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

<p>Neutrino tensor interactions have gained prominence in the study of coherent elastic neutrino-nucleus scattering (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math>) recently. We perform a systematical examination of the nuclear effect, which plays a crucial role in evaluating the cross section of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math> in the presence of tensor interactions. Our analysis reveals that the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math> cross section induced by tensor interactions is not entirely nuclear spin suppressed and can be enhanced by a few orders of magnitude compared to the conventional studies. The neutrino magnetic moment induced by the loop effect of tensor interactions is also taken into account due to its sizable contribution to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math> cross section. We also employ data from the COHERENT experiment and recent observations of solar <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi mathvariant="normal">B</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>8</mn></mrow></mmultiscripts></mrow></math> neutrinos from dark matter direct detection experiments to scrutinize the parameter space of neutrino tensor interactions.</p>

Jiajun Liao

Jian Tang

Bing-Long Zhang

Tensor interaction in coherent elastic neutrino-nucleus scattering

The Gallium anomaly is an unexplained deficit in the neutrinos observed during the calibration of GALLEX and SAGE using a Cr radioactive source and recently confirmed by BEST. The possible explanations for this deficit include an overestimation of the neutrino absorption cross section in Ga, an incorrect measurement of the source activity or the existence of sterile neutrinos. However, as this deficit has only been observed in Ga detectors, it has not been possible to distinguish among various proposals. Therefore, we propose an experiment using the same radioactive source but with a different detection method, electron-neutrino scattering. We discuss potential locations for such an experiment, estimating the main backgrounds and expected event rates, considering various target masses and source positions. Even if the anomaly does not result from the detection method, such an experiment can provide an independent determination of the branching ratio of the Cr decay by using the spectral information or observing the scattering angle. It is also sensitive to an eventual baseline dependence of the anomaly, as is predicted in sterile neutrino models.

Emilio Ciuffoli

Jarah Evslin

Ruixuan Gao

Haixing Lin

Testing the Gallium anomaly using electron-neutrino scattering

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 China Jinping underground Laboratory (CJPL) is an excellent location for studying solar, terrestrial, and supernova neutrinos due to its 2400-meter vertical rock overburden. Its unparalleled depth gives an opportunity to investigate the cosmic-ray muons with exceptionally high average energy at <math><mo>∼</mo><mn>360</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. This paper details a study of muon-related backgrounds based on 1178 days of data collected by the 1-ton prototype neutrino detector used for the Jinping Neutrino Experiment (JNE) since 2017. The apparent effects for the leakage of muons’ secondary particles due to detector’s finite size on the measured neutron yield are first discussed in detail. The analysis of 493 cosmic-ray muon candidates and <math><mn>13.6</mn><mo>±</mo><mn>5.7</mn></math> cosmogenic neutron candidates, along with a thorough evaluation of detection efficiency and uncertainties, gives a muon flux of <math><mrow><mo>(</mo><mn>3.56</mn><mo>±</mo><msub><mn>0.16</mn><mrow><mrow><mi>stat</mi></mrow></mrow></msub><mo>±</mo><msub><mn>0.10</mn><mrow><mrow><mi>syst</mi></mrow></mrow></msub><mo>)</mo><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>10</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mi>cm</mi><mrow><mo>−</mo><mn>2</mn></mrow></msup><mtext> </mtext><msup><mi>s</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> and a cosmogenic neutron yield of <math><mrow><mo>(</mo><mn>3.37</mn><mo>±</mo><mn>1.4</mn><msub><mrow><mn>1</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>0.3</mn><msub><mrow><mn>1</mn></mrow><mrow><mi>syst</mi></mrow></msub><mo>)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><mtext> </mtext><msup><mrow><mi>g</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><mtext> </mtext><msup><mrow><mi>cm</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> in LAB-based liquid scintillator.

Xinshun Zhang

Jinjing Li

Wei Dou

Haoyang Fu

Ye Liang

Qian Liu

Wentai Luo

Ming Qi

Wenhui Shao

Haozhe Sun

Yuyi Wang

Zhe Wang

Changxu Wei

Jun Weng

Yiyang Wu

Benda Xu

Chuang Xu

Tong Xu

Yuzi Yang

Aiqiang Zhang

Bin Zhang

Study of neutron production for 360 GeV cosmic muons

Dark matter direct detection experiments are approaching the neutrino floor, with a significant probability of measuring coherent elastic neutrino-nucleus scattering (CEνNS) and exploring potential neutrino-related new physics (νNP). In the present study, the simultaneous presence of dark matter and νNP is emphatically investigated, revealing a response similar to Standard Model neutrino backgrounds in Xenon-based dark matter experiments. Through analyses of three U(1) extension models, it is determined that dark matter signals can be differentiated from an excess or a depletion of neutrino contributions from νNP by applying a statistically defined distinction method to nuclear and electronic recoil spectra. Additionally, an investigation is conducted into how νNP affects the exclusion limits for spin-independent dark matter-nucleon interactions. The present findings could facilitate the identification of new physics in future dark matter experiments.

Dark matter, CEνNS and neutrino new physics scrutinized by a statistical method in Xenon-based experiments

A muonium consists of a positive muon associated with an orbital electron, and the spontaneous conversion to antimuonium serves as a clear indication of new physics beyond the Standard Model in particle physics. One of the most important aspects in muonium-to-antimuonium conversion experiment is to increase the muonium yield in vacuum to challenge the latest limit obtained in 1999. This study focuses on a simulation of the muonium formation and diffusion in the perforated silica aerogel. The independent simulation results can be well-validated by experimental data. By optimizing the target geometry, we find a maximum muonium emission efficiency of 7.92(2)% and a maximum vacuum yield of 1.134(2)% with a typical surface muon beam, indicating a 2.6 times and a 2.1 times enhancement, respectively. Our results will pave the way for muonium experiments.