In this work, we investigate the resonance structures in the $ \Sigma(1/2^-) $ system from both three-quark and five-quark perspectives within the framework of the chiral quark model. An accurate few-body computational approach, the Gaussian expansion method, is employed to construct the orbital wave functions of multiquark states. To reduce the model dependence on parameters, we fit two sets of parameters to check the stability of the results. The calculations show that our results remain stable despite changes in the parameters. In the three-quark calculations, two $ \Sigma(1/2^-) $ states are obtained with energies around 1.8 GeV, which are good candidates for the experimentally observed $ \Sigma(1750) $ and $ \Sigma(1900) $ . In the five-quark configuration, several stable resonance states are identified, including $ \Sigma \pi $ , $ N \bar{K} $ , and $ N \bar{K}^{*} $ . These resonance states survive the channel-coupling calculations under the complex-scaling framework and manifest as stable structures. Our results support the existence of a two-pole structure for the $ \Sigma(1/2^-) $ system, predominantly composed of $ \Sigma \pi $ and $ N \bar{K} $ configurations, analogous to the well-known $ \Lambda(1380) $ - $ \Lambda(1405) $ ( $ \Sigma \pi $ - $ N \bar{K} $ ) system. On the other hand, although the energy of the $ N \bar{K}^{*} $ configuration is close to that of $ \Sigma(1750) $ and $ \Sigma(1900) $ , the obtained width is not consistent with the experimental values. This suggests that the $ N \bar{K}^{*} $ state needs to mix with three-quark components to better explain the experimental $ \Sigma(1750) $ and $ \Sigma(1900) $ states. According to our decay width calculations, the predicted two resonance states are primarily composed of $ \Sigma \pi $ and $ N \bar{K} $ , with their main decay channel being $ \Lambda \pi $ . Therefore, we encourage experimental groups to search for the predicted two-pole structure of the $ \Sigma(1/2^-) $ system in the invariant mass spectrum of $ \Lambda \pi $ .

China

Yu Yao

Xuejie Liu

Xiaoyun Chen

Yuheng Wu

Jialun Ping

Yue Tan

Qi Huang

Investigation of resonances in the Σ(1/2$^{–}$) system based on the chiral quark model * Supported partly by the National Science Foundation of China (12205249, 12305087). Yue Tan is supported by the Funding for School-Level Research Projects of Yancheng Institute of Technology (xjr2022039) and the Qinglan Project Fund of Jiangsu Province. Qi Huang is supported by the Start-up Funds of Nanjing Normal University (184080H201B20)

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

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  

Photomultiplier tubes (PMTs) are widely used in particle experiments for photon detection. PMT waveform analysis is crucial for high-precision measurements of the position and energy of incident particles in liquid scintillator (LS) detectors. A key factor contributing to the energy resolution in large liquid scintillator detectors with PMTs is the charge smearing of PMTs. This paper presents a machine-learning-based photon counting method for PMT waveforms and its application to the energy reconstruction, using the JUNO experiment as an example. The results indicate that leveraging the photon counting information from the machine learning model can partially mitigate the impact of PMT charge smearing and lead to a relative 2.0–2.8% improvement on the energy resolution in the energy range of [1, 9] MeV.

Wei Jiang

Guihong Huang

Zhen Liu

Wuming Luo

Liangjian Wen

Jianyi Luo

Machine-learning based photon counting for PMT waveforms and its application to the improvement of the energy resolution in large liquid scintillator detectors

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).

Mass testing and characterization of 20-inch PMTs for JUNO