Collinear radiative electron-positron scattering in the leading logarithmic approximation

Radiative corrections to the cross section of the radiative large-angle Bhabha scattering process at high energies are calculated. The kinematics in which a hard photon is emitted along one of the momentum directions of the charged fermions is considered. Contributions coming from the emission of virtual, soft, and hard additional photons are taken into account in the leading logarithmic approximation. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 851–855 (25 June 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Baryon stopping in proton–nucleus collisions

We calculate the inclusive small-x valence quark production cross section in proton–nucleus collisions at high energies. The calculation is performed in the framework of the Color Glass Condensate formalism. We consider both the case when the valence quark originates inside the nucleus and the case when it originates inside the proton. We first calculate the cross section in the quasi-classical approximation resumming the multiple rescatterings with the nucleus. Then we include the effects of double logarithmic reggeon evolution and leading logarithmic gluon evolution in the obtained cross section. The calculated nuclear modification factor for the stopped baryons exhibits Cronin enhancement in the quasi-classical approximation and suppression at high energies/rapidities when quantum evolution corrections are included, providing a new observable which can be used to test Color Glass physics.     

One-loop corrections to e+e− → e+e− in the weinberg model

Radiative corrections to Bhabha scattering are calculated in the simplest example of non-Abelian gauge theories. A detailed analysis of the higher-order effects is presented and the total differential cross section including weak corrections is evaluated at different angles in an energy range up to 70 GeV per beam. The effects of weak interactions appear to be negligible up to the production of the neutral vector boson.     

Violation of the factorization theorem in large angle radiative Bhabha scattering

The lowest order QED radiative corrections to the radiative large angle Bhabha scattering process in the region where all kinematic invariants are large compared to the electron mass are considered. We show that the leading logarithmic corrections do not factorize before the Born cross section, contrary to the picture assumed in the renormalization group approach. The leading and non leading contributions for typical kinematics of the hard process at the energy of the Φ factory are estimated. Zh. éksp. Teor. Fiz. 115, 392–403 (February 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Emission in the final state in processes with the production of charged pions and light leptons

The Drell-Yan form is proposed for the decay widths of heavy quarks and cross sections for high-energy scattering with the production of charged pions and light leptons including radiative corrections in the final state in the leading logarithmic approximation. The corresponding spectral distributions are given in terms of the convolution of the cross section (decay width) in the Born approximation with the structure functions of pions and leptons. The pion structure function is given in the explicit form.     

QCD corrections to electroweak vector boson scattering at small scattering angles

We investigate the role of a certain class of QCD corrections to electroweak vector boson scattering at small scattering angles and large energies. These are present since, from the perturbative analysis, the vector bosons may dissociate into quark-antiquark pairs giving rise to color dipoles interacting through gluon exchanges. After the computation of the vector boson impact factors, we present expressions for the lowest order QCD scattering amplitude and for the leading logarithmic BFKL amplitude. Particularly we discuss numerical results for the process . The QCD corrections to the cross section resulting from the interference with the electroweak ones are estimated and compared with the leading pure electroweak part. Corrections resulting from the leading log BFKL amplitude are of the order of a few percent already at the 0.5-1 TeV energy range.Received: 21 May 2003, Published online: 29 August 2003     

Monte-Carlo generator photon jets for the process e+e?→γγ

Monte-Carlo generator with photon jets radiation in collinear regions for the process e ⁺ e ⁻→γγ is described in detail. Radiative corrections in the first order of α are treated exactly. Large leading logarithmic corrections coming from collinear regions are taken into account in all orders of α by applying the Structure Function approach. Theoretical precision of the cross section with radiative corrections is estimated to be 0.2%. This process is considered as an additional tool to measure luminosity in forthcoming experiments with the CMD-3 detector at the e ⁺ e ⁻ collider VEPP-2000.     

Radiative corrections to low-energy ππ scattering

Radiative corrections to low-energy ππ scattering are calculated. A chiral SU(2) × SU(2) Lagrangian is used to describe low-energy scattering. This strong interaction Lagrangian is modified in the presence of the electromagnetic field in a gauge invariant way. It is found that photons do not probe the strong vertex. Corrections to the cross sections are calculated to O(α). All the ultra-violet divergences cancel, and the results are independent of cut-off parameters. Corrections to the Weinberg scattering lengths of the order of 1% are defined by removal of the Coulomb pole terms. The field theoretic calculation is compared with a potential theory approach. It is argued that the potential theory calculation of radiative corrections is more reliable.     

Hard pair production in large-angle Bhabha scattering

The cross section of hard pair production in large-angle Bhabha scattering is calculated in the leading and next-to-leading logarithmic approximations. Eight regions of the collinear kinematics, when the final particles imitate a process of the 2 → 2 type, and three semicollinear regions, when the final particles imitate a process of the 2 → 3 type, are considered. Analytical formulae for differential cross sections are presented.     

Monte-Carlo generator for e+e- annihilation into lepton and hadron pairs with precise radiative corrections

Recently, various cross sections of e⁺e^- annihilation into hadrons were accurately measured in the energy range from 0.37 to 1.39 GeV with the CMD-2 detector at the VEPP-2M collider. In the π⁺π^- channel a systematic uncertainty of 0.6% has been achieved. A Monte-Carlo Generator Photon Jets (MCGPJ) was developed to simulate events of Bhabha scattering as well as production of two charged pions, kaons and muons. Based on the formalism of structure functions, the leading logarithmic contributions related to the emission of photon jets in the collinear region are incorporated into the MC generator. Radiative corrections (RC) in the first order of α are accounted for exactly. The theoretical precision of the cross sections with RC is estimated to be better than 0.2%. Numerous tests of the program as well as a comparison with other MC generators and CMD-2 experimental data are presented.     

QCD corrections to γγ→ZZ at small scattering angles

QCD corrections to the electroweak cross section of γγ→ZZ at high energies and small scattering angles have been calculated. The dominant contributions are due to t-channel gluon exchange, i.e., photons dissociate into quark–antiquark pairs giving rise to two colour dipoles which interact through gluons. Corrections resulting from the leading log BFKL amplitude are of the order of a few percent close to the forward region already at the 1 TeV energy range and are rising with the scattering energy. We also considered the helicity non-conserving cases in which the QCD corrections in comparison to the electroweak part of the amplitude strongly grow with energy. The helicity non-conserving scattering process is of particular interest since it is sensitive to the Higgs sector.     

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.     

An inclusive approach to scanning e + e −→π+π− cross section below 1 GeV by the radiative-return method

An inclusive approach to measuring e ⁺ e ^?→π⁺π^? cross section by the radiative-return method is discussed. This approach is substantially based on the choice of selection rules that exclude three-pion events and reduce the radiation background in the final state. Radiative corrections in the process with emission in the initial state are calculated for the DAPHNE conditions by treating the cross section form and the kinematics of the radiative process in the quasi-real electron approximation.     

Radiative corrections to polarized inelastic scattering in the coincidence setup

We completely analyze the model-independent leading radiative corrections to the cross section and polarization observables in the semi-inclusive deep-inelastic electron-nucleus scattering with the detection of a proton and the scattered electron in coincidence. The calculations are based on representing the spin-independent and spin-dependent parts of the cross section in terms of the electron structure functions similarly to the Drell-Yan-like representation in electrodynamics. As the applications, we consider the polarization transfer effect from a longitudinally polarized electron beam to the detected proton and the scattering by a polarized target.     

Deep inelastic scattering with tagged photons at HERA

We calculate cross-sections for neutral current deep inelastic scattering at HERA with photon tagging. Both, the exact lowest-order cross-section and a leading logarithmic approximation of next-order corrections are calculated. The latter amounts to less than 20% in a large kinematical range. The integrations are performed numerically but without relying on Monte Carlo methods.     

Leading log radiative corrections to deep inelastic neutral and charged current scattering at HERA

TheO(α) radiative corrections for neutral and charged current deep inelastic scattering are calculated in the leading log approximation. The numerical results are found to agree within a few per cent with the results of a completeO(α) calculation by Bardin et al. It is demonstrated that both for the leading log and completeO(α) calculation all light quark mass terms can be eliminated from the cross section.     

Radiative corrections to the cross section for <Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> + <Emphasis Type="Italic">p</Emphasis> → <Emphasis Type="Italic">v + n</Emphasis> and the crossed processes

The Born cross section and the radiative corrections to its lowest order are considered in the framework of QED with structureless nucleons including the emission of virtual and real photons. The result is generalized to take into account the radiative corrections in higher orders of the perturbation theory in the leading and next-to-leading logarithmic approximation. The crossing processes are considered in the leading approximation. The text was submitted by the authors in English.     

Dispersion corrections to the forward Rayleigh scattering amplitudes around the L‐shell of tantalum and lead

Dispersion corrections to the forward Rayleigh scattering amplitudes of tantalum and lead in the photon energy range 6.4–24.14 keV were determined by a numerical evaluation of the dispersion integral that relates them through the optical theorem to the photoelectric cross‐sections. The photoelectric cross‐sections were extracted by subtracting the coherent and incoherent scattering contribution from the measured total attenuation cross‐section, using a high‐resolution, high‐purity germanium detector in a narrow‐beam good geometry setup. The real part of the dispersion correction to which the relativistic corrections calculated by Kissel and Pratt (S‐matrix approach) or Creagh and McAuley (multipole corrections) have been included are in better agreement with the available theoretical values than those values to which the relativistic corrections calculated by Cromer and Liberman (dipole corrections) are added. Copyright © 2006 John Wiley & Sons, Ltd.     

Tagged-photon events in polarized deep inelastic scattering

Deep inelastic scattering events of a longitudinally polarized electron by a polarized proton with a tagged collinear photon radiated from the initial-state electron are considered. The corresponding cross section is derived in the Born approximation. The model-independent radiative corrections to the Born cross section are also calculated. The obtained result is applied to the elastic scattering.