A.A. Akhundov

A high statistics measurement of the proton structure functions F2(x, Q2) and R from deep inelastic muon scattering at high Q2

Abstract We present results on a high statistics study of the proton structure functions F 2 ( x , Q 2 ) and R = σ L / σ T measured in deep inelastic scattering of muons on a hydrogen target. The analysis is based on 1.8 × 10 6 events after all cuts, recorded at beam energies of 100, 120, 200 and 280 GeV and covering a kinematic range 0.06 ⩽ x ⩽ 0.80 and 7 GeV 2 ⩽ Q 2 ⩽260 GeV 2 . At small x , we find R to be different from zero in agreement with predictions of perturbative QCD.

Electroweak One Loop Corrections to the Decay of the Neutral Vector Boson

The electroweak radiative corrections to the partial decay widths of the Z-boson into a pair of leptons or quarks have been calculated in the standard theory: Z → ll, νν, qq. Results are presented in terms of two electroweak form factors, ϱ and κ, with simple physical interpretation. As a result of the calculational scheme used, the corrections are at most of the order of a few percent. They are rather stable against a variation of the Higgs boson mass MH. In the case of a heavy t-quark, the effective mixing parameter κ sin2θW may deviate from sin2θW  1 − MW2 / MZ2 by about 10%.

Model Independent QED Corrections to the Process ep eX

We give an exhaustive presentation of the semi-analytical approach to the model independent leptonic QED corrections to deep inelastic neutral current lepton-nucleon scattering. These corrections include photonic bremsstrahlung from and vertex corrections to the lepton current of the order φ(α) with soft photon exponentiation. A common treatment of these radiative corrections in several variables — leptonic, hadronic, mixed, Jaquet-Blondel variables — has been developed and double differential cross sections are calculated. In all sets of variables we use some structure functions, which depend on the hadronic variables and which do not have to be defined in the quark parton model. The remaining numerical integrations are twofold (for leptonic variables) or onefold (for all other variables). For the case of hadronic variables, all phase space integrals have been performed analytically. Numerical results are presented for a large kinematical range, covering fixed target as well as collider experiments at HERA or LEP⊗LHC, with a special emphasis on HERA physics.

Test of QCD and a measurement of Λ from scaling violations in the proton structure function F2(x, Q2) at high Q2

Abstract Scaling violations in the proton structure function F 2 ( x , Q 2 ) measured with high statistics in deep inelastic scattering of muons on a hydrogen target are compared to predictions of perturbative QCD. Excellent agreement is observed with numerical solutions of the evolution equations in leading and next-to-leading order. The QCD mass scale parameter Λ is determined from these data both in a flavour nonsinglet approximation and with a complete flavour singlet and nonsinglet treatment. An estimate of the gluon distribution in the proton is given.

Test of QCD and a measurement of Λ from scaling violations in the nucleon structure function F2(x,Q2)

Scaling violations in the nucleon structure function F2(x,Q2) measured with high statistics in deep inelastic scattering of muons on a carbon target are compared to predictions of perturbative QCD. Excellent agreement is observed with numerical solutions of the Altarelli-Parisi evolution equations over the entire x and Q2 range of data. In a next-to-leading order nonsinglet approximation, the QCD mass scale parameter ΛMS is determined to be 230±20(stat.)±60(syst.) MeV. A singlet to the data favours a soft gluon distribution.

Gravitational interaction to one loop in effective quantum gravity

We carry out the first step of a program conceived, in order to build a realistic model, having the particle spectrum of the standard model and renormalized masses, interaction terms and couplings, etc. which include the class of quantum gravity corrections, obtained by handling gravity as an effective theory. This provides an adequate picture at low energies, i.e. much less than the scale of strong gravity (the Planck mass). Hence our results are valid, irrespectively of any proposal for the full quantum gravity as a fundamental theory. We consider only non-analytic contributions to the one-loop scattering matrix elements, which provide the dominant quantum effect at long distance. These contributions are finite and independent from the finite value of the renormalization counter terms of the effective lagrangian. We calculate the interaction of two heavy scalar particles, i.e. close to rest, due to the effective quantum gravity to the one loop order and compare with similar results in the literature.

Leptonic QED corrections to the process ep → eX in Jaquet-Blondel variables

Abstract For the study of deep inelastic scattering at HERA, the use of Jaquet-Blondel variables is advantageous in several respects. We calculate the complete leptonic O (α) QED corrections for the reaction ep → eX in these variables. All but one phase space integrations are performed analytically. After exponentiation of soft photon corrections, an accuracy of at least 1% is matched. Numerical results are presented and compared to estimates based on the leading logarithmic approximation.

QED radiative corrections to massive fermion production in e+e− annihilation

Abstract Analytical formulae are obtained for the initial state QED corrections to massive fermion pair production in e + e − →f + f − . Results are presented in a form immediately applicable to the exchange of extra Z bosons. They include a cut on the photon energy and soft photon exponentiation. In addition to applications to top-quark production, numerical importance was found for γ exchange and τ and b-quark production at LEP/SLC energies.

Hunting the hidden standard Higgs

Abstract The mass of the Higgs scalar of the standary theory may be estimated through its influence on radiative corrections from a precise measurement of M Z and sin 2 θ W at SLC or LEP.

An effective field theory approach to the electroweak corrections at LEP energies

Abstract In the framework of the effective field theory (EFT) we discuss the electroweak (EW) corrections at LEP energies. We obtain the effective Lagrangian in the large m t limit, and reproduce analytically the dominant EW corrections to the LEP2 processes e + e − → γZ and e + e − → ZZ . To include effects of finite top-quark and Higgs masses, we use the effective Lagrangian at tree level and fit LEP1/SLD observables with four arbitrary parameters, plus α s ( m Z ). The EFT approach works remarkably well. Using the effective couplings determined from the fit, and tree-level EFT formulae, we predict the cross sections for e + e − → ZZ , γZ at a level better than 1%.