to extract the resonance energy and width of ¹²²Zr. The results are compared with those obtained from the analytic continuation in the coupling approach and scattering phase-shift methods.     

Target fragmentation in pp, ep and γp collisions at high energies

We calculate target fragmentation in pp→nX and γp→nX reactions in the meson cloud picture of the nucleon. The pp→nX reaction is used to fix the pnπ⁺ form factor for three different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and small x _Bj electroproduction of forward neutrons at HERA. Here the qˉq dipoles in the photon can rescatter on the residual neutron. In photoproduction we observe slightly less absorption than in the hadronic reaction. For deep inelastic events (Q ² > 10 GeV²) screening is weaker but still present at large Q ². The signature for this absorptive rescattering is a shift of the dσ/dE_n distribution to higher neutron energies for photofragmentation. Received: 12 June 1999 / Revised version: 12 October 1999     

Annihilation mechanisms of e+e− and μ+μ− production in relativistic nuclear collisions

We revise the μ⁺μ^? and $q\bar q$ annihilation mechanisms of dilepton production during relativistic nuclear collisions. We focus on the modifications caused by the specific features of in-medium pion and quark states rather than by medium modification of the ρ-meson spectral density. The main ingreditent emerging in our approach is a form-factor of the multi-pion (multi-quark) system. Replacing the usual delta-function the form-factor plays the role of distribution which, in some sense, “connects” the total 4-momenta of the annihilating and outgoing particles. The difference between the c.m.s. velocities attributed to annihilating and outgoing particles is a particular consequence of this replacement and results in the appearance of a new factor in the formula for the lepton pair production rate. We obtained that the form-factor of the multi-pion (multi-quark) system causes broadening of the rate which is most pronounced for small invariant masses, in particular, we obtain a growth of the rate for the invariant masses below two masses of the annihilating particles.     

Signals of the littlest Higgs model with T-parity at eγ and ep collisions

The littlest Higgs model with T-parity predicts the existence of the neutral, weakly interacting, new gauge boson BH, which can be seen as an attractive dark matter candidate. We study production of the new gauge boson BH via eγ and ep collisions. We find that BH can be abundantly produced via the subprocesses e-γ→L-BH and γq→BHQ, which might give rise to characteristic signals. Some discussions about the SM backgrounds for this kind of signals are also given.     

Signals of the littlest Higgs model with T-parity at eγ and ep collisions

The littlest Higgs model with T-parity predicts the existence of the neutral, weakly interacting, new gauge boson B_H, which can be seen as an attractive dark matter candidate. We study production of the new gauge boson B_H via eγ and ep collisions. We find that B_H can be abundantly produced via the subprocesses e^－γ→L^－B_H and γq→B_HQ, which might give rise to characteristic signals. Some discussions about the SM backgrounds for this kind of signals are also given.