Wed·Jul 23, 2014Wednesday·July 23, 2014

1. 01*

   Investigation of rare nuclear decays with BaF${}_2$ crystal scintillator contaminated by radium

   P. Belli (1)🇮🇹 · R. Bernabei (1,2)🇮🇹 · F. Cappella (3,4)🇮🇹 · V. Caracciolo (5)🇮🇹 · R. Cerulli (5)🇮🇹 · F. A. Danevich (6)🇺🇦 · A. Di Marco (2)🇮🇹 · A. Incicchitti (3)🇮🇹 · D. V. Poda (6)🇺🇦 · O. G. Polischuk (3,6)🇺🇦 · V. I. Tretyak (3,6) ((1) INFN Roma Tor Vergata, (2) Univ. Tor Vergata, (3) INFN Roma, (4) Univ. Roma, (5) INFN LNGS, (6) INR Kiev)🇺🇦

   The radioactive contamination of a BaF${}_2$ scintillation crystal with mass of 1.714 kg was measured over 101 hours in the low-background DAMA/R&D set-up deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (LNGS, Italy). The half-life of ${}^{212}$Po (present in the crystal scintillator due to contamination by radium) was measured as $T_{1/2}{(}^{212}$Po) = 298.8$\pm$0.8(stat.)$\pm$1.4(syst.) ns by analysis of the events' pulse profiles. The ${}^{222}$Rn nuclide is known as 100% decaying via emission of $\alpha$ particle with $T_{1/2}$ = 3.82 d; however, its $\beta$ decay is also energetically allowed with $Q_{\beta }=24\pm 21$ keV. Search for decay chains of events with specific pulse shapes characteristic for $\alpha$ or for $\beta /\gamma$ signals and with known energies and time differences allowed us to set, for the first time, the limit on the branching ratio of ${}^{222}$Rn relatively to $\beta$ decay as $B_{\beta }<0.13$% at 90% C.L. (equivalent to limit on partial half-life $T_{1/2}^{\beta }>8.0$ y). Half-life limits of ${}^{212}$Pb, ${}^{222}$Rn and ${}^{226}$Ra relatively to $2\beta$ decays are also improved in comparison with the earlier results.

   nucl-exphysics.ins-detEPJA(2014)·21 citations
2. 02*

   Liquid Crystal Polarimetry for Metastability Exchange Optical Pumping of 3He

   James D. Maxwell🇺🇸 · Charles S. Epstein · Richard G. Milner🇺🇸

   We detail the design and operation of a compact, discharge light polarimeter for metastability exchange optical pumping of 3He gas near 1 torr under a low magnetic field. The nuclear polarization of 3He can be discerned from its electron polarization, measured via the circular polarization of 668 nm discharge light from an RF excitation. This apparatus measures the circular polarization of this very dim discharge light using a nematic liquid crystal wave retarder (LCR) and a high-gain, transimpedance amplified Si photodiode. We outline corrections required in such a measurement, and discuss contributions to its systematic error.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2014)·11 citations
3. 03*

   Test and characterization of a prototype silicon-tungsten electromagnetic calorimeter

   Sanjib Muhuri🇮🇳 · Sourav Mukhopadhyay🇮🇳 · Vinay B. Chandratre🇮🇳 · Menka Sukhwani🇮🇳 · Satyajit Jena🇮🇳 · Shuaib Ahmad Khan🇮🇳 · Tapan K. Nayak🇮🇳 · Jogender Saini🇮🇳 · Rama Narayana Singaraju🇮🇳

   New generation high-energy physics experiments demand high precision tracking and accurate measurements of a large number of particles produced in the collisions of lementary particles and heavy-ions. Silicon-tungsten (Si-W) calorimeters provide the most viable technological option to meet the requirements of particle detection in high multiplicity environments. We report a novel Si-W calorimeter design, which is optimized for $\gamma /{\pi }^0$ discrimination up to high momenta. In order to test the feasibility of the calorimeter, a prototype mini-tower was constructed using silicon pad detector arrays and tungsten layers. The performance of the mini-tower was tested using pion and electron beams at the CERN Proton Synchrotron (PS). The experimental results are compared with the results from a detailed GEANT-4 simulation. A linear relationship between the observed energy deposition and simulated response of the mini-tower has been obtained, in line with our expectations.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2014)·21 citations
4. 04*

   Long-range angular correlations at the LHC with ALICE

   Leonardo Milano (for the ALICE Collaboration)🇨🇭

   The observation of long-range correlations on the near and away side -the double ridge- in high-multiplicity p-Pb collisions at sqrt(s_NN) = 5.02 TeV and its similarity to Pb-Pb collisions remains one of the open questions from the p-Pb run at the Large Hadron Collider (LHC). It has been attributed to mechanisms that involve initial-state effects, such as gluon saturation and colour connections forming along the longitudinal direction, and final-state effects, such as parton-induced interactions and collective effects developing in a high-density system possibly formed in these collisions. In order to understand the nature of this double- ridge structure the two-particle correlation analysis has been extended to identified particles. The observed mass dependence in p-Pb resembles the pattern observed in Pb-Pb collisions and is compatible with expectations from hydrodynamics. The subtraction of the long-range structures allows the study of the hadron production belonging to the fragmentation of jets originating from low momentum-transfer scatterings (minijets).

   ↳ hep-exnucl-exNPA(2014)·14 citations
5. 05*

   Probing the Short Range Spin Dependent Interactions by Polarized ${}^{3}He$ Atom Beams

   H.Yan

   Experiments using polarized ${}^{3}He$ atom beams to search for short range spin dependent forces are proposed. High intensity, high polarization, small beam size ${}^{3}He$ atom beams have been successfully produced and used in surface science researches. By incorporating background reduction designs as combination shielding by $\mu$-metal and superconductor and double beam pathes, the precision of spin rotation angle per unit length could be improved by a factor of $\sim 10^4$. By this precision, in combination with using a high density and low magnetic susceptibility sample source mass,and reversing one beam path if necessary, sensitivities on three different types of spin dependent interactions could be possibly improved by as much as $\sim 10^2$ to $\sim 10^8$ over the current experiments at the millimeter range.

   ↳ physics.ins-detnucl-exphysics.atom-phEPJC(2014)·9 citations
6. 06*

   Systematic study of breakup effects on complete fusion at energies above the Coulomb barrier

   Bing Wang🇨🇳 · Wei-Juan Zhao🇨🇳 · P. R. S. Gomes🇧🇷 · En-Guang Zhao🇨🇳 · Shan-Gui Zhou🇨🇳

   A large number of complete fusion excitation functions of reactions including the breakup channel were measured in recent decades, especially in the last few years. It allows us to investigate the systematic behavior of the breakup effects on the complete fusion cross sections. To this end, we perform a systematic study of the breakup effects on the complete fusion cross sections at energies above the Coulomb barrier. The reduced fusion functions F(x) are compared with the universal fusion functions which are used as a uniform standard reference. The complete fusion cross sections at energies above the Coulomb barrier are suppressed by the breakup of projectiles. This suppression effect for reactions induced by the same projectile is independent of the target and mainly determined by the lowest energy breakup channel of the projectile. There holds a good exponential relation between the suppression factor and the energy corresponding to the lowest breakup threshold.

   ↳ nucl-thnucl-exPRC(2014)·78 citations
7. 07*

   Energy-Dependence of Nucleus-Nucleus Potential and Friction Parameter in Fusion Reactions

   Kai Wen🇯🇵 · Fumihiko Sakata · Zhu-Xia Li🇨🇳 · Xi-Zhen Wu🇨🇳 · Ying-Xun Zhang🇨🇳 · Shan-Gui Zhou🇨🇳

   Applying a macroscopic reduction procedure on the improved quantum molecular dynamics (ImQMD) model, the energy dependences of the nucleus-nucleus potential, the friction parameter, and the random force characterizing a one-dimensional Langevin-type description of the heavy-ion fusion process are investigated. Systematic calculations with the ImQMD model show that the fluctuation-dissipation relation found in the symmetric head-on fusion reactions at energies just above the Coulomb barrier fades out when the incident energy increases. It turns out that this dynamical change with increasing incident energy is caused by a specific behavior of the friction parameter which directly depends on the microscopic dynamical process, i.e., on how the collective energy of the relative motion is transferred into the intrinsic excitation energy. It is shown microscopically that the energy dissipation in the fusion process is governed by two mechanisms: One is caused by the nucleon exchanges between two fusing nuclei, and the other is due to a rearrangement of nucleons in the intrinsic system. The former mechanism monotonically increases the dissipative energy and shows a weak dependence on the incident energy, while the latter depends on both the relative distance between two fusing nuclei and the incident energy. It is shown that the latter mechanism is responsible for the energy dependence of the fusion potential and explains the fading out of the fluctuation-dissipation relation.

   ↳ nucl-thnucl-exPRC(2014)·16 citations
8. 08*

   Dispersive evaluation of the D-term form factor in deeply virtual Compton scattering

   B. Pasquini (Pavia U. and INFN, Pavia)🇮🇹 · M.V. Polyakov (Ruhr U., Bochum)🇩🇪 · M. Vanderhaeghen (Mainz U., Inst. Kernphys. and U. Mainz, PRISMA)🇩🇪

   We present a dispersive representation of the D-term form factor for hard exclusive reactions, using unsubtracted $t$-channel dispersion relations. The $t$-channel unitarity relation is saturated with the contribution of two-pion intermediate states, using the two-pion distributions amplitude for the ${\gamma }^{\ast }\gamma \to \pi \pi$ subprocess and reconstructing the $\pi \pi \to N\bar{N}$ subprocess from available information on pion-nucleon partial-wave helicity amplitudes. Results for the D-term form factor as function of $t$ as well as at $t=0$ are discussed in comparison with available model predictions and phenomenological parametrizations.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2014)·96 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.