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.     

Decay properties of isomeric states in radium isotopes close to N = 126

Isomeric states in ^210-215Ra have been populated by the decay of the compound nuclei ^216,220Ra produced in irradiations of ^204,208Pb with ¹²C at MeV. Published values for -ray energies and half-lives were confirmed for Ra. Our data for Ra agree with the -energies and the half-life measured at the RITU separator, University of Jyväskylä (Finland). Its decay pattern is complex. Two series of -rays of keV and keV were observed. A half-life of s was measured. The isomeric state is attributed to an 8 ⁺ state at E ^* = 2053.8keV. A previously unknown isomeric state was assigned to Ra. It has a half-life of ( ) and it decays by emission of -rays with energies of 396.1keV and 802.0keV. It is attributed to a 13/2 ⁺ state at E ^* = 1198.1 keV.PACS: 23.60. + e decay - 27.90. + b      

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      

Prompt fission neutron spectra of <Superscript>238 </Superscript>U(n,f) above emissive fission threshold

Model calculations were performed to interpret prompt fission neutron spectra (PFNS) of the ²³⁸ U(n, f) reaction for incident neutron energies -18 MeV. Pre-fission (pre-saddle) reaction neutron spectra were calculated with Hauser-Feshbach statistical model, ²³⁸ U fission and reaction cross-section data being described consistently. The increase of the cut-off energy of (n, nf) reaction neutron spectra with excitation energy of fissioning nucleus is described. For -9 MeV the low-energy PFNS component, which is due to the contribution of pre-fission (n, nf) neutrons, is compatible with measured data. Average energy of prefission (n, nf) neutrons is shown to be rather dependent on . For -18 MeV, a decrease of measured PFNS average neutron energies is interpreted. Spectra of neutrons, evaporated from fission fragments, were approximated as a sum of two Watt distributions. The reduced fission fragment velocity is assumed for the neutron emission during fragment acceleration. Several interpretations of observed soft neutron excess are investigated, i.e., possible uncertainties of emissive fission contributions and additional neutron source. We claim the soft neutron excess cannot be attributed to the pre-saddle neutrons contribution.Received: 3 February 2003, Revised: 24 April 2003, Published online: 9 October 2003PACS: 25.85.Ec Neutron-induced fission     

Isomeric and ground-state decay of 215 Bi

A new high-spin isomer in ²¹⁵Bi, with a half-life of 36.9(6) s, has been identified at the PSB-ISOLDE on-line mass separator using the pulsed-release technique combined with the element selective RILIS source. A decay scheme of Bi was constructed and complemented with the low-spinstructure observed in Bi decay. The population of a cascade on top of the level in ²¹⁵Poprovides evidence for Gamow-Teller -decay of the high-spin ²¹⁵Bi isomer.Received: 3 March 2003, Revised: 10 June 2003, Published online: 9 October 2003PACS: 23.20.Lv transitions and level energies - 27.80.+w - 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.     

\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     

Alpha-gamma decay studies of <Superscript>251, 253</Superscript>No and their daughter products <Superscript>247, 249</Superscript>Fm

The isotopes ²⁵¹No and ²⁵³No were produced in nuclear reactions ²⁰⁶Pb(⁴⁸Ca,3n)²⁵¹No and ²⁰⁷Pb (⁴⁸Ca,2n)²⁵³No. Radioactive decay of these isotopes and their daughter products has been investigated by means of - and - - spectroscopy. An isomeric state ^251m No, having a half-life of s and decaying by emission of particles of keV was identified. The measured decay data allowed for the construction of partial level schemes for ²⁵¹No, ^247,249Fm and ^243,245Cf and an extrapolation of energy systematics of single particle levels of N = 145, 147 and 149 isotones with even Z towards higher atomic numbers up to Z = 102.PACS: 23.60. + e decay - 27.90. + b - 21.10.-k Properties of nuclei; nuclear energy levels     

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     

Chiral approach to nuclear matter: Role of explicit short-range <Emphasis Type="Italic">NN</Emphasis>-terms

We extend a recent chiral approach to nuclear matter by including the most general (momentum-independent) NN-contact interaction. Iterating this two-parameter contact vertex with itself and with one-pion exchange the emerging energy per particle exhausts all terms possible up to and including fourth order in the small momentum expansion. Two (isospin-dependent) cut-offs are introduced to regularize the (linear) divergences of some three-loop in-medium diagrams. The equation of state of pure neutron matter, , can be reproduced very well up to quite high neutron densities of by adjusting the strength of a repulsive nn-contact interaction. Binding and saturation of isospin-symmetric nuclear matter is a generic feature of our perturbative calculation. Fixing the maximum binding energy per particle to MeV we find that any possible equilibrium density lies below . The additional constraint from the neutron matter equation of state leads however to a somewhat too low saturation density of . We also investigate the effects of the NN-contact interaction on the complex single-particle potential U(p,k _f ) + i W(p,k _f ). We find that the effective nucleon mass at the Fermi surface is bounded from below by . This property keeps the critical temperature of the liquid-gas phase transition at somewhat too high values MeV. The downward bending of the asymmetry energy A(k _f ) above nuclear-matter saturation density is a generic feature of theapproximation to fourth order. We furthermore investigate the effects of the NN-contact interaction on the -term in the nuclear energy density functional . Altogether, there is within this complete fourth-order calculation no magic set of adjustable short-range parameters with which one could reproduce simultaneously and accurately all semi-empirical properties of nuclear matter. In particular, the conditions for a good neutron matter equation of state and for good single-particle properties are mutually exclusive.Received: 28 October 2003, Revised: 9 December 2003, Published online: 23 July 2004PACS: 12.38.Bx Perturbative calculations - 21.65. + f Nuclear matter - 24.10.Cn Many-body theory - 31.15.Ew Density-functional theory     

The N = Z nucleus 76 Sr: Gamow-Teller strength and nuclear deformation

Challenged by recent theoretical work, a study of the -EC decay of the N = Z even-even nucleus ⁷⁶ Sr has been undertaken in order to assign the parent ground-state deformation. In this study 13 levels with have been located in ⁷⁶ Rb. The beta-delayed proton emission has been observed for the first time in an N = Z even-even nucleus. The p branching ratio has been determined to be . The ⁷⁶ Sr half-life has been remeasured and a more precise value of s has been obtained. On the basis of the comparison of measured Gamow-Teller strength with calculated strength distributions for both oblate and prolate deformation, it is concluded that the ⁷⁶ Sr has strong prolate deformation in the ground state.Received: 26 June 2003, Revised: 5 November 2003, Published online: 18 June 2004PACS: 21.10.Hw Spin, parity, and isobaric spin - 23.20.Lv transitions and level energies - 23.40.Hc Relation with nuclear matrix elements and nuclear structure - 27.50. + e J. Giovinazzo: Present address: Centre d Etudes Nucléaires de Bordeaux-Gradignan, Le Haut Vigneau, F-33175 Gradignan Cedex, France.M. Ramdhane: Present address: University Mentouri, 25000 Constantine, Algeria.     

Jet production in charged current deep inelastic <Emphasis Type="Italic">e</Emphasis><Superscript> + </Superscript><Emphasis Type="Italic">p</Emphasis> scatteringat HERA

The production rates and substructure of jets have been studied in charged current deep inelastic e ⁺ p scattering for Q ² > 200 GeV² with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb^-1. Inclusive jet cross sections are presented for jets with transverse energies GeV and pseudorapidities in the range . Dijet cross sections are presented for events with a jet having GeV and a second jet having GeV. Measurements of the mean subjet multiplicity, , of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-to-leading-order QCD calculations are compared to the measurements. The value of , determined from at for jets with GeV, is . The mean subjet multiplicity as a function of Q ² is found to be consistent with that measured in NC DIS.Received: 5 June 2003, Published online: 10 October 2003     

Two-quasiparticle and collective excitations in transitional 108,110 Pd nuclei

High-spin states in ^108,110Pd isotopes are studied by -ray spectroscopy of heavy-ion-induced fission. The Pd isotopes are produced in the fission channel of the ³¹P + ¹⁷⁶Yb reaction at beam energy 152 MeV. The prompt -rays are detected with the EUROBALL4 multidetector array. The yrast states of ^108,110Pd have been observed above the region of the first backbend. The level scheme of ¹⁰⁸Pd was extended with a new negative-parity band. The yrast sequence in ¹¹⁰Pd is observed up to spin I = 14 ⁺ and negative-parity bands have also been identified. The backbending in these even-mass Pd isotopes is associated with the alignment of the neutron (h _11/2)² pair. The negative-parity states arise from two neutron configurations and and they are interpreted in the frame of two-quasiparticle + rotor model as semidecoupled bands. The observed experimental staggering in the -bands of ^108,110Pd supports the theoretical predictions for -instability of their shapes.Received: 22 April 2003, Revised: 27 June 2003, Published online: 2 December 2003PACS: 21.60.-n Nuclear structure models and methods - 23.20.Lv transitions and level energies - 25.70.Jj Fusion and fusion-fission reactions - 27.60. + j      

Absolute resonance strengths in the $^{6,7}Li(\alpha, \gamma)^{10,11}B$ reactions

The absolute strengths of the keV resonance in the reaction and of the keV resonance in the reaction have been measured to meV and meV, respectively, in good agreement with previous values. These resonances can be used to measure the absolute acceptance of the recoil separator ERNA to a precision of about 10%.Received: 12 December 2003, Revised: 10 February 2004, Published online: 3 August 2004PACS: 24.30.-v Resonance reactions - 25.40.Lw Radiative capture - 26.20. + f Hydrostatic stellar nucleosynthesis     

A new isomer in 136 Ba populated by deep inelastic collisions

Excited states in ¹³⁶Ba, populated in deep inelastic collisions by the interaction of 450 MeV ⁸²Se ions with a ¹³⁹La target, have been studied by means of in-beam -ray spectroscopy. A new isomer with has been identified at an excitation energy E_x = 3.357 MeV. The half-life was determined as ns. The extracted B(E2) value is much smaller than those in ¹³²Te and ¹³⁴Xe. This hindrance is investigated by a shell model calculation.Received: 22 September 2003, Revised: 11 November 2003, Published online: 6 April 2004PACS: 21.10.Tg Lifetimes - 23.20.Lv transitions and level energies - 27.60. + j      

The $\eta_{c}(2980)$ formation in two-photon collisions at LEP energies

production in interactions has been detected via its decays into ,K ⁺ K ^- K ⁺ K ^- and in the data taken with the DELPHI detector at LEP1 and LEP2 energies. The two-photon radiative width averaged over all observed decay channels is = 13.9 2.0 (stat.) 1.4(syst.) 2.7 (BR) keV. No direct decay channel has been observed. An upper limit < 5.5 keV at 95% confidence level has been evaluated for this decay mode.Received: 3 July 2003, Published online: 7 November 2003     

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     

Study of <Emphasis Type="Italic">N</Emphasis> = <Emphasis Type="Italic">Z</Emphasis> nuclei in variation-after-projection framework

Variation-after-projection (VAP) calculations in conjunction with the Hartree- Bogoliubov (HB) ansatz have been carried out for A = 68-88, N = Z nuclei. In this framework, the yrast spectra with , B(E2) transition probabilities and deformation parameter ( ) have been obtained. A pairing interaction for like particles as well as protons and neutrons has been included in the model for a two-body interaction.Received: 28 April 2003, Revised: 20 March 2004, Published online: 14 September 2004PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.60.-n Nuclear structure models and methods - 27.50. + e      

On kaonic hydrogen. Quantum field theoretic and relativistic covariant approach

We study kaonic hydrogen, the bound K ^- p state A _{K p} . Within a quantum field theoretic and relativistic covariant approach we derive the energy level displacement of the ground state of kaonic hydrogen in terms of the amplitude of K ^- p scattering for arbitrary relative momenta. The amplitude of low-energy K ^- p scattering near threshold is defined by the contributions of three resonances , and and a smooth elastic background. The amplitudes of inelastic channels of low-energy K ^- p scattering fit experimental data on the near-threshold behaviour of the cross-sections and the experimental data by the DEAR Collaboration. We use the soft-pion technique (leading order in Chiral Perturbation Theory) for the calculation of the partial width of the radiative decay of pionic hydrogen and the Panofsky ratio. The theoretical prediction for the Panofsky ratio agrees well with experimental data. We apply the soft-kaon technique (leading order in Chiral Perturbation Theory) to the calculation of the partial widths of radiative decays of kaonic hydrogen and . We show that the contribution of these decays to the width of the energy level of the ground state of kaonic hydrogen is less than 1 .Received: 7 October 2003, Revised: 29 November 2003, Published online: 22 June 2004PACS: 11.10.Ef Lagrangian and Hamiltonian approach - 13.75.Gx Pion-baryon interactions - 21.10.-k Properties of nuclei; nuclear energy levels - 36.10.-k Exotic atoms and molecules (containing mesons, muons, and other unusual particles)A.N. Ivanov: Permanent address: State Polytechnical University, Department of Nuclear Physics, 195251 St. Petersburg, Russian FederationN.I. Troitskaya: Permanent address: State Polytechnical University, Department of Nuclear Physics, 195251 St. Petersburg, Russian Federation.     

Nucleon deformation

The conjectured deformation of hadrons and its experimental verification offer a particularly fertile ground for understanding the intricate dynamics of their constituents and QCD at the confiment scale. The detailed study of the transition is viewed as the preferred method of experimental investigation of this central issue in hadronic physics. A brief overview of the field is presented, followed by a presentation of the most recent results from Bates program. The new Bates/OOPS data at Q ² = 0.127 GeV/c ²) yield and and they exclude a spherical nucleon and/or . The magnitude and the origin of the deformation is the focus of the ongoing and planned investigations.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 13.88. + e Polarization in interactions and scattering - 13.40.Gp Electromagnetic form factors - 14.20.Gk Baryon resonances with S = 0C.N. Papanicolas: Invited plenary talk