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1. Sensitivity to neutrinos from the solar CNO cycle in Borexino

   https://doi.org/10.1140/epjc/s10052-020-08534-2  

   Agostini, M.; Altenmüller, K.; Appel, S.; Atroshchenko, V.; Bagdasarian, Z.; Basilico, D.; Bellini, G.; Benziger, J.; Biondi, R.; Bravo, D.; et al (November 2020, The European Physical Journal C)

   null (Ed.)

   Abstract Neutrinos emitted in the carbon, nitrogen, oxygen (CNO) fusion cycle in the Sun are a sub-dominant, yet crucial component of solar neutrinos whose flux has not been measured yet. The Borexino experiment at the Laboratori Nazionali del Gran Sasso (Italy) has a unique opportunity to detect them directly thanks to the detector’s radiopurity and the precise understanding of the detector backgrounds. We discuss the sensitivity of Borexino to CNO neutrinos, which is based on the strategies we adopted to constrain the rates of the two most relevant background sources, $$pep$$ pep neutrinos from the solar pp -chain and $$^{210}$$ 210 Bi beta decays originating in the intrinsic contamination of the liquid scintillator with $$^{210}$$ 210 Pb. Assuming the CNO flux predicted by the high-metallicity Standard Solar Model and an exposure of 1000 days $$\times $$ × 71.3 t, Borexino has a median sensitivity to CNO neutrino higher than 3 $$\sigma $$ σ . With the same hypothesis the expected experimental uncertainty on the CNO neutrino flux is 23%, provided the uncertainty on the independent estimate of the $$^{210}\text {Bi}$$ 210 Bi  interaction rate is 1.5 $$\hbox {cpd}/100~\hbox {ton}$$ cpd / 100 ton  . Finally, we evaluated the expected uncertainty of the C and N abundances and the expected discrimination significance between the high and low metallicity Standard Solar Models (HZ and LZ) with future more precise measurement of the CNO solar neutrino flux. 

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2. Search for low-energy signals from fast radio bursts with the Borexino detector

   https://doi.org/10.1140/epjc/s10052-022-10197-0  

   Appel, S.; Bagdasarian, Z.; Basilico, D.; Bellini, G.; Benziger, J.; Biondi, R.; Caccianiga, B.; Calaprice, F.; Caminata, A.; Chepurnov, A.; et al (March 2022, The European Physical Journal C)

   Abstract The search for neutrino events in correlation with 42 most intense fast radio bursts (FRBs) has been performed using the Borexino dataset from 05/2007 to 06/2021. We have searched for signals with visible energies above 250 keV within a time window of $$\pm \, 1000$$ ± 1000  s corresponding to detection time of a particular FRB. We also applied an alternative approach based on searching for specific shapes of neutrino-electron scattering spectra in the full exposure data of the Borexino detector. In particular, two incoming neutrino spectra were considered: the monoenergetic line and the spectrum expected from supernovae. The same spectra were considered for electron antineutrinos detected through inverse beta-decay reaction. No statistically significant excess over the background was observed. As a result, the strongest upper limits on FRB-associated neutrino fluences of all flavors have been obtained in the 0.5–50 MeV neutrino energy range. 

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3. Configuration and performance of the ATLAS b-jet triggers in Run 2

   https://doi.org/10.1140/epjc/s10052-021-09775-5  

   Aad, G.; Abbott, B.; Abbott, D. C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D. K.; Abidi, S. H.; AbouZeid, O. S.; Abraham, N. L.; Abramowicz, H.; et al (December 2021, The European Physical Journal C)

   Abstract Several improvements to the ATLAS triggers used to identify jets containing b -hadrons ( b -jets) were implemented for data-taking during Run 2 of the Large Hadron Collider from 2016 to 2018. These changes include reconfiguring the b -jet trigger software to improve primary-vertex finding and allow more stable running in conditions with high pile-up, and the implementation of the functionality needed to run sophisticated taggers used by the offline reconstruction in an online environment. These improvements yielded an order of magnitude better light-flavour jet rejection for the same b -jet identification efficiency compared to the performance in Run 1 (2011–2012). The efficiency to identify b -jets in the trigger, and the conditional efficiency for b -jets that satisfy offline b -tagging requirements to pass the trigger are also measured. Correction factors are derived to calibrate the b -tagging efficiency in simulation to match that observed in data. The associated systematic uncertainties are substantially smaller than in previous measurements. In addition, b -jet triggers were operated for the first time during heavy-ion data-taking, using dedicated triggers that were developed to identify semileptonic b -hadron decays by selecting events with geometrically overlapping muons and jets. 

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4. Neutron-Antineutron Oscillation Search using a 0.37 Megaton·Year Exposure of Super-Kamiokande

   Super-Kamiokande, Collaboration (January 2021, Physical review)

   We performed a n − ¯n oscillation search with SK-I-IV data using a multivariate analysis. Compared to previous results [15], the updated final state interaction model predicts fewer pions and less separation between signal and neutrino backgrounds. With the advanced MVA method and the inclusion of multiple new variables, the sensitivity of this analysis is still greatly enhanced. For the 0.37 megaton-year exposure at SK, we observed 11 events with an expected background of 9.3  2.7 events. There is no statistically significant excess of data events, so a lower limit on the neutron lifetime is set at 3.6 × 1032 years at 90% C.L., corresponding to a lower limit on the neutron-antineutron oscillation time in 16O of τn→¯n > 4.7 × 108 s. This is the world’s most stringent limit on neutron-antineutron oscillation so far, with 90% improvement from the previous best limit [15], and is reaching the predicted parameter space of some theoretical models. 

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5. Offline tagging of radon-induced backgrounds in XENON1T and applicability to other liquid xenon time projection chambers

   https://doi.org/10.1103/PhysRevD.110.012011  

   Aprile, E; Aalbers, J; Abe, K; Ahmed_Maouloud, S; Althueser, L; Andrieu, B; Angelino, E; Angevaare, J R; Antón_Martin, D; Arneodo, F; et al (July 2024, Physical Review D)

   This paper details the first application of a software tagging algorithm to reduce radon-induced backgrounds in liquid noble element time projection chambers, such as XENON1T and XENONnT. The convection velocity field in XENON1T was mapped out using ${}^{222}\mathrm{Rn}$and ${}^{218}\mathrm{Po}$events, and the rms convection speed was measured to be $0.30\pm 0.01\mathrm{cm}/\mathrm{s}$. Given this velocity field, ${}^{214}\mathrm{Pb}$background events can be tagged when they are followed by ${}^{214}\mathrm{Bi}$and ${}^{214}\mathrm{Po}$decays, or preceded by ${}^{218}\mathrm{Po}$decays. This was achieved by evolving a point cloud in the direction of a measured convection velocity field, and searching for ${}^{214}\mathrm{Bi}$and ${}^{214}\mathrm{Po}$decays or ${}^{218}\mathrm{Po}$decays within a volume defined by the point cloud. In XENON1T, this tagging system achieved a ${}^{214}\mathrm{Pb}$background reduction of ${6.2}_{-0.9}^{+0.4}\%$with an exposure loss of $1.8\pm 0.2\%$, despite the timescales of convection being smaller than the relevant decay times. We show that the performance can be improved in XENONnT, and that the performance of such a software-tagging approach can be expected to be further improved in a diffusion-limited scenario. Finally, a similar method might be useful to tag the cosmogenic ${}^{137}\mathrm{Xe}$background, which is relevant to the search for neutrinoless double-beta decay. Published by the American Physical Society2024 

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