qq̄ polarisation effects for pions interacting with nucleons

We study the polarization effects arising for pions propagating in a baryonic medium via the virtual excitation of qq̄ pairs. We show that the resulting quenching of the pion field in the interior of the baryon is, to a large extent, compensated by the necessary renormalization of the coupling strength. We also investigate the possibility of mimicking the pion quenching by the introduction of a position-dependent “pion mass” which acts like a repulsive potential.     

Dissociation of expanding cc̄ states in heavy ion collisions

We study J/ψ suppression in AB collisions assuming that the charmonium states evolve from small, color transparent configurations. Their interaction with nucleons and nonequilibrated, secondary hadrons is simulated using the microscopic model UrQMD. The Drell-Yan lepton pair yield and the J/ψ/Drell-Yan ratio are calculated as a function of the neutral transverse energy in Pb+Pb collisions at 160 GeV and found to be in reasonable agreement with existing data.     

Investigations into beam monitors at the AEg ̄ IS experiment

Detailed diagnostic of antiproton beams at low energies is required for essentially all experiments at the Antiproton Decelerator (AD), but will be particularly important for the future Extra Low ENergy Antiproton ring (ELENA) and its keV beam lines to the different experiments. Many monitors have been successfully developed and operated at the AD, but in particular beam profile monitoring remains a challenge. A dedicated beam instrumentation and detector test stand has recently been setup at the AE \(\bar {g}\) IS experiment (Antimatter Experiment: Gravity, Interferometry, Spectroscopy). Located behind the actual experiment, it allows for parasitic use of the antiproton beam at different energies for testing and calibration. With the aim to explore and validate different candidate technologies for future low energy beam lines, as well as the downstream antihydrogen detector in AE \(\bar {g}\) IS, measurements have been carried out using Silicon strip and pixel detectors, a purpose-built secondary emission monitor and emulsions. Here, results from measurements and characterization of the different detector types with regard to their future use at the AD complex are presented.     

Search for exotic processes at the CERN pp̄ collider

The total UA2 data sample at the CERN pp̄ Collider corresponds to an integrated luminosity of 910 nb⁻¹. Limits on various hypothetical processes, such as production of excited electrons, additional charged or neutral vector bosons, or supersymmetric particles, are presented from the analysis of this sample.     

Four-body calculations of elastic scattering in H–H̄ collisions

We present a nonadiabatic treatment of the hydrogen-antihydrogen system. The technique used to describe H- H? collisions is based on the coupled rearrangement channels method. Within this approach the total, nonadiabatic wave function of the system is divided into two parts: an inner and an outer one. To describe the inner part a set of square-integrable 4-body functions is used. These functions are obtained by a diagonalization of the total Hamiltonian projected on a chosen L ² subspace, they explicitly contain components of various arrangement channels expressed in terms of corresponding Jacobi coordinates. The outer part of the total wave function reflects its asymptotic character. Our procedure leads to the system of non-local integro-differential equations that are solved iteratively and simultaneously determine both the shape of the outer part of the wave function and the coefficients in the four-body expansion of the inner part. Using this formalism we perform the one-channel calculation of the elastic scattering to obtain the S-matrix and nonadiabatic scattering length.     

Isospin invariance,CP violation and B−B̄ mixing

With large B⁰−B̄⁰ mixing, the CP asymmetry of certain B decays become nearly maximal. However, the clear identification of relevant B meson decays required for experimental observation of such effects is difficult. We point out that symmetry relations among various B meson decay channels lead to additional constraints which can be useful in extracting CP violating amplitudes. As an example, we consider decay amplitudes to final states containing both a J/ψ and a K_S, whose interference terms provide information on CP violation. We show that these decays are ΔI=0 transitions and obtain isospin relations between the direct terms in the amplitude and experimental results from corresponding decays involving charged kaons.     

Total spin-dependent p̄d cross sections at low and intermediate energies

There may be unique (“smoking-gun”) signatures of the breakdown of CPT symmetry, induced in some models of Quantum Gravity entailing decoherence for quantum matter. Such effects can be observed in entangled states of neutral mesons via modifications of the respective Einstein-Podolsky-Rosen (EPR) correlators (“ω-effect”). In the talk I discuss experimental signatures and bounds of the ω-effect in Φ- and B-factories, and argue that the effect might be falsifiable at the next generation facilities.     

Design studies of the PWO Forward End-cap calorimeter for P̄ANDA

The P?ANDA detection system at FAIR, Germany, is designed to study antiproton-proton annihilations, in order to investigate, among others, the realm of charm-meson states and glueballs, which has still much to reveal. The yet unknown properties of this field are to be unraveled through studying QCD phenomena in the non-perturbative regime. The multipurpose P?ANDA detector will be capable of tracking, calorimetry, and particle identification, and is planned to run at high luminosities providing average reaction rates up to 2 · 10⁷ interactions/s. The envisaged physics program requires measurements of photons and charged particles with excellent energy, position, and time resolutions. The electromagnetic calorimeter (EMC) will serve as one of the basic components of the detector setup and comprises cooled lead-tungstate (PbWO₄) crystals. This paper presents the mechanical design of the Forward End-cap calorimeter and analyzes the response of the Forward End-cap calorimeter in conjunction with the full EMC and the complete P?ANDA detector. The simulation studies are focused on the performance of the planned EMC with respect to the energy and spatial resolution of the reconstructed photons. Results of the Monte Carlo simulations, excluding very low-energy photons, have been validated by data obtained from a prototype calorimeter and shown to fulfil the requirements imposed by the P?ANDA physics program.     

Baryon asymmetry,stable proton and n-n̄ oscillations in superstring models

The violation of baryon number is discussed in the context of a gauge model inspired by the E₈ × E₈ superstring theory. Lepton number is an accidental unbroken symmetry of the model. The proton, as a consequence, is essentially stable. The model yields an acceptable value (∼10⁻¹⁰) for the baryon asymmetry in the universe. It also predicts n-n̄ oscillations at a rate which may be amenable to ongoing experimental searches.