Mon·Sep 25, 2017Monday·September 25, 2017

1. 01*

   Reorientation-effect measurement of the first 2${}^{+}$ state in ${}^{12}$C: confirmation of oblate deformation

   M. Kumar Raju · J. N. Orce · P. Navratil · G. C. Ball · T. E. Drake · S. Triambak · G. Hackman · C. J. Pearson · the TIGRESS/UWC Collaboration

   A Coulomb-excitation reorientation-effect measurement using the TIGRESS $\gamma -$ray spectrometer at the TRIUMF/ISAC II facility has permitted the first determination of the $⟨2_1^{+}\mid \mid \widehat{E2}\mid \mid 2_1^{+}⟩$ diagonal matrix element in ${}^{12}$C from particle$-\gamma$ coincidence data. Required state-of-the-art no-core shell model calculations of the nuclear polarizability for the ground and first-excited (2${}_1^{+}$) states in ${}^{12}$C using chiral NN N${}^4$LO500 and NN+3NF350 interactions have been performed. Consistent predictions show a larger polarizability than previously anticipated. The polarizability of the 2${}_1^{+}$ state is introduced into the current and previous Coulomb-excitation reorientation-effect analysis of ${}^{12}$C. Spectroscopic quadrupole moments of $Q_{{}_S}(2_1^{+})=+0.053(44)$ eb and $Q_{{}_S}(2_1^{+})=+0.08(3)$ eb are determined, respectively, yielding a weighted average of $Q_{{}_S}(2_1^{+})=+0.071(25)$ eb, in agreement with recent ab initio calculations. The present measurement confirms that the 2${}_1^{+}$ state of ${}^{12}$C is oblate and emphasizes the important role played by the nuclear polarizability in Coulomb-excitation studies of light nuclei.

   nucl-exnucl-thPLB(2018)·25 citations
2. 02*

   High precision analytical description of the allowed $\beta$ spectrum shape

   Leendert Hayen🇧🇪 · Nathal Severijns🇧🇪 · Kazimierz Bodek🇵🇱 · Xavier Mougeot🇫🇷 · Dagmara Rozpedzik🇵🇱

   A fully analytical description of the allowed $\beta$ spectrum shape is given in view of ongoing and planned measurements. Its study forms an invaluable tool in the search for physics beyond the standard electroweak model and the weak magnetism recoil term. Contributions stemming from finite size corrections, mass effects, and radiative corrections are reviewed. A particular focus is placed on atomic and chemical effects, where the existing description is extended and analytically provided. The effects of QCD-induced recoil terms are discussed, and cross-checks were performed for different theoretical formalisms. Special attention was given to a comparison of the treatment of nuclear structure effects in different formalisms. Corrections were derived for both Fermi and Gamow-Teller transitions, and methods of analytical evaluation thoroughly discussed. In its integrated form, calculated $f$ values were in agreement with the most precise numerical results within the aimed for precision. We stress the need for an accurate evaluation of weak magnetism contributions, and note the possible significance of the oft-neglected induced pseudoscalar interaction. Together with improved atomic corrections, we then present an analytical description of the allowed $\beta$ spectrum shape accurate to a few parts in $10^{-4}$ down to 1\,keV for low to medium $Z$ nuclei, thereby extending the work by previous authors by nearly an order of magnitude.

   ↳ nucl-thnucl-exRMP(2018)·132 citations
3. 03*

   ${}^{100}$Mo-enriched Li${}_2$MoO${}_4$ scintillating bolometers for $0\nu 2\beta$ decay search: from LUMINEU to CUPID-0/Mo projects

   D.V. Poda (for LUMINEU, EDELWEISS, and CUPID-0/Mo Collaborations)🇺🇦

   A scintillating bolometer technology based on ${}^{100}$Mo-enriched lithium molybdate (Li${}_2$${}^{100}$MoO${}_4$) crystals has been developed by LUMINEU to search for neutrinoless double-beta ($0\nu 2\beta$) decay of ${}^{100}$Mo. The results of several low temperature tests at underground environments have proved the reproducibility of high detector performance and crystal radiopurity: in particular $\sim$5--6~keV FWHM energy resolution and at least 9$\sigma$ rejection of $\alpha$'s in the vicinity of the $0\nu 2\beta$ decay of ${}^{100}$Mo (3034 keV) and below 10~$\mu$Bq/kg bulk activity of ${}^{228}$Th and ${}^{226}$Ra. A modest acquired exposure (0.1~kg$\times$yr) is a limiting factor of the LUMINEU experiment sensitivity to the $0\nu 2\beta$ decay half-life of ${}^{100}$Mo ($T_{1/2}$ $\ge$ 0.7$\times$10${}^{23}$ yr at 90\% C.L.), however the two-neutrino $2\beta$ decay has been measured with the best up to-date accuracy, $T_{1/2}$ = $\left[6.92\pm 0.06(stat.)\pm 0.36(syst.)\right]\times 10^{18}$ yr. The applicability of the LUMINEU technology for a tonne-scale $0\nu 2\beta$ decay bolometric project CUPID is going to be demonstrated by the CUPID-0/Mo experiment with $\sim$5~kg of ${}^{100}$Mo embedded in forty 0.2~kg Li${}_2$${}^{100}$MoO${}_4$ scintillating bolometers. A first phase of the experiment with twenty Li${}_2$${}^{100}$MoO${}_4$ detectors is in preparation at the Modane underground laboratory (France) to start by the end of 2017.

   ↳ physics.ins-detnucl-exAIP Conf.Proc.(2017)·42 citations
4. 04*

   Machine and deep learning techniques in heavy-ion collisions with ALICE

   Rüdiger Haake (for the ALICE Collaboration)🇨🇭

   Over the last years, machine learning tools have been successfully applied to a wealth of problems in high-energy physics. A typical example is the classification of physics objects. Supervised machine learning methods allow for significant improvements in classification problems by taking into account observable correlations and by learning the optimal selection from examples, e.g. from Monte Carlo simulations. Even more promising is the usage of deep learning techniques. Methods like deep convolutional networks might be able to catch features from low-level parameters that are not exploited by default cut-based methods. These ideas could be particularly beneficial for measurements in heavy-ion collisions, because of the very large multiplicities. Indeed, machine learning methods potentially perform much better in systems with a large number of degrees of freedom compared to cut-based methods. Moreover, many key heavy-ion observables are most interesting at low transverse momentum where the underlying event is dominant and the signal-to-noise ratio is quite low. In this work, recent developments of machine- and deep learning applications in heavy-ion collisions with ALICE will be presented, with focus on a deep learning-based b-jet tagging approach and the measurement of low-mass dielectrons. While the b-jet tagger is based on a mixture of shallow fully-connected and deep convolutional networks, the low-mass dielectron measurement uses gradient boosting and shallow neural networks. Both methods are very promising compared to default cut-based methods.

   ↳ physics.data-annucl-exPoS(2017)·9 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.