abstract

Recent data from proton–antiproton collisions at high energy provide information on the masses of the Top quark and \(W\) boson. The \(W\) asymmetry data constrains the slope of the \(d/u\) quark distributions and significantly reduces the systematic error on the extracted value of the \(W\) mass. Drell–Yan dilepton production at high invariant mass yield limits on extra \(Z^\prime \) bosons, and place strong limits on quark substructure. Compositeness limits from CDF Run 1, and expected sensitivity in Run II and TEV33 are presented.

abstract

The analytical approach is applied for description of small angle Bhabha scattering at LEP1. The QED correction to the Born cross-section is calculated with leading and next-to-leading accuracy in the second order of the perturbation theory and with leading one in the third order. All contributions due to photon emission and pair production in the second order are calculated starting from essential Feynman diagrams. The third order corrections are computed by means of the electron structure function method. Inclusive and calorimeter event selections for asymmetrical wide-narrow circular detectors are investigated.

abstract

We describe the state of the art in the field of radiative corrections for deep inelastic scattering. Different methods of calculation of radiative corrections are reviewed. Some new results for QED radiative corrections for polarized deep inelastic scattering at HERA are presented. A comparison of results obtained by the codes POLRAD and HECTOR is given for the kinematic regime of the HERMES experiment. Recent results on radiative corrections to deep inelastic scattering with tagged photons are briefly discussed.

abstract

Selected HERA results on QCD and EW interactions are presented. They include the measurement of the proton structure function and its analysis in terms of the QCD evolution, as well as results concerning deep inelastic scattering at very low and very high \(Q^2\). Selected HERA limits on new physics and parameters which extend the standard model are also presented.

abstract

Spin properties of the nucleon are discussed based on the ongoing and planned measurements. Role, method and features of radiative corrections applied in the analyses are presented. Future prospects of the spin physics are reviewed.

abstract

Physics of the radiative corrections to deep inelastic inclusive and semi-inclusive experiments of polarized particles is discussed. The new version of FORTRAN code POLRAD 2.0 is presented. Current status is described.

abstract

Predictions of perturbative QCD (pQCD) for inclusive production of direct photons and mesons at high \(p_T\) are tested using new high-statistics measurements from Fermilab experiment E706. Inclusive cross sections are presented for 515 GeV/\(c\) \(\pi ^-\) and 530 and 800 GeV/\(c\) proton beams incident on a Be target, and for the kinematic range 4< \(p_T\) <10 GeV/\(c\) and central rapidities. Current Next-to-Leading Log (NLL) QCD calculations fail to accommodate the data for usual choices of scales. The data indicate the presence of a substantial effective \(k_T\); a phenomenological model of \(k_T\) effects improves the agreement between the calculations and the cross section data.

abstract

A brief overview is presented of recent developments concerning resummed small-\(x\) evolution, based upon the renormalization group equation. The non-singlet and singlet structure functions are discussed for both polarized and unpolarized deep-inelastic scattering. Quantitative results are displayed and uncertainties from uncalculated subleading terms are discussed.

abstract

The three-loop QCD correction to the \(R_{e^+e^-}\) ratio is discussed. It is pointed out that the three-loop coefficient is dominated by the term proportional to \(\pi ^2\), which appears as a result of analytic continuation from spacelike to timelike momenta. The possibility of all-order resummation of some of the large contributions of this type is considered. It is demonstrated that the resummed predictions are much less sensitive to the change of the renormalization scheme than the predictions obtained with the conventional expansion. Also the difference between two-loop and three-loop results is significantly reduced. Similar remarks are shown to apply in the case of QCD correction to \(\mit \Gamma ^{{\rm had}}_Z\).

abstract

We discuss some properties of the algorithm ALPHA developed in collaboration with M. Moretti (F. Caravaglios, M. Moretti. Phys. Lett. B358, 332 (1995); F. Caravaglios, M. Moretti, Oxford University preprint OUTP-9613P, e-Print: hep-ph/9604316).

abstract

The calculation of the \(\mathcal {O}(N_f \alpha ^2\)) corrections to muon decay is described. These are the 2-loop diagrams containing a massless fermion loop and they form an important gauge-invariant subclass. It is shown that all such diagrams can be expressed in terms of a universal master integral. We focus on the calculation of box diagrams and in particular on the removal of their infrared divergences.

abstract

Studies of photon radiation in leptonic reactions recorded with the four LEP experiments are presented. The predictions of the Monte-Carlo programs for photon spectra and angular distributions show excellent agreement with data. Events with photon radiation in the initial state provide information about lepton-pair production at reduced centre-of-mass energies. A large number of the events recorded at nominal centre-of-mass energies well above the Z resonance are due to the “radiative return to the Z”. Separating these events from the “genuine high energy events” allows to measure fermion-pair production at 130 GeV < \(\sqrt {s}\) < 140 GeV. The measurement of photon radiation in the reactions \(e^+e^- \to \mu ^+ \mu ^- \gamma \) and \(e^+e^- \to \nu \bar \nu \gamma \) puts limits on the existence of anomalous Z\(\gamma \) couplings.

abstract

The most interesting theoretical features of \(W\)-pair production in \(e^+e^-\) collisions are reviewed. Based on an analysis of on-shell \(W\)-pairs, it is shown that the mere inclusion of leading \(\mathcal {O}(\alpha \)) corrections — such as initial-state radiation, effects from the universal quantities \(\Delta \alpha \) and \(\Delta r\), and the Coulomb singularity — cannot be expected to approximate the \(\mathcal {O}(\alpha \))-corrected cross-section of \(e^+e^- \to WW \to 4f\) to better than 1-2% for LEP2 energies. The importance of the gauge-invariance problem, arising from the introduction of finite decay widths, is discussed. The simplest consistent method to include \(\mathcal {O}(\alpha \)) corrections at least to the doubly resonant contributions, \(viz\) a pole expansion around the double resonance, is also briefly described.

abstract

The status of the LEP 1 results, the LEP 2 perspectives and some recent developments in high energy physics at \(e^+e^-\) machines are briefly discussed.

abstract

Recent data on precision tests of the standard model at LEP are presented and compared with the theoretical expectations. These results are obtained by a preliminary analysis of all the data collected at LEP between 1990 and 1995.

abstract

The importance of \(\alpha (m^2_{\rm Z})\) for the Standard Model fits is discussed. It is shown that the error of \(\alpha (m^2_{\rm Z})\) ultimately limits the Standard Model interpretation of the \(\sin ^2\theta ^{{\rm lept}}_{{\rm eff}}\) measurements. Possibilities for improvements are being discussed.

abstract

A survey is given of the various gauge-invariance-related aspects that play a role when dealing with unstable gauge bosons.

abstract

Status of wide angle Bhabha Monte Carlo generators is reviewed, referring to experimental searches for excited electrons in \(e^+ e^-\) collisions at LEP2.

abstract

The DELPHI collaboration has published an investigation of the effects of interference between initial state and final state radiation in the process \(e^+ e^- \to \mu ^+\mu ^-\), by studying the forward-backward asymmetry as a function of the acoplanarity angle between the muons.

abstract

We present a study of single-\(W\) production \((e^+ e^- \to e^- \bar \nu _e W^+)\) as a new probe of the anomalous couplings at the LEP energy region. The cross-section measurement of the single-\(W\) process is found to give complementary bounds on the anomalous couplings to those obtained from \(W\)-pair analysis at LEP2.

abstract

Determinations of \(\alpha _s\) are reviewed. Current results are limited to a precision of around 3–20%, largely by theoretical uncertainties. All measurements are consistent with a ‘world average’ value of 0.118 \(\pm \) 0.005 and there is no evidence of any discrepancy between ‘low-\(Q^2\)’ and ‘high-\(Q^2\)’ results.

abstract

The talk briefly reviews the current state of the art in doing multiloop QCD calculations in a completely analytic way. In particular, we discuss recent analytical calculations of 4-loop \(\mathcal O(\alpha ^3_s)\) gluino contribution to \(R(s)\) and its implications to \(\mit \Gamma _{{\rm tot}}(Z \to \) hadrons) and \(\mit \Gamma (\tau ^- \to \nu _{\tau }\) + hadrons).

abstract

Recent theoretical results on heavy flavor production and decay in the framework of perturbative QCD are reviewed. This includes calculations for top production at hadron colliders, inclusive charmonium production and the comparison between the singlet and octet mechanisms. Predictions for heavy flavor production in \(e^+e^-\) annihilation will be discussed in some detail, covering both the threshold and the high energy region. The first results in NLO for heavy flavor decays will also be reviewed.

abstract

I review the status of the modern theoretical approach to weak decays of heavy flavor hadrons based on the \(1/m_Q\) expansion in QCD. The qualitative features are explained and the subtleties in simultaneously incorporating perturbative and power-suppressed effects are addressed. A few topical phenomenological applications are discussed in quantitative detail.

abstract

New experimental results on heavy flavour physics obtained in the study of \(Z^0\) decays by the four LEP experiments and SLD are presented. These include production, spectroscopy, lifetimes, \(B\)-mixing and decay properties.

abstract

We review recent experimental results on hadronic decays and lifetimes of hadrons containing \(b\) and \(c\) quarks (T.E. Browder, K. Honscheid, D. Pedrini, UH-515-848-96). We discuss charm counting and the semileptonic branching fraction in \(B\) decays, the color suppressed amplitude in \(B\) decay, and the search for gluonic penguins in \(B\) decay.

abstract

We analyze the one-loop effects (strong and electroweak) on \(t \to W^+ b\) and on the unconventional mode \(t \to H^+ b\) within the MSSM. The latter decay turns out to be an excellent laboratory to unveil “virtual” Supersymmetry.

abstract

The corrections induced by a heavy top on the main precision observables are now available up to \(O(\alpha ^2m^2_t/M^2_w)\). The new results imply a significant reduction of the theoretical uncertainty and can have a sizable impact on the determination of \(\sin ^2 \theta ^{lept}_{eff}\).

abstract

Complete two-loop electroweak corrections to leptonic anomalous magnetic moments have been calculated recently using asymptotic expansions of Feynman diagrams. Techniques developed in that context can also be applied to the electric dipole moments (EDM) of fermions. In the Standard Model the EDM was proved to vanish at two loops. In this talk we discuss a simplification of that proof.

abstract

In the recent past procedures for the calculation of two-loop Feynman diagrams were developed at the University of Mainz. They solve self-energy and vertex diagrams involving arbitrary massive particles. The procedures are bound together to a program package called XLOOPS which is designed to treat Feynman diagrams up to the two-loop level in a completely automatic way.

abstract

A brief overview of some recent publications related to the evaluation of two-loop Feynman diagrams is given.

abstract

I discuss the state of the art and outline direction for research in event generation for electroweak physics at LEP2 and \(e^+e^-\) Linear Colliders.

abstract

We briefly summarize theoretical methods for carrying out QCD calculations to next-to-leading order in perturbation theory. In particular, we describe a new general algorithm that can be used for computing arbitrary jet cross sections in arbitrary processes and can be straightforwardly implemented in general-purpose Monte Carlo programs.

abstract

Recent, QCD results from the CDF and DO detectors at the Tevatron \(\bar pp\) collider are presented. An outlook for future QCD tests at the Tevatron collider is also briefly discussed.

abstract

The LEP collaborations ALEPH, DELPHI, L3 and OPAL were able to measure the accelerator luminosity with an experimental uncertainty smaller than 0.1%. Motivations, method, technological aspects and main difficulties of the measurements are reviewed.

abstract

We present the current status of the YFS Monte Carlo approach to high precision calculations of both small and large angle Bhabha scattering at high energies. We discuss comparisons which we have made with the available literature where possible, at both LEP1/SLC energies and at LEP2 energies. Throughout the discussion, we pay attention to the luminosity determination at LEP1/SLC for the small angle process and the analysis of wide angle Bhabha \(Z\) physics parameters and possible new LEP2 physics backgrounds for the wide angle process. In this way, the role of high precision Bhabha scattering calculations in exploration of the Standard Model and its possible extensions is made more manifest.

abstract

Automated systems are reviewed focusing on their general structure and requirement specific to the calculation of radiative corrections. Detailed description of the system and its performance is presented taking GRACE as a concrete example.

abstract

The current experimental error in the electron \((g_e-2)\), 4 ppb, is now bigger than corresponding theoretical error, which is 1 ppb. We review shortly the latest  theoretical results, concentrating mainly in the analytical calculation of the QED 3-loop contributions, and then we discuss the possibility of a 1% numerical calculation of the 4-loop contributions, aiming at a final theoretical error less than 1ppb.

abstract

The main topics covered in this summary talk are the \(R\) ratio in \(e^+e^-\) annihilation, jet cross sections at next-to-leading order, physics at low \(x\), the strong coupling constant, the large transverse energy jet excess, the gluon density function and direct photon production.

abstract

We describe the status of precision tests of the Standard Model and the implications on the search for new physics.