We evaluate discovery prospects for photophobic axion-like particles (ALPs) in the $\textit{WWjj}$ final state at the High-Luminosity LHC (HL-LHC; $\sqrt{s}=14\ {\rm{TeV}}$ , ${\cal{L}}=3\ {\rm{ab}}^{-1}$ ). In the photophobic limit ( $g_{a\gamma\gamma}=0$ ), ALPs couple to electroweak gauge bosons and are produced in association with two jets ( $ pp\to jj\ a $ ) via both $\textit{s}$-channel electroweak exchange and vector boson fusion (VBF)–like topologies, followed by $a\to W^+W^-$ decay. We target the different-flavour dilepton mode $W^+W^- \to e^\pm\mu^\mp\nu \bar{\nu}$ with two jets and moderate missing transverse momentum. The analysis employs a two-step strategy: initial preselection that defines the signal-like final state, followed by a multivariate analysis (MVA) trained on dijet and dileptonic-$\textit{WW}$ kinematics from both the $\textit{s}$-channel and VBF-like production mechanisms to separate signal from background; the MVA threshold is optimized independently at each $m_a$ . We present 2$\textit{σ}$ and 5$\textit{σ}$ discovery sensitivities for the ALP–$\textit{W}$ coupling $g_{aWW}$ across the 170–4000 GeV mass range. For $260\ {\rm{GeV}}\le m_a\le1500\ {\rm{GeV}}$ , the 2$\textit{σ}$ (5$\textit{σ}$) sensitivity is approximately flat around $ 0.61(0.76)\ {\rm{TeV}}^{-1}$ . At large masses/couplings, the mapping between an experimental rate and a single EFT parameter $g_{aWW}$ can become UV sensitive, and we treat the extreme high-mass/high-coupling corner as an extrapolation; therefore, we also report model-independent discovery thresholds for the fiducial quantity $ \sigma(pp\to jj\ a)\times\rm{Br}(a\to W^+W^-) $ over the same mass range to enable reinterpretation for other models. These results indicate that the $WWjj$ topology offers competitive and complementary sensitivity to heavy photophobic ALPs at the HL-LHC.

China

Jiaojiao Feng

Ying-nan Mao

Kechen Wang

Discovery prospects for photophobic axion-like particles in the $\textit{WWjj}$ final state at the High-Luminosity LHC * Jiaojiao Feng and Kechen Wang are supported by the National Natural Science Foundation of China (11905162), the Excellent Young Talents Program of the Wuhan University of Technology (40122102, 40122103) and the research program of the Wuhan University of Technology (2020IB024, 104972025KFYjc0101). Ying-nan Mao is supported by the National Natural Science Foundation of China (12205227). The simulation and analysis work of this article was completed with the computational cluster provided by the Theoretical Physics Group at the Department of Physics, School of Physics and Mechanics, Wuhan University of Technology

The processes of $ K^-p \to \pi^0 \pi^0 \Sigma^0 $ and $ K^- p \to \pi^0 \Lambda(1405) $ are studied within the effective Lagrangian approach. In addition to the “background” contribution from the $\textit{u}$-channel nucleon pole term, the contribution from the $ \Sigma(1660) $ resonance with spin-parity $ J^P=1/2^+ $ is also considered. For the $ K^-p \to \pi^0 \pi^0 \Sigma^0 $ reaction, we perform a calculation for the total and differential cross sections by considering the contribution from the $ \Sigma(1660) $ intermediate resonance decaying into $ \pi^0 \Lambda(1405) $ with $ \Lambda(1405) $ decaying into $ \pi^0 \Sigma^0 $ . With our model parameters, the available experimental data on both the $ K^-p \to \pi^0 \pi^0 \Sigma^0 $ and $ K^- p \to \pi^0 \Lambda(1405) $ reactions can be fairly well reproduced. It is shown that the contribution from the $ \Sigma(1660) $ resonance is necessary, and that these experimental measurements could be used to determine some properties of the $ \Sigma(1660) $ resonance.

Xing-Yi Ji

Si-Wei Liu

Wen-Tao Lyu

De-Min Li

En Wang

Ju-Jun Xie

Role of Σ(1660) in the $\textit{K}$ $^{−}$ $\textit{p}$ → $\textit{π}$ $^{0}$ $\textit{π}$ $^{0}$Σ$^{0}$ reaction * Supported by the National Key R&D Program of China (2023YFA1606703, 2024YFE0105200), the National Natural Science Foundation of China (12435007, 12475086, 12192263, 12361141819, 1252200936), the Natural Science Foundation of Henan (232300421140, 252300423951) and the Zhengzhou University Young Student Basic Research Projects (PhD students) (ZDBJ202522)

In this study, we investigate the possibility of enhancing the di-jet resonance searches by tagging the final state radiation (FSR) jet using an event-level deep neural network. It is found that solely relying on the 4-momenta of the leading three jets allows the algorithm to achieve good discriminating power that can identify the hardest FSR jet in the signal while rejecting other soft jets. Once the invariant mass is corrected with the tagged FSR jet, the mass resolution of the signal is greatly enhanced, and the sensitivity of the search is also improved by more than 10%. By crafting the input variables carefully, the algorithm introduces minimal mass sculpting for the background, and its applicability extends to a broad mass range. This work proves that FSR jet tagging can potentially enhance di-jet resonance searches, suiting various stages of the physics programmes at the Large Hadron Collider (LHC) and High-Luminosity LHC (HL-LHC).

Bingxuan Liu

Yuxuan Shen

Yuanshunzi Sui

Enhancing di-jet resonance searches via a final-state radiation jet tagging algorithm * Bingxuan Liu is supported by Shenzhen Campus of the Sun Yat-sen University under project 74140-12255011, and by the Young Scientists Fund (C Class) of the National Natural Science Foundation of China (12405122). Both Yuxuan Shen and Yuanshunzi Sui are supported by College Students’ Innovative Entrepreneurial Training Plan Program

The charmed baryon was first observed experimentally in 1975, one year after the charm quark's confirmation via the discovery of the $ J/\psi $ particle. Studying charmed baryon decays provides a pathway to investigate both strong and weak interactions, leveraging the weak decays of the embedded charm quark. However, for approximately three decades following its discovery, experimental knowledge of charmed baryons remained significantly limited compared to those of the hidden-charm $\textit{ψ}$ mesons and open-charm $ D_{(s)} $ mesons. This situation changed markedly starting in 2014, when dedicated data collection for charmed baryons commenced at BESIII. In this article, we review the experimental progress achieved since 2014 in understanding the weak decays of the charmed baryons.

Pei-Rong Li

Xiao-Rui Lyu

Yangheng Zheng

Experimental overview on the charmed baryon decays * The authors thank Fusheng Yu for useful discussions. The authors are supported in part by National Natural Science Foundation of China (12221005, 12422504); CAS Project for Young Scientists in Basic Research (YSBR-117); Fundamental Research Funds for the Central Universities, Lanzhou University (lzujbky-2025-ytB01, lzujbky-2023-stlt01, lzujbky-2023-it32), University of Chinese Academy of Sciences

We propose a novel method to detect reactor $ \overline{\nu}^{}_e \to \overline{\nu}^{}_\mu $ and $ \overline{\nu}^{}_e \to \overline{\nu}^{}_\tau $ oscillations by using elastic antineutrino-electron scattering processes $ \overline{\nu}^{}_\alpha + e^- \to \overline{\nu}^{}_\alpha + e^- $ (for $ \alpha = e, \mu, \tau $ ), among which the $ \overline{\nu}^{}_e $ events can be singled out by accurately measuring the $ \overline{\nu}^{}_e $ flux via the inverse beta decay $ \overline{\nu}^{}_e + p \to e^+ + n $ . A proof-of-concept study shows that such measurements will not only be able to test the conservation of probability for reactor antineutrino oscillations, but also offer a new possibility to probe leptonic CP violation at the one-loop level.

Yifang Wang

Zhi-zhong Xing

Shun Zhou

Towards a detection of reactor ${\overline {\boldsymbol v}_{\boldsymbol e} \boldsymbol\to \overline {\boldsymbol v}_{\boldsymbol\mu} }$ and ${\overline {\boldsymbol v}_{\boldsymbol e} \boldsymbol\to \overline {\boldsymbol v}_{\boldsymbol\tau} }$ oscillations with possible CP violation * Supported in part by the National Natural Science Foundation of China (12475113, 12535007), the CAS Project for Young Scientists in Basic Research (YSBR-099), and the Scientific and Technological Innovation Program of IHEP (E55457U2)

In this letter, we present rephasing invariant formulae $ \delta^{(\alpha i)} = \arg [{ V_{\alpha 1} V_{\alpha 2} V_{\alpha 3} V_{1i} V_{2i} V_{3i} / V_{\alpha i }^{3} \det V }] $ for CP phases $ \delta^{(\alpha i)} $ associated with nine Euler-angle-like parameterizations of a flavor mixing matrix. Here, $\textit{α}$ and $\textit{i}$ denote the row and column carrying the trivial phases in a given parameterization. Furthermore, we show that the phases $ \delta^{(\alpha i)} $ and the nine angles $ \Phi_{\alpha i} $ of unitarity triangles satisfy compact sum rules $ \delta^{(\alpha, i+2)} - \delta^{(\alpha, i+1)} = \Phi_{\alpha+1, i} - \Phi_{\alpha+2, i} $ and $ \delta^{(\alpha+1, i)} - \delta^{(\alpha+2, i)} = \Phi_{\alpha, i+2} - \Phi_{\alpha, i+1} $ where all indices are taken cyclically modulo three. These relations are natural generalizations of the previous result $ \delta_{\mathrm{PDG}}+\delta_{\mathrm{KM}}=\pi-\alpha+\gamma. $

Japan

Masaki J.S. Yang

Rephasing invariant formulae for CP phases in general parameterizations of flavor mixing matrix and exact sum rules with unitarity triangles * The study is partly supported by the MEXT Leading Initiative for Excellent Young Researchers (JP2023L0013)

We present an investigation on cosmological implications resulting from spontaneous dark $ S U(2)_d $ symmetry breaking in conjunction with the Witten effect. Furthermore, we examine the mass of hidden monopoles generated by phase transition as well as the impact of axion-monopole interactions on the axion mass. Following spontaneous breaking of the PQ symmetry, axions emitted by cosmic strings or domain walls as well as hidden monopoles generated during this transition may collectively contribute to the observed dark matter relic density. Additionally, the stochastic gravitational wave background generated by sub-GeV phase transitions and by the decay of axionic domain walls formed during sub-ZeV phase transitions could account for the low-frequency gravitational wave signals detected by PTA experiments.

Ruiyu Zhou

Ligong Bian

Gravitational waves and dark matter with Witten effect * Supported by the National Key Research and Development Program of China (2021YFC2203004). Ruiyu Zhou is supported by the National Natural Science Foundation of China (12305109, 12147102), Chongqing Natural Science Foundation project (CSTB2022NSCQ-MSX0534), and Science and Technology Research Project of Chongqing Municipal Education Commission (KJQN202300614). Ligong Bian is supported by the National Natural Science Foundation of China (12322505, 12347101). Ligong Bian also acknowledges Chongqing Natural Science Foundation (CSTB2024NSCQ-JQX0022) and Chongqing Talents: Exceptional Young Talents Project (cstc2024ycjhbgzxm0020).

This study investigates the intrinsic electric dipole moment (EDM) of the $\textit{τ}$ lepton, which is an important quantity in the search for physics beyond the Standard Model (BSM). In preparation for future measurements at the Super Tau-Charm Facility (STCF), we employ Monte Carlo simulations of the $ e^+e^- \rightarrow \tau^+\tau^- $ process and optimize the analysis methodology for EDM extraction. Machine learning techniques are implemented to efficiently identify signal events ( $ \tau^\pm\rightarrow \pi^\pm\pi^0\nu_\tau $ ), which result in a significant improvement in signal-to-noise ratio. Our optimized event selection algorithm achieves 80.0% signal purity with 6.3% efficiency. We develop an analytical approach for $\textit{τ}$ lepton momentum reconstruction and derive the squared spin density matrix along with optimal observables, which maximize the sensitivity to $ d_\tau $ . The relationship between these observables and the EDM is established with the estimated sensitivity of $ |d_\tau| \lt 3.89\times 10^{-18}\,e\cdot\mathrm{cm} $ at a 68% confidence level. These results provide a foundation for future experimental measurements of the $\textit{τ}$ lepton EDM in STCF experiments.

Xulei Sun

Yongcheng Wu

Xiaorong Zhou

Sensitivity study of the tau lepton electric dipole moment at the Super Tau-Charm Facility * Supported by the National Key R&D Program of China (2022YFA1602200, 2023YFA1607200); the National Natural Science Foundation of China (NSFC) (12341501, 12341503, 12341504); the international partnership program of the Chinese Academy of Sciences (211134KYSB20200057). Xulei Sun is supported by the Undergraduate Research Program of the University of Science and Technology of China and the Xinhe Scholar Program of the School of the Gifted Young

We introduce a novel level crossing phenomenon in the mass mixing between QCD axions: one canonical QCD axion and one $ Z_{{\cal{N}}} $ axion. The level crossing can occur at or slightly before the QCD phase transition critical temperature, depending on the ratio of the axion decay constants, $ \sim 1.69 $ . The cosmological evolution of the mass eigenvalues in these two scenarios is similar; however, the transition of axion energy density differs significantly. Finally, we estimate the relic density of the QCD axion dark matter in this context. Additionally, this level crossing may have some interesting cosmological implications.

Hai-Jun Li

Yu-Feng Zhou

Mass mixing between QCD axions * Supported by the CAS Project for Young Scientists in Basic Research YSBR-006, the National Key R&D Program of China (2017YFA0402204), and the National Natural Science Foundation of China (11821505, 11825506, 12047503)

We discuss the landscape of flavor physics at the Circular Electron-Positron Collider (CEPC), based on the nominal luminosity outlined in its Technical Design Report. The CEPC is designed to operate in multiple modes to address a variety of tasks. At the $\textit{Z}$ pole, the expected production of 4 Tera $\textit{Z}$ bosons will provide unique and highly precise measurements of $\textit{Z}$ boson couplings, while the substantial number of boosted heavy-flavored quarks and leptons produced in clean $\textit{Z}$ decays will facilitate investigations into their flavor physics with unprecedented precision. We investigate the prospects of measuring various physics benchmarks and discuss their implications for particle theories and phenomenological models. Our studies indicate that, with its highlighted advantages and anticipated excellent detector performance, the CEPC can explore beauty and $\textit{τ}$ physics in ways that are superior to or complementary with the Belle II and Large-Hadron-Collider-beauty experiments, potentially enabling the detection of new physics at energy scales of 10 TeV and above. This potential also extends to the observation of yet-to-be-discovered rare and exotic processes, as well as testing fundamental principles such as lepton flavor universality, lepton and baryon number conservation, etc., making the CEPC a vibrant platform for flavor physics research. The $\textit{WW}$ threshold scan, Higgs-factory operation and top-pair productions of the CEPC further enhance its merits in this regard, especially for measuring the Cabibbo-Kobayashi-Maskawa matrix elements, and Flavor-Changing-Neutral-Current physics of Higgs boson and top quarks. We outline the requirements for detector performance and considerations for future development to achieve the anticipated scientific goals. The role of machine learning for innovative detector design and advanced reconstruction algorithms is also stressed. The CEPC flavor physics program not only develops new capabilities for exploring flavor physics beyond existing projects but also enriches the physics opportunities of this machine. It should be remarked that, given the richness of the CEPC flavor physics, this manuscript is not meant to be a comprehensive survey, but rather an investigation of representative cases. Uncovering the full potential of flavor physics at the CEPC will require further dedicated explorations in the future.

Xiaocong Ai

United States

Wolfgang Altmannshofer

Peter Athron

Xiaozhi Bai

Lorenzo Calibbi

Germany

Lu Cao

Yuzhi Che

Chunhui Chen

Ji-Yuan Chen

Long Chen

Mingshui Chen

Shanzhen Chen

Xuan Chen

Shan Cheng

Cheng-Wei Chiang

Switzerland

Andreas Crivellin

Hanhua Cui

France

Olivier Deschamps

Sébastien Descotes-Genon

Xiaokang Du

Shuangshi Fang

Yu Gao

Yuanning Gao

Li-Sheng Geng

Pablo Goldenzweig

Jiayin Gu

Feng-Kun Guo

Yuchen Guo

Zhi-Hui Guo

Tao Han

Hong-Jian He

Jibo He

Miao He

Xiaogang He

Yanping Huang

Gino Isidori

Quan Ji

Jianfeng Jiang

Xu-Hui Jiang

Slovenia

Jernej F. Kamenik

Tsz Hong Kwok

Gang Li

Geng Li

Haibo Li

Haitao Li

Hengne Li

Honglei Li

Liang Li

Lingfeng Li

Qiang Li

Shu Li

Xiaomei Li

Xin-Qiang Li

Yiming Li

Yubo Li

Yuji Li

Zhao Li

Hao Liang

Zhijun Liang

Libo Liao

Zoltan Ligeti

Jia Liu

Jianbei Liu

Tao Liu

Yi Liu

Yong Liu

Zhen Liu

Xinchou Lou

Peng-Cheng Lu

Italy

Alberto Lusiani

Hong-Hao Ma

Kai Ma

Farvah Mahmoudi

Yajun Mao

Yaxian Mao

David Marzocca

Juan-Juan Niu

Soeren Prell

Huirong Qi

Sen Qian

Zhuoni Qian

Qin Qin

Ariel Rock

Jonathan L. Rosner

Manqi Ruan

Dingyu Shao

Chengping Shen

Xiaoyan Shen

Haoyu Shi

United Kingdom

Liaoshan Shi

Zong-Guo Si

Cristian Sierra

Huayang Song

Shufang Su

Wei Su

Zhijia Sun

Michele Tammaro

Dayong Wang

Flavor physics at the CEPC: a general perspective * We acknowledge financial support from the National Natural Science Foundation of China (NSFC) (12125507, 12047503, 12035008, 2211530479, 12475094, 12135006, 12075097, 12375086, 2022YFA1601903, 12061141007, 12375091, 12342502, 12235018, 12335003, 12105100, 12475106, 11961141015, 12188102, 12175245, 12205171, 12321005, tsqn202312052, 2024HWYQ-005, 12405121, 12447167, 12061141006, 12405102, 12125503,12305115, 12075213, 12335005, 12235008); the Chinese Academy of Sciences (YSBR-101, XDB34030000); the National Key R&D Program of China (2022YFE0116900, 2023YFA1606703, 2022YFA1601901); the National Key Research and Development Program of China (2023YFA1606300); the Excellent Postdoctoral Program of Jiangsu Province (2023ZB891); the Shenzhen Science and Technology Program (202206193000001, 20220816094256002); the Natural Science Foundation for Distinguished Young Scholars of Henan Province (242300421046); the Beijing Municipal Natural Science Foundation (JQ22002); the Area of Excellence (AoE/P-404/18-3) and the General Research Fund (16304321) (both grants are issued by the Research Grants Council of Hong Kong S.A.R); the MOST National Key R&D Program (2023YFA1606303); the Shanghai Key Laboratory for Particle Physics and Cosmology, Key Laboratory for Particle Astrophysics and Cosmology (Ministry of Education), Shanghai Jiao Tong University