Tue·May 26, 2015Tuesday·May 26, 2015

1. 01*

   K*(892)+ production in proton-proton collisions at E_beam = 3.5 GeV

   HADES Collaboration: G. Agakishiev🇷🇺 · O. Arnold🇩🇪 · D. Belver🇪🇸 · A. Belyaev🇷🇺 · J. C. Berger-Chen🇩🇪 · A. Blanco🇵🇹 · M. Böhmer🇩🇪 · J. L. Boyard🇫🇷 · P. Cabanelas🇪🇸 · S. Chernenko🇷🇺 · A. Dybczak🇵🇱 · E. Epple🇩🇪 and 86 other authors

   We present results on the K*(892)+ production in proton-proton collisions at a beam energy of E = 3.5 GeV, which is hitherto the lowest energy at which this mesonic resonance has been observed in nucleon-nucleon reactions. The data are interpreted within a two-channel model that includes the 3-body production of K*(892)+ associated with the Lambda- or Sigma-hyperon. The relative contributions of both channels are estimated. Besides the total cross section sigma(p+p -> K*(892)+ + X) = 9.5 +- 0.9 +1.1 -0.9 +- 0.7 mub, that adds a new data point to the excitation function of the K*(892)+ production in the region of low excess energy, transverse momenta and angular spectra are extracted and compared with the predictions of the two-channel model. The spin characteristics of K*(892)+ are discussed as well in terms of the spin-alignment.

   nucl-exPRC(2015)·11 citations
2. 02*

   Simultaneous pi/2 rotation of two spin species of different gyromagnetic ratios

   Ping-Han Chu🇺🇸 · Jen-Chieh Peng🇺🇸

   We examine the characteristics of the pi/2 pulse for simultaneously rotating two spin species of different gyromagnetic ratios with the same sign. For a pi/2 pulse using a rotating magnetic field, we derive the equation relating the frequency and strength of the pulse to the gyromagnetic ratios of the two particles and the strength of the constant holding field. For a pi/2 pulse using a linear oscillatory magnetic field, we obtain the solutions numerically, and compare them with the solutions for the rotating pi/2 pulse. Application of this analysis to the specific case of rotating neutrons and 3He atoms simultaneously with a pi/2 pulse, proposed for a neutron electric dipole moment experiment, is also presented.

   nucl-exphysics.atom-phNucl.Instrum.Meth.A(2015)·4 citations
3. 03*

   Recent ALICE results on hadronic resonance production

   Angela Badalà (for the ALICE Collaboration)🇮🇹

   Hadronic resonances are a valuable tool to study the properties of the medium formed in heavy-ion collisions. In particular, they can provide information on particle-formation mechanisms and on the properties of the medium at chemical freeze-out. Furthermore they contribute to the systematic study of parton energy loss and quark recombination. Measurements of resonances in pp and in p-Pb collisions provide a necessary baseline for heavy-ion data and help to disentangle initial-state effects from medium-induced effects. In this paper the latest ALICE results on mid-rapidity K*(892)^0 and {\phi}(1020) production in pp, p-Pb and Pb-Pb collisions at LHC energies are presented

   ↳ hep-exnucl-exEPJ Web Conf.(2015)·1 citation
4. 04*

   Cherenkov and Fano effects at the origin of asymmetric vector mesons in nuclear media

   I.M. Dremin🇷🇺

   It is argued that the experimentally observed phenomenon of asymmetric vector mesons produced in nuclear media during high energy nucleus-nucleus collisions can be explained as Cherenkov and Fano effects. The mass distributions of lepton pairs created at meson decays decline from the traditional Breit-Wigner shape in the low-mass wing of the resonance. That is explained by the positive real part of the amplitude in this wing for classic Cherenkov treatment and further detalized in quantum mechanics as the interference of direct and continuum states in Fano effect. The corresponding parameters are found from the comparison with rho-meson data and admit reasonable explanation.

   ↳ hep-phhep-exnucl-exnucl-th0 citations
5. 05*

   Test of a prototype neutron spectrometer based on diamond detectors in a fast reactor

   M. Osipenko🇮🇹 · F. Pompili · M. Ripani🇮🇹 · M. Pillon · G. Ricco🇮🇹 · B. Caiffi🇮🇹 · R. Cardarelli🇮🇹 · G. Verona-Rinati · S. Argiro🇮🇹

   A prototype of neutron spectrometer based on diamond detectors has been developed. This prototype consists of a ${}^6$Li neutron converter sandwiched between two CVD diamond crystals. The radiation hardness of the diamond crystals makes it suitable for applications in low power research reactors, while a low sensitivity to gamma rays and low leakage current of the detector permit to reach good energy resolution. A fast coincidence between two crystals is used to reject background. The detector was read out using two different electronic chains connected to it by a few meters of cable. The first chain was based on conventional charge-sensitive amplifiers, the other used a custom fast charge amplifier developed for this purpose. The prototype has been tested at various neutron sources and showed its practicability. In particular, the detector was calibrated in a TRIGA thermal reactor (LENA laboratory, University of Pavia) with neutron fluxes of $10^8$ n/cm${}^2$s and at the 3 MeV D-D monochromatic neutron source named FNG (ENEA, Rome) with neutron fluxes of $10^6$ n/cm${}^2$s. The neutron spectrum measurement was performed at the TAPIRO fast research reactor (ENEA, Casaccia) with fluxes of 10${}^9$ n/cm${}^2$s. The obtained spectra were compared to Monte Carlo simulations, modeling detector response with MCNP and Geant4.

   ↳ physics.ins-detnucl-ex5 citations
6. 06*

   Proton recoil telescope based on diamond detectors for measurement of fusion neutrons

   B. Caiffi🇮🇹 · M. Osipenko🇮🇹 · M. Ripani🇮🇹 · M. Pillon · M. Taiuti🇮🇹

   Diamonds are very promising candidates for the neutron diagnostics in harsh environments such as fusion reactor. In the first place this is because of their radiation hardness, exceeding that of Silicon by an order of magnitude. Also, in comparison to the standard on-line neutron diagnostics (fission chambers, silicon based detectors, scintillators), diamonds are less sensitive to $\gamma$ rays, which represent a huge background in fusion devices. Finally, their low leakage current at high temperature suppresses the detector intrinsic noise. In this talk a CVD diamond based detector has been proposed for the measurement of the 14 MeV neutrons from D-T fusion reaction. The detector was arranged in a proton recoil telescope configuration, featuring a plastic converter in front of the sensitive volume in order to induce the (n,p) reaction. The segmentation of the sensitive volume, achieved by using two crystals, allowed to perform measurements in coincidence, which suppressed the neutron elastic scattering background. A preliminary prototype was assembled and tested at FNG (Frascati Neutron Generator, ENEA), showing promising results regarding efficiency and energy resolution.

   ↳ physics.ins-detnucl-exIEEE Trans.Nucl.Sci.(2016)·5 citations
7. 07*

   The full weak charge density distribution of 48Ca from parity violating electron scattering

   Z. Lin🇺🇸 · C. J. Horowitz🇺🇸

   Background: The ground state neutron density of a medium mass nucleus contains fundamental nuclear structure information and is at present relatively poorly known. Purpose: We explore if parity violating elastic electron scattering can provide a feasible and model independent way to determine not just the neutron radius but the full radial shape of the neutron density ${\rho }_n(r)$ and the weak charge density ${\rho }_W(r)$ of a nucleus. Methods: We expand the weak charge density of ${}^{48}$Ca in a model independent Fourier Bessel series and calculate the statistical errors in the individual coefficients that might be obtainable in a model parity violating electron scattering experiment. Results: We find that it is feasible to determine roughly six Fourier Bessel coefficients of the weak charge density of 48Ca within a reasonable amount of beam time. However, it would likely be much harder to determine the full weak density of a significantly heavier nucleus such as 208Pb. Conclusions: Parity violating elastic electron scattering can determine the full weak charge density of a medium mass nucleus in a model independent way. This weak density contains fundamental information on the size, surface thickness, shell oscillations, and saturation density of the neutron distribution in a nucleus. The measured ${\rho }_W(r)$, combined with the previously known charge density ${\rho }_{ch}(r)$, will literally provide a detailed textbook picture of where the neutrons and protons are located in an atomic nucleus.

   ↳ nucl-thnucl-exPRC(2015)·12 citations
8. 08*

   Neutral pion photoproduction on the nucleon in a chiral quark model

   Li-Ye Xiao🇨🇳 · Xu Cao🇨🇳 · Xian-Hui Zhong🇨🇳

   A chiral quark-model approach is adopted to study the $\gamma p\to {\pi }^{0}p$ and $\gamma n\to {\pi }^{0}n$ reactions. Good descriptions of the total and differential cross sections and single-polarization observables are obtained from the pion production threshold up to the second resonance region. It is found that (i) the $n=0$ shell resonance $\Delta (1232)P_{33}$, the $n=1$ shell resonances $N(1535)S_{11}$ and $N(1520)D_{13}$, and the $n=2$ shell resonance $N(1720)P_{13}$ play crucial roles in these two processes. They are responsible for the first, second and third bump structures in the cross sections, respectively. (ii) Furthermore, obvious evidences of $N(1650)S_{11}$ and $\Delta (1620)S_{31}$ are also found in the reactions. They notably affect the cross sections and the polarization observables from the second resonance region to the third resonance region. (iii) The $u$-channel background plays a crucial role in the reactions. It has strong interferences with the $s$-channel resonances. (iv) The $t$-channel background seems to be needed in the reactions. Including the $t$-channel vector-meson exchange contribution, the descriptions in the energy region $E_{\gamma }=600\sim 900$ MeV are improved significantly. The helicity amplitudes of the main resonances, $\Delta (1232)P_{33}$, $N(1535)S_{11}$, $N(1520)D_{13}$, $N(1720)P_{13}$, $N(1650)S_{11}$ and $\Delta (1620)S_{31}$, are extracted and compared with the results from other groups.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2015)·19 citations
9. 09*

   Neutron spectrometer for fast nuclear reactors

   M. Osipenko🇮🇹 · M. Ripani🇮🇹 · G. Ricco🇮🇹 · B. Caiffi🇮🇹 · F. Pompili · M. Pillon · M. Angelone🇮🇹 · G. Verona-Rinati · R. Cardarelli🇮🇹 · G. Mila🇮🇹 · S. Argiro🇮🇹

   In this paper we describe the development and first tests of a neutron spectrometer designed for high flux environments, such as the ones found in fast nuclear reactors. The spectrometer is based on the conversion of neutrons impinging on ${}^6$Li into $\alpha$ and $t$ whose total energy comprises the initial neutron energy and the reaction $Q$-value. The ${}^6$LiF layer is sandwiched between two CVD diamond detectors, which measure the two reaction products in coincidence. The spectrometer was calibrated at two neutron energies in well known thermal and 3 MeV neutron fluxes. The measured neutron detection efficiency varies from 4.2$\times 10^{-4}$ to 3.5$\times 10^{-8}$ for thermal and 3 MeV neutrons, respectively. These values are in agreement with Geant4 simulations and close to simple estimates based on the knowledge of the ${}^6$Li(n,$\alpha$)$t$ cross section. The energy resolution of the spectrometer was found to be better than 100 keV when using 5 m cables between the detector and the preamplifiers.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2015)·8 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.