Wed·Jun 3, 2020Wednesday·June 3, 2020

1. 01*

   Precision mass measurements of neutron-rich scandium isotopes refine the evolution of $N=32$ and $N=34$ shell closures

   E. Leistenschneider · E. Dunling · G. Bollen · B.A. Brown · J. Dilling · A. Hamaker · J.D. Holt · A. Jacobs · A.A. Kwiatkowski · T. Miyagi · W.S. Porter · D. Puentes and 8 other authors

   We report high-precision mass measurements of ${}^{50-55}$Sc isotopes performed at the LEBIT facility at NSCL and at the TITAN facility at TRIUMF. Our results provide a substantial reduction of their uncertainties and indicate significant deviations, up to 0.7 MeV, from the previously recommended mass values for ${}^{53-55}$Sc. The results of this work provide an important update to the description of emerging closed-shell phenomena at neutron numbers $N=32$ and $N=34$ above proton-magic $Z=20$. In particular, they finally enable a complete and precise characterization of the trends in ground state binding energies along the $N=32$ isotone, confirming that the empirical neutron shell gap energies peak at the doubly-magic ${}^{52}$Ca. Moreover, our data, combined with other recent measurements, does not support the existence of closed neutron shell in ${}^{55}$Sc at $N=34$. The results were compared to predictions from both \emph{ab initio} and phenomenological nuclear theories, which all had success describing $N=32$ neutron shell gap energies but were highly disparate in the description of the $N=34$ isotone.

   nucl-exPRL(2021)·41 citations
2. 02*

   Photoproduction of $\eta$ mesons off the proton for $1.2<E_{\gamma }<4.7$ GeV using CLAS at Jefferson Laboratory

   T. Hu🇺🇸 · Z. Akbar🇺🇸 · V. Crede🇺🇸 · K.P. Adhikari🇺🇸 · S. Adhikari🇺🇸 · M.J. Amaryan🇺🇸 · G. Angelini🇺🇸 · G. Asryan🇦🇲 · H. Atac🇺🇸 · C. Ayerbe Gayoso🇺🇸 · L. Barion🇮🇹 · M. Battaglieri🇺🇸 and 139 other authors

   Photoproduction cross sections are reported for the reaction $\gamma p\to p\eta$ using energy-tagged photons and the CLAS spectrometer at Jefferson Laboratory. The $\eta$ mesons are detected in their dominant charged decay mode, $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$, and results on differential cross sections are presented for incident photon energies between 1.2 and 4.7 GeV. These new $\eta$ photoproduction data are consistent with earlier CLAS results but extend the energy range beyond the nucleon resonance region into the Regge regime. The normalized angular distributions are also compared with the experimental results from several other experiments, and with predictions of $\eta$ MAID\,2018 and the latest solution of the Bonn-Gatchina coupled-channel analysis. Differential cross sections $d\sigma /dt$ are presented for incident photon energies $E_{\gamma }>2.9$ GeV ($W>2.5$ GeV), and compared with predictions which are based on Regge trajectories exchange in the $t$-channel (Regge models). The data confirm the expected dominance of $\rho$, $\omega$ vector-meson exchange in an analysis by the Joint Physics Analysis Center.

   nucl-exhep-exPRC(2020)·11 citations
3. 03*

   Mapping reactor neutrino spectra from TAO to JUNO

   Francesco Capozzi🇩🇪 · Eligio Lisi🇮🇹 · Antonio Marrone🇮🇹

   The Jiangmen Underground Neutrino Observatory (JUNO) project aims at probing, at the same time, the two main frequencies of three-flavor neutrino oscillations, as well as their interference related to the mass ordering (normal or inverted), at a distance of ~53 km from two powerful reactor complexes in China, at Yangjiang and Taishan. In the latter complex, the unoscillated spectrum from one reactor core is planned to be closely monitored by the Taishan Antineutrino Observatory (TAO), expected to have better resolution (x 1/2) and higher statistics (x 30) than JUNO. In the context of neutrino energy spectra endowed with fine-structure features from summation calculations, we analyze in detail the effects of energy resolution and nucleon recoil on observable event spectra. We show that a model spectrum in TAO can be mapped into a corresponding spectrum in JUNO through appropriate convolutions. The mapping is exact in the hypothetical case without oscillations, and holds to a very good accuracy in the real case with oscillations. We then analyze the sensitivity to mass ordering of JUNO (and its precision oscillometry capabilities) assuming a single reference spectrum, as well as bundles of variant spectra, as obtained by changing nuclear input uncertainties in summation calculations from a publicly available toolkit. We show through a chi-squared analysis that variant spectra induce little reduction of the sensitivity in JUNO, especially when TAO constraints are included. Subtle aspects of the statistical analysis of variant spectra are also discussed.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2020)·17 citations
4. 04*

   Identifying groomed jet splittings in heavy-ion collisions

   James Mulligan🇺🇸 · Mateusz Ploskon🇺🇸

   Measurements of jet substructure in heavy-ion collisions may provide key insight to the nature of jet quenching in the quark-gluon plasma. Jet grooming techniques from high-energy physics have been applied to heavy-ion collisions in order to isolate theoretically controlled jet observables and explore possible modification to the hard substructure of jets. However, the grooming algorithms used have not been tailored to the unique considerations of heavy-ion collisions, in particular to the experimental challenge of reconstructing jets in the presence of a large underlying event. We report a set of simple studies illustrating the impact of the underlying event on identifying groomed jet splittings in heavy-ion collisions, and on associated groomed jet observables. We illustrate the importance of the selection of grooming algorithm, as certain groomers are more robust to these effects, while others, including those commonly used in heavy-ion collisions, are susceptible to large background effects -- which, when uncontrolled, can mimic a jet quenching signal. These experimental considerations, along with appropriate theoretical motivation, provide input to the choice of grooming algorithms employed in heavy-ion collisions.

   ↳ hep-phnucl-exPRC(2020)·45 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.