Wed·Nov 24, 2021Wednesday·November 24, 2021

1. 01*

   Dark Matter Search with the Nuclear Isomer Ta-180m

   Bjoern Lehnert🇺🇸

   There is compelling cosmological and astrophysical evidence of dark matter comprising 27% of the energy budget of the Universe. However, dark matter has never been observed in direct detection experiments. The long-time favorite model of Weakly Interacting Massive Particles saw a large experimental effort with steady progress over recent decades. Since also these large-scale searches remain unsuccessful to date, it is compelling to look at more exotic dark matter models which can be constrained with new approaches and much less scientific resources. Using nuclear isomers is one of these approaches. ${}^{180m}$Ta is the rarest known isotope with the longest-lived meta-stable state whose partial half-life limits are on the order of 10${}^{14}$-10${}^{16}$ yr. We investigate how strongly interacting dark matter and inelastic dark dark matter collides with ${}^{180m}$Ta, leading to its de-excitation. The energy stored in the meta-stable state is released in the transition, which becomes the signature for thermalized dark matter in a well-shielded underground experiment. We report on a direct detection experiment searching for these dark-matter-induced decay signatures which has further constrained the open parameter space. We also propose an indirect geochemical experiment to search for decay products of ${}^{180m}$Ta in tantalum minerals accumulated over 1 billion years.

   nucl-exastro-ph.GAJ.Phys.Conf.Ser.(2021)·2 citations
2. 02*

   Constraints on partial half-lives of Ce-136 and Ce-138 double electron captures

   B. Lehnert🇺🇸 · M. Hult🇧🇪 · G. Lutter🇧🇪 · G. Marissens🇧🇪 · S. Oberstedt🇧🇪 · H. Stroh🇧🇪 · J. Kotila🇫🇮 · A. Oberstedt · K. Zuber🇩🇪

   The gamma-ray emissions from a radiopure cerium-bromide crystal with a mass of 4381 g were measured for a total of 497.4 d by means of high-resolution gamma-ray spectrometry in the HADES underground laboratory at a depth of 500 m.w.e. A search for 0/2nee and 0/2neb+ double beta decay transitions of Ce-136 and Ce-138 was performed using Bayesian analysis techniques. No signals were observed for a total of 35 investigated decay modes. 90% credibility limits were set in the order of 1e18-1e19 a. Existing constraints from a cerium oxide powder measurement were tested with a different cerium compound and half-life limits could be improved for most of the decay modes. The most likely accessible decay mode of the Ce-136 2nee transition into the 0+1 state of Ba-136 results in a new best 90% credibility limit of 5.0e18 a.

   nucl-exPRC(2022)·2 citations
3. 03*

   Dynamic neutron sources from the ${}^{207}$Pb($\gamma$,n) and ${}^{205}$Tl($\gamma$,n) reactions

   Sylvian Kahane · Yair Ben-Dov (Birenbaum) · Raymond Moreh

   Mono-energetic gamma-beams ($\Delta \sim 10$ eV) based on thermal neutron capture, in a nuclear reactor, using the V(n, $\gamma$) and Fe(n,$\gamma$) reactions, were utilized for generating fast neutron sources from lead and thallium respectively, via the ${}^{207}$Pb($\gamma$,n) and ${}^{205}$Tl($\gamma$,n) reactions. It so happened that one of the incident gamma-lines of the V source, E${}_{\gamma }$ = 7163 keV, photoexcites by chance a resonance level in ${}^{207}$Pb, which emits neutrons at an energy of 423 keV. In a similar manner, the incident $\gamma$-line at E${}_{\gamma }$ = 7646 keV of the Fe(n, $\gamma$) source photoexcites by chance a resonance level in the ${}^{205}$Tl isotope, which emits neutrons at an energy of 99 keV. The cross-sections for the neutron emission process were measured and found to be $\sigma$($\gamma$,n) = 35+/-6 mb and 107+/-17 mb respectively with intensities of the order of $10^4$ n/sec.

   nucl-exphysics.ins-det0 citations
4. 04*

   Observation of a multiplicity dependence in the $p_{\mathrm{T}}$-differential charm baryon-to-meson ratios in proton-proton collisions at $\sqrt{s}=13$ TeV

   ALICE Collaboration

   The production of prompt $D^0$, $D_{\mathrm{s}}^{+}$, and ${\Lambda }_{\mathrm{c}}^{+}$ hadrons, and their ratios, $D_{\mathrm{s}}^{+}$/$D^0$ and ${\Lambda }_{\mathrm{c}}^{+}$/$D^0$, are measured in proton-proton collisions at $\sqrt{s}$ = 13 TeV at midrapidity ($|y|<0.5$) with the ALICE detector at the LHC. The measurements are performed as a function of the charm-hadron transverse momentum ($p_{\mathrm{T}}$) in intervals of charged-particle multiplicity, measured with two multiplicity estimators covering different pseudorapidity regions. While the strange to non-strange $D_{\mathrm{s}}^{+}$/$D^0$ ratio indicates no significant multiplicity dependence, the baryon-to-meson $p_{\mathrm{T}}$-differential ${\Lambda }_{\mathrm{c}}^{+}$/$D^0$ ratio shows a multiplicity-dependent enhancement, with a significance of 5.3$\sigma$ for $1<p_{\mathrm{T}}<12$ GeV/$c$, comparing the highest multiplicity interval with respect to the lowest one. The measurements are compared with a theoretical model that explains the multiplicity dependence by a canonical treatment of quantum charges in the statistical hadronisation approach, and with predictions from event generators that implement colour reconnection mechanisms beyond the leading colour approximation to model the hadronisation process. The ${\Lambda }_{\mathrm{c}}^{+}$/$D^0$ ratios as a function of $p_{\mathrm{T}}$ present a similar shape and magnitude as the $\Lambda /K_s^0$ ratios in comparable multiplicity intervals, suggesting a potential common mechanism for light- and charm-hadron formation, with analogous multiplicity dependence. The $p_{\mathrm{T}}$-integrated ratios, extrapolated down to $p_{\mathrm{T}}$=0, do not show a significant dependence on multiplicity within the uncertainties.

   nucl-exhep-exPLB(2022)·91 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.