Wed·Dec 14, 2016Wednesday·December 14, 2016

1. 01*

   Low-energy enhancement and fluctuations of $\gamma$-ray strength functions in ${}^{56,57}$Fe: test of the Brink-Axel hypothesis

   A. C. Larsen🇳🇴 · M. Guttormsen🇳🇴 · N. Blasi🇮🇹 · A. Bracco🇮🇹 · F. Camera🇮🇹 · L. Crespo Campo🇳🇴 · T. K. Eriksen🇳🇴 · A. Görgen🇳🇴 · T. W. Hagen🇳🇴 · V. W. Ingeberg🇳🇴 · B. V. Kheswa🇳🇴 · S. Leoni🇮🇹 and 12 other authors

   Nuclear level densities and $\gamma$-ray strength functions of ${}^{56,57}$Fe have been extracted from proton-$\gamma$ coincidences. A low-energy enhancement in the $\gamma$-ray strength functions up to a factor of 30 over common theoretical E1 models is confirmed. Angular distributions of the low-energy enhancement in ${}^{57}$Fe indicate its dipole nature, in agreement with findings for ${}^{56}$Fe. The high statistics and the excellent energy resolution of the large-volume LaBr${}_3$(Ce) detectors allowed for a thorough analysis of $\gamma$ strength as function of excitation energy. Taking into account the presence of strong Porter-Thomas fluctuations, there is no indication of any significant excitation-energy dependence in the $\gamma$-ray strength function, in support of the generalized Brink-Axel hypothesis.

   nucl-exJ.Phys.G(2017)·30 citations
2. 02*

   Neutron background measurements at China Jinping underground laboratory with a Bonner Multi-sphere Spectrometer

   Qingdong Hu🇨🇳 · Hao Ma🇨🇳 · Zhi Zeng🇨🇳 · Jianping Cheng🇨🇳 · Yunhua Chen🇨🇳 · Shenming He🇨🇳 · Junli Li🇨🇳 · Manbin Shen🇨🇳 · Shiyong Wu🇨🇳 · Qian Yue🇨🇳 · Jianfeng Yue🇨🇳 · Hui Zhang🇨🇳

   The neutron background spectrum from thermal neutron to 20 MeV fast neutron was measured at the first experimental hall of China Jinping underground laboratory with a Bonner multi-sphere spectrometer. The measurement system was validated by a Cf252 source and inconformity was corrected. Due to micro charge discharge, the dataset was screened and background from the steel of the detectors was estimated by MC simulation. Based on genetic algorithm we obtained the energy distribution of the neutron and the total flux of neutron was (2.69 +/-1.02) *10^-5 cm^-2s^-1

   ↳ physics.ins-dethep-exnucl-exNucl.Instrum.Meth.A(2017)·17 citations
3. 03*

   Optically Polarized ${}^3$He

   T. R. Gentile🇺🇸 · P. J. Nacher🇫🇷 · B. Saam🇺🇸 · T. G. Walker🇺🇸

   This article reviews the physics and technology of producing large quantities of highly spin-polarized, or hyperpolarized, ${}^3$He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping, and surveys applications of polarized ${}^3$He. Several recent developments are emphasized for each method. For SEOP, the use of spectrally narrowed lasers and Rb/K mixtures has substantially increased the achievable polarization and polarizing rate. MEOP in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and has led to the observation of a light-induced relaxation mechanism. In both methods the increased capabilities have led to more extensive study and modeling of the basic underlying physics. New unexplained dependences of relaxation on temperature and magnetic field have been discovered in SEOP cells. Applications of both methods are also reviewed, including targets for charged particle and photon beams, neutron spin filters, magnetic resonance imaging, and precision measurements.

   ↳ physics.atom-phnucl-exphysics.ins-detphysics.med-phRMP(2017)·101 citations
4. 04*

   Dijet Asymmetry in the Resummation Improved Perturbative QCD Approach

   Lin Chen🇨🇳 · Guang-You Qin🇨🇳 · Shu-Yi Wei🇨🇳 · Bo-Wen Xiao🇨🇳 · Han-Zhong Zhang🇨🇳

   We develop the first systematic theoretical approach to dijet asymmetries in hadron-hadron collisions based on the perturbative QCD (pQCD) expansion and the Sudakov resummation formalism. We find that the pQCD calculation at next-to-leading order is indispensable to describe the experimental data, while the Sudakov resummation formalism is vital near the end points where the pQCD expansion fails to converge due to the appearance of large Sudakov logarithms. Utilizing our resummation improved pQCD approach, we obtain good agreement with the most up-to-date fully corrected ATLAS data on dijet asymmetry in $pp$ collisions. Combining with the BDMPS jet energy loss formalism, we extract the value of jet transport coefficient ${\hat{q}}_0\sim 2$-$6{\text{GeV}}^2/\text{fm}$ for the quark-gluon-plasma created in $PbPb$ collisions at 2.76A TeV. This work paves the way for a more complete and deeper understanding of the properties of strongly-coupled QCD medium via the studies of dijet asymmetries in relativistic heavy-ion collisions.

   ↳ hep-phnucl-exnucl-thPLB(2018)·52 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.