Large-scale organic liquid scintillator detectors are highly efficient in the detection of MeV-scale electron antineutrinos. These signal events can be detected through inverse beta decay on protons, which produce a positron accompanied by a neutron. A noteworthy background for antineutrinos coming from nuclear power reactors and from the depths of the Earth (geoneutrinos) is generated by ( $$\alpha ,\,n$$ ) reactions. In organic liquid scintillator detectors, $$\alpha $$ particles emitted from intrinsic contaminants such as $$^{238}$$ U, $$^{232}$$ Th, and $$^{210}$$ Pb/ $$^{210}$$ Po, can be captured on $$^{13}$$ C nuclei, followed by the emission of a MeV-scale neutron. Three distinct interaction mechanisms can produce prompt energy depositions preceding the delayed neutron capture, leading to a pair of events correlated in space and time within the detector. Thus, ( $$\alpha ,\,n$$ ) reactions represent an indistinguishable background in liquid scintillator-based antineutrino detectors, where their expected rate and energy spectrum are typically evaluated via Monte Carlo simulations. This work presents results from the open-source SaG4n software, used to calculate the expected energy depositions from the neutron and any associated de-excitation products. Also simulated is a detailed detector response to these interactions, using a dedicated Geant4-based simulation software from the JUNO experiment. An expected measurable $$^{13}$$ C $$(\alpha ,\,n)^{16}$$ O event rate and reconstructed prompt energy spectrum with associated uncertainties, are presented in the context of JUNO, however, the methods and results are applicable and relevant to other organic liquid scintillator neutrino detectors.

France

Thomas Adam

Germany

Kai Adamowicz

Pakistan

Shakeel Ahmad

Rizwan Ahmed

Italy

Sebastiano Aiello

China

Fengpeng An

United Kingdom

Costas Andreopoulos

Giuseppe Andronico

Russia

Nikolay Anfimov

Vito Antonelli

Tatiana Antoshkina

João Athayde Marcondes de André

Didier Auguste

Weidong Bai

Nikita Balashov

Andrea Barresi

Davide Basilico

Eric Baussan

Marco Beretta

Antonio Bergnoli

Nikita Bessonov

Daniel Bick

Lukas Bieger

Svetlana Biktemerova

Thilo Birkenfeld

Simon Blyth

Anastasia Bolshakova

Mathieu Bongrand

Matteo Borghesi

Dominique Breton

Augusto Brigatti

Riccardo Brugnera

Riccardo Bruno

Marcel Büchner

Antonio Budano

Jose Busto

Anatael Cabrera

Barbara Caccianiga

Hao Cai

Xiao Cai

Yanke Cai

Zhiyan Cai

Stéphane Callier

Steven Calvez

United Arab Emirates

Antonio Cammi

Chuanya Cao

Guofu Cao

Jun Cao

Yaoqi Cao

Rossella Caruso

Cédric Cerna

Vanessa Cerrone

Jinfan Chang

Taiwan

Yun Chang

Thailand

Auttakit Chatrabhuti

Chao Chen

Guoming Chen

Jiahui Chen

Jian Chen

Jing Chen

Junyou Chen

Pingping Chen

Shaomin Chen

Shiqiang Chen

Xin Chen

Yiming Chen

Yixue Chen

Yu Chen

Ze Chen

Zhangming Chen

Zhiyuan Chen

Jie Cheng

Yaping Cheng

Yu Cheng

Alexander Chepurnov

Alexey Chetverikov

Davide Chiesa

Brazil

Pietro Chimenti

Po-Lin Chou

Ziliang Chu

Artem Chukanov

Gérard Claverie

Catia Clementi

Belgium

Barbara Clerbaux

Claudio Coletta

Selma Conforti Di Lorenzo

Simon Csakli

Chenyang Cui

United States

Olivia Dalager

Christophe Taille

Zhi Deng

Ziyan Deng

Xiaoyu Ding

Xuefeng Ding

Yayun Ding

Bayu Dirgantara

Carsten Dittrich

Sergey Dmitrievsky

David Doerflinger

Dmitry Dolzhikov

Simulation of the background from $$^{13}$$ C $$(\alpha ,\,n)^{16}$$ O reaction in the JUNO scintillator

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment under construction in South China. This paper presents an updated estimate of JUNO’s sensitivity to neutrino mass ordering using the reactor antineutrinos emitted from eight nuclear reactor cores in the Taishan and Yangjiang nuclear power plants. This measurement is planned by studying the fine interference pattern caused by quasi-vacuum oscillations in the oscillated antineutrino spectrum at a baseline of 52.5 km and is completely independent of the CP violating phase and neutrino mixing angle θ $_{23}$. The sensitivity is obtained through a joint analysis of JUNO and Taishan Antineutrino Observatory (TAO) detectors utilizing the best available knowledge to date about the location and overburden of the JUNO experimental site, local and global nuclear reactors, JUNO and TAO detector responses, expected event rates and spectra of signals and backgrounds, and systematic uncertainties of analysis inputs. We find that a 3σ median sensitivity to reject the wrong mass ordering hypothesis can be reached with an exposure of about 6.5 years × 26.6 GW thermal power.

Chile

Angel Abusleme

Muhammad Akram

Abid Aleem

Qi An

JINR

Burin Asavapibhop

João Pedro Athayde Marcondes de André

Wander Baldini

Marco Bellato

Iwan Morton-Blake

David Blum

Clément Bordereau

Agustin Campeny

Chi Chan

Zikang Chen

Yu Chin Cheng

Yen-Ting Chin

Marta Colomer Molla

Selma Conforti DiLorenzo

Alberto Coppi

Daniele Corti

Flavio Dal Corso

Jaydeep Datta

Christophe De La Taille

Czechia

Tadeas Dohnal

Potential to identify neutrino mass ordering with reactor antineutrinos at JUNO  

We explore the decay of bound neutrons in the JUNO liquid scintillator detector into invisible particles (e.g., $$n\rightarrow 3 \nu $$ or $$nn \rightarrow 2 \nu $$ ), which do not produce an observable signal. The invisible decay includes two decay modes: $$ n \rightarrow { inv} $$ and $$ nn \rightarrow { inv} $$ . The invisible decays of -shell neutrons in $$^{12}\textrm{C}$$ will leave a highly excited residual nucleus. Subsequently, some de-excitation modes of the excited residual nuclei can produce a time- and space-correlated triple coincidence signal in the JUNO detector. Based on a full Monte Carlo simulation informed with the latest available data, we estimate all backgrounds, including inverse beta decay events of the reactor antineutrino $${\bar{\nu }}_e$$ , natural radioactivity, cosmogenic isotopes and neutral current interactions of atmospheric neutrinos. Pulse shape discrimination and multivariate analysis techniques are employed to further suppress backgrounds. With two years of exposure, JUNO is expected to give an order of magnitude improvement compared to the current best limits. After 10 years of data taking, the JUNO expected sensitivities at a 90% confidence level are $$\tau /B( n \rightarrow { inv} ) > 5.0 \times 10^{31} \, \textrm{years}$$ and $$\tau /B( nn \rightarrow { inv} ) > 1.4 \times 10^{32} \, \textrm{years}$$ .

João André

Iwan Blake

Zelin Chen

Marta Molla

Selma Lorenzo

Flavio Corso

JUNO sensitivity to invisible decay modes of neutrons

This paper presents an energy resolution study of the JUNO experiment, incorporating the latest knowledge acquired during the detector construction phase. The determination of neutrino mass ordering in JUNO requires an exceptional energy resolution better than 3% at 1 MeV. To achieve this ambitious goal, significant efforts have been undertaken in the design and production of the key components of the JUNO detector. Various factors affecting the detection of inverse beta decay signals have an impact on the energy resolution, extending beyond the statistical fluctuations of the detected number of photons, such as the properties of the liquid scintillator, performance of photomultiplier tubes, and the energy reconstruction algorithm. To account for these effects, a full JUNO simulation and reconstruction approach is employed. This enables the modeling of all relevant effects and the evaluation of associated inputs to accurately estimate the energy resolution. The results of this study reveal an energy resolution of 2.95% at 1 MeV. Furthermore, this study assesses the contribution of major effects to the overall energy resolution budget. This analysis serves as a reference for interpreting future measurements of energy resolution during JUNO data collection. Moreover, it provides a guideline for comprehending the energy resolution characteristics of liquid scintillator-based detectors.

YuChin Cheng

Prediction of energy resolution in the JUNO experiment  

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator detector designed to explore many topics in fundamental physics. In this study, the potential of searching for proton decay in the   $ p\to \bar{\nu} K^+ $   mode with JUNO is investigated. The kaon and its decay particles feature a clear three-fold coincidence signature that results in a high efficiency for identification. Moreover, the excellent energy resolution of JUNO permits suppression of the sizable background caused by other delayed signals. Based on these advantages, the detection efficiency for the proton decay via   $ p\to \bar{\nu} K^+ $   is 36.9% ± 4.9% with a background level of   $ p\to \bar{\nu} K^+ $     $ p\to \bar{\nu} K^+ $   events after 10 years of data collection. The estimated sensitivity based on 200 kton-years of exposure is   $ p\to \bar{\nu} K^+ $   years, which is competitive with the current best limits on the proton lifetime in this channel and complements the use of different detection technologies.

Sylvie Blin

Mario Buscemi

Ilya Butorov

Riccardo Callegari

Po-An Chen

Xurong Chen

Yi-Wen Chen

Zhang Chen

Wilfried Depnering

Marco Diaz

Georgy Donchenko

Jianmeng Dong

Evgeny Doroshkevich

Marcos Dracos

Frédéric Druillole

Ran Du

Shuxian Du

Stefano Dusini

Martin Dvorak

Finland

Timo Enqvist

Heike Enzmann

Andrea Fabbri

Ulrike Fahrendholz

Donghua Fan

Lei Fan

JUNO sensitivity on proton decay →   Searches  

Main goal of the JUNO experiment is to determine the neutrino mass ordering using a 20 kt liquid-scintillator detector. Its key feature is an excellent energy resolution of at least 3% at 1 MeV, for which its instruments need to meet a certain quality and thus have to be fully characterized. More than 20,000 20-inch PMTs have been received and assessed by JUNO after a detailed testing program which began in 2017 and elapsed for about four years. Based on this mass characterization and a set of specific requirements, a good quality of all accepted PMTs could be ascertained. This paper presents the performed testing procedure with the designed testing systems as well as the statistical characteristics of all 20-inch PMTs intended to be used in the JUNO experiment, covering more than fifteen performance parameters including the photocathode uniformity. This constitutes the largest sample of 20-inch PMTs ever produced and studied in detail to date, i.e. 15,000 of the newly developed 20-inch MCP-PMTs from Northern Night Vision Technology Co. (NNVT) and 5000 of dynode PMTs from Hamamatsu Photonics K. K.(HPK).

Tsagkarakis Alexandros

Mass testing and characterization of 20-inch PMTs for JUNO

JUNO is a multi-purpose neutrino observatory under construction in the south of China. This publication presents new sensitivity estimates for the measurement of the   $ \Delta m^2_{31} $  ,   $ \Delta m^2_{31} $  ,   $ \Delta m^2_{31} $  , and   $ \Delta m^2_{31} $   oscillation parameters using reactor antineutrinos, which is one of the primary physics goals of the experiment. The sensitivities are obtained using the best knowledge available to date on the location and overburden of the experimental site, the nuclear reactors in the surrounding area and beyond, the detector response uncertainties, and the reactor antineutrino spectral shape constraints expected from the TAO satellite detector. It is found that the   $ \Delta m^2_{31} $   and   $ \Delta m^2_{31} $   oscillation parameters will be determined to 0.5% precision or better in six years of data collection. In the same period, the   $ \Delta m^2_{31} $   parameter will be determined to about   $ \Delta m^2_{31} $  % precision for each mass ordering hypothesis. The new precision represents approximately an order of magnitude improvement over existing constraints for these three parameters.

Sub-percent precision measurement of neutrino oscillation parameters with JUNO  

The presence of a super-light sterile neutrino can lead to a dip in the survival probability of solar neutrinos, and explain the suppression of the upturn in the low energy solar neutrino data. In this work, we systematically study the survival probabilities in the 3+1 framework by taking into account of the non-adiabatic transitions and the coherence effect. We obtain an analytic equation that can predict the position of the dip. We also place constraints on the parameter space of sterile neutrinos by using the latest Borexino and KamLAND data. We find that the low and high energy neutrino data at Borexino are sensitive to different regions in the sterile neutrino parameter space. In the case with only θ 01 being nonzero, the 8B data sets the strongest bounds at   <math> <mtext>∆</mtext> <msubsup> <mi>m</mi> <mn>01</mn> <mn>2</mn> </msubsup> </math>  $$ \Delta {m}_{01}^2 $$  ≈ (1.1 ∼ 2.2)  <math> <mtext>∆</mtext> <msubsup> <mi>m</mi> <mn>21</mn> <mn>2</mn> </msubsup> </math>  $$ \Delta {m}_{21}^2 $$ , while the low energy neutrino data is more sensitive to other mass-squared regions. The lowest bounds on   <math> <mtext>∆</mtext> <msubsup> <mi>m</mi> <mn>01</mn> <mn>2</mn> </msubsup> </math>  $$ \Delta {m}_{01}^2 $$  from the pp data can reach 10 −12 eV2 because of the coherence effect. Also, due to the presence of non-adiabatic transitions, the bounds in the range of 10 −9 eV2 ≲   <math> <mtext>∆</mtext> <msubsup> <mi>m</mi> <mn>01</mn> <mn>2</mn> </msubsup> </math>  $$ \Delta {m}_{01}^2 $$  ≲ 10 −5 eV2 become weaker as   <math> <mtext>∆</mtext> <msubsup> <mi>m</mi> <mn>01</mn> <mn>2</mn> </msubsup> </math>  $$ \Delta {m}_{01}^2 $$  or sin2 2θ 01 decreases. We also find that in the case with only θ 02 or θ 03 being nonzero, the low energy solar neutrino data set similar but weaker bounds as compared to the case with only θ 01 being nonzero. However, the bounds from the high energy solar data and the KamLAND data are largely affected by the sterile mixing angles.

Jiajun Liao

Jiajie Ling

Baobiao Yue

Constraining super-light sterile neutrinos at Borexino and KamLAND

We study damping signatures at the Jiangmen Underground Neutrino Observatory (JUNO), a medium-baseline reactor neutrino oscillation experiment. These damping signatures are motivated by various new physics models, including quantum decoherence, ν 3 decay, neutrino absorption, and wave packet decoherence. The phenomenological effects of these models can be characterized by exponential damping factors at the probability level. We assess how well JUNO can constrain these damping parameters and how to disentangle these different damping signatures at JUNO. Compared to current experimental limits, JUNO can significantly improve the limits on τ 3/m 3 in the ν 3 decay model, the width of the neutrino wave packet σ  x , and the intrinsic relative dispersion of neutrino momentum σ rel.

Jun Wang

Wei Wang

Slovakia

Andrej Babic

Jiawei Deng

Damping signatures at JUNO, a medium-baseline reactor neutrino oscillation experiment

This work presents a sensitivity study of a reactor liquid scintillator detector to three kinds of dark bosons with masses below 1 MeV, such as dark photons, axion-like particles, and light scalar bosons. The JUNO-TAO detector with Taishan nuclear reactor is taken as a reference. With a proposed 180 days of data taking, the best sensitivity result at the level of <math><mrow><mo>∼</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup></mrow></math> 95% C.L. is achieved for dark photons with an optimized signal to background ratio for the electron coupling constant <math><mrow><msub><mrow><mi>g</mi></mrow><mrow><mi>X</mi></mrow></msub></mrow></math> through inverse Compton-like scattering. Similar calculations are completed for axion-like particles and scalar bosons. The background systematic uncertainty presents as the main limiting factor for the further sensitivity improvement. Several remarks are made to the controversial analysis for the NEOS experiment. Additionally the differential and the inverse differential cross sections have been derived for all three boson types and their interactions with electrons in liquid scintillator.

Light dark bosons in the JUNO-TAO neutrino detector