abstract

We describe particle production in the framework of an independent string model: the dual parton model. We show that an improved version of this model, containing a diquark breaking component, allows to describe the bulk of particle production and, in particular, baryon stopping and most of the observed enhancement of strange baryons. Only for very rare processes, such as \({\mit \Omega }\) or \(J/\psi \) production, the model has to be supplemented with final state interaction (comovers interaction). Recent data on event–by–event fluctuations in \(p_{\rm T}\) are also described by the model. Predictions for RHIC and LHC are presented and the effect of nuclear shadowing is discussed.

abstract

We review the current status of strangeness as signature of the formation and dissociation of the deconfined QGP at the SPS energy scale, and present the status of our considerations for RHIC energies. By analyzing, within the framework of a Fermi statistical model, the hadron abundance and spectra, the properties of a disintegrating, hadron evaporating, deconfined QGP fireball are determined and can be compared with theory for the energy range 160–200\(A\) GeV on fixed target. We discuss in more detail our finding that the pion yields occur near to pion condensation condition. Dynamical models of chemical strangeness equilibration are developed and applied to obtain strangeness production in a QGP phase at conditions found at SPS and expected at RHIC. The sudden QGP break up model that works for the SPS data implies at RHIC dominance of both baryon, and antibaryon, abundances by the strange baryon and antibaryon yields.

abstract

The suppression of \(J/\psi \) production, proposed as a possible signature of the formation of a Quark–Gluon Plasma in heavy ion collisions, is reviewed in these lectures both experimentally and theoretically. A special emphasis is put on the recent results obtained by the NA50 collaboration at CERN in Pb–Pb collisions where new features seem to appear.

abstract

The experimental results on the pion, strangeness and \(J/\psi \) production in high energy nuclear collisions are discussed. The anomalous energy dependence of pion and strangeness production is consistent with the hypothesis that a transition to a deconfined phase takes place between the top AGS (\(\approx 15\; A\cdot \)GeV) and the SPS (\(\approx 200\; A\cdot \)GeV) energies. The \(J/\psi \) production systematics at the SPS can be understood assuming that the \(J/\psi \) mesons are created at hadronization according to the available hadronic phase space. This new interpretation of the \(J/\psi \) data allows one to establish a coherent picture of high energy nuclear collisions based on the statistical approaches of the collision early stage and hadronization. Surprisingly, the statistical model of strong interactions is successful even in the region reserved up to now for pQCD based models.

abstract

We review the properties of energetic parton propagation in hot or cold QCD matter, as obtained in recent work. The medium induced energy loss is studied. It has the remarkable feature to grow as \(L^2\), the length of the traversed matter squared. Numerical estimates suggest that it may be significantly enhanced in hot matter compared to cold matter, thus pointing towards a possible signal for quark–gluon plasma formation. The more realistic case of an expanding (longitudinally) QCD plasma is studied. The resulting radiative energy loss can be as large as 6 times the corresponding one in a static plasma at the reference temperature \(T(L)\) which is reached after the parton propagates on a distance \(L\). Finally, the spectrum of soft radiated gluons is studied, leading to the calculation of the medium dependent energy lost by a jet with opening angle \(\theta _{\rm cone}\). It is shown that the fraction of this energy loss to the integrated one exhibits a universal behavior in terms of \(\theta _{\rm cone}^2 L^3 \widehat {q}\) where \(\widehat {q}\) is the transport coefficient characterizing the medium. Phenomenological implications for the difference between hot and cold matter are discussed.

abstract

The \(B_c\) meson is the bound state of \(b\bar {c}\) (or \(\bar {b}c\)) whose recent detection is the first step toward completion of the spectroscopy of heavy quark mesonic states. The \(b\)-\(c\) states have properties that conveniently fill the gap between the \(J/\psi \) and the \({\mit \Upsilon }\) states. Thus it is probable that at RHIC the \(B_c\) mesons will serve as a probe of deconfined matter. We find that significant differences arise for \(B_c\) formation in deconfined and confined matter. Our initial calculations suggest that:
(a) The rates of normal hadronic production mechanisms at RHIC energies are not sufficient to produce a detectable number of \(B_c\) mesons.
(b) If a region of deconfined quarks and gluons is formed, the production (and survival) rate can be enhanced by several orders of magnitude.
(c) The observation of \(B_c\) mesons at RHIC would signal a source of deconfined charmed quarks, and the rate of \(B_c\) production will be a measure of the initial density and temperature of that source.

abstract

Applications of perturbative QCD to deeply virtual Compton scattering and hard exclusive electroproduction processes require a generalization of usual parton distributions for the case when long-distance information is accumulated in nonforward matrix elements of quark and gluon light-cone operators. We describe two types of nonperturbative functions parametrizing such matrix elements: double distributions \( F(x,y;t)\) and skewed distribution functions \({\cal F}_{\zeta }(X;t)\), discuss their properties, and basic uses in the QCD description of hard exclusive processes.

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Of late, the field of BFKL physics has been the subject of significant developments. The calculation of the NLL terms was recently completed, and they turned out to be very large. Techniques have been proposed to resum these corrections. These lectures provide an introduction to the BFKL equation and some of the recent developments, using DGLAP evolution as the starting point.

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In these lectures, I shall discuss small x physics and the consequences of the high gluon density which arises as x decreases. I argue that an understanding of this problem would lead to knowledge of the high energy asymptotics of hadronic processes. The high gluon density should allow a first principles computation of these asymptotics from QCD. This physics might be experimentally probed in heavy ion colliders or in high energy electron-nuclear collisions

abstract

In hadrons and nuclei at very small \(x\), parton distributions saturate at a scale \(Q_s(x)\). Since the occupation number is large, and \(Q_s(x)\gg {\mit \Lambda }_{\rm QCD}\), classical weak coupling methods may be used to study this novel regime of non-linear classical fields in QCD. In these lectures, we apply these methods to compute structure functions in deeply inelastic scattering (DIS) and the energy density of gluons produced in high energy nuclear collisions.

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In this talk we present a calculation for the cross sections for neutrino interaction with the nucleon. Parton distributions are calculated using the unified BFKL/DGLAP formalism which embodies also important subleading \(\ln 1/x\) effects. It is shown that this calculation is consistent with the other based on GRV and CTEQ parton distributions up to \(40\%\) for the highest energies: \(\sim 10^{12}\) GeV. We also calculate the attenuation of neutrinos on their way through the Earth to the detector. We solve the transport equation which also embodies the regeneration due to neutral current interactions besides attenuation. We present the results for different angles and fluxes originating from different sources like active galactic nuclei, gamma ray bursts and top–down models.

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In these lectures, a simple introduction to the phenomenon of diffraction in deep inelastic scattering and its theoretical description is given. While the main focus is on the diffractive structure function \(F_2^D\), some issues in diffractive vector meson production are also discussed.

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In the Model of the Stochastic Vacuum the infrared behaviour of QCD is approximated by a Gaussian stochastic process in the gluon field strength. This assumption leads already to confinement for non-Abelian gauge theories. The main part of the contribution is dedicated to the application of the model to soft high energy reactions as hadron–hadron scattering and electroproduction. The special role of the odderon is also investigated.

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This talk gives an elementary introduction to the basic properties of positronium. Recent progress in theoretical studies of the hyperfine splitting and lifetime of the ground state is reviewed. Sensitivity of these precisely measured quantities to some New Physics effects is discussed.

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The strong \(g\)-coupling characterizes the interaction of heavy mesons with pions in typical vertices \(H^*H\pi \), \(H^*H^*\pi \), where \((H^*;H)\) stands for vector and pseudoscalar \((B^*;B)\) or \((D^*;D)\) heavy mesons. Its estimation by different theoretical methods has led to a wide range of possible values. We describe a new approach to the determination of \(g\), which exploits the rare radiative decays \(B^*\rightarrow B\gamma \gamma \) and \(D^*\rightarrow D\gamma \gamma \). It is shown that the branching ratio of \(D^*\rightarrow D\gamma \gamma \) can be expressed as a function of a single unknown \(g\) and we calculate it to be in the measurable range between \(1.6\times 10^{-6}\) and \(3.3\times 10^{-5}\) for \(0.25 \lt g \lt 1\).

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The search for new physics beyond the standard model is proceeding nowadays intensively along experimental and theoretical lines. We review here the sector of charm radiative decays in this context. The calculation of \(D\rightarrow V\gamma \), \(D\rightarrow \ell ^+\ell ^-\gamma \) transitions reveals their unequivocal dominance by long-distance contributions. On the other hand, the beauty-conserving charm-changing electroweak transition \(B_c\rightarrow B_u^*\gamma \) is shown to have unique properties which make it a promising avenue in the search for new physics. We describe a calculation of short- and long-distance contributions to this decay which finds them to be of comparable size. The branching ratio of this decay in the standard model is estimated to be \(\simeq 10^{-8}\).

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The newly developped Monte-Carlo event generator APACIC++ suitable to describe multijet-events in high-energetic electron–positron annihilations is presented. A new ansatz to match the corresponding matrix elements for the production of jets via the strong and electroweak interactions to the subsequent parton shower modelling the inner-jet evolution is discussed in some detail. Results obtained with APACIC++ are compared to other QCD event generators and to some representative experimental data.

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The idea of coarse-grained gluon field is discussed. We recall motivation for introducing such a field. Next, we outline the approach to small momenta limit of lattice coarse-grained gluon field presented in our paper hep-ph/9803392. This limit points to color dielectric type models with a number of scalar and tensor fields instead of single scalar dielectric field.

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Kibble-Zurek scenario of topological defects formation is extended to inhomogeneous first and second order transitions. In both cases there is characteristic threshold velocity of critical front propagation below which no topological defects are produced. Instead oriented condensate is grown behind moving temperature or pressure front.

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Overview of the ATLAS magnet system and transition radiation tracker is presented.

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This article presents short overwiew of the physics programme which should be possible with the ATLAS detector, as documented in ATLAS Detector and Physics Performance Technical Design Report. The physics potential studied in previous documents (ATLAS Letter of Intent and ATLAS Technical Proposal) have been re-examined and many new strategies proposed. Here search for the Higgs boson is discussed in somewhat more details, while only highlights of the new results are given for each of the other important aspects in this very broad physics programme.