Monday, March 11, 2002 - DPG-Tagungen

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Nuclear Physics Tuesday The results of this analysis are reported together with measurements of B → charmonium branching fractions. HK 19.3 Tue 17:45 D Hard exclusive electroproduction of real photons and π + on the proton at HERMES — •Björn Seitz for the HERMEScollaboration — II. Physikalisches Insitut, Justus–Liebig Universität Giessen, Heinrich–Buff Ring 16, 35392 Giessen, F.R.G. The production of mesons (or photons) in deep–inelastic lepton scattering gives access to information on the structure of hadrons that is otherwise hard to obtain. When the production process involves at least on hard scale and is exclusive, the data can be interpreted in terms of the recently introduced generalized parton distributions (GPDs). These GPDs provide a unified description of hadronic structure, which can be applied to many different reactions. Single Spin Asymmetries in the hard, exclusive electroproduction of real photons (DVCS) and π + on the proton have been measured for the first time by HERMES. Sizeable asymmetries for DVCS using a polarized beam and unpolarized target have been observed. A large asymmetry using an unpolarized beam and a longitudinal polarized target has been observed in the exclusive electroproduction of π + . These data provide a first testing ground for the GPD formalism. HK 19.4 Tue 18:00 D Azimuthal asymmetries in pion and kaon production in SIDIS off longitudinally polarized proton and deuterium targets at HERMES — •Peter Schweitzer 1 , Klaus Goeke 2 ,andAnatoli Efremov 3 — 1 Dipartimento di Fisica Nucleare e Teorica, Universitá degli Studi di Pavia, Pavia, Italy — 2 Institut für Theoretische Physik II, Ruhr-Universität Bochum, Germany — 3 Joint Institute for Nuclear Research, Dubna, 141980 Russia Recently azimuthal asymmetries in pion production from SIDIS off a polarized proton target have been measured by HERMESand SMC. New HERMESdata from a longitudinally polarized deuetrium target will be released soon (possibly in February). The asymmetries can be explained by the Collins effect and contain information on the transversity distribution function and the T-odd Collins’ fragmentation function. Recently a very successful approach has been developed which is based on 2 ingredients and explains well existing data and allows unambigous predictions for new experiments with no free parameters. Ingredient (1) HK20 Heavy Ions II is experimental information on the Collins fragmentation function from DELPHI. Ingredient (2) are results from non-perturbative calculations of the transversity distribution function in the chiral quark soliton model and in the instanton model of the QCD-vacuum. HK 19.5 Tue 18:15 D Extraction of polarized quark distributions of the nucleon at HERMES — •Brecht Hommez — University of Gent, Proeftuinstraat 86, B 9000 Gent, Belgium New results from the HERMESexperiment on polarized quark distributions for the valence and the sea quarks in the nucleon will be presented. The HERMESexperiment has measured double spin asymmetries in the cross section for deep-inelastic scattering of longitudinal polarised positrons off longitudinal polarised hydrogen and deuterium targets. From these asymmetries, based on inclusive and semi-inclusive measurements, polarised quark distributions were extracted as a function of x. Since 1998, a dual-radiator Ring Imaging Cherenkov detector has been installed in HERMES, which allows the identification of kaons, pions and protons over almost the entire kinematic range of the experiment. Semiinclusive kaon asymmetries will provide an enhanced sensitivity on the polarisation of the strange sea quarks in the sea. HK 19.6 Tue 18:30 D η photo- and electroproduction on nucleons — •Eugenio Marco, Bugra Borasoy, and Stefan Wetzel — Physik- Department, Technische Universität München The Swave contribution to photo- and electroproduction of the η ′ meson on both the proton and neutron is investigated within a relativistic chiral unitary approach based on coupled channels. We work with an effective chiral Lagrangian which includes the η ′ as an explicit degree of freedom and incorporates important features of the underlying QCD Lagrangian such as the axial U(1) anomaly. Unitarity constraints are imposed in performing the resummation of the amplitudes obtained from chiral perturbation theory and cross sections of η ′ photo- and electroproduction from nucleons are obtained. The investigation of the η ′ -nucleon system may offer new insights into the role of gluons in chiral dynamics. Work supported in part by the DFG and the Alexander von Humboldt Foundation. Time: Tuesday 16:45–18:45 Room: E Group Report HK 20.1 Tue 16:45 E The Compressed Baryonic Matter experiment at the future facility at GSI — •Volker Friese 1 , Anton Andronic 1 , Peter Braun-Munzinger 1 , Christian Finck 1 , Bengt Friman 1 , Norbert Herrmann 2 , Romain Holzmann 1 , Wolfgang Koenig 1 , Matthias Lutz 1 , Peter Senger 1 , Yanghwan Shin 1 , Reinhard Simon 1 , Herbert Ströbele 3 , and Joachim Stroth 1,3 — 1 GSI Darmstadt — 2 Univ. Heidelberg — 3 Univ. Frankfurt A major field of research at the proposed accelerator facility at GSI will be the production and investigation of super-dense strongly-interacting matter. The exploration of the QCD phase diagram in the region of high baryon densities is complementary to the studies of matter at high temperatures performed at the CERN-SPS, RHIC and the future LHC. The planned experimental program will focus on diagnostic probes which have not been measured before in the beam energy range between 2 and 40 AGeV: light vector mesons decaying into electron-positron pairs, hidden and open charm and multi-strange hyperons. In addition, hadronic observables such as protons, pions and kaons will be detected with large acceptance. The experimental challenge is the efficient identification of rare probes (both hadrons and electrons) embedded in events with charged particle multiplicities of up to 1000 at reaction rates of up to 10 MHz. The proposed layout of the detector system and performance simulations will be presented. Group Report HK 20.2 Tue 17:15 E Kaon and Antikaon Production in Nucleus-Nucleus Collisions at SIS Energies — •Florian Uhlig for the KaoScollaboration — TU Darmstadt The study of the properties of hadrons in dense matter and the nuclear equation-of-state at high baryon densities represents a major goal of today’s heavy-ion collision experiments. The production of strange particles serves as a sensitive tool for probing both issues [1][2]. Systematic measurements of kaons and antikaons emitted in C+C, Ni+Ni and Au+Au collisions were performed with the Kaon Spectrometer KaoSat SIS/GSI. The particle yields were determined as function of momentum, collision centrality and emission angle. Of particular interest with respect to in-medium effects is the azimuthal emission pattern of kaons and antikaons. Recent results will be presented. [ ∗ ] supported by BMBF and GSI [1] F. Laue, C. Sturm et al., Phys. Rev. Lett. 82 (1999) 1640 [2] C.Sturm et al., Phys. Rev. Lett. 86 (2001) 39 HK 20.3 Tue 17:45 E Measurement of long-lived strange resonances in FOPI ∗ — •Markus Merschmeyer for the FOPI collaboration — Physikalisches Institut der Universität Heidelberg K 0 and Λ have been measured in the reactions Ni+Ni at 1.93 AGeV and Ru+Ru at 1.69 AGeV. Spectra and rapidity distributions are discussed and point, as is the case for charged kaons, in the theoretical description to the necessity for introducing in-medium potentials. Further information on this topic can be gained from the investigation of subthreshold production of double strange baryons at SIS energies. The
Nuclear Physics Tuesday capability of the FOPI detector for measuring Ξ − and theoretical predictions from thermal model calculations are presented. ∗ supported by BMBF (06HD953) and GSI (HD-PEL) HK 20.4 Tue 18:00 E Direct Measurement of Delta Production in 40 Ar + nat Ca at 0.8A GeV — •Ana Marin for the TAPScollaboration — Gesellschaft für Schwerionenforschung, D-64291 Darmstadt, Germany Charged pions and protons can be identified in the modularized photon spectrometer TAPSif one restricts the analysis to isolated BaF2 crystals in the hit response and if one correlates time–of–flight and deposited energy. This method is exploited in 40 Ar+ nat Ca at 0.8A GeV to investigate the production of ∆(1232) resonances in the rapidity range 0.2
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Page 55 and 56: Nuclear Physics Thursday The effect
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Page 65 and 66: Nuclear Physics Friday HK49 Plenary
Page 67 and 68: M. Ding3 , M.O. Distler3 , P. Drago
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Page 75 and 76: Friese, J. . HK 14.1, HK 14.3, HK 4
Page 77 and 78: Rusev, G. ..................HK 10.1

Monday, March 11, 2002 - DPG-Tagungen

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