Fri·Jan 3, 2020Friday·January 3, 2020

1. 01*

   Electromagnetic character of the competitive $\gamma \gamma /\gamma$-decay from ${}^{137\mathrm{m}}$Ba

   P.-A. Söderström🇯🇵 · L. Capponi · E. Açıksöz · T. Otsuka🇯🇵 · N. Tsoneva🇩🇪 · Y. Tsunoda🇯🇵 · D. L. Balabanski🇷🇴 · N. Pietralla🇩🇪 · G. L. Guardo🇮🇹 · D. Lattuada🇮🇹 · H. Lenske🇩🇪 · C. Matei🇷🇴 and 3 other authors

   Second-order processes in physics is a research topic focusing attention from several fields worldwide including, for example, non-linear quantum electrodynamics with high-power lasers, neutrinoless double-$\beta$ decay, and stimulated atomic two-photon transitions. For the electromagnetic nuclear interaction, the observation of the competitive double-$\gamma$ decay from ${}^{137\mathrm{m}}$Ba has opened up the nuclear structure field for detailed investigation of second-order processes through the manifestation of off-diagonal nuclear polarizability. Here we confirm this observation with an $8.7\sigma$ significance, and an improved value on the double-photon versus single-photon branching ratio as $2.62\times 10^{-6}(30)$. Our results, however, contradict the conclusions from the original experiment, where the decay was interpreted to be dominated by a quadrupole-quadrupole component. Here, we find a substantial enhancement in the energy distribution consistent with a dominating octupole-dipole character and a rather small quadrupole-quadrupole element in the decay, hindered due to an evolution of the internal nuclear structure. The implied strongly hindered double-photon branching in ${}^{137\mathrm{m}}$Ba opens up the possibility of the double-photon branching as a feasible tool for nuclear-structure studies on off-diagonal polarizability in nuclei where this hindrance is not present.

   nucl-exnucl-thNature Commun.(2020)·21 citations
2. 02*

   Experimental study of the 2n-transfer reaction ${}^{138}$Ba(${}^{18}$O,${}^{16}$O)${}^{140}$Ba in the projectile energy range 61-67 MeV

   A. Khaliel (1) · T.J. Mertzimekis (1)🇬🇷 · F.C.L. Crespi (2)🇮🇹 · G. Zagoraios (1) · D. Papaioannou (1) · N. Florea (3) · A. Turturica (3)🇷🇴 · L. Stan (3)🇷🇴 · N. Marginean (3) ((1) Department of Physics, National and Kapodistrian University of Athens, Athens, Greece) ((2) Universita degli Studi di Milano and INFN sez. Milano, Milano, Italy) ((3) National Institute for Physics and Nuclear Engineering, Magurele, Romania)🇷🇴

   Two-neutron transfer reactions serve as an important tool for nuclear structure studies in the neutron rich part of the nuclear chart. In this article, we report on the first experimental attempt to populate the excited states of ${}^{140}$Ba employing the 2n-neutron transfer reaction ${}^{138}$Ba(${}^{18}$O,${}^{16}$O)${}^{140}$Ba. ${}^{140}$Ba is highly important, as it is placed on the onset of octupole correlations and the lifetimes of its excited states are completely unknown, with the sole exception of the first 2${}^{+}$ state. The experiment was carried out at the Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH) in Magurele, Romania. Lower limits on the lifetimes of ground state band up to the 8${}^{+}$ state are reported. Furthermore, relative cross sections regarding the 2n-transfer reaction with respect to the fusion and the total inelastic reaction channels have been deduced. Further investigation directions of the nuclear structure of ${}^{140}$Ba are also discussed.

   nucl-exEPL(2019)·3 citations
3. 03*

   Event-By-Event Fluctuation of Maximum Particle Density in Narrow Pseudo-Rapidity Interval at a Few AGeV/c

   Swarnapratim Bhattacharyya🇮🇳

   A detailed study of event by event fluctuation of maximum particle density of the produced particles in narrow pseudo-rapidity interval in terms of the scaled variance {\omega} has been carried out for 16O-AgBr, 28Si-AgBr and 32S-AgBr interactions at an incident momentum of 4.5 AGeV/c. For all the interactions the values of scaled variance are found to be greater than zero indicating the presence of strong event by event fluctuation of maximum particle density values in the multiparticle production process. The event by event fluctuations are found to decrease with the increase of pseudo-rapidity interval. Experimental analysis has been compared with the results obtained from the analysis of events simulated by the Ultra Relativistic Quantum Molecular Dynamics (UrQMD) model. UrQMD model could not replicate the experimental results.

   nucl-exEPL(2020)·7 citations
4. 04*

   Machine learning technique to improve anti-neutrino detection efficiency for the ISMRAN experiment

   D. Mulmule🇮🇳 · P. K. Netrakanti🇮🇳 · L. M. Pant🇮🇳 · B. K. Nayak🇮🇳

   The Indian Scintillator Matrix for Reactor Anti-Neutrino detection - ISMRAN experiment aims to detect electron anti-neutrinos (${\bar{\nu }}_e$) emitted from a reactor via inverse beta decay reaction (IBD). The setup, consisting of 1 ton segmented Gadolinium foil wrapped plastic scintillator array, is planned for remote reactor monitoring and sterile neutrino search. The detection of prompt positron and delayed neutron from IBD will provide the signature of ${\bar{\nu }}_e$ event in ISMRAN. The number of segments with energy deposit (${\mathrm{N}}_{\mathrm{bars}}$) and sum total of these deposited energies are used as discriminants for identifying prompt positron event and delayed neutron capture event. However, a simple cut based selection of above variables leads to a low ${\bar{\nu }}_e$ signal detection efficiency due to overlapping region of ${\mathrm{N}}_{\mathrm{bars}}$ and sum energy for the prompt and delayed events. Multivariate analysis (MVA) tools, employing variables suitably tuned for discrimination, can be useful in such scenarios. In this work we report the results from an application of artificial neural network -- the multilayer perceptron (MLP), particularly the Bayesian extension -- MLPBNN, to the simulated signal and background events in ISMRAN. The results from application of MLP to classify prompt positron events from delayed neutron capture events on Hydrogen, Gadolinium nuclei and also from the typical reactor $\gamma$-ray and fast neutron backgrounds is reported. An enhanced efficiency of $\sim$91$\%$ with a background rejection of $\sim$73$\%$ for prompt selection and an efficiency of $\sim$89$\%$ with a background rejection of $\sim$71$\%$ for the delayed capture event, is achieved using the MLPBNN classifier for the ISMRAN experiment.

   ↳ physics.data-annucl-exphysics.ins-detJINST(2020)·6 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.