Radiative effects in processes of diffractive vector meson electroproduction

The electromagnetic radiative correction to the cross section of the vector meson electroproduction is calculated. Explicit covariant formulae for the observed cross section are obtained. The dependence of the radiative correction on the experimental resolution and on the inelasticity cut is discussed. The FORTRAN code DIFFRAD, based on both exact (ultrarelativistic) and approximate sets of the formulae for the radiative correction to the cross section, is presented. Detailed numerical analysis for kinematical conditions of the recent experiments on the diffractive electroproduction of vector mesons is given. Received: 23 August 1998 / Published online: 15 April 1999     

Bremsstrahlung pair production in relativistic heavy ion collision

We calculate production of electron- and muon-pairs by the bremsstrahlung process in hadron collisions and compare it with the dominant two-photon process. Results for the total cross section are given for proton-proton and heavy-ion collisions at energies of the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). Received: 4 March 1997 / Revised version: 8 July 1997 / Published online: 20 February 1998     

Deuteron stripping on beryllium target in the 100–2300 MeV energy range

Cross sections for stripping and dissociation of deuterons interacting with Be targets in the 100–2300 MeV energy range have been measured. Comparisons with model calculations suggest a dominant contribution of the stripping process. It is also shown that the deuteron break-up cross section exhibits the same energy dependence as the nucleon-nucleon cross section. Received: 8 September 1998 / Revised version: 15 March 1999     

Soft and hard Pomeron in the structure function of the proton at low x and low Q^2

We study inclusive electroproduction on the proton at low x and low using a soft and a hard Pomeron. The contribution of the soft Pomeron is based on the Stochastic Vacuum Model, in which a nonperturbative dipole-dipole cross section can be calculated by means of a gauge invariant gluon field strength correlator. To model the hard Pomeron exchange we phenomenologically extend the leading order evolution of a power-behaved structure function, , proposed by López and Ynduráin. This extension allows to consider both the case and the region of higher on the basis of the same parametrization. A good simultaneous fit to the data on and on the cross section of real photoproduction is obtained for . With four parameters we achieve a for 222 data points. In addition, we use our model of the inclusive interaction to compute the longitudinal structure function . Received: 6 December 1998 / Revised version: 19 April 1999 / Published online: 18 June 1999     

High Energy Proton-Proton Elastic Scattering in the Pomeron Exchange Model

We study high energy proton-proton elastic scattering in the framework of Pomeron exchange model. The cross section of the process are calculated without any free parameters. Our finding is that Pomeron exchange theory gives perfect fits to total cross section at the energy of √(s) higher than 10 GeV and to differential cross section at the momentum transfer |t| less than 1.5 GeV². For total cross section at lower energy √(s)<10 GeV and differential cross section at larger momentum transfer region of |t|>1.5 GeV², the Pomeron exchange theory needs to be improved.     

Calculations of one-loop supersymmetric corrections to large-E_T jet cross sections

We have calculated the one-loop supersymmetric corrections to the parton scattering subprocesses and , including form-factor corrections and box diagrams with internal squarks and gluinos of arbitrary mass. In general, these exhibit cusps at the corresponding direct-channel sparticle thresholds. We use these calculations to make numerical estimates of the possible threshold effects at the Fermilab Tevatron collider and at the LHC, which depend on the rapidity range selected, but can be as large as a few percent. These effects are diluted in the integrated large- cross section, where they are negative. Received: 18 August 1997 / Published online: 20 February 1998     

Inclusive D production in $\gamma \gamma$ collisions: including the single-resolved contribution with massive quarks

We have calculated the next-to-leading order cross section for the inclusive production of charm quarks as a function of the transverse momentum p_T and the rapidity in two approaches using massive or massless charm quarks. For the single-resolved cross section we have derived the massless limit from the massive theory. We find that this limit differs from the genuine massless version with factorization by finite corrections. By adjusting subtraction terms we establish a massive theory with subtraction which approaches the massless theory very fast with increasing transverse momentum. With these results and including the equivalent results for the direct cross section obtained previously as well as double-resolved contributions, we calculate the inclusive cross section in collisions using realistic evolved non-perturbative fragmentation functions and compare with recent data from the LEP collaborations ALEPH, L3 and OPAL. We find good agreement. Received: 14 February 2003 / Published online: 5 May 2003     

An analysis of diffraction in deep-inelastic scattering

We propose a simple parametrization for the deep-inelastic diffractive cross section. It contains the contribution of production to both the longitudinal and the transverse diffractive structure functions, and of the production of final states from transverse photons. We start from the hard region and perform a suitable extrapolation into the soft region. We test our model on the 1994 ZEUS and H1 data, and confront it with the H1 conjecture of a singular gluon distribution. Received: 30 June 1998 / Revised version: 3 September 1998 / Pulished online: 3 December 1998     

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     

Stronger neutrino interactions at extremely high energies and the muon anomalous magnetic moment

A specific model of parity-conserving lepton substructure is considered. We show that a positive-definite contribution to the muon at the possible level of about can be related to a significant increase in the interaction cross section for cosmic-ray neutrinos with energies above about eV. The additional cross section at eV is calculated to be cm, which is about 100 times the standard weak-interaction cross section. The model involves an extremely massive, neutral lepton, with GeV fixed by the new contribution to . Received: 28 May 2001 / Revised version: 13 November 2001 / Published online: 11 January 2002     

Evidence for production of single top quarks and first direct measurement of |Vtb|

The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron pp[over ] collider. Using a 0.9 fb(-1) dataset, we apply a multivariate analysis to separate signal from background and measure sigma(pp[over ]-->tb+X,tqb+X)=4.9+/-1.4 pb. The probability to measure a cross section at this value or higher in the absence of a signal is 0.035%, corresponding to a 3.4 standard deviation significance. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa matrix element that describes the Wtb coupling and find 0.68<|V(tb)|相似文献   

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     

Compton and double-compton scattering processes at colliding electron-photon beams

Radiative corrections to the Compton scattering cross section are calculated in the leading and next-to-leading logarithmic approximations in the case of colliding high-energy photon-electron beams. Radiative corrections to the double-Compton scattering cross section in the same experimental setup are calculated in the leading logarithmic approximation. We consider the case where no pairs are created in the final state. We show that the differential cross section can be written in the form of the Drell-Yan process cross section. Numerical values of the K-factor and the leading-order distribution on the scattered electron energy fraction and scattering angle are presented.     

Electroweak radiative corrections to polarized Møller scattering at high energies

The cross section for with arbitrary electron polarizations is calculated within the Electroweak Standard Model for energies large compared to the electron mass, including the complete virtual and soft-photonic radiative corrections. The relevant analytical results are listed, and a numerical evaluation is presented for the unpolarized and polarized cross sections as well as for polarization asymmetries. The relative weak corrections are typically of the order of 10%. At low energies, the bulk of the corrections is due to the running of the electromagnetic coupling constant. For left-handed electrons, at high energies the vertex and box corrections involving virtual W bosons become very important. The polarization asymmetry is considerably reduced by the weak radiative corrections. Received: 22 July 1998 / Published online: 8 September 1998     

The QCD pomeron in ultraperipheral heavy ion collisions: I. The double $J/\Psi$ production

The contribution of the QCD pomeron to the process is discussed. We focus on the photon-photon collision, with the quasi-real photon coming from the Weizs?cker-Williams spectrum of the nuclei. We calculate the cross section for this process considering the solution of the LLA BFKL equation at zero momentum transfer using a small t approximation for the differential cross section of the subprocess. Furthermore, the impa ct of non-leading corrections to the BFKL equation is also analyzed. In both cases the cross section is found to increase with the energy, predicting considerable values for the LHC energies. Moreover, we compare our results with the Born two-gluon approximation, which is energy independent at the photon level. Our results indicate that the experimental analyses of this process can be useful to discriminate the QCD dynamics at high energies. Received: 12 December 2002 / Published online: 7 March 2003 RID="a" ID="a" e-mail: barros@ufpel.tche.br RID="b" ID="b" e-mail: magnus@if.ufrgs.br     

Spin correlations in production and decay of charginos

We study the production of charginos with polarized beams and the subsequent decays and , including the complete spin correlations between production and decay. Analytical formulae are presented for the joint spin-density matrix of the charginos, for the chargino decay matrix and for the differential cross section of the combined processes of production and decays. We present numerical results for pair production of the lighter chargino with unpolarized beams and the leptonic decay of into the lightest neutralino . The lepton angular distribution and the forward-backward asymmetry are studied in four representative scenarios for GeV and GeV. Received: 28 April 1998 / Revised version: 18 June 1998 / Published online: 8 September 1998     

Neutrino oscillation and magnetic moment from \nu - e^{-} elastic scattering

We discuss how the measurement of the elastic cross section at reactor energies can be used to extract new information on the neutrino oscillation parameters. We also consider the magnetic moment contribution and show how both effects tend to cancel each other when the total cross section is measured. To achieve the separation of each of the effects, experiments capable of measuring angular and energy distributions with respect to the outgoing electron become necessary. The sensitivity of these kind of experiments to magnetic moments, masses and mixings is discussed. We also discuss the possibility of measuring the magnetic moment of neutrinos via oscillation. Received: 12 September 1997 / Revised version: 22 December 1997 / Published online: 10 March 1998     

High Energy Proton-Proton Elastic Scattering in the Pomeron Exchange Model

We study high energy proton-proton elastic scattering in the framework of Pomeron exchange model. The cross section of the process are calculated without any free parameters. Our finding is that Pomeron exchange theory gives perfect fits to total cross section at the energy of√s higher than 10 GeV and to differential cross section at the momentum transfer [t] less than 1.5 GeV2. For total cross section at lower energy √s ＜ 10 GeV and differential cross section at larger momentum transfer region of |t| ＞ 1.5 GeV2, the Pomeron exchange theory needs to be improved.