Two-photon-exchange contribution to proton form factors in both space-like and time-like regions

The two two-photon exchange corrections to the unpolarized cross section and polarized observable PT,PL in elastic ep scattering are discussed in a simple hadronic model.Comparing with previous results,theΔ contribution are re-analysed.And the similar corrections in e+e-→ p(p-)are also discussed.     

Electroweak radiative corrections to e+e− → Z0Z0

The cross section for e⁺e⁻ → Z⁰Z⁰ with arbitrary polarizations of the leptons and bosons is calculated in the standard electroweak model including the complete one-loop virtual and soft-photon bremsstrahlung corrections. All necessary analytical formulas are presented; numerical results are discussed for the unpolarized case and for the polarization asymmetry. At LEP 200 energies the weak corrections are dominated by the self-energy of the external Z⁰-bosons which contributes about +15%. With increasing energy, the weak corrections decrease up to -18% at 1 TeV due to other contributions.     

On radiative corrections for unpolarized electron-proton elastic scattering

A statistical analysis of the elastic unpolarized electron-proton scattering data shows that at large momentum transfer the size and the ε dependence of the radiative corrections, as traditionally calculated and applied, may induce large correlations of the parameters of the Rosenbluth fit, which prevent a correct extraction of the electric proton form factor. Using the electron QED structure (radiation) function approach, the cross section of elastic electron-proton scattering in leading and next-to-leading approximations is calculated and expressed as a correction to the Born cross section, which is different for the electric and magnetic contributions. When properly applied to the data, it may yield the solution to the problem of the discrepancy of the polarized and unpolarized results on electron-proton scattering. The text was submitted by the author in English.     

Electroweak radiative corrections toe + e −→HZ

The cross section fore ⁺ e ^–HZ with arbitrary lepton andZ-boson polarizations is calculated within the electroweak standard model including the completeO() virtual and soft photonic corrections. These were obtained using the computer-algebra packagesFeynArts andFeynCalc. We list the relevant analytical results and discuss the influence of the weak radiative corrections on the unpolarized as well as the polarized cross sections. For LEP200 energies the weak radiative corrections amount to several per cent. For higher energies the corrections are usually of the same order for the total unpolarized cross section. However, for large values of the Higgs mass or for the suppressed cross section of transversely polarizedZ-bosons they reach +30% and –40%, respectively. The differential cross section in the forward and backward directions gets even larger corrections for high energies, where the box diagrams constitute the dominant part of the radiative corrections.     

Determination of the strong coupling constant using available experimental data

We determine the strong coupling constant α s up to 4-loop in perturbative QCD.Testing QCD requires the measurement of α s over ranges of energy scales.In this analysis,the value of α s is determined from the unpolarized structure functions data points by minimizing the χ 2 function between the theory result and experimental data.Using perturbative QCD calculations from threshold corrections,we obtain α s (M 2 Z ) = 0.1139±0.0020 at N 3 LO which is in good agreement with the very recently results from the inclusive jet cross section in pp collisions at√ s=1.96 TeV.     

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     

QCD corrections to the reactionp + \bar p \to W + \gamma + X

The complete order α _S QCD corrections to the cross section and differential distributions for \(p + \bar p \to W + \gamma + X\) are presented. At the quark level this involves the computation of the contributions from the reactions \(q + \bar q \to W + \gamma + g and q(\bar q) + g \to W + \gamma + q + (\bar q)\) . We discuss how these corrections modify the factorization property of the lowest order amplitude and give results for future experiments at CERN and Fermilab.     

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.     

Large-angle compton scattering in perturbative QCD

The processes γp→γp and γn→γn are studied in perturbative QCD for large scattering angles. The unpolarized cross sections, as well as the cross sections for polarized beams and targets, are given for various choices of the baryon wavefunction. The predictions for the unpolarized cross section of γp→γp are compared with the available data. Possible future experimental verifications of the theory are discussed.     

In-medium Δ Absorption Cross Section

An exact expression for calculating the in-medium △ absorption cross section is obtained within the framework of the self-consistent relativistic BUU approach. The medium effects on the △N→NN cross section is investigated, and it is found that the effective cross sation is suppressed in the medium near the threshold energy. The results are in a good agreement with the most recent experimental data of the TAPS collaboration.     

In-medium Nucleon-Nucleon Inelastic Scattering Cross Section(Ⅰ)

The explicit expressions for in-medium NN→N△ cross section are derived within the relativistic Boltzmann-Uehling-Uhlenbeck approach,which are given simultalleously with the other integrants of transport model such as the mean field, NN elastic scattering cross section as well as the transport equation itself based on the effective Lagrangian.Our results can reproduce the experimental data of free inelastic cross section nicely.The in-medium inelastic cross section is calculated up to twice nuclear matter density and is in agreement with the Dirac-Brueckner calculations.     

Radiative effects in the processes of hadron electroproduction

An approach to calculate radiative corrections to the unpolarized cross section of semi-inclusive electroproduction is developed. Explicit formulae for the lowest order QED radiative correction are presented. A detailed numerical analysis is performed with the kinematics of experiments with fixed targets. Received: 17 March 1999 / Revised version: 18 June 1999 / Published online: 28 September 1999     

Measurement of the analyzing power in p-->d-->(p p)n with a fast forward 1S0 proton pair

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.     

△共振态的硬过程及软过程产生截面在同位旋不对称核体系下的介质修正研究

基于一个相对论的BUU方法,研究了△共振态的硬过程（NN → N△）及软过程（Nπ → △）产生截面及△的衰变宽度在同位旋不对称核体系下的介质修正（包括能量、密度、特别是同位旋依赖的）效应。发现类似于核子-核子弹性散射过程,△硬过程产生截面的密度修正及在同位旋不对称体系下的质量劈裂效应都比较强烈,而△的软过程产生截面及衰变宽度的密度依赖和质量劈裂效应都相对较弱。对硬过程,其截面最大的劈裂效应出现在△++和△-的产生道中,而对软过程,△++和△-的产生道中的劈裂效应则最小且与硬过程的相反。Within the framework of the relativistic BUU approach, we investigate the effect of energy-, density-, and especially isospin-dependent medium modifications on △ production cross sections of both hard (NN → N△) and soft (Nπ → △) processes as well as its decay width. It is found that, similar to the nucleon-nucleon elastic scattering, the △ production cross section from the hard process is strongly dependent on both density and the mass splitting effect in the isospin asymmetric matter. While the dependence is relative weak from the soft one, and so is the △ decay width. Further, in the hard (soft) process, the splitting effect is largest (smallest) and of opposite sign for the △++ and △- states.     

Photoionization Cross Section and Resonance Structure of Mn+

A photoionization cross section calculation of Mn⁺ is performed in the formalism of many-body perturbation theory for photon energies ranging from 48 eV to 56 eV. We consider excitations from the 3p, 3d, and 4s subshells. The effects of the strong 3p→3d and 3p→4s transitions are included as resonant contributions to the total cross sections. Good agreement with experiment is found.     

Radiative corrections to polarization observables in elastic electron-deuteron scattering in leptonic variables

The model-independent QED radiative corrections to polarization observables in elastic scattering of unpolarized and longitudinally polarized electron beams by a deuteron target are calculated in leptonic variables. The experimental setup when the deuteron target is arbitrarily polarized is considered and the procedure for applying the derived results to the vector or tensor polarization of the recoil deuteron is discussed. The calculation is based on taking all essential Feynman diagrams into account, which results in the form of the Drell-Yan representation for the cross section, and the use of the covariant parameterization of the deuteron polarization state. Numerical estimates of the radiative corrections are given in the case where event selection allows undetected particles (photons and electron-positron pairs) and the restriction on the lost invariant mass is used.     

Isolated photon plus jet photoproduction as a toolto constrain the gluon distribution in the proton and the photon

We analyse how the reaction can serve to constrain the gluon distributions. Our results are based on a code of partonic event generator type which includes full NLO corrections. We conclude that there are phase space domains in which either the gluon in the photon or the gluon in the proton give important contributions to the cross section, which should be observable in HERA experiments.Received: 8 December 2003, Revised: 19 January 2004, Published online: 12 March 2004     

Double-charm production e+e- -->J/psi + cc at B factories with next-to-leading-order QCD corrections

The inclusive J/psi production in e;{+}e;{-}-->J/psicc at B factories is one of the most challenging open problems in heavy quarkonium physics. The observed cross section of this double-charm production process is larger than existing leading order (LO) QCD predictions by a factor of 5. In the nonrelativistic QCD (NRQCD) factorization formalism, we calculate the next-to-leading order (NLO) QCD virtual and real corrections to this process, and find that these corrections can substantially enhance the cross section with a K factor of about 1.8. We further take into account the feeddown contributions from higher charmonium states [mainly the psi(2S) as well as chi_{cJ}] and the two-photon contributions, and find that the discrepancy between theory and experiment can be largely removed.     

Studies of unitarity at small x using the dipole formulation

Mueller's dipole formulation of onium-onium scattering is used to study unitarity corrections to the BFKL power growth at high energies. After a short discussion of the spatial distribution of colour dipoles in a heavy quarkonium and the associated fluctuations, results are presented showing that the one- and two-pomeron contributions to the total cross section are the same at a rapidity Y ≅ 14. Above this rapidity the large fluctuations in the onium wave function cause the multiple pomeron series to diverge. Resumming the series allows one to show that unitarity corrections set in gradually for the total cross section, which is dominated by rare, large, configurations of the onia. The elastic cross section comes mostly from much smaller impact parameters and has significant unitarity corrections starting at a rapidity Y ≅ 8.