Thu·Jul 8, 2021Thursday·July 8, 2021

1. 01*

   Measurement of the ${}^{239}$Pu(n,f)/${}^{235}$U(n,f) Cross-Section Ratio with the NIFFTE fission Time Projection Chamber

   L. Snyder🇺🇸 · M. Anastasiou🇺🇸 · N.S. Bowden🇺🇸 · J. Bundgaard🇺🇸 · R.J. Casperson · D.A. Cebra🇺🇸 · T. Classen🇺🇸 · D.H. Dongwi🇺🇸 · N. Fotiades🇺🇸 · J. Gearhart🇺🇸 · V. Geppert-Kleinrath🇺🇸 · U. Greife🇺🇸 and 28 other authors

   The ${}^{239}$Pu(n,f)/${}^{235}$U(n,f) cross-section ratio has been measured with the fission Time Projection Chamber (fissionTPC) from 100 keV to 100 MeV. The fissionTPC provides three-dimensional reconstruction of fission-fragment ionization profiles, allowing for a precise quantification of measurement uncertainties. The measurement was performed at the Los Alamos Neutron Science Center which provides a pulsed white source of neutrons. The data are recommended to be used as a cross-section ratio shape. A discussion of the status of the absolute normalization and comparisons to ENDF evaluations and previous measurements is included.

   nucl-ex3 citations
2. 02*

   Using spin alignment of inelastically-excited fast beams to make spin assignments: the spectroscopy of 13O as a test case

   R.J. Charity🇺🇸 · T.B. Webb🇺🇸 · J.M. Elson🇺🇸 · D.E.M. Hoff🇺🇸 · C.D. Pruitt🇺🇸 · L.G. Sobotka🇺🇸 · P. Navratil🇨🇦 · G. Hupin🇫🇷 · K. Kravvaris🇺🇸 · S. Quaglioni🇺🇸 · K.W. Brown🇺🇸 · G. Cerizza🇺🇸 and 14 other authors

   Excited states in 13O were investigated using inelastic scattering of an E/A=69.5-MeV 13O beam off of a 9Be target. The excited states were identified in the invariant-mass spectra of the decay products. Both single proton and sequential two-proton decays of the excited states were examined. For a number of the excited states, the protons were emitted with strong anisotropy where emissions transverse to the beam axis are favored. The measured proton-decay angular distributions were compared to predictions from distorted-wave born-approximation (DWBA) calculations of the spin alignment which was shown to be largely independent of the excitation mechanism. The deduced ${}^{13}$O level scheme is compared to ab initio no-core shell model with continuum (NCSMC) predictions. The lowest-energy excited states decay isotropically consistent with predictions of strong proton 1s1/2 structure. Above these states in the level scheme, we observed a number of higher-spin states not predicted within the model. Possibly these are associated with rotational bands built on deformed cluster configurations predicted by antisymmetrized molecular dynamics (AMD) calculations. The spin alignment mechanism is shown to be useful for making spin assignments and may have widespread use.

   nucl-exnucl-thPRC(2021)·7 citations
3. 03*

   Joint Measurement of the ${}^{235}$U Antineutrino Spectrum by Prospect and Stereo

   H. Almazán🇩🇪 · M. Andriamirado🇺🇸 · A. B. Balantekin🇺🇸 · H. R. Band🇺🇸 · C. D. Bass🇺🇸 · D. E. Bergeron🇺🇸 · L. Bernard🇫🇷 · A. Blanchet🇫🇷 · A. Bonhomme🇩🇪 · N. S. Bowden🇺🇸 · C. D. Bryan🇺🇸 · C. Buck🇩🇪 and 73 other authors

   The PROSPECT and STEREO collaborations present a combined measurement of the pure ${}^{235}$U antineutrino spectrum, without site specific corrections or detector-dependent effects. The spectral measurements of the two highest precision experiments at research reactors are found to be compatible with ${\chi }^2/\mathrm{ndf}=24.1/21$, allowing a joint unfolding of the prompt energy measurements into antineutrino energy. This ${\bar{\nu }}_e$ energy spectrum is provided to the community, and an excess of events relative to the Huber model is found in the 5-6 MeV region. When a Gaussian bump is fitted to the excess, the data-model ${\chi }^2$ value is improved, corresponding to a $2.4\sigma$ significance.

   nucl-exhep-exPRL(2022)·37 citations
4. 04*

   Study of coherent $J/\psi$ production in lead-lead collisions at $\sqrt{s_{NN}}=5TeV$

   R. Aaij · C. Abellán Beteta · T. Ackernley · B. Adeva · M. Adinolfi · H. Afsharnia · C.A. Aidala · S. Aiola · Z. Ajaltouni · S. Akar · J. Albrecht · F. Alessio and 946 other authors

   Coherent production of $J/\psi$ mesons is studied in ultraperipheral lead-lead collisions at a nucleon-nucleon centre-of-mass energy of 5 TeV, using a data sample collected by the LHCb experiment corresponding to an integrated luminosity of about $10\mu b^{-1}$. The $J/\psi$ mesons are reconstructed in the dimuon final state and are required to have transverse momentum below 1 GeV. The cross-section within the rapidity range of $2.0<y<4.5$ is measured to be $4.45\pm 0.24\pm 0.18\pm 0.58$ mb, where the first uncertainty is statistical, the second systematic and the third originates from the luminosity determination. The cross-section is also measured in $J/\psi$ rapidity intervals. The results are compared to predictions from phenomenological models.

   ↳ hep-exnucl-exJHEP(2022)·54 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.