Mon·Feb 13, 2017Monday·February 13, 2017

1. 01*

   Precise neutron lifetime experiment using pulsed neutron beams at J-PARC

   Naoki Nagakura🇯🇵 · Katsuya Hirota🇯🇵 · Sei Ieki🇯🇵 · Takashi Ino🇯🇵 · Yoshihisa Iwashita🇯🇵 · Masaaki Kitaguchi🇯🇵 · Ryunosuke Kitahara🇯🇵 · Kenji Mishima🇯🇵 · Aya Morishita🇯🇵 · Hideyuki Oide🇮🇹 · Hidetoshi Otono🇯🇵 · Risa Sakakibara🇯🇵 and 13 other authors

   The neutron lifetime is one of the basic parameters in the weak interaction, and is used for predicting the light element abundance in the early universe. Our group developed a new setup to measure the lifetime with the goal precision of 0.1% at the polarized beam branch BL05 of MLF, J-PARC. The commissioning data was acquired in 2014 and 2015, and the first set of data to evaluate the lifetime in 2016, which is expected to yield a statistical uncertainty of O(1)%. This paper presents the current analysis results and the future plans to achieve our goal precision.

   nucl-exphysics.ins-detPoS(2017)·9 citations
2. 02*

   Low energy magnetic radiation enhancement in the f${}_{7/2}$ shell

   S. Karampagia · B. A. Brown🇺🇸 · V. Zelevinsky🇺🇸

   Studies of the $\gamma$-ray strength functions can reveal useful information concerning underlying nuclear structure. Accumulated experimental data on the strength functions show an enhancement in the low $\gamma$ energy region. We have calculated the M1 strength functions for the ${}^{49,50}$Cr and ${}^{48}$V nuclei in the $f_{7/2}$ shell-model basis. We find a low-energy enhancement for gamma decay similar to that obtained for other nuclei in previous studies, but for the first time we are also able to study the complete distribution related to M1 emission and absorption. We find that M1 strength distribution peaks at zero transition energy and falls off exponentially. The height of the peak and the slope of the exponential are approximately independent of the nuclei studied in this model space and the range of initial angular momenta. We show that the slope of the exponential fall off is proportional to the energy of the $T=1$ pairing gap.

   ↳ nucl-thnucl-exPRC(2017)·33 citations
3. 03*

   Large single transverse spin asymmetry for forward neutrons in ultraperipheral polarized proton-nucleus collisions in explanation of measurements at RHIC-PHENIX

   Gaku Mitsuka🇺🇸

   The PHENIX experiment at BNL-RHIC recently reported the single transverse spin asymmetry $A_N$ for forward neutrons measured in polarized proton-nucleus collisions at $\sqrt{s_{NN}}=200$GeV; $A_N$ in proton-aluminum and proton-gold collisions are -0.015 and 0.18, respectively, which are clearly different from $A_N=-0.08$ in proton-proton collisions. In this paper, we propose large $A_N$ for forward neutrons in ultraperipheral polarized proton-nucleus collisions as an explanation of the PHENIX measurements. The proposed model is demonstrated using two Monte Carlo simulations organized as follows. In the ultraperipheral collision simulation, we use the STARlight event generator for the simulation of the virtual photon flux and then use the MAID2007 unitary isobar model for the simulation of the neutron production in the interactions of a virtual photon with a polarized proton. In the proton-nucleus hadronic interaction simulation, the differential cross sections of forward neutron production are predicted by a simple one-pion exchange model and the Glauber model. The simulated $A_N$ values accumulating the both contribution of ultraperipheral collisions and hadronic interactions are in good agreement with the PHENIX results.

   ↳ nucl-thnucl-exPRC(2017)·16 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.