HERA Energies Research Articles

Deep inelastic production of charged vector bosons at HERA energies

We discuss the production of gauge bosons in polarized and unpolarized deep inelastice P-scattering in the context of the standard modelSU(3)×SU(2)×U(1) of the strong and electroweak interactions. We present results for the total and the differential cross sections as functions of the parameters of the outgoing lepton for energies available at HERA in the near future. Besides the γ-exchange diagrams we also have included the contributions ofW- andZ-exchange. We find that they cannot be neglected especially for the processe−P→veW−X.

Characteristics of heavy flavour production inep collisions

The production of heavy flavours inep collisions at the HERA energy is studied using a model based on boson-gluon fusion into a heavy quark-antiquark pair followed by gluon emission and string hadronization. Total cross-sections and dependence on basic kinematical variables are given as well as distributions of the most important variables at both the quark and hadron level, e.g. rapidity and transverse momentum. Charm, bottom and top production is compared and signatures for their separation are discussed in terms of decay muons and global event shape properties.

J/ψ and γ production in high energy electron-proton collisions

Abstract Differential cross sections for electroproduction of J/ψ and γ are predicted for HERA and LHC energies.

Exotic fermion production in a new left-right model at ep colliders

We consider the production at ep colliders of exotic fermions expected in E6 grand unified theories within the context of a new, superstring-inspired, left-right symmetric model. The process e−p→nh+X (with n and h being exotic fermions) proceeds via t-channel WR exchange and can lead to significant production cross sections at HERA energies (√s = 314 GeV) as well as at higher energy ep colliders.

Gaugino-higgsino mixing and slepton-squark production in ep collisions

We consider gaugino-higgsino mixing in the minimal supersymmetric extension of the standard model and determine the mass eigenstates and eigenvalues taking the physical masses of the lightest chargino and neutralino as input in the diagonalization procedure. Using the results we calculate cross sections and charge asymmetries for the associated production of sleptons and squarks in ep collisions and investigate the dependence on the chargino and neutralino properties and on the slepton and squark spectrum. The numerical analysis is performed within the minimal supergravity model as well as in a more general framework. Although predictions are made also for higher energies, the main focus is on the HERA energy range. We indicate the values of sparticle masses accessible to SUSY searches at HERA and illustrate the expected reach beyond the present bounds.

Photon gluon fusion cross sections at HERA energy

We present cross sections for heavy flavour production through photon gluon fusion in electron proton collisions at HERA energy. The electron photon vertex is taken into account explicitly, and theQ 2 of the exchanged photon ranges from nearly zero (almost real photon) to the kinematically allowed maximum. In our approach the scale is set by the mass of the produced quarks. Our formalism is also applicable to the production of light quarks as long as the invariant mass of the pair is sufficiently high, so we also give cross sections for $$u\bar u,d\bar d$$ and $$s\bar s$$ production.

Top quark production at HERA

Top quark production in ep-collisions at HERA energies is studied. In particular the reaction ep → ν tbX is analyzed. The exact analytic expression for the single top production cross section, including all quark mass effects, is derived and evaluated for different values of the t-quark mass m t. The results are compared with the rates obtained from e b → ν tX where the b-quark is regarded as a sea quark in the proton and also with the rates for top-quark pair production. At HERA, single production of t-quarks is found to dominate over t t production for m t ⪆ 60 GeV . The exact pair production rate for top quarks agrees with the one in the Weizsäcker-Williams approximation up to ∼ 15 %. A TeV ep-collider will give access to singly produced top quarks with masses up to several hundred GeV.

Radiative corrections to charged current deep inelastic electron-proton scattering at HERA

We present analytic formulas and numerical results for the complete electroweak radiative corrections of O( α 3) to charged current deep inelastic electron-proton scattering at HERA energies. The calculations are performed in the framework of the quark parton model and the electroweak standard theory. Hard bremsstrrahlung contributions integrated over the full available phase space are included.

Production of charged Higgs particles in the two-photon process at e-p scattering (HERA)

The production of charged Higgs particles via a two-photon process at the e-p collider (HERA) is calculated. We consider two cases. For Q 2 ⩽ 1 GeV 2 the process is considered quasi-elastically and the proton form factor was taken into account. For Q 2 ⩾1 GeV 2 the process is considered deep inelastically. It is shown that the production of charged Higgs particles via a two-photon process in the ep collider is the most significant one at the expected HERA and higher energy. Expected numbers of H +H − events at HERA are given.

Radiative corrections to neutral current deep inelastic lepton nucleon scattering at HERA energies

We calculate the complete electromagnetic and weak radiative corrections of O(α3) to neutral current deep inelastic lepton proton scattering at HERA energies in the framework of the quark parton model. QCD scaling violations in the leading logarithmic approximation are also included. We give predictions for the unpolarized cross section and the polarization and charge asymmetries and discuss the theoretical uncertainties due to the dependence of the radiative corrections on electroweak parameters, quark masses and parton distribution functions.

THE PRODUCTION OF WEAK INTERMEDIATE BOSONS IN e-p REACTIONS

The calculations of production cross sections of W’ s and Z0’ s in e-p reactions at HERA energies and beyond are revised, improved and updated. Comparison with previous calculations show that in some cases the cross sections were considerably overestimated. The effects of a possible deviation of the W anomalous magnetic moment from the standard model value are also discussed.

Signals for compositeness atep colliders: ?Leptogluons? and exotic colored vectorbosons

Production rates and signals for coloroctet leptonsl 8 atep machines like Hera and a $$\sqrt s = 2$$ TeV collider are presented. In case of very heavy leptogluons:m 8≈0(100 GeV) we argue that rates based on direct electron-gluon fusion are possibly strongly overestimated in the literature. In composite models the appearance of leptogluons always implies the existence of color exotic vectorbosons. Therefore we considerl 8 production in electron-quark scatterings. We find that even at HERA energies such reactions should be detectable if there is nearby compositeness (Λ H ∼ several TeV) and the mass of the coloroctet neutrinom v8<180 GeV. From such events it would be possible to extract information on the deeper structure of the preon model.

The deep Compton scattering: Single photon spectrum and photon-hadron correlations beyond leading logarithms

We have calculated higher order QCD corrections to the Deep Inelastic Compton single inclusive cross-section. The perturbation expansion seems to be well behaved: the corrections are small and the fully corrected cross-section depends little on the factorization scale which is chosen. A complete phenomenological study at SPS, Tevatron and HERA energies is performed and theoretical predictions tend to be in good agreement with preliminary experimental data. The corrections to the double inclusive cross-section (σ(γp→γhX) are also calculated and found to be small in the region of physical interest for σ(γp→γπ+X)−σ(γp→γπ−X)

The nonforward QCD ladder diagrams

We extend the standard analysis of the QCD planar ladder diagrams to the nonforward direction. Results are used for calculating exclusive and semiinclusive cross sections of diffractive photoproduction in the small-x region ofep-collisions. As an example we estimate the event rate for diffractive photoproduction of the neutral vector boson at Hera energies.

QCD and hadronic energy flow at SPS and HERA energies

Studies angular distributions of the hadronic energy released in muon (electron)-nucleon deep inelastic scattering, to the first order in perturbative QCD, over a conveniently extended phase-space region, namely from SPS accelerator energies where the quark content of the target dominates, to the expected HERA regime where the gluonic component is proved the most important.

Radiative corrections to very high energy electron-proton scattering

A “leading log” analysis of radiative corrections to inclusive ep scattering at HERA energies is presented. Neutral current weak interactions are considered at the level of the Born cross section as well as of the modifications of vertex and vacuum polarization parts. The leading log approximation has been also improved in the single hard and multiple soft photon emission by appropriate kinematical considerations. Some numerical results are presented for polarized electron and positron beams.