Fri·Dec 15, 2017Friday·December 15, 2017

1. 01*

   Experimental signals for broken axial symmetry in excited heavy nuclei from the valley of stability

   Eckart Grosse🇩🇪 · Arnd R. Junghans🇩🇪

   An increasing number of experimental data indicates the breaking of axial symmetry in many heavy nuclei already in the valley of stability: Multiple Coulomb excitation analysed in a rotation invariant way, gamma transition rates and energies in odd nuclei, mass predictions, the splitting of Giant Resonances (GR), the collective enhancement of nuclear level densities and Maxwellian averaged neutron capture cross sections. For the interpretation of these experimental observations the axial symmetry breaking shows up in nearly all heavy nuclei as predicted by Hartree-Fock-Bogoliubov (HFB) calculations [1] ; this indicates a nuclear Jahn-Teller effect. We show that nearly no parameters remain free to be adjusted by separate fitting to level density or giant resonance data, if advance information on nuclear deformations, radii etc. are taken from such calculations with the force parameters already fixed. The data analysis and interpretation have to include the quantum mechanical requirement of zero point oscillations and the distinction between static vs. dynamic symmetry breaking has to be regarded.

   nucl-exnucl-thActa Phys.Polon.Supp.(2018)·0 citations
2. 02*

   Weak Neutral Current Studies with Positrons

   S. Riordan🇺🇸

   Weak neutral current interactions with charged leptons have offered unique opportunities to study novel aspects of hadronic structure and search for physics beyond the standard model. These studies in the medium energy community have been primarily through parity-violating processes with electron beams, but with the possibility of polarized positron beams, new and complementary observables can be considered in experiments analogous to their electron counterparts. Such studies include elastic proton, deep inelastic, and electron target scattering. Potential positron neutral current experiments along with their potential physics reach, requirements, and feasibility are presented.

   nucl-exAIP Conf.Proc.(2018)·0 citations
3. 03*

   Optimal Design of Waveform Digitisers for Both Energy Resolution and Pulse Shape Discrimination

   Jirong Cang🇨🇳 · Tao Xue🇨🇳 · Ming Zeng🇨🇳 · Zhi Zeng🇨🇳 · Hao Ma🇨🇳 · Jianping Cheng🇨🇳 · Yinong Liu🇨🇳

   Fast digitisers and digital pulse processing have been widely used for spectral application and pulse shape discrimination (PSD) owing to their advantages in terms of compactness, higher trigger rates, offline analysis, etc. Meanwhile, the noise of readout electronics is usually trivial for organic, plastic, or liquid scintillator with PSD ability because of their poor intrinsic energy resolution. However, LaBr3(Ce) has been widely used for its excellent energy resolution and has been proven to have PSD ability for alpha/gamma particles. Therefore, designing a digital acquisition system for such scintillators as LaBr3(Ce) with both optimal energy resolution and promising PSD ability is worthwhile. Several experimental research studies about the choice of digitiser properties for liquid scintillators have already been conducted in terms of the sampling rate and vertical resolution. Quantitative analysis on the influence of waveform digitisers, that is, fast amplifier (optional), sampling rates, and vertical resolution, on both applications is still lacking. The present paper provides quantitative analysis of these factors and, hence, general rules about the optimal design of digitisers for both energy resolution and PSD application according to the noise analysis of time-variant gated charge integration.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2018)·4 citations
4. 04*

   Partial-wave analysis of proton Compton scattering data below the pion-production threshold

   Nadiia Krupina🇩🇪 · Vadim Lensky🇩🇪 · Vladimir Pascalutsa🇩🇪

   Low-energy Compton scattering off the proton is used for determination of the proton polarizabilities. However, the present empirical determinations rely heavily on the theoretical description(s) of the experimental cross sections in terms of polarizabilities. The most recent determinations are based on either the fixed-$t$ dispersion relations (DR) or chiral perturbation theory in the single-baryon sector ($\chi$PT). The two approaches obtain rather different results for proton polarizabilities, most notably for ${\beta }_{M1}$ (magnetic dipole polarizability). We attempt to resolve this discrepancy by performing a partial-wave analysis of the world data on proton Compton scattering below threshold. We find a large sensitivity of the extraction to a few "outliers", leading us to conclude that the difference between DR and $\chi$PT extraction is a problem of the experimental database rather than of "model-dependence". We have specific suggestions for new experiments needed for an efficient improvement of the database. With the present database, the difference of proton scalar polarizabilities is constrainedto a rather broad interval: ${\alpha }_{E1}-{\beta }_{M1}=(6.8\dots 10.9)\times 10^{-4}$ fm${}^3$, with their sum fixed much more precisely [to $14.0(2)$] by the Baldin sum rule.

   ↳ nucl-thhep-phnucl-exPLB(2018)·21 citations
5. 05*

   Simulation Study of Energy Resolution with Changing Pixel Size for Radon Monitor Based on \textit{Topmetal-${II}^{-}$} TPC

   Mengyao Huang · Hua Pei🇨🇳 · Xiangming Sun🇨🇳 · Shuguang Zou

   In this paper, we study how pixel size influences energy resolution for a proposed pixelated detector---a high sensitivity, low cost, and real-time radon monitor based on \textit{Topmetal-${II}^{-}$} time projection chamber (TPC). Using \textit{Topmetal-${II}^{-}$} sensors assembled by 0.35 $\mu$m CMOS Integrated Circuit process, this monitor is designed to improve the spatial resolution of detecting radon alpha particles. Concerning small pixel size might has a side effect of worsening energy resolution due to lower signal to noise ratio, a Great4-based simulation is used to figure out energy resolution dependence on pixel size ranging from 60 $\mu$m to 600 $\mu$m. A non-monotonic trend in this region shows a combination effect of pixel size with threshold on pixel, and is analyzed by introducing an empirical expression. Noise on pixel contributes 50 keV Full Width at Half Maximum (FWHM) energy resolution for 400 $\mu$m pixel size at 1 $\sim$ 4 $\sigma$ threshold, which is comparable to the energy resolution caused by energy fluctuation in ionization process of TPC ($\sim$ 20 keV). The total energy resolution after combining both factors is estimated to be 54 keV for 400 $\mu$m pixel size at 1 $\sim$ 4 $\sigma$ threshold. The analysis presented in this paper is helpful to choosing suitable pixel size for future pixelated detectors.

   ↳ physics.ins-detnucl-exNucl.Sci.Tech.(2019)·3 citations
6. 06*

   TWOPEG-D: An Extension of TWOPEG for the Case of a Moving Proton Target

   Iu. Skorodumina🇺🇸 · G.V. Fedotov🇺🇸 · R.W. Gothe🇺🇸

   A new TWOPEG-D version of the event generator TWOPEG was developed. This new version simulates the quasi-free process of double-pion electroproduction off the proton that moves in the deuteron target. The underlying idea is the equivalence of the moving proton experiment performed with fixed laboratory beam energy to the proton at rest experiment conducted with effective beam energy different from the laboratory one. This effective beam energy differs event by event and is determined by the boost from the Lab system to the proton rest frame. The Fermi momentum of the target proton is generated according to the Bonn potential. The specific aspects of the deuteron target data analysis are discussed. The plots that illustrate the performance of TWOPEG-D are given. The link to the code is provided. The generator was tested in the analysis of the CLAS data on electron scattering off the deuteron target.

   ↳ physics.data-annucl-ex3 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.