{\bar{\rm P}}{\rm ANDA} at FAIR

The ${\bar{\rm P}}{\rm ANDA}$ experiment represents the central part of the hadron physics branch of the antiproton program of the new Facility for Antiproton and Ion Research (FAIR) at Darmstadt/Germany. It will investigate antiproton annihilations with an almost 4?? acceptance from two sequent spectrometer in the momentum range from 1.5?to 15?GeV/c. The gluon rich reaction product of antiproton-proton and antiproton-nucleus collisions on one hand and the high intensity and phase space cooled antiproton beam of the HESR on the other hand constitutes an ideal environment to study the sector of non-conventional hadronic states.     

The \overline{\mbox{\sf P}}{\sf ANDA} detector at FAIR

Selected problems of collisional processes in exotic atoms are discussed. The emphasis is on the collisional effects in antiprotonic helium including formation of antiprotonic atoms, collisional quenching of hot and thermalized metastable antiprotonic helium, shift and broadening of E1 and M1 spectral lines.     

Time-like nucleon form factor measurements at \overline{\textbf{P}}\textbf{ANDA}

The electromagnetic probe is an excellent tool to investigate the structure of the nucleon. The nearly 4π detector PANDA, to be installed on the FAIR accelerator complex at Darmstadt, will allow to make a precise determination of the electromagnetic form factors of the proton in the time-like (TL) region with unprecedented precision. In the framework of the one-photon exchange, the center of mass unpolarized differential cross section of the reaction $\overline{p} p \rightarrow e^+ e^- $ is a linear combination of the squared moduli of the electric $G^{p}_E$ and magnetic $G^{p}_M$ proton form factors. The precise measurement of the angular distribution over almost full angular range then directly gives these quantities. Only two experiments have provided the ratio $R = {|G^{p}_E|/|G^{p}_M|}$ but with very large statistical uncertainties. Within PANDA, there is a unique opportunity to measure separately the moduli of these two proton form factors $G^{p}_E$ and $G^{p}_M$ in good conditions, up to around q ² = 14 GeV² .     

Measurement of the {\rm\bf B_{\bf d}^{\bf 0}- {\bf \bar{B}}_{\bf d}^{\bf 0}} oscillation frequency

Time-dependent mixing is studied using about two million hadronic Z decays registered by L3 in 1994 and 1995. For this study three techniques are used. Tagging of the b-quark charge at decay time is performed by identifying leptons from semileptonic B decays. The flavour of the b quark at production time is determined from the charge of the lepton in the opposite hemisphere or by using a jet-charge technique. The proper time of the B-particle decay is obtained by reconstructing the production and decay vertices or by a measurement of the lepton impact parameter. The combined result for the frequency of meson oscillations is Received: 20 February 1998 / Revised version: 23 March 1998 / Published online: 12 August 1998     

Study of Bose-Einstein correlations in {\rm e}^ + {\rm e}^-\to {\rm W}^ + {\rm W}^- events at LEP

Bose-Einstein correlations between like-sign charged-particle pairs in events recorded with the OPAL detector at LEP at centre-of-mass energies between 183 GeV and 209 GeV are studied. Recently proposed methods which allow direct searches for correlations in the data via distributions of test variables are used to investigate the presence of correlations between hadrons originating from different W bosons in events. Within the statistics of the data sample no evidence for inter-WW Bose-Einstein correlations is obtained. The data are also compared with predictions of a recent implementation of Bose-Einstein correlation effects in the Monte Carlo model PYTHIAReceived: 24 March 2004, Revised: 7 June 2004, Published online: 20 July 2004     

Measurements of flavour-dependent fragmentation functions in {\bf Z^{0} \rightarrow{\rm q}\bar{\rm q}} events

Fragmentation functions for charged particles in events have been measured for bottom (b), charm (c) and light (uds) quarks as well as for all flavours together. The results are based on data recorded between 1990 and 1995 using the OPAL detector at LEP. Event samples with different flavour compositions were formed using reconstructed mesons and secondary vertices. The distributions and the position of their maxima are also presented separately for uds, c and b quark events. The fragmentation function for b quarks is significantly softer than for uds quarks. Received: 29 May 1998 / Published online: 25 January 1999     

Feasibility studies of the time-like proton electromagnetic form factor measurements with \overline{{P}}ANDA at FAIR

The possibility of measuring the proton electromagnetic form factors in the time-like region at FAIR with the $ \overline{{P}}$ ANDA detector is discussed. Detailed simulations on signal efficiency for the annihilation of $ \bar{{p}}$ + p into a lepton pair as well as for the most important background channels have been performed. It is shown that precise measurements of the differential cross-section of the reaction $ \bar{{p}}$ + p $ \rightarrow$ e ^- + e ⁺ can be obtained in a wide kinematical range. The determination of the ratio R of the moduli of the electric and magnetic proton form factors will be possible up to a value of momentum transfer squared of q ² ? 14 (GeV/c)^2 with absolute precision from 0.01 to 0.5 (for R ～ 1 . The total $ \bar{{p}}$ + p $ \rightarrow$ e ^- + e ⁺ cross-section will be measured up to q ² ? 28 (GeV/c)^2. The results obtained from simulated events are compared to the existing data. Sensitivity to the two-photon exchange mechanism is also investigated.