Prospects for measurements of parity-violatingphotoproduction of \pi^\pm

I address the experimental feasibility of two measurements related to the photoproduction of pions, in the context of the G⁰ experiment. The first involves an extraction of the parity-violating pion-nucleon coupling constant via a measurement of parity-violating threshold pion photoproduction. The second involves an extraction of , which parameterizes parity-violating photoproduction of pions on the -resonance. The second process might have an anomalously large asymmetry, from a model based on hyperon decays.Received: 30 September 2002, Published online: 22 October 2003PACS: 11.30.Er Charge conjugation, parity, time reversal, and other discrete symmetries - 13.60.Le Meson production - 14.20.Gk Baryon resonances with S = 0J.W. Martin: For the G⁰ Collaboration     

Exclusive and semi-inclusive strangeness and charm production in \pi N and NN reactions

Using the Quark-Gluon Strings Model (QGSM) combined with Regge phenomenology we consider the reactions and which are dominated by the contributions of the K ^* and D ^* Regge trajectories, respectively. The spin structure of the amplitudes is described by introducing Reggeized Born terms. It is found that the existing data for the reaction are in reasonable agreement with the model predictions. To describe the absolute values of the cross-sections it is necessary to introduce also suppression factors which can be related to absorption corrections. Furthermore, assuming the SU(4) symmetry to hold for Regge residues and the universality of absorption corrections we calculate the cross-section of the reaction . Employing the latter results from reactions we then estimate the contributions of the pion exchange mechanism to the cross-sections of the reactions and and compare them with the contributions of the K and D exchanges. We find that the NN reactions are dominated not by pion exchange but by K and D exchanges, respectively. Moreover, assuming the SU(4) symmetry to hold approximately for the coupling constants = we analyze also the production of leading -hyperons in the reaction . It is shown that the non-perturbative mechanism should give an essential contribution to the yield for .Received: 30 September 2002, Published online: 22 October 2003PACS: 13.85.Fb Inelastic scattering: two-particle final states - 13.85.Hd Inelastic scattering: many-particle final states - 14.20.Lq Charmed baryons - 14.40.Lb Charmed mesons     

Transport analysis of in-medium hadron effects in pA and AA collisions

The production and decay of vector mesons ( ) in pA and AA reactions is studied with particular emphasis on their in-medium spectral functions. It is explored within transport calculations if hadronic in-medium decays like or might provide complementary information to their dilepton (e ⁺ e ^-) decays. Whereas the signal from the -meson is found to be strongly distorted by pion rescattering, the -meson Dalitz decay to appears promising even for more heavy nuclei in and pA reactions. Furthermore, the influence of nucleon and kaon/antikaon potentials on the yields and spectra in pA collisions is calculated and compared to the recent data from the ANKE Collaboration.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 13.75.Jz Kaon-baryon interactions - 14.40.Aq , K, and mesons - 25.40.-h Nucleon-induced reactionsW. Cassing: In collaboration with E.L. Bratkovskaya, M. Büscher, Ye.S. Golubeva, V. Grishina, V. Hejny, V. Metag, J. Messchendorp, B. Kamys, L.A. Kondratyuk, P. Kulessa, Z. Rudy, S. Schadmand, A.A. Sibirtsev, H. Ströher     

Photoproduction of πmesons from nuclei

Photoproduction of neutral pions from nuclei (carbon, calcium, niobium, lead) has been studied for incident-photon energies from 200 MeV to 800 MeV with the TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI accelerator. Data were obtained for the inclusive photoproduction of neutral pions and the partial channels of quasifree single- , double- , and photoproduction. They have been analyzed in terms of the in-medium behavior of nucleon resonances and the pion-nucleus interaction. They are compared to earlier measurements from the deuteron and to the predictions of a Boltzmann-Uehling-Uhlenbeck (BUU) transport model for photon-induced pion production from nuclei.PACS: 13.60.Le Meson production - 25.20.Lj Photoproduction reactions     

Experimental signals of \sigma-mesons in nuclei and chiral symmetry

The interaction in the scalar isoscalar channel is studied as a function of the baryonic density in the framework of a chiral unitary approach which successfully reproduces vacuum - phase shifts. We present some results on the -meson pole, which is generated dynamically in our model, in nuclear matter. Finally, we analyze the ( ) reaction on nucleons and nuclei in the kinematical region where the scalar isoscalar scattering amplitude is influenced by the low mass of the in nuclei, and thus, presents a large enhancement close to the position of its pole. Indeed, we find, that the final-state interaction of the pions modified by the nuclear medium produces a large shift of strength of the two-pion invariant-mass distribution in the ( ) channel consistent with recent experimental data.Received: 30 September 2002, Published online: 22 October 2003PACS: 14.40.-n Properties of specific particles: Mesons - 25.20.-x Photonuclear reactions - 21.65. + f Nuclear matter     

Cross-sections and spin observables in proton-proton elastic scattering: Results from EDDA at COSY

At the Cooler-Synchrotron COSY/Jülich polarized and unpolarized elastic proton-proton scattering has been investigated with the EDDA-Experiment in the energy range ( -2.5 GeV). By taking scattering data during the acceleration of the beam with a large-acceptance ( - ) detector, precise excitation functions for differential cross-section and analyzing power have been measured in small energy steps with consistent normalization with respect to luminosity and polarization. These data have helped to improve the determination of phase-shifts at higher energies and impose tight quantitative upper bounds on possible resonant contributions to pp elastic scattering, as they might arise from exotic 6-quark configurations. Recently, with polarized beam and target, the spin-correlation parameters , , and have been determined at 10 energies between 0.8 and 2.5 GeV. The observable has been measured the first time above 800 MeV and our results are in sharp contrast to phase-shift predictions at higher energies.Received: 30 September 2002, Published online: 22 October 2003PACS: 24.70. + s Polarization phenomena in reactions - 25.40.Cm Elastic proton scattering - 11.80.Et Partial-wave analysis - 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.)     

S = -1 meson-baryon scattering in coupled-channel unitarized Chiral Perturbation Theory

The s-wave meson-baryon scattering amplitude is analyzed for the strangeness S = -1 and isospin I = 0 sector in a Bethe-Salpeter coupled-channel formalism incorporating Chiral Symmetry. Four two-body channels have been considered: , , , . The needed two-particle irreducible matrix amplitude is taken from lowest-order Chiral Perturbation Theory in a relativistic formalism. Off-shell behaviour is parameterized in terms of low-energy constants, which outnumber those assumed in previous works and provide a better fit to the data. The position of the complex poles in the second Riemann sheet of the scattering amplitude determines masses and widths of the and resonances which compare well with accepted numbers.Received: 30 September 2002, Published online: 22 October 2003PACS: 11.10.St Bound and unstable states; Bethe-Salpeter equations - 11.30.Rd Chiral symmetries - 11.80.Et Partial-wave analysis - 13.75.Lb Meson-meson interactionsE. Ruiz Arriola: Spokesperson     

Hadrons with charmed quarks in matter

We investigate the decay width of excited charmonium states at finite nuclear density with simultaneous modification of both D- and -mesons in nuclear matter. The strongest effect is found for the -meson. The medium modification can be detected by dilepton spectroscopy as substantial broadening and anomalous absorption.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.25.Gv Decays of , , and other quarkonia - 14.40.Lb Charmed mesons - 14.65.Dw Charmed quarks - 24.85. + p Quarks, gluons, and QCD in nuclei and nuclear processes     

High-resolution in-beam particle-gamma coincidence spectroscopy

A short summary of the present status of prompt particle decays in the mass region is presented. It includes recent results from a GAMMASPHERE experiment, which aimed at the combined high-resolution spectroscopy of light charged particles and -rays to allow for more detailed studies of known decays and the identification of new cases of discrete prompt proton and -particle emission from highly and superdeformed states.Received: 10 October 2002, Published online: 17 February 2004PACS: 23.50. + z Decay by proton emission - 23.60. + e decay - 27.40. + z - 27.50. + e      

Parity non-conservation in proton-proton elastic scattering

The parity-non-conserving longitudinal asymmetry in proton-proton (p p) elastic scattering is calculated in the lab energy range 0-350 MeV using contemporary, realistic strong-interaction potentials combined with a weak-interaction potential comprised of - and -meson exchanges as exemplified by the DDH model. Values for the - and -meson coupling constants, and , are determined from comparison with the measured asymmetries at 13.6 MeV, 45 MeV, and 221 MeV.Received: 30 September 2002, Published online: 22 October 2003PACS: 21.30.-x Nuclear forces - 24.80. + y Nuclear tests of fundamental interactions and symmetries - 25.40.Cm Elastic proton scattering     

Helicity dependence of the \gamma p\rightarrow N \pi channels and multipole analysis in the \Delta region

A high-quality double-polarization data set for the helicity dependence of the total and differential cross-sections for both channels in the region has been obtained in the framework of the GDH experiment. The experiment, performed at the Mainz microtron MAMI, used a 4 detection system, a circularly polarized photon beam, and a longitudinally polarized frozen-spin target. These data are included in the database to perform a multipole analysis to determine the properties of the -resonance. For the resonant (1232) multipoles we find a very good agreement with previous analyses, while the nonresonant ones show significant deviations.Received: 11 July 2003, Revised: 16 January 2004, Published online: 17 August 2004PACS: 13.60.Le Meson production - 14.20.Gk Baryon resonances with S = 0 - 25.20.Lj Photoproduction reactions     

\pi\pi correlations in \gamma + A reactions

Preliminary differential cross-sections of the reactions and with A = ¹ H, ¹² C, and ^nat Pb are presented. A significant nuclear-mass dependence of the invariant-mass distribution is found in the channel. The dependence is not observed in the channel. The in-medium observation in the channel is consistent with an in-medium modification of the interaction in the I = J = 0 channel, changing width and pole position of a resonant state.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 21.65. + f Nuclear matterJ.G. Messchendorp: For the TAPS and A2 Collaborations     

Cluster structure of <Superscript>16</Superscript>O

A folding potential describing the -scattering on ¹⁶O over a broad energy range 25.8-146.0 MeV is constructed on the basis of -like cluster and unclustered-nucleon configurations of ¹⁶O. The resulting potential does not need any renormalization to fit the angular distribution of elastic cross-sections. The effects of the repulsive part of - and -nucleon interactions are investigated. The analysis suggests that both the - repulsive potential and the unclustered nucleonic configuration in the target are important to describe the scattering data over a broad range of incident energies. The root-mean-square radius for the ¹⁶O nucleus is deduced.Received: 5 December 2002, Published online: 9 October 2003PACS: 25.55.Ci Elastic and inelastic scattering - 24.10.Ht Optical and diffraction models - 21.60.Gx Cluster models     

Chromofields of strings and baryons

We calculate color electric fields of quark/antiquark ( ) and 3-quark (qqq) systems within the Chromodielectric Model (CDM). We explicitly evaluate the string tension of flux tubes in the -system and analyze their profile. To reproduce results of lattice calculations we use a bag pressure from which an effective strong-coupling constant follows. With these parameters we get a Y-shaped configuration for large qqq-systems.Received: 30 September 2002, Published online: 22 October 2003PACS: 11.10.Lm Field theory: Nonlinear or nonlocal theories and models - 11.15.Kc Gauge field theories: Classical and semiclassical techniques - 12.39.Ba Phenomenological quark models: Bag model     

Some physics highlights from the EUROBALL spectrometer

Exotic, neutron-rich proton-induced spallation products of ²³²Th and ²³⁸U obtained from the PS Booster ISOLDE facility have been investigated by - , - coincidence and spectrum-multiscaling measurements. A new method for the reduction of isobaric contamination enabled to study the unknown region beyond ²⁰⁸Pb for the decay chain A = 217. A new isotope ²¹⁷Bi with a half-life of s was discovered and its -decay studied. For the first time, a half-life value of s for the -decay of ²¹⁷Po was measured.Received: 3 March 2003, Revised: 13 May 2003, Published online: 30 September 2003PACS: 23.20.Lv transitions and level energies - 23.60.+e decay - 27.80.+w 190 A 219 - 29.30.Kv X- and -ray spectroscopyV. Fedoseyev: Present address: ISOLDE, CERN-PPE, CH-1211, Geneva 23, Switzerland.M. Górska: Present address: GSI, Darmstadt, D-64220, Germany.M. Huhta: Present address: Nokia, Tampere, Finland.     

Inclusive $\omega$ photoproduction off nuclei

We investigate inclusive photoproduction off complex nuclei, concentrating on the feasibility to examine a possible in-medium change of the properties by observing the invariant-mass spectrum. The simulations are performed by means of a BUU transport model including a full coupled-channel treatment of the final-state interactions. In-medium changes of the spectral density are found to yield a moderate modification of the observables as compared to the situa tion in free space. Also the effects of a momentum dependence of the strong potential are discussed.Received: 28 October 2003, Revised: 26 November 2003, Published online: 8 June 2004PACS: 25.20.-x Photonuclear reactions - 13.60.-r Photon and charged-lepton interactions with hadrons - 13.60.Le Meson production - 14.40.-n Mesons     

Boltzmann-Uehling-Uhlenbech calculation of total reaction cross-section and fragmentation cross-section

, and have been calculated via the BUU model with soft EOS and 0.8 times of . The density distribution without any adjustable parameters which comes from the RMF model has been introduced into the BUU calculation to replace the normally used one-parameter square-type distribution. The calculated results can reproduce the experimental data well for both halo- and stable-nuclei-induced reactions. Here or is calculated as the difference between of halo nucleus and core nucleus, by assuming . It indicates that this assumption works very well at high energy in the BUU calculation. More experimental measurements are necessary to test the validity of this assumption at intermediate energy.Received: 12 June 2003, Revised: 29 September 2003, Published online: 27 April 2004PACS: 24.10.-i Nuclear reaction models and methods - 25.60.Dz Interaction and reaction cross-sections - 25.60.Gc Breakup and momentum distributions - 27.20. + n      

Pseudo-spin band in the odd-odd nucleus 172Lu

High-spin states in the odd-odd nucleus ¹⁷²Lu have been populated in a ¹⁷⁰Er(⁷Li, 5n) reaction and the emitted -radiation was detected with the GASP array. Two sequences of a new identical band have been observed with the transition energies in the favoured and unfavoured sequences being identical within keV at low spins and keV at high spins over the whole observed spin range. Aninterpretation as a pseudo-spin singlet band of configuration is proposed. It represents the best example of a pseudo-spin singlet band in normal deformed nuclei known until now.Received: 19 February 2003, Revised: 27 March 2003, Published online: 12 August 2003PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.70.+q      

Associated strangeness production at threshold

The associated strangeness dissociation at threshold has been studied at the COSY-11 facility measuring the hyperon and the K ⁺ K ^- meson pair production. Measurements of the near-threshold and production via the reaction (S. Sewerinet al., Phys. Rev. Lett. 83, 682 (1999)) at COSY-11 have shown that the cross-section ratio exceeds the value at high excess energies ( MeV (A. Baldiniet al., Total Cross-Sections for Reactions of High-Energy Particles, Landolt-Börnstein, New Series, Vol. I/12 (Springer, Berlin, 1988))) by an order of magnitude. For a better understanding additional data have been taken between 13 MeV and 60 MeV excess energy. The near-threshold production of the charged kaon-antikaon pair is related to the discussion about the nature of the scalar states in the 1 GeV/c ² mass range, i.e. the f ₀(980) and a ₀(980) (O. Krehl, R. Rapp, J. Speth, Phys. Lett. B 390, 23 (1997)). The interpretation as a molecule is strongly dependent on the K- interaction which can be studied via the production channel. A first total cross-section value on the reaction at an excess energy of 17 MeV (C. Quentmeieret al., Phys. Lett. B 515, 276 (2001)), i.e. below the production threshold, was measured.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 14.20.Jn Hyperons - 14.40.Aq , K, and mesons - 25.40.Ep Inelastic proton scattering     

Evidence for an isomer in 76 Ni

In the experiment performed at the LISE2000 spectrometer at GANIL neutron-rich nickel isotopes were studied by microsecond isomer spectroscopy. Evidence for an isomer in ⁷⁶Ni is found, consistently with the shell model prediction of an 8 ⁺ state of structure.Received: 24 October 2002, Published online: 17 February 2004PACS: 23.20.Lv transitions and level energies - 27.50. + e