Regular Series

Vol. 33 (2002), No. 11, pp. 3383 - 3997

DESY’s Future High Energy Physics Programme

Acta Phys. Pol. B 33, 3383 (2002)

page 3383 •


The future accelerator related high energy physics programme of DESY is reviewed: After the successful completion of the HERAI data taking in 2000 and the upgrade of HERA and the HERA experiments in 2000–2001, the priority for DESY’s high energy programme until 2006 is HERAII: 1 \(\mathrm {fb^{-1}}\) of luminosity for the collider experiments H1 and ZEUS and data for HERMES and HERAb. After the completion of the HERAII programme the priority will shift to experimentation at a high energy linear \(e^+e^-\) collider.

Future and Perspectives of QCD

Acta Phys. Pol. B 33, 3397 (2002)

page 3397 •


I discuss various areas of perturbative QCD where there is much current activity and which are likely to lead to significant developments over the next few years.

Results on Inclusive Diffraction at ZEUS

Acta Phys. Pol. B 33, 3407 (2002)

page 3407 •


The diffractive dissociation of virtual photons, \(\gamma ^*p \rightarrow Xp\), has been studied in \(ep\) interactions at HERA. The data are presented in terms of the diffractive structure function \(F_2^{\rm D}\) and \(d\sigma \)/\(dM_X\). The Pomeron intercepts, extracted from diffractive and inclusive \(ep\) interactions, are compared. The \(Q^2\)variation of the ratio of the diffractive to inclusive cross sections on \(W\), the photon–proton center of mass energy, illuminates the transition from the perturbative, high \(Q^2\), region to the photoproduction limit. The ranges studied in both \(W\) and \(Q^2\) are extended with respect to previously available results.

New Results on Inclusive Diffraction

Acta Phys. Pol. B 33, 3413 (2002)

page 3413 •


Two new measurements of diffractive DIS events (\(ep \rightarrow eXp\)) where there is a large gap in rapidity between the hadronic system \(X\) and the leading proton \(p\) are presented, measured with the H1 detector at HERA. The first technique measures the full final state including the leading proton. The \(t\) dependence of the data, parameterised by \({d\sigma }\)/\({dt} \propto \mathrm {e} ^{Bt}\) gives a value of \(B = 5.0\,\pm 0.3\,({\rm stat}) \pm 0.8\,({\rm syst})\,{\rm GeV^{-2}}\). The second, higher statistics, measurement technique selects diffractive events on the basis of a large rapidity gap separating \(X\) and \(p\). The reduced cross section \(\sigma _{\rm r}^{\rm D(3)}\) (\(=F_2^{\rm D(3)}\) if \(F_{\rm L}^{\rm D(3)}\! = 0\)) is extracted and good agreement is found between the two techniques. A value of \(\alpha _{\Bbb P}(0) \! = \! 1.173 \pm 0.018\,({\rm stat}) \pm 0.017\,({\rm syst})_{-0.035}^{+0.063}\,({\rm model})\) is measured for the effective pomeron intercept and the \(Q^2\) and \(\beta \) dependence of the data are described by a NLO QCD fit to the data including a Regge factorisation hypothesis. The logarithmic \(Q^2\) derivative of the ratio of the diffractive to the inclusive cross section is measured and found to be consistent with zero in the bulk of phase space.

NLO QCD Fit to H1 Diffractive DIS Data

Acta Phys. Pol. B 33, 3419 (2002)

page 3419 •


A new NLO DGLAP QCD fit to recent inclusive diffractive DIS data from the H1 collaboration is presented. Diffractive parton distributions are extracted, including their experimental and theoretical uncertainties. The parton distributions are used for comparisons with recent diffractive final state data from HERA and the Tevatron.

QCD Analysis of the Diffractive Measurements at HERA and Tevatron

Acta Phys. Pol. B 33, 3425 (2002)

page 3425 •


In the following, we present a QCD analysis of CDF data on single diffractive events and we extract the gluon fraction in the Pomeron from this study. Then, we combine both HERA and Tevatron results on diffraction in a same QCD framework to search for common parton distributions. As the dijet mass fraction, measured at CDF with a double diffractive exchange sample of events, is very sensitive to the gluon density in the Pomeron, we present some comparisons of this dijet mass fraction with gluon densities extracted from HERA or CDF single diffractive data.

Diffraction and \(\sigma _{\gamma ^* p}\)

Acta Phys. Pol. B 33, 3431 (2002)

page 3431 •


The empirical scaling law, wherein the total photo-absorption cross section depends on the single variable \(\eta =(Q^2 + m^2_0)\)/\({\mit \Lambda }^2 (W^2)\), provides empirical evidence for saturation in the sense of \(\sigma _{\gamma ^* p}(W^2,Q^2)\)/\( \sigma _{\gamma p} (W^2) \rightarrow 1\) for \(W^2 \rightarrow \infty \) at fixed \(Q^2\). The total photo-absorption cross section is related to elastic diffraction in terms of a sum rule. The excess of diffractive production over the elastic component is due to inelastic diffraction that contains the production of hadronic states of higher spins. Motivated by the diffractive mass spectrum, the Generalized Vector Dominance/Color Dipole Picture (GVD/CDP) is extended to successfully describe the DIS data in the full region of \(x \le 0.1\), all \(Q^2 \ge 0\), where the diffractive two-gluon exchange mechanism dominates.

Large Geometric Scaling and QCD Evolution

Acta Phys. Pol. B 33, 3439 (2002)

page 3439 •


We study the impact of the QCD DGLAP evolution on the geometric scaling of the gluon distributions which is expected to hold at small \(x\) within the saturation models. To this aim we solve the DGLAP evolution equations with the initial conditions provided along the critical line \(Q^2=Q_{\rm s}^2(x)\) with \(Q_{\rm s}^2(x) \sim x^{-\lambda }\) and satisfying geometric scaling. Both fixed and running coupling cases are studied. We show that in the fixed coupling case the geometric scaling at low \(x\) is stable against the DGLAP evolution for sufficiently large values of the parameter \(\lambda \) and in the double logarithmic approximation of the DGLAP evolution this happens for \(\lambda \ge 4N_{\rm c}\alpha _{\rm s}\)/\(\pi \). In the running coupling case geometric scaling is found to be approximately preserved at very small \(x\). The residual geometric scaling violation in this case can be approximately factored out and the corresponding form-factor controlling this violation is found.

Rapidity Gaps Between Jets at H1

Acta Phys. Pol. B 33, 3445 (2002)

page 3445 •


Dijet events in photoproduction with a large rapidity separation between the two highest \(E_{\rm T}\) jets have been measured using the H1 detector at HERA. Rapidity gap events are defined as events where the sum of the transverse energy with a rapidity between the two highest \(E_{\rm T}\) jet axes, \(E_{\rm T}^{\rm gap}\), is less than \(E_{\rm T}^{\rm cut}\) for \(E_{\rm T}^{\rm cut} = 0.5, 1.0, 1.5, 2.0 {\rm GeV}\). An excess is seen over predictions from standard photoproduction models for small values of \(E_{\rm T}^{\rm cut}\). The gap fraction, defined as the ratio of dijet events with a rapidity gap to the inclusive dijet cross section, is plotted differentially in the rapidity separation of the dijets, \(\Delta \eta \), and the fraction of the photon and proton momentum participating in the production of the dijets, \(x_\gamma ^{\rm jets}\) and \(x_p^{\rm jets}\), respectively. Comparisons are made to models containing a colour singlet exchange.

Diffractive Processes in D0 Experiment

Acta Phys. Pol. B 33, 3451 (2002)

page 3451 •


With the D0 detector, we have investigated events produced in \(\bar {p}p\) collisions with large rapidity gaps and with jet production. We present the result of study at two center-of-mass energies, 630 GeV and 1800 GeV. The fractions of forward and central jet events associated with such rapidity gaps are measured and compared to predictions from Monte Carlo models with various structure functions of Pomeron. Hard diffractive events with production of intermediate vector bosons \(W,Z\) have been investigated.

Hard Diffraction in CDF

Acta Phys. Pol. B 33, 3461 (2002)

page 3461 •


We present Run I results on hard diffraction obtained by the CDF Collaboration in proton-antiproton collisions at the Fermilab Tevatron. They are compared with results from the DESY \(ep\) collider HERA and/or theoretical predictions to test factorization in hard diffraction. In addition, the CDF program for diffractive studies in Run II is presented briefly.

Double-Gap Soft Diffraction Results from CDF

Acta Phys. Pol. B 33, 3467 (2002)

page 3467 •


We present a study of \(\bar pp\) collisions with a leading antiproton and a rapidity gap in addition to that associated with the antiproton. The second gap is either within the region available to the proton dissociation products, \(\bar p+p\rightarrow (\bar p+{\rm gap})+X+{\rm gap}+Y\), or adjacent to the outgoing proton \(\bar p+p\rightarrow (\bar p+{\rm gap})+X+({\rm gap}+p)\). Results are reported for two-gap to one-gap event ratios and compared with one-gap to no-gap ratios and with theoretical expectations.

Forward Proton Tagging as a Way to Identify a Light Higgs Boson at the LHC

Acta Phys. Pol. B 33, 3473 (2002)

page 3473 •


We show that exclusive double-diffractive Higgs production, \(pp\rightarrow p+H+p\), followed by the \(H\rightarrow b\bar {b}\) decay, could play an important role in identifying a ‘light’ Higgs boson at the LHC, provided that the forward outgoing protons are tagged. We predict the cross sections for the signal and for all possible \(b\bar {b}\) backgrounds.

Diffractive Higgs Production: Soft Colour Interactions Perspective

Acta Phys. Pol. B 33, 3479 (2002)

page 3479 •


We briefly present the soft colour interaction models which are successful in reproducing a multitude of diffractive hard scattering data, and give predictions for diffractive Higgs production at the Tevatron and LHC. Only a few diffractive Higgs events may be produced at the Tevatron, but we predict a substantial rate at the LHC.

Higgs Boson Production via Double Pomeron Exchange at the Tevatron and the LHC

Acta Phys. Pol. B 33, 3485 (2002)

page 3485 •


Double diffractive Higgs boson production is assessed in the picture of composite Pomeron collisions. It is shown how the introduction of Pomeron parton densities allows to describe some critical aspects of the existing data, and how these and future measurements of double diffractive dijet production will allow to constrain the non-perturbative parameters involved in the process.

Discussion Session on Diffractive Higgs Production

Acta Phys. Pol. B 33, 3491 (2002)

page 3491 •


This note summarizes the discussion session on diffractive Higgs production at the DIS2002 workshop.

Investigation of Pomeron- and Odderon Induced Photoproduction of Mesons Decaying to Pure Multiphoton Final States at HERA

Acta Phys. Pol. B 33, 3499 (2002)

page 3499 •


In this contribution the first search at HERA for Odderon induced reactions is presented and contrasted with cross section measurements for Pomeron induced processes. The searches are performed in the channels \(\gamma p\to \pi ^{0}N^{*}\), \(\gamma p\to f_{2}(1270)X\) and \(\gamma p\to a_{2}X\), where \(N^{\ast }\) denotes an excited nucleon state. The rates found are compatible with the background alone, and the upper limits derived therefrom are confronted with the expectations of a specific non-perturbative QCD model. In contrast, to these findings the cross sections for the Pomeron mediated processes — \(\gamma p\to \omega p\) and \(\gamma p\to \omega \pi ^{0} X\) — were found to be in perfect agreement with earlier measurements and the expectations from Regge theory with soft Pomeron exchange. The mean \(\gamma p\) centre-of-mass energies were \(\left \lt W \right \gt \) = 200 GeV and 215 GeV, respectively.

Hard pQCD Jets and Charm in Diffractive DIS

Acta Phys. Pol. B 33, 3505 (2002)

page 3505 •


A two gluon model of diffractive DIS is used to describe diffractive \(D^*\) production and diffractive dijets. Using three different unintegrated gluon densities a comparison with H1 data is made. The 2-gluon model fairly well describes both processes at \(x_{\mathbb P} \lt 0.01\).

Diffractive Vector Mesons at Large Momentum Transfer from the BFKL Equation

Acta Phys. Pol. B 33, 3511 (2002)

page 3511 •


Diffractive vector meson photoproduction accompanied by proton dissociation is studied for large momentum transfer. The process is described by the non-forward BFKL equation, for which an analytical solution is found for all conformal spins, giving the scattering amplitude. Results are compared to HERA data on \(\rho \) production.

Diffractive Vector Meson Production in \(k_{\rm t}\)-Factorization Approach

Acta Phys. Pol. B 33, 3517 (2002)

page 3517 •


We describe the current status of the diffractive vector meson production calculations within the \(k_{\rm t}\) factorization approach. Since the amplitude of the vector meson production off a proton is expressed via the differential gluon structure function (DGSF), we take a closer look at the latter and present results of our new improved determination of the DGSF from the structure function \(F_{2p}\). Having determined the differential glue, we proceed to the \(k_{\rm t}\)-factorization results for the production of various vector mesons. We argue that the properties of the vector meson production can reveal the internal spin-angular and radial structure of the vector meson.

Hard Diffraction in Hadron–Hadron Collisions

Acta Phys. Pol. B 33, 3523 (2002)

page 3523 •


Breakdown of factorization observed recently in the diffractive dijet production in deep inelastic lepton induced and hadron induced processes is explained using the Good-Walker picture of diffraction dissociation. Numerical estimates agree with the recent data.

Diffractive \(\rho \) Meson Electroproduction at High \(Q^2\) and High \(|t|\)

Acta Phys. Pol. B 33, 3529 (2002)

page 3529 •


The electroproduction of \(\rho \) mesons is studied at HERA with the H1 detector at high \(Q^2\) and high \(|t|\). Cross sections are measured as a function of \(Q^2\), \(W\) and \(t\). The \(W\) dependence of the \(\gamma ^{*} p\) cross section is observed to increase with \(Q^2\) from values compatible with soft Pomeron exchange at low \(Q^2\) to a hard dependence at large \(Q^2\). Spin density matrix elements are measured and their dependence is compared with a two gluon exchange model.

Diffractive Photoproduction of \(\psi (2S)\) Mesons at HERA

Acta Phys. Pol. B 33, 3535 (2002)

page 3535 •


The diffractive photoproduction of the \(\psi (2S)\) meson is measured using a data set collected between 1996 and 2000 by the H1 detector at HERA corresponding to a luminosity of 77 pb\(^{-1}\). The ratio of the integrated diffractive cross sections for \(\psi (2S)\) and \(J\)/\(\psi \) production is presented as a function of the photon–proton centre-of-mass energy \(W_{\gamma p}\). The dependences of elastic and proton-dissociative \(\psi (2S)\) production on the four-momentum transfer squared \(t\) at the proton vertex are also presented. The results are compared to theoretical predictions calculated within the colour dipole framework.

Proton-Dissociative Diffractive Photoproduction of Vector Mesons at High Momentum Transfer at HERA

Acta Phys. Pol. B 33, 3541 (2002)

page 3541 •


Diffractive photoproduction of vector mesons, \(\gamma p \rightarrow VY\), where \(Y\) is the proton-dissociative system, has been measured in \(e^{+}p\) interactions with the ZEUS detector at HERA using an integrated luminosity of 25 pb\(^{-1}\). The differential cross section, \(d\sigma \)/\(dt\), and a decay-angle analysis for \(\rho ^0\), \(\phi \) and \(J\)/\(\psi \) mesons are presented for a photon-proton centre-of-mass energy \(80\lt W\lt 120\) GeV and \(-t\lt 12\) GeV\(^2\), where \(t\) is the square of the four-momentum transferred to the vector meson. The \(t\) distributions are well fit by a power law, \(d\sigma \)/\(dt \propto (-t)^n\). The slope of the Pomeron trajectory, measured from the W dependence of the \(\rho \) and \(\phi \) cross sections in bins of \(t\), is consistent with zero. The ratios \(d\sigma _{\gamma p \rightarrow \phi Y}/dt\) to \(d\sigma _{\gamma p \rightarrow \rho Y}/dt\) and \(d\sigma _{\gamma p \rightarrow J/\psi Y}/dt\) to \(d\sigma _{\gamma p \rightarrow \rho Y}/dt\) increase with increasing \(-t\). For the \(\rho ^0\) and \(\phi \) mesons a contribution from single and double helicity flip is observed. The results are compared to expectations of theoretical models.

Energy Dependence of Exclusive Vector–Meson Production in \(ep\) Interactions at HERA

Acta Phys. Pol. B 33, 3547 (2002)

page 3547 •


The energy dependence of exclusive vector–meson (\(V\)) production is studied using the ZEUS data. The SU(4) universality of \(V\) cross sections in the \(Q^2+M_{V}^2\) scale is tested. The energy dependence of the ratio of the cross sections for \(V\) production to the total \(\gamma ^*p\) cross section is compared with expectations based on pQCD and Regge approaches.

Deeply Virtual Compton Scattering at HERA

Acta Phys. Pol. B 33, 3555 (2002)

page 3555 •


Results on Deeply Virtual Compton Scattering in electron proton interactions by the H1 and ZEUS experiments are reviewed. Measured cross sections as a function of the photon virtuality \(Q^2\) and the photon–proton center of mass energy \(W\) are presented and compared to different theoretical predictions based on the colour dipole model and Generalised Parton Distributions.

DVCS \(vs\) GPDs: What Does DVCS Tell Us About GPDs?

Acta Phys. Pol. B 33, 3561 (2002)

page 3561 •


As recent studies have shown, the most popular models for generalized parton distributions cannot describe the new data from the H1, ZEUS, HERMES and CLAS experiments on Deeply Virtual Compton Scattering (DVCS) if a full QCD analysis including evolution is performed. In this note, we will discuss why this is the case and how the problem can be cured thereby producing a very good description of the H1 data.

Colour Dipoles and Deeply Virtual Compton Scattering

Acta Phys. Pol. B 33, 3567 (2002)

page 3567 •


I report on an analysis of Deeply Virtual Compton Scattering (DVCS) within the dipole model, done in collaboration with M. McDermott and G. Shaw. The two models considered here are distinct in their structure and implications. They both agree with the available cross-section data on DVCS from HERA (see M. McDermott, R. Sandapen, G. Shaw, Eur. Phys. J. C22, 655 (2002)). Predictions for various asymmetries are also given.

Saturation and Vector Mesons

Acta Phys. Pol. B 33, 3573 (2002)

page 3573 •


Through an analysis of diffractive vector meson production, we show that the proton appears quite dense to a small size probe at present HERA energies. This means that saturation effects are already important.

Diffractive Contribution to \(A_\perp \) Asymmetry

Acta Phys. Pol. B 33, 3579 (2002)

page 3579 •


We consider double spin asymmetries for longitudinally polarized leptons and transversely polarized protons in diffractive \(Q \bar Q\) production which is connected with \(A_\perp \) asymmetry. The predicted asymmetry is large and can be used to obtain the information on the polarized skewed gluon distributions in the proton.

Prospects for Diffraction at HERA-II

Acta Phys. Pol. B 33, 3585 (2002)

page 3585 •


New opportunities for the Study of Diffraction in the second phase of HERA operation are discussed.

Diffraction and Low-\(x\) at the LHC

Acta Phys. Pol. B 33, 3591 (2002)

page 3591 •


Opportunities for hard diffraction and low-\(x\) studies at the LHC are recalled. Such studies will need a central detector such as ATLAS or CMS, but equipped with forward detectors.

Future of Small-\(x\) and Diffraction After 2006 (Except LHC)

Acta Phys. Pol. B 33, 3599 (2002)

page 3599 •


The initial phase of HERA running has produced exciting and fundamental results on the nature of strong interactions. These results are summarized, and the case is made for a new round of precision measurements on low-\(x\) and diffractive physics.

Diffraction and Nuclear Shadowing

Acta Phys. Pol. B 33, 3609 (2002)

page 3609 •


I present results from our recent leading twist QCD analysis of nuclear shadowing and contrast them with predictions using the eikonal model. By exploiting QCD factorisation theorems, the leading twist approach employs diffractive parton distributions, extracted from diffractive DIS measurements at HERA, to calculate the nuclear shadowing correction on the parton level. Large nuclear shadowing effects are found for the gluon channel which are reflected in the predictions for \(F_{\rm L}^A\).

QCD, Diffraction and String Theory

Acta Phys. Pol. B 33, 3615 (2002)

page 3615 •


Recently, string theory on some specific curved background spacetime geometries has been conjectured to be equivalent to certain gauge theories (AdS/CFT correspondence). This correspondence may be used to investigate the non-perturbative regime of gauge theories. I describe its application to the study of soft scattering amplitudes in a confining gauge theory. I describe two qualitatively different applications: amplitudes with vacuum quantum number exchange (Pomeron-like), amplitudes with Reggeon exchange. The last case requires going beyond eikonal approximation on the gauge theory side.

Spectrum of the Multi-Reggeon Compound States in Multi-Colour QCD

Acta Phys. Pol. B 33, 3621 (2002)

page 3621 •


We study the properties of the colour-singlet compound states of reggeized gluons in multi-colour QCD. Applying the methods of integrable models, we calculate their spectrum and discuss the application of the obtained results to high-energy asymptotics of the scattering amplitudes in perturbative QCD.

Spin-Discriminate Exchange in High Energy Diffraction

Acta Phys. Pol. B 33, 3627 (2002)

page 3627 •


We speculate that in high energy diffractive scattering many features of data can be explained under assumption that the scattering amplitude contains sizable part sensitive to the spin of colliding particles. This spin-dependent part of the amplitude does not vanish at high energies and becomes leading at momentum transfer \(-t\gt 1\)–2 GeV\(^2\) and energy \(\sqrt {s}\gt 10\)–20 GeV. In terms of Regge approach, the amplitude corresponds to exchange of a reggeon with vacuum quantum numbers, negative signature, intercept \(\alpha (0)\approx 1\) and zero slope.

Instantons and Saturation in the Colour Dipole Picture

Acta Phys. Pol. B 33, 3633 (2002)

page 3633 •


We pursue the intriguing possibility that larger-size instantons build up diffractive scattering, with the marked instanton-size scale \(\left \lt \rho \right \gt \approx 0.5\) fm being reflected in the conspicuous “geometrization” of soft QCD. As an explicit illustration, the known instanton contribution to DIS is transformed into the intuitive colour dipole picture. With the help of lattice results, the \(q\bar {q}\)-dipole size \(r\) is carefully increased towards hadronic dimensions. Unlike pQCD, one now observes a competition between two crucial length scales: the dipole size \(r\) and the size \(\rho \) of the background instanton that is sharply localized around \(\left \lt \rho \right \gt angle \approx 0.5\) fm. For \(r\,\gtrsim \,\left \lt \rho \right \gt \), the dipole cross section indeed saturates towards a geometrical limit, proportional to the area \(\pi \,\left \lt \rho \right \gt ^2\), subtended by the instanton.

Diffractive Exclusive Electroproduction of \(\rho ^{0}\) Mesons at HERMES

Acta Phys. Pol. B 33, 3639 (2002)

page 3639 •


Recent Hermes measurements are presented on the coherent and incoherent part of the cross section for the exclusive diffractive production of \(\rho ^{0}\) mesons. Based on data taken with a variety of targets, \(^{1}\)H, \(^{2}\)H,\(^{3}\)He,\(^{14}\)N, \(^{20}\)Ne and \(^{84}\)Kr, the method to extract the coherent to incoherent cross section ratios as a function of coherence length \(l_{\rm coh}\) and momentum transfer \(Q^{2}\) will be presented. The measurement of those ratios could contribute to the study of how quark–antiquark pairs interact with the nuclear medium. Using the \(^{1}\)H and \(^{14}\)N targets, the nuclear transparency of \(\rho ^{0}\) production has been measured as a function of coherence length. The data have been analysed to search for a possible onset of color transparency and are compared with recent theoretical calculations.

The Diffractive Interactions Working Group Summary

Acta Phys. Pol. B 33, 3645 (2002)

page 3645 •


Diffractive interactions represent a lively domain of investigations, as confirmed by the progresses reported during the conference. We summarize the diffractive interactions session and put the new experimental data (Section 1), developments in modeling diffraction (Section 2) and the theoretical relations with Quantum Chromodynamics (Section 3) in perspective.

New Precision Results on the Spin Structure Function \(g_1^d\)

Acta Phys. Pol. B 33, 3671 (2002)

page 3671 •


The HERMES experiment studies the spin structure of the nucleon using the \(27.6\) GeV longitudinally polarized positron beam of HERA and an internal target of pure gases. Recently, HERMES presented preliminary results on the deuteron spin structure function \(g_1^d\) in the kinematic range \(0.0021\lt x\lt 0.85\) and \(0.1\lt Q^2\lt 20\) GeV \(\!^2\) based on a restricted data set. Here, new, precise results are presented using the superior statistics of the 2000 data taking period. A reduction of the systematic uncertainty which could be achieved in this preliminary analysis relies in particular on the excellent performance of HERA and of the HERMES target. The data will be discussed in comparison with previous measurements performed at SLAC and CERN.

Precision Measurement of the Proton and Deuteron Spin Structure Functions \(g_{2}\)

Acta Phys. Pol. B 33, 3677 (2002)

page 3677 •


We measured the spin structure functions \(g_{2}^{p}\) and \(g_{2}^{d}\) in the range \(0.02\leq x \leq 0.8\) and \(0.7 \leq Q^{2} \leq 20\) GeV\(^2\) by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH\(_3\) and \(^6{\rm LiD}\) targets. \(g_2\) approximately follows the twist-2 Wandzura–Wilczek calculation. The twist-3 reduced matrix elements \(d_{2}^{p}\) and \(d_{2}^{n}\) are less than two standard deviations from zero. The data are inconsistent with the Burkhardt–Cottingham sum rule if there is no pathological behavior as \(x\rightarrow 0\). The Efremov–Leader–Teryaev integral is consistent with zero.

Neutron Spin Structure Experiments at Jefferson Lab

Acta Phys. Pol. B 33, 3683 (2002)

page 3683 •


Two experiments at Jefferson Lab have recently measured the neutron asymmetry \(A_1^n\) at \(0.3 \leqslant x_{\rm Bj}\leqslant 0.6\) and the neutron spin structure function \(g_2^n\) at \(x_{\rm Bj}\simeq 0.2\) (\(0.6\) GeV\(^2 \leqslant Q^2 \leqslant 1.4\) GeV\(^2\)) in the deep inelastic region. A brief description of both experiments is given and preliminary results for the \(A_1^n\) are presented.

Experimental Evidence for Quark–Hadron Duality in Spin Structure Function

Acta Phys. Pol. B 33, 3689 (2002)

page 3689 •


First results on quark–hadron duality in the spin sector from the HERMES experiment are reported in the range \(1.2\le Q^2 \le 12\) GeV\(^2\) and \(1\le W^2 \le 4\) GeV\(^2\).

A New Evaluation of Polarized Parton Densities in the Nucleon

Acta Phys. Pol. B 33, 3695 (2002)

page 3695 •


We present a new Next-to-Leading Order (NLO) QCD analysis of the world data on inclusive polarized deep inelastic scattering. A new set of polarized parton densities is extracted from the data and the sensitivity of the results to the newly incorporated SLAC/E155 proton data is discussed.

GVMD Model Predictions for the Low \(Q^2\) Behaviour of the Spin Structure Function \(g_1(x,Q^2)\) and of the DHGHY Integral \(I(Q^2)\)

Acta Phys. Pol. B 33, 3701 (2002)

page 3701 •


Predictions for \(g_1(x,Q^2)\) at low \(Q^2\) are obtained in the framework of the GVMD model. Contributions from both light and heavy vector mesons are evaluated. The DHGHY sum rule is employed to fix the magnitude of the light vector meson contribution to \(g_1\), using the recent measurements in the region of baryonic resonances. The DHGHY moment function is calculated. Predictions are compared to the data.

The Status of the COMPASS Experiment

Acta Phys. Pol. B 33, 3707 (2002)

page 3707 •


One of the important goals of the COMPASS experiment is the determination of the gluonic contribution to the spin of the nucleon. By using the Photon Gluon Fusion (PGF) process in polarised deep inelastic scattering direct access to the gluon polarisation can be obtained. The PGF is selected via the detection of open charm or high \(p_{\rm T}\) hadron pairs. In 2001 a large part of the experiment had been setup and during a two weeks period first data was taken. In this paper some achievements of the run in 2001 are presented together with first preliminary analysis results.

A Statistical Approach for Polarized Parton Distributions

Acta Phys. Pol. B 33, 3713 (2002)

page 3713 •


A global next-to-leading order QCD analysis of unpolarized and polarized deep-inelastic scattering data is performed with parton distributions constructed in a statistical physical picture of the nucleon. The chiral properties of QCD lead to strong relations between quarks and antiquarks distributions and the importance of the Pauli exclusion principle is also emphasized. We obtain a good description, in a broad range of \(x\) and \(Q^2\), of all measured structure functions in terms of very few free parameters. Forthcoming experiments at RHIC–BNL are sensitive tests of the statistical model for the behavior of the \(\bar d(x)\)/\(\bar u(x)\) ratio for \(x \geq 0.2\) and for the magnitude and sign of \(\Delta \bar u(x)\) and \(\Delta \bar d(x)\).

Universal QED Corrections to Polarized Electron Scattering in Higher Orders

Acta Phys. Pol. B 33, 3719 (2002)

page 3719 •


We derive QED radiators for the universal corrections to polarized electron scattering. To 5\(^{\rm th}\) order in the coupling constant the flavor non-singlet and singlet contributions are calculated. We derive the non-singlet and singlet exponentiation of the leading terms \(\propto (\alpha \ln ^2(x))^k\) to all orders.

QCD Analysis of Polarized Scattering Data and New Polarized Parton Distributions

Acta Phys. Pol. B 33, 3725 (2002)

page 3725 •


In this talk results from a new QCD analysis in Leading (LO) and Next-to-Leading (NLO) Order are presented. New parametrizations of the polarized quark and gluon densities are derived together with parametrizations of their fully correlated 1\(\sigma \) error bands. Furthermore the value of \(\alpha _{\rm s}(M_Z^2)\) is determined. Finally a number of low moments of the polarized parton densities are compared with results from lattice simulations. All details of the analysis are given in J. Blümlein, H. Böttcher, Nucl. Phys. B636, 225 (2002).

Recent Results on the Helicity Structure of the Nucleon from HERMES

Acta Phys. Pol. B 33, 3731 (2002)

page 3731 •


The HERMES experiment at DESY uses the HERA polarized positron beam of 27.6 GeV in combination with internal polarized gas targets in order to investigate the spin structure of the nucleon via deep inelastic scattering. Inclusive and semi-inclusive double-spin asymmetries from polarized hydrogen and deuterium targets have been measured in the kinematic range \(0.023\lt x\lt 0.6\) and 1 GeV\(^2\lt Q^2\lt 10\) GeV\(^2\). The installation of a Ring Imaging Čerenkov (RICH) detector in 1998 allowed for the first time the measurement of charged kaon asymmetries. Based on the measured set of hydrogen and deuterium asymmetries, the polarized quark and anti-quark distributions in the proton were extracted in leading-order pQCD as a function of \(x\) for all flavors separately. In particular, the first measurement of the light-antiquark asymmetry \(\Delta \bar {u}-\Delta \bar {d}\) is presented.

Single Spin Asymmetries in Semi-Inclusive DIS at HERMES

Acta Phys. Pol. B 33, 3737 (2002)

page 3737 •


The new high statistics deuterium data set of HERMES shows significant semi-inclusive single spin asymmetries of identified pions and kaons. The asymmetries observed on the deuterium target differ from those measured on the proton target. The appearance of non-zero single spin asymmetries can be explained in terms of a non-zero transversity distribution combined with a non-zero Collins fragmentation function. However, the detailed interpretation of the data is model dependent as it turns out that the asymmetries are dominated by higher-twist effects. HERMES data that are currently being taken on a transversely polarized target will allow for a model-independent extraction of the transversity distribution.

Fragmentation Functions and Their Role in Determining the Polarized Parton Densities

Acta Phys. Pol. B 33, 3743 (2002)

page 3743 •


We extract the pion fragmentation functions and their uncertainties from a judicious choice of \(e^+e^-\) and semi-inclusive DIS data. These are used to study the error propagation in the extraction of polarized parton densities from semi-inclusive DIS asymmetries. We conclude that the uncertainties on polarized PDs have been underestimated in the past.

Spin-Dependent, Interference and \(T\)-Odd Fragmentation and Fracture Functions

Acta Phys. Pol. B 33, 3749 (2002)

page 3749 •


Fracture functions, originally suggested to describe the production of diffractive and leading hadrons in semi-inclusive DIS, may be also applied at fixed target energies. They may also include interference and final state interaction, providing a source for azimuthal asymmetries at HERMES and (especially) \({\mit \Lambda }\) polarization at NOMAD. The recent papers by Brodsky, Hwang and Schmidt, and by Gluck and Reya, may be understood in terms of fracture functions.

Azimuthal Asymmetries and Collins Analyzing Power

Acta Phys. Pol. B 33, 3755 (2002)

page 3755 •


Spin azimuthal asymmetries in pion electro-production in deep inelastic scattering off longitudinally polarized protons, measured by HERMES, are well reproduced theoretically with no adjustable parameters. Predictions for azimuthal asymmetries for a longitudinally polarized deuteron target are given. The \(z\)-dependence of the Collins fragmentation function is extracted. The first information on \(e(x)\) is extracted from CLAS \(A_{\rm LU}\) asymmetry.

Estimate of the Collins Function in a Chiral Invariant Approach

Acta Phys. Pol. B 33, 3761 (2002)

page 3761 •


We estimate the Collins function at a low energy scale by calculating the fragmentation of a quark into a pion at the one-loop level in the chiral invariant model of Manohar and Georgi. We give a useful parametrization of our results and we briefly discuss different spin and/or azimuthal asymmetries containing the Collins function and measurable in semi-inclusive DIS and \(e^+ e^-\) annihilation.

First Polarized Proton Collisions at PHENIX

Acta Phys. Pol. B 33, 3767 (2002)

page 3767 •


The RHIC started operation as a polarized proton collider. We took data of transversely polarized proton collisions at \(\sqrt {s}\) = 200 GeV for the single transverse-spin asymmetry measurements of many channels with the PHENIX detector. The operation and data taking in the 2001–2002 run will be reported.

full authors' list

N. d'Hose, E. Burtin, P.A.M. Guichon, S. Kerhoas-Cavata, J. Marroncle, L. Mossé

Feasibility Study of Deeply Virtual Compton Scattering Using COMPASS at CERN

Acta Phys. Pol. B 33, 3773 (2002)

page 3773 •


Deeply virtual Compton scattering is a very suitable tool to learn about Generalized parton distributions. We propose to use the 190 GeV (or 100 GeV) muon beam at CERN to study Deeply Virtual Compton Scattering. The high energy of the lepton beam and the present luminosity allows to measure absolute cross section or beam charge asymmetry in a large range of \(Q^2\) and \(x_{\rm Bj}\) (1 \(\leq Q^2 \leq \) 7 GeV\(^2\) and \(0.03 \leq x_{\rm Bj} \leq 0.27\)). We discuss the experimental implications for the existing COMPASS set-up.

Recent HERMES Results on DVCS Associated Asymmetries

Acta Phys. Pol. B 33, 3779 (2002)

page 3779 •


The latest HERMES measurements of the beam–spin and beam–charge azimuthal asymmetries in the hard exclusive electroproduction of photons are reported. The asymmetries are associated with the Deeply Virtual Compton Scattering (DVCS) process and can provide new information on the structure of the nucleon.

Study of \({\mit \Lambda }\) Hyperon Production in the HERMES Experiment

Acta Phys. Pol. B 33, 3785 (2002)

page 3785 •


Semi-inclusive \({\mit \Lambda }\) hyperon production has been studied in the HERMES experiment using the \(E_{\rm e}=27.5\) GeV polarized positron beam incident on polarized or unpolarized internal gas target. The multiplicity distribution over fractional \({\mit \Lambda }\) energy \(z\) has been investigated and the fragmentation function \(D^{{\mit \Lambda }}_{u}(z)\) has been extracted. The \(D^{{\mit \Lambda }}_{u}(z)\) found by HERMES is well described with the help of the parametrization based on the experiments on \({\mit \Lambda }\) production in high energy proton–proton collisions, but it is substantially smaller then that deduced from the \(e^+e^-\) annihilation data. The distribution over \({\mit \Lambda }\) transverse momentum squared \(p^{2}_{\rm T}\) has also been analyzed. The results show that at \(z\gt 0.2\) the \(p^{2}_{\rm T}\) distribution is dominated by the quark transverse motion in the fragmentation process. The longitudinal spin transfer from the beam to the \({\mit \Lambda }\) has been measured. The systematic uncertainty of the spin transfer has been reduced by reversal of the beam polarization several times during the data taking period. The spin transfer coefficient is found to be \(S_{{\mit \Lambda }}=0.04 \pm 0.08({\rm stat}) \pm 0.03({\rm syst})\) at an average fractional energy of the produced \({\mit \Lambda }\) hyperons of \(\left \lt z\right \gt =0.45\). The dependence of the longitudinal spin transfer on \(z\) is presented and compared with recent theoretical calculations.

Measurement of \({\mit \Lambda }^0\) and \(\bar {\mit \Lambda } ^0\) Polarization in \(\nu _\mu \) CC Interactions in NOMAD

Acta Phys. Pol. B 33, 3791 (2002)

page 3791 •


The \({\mit \Lambda }^0\) and \(\bar {\mit \Lambda } ^0\) polarizations in \(\nu _\mu \) charged current interactions have been measured in the NOMAD experiment. The event sample (8087 reconstructed \({\mit \Lambda }^0\)’s and 649 \(\bar {\mit \Lambda } ^0\)’s) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. For the \({\mit \Lambda }^0\) hyperons we observe negative polarization along the \(W\)-boson direction which is enhanced in the target fragmentation region: \(P_x (x_{\rm F} \lt 0) = -0.21 \pm 0.04 \textrm {(stat)} \pm 0.02 \textrm {(syst)}\). In the current fragmentation region we find \(P_x (x_{\rm F} \gt 0) = -0.09 \pm 0.06 \textrm {(stat)} \pm 0.03 \textrm {(syst)}\). A significant transverse polarization (in the direction orthogonal to the \({\mit \Lambda }^0\) production plane) has been observed for the first time in a neutrino experiment: \(P_y = -0.22 \pm 0.03 \textrm {(stat)} \pm 0.01 \textrm {(syst)}\). The dependence of the absolute value of \(P_y\) on the \({\mit \Lambda }^0\) transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments. The polarization vector of \(\bar {\mit \Lambda } ^0\) hyperons measured for the first time in neutrino interactions is found to be consistent with zero.

Transverse Polarization of \({\mit \Lambda }\) and \(\bar {\mit \Lambda }\) Produced Inclusively in \(eN\) Scattering at HERMES

Acta Phys. Pol. B 33, 3797 (2002)

page 3797 •


The transverse polarization of inclusively produced \({\mit \Lambda }\) and \(\bar {\mit \Lambda }\) hyperons has been studied at HERMES using the 27.6 GeV positron beam of HERA and an internal gas target. From the data taken in the years 1996–2000, 386,000 \({\mit \Lambda }\) and 72,000 \(\bar {{\mit \Lambda }}\) events have been reconstructed, allowing the measurement of the \({\mit \Lambda }\) and \(\bar {\mit \Lambda }\) polarizations with high statistical accuracy. Averaged over the full kinematic range of the data, the transverse polarizations were measured to be \(P_n^{\mit \Lambda } =5.4 \pm 0.5\,\textrm {(stat)} \pm 1.5\,\textrm {(syst)}\,\%\) and \(P_n^{\mit \bar {\Lambda }} = -4.0 \pm 1.3\,\textrm {(stat)} \pm 1.2\,\textrm {(syst)}\,\%\). The dependence of the polarization on several transverse momentum \(p_{\rm T}\) and on the hyperons’ light cone momentum fraction \(\zeta \) has been investigated.

Intrinsic Polarized Strangeness and \({\mit \Lambda }^0\) Polarization in Deep-Inelastic Production

Acta Phys. Pol. B 33, 3803 (2002)

page 3803 •


We propose a model for the longitudinal polarization of \({\mit \Lambda }^0\) baryons produced in deep-inelastic lepton scattering at any \(x_{\rm F}\), based on static SU(6) quark-diquark wave functions and polarized intrinsic strangeness in the nucleon associated with individual valence quarks. Free parameters of the model are fixed by fitting the NOMAD data on the longitudinal polarization of \({\mit \Lambda }^0\) hyperons in neutrino interactions. Our model correctly reproduces the observed dependences of \({\mit \Lambda }^0\) polarization on the kinematic variables. Within the context of our model, the NOMAD data imply that the intrinsic strangeness associated with a valence quark has anticorrelated polarization. We also compare our model predictions with results from the HERMES and E665 experiments using charged leptons. Predictions of our model for the COMPASS experiment are also presented.

Possibilities of COMPASS Spectrometer for the \({\mit \Lambda }\) Hyperons Polarisation Measurements

Acta Phys. Pol. B 33, 3809 (2002)

page 3809 •


The possibilities of the COMPASS spectrometer for the measurement of \({\mit \Lambda }\) polarisation were investigated. The COMPASS experiment can provide \({\mit \Lambda }\) polarisation measurement in the deep-inelastic scattering process with high precision, which is comparable to the most precise existing data.

Summary of the Spin Physics Working Group at DIS2002

Acta Phys. Pol. B 33, 3815 (2002)

page 3815 •


We summarize in this report the experimental and theory talks which were presented in the Working Group 3 “Spin Physics” at the DIS2002 workshop. Recent progress achieved in several interesting topics will be underlined and also what to expect in the future.

Precision Electroweak Measurement at LEP

Acta Phys. Pol. B 33, 3831 (2002)

page 3831 •


LEP started in 1989 and finished its operation in November 2000. The four experiments of LEP, ALEPH, DELPHI, L3 and OPAL, collected data and have been performing series of electroweak (EW) precision measurements. This article presents current status of the EW precision measurements at LEP.

A Search for New Physics in the High Mass Dilepton Spectrum at CDF

Acta Phys. Pol. B 33, 3837 (2002)

page 3837 •


The high mass dilepton data can be used in searches for a variety of new physics processes. This paper summarises some of the limits obtained in Run I at the Tevatron and the possible Run II reaches. A first glimpse at the initial dilepton data from Collider Detector at Fermilab’s (CDF) Run II is shown and the potential capability of the Time-of-Flight detector for cosmic ray rejection is discussed.

Precision Electroweak Measurements from NuTeV

Acta Phys. Pol. B 33, 3843 (2002)

page 3843 •


The NuTeV experiment has extracted the electroweak parameter, \(\sin ^2 \theta _W\), from the high precision measurement of the ratio of neutral-current to charged-current cross-sections in deep-inelastic neutrino and anti-neutrino scattering off a steel target. Our measurement, \(\sin ^2 \theta _W^{\rm on-shell} = 0.2277 \pm 00013({\rm stat}) \pm 0.0009({\rm syst})\), is \(3 \sigma \) above the standard model prediction. We discuss the plausibility of the hypothesis that this discrepancy is due to unaccounted QCD effects, especially a strange and anti-strange sea asymmetry. Taking into account results from NuTeV, CCFR, and charged-lepton deep-inelastic cross-section measurements, we do not find support for this hypothesis.

Higgs at LEP

Acta Phys. Pol. B 33, 3849 (2002)

page 3849 •


The search for standard, supersymmetric and non-standard Higgs bosons at LEP is shortly reviewed.

Higgs Prospects at the Tevatron

Acta Phys. Pol. B 33, 3855 (2002)

page 3855 •


Searching for the Higgs boson is one of the main physics aims for the CDF and D0 collaborations at the Tevatron collider and Run II should have the sensitivity to cover much of the parameter space favoured by electroweak fits. The search strategy at the Tevatron is highly constrained by the hadronic physics environment. For all the searches the ability to trigger on the decay of heavy vector bosons and accurate lepton identification are essential. In the case of a light Higgs (mass less then \(\sim \)135 GeV) \(b\)-tagging is crucial in order to identify the Higgs. The Tevatron is currently taking data and results are presented from D0 and CDF which highlight the ability to identify the basic elements required for a successful Higgs search.

Top Quark Physics at the Tevatron Results and Prospects

Acta Phys. Pol. B 33, 3861 (2002)

page 3861 •


The methodology of CDF and D0 top quark analyzes and their underlying assumptions are summarized. The CDF and D0 top mass averages, obtained from measurements in several channels and based on about 100 pb\(^{-1}\) of data from \(p\bar {p}\) collisions at \(\sqrt {\rm s} = 1.8\) TeV collected by each experiment in Run I, are: \(M_{\rm t}=176.1\pm 4.0 (\rm stat) \pm 5.1 (\rm syst)\) GeV/\(c^2\) and \(M_{\rm t}=172.1\pm 5.2 (\rm stat) \pm 4.9 (\rm syst)\) GeV/\(c^2\), respectively. The combined Tevatron measurement of the top quark mass is \(M_{\rm t}= 174.3 \pm 3.2 (\rm stat) \pm 4.0 (\rm syst)\) GeV/\(c^2\). The CDF measurement of the \(t\bar {t}\) cross section (assuming \(M_{\rm t}=175\) GeV/\(c^2\)) is \(\sigma _{tt}=6.5 \pm ^{1.6}_{1.4}\) pb, and the D0 value (assuming \(M_{\rm t}=172.1\) GeV/\(c^2\)) is \(\sigma _{tt}=5.9\pm 1.7\) pb. In anticipation of much larger statistics, prospects for top physics in Tevatron Run II are summarized. The fact that top quark analyzes are among the best windows to physics beyond the Standard Model is emphasized.

Theoretical Aspects of Supersymmetry

Acta Phys. Pol. B 33, 3869 (2002)

page 3869 •


Some theoretical aspects of the minimal supersymmetric standard model and problems in unravelling its underlying structure are briefly discussed.

Supersymmetry at HERA, Results and Prospects

Acta Phys. Pol. B 33, 3875 (2002)

page 3875 •


The existing results from HERA on searches for supersymmetry are reviewed in this article. Within the framework of the Minimal Supersymmetric Standard Model with \(R_p\) conservation, no evidence for the production of supersymmetric particles was found by H1 and ZEUS. HERA is particularly sensitive to the resonant production of squarks in SUSY models with \(R_p\)-violation (\(/\hspace {-7pt}R_p\)). Searching for the process \(eq \rightarrow \tilde {q} \rightarrow eq \) (or \(e\chi \)), in a large number of possible decay modes of the \(\chi \) no evidence for \(\tilde {q}\) production was found. The limit on the corresponding Yukawa coupling \(\lambda '\) was found to be weakly dependent of the free MSSM parameters and extends to domains not excluded by other direct or indirect searches. Squark masses up to 260 GeV can be ruled out for couplings of electro-magnetic strength. The interpretation of the HERA results in the framework of various constrained supersymmetric models are compared to the results from other experiments. The perspectives of SUSY searches at HERA are reviewed.

Search for Supersymmetry at LEP

Acta Phys. Pol. B 33, 3881 (2002)

page 3881 •


Search for supersymmetric particles are performed with the data collected by the four LEP detectors, ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies up to 209 GeV, between 1995 and 2000. No evidence for a signal related to the production of sfermions, charginos and neutralinos in the framework of the Minimal Supersymmetric Standard Model (MSSM) is observed. The number of candidate events observed is in agreement with that expected from Standard Model (SM) background sources, for each signal topology. The absence of any excess is turned into exclusions domains in the space of the relevant MSSM parameters and lower limits on the mass of the supersymmetric particles are derived at 95% Confidence Level (C.L.).

SUSY Searches at the Tevatron Latest Run I Results, Prospects for Run II

Acta Phys. Pol. B 33, 3887 (2002)

page 3887 •


In this article we will present resent results of SUSY searches for Run I and we will give an outlook on prospects for SUSY searches in selected channels for Run II.

Leptoquarks Searches at HERA

Acta Phys. Pol. B 33, 3893 (2002)

page 3893 •


Results from the leptoquark searches at HERA using the reaction \(e^{\pm }p \rightarrow e^{\pm }(\nu ) X \), are reported. The data was collected by the H1 and ZEUS experiments from 1994 to 2000, at c.m. energies of 300 and 318 GeV and correspond to a total integrated luminosity \(\sim 120 \) pb\(^{-1}\) for each experiment. No signal was seen and limits were set on leptoquark Yukawa couplings for leptoquark masses both above and below \(\sqrt {s}\). The results are compared to those obtained in direct and indirect searches at other colliders.

Search for Excited Fermions in \(ep\) Collisions at HERA

Acta Phys. Pol. B 33, 3899 (2002)

page 3899 •


Heavy excited electrons and neutrinos have been sought by the H1 and ZEUS experiments at HERA. For the \(e^*\,(\nu ^*\)) searches, 120 pb\(^{-1}\) (16 pb\(^{-1}\)) of \(ep\) collision data have been analysed. No evidence for any excited lepton has been found, and limits on the characteristic couplings have been derived.

Lepton Flavour Violation at HERA

Acta Phys. Pol. B 33, 3905 (2002)

page 3905 •


Results obtained by the H1 and ZEUS collaborations on searches for Lepton Flavour Violation (LFV) are reported. No evidence was found for lepton–flavour violations and constraints were derived on the production of leptoquarks which could mediate such interactions. New limits in the muon channel obtained by ZEUS using 1999 and 2000 data, corresponding to an integrated luminosity of 66 pb\(^{-1}\), have been combined with previous ZEUS results, thus using the whole 1994–2000 statistics (130 pb\(^{-1}\)). All limits have been then compared to those obtained by low energy experiments.

Isolated Leptons, \(W\) and Single Top at HERA

Acta Phys. Pol. B 33, 3911 (2002)

page 3911 •


Standard Model \(W\) production in \(ep\) collisions is characterised by a high \(p_{\rm T}\) isolated lepton and missing overall \(p_{\rm T}\) in the leptonic decay channel and three high \(p_{\rm T}\) jets in the hadronic decay channel. These topologies are also the final state of single top production via a FCNC \(\kappa _{tu\gamma }\) vertex. Results of searches for these topologies are presented and consequent upper limits on the \(\kappa _{tu\gamma }\) coupling are derived.

Tevatron Searches for Large Extra Dimensions and Leptoquarks

Acta Phys. Pol. B 33, 3917 (2002)

page 3917 •


This paper presents searches for large extra dimensions and leptoquarks in \(p\overline {p}\) collisions from Run 1 at the Tevatron. Large extra dimensions are searched for in real graviton production with a monojet or monophoton and in virtual graviton exchange processes with electron or photon pairs. Results from leptoquark searches are presented for three generations of leptoquarks. No evidence of signal is found in any searches for large extra dimensions or leptoquarks and limits are placed. Prospectives for these searches in the Tevatron’s Run 2 are discussed and initial Run 2 data is presented.

Searches for Contact Interactions at HERA

Acta Phys. Pol. B 33, 3923 (2002)

page 3923 •


During the years 1994–2000 the HERA \(ep\) collider has been running with electrons and positrons at center-of-mass energies \(\sqrt {s}=300\)–320 GeV. The reaction \(ep\to eX\) is sensitive to new physics at mass scales in the \(\mathrm {TeV}\) range. Contact interaction analyses of the data at high momentum transfer \(Q^2=200\)–\(50000\,\mathrm {GeV}^2\) performed by the H1 and ZEUS collaborations are presented here, investigating compositeness models, leptoquarks, quarks of finite size and large extra dimensions.

Physics at LHC

Acta Phys. Pol. B 33, 3929 (2002)

page 3929 •


The LHC discovery potential is briefly reviewed with an emphasis on hard processes studied by ATLAS and CMS. It covers the Standard Model Higgs, supersymmetry and many other models including those with extra spatial dimensions.

HERA Upgrade and Prospects

Acta Phys. Pol. B 33, 3937 (2002)

page 3937 •


The upgrade of HERA offers exciting possibilities to further study electron proton scattering at high energy. The increased luminosity will allow precision measurements of deep inelastic scattering to be extended to the highest \(Q^2\). Polarisation will open up many new physics areas, providing increases sensitivity to Standard Model and new physics alike. HERA will have enhanced potential to discover physics beyond the Standard Model in a wide range of new physics scenarios.

Polarised \(e^{\pm }\) at HERA

Acta Phys. Pol. B 33, 3943 (2002)

page 3943 •


After a short summary of experience with \(e^{\pm }\) polarisation at the pre-upgraded HERA, the impact of the luminosity upgrade on polarisation is reviewed. Polarisation tuning requires a machine in stable and reproducible conditions, which have not been established yet. Priority has naturally been given to the luminosity operation and until now no attempt has been made to measure and optimise polarisation after the upgrade, but we hope to start as soon as possible.

Polarisation Measurement at HERA II

Acta Phys. Pol. B 33, 3949 (2002)

page 3949 •


After its recent upgrade, the HERA storage ring will provide longitudinally polarised leptons not only to the fixed target experiment HERMES, but also to the two collider experiments H1 and ZEUS, requiring a more precise polarisation measurement compared to run I. The upgrade of the transverse polarimeter is nearly finished and shows first promising results indicating a much improved performance. An upgrade of the longitudinal polarimeter is underway.

Physics at Large \(p_{\rm T}^2\) and \(Q^2\): Summary

Acta Phys. Pol. B 33, 3955 (2002)

page 3955 •


We summarize the results presented in the “Physics at large \(p_{\rm T}^2\) and \(Q^2\,\)” working group at the DIS’2002 Workshop. Higgs searches, precision measurements as well as searches for physics beyond the Standard Model at current and future experiments are reviewed.

Summary Talk

Acta Phys. Pol. B 33, 3983 (2002)

page 3983 •


Closing remarks at the X International Workshop on Deep Inelastic Scattering (DIS2002); Cracow, 30 April–4 May 2002.


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