Non standard weak bosons at HERA collider

We compare the effects of non-standard weak bosons (NSB) expected fromE ₆-superstrings (Z′), strong Higgs (V ₀) and composite (spin 0, 1, 2) models by using the classical inclusive deep-inelastic “ep” scattering at HERA energies. TheX ² associated to polarized and unpolarized cross-sections, as well as the six combinations of asymmetries, allow us to derive significant bounds on the masses of the new bosons of various spins associated to some composite models with exception of the excitedZ ^*. We have also obtained some lower bounds for spin one bosons of different models (Z′,V ₀,Z ^*) which are stronger than the present experimental limits.     

Diffractive photoproduction of charm at the HERA ep collider

For various kinematical domains, the cross section for the diffractive photoproduction of D* mesons at the HERA ep collider is calculated within a model based on perturbation theory. The results obtained by using different models of the Pomeron are compared.     

Deep inelastic Compton scattering at theep collider HERA

Deep inelastic Compton scattering at HERA is investigated with the intention of determining the usefulness of this process in pinning down the photon and proton structure functions. We examine the contributions of the various _s and _s ² subprocesses that arise from the nonelementary structure of the photon atS _p =30000 GeV². An assessment is made of the sensitivity of this process to the various parton and photon structure functions presently available. In particular we study the possibility of directly measuring the gluon content of the proton and the photon as well as the quark fragmentation into a photon with this process. Theep laboratory frame helps to separate out the different contributions and in particular may allow a quantitative study of the box diagram term.     

Yang effect in multiparticle hadron production at the HERA collider

It is argued that the mean multiplicities in a deep-inelastic process that are measured at the HERA collider grow with increasing photon virtuality at a fixed invariant mass of final hadron states. This is yet another piece of experimental evidence in favor of the qualitative hypothesis put forth by C.N. Yang and his colleagues and of the quantitative predictions obtained by the present authors on the basis of QCD.     

Deep-inelastic heavy-quark production at the HERA collider within the QCD semihard approach

Deep-inelastic heavy-quark production in electron-proton interactions at the HERA collider energies is considered within the QCD semihard (k _T-factorization) approach. The dependence of the total and differential cross sections for the production of b quarks (and for muons arising in the subsequent semileptonic decay of B mesons) on the choice of unintegrated distributions of gluons in the proton is investigated. In particular, the gluon distributions obtained by solving the Catani-Ciafaloni-Fiorani-Marchesini evolution equation and the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-Balitsky-Fadin-Kuraev-Lipatov combined equation are used in numerical calculations. The results of the theoretical calculations are compared with latest experimental data obtained by the H1 and ZEUS Collaborations at the HERA collider.     

Coherent instabilities in the NICA collider

The thresholds of coherent beam instabilities in the NICA collider are analyzed in the present work. Studies were limited on the coherent oscillations in one of the rings due to the weakness of the beam-beam interaction forces when compared to the single-beam Coulomb forces. The thresholds of the single-beam and multiple-beam instabilities are estimated for the chosen collider operation scenario. Measures that have to be taken to suppress the instabilities are discussed.     

Signals for scalar top quark atep collider HERA

In the framework of the minimal supersymmetric standard model (MSSM) and theR-parity breaking model (RBM), we investigate production processes of the scalar top (stop) at HERA energies. These models are characterized by the possible existence of the light stop whose mass is lighter than those of the top quark and the other squarks. It is shown that in the MSSM the stop pair production via boson-gluon fusion gives a sizeable cross section and the most serious background $ep \to ec\bar cX$ could be suppressed by appropriate kinematical cuts. We also show that in the RBM the stop is singly produced in the neutral current processes and we have a clear signal as a sharp peak in the Bjorken parameterx distribution of the scattered electron.     

Coherent bremsstrahlung from relativistic channelled positrons

Poor beam collimation leads to overcompensation of suppression of coherent bremsstrahlung in the axial channelling case. This fact has been used to study the effect of beam divergence on the radiation emitted by relativistic (axially) channelled positrons. It has been found that due to beam divergence in the experiment of Alguard and co-workers in which radiation of 56 MeV positrons channelling along 〈110〉 rows of a silicon crystal is observed, coherent bremsstrahlung becomes an important contributing factor to the high frequency part of the observed spectrum.     

Coherent bremsstrahlung of relativistic electrons in antiferromagnets

The coherent bremssstrahlung (CB) of relativistic electrons in antiferromagnetic crystals is studied theoretically. It is shown that the internal magnetic field of an antiferromagnet has a negligible effect on CB. The complete CB spectrum is calculated for hematite, -Fe₂O₃.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 57–61, February, 1988.     

Investigation of the inelastic electroproduction of J/ψ mesons at the HERA collider within the semihard QCD approach

The results of theoretical calculations within the semihard (k _T-factorization) approach are compared with the latest data obtained in the ZEUS experiment at the HERA collider for the inelastic electroproduction of J/ψ mesons in the kinematical region specified by the inequalities 2 GeV² < Q ² < 80 GeV², 50 GeV < W < 250 GeV, 0.2 < z < 0.9, and ?1.6 < y _ψlab < 1.3. The dependence of these theoretical results on the choice of parametrization among three widely used parametrizations of unintegrated gluon distributions is studied.     

HadronicW-decays at HERA

ep collisions at HERA will produce realW's with a cross section of almost 1 pb. We discuss to what extent the hadronic decays of theseW's will be visible above the QCD background. Using optimal cuts to enhance the hadronicW signal, a clearW peak should be visible after several years of running at HERA.     

Ultimate parameters of the photon collider at the international linear collider

At linear colliders, the e ⁺ e ⁻ luminosity is limited by beam-collision effects, which determine the required emittances of beams in damping rings (DRs). In γγ collisions at the photon collider, these effects are absent, and so smaller emittances are desirable. In the present damping ring designs, nominal DR parameters correspond to those required for e ⁺ e ⁻ collisions. In this note, I would like to stress once again that as soon as we plan the photon collider mode of ILC operation, the damping ring emittances are dictated by the photon collider requirements — namely, they should be as small as possible. This can be achieved by adding more wigglers to the DRs; the incremental cost is easily justified by a considerable potential improvement of the γγ luminosity. No expert analysis exists as of now, but it seems realistic to obtain a factor five increase of the γγ luminosity compared to the ‘nominal’ DR design.      

The lay-out of the photon collider at the international linear collider

One of the interaction regions at the linear colliders should be compatible both with e ⁺ e ⁻ and γγ, γe modes of operation. In this paper, the differences in requirements and possible design solutions are discussed.      

Physics at the linear collider

The physics at the plannede ⁺ e ^- colliders is discussed around three main topics corresponding to different manifestations of symmetry breaking:W physics in the no Higgs scenario, studies of the properties of the Higgs and precision tests of SUSY. A comparison with the LHC is made for all these cases. The γγ mode of the linear collider will also be reviewed.