Evaluation of gadolinium’s action on water Cherenkov detector systems with EGADS

Artículo escrito por un elevado número de autores, sólo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiera, y los autores pertenecientes a la UAMUsed for both proton decay searches and neutrino physics, large water Cherenkov (WC) detectors have been very successful tools in particle physics. They are notable for their large masses and charged particle detection capabilities. While current WC detectors reconstruct charged particle tracks over a wide energy range, they cannot efficiently detect neutrons. Gadolinium (Gd) has the largest thermal neutron capture cross section of all stable nuclei and produces an 8 MeV gamma cascade that can be detected with high efficiency. Because of the many new physics opportunities that neutron tagging with a Gd salt dissolved in water would open up, a large-scale R&D program called EGADS was established to demonstrate this technique’s feasibility. EGADS features all the components of a WC detector, chiefly a 200-ton stainless steel water tank furnished with 240 photo-detectors, DAQ, and a water system that removes all impurities from water while keeping Gd in solution. In this paper we discuss the milestones towards demonstrating the feasibility of this novel technique, and the features of EGADS in detailThis work was supported by the JSPS KAKENHI Grant Numbers JP21224004, JP26000003, JP24103004 and JP17H06365. Funding support was provided by Kavli IPMU (WPI), the University of Tokyo and the US Department of Energy. We thank the “Consorcio Laboratorio Subterraneo de Canfranc” (Spain) and the Boulby Underground Research Laboratory and in particular the staff of the BUGS facility (UK) for supporting the low-background materials screening work. Some of us have been supported by funds from the European Union H2020-MSCA-RISE-GA872549-SK2HK, the Spanish Ministry of Science and Innovation (grant PGC2018-099388-B-100), the Science and Technology Facilities Council (STFC) and GridPP, UK, and the European Union’s H2020 -MSCA-RISE-2018 JENNIFER2 grant agreement no. 82207

Diffuse supernova neutrino background search at Super-Kamiokande

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMWe have conducted a new search for the diffuse supernova neutrino background (DSNB) flux at Super-Kamiokande (SK), with a 22.5 × 2970-kton · day exposure from its fourth operational phase IV. With the new analysis we improve on the existing background reduction techniques and systematic uncertainties and take advantage of an improved neutron tagging algorithm to lower the energy threshold compared to the previous phases of SK. This allows for setting the world's most stringent upper limit on the extraterrestrial ν¯e flux, for neutrino energies below 31.3 MeV. The SK-IV results are combined with the ones from the first three phases of SK to perform a joint analysis using 22.5 × 5823 kton·days of data. This analysis has the world's best sensitivity to the DSNB ν¯e flux, comparable to the predictions from various models. For neutrino energies larger than 17.3 MeV, the new combined 90% CL upper limits on the DSNB ν¯e flux lie around 2.7 cm-2 · sec-1, strongly disfavoring the most optimistic predictions. Finally, potentialities of the gadolinium phase of SK and the future Hyper-Kamiokande experiment are discusse

Evidence for the Appearance of Atmospheric Tau Neutrinos in Super-Kamiokande

Super-Kamiokande atmospheric neutrino data were fit with an unbinned maximum likelihood method to search for the appearance of tau leptons resulting from the interactions of oscillation-generated tau neutrinos in the detector. Relative to the expectation of unity, the tau normalization is found to be 1.42 \pm 0.35 \ (stat) {\}^{+0.14}_{-0.12}\ (syst) excluding the no-tau-appearance hypothesis, for which the normalization would be zero, at the 3.8$\sigma$ level. We estimate that 180.1 \pm 44.3\ (stat) {\}^{+17.8}_{-15.2}\ (syst) tau leptons were produced in the 22.5 kton fiducial volume of the detector by tau neutrinos during the 2806 day running period. In future analyses, this large sample of selected tau events will allow the study of charged current tau neutrino interaction physics with oscillation produced tau neutrinos.Comment: 7 pages, 4 figures. This is the version as published in Physical Review Letters including the supplemental figure. A typographical error in the description of figure 3 is also correcte

Search for dinucleon decay into pions at Super-Kamiokande

A search for dinucleon decay into pions with the Super-Kamiokande detector has been performed with an exposure of 282.1 kiloton-years. Dinucleon decay is a process that violates baryon number by two units. We present the first search for dinucleon decay to pions in a large water Cherenkov detector. The modes $^{16}$O$(pp) \rightarrow$ $^{14}$C$\pi^{+}\pi^{+}$, $^{16}$O$(pn) \rightarrow$ $^{14}$N$\pi^{+}\pi^{0}$, and $^{16}$O$(nn) \rightarrow$ $^{14}$O$\pi^{0}\pi^{0}$ are investigated. No significant excess in the Super-Kamiokande data has been found, so a lower limit on the lifetime of the process per oxygen nucleus is determined. These limits are: $\tau_{pp\rightarrow\pi^{+}\pi^{+}} > 7.22 \times 10^{31}$ years, $\tau_{pn\rightarrow\pi^{+}\pi^{0}} > 1.70 \times 10^{32}$ years, and $\tau_{nn\rightarrow\pi^{0}\pi^{0}} > 4.04 \times 10^{32}$ years. The lower limits on each mode are about two orders of magnitude better than previous limits from searches for dinucleon decay in iron.Comment: 20 pages, 17 figures. Accepted for publication in Physical Review D on March 30, 201

Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn

Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néeltemperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit(Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transportproperties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15% has been found, which is much larger than that for a bare IrMn layer. Interestingly, it has been observed that anisotropic magnetoresistance is strongly influenced by the field cooling conditions, signaling the dependence of the found response on the formation of domains at the magnetic ordering temperature