Photodissociation of p-process nuclei studied by bremsstrahlung induced activation

A research program has been started to study experimentally the near-threshold photodissociation of nuclides in the chain of cosmic heavy element production with bremsstrahlung from the ELBE accelerator. An important prerequisite for such studies is good knowledge of the bremsstrahlung distribution which was determined by measuring the photodissociation of the deuteron and by comparison with model calculations. First data were obtained for the astrophysically important target nucleus 92-Mo by observing the radioactive decay of the nuclides produced by bremsstrahlung irradiation at end-point energies between 11.8 MeV and 14.0 MeV. The results are compared to recent statistical model calculations.Comment: 6 pages, 8 figures, Proceedings Nuclear Physics in Astrophysics II, May 16-20, 2005, Debrecen, Hungary. The original publication is available at www.eurphysj.or

Photon strength distributions in stable even-even molybdenum isotopes

Electromagnetic dipole-strength distributions up to the particle separation energies are studied for the stable even-even nuclides $^{92,94,96,98,100}$Mo in photon scattering experiments at the superconducting electron accelerator ELBE of the Forschungszentrum Dresden-Rossendorf. The influence of inelastic transitions to low-lying excited states has been corrected by a simulation of $\gamma$ cascades using a statistical model. After corrections for branching ratios of ground-state transitions, the photon-scattering cross-sections smoothly connect to data obtained from $(\gamma,n)$-reactions. With the newly determined electromagnetic dipole response of nuclei well below the particle separation energies the parametrisation of the isovector giant-dipole resonance is done with improved precision.Comment: Proceedings Nuclear Physics in Astrophysics 3, March 2007, Dresden Journal of Physics G, IOP Publishin

Study of (n,xng) reactions on 238U

Prompt-gamma spectroscopy and time-of-flight techniques were used to measure (n,xn gamma) cross-sections on several nuclei of interest for nuclear reactors. Experiments were performed at the GELINA facility which provides a pulsed white neutron beam of maximum energy about 20 MeV. Preliminary results concerning 238U will be presented. This work was supported by PACEN/GEDEPEONand by the European Commission within the Sixth Framework Programme through I3-EFNUDAT (EURATOMcontract no. 036434) and NUDAME (Contract FP6-516487), and within the Seventh Framework Programme through EUFRAT (EURATOM contract no. FP7-211499) and through ANDES (EURATOM contract no. FP7-249671).JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Search for Doubly-Charged Higgs Boson Production at HERA

A search for the single production of doubly-charged Higgs bosons H^{\pm \pm} in ep collisions is presented. The signal is searched for via the Higgs decays into a high mass pair of same charge leptons, one of them being an electron. The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment at HERA. No evidence for doubly-charged Higgs production is observed and mass dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only decays into an electron and a muon via a coupling of electromagnetic strength h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3, masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl

Slowing down of relativistic few-electron heavy ions

Abstract Experimental data on energy loss and energy-loss straggling of fully ionized relativistic heavy ions agree well with the theory of Lindhard and Sùrensen (LS). However, when heavy ions penetrate matter with many¯uctuating ionic charge states the theoretical description is more complicate and less accurate. A novel exploratory step to contribute to a better understanding of the slowing down of heavy ions has been done with the present experiment in an energy region where the atomic interaction is still dominated by bare and few-electron projectiles. In the energy range of 100±1000 MeV/u we measured with the high-resolution magnetic spectrometer FRS the stopping powers, the energyloss straggling and the charge-state distributions of 197 Au, 208 Pb and 209 Bi projectiles in charge-state equilibrium interacting with solids ranging from beryllium to lead targets. Additionally, charge exchange cross-sections have been measured to support a better analysis and interpretation of the energy-loss data. The experimental results on stopping power and energy-loss straggling clearly demonstrate the contribution of ions in dierent charge states. A novel application of the slowing down of relativistic exotic heavy ions is presented.

Study of Charm Fragmentation into D^{*\pm} Mesons in Deep-Inelastic Scattering at HERA

The process of charm quark fragmentation is studied using $D^{*\pm}$ meson production in deep-inelastic scattering as measured by the H1 detector at HERA. Two different regions of phase space are investigated defined by the presence or absence of a jet containing the $D^{*\pm}$ meson in the event. The parameters of fragmentation functions are extracted for QCD models based on leading order matrix elements and DGLAP or CCFM evolution of partons together with string fragmentation and particle decays. Additionally, they are determined for a next-to-leading order QCD calculation in the fixed flavour number scheme using the independent fragmentation of charm quarks to $D^{*\pm}$ mesons.Comment: 33 pages, submitted to EPJ

Jet production in ep collisions at high Q(2) and determination of alpha(s)

The production of jets is studied in deep-inelastic e(+/-) p scattering at large negative four momentum transfer squared 150 LT Q(2) LT 15000 GeV2 using HERA data taken in 1999-2007, corresponding to an integrated luminosity of 395 pb(-1). Inclusive jet, 2-jet and 3-jet cross sections, normalised to the neutral current deep-inelastic scattering cross sections, are measured as functions of Q(2), jet transverse momentum and proton momentum fraction. The measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. The strong coupling as determined from these measurement

The limits of the GAINS spectrometer

The Gamma Array for Neutron Inelastic Scattering (GAINS) is currently operating at the GELINA (Geel Linear Accelerator) neutron source producing highly precise neutron inelastic scattering data. A series of recent investigations explored the limits of the experimental setup and technique. Measurements on 12C and 57Fe attempted the determination of very high and very low energy gamma production cross sections, respectively. An extended analysis was directed towards the generation of covariance matrices specifically for this experimental approach.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard