In this work, we present a systematic study of the event characteristics and underlying physics relevant to neutrino-antineutrino discrimination in atmospheric neutrino charged-current interactions in large liquid scintillator detectors. This study encompasses the primary neutrino interactions, the subsequent secondary interactions of final-state particles, and the ensuing neutron captures. We investigate in detail the properties of final-state charged leptons and hadrons, deriving distinct distributions of inelasticity and neutron-capture multiplicity for both neutrino and antineutrino interactions. These distributions are used to quantify the performance of neutrino-antineutrino discrimination. Our findings lay the groundwork for atmospheric neutrino oscillation studies in large liquid scintillator detectors, particularly for determining the neutrino mass ordering.

China

Xinhai He

Gao-song Li

Yu-Feng Li

Wuming Luo

Liang-jian Wen

Atmospheric neutrino charged-current interactions at large liquid- scintillator detectors: I. physics of neutrino-antineutrino discrimination * Supported in part by the National Natural Science Foundation of China (12125506, 12075255), and the CAS Project for Young Scientists in Basic Research (YSBR-099)

In this study, we develop a framework for producing exotic muonic kaon atoms ( $ K\mu $ ) in semileptonic $ D^{0} $ decays using an effective weak Hamiltonian, a helicity-based treatment of leptonic current, and a nonrelativistic bound-state projection. The resulting branching ratio $ BR(D^{0} \to(K\mu )\nu_{\mu})=2.29\times10^{-10} $ is implemented in a ROOT-based code to estimate yields at a relativistic heavy-ion collider (RHIC), large hadron collider (LHC), and super tau-charm facility (STCF). We demonstrate quantitatively that $ K\mu $ atoms, which are also produced through coalescence in the quark–gluon plasma (QGP), offer a sensitive probe of low-momentum primordial muons and early-time electromagnetic radiation, acting as complementary constraints in an otherwise unexplored phase space for thermal dilepton and photon emission. Newly estimated dissociation cross-sections in detector material indicate that secondary-vertex reconstruction should be experimentally feasible, enabling the clean experimental identification of atoms. Projected yields from QGP coalescence in LHC and RHIC heavy-ion collisions and from $ D^{0} $ decays in LHC high-luminosity $ p+p $ collisions indicate that the first observation of $ K\mu $ atoms is within reach.

Xiaofeng Wang

Zebo Tang

United States

Zhangbu Xu

Chi Yang

Wangmei Zha

Yifei Zhang

Production of muonic kaon atoms at high-energy colliders * This work was supported in part by the National Natural Science Foundation of China (12361141827, 12422510), and by the Office of Nuclear Physics within the U.S. Department of Energy Office of Science (DE-FG02-89ER40531). The National Key Research and Development Program of China (2022YFA1604900). W. Zha acknowledges support from the Anhui Provincial Natural Science Foundation (2508085JX002), the Youth Innovation Promotion Association of the Chinese Academy of Sciences, and the Chinese Academy of Sciences (YSBR088)

In this work, we propose a method for quantifying the difference between nuclear parton distribution functions in different nuclei and parton distribution functions in free nucleons using relative entropy (also known as the Kullback-Leibler divergence), a measure widely employed in quantum information theory. By introducing certain constraints and the ''minimum relative entropy'' hypothesis, we can determine the shape of the structure function in the intermediate-$\textit{x}$ region, which is closely connected to the renowned EMC effect. For quark structure functions, our results are consistent with the latest global fits to experimental data. This agreement suggests that the relative entropy-based methodology may provide novel insights into nucleon structure, particularly in cases where experimental data and theoretical QCD constraints are limited, such as those relevant to gluon nPDFs. Therefore, we apply this methodology to gluon nPDFs, analyzing the results from two commonly used global fitting groups, EPPS21 and nNNPDF3.0. Our analysis suggests that the central values of EPPS21 align more closely with the ''minimum relative entropy'' hypothesis. This finding underscores the utility of the proposed method and provides a valuable reference for future global fits of nPDFs.

Shu-Man Hu

Ao-Sheng Xiong

Ji Xu

Fu-Sheng Yu

Ji-Xin Yu

An analysis of nuclear parton distribution function based on relative entropy * Supported in part by the National Natural Science Foundation of China (12335003), the Fundamental Research Funds for the Central Universities (lzujbky-2023-stlt01, lzujbky-2024-oy02, and lzujbky-2025-eyt01), and the Scientific Research Innovation Capability Support Project for Young Faculty (ZYGXQNJSKYCXNLZCXM-P2). Ji Xu is supported in part by the National Natural Science Foundation of China (12475098, 12105247)

A dark photon is an Abelian gauge boson arising from a new $ U(1)_D $ gauge symmetry, coupled to the Standard Model through kinetic mixing. The mixing parameter $\textit{ϵ}$ induces an effective coupling to the electromagnetic current, while $ g_\chi $ couples the dark photon to a stable dark matter particle $\textit{χ}$. We study $ J/\psi $ two-body and four-body decays mediated by a light dark photon ( $ m_U \lt 3.0 $ GeV) within the non-relativistic QCD (NRQCD) framework, considering both visible decays of the dark photon into SM fermions and invisible decays into dark sector particles. We investigate the detection sensitivity of BESIII and STCF experiments to the dark photon mass $ m_U $ and kinetic mixing parameter $\textit{ϵ}$. Our results show that, for two-body final states with $ m_U \lt 2m_\chi $ , BESIII sets $\textit{ϵ}$ upper limits of $ 9.3\times10^{-4} $ and $ 7.6\times10^{-4} $ for lepton-pair and hadronic signals, respectively, while STCF yields $ 3.7\times10^{-4} $ and $ 3.1\times10^{-4} $ . For invisible decays ( $ m_U\ge 2m_\chi $ ), BESIII achieves an $\textit{ϵ}$ limit of $ 1.4\times10^{-3} $ in the mass range $ 0.3\sim0.8 $ GeV, and STCF reaches $ 2.3\times10^{-4} $ in $ 0.3\sim1.9 $ GeV; no signals are expected in other mass regions, and visible decays are severely suppressed throughout. For four-body decay channels, BESIII yields an $\textit{ϵ}$ upper limit of $ 7.6\times10^{-5} $ for $ m_U \lt 2.2 $ GeV, whereas STCF achieves $ 1.2\times10^{-5} $ over the full mass range. When $ m_U\ge 2m_\chi $ , visible modes are nearly excluded; BESIII and STCF set $\textit{ϵ}$ limits from invisible decays of $ 8.8\times10^{-5} $ for $ m_U \lt 2.4 $ GeV and $ 1.4\times10^{-5} $ for $ m_U \lt 2.8 $ GeV, respectively, with no detectable signals at higher masses. Except for the limit of $ 9.3\times10^{-4} $ , all the above $\textit{ϵ}$ bounds lie in regions that are not currently excluded by collider experiments. Compared with the constraints from two-body final state processes, the limits derived from four-body decay channels lie well below existing experimental bounds, providing supportive references for constraining this parameter in BESIII and STCF experiments. Numerical results for the decay ratios $ \Gamma/\Gamma_{J/\psi} $ , expected event numbers, significance $ S/\sqrt{B} $ , and $ p_T $ distributions are presented where applicable.

Xiao Liang

Chun-Yuan Li

Bin-Peng Shang

Zong-Guo Si

Hong-Xin Wang

Xing-Hua Yang

Dai-Xing Zhang

Searching for dark photons in $\textit{J/ψ}$ decays * Supported in part by the National Natural Science Foundation of China (12105162, 12305106, 12235008, 12321005), the Natural Science Foundation of Shandong Province (ZR2021QA058, ZR2021QA040), and the Youth Innovation Technology Project of Higher School in Shandong Province (2023KJ146)

Motivated by the recent near-threshold enhancement in top-quark pair production reported by CMS and ATLAS, we study the $\textit{S}$-wave spectral structure of heavy-light systems containing a single top quark, namely $ t\bar{q} $ , $ t\bar{c} $ , and $ t\bar{b} $ , within the instantaneous Bethe-Salpeter formalism. Because the top quark decays on a timescale much shorter than the typical hadronization time, the discrete eigenvalues we obtain should be interpreted as model-dependent reference positions of possible quasi-bound heavy-light configurations, rather than as predictions for fully formed conventional hadrons. The numerical results indicate that the masses of these configurations lie close to the top-quark mass. For the $ t\bar{b} $ system, the masses of the first four $\textit{S}$-wave $ 0^{-} $ radial states are about $ 5.1 $ , $ 5.4 $ , $ 5.6 $ , and $ 5.7 $ GeV above the top-quark mass, respectively. For the $ t\bar{c} $ system, the corresponding values are about $ 1.9 $ , $ 2.2 $ , $ 2.5 $ , and $ 2.6 $ GeV. We also briefly discuss possible production and decay patterns at a qualitative level, which may serve as a reference for future dedicated phenomenological studies or for experimental constraints.

Jun-Hao Zhang

Shuo Yang

Bing-Dong Wan

The $\textit{S}$-wave topped meson * Supported in part by the National Natural Science Foundation of China (12575106, 12147214), and the Specific Fund of Fundamental Scientific Research Operating Expenses for Undergraduate Universities in Liaoning Province (LJ212410165019)

Motivated by the renewed attention from the recent BESIII experiment on the semileptonic decay $$D\rightarrow V \ell \nu _{\ell }$$ (where $\textit{V}$ denotes a vector meson), we investigate semileptonic decay $$D^+\rightarrow \omega \ell ^+\nu _{\ell }$$ within the framework of QCD light-cone sum rule in this work. By constructing correlation function with right-handed chiral current, the transverse twist-2 light-cone distribution amplitudes (LCDA) $$\phi ^{\perp }_{2;\omega }(x,\mu )$$ dominates the contribution in TFFs. We study the properties of twist-2 LCDA $$\phi ^{\perp }_{2;\omega }(x,\mu )$$ through light-cone harmonic oscillator model. Applying it to the TFFs, we obtained $$A_1(0)=0.537^{+0.053}_{-0.053}$$ , $$A_2(0)=0.540^{+0.068}_{-0.068}$$ , $$V(0)=0.754^{+0.079}_{-0.079}$$ , and $$A_0(0)=0.553^{+0.044}_{-0.043}$$ at large recoil point. Two TFF ratios are $$r_V=1.40^{+0.21}_{-0.19}$$ and $$r_2=1.01^{+0.17}_{-0.16}$$ . After extrapolating these TFFs to the whole physical $$q^2$$ region via simplified $$z(q^2,t)$$ series expansion, the ratio of longitudinal and transverse decay widths is $$\Gamma _\mathrm{{L}}/\Gamma _\mathrm{{T}}=0.987^{+0.107}_{-0.121}$$ . Then, we get branching fraction $$\mathcal {B}(D^+\rightarrow \omega e^+\nu _e)=(1.848^{+0.365}_{-0.330})\times 10^{-3}$$ and $$\mathcal {B}(D^+\rightarrow \omega \mu ^+\nu _{\mu })=(1.782^{+0.334}_{-0.303})\times 10^{-3}$$ , which is in good agreement with BESIII and CLEO Collaborations. Taking into account the secondary decay $$\omega \rightarrow \pi ^+\pi ^-\pi ^0$$ , we predict branching fraction of five body decay as $$\mathcal {B}(D^+\rightarrow \omega (\rightarrow \pi ^+\pi ^-\pi ^0)e^+\nu _{e})=(1.648^{+0.341}_{-0.305})\times 10^{-3}$$ and $$\mathcal {B}(D^+\rightarrow \omega (\rightarrow \pi ^+\pi ^-\pi ^0)\mu ^+\nu _{\mu })=(1.589^{+0.313}_{-0.281})\times 10^{-3}$$ . Finally, we predict the forward-backward asymmetry $$A_\mathrm{{FB}}^{\ell }$$ , lepton-side convexity parameter $$C^{\ell }_\mathrm{{F}}$$ , longitudinal (transverse) polarization $$P_\mathrm{{L}(\textrm{T})}^{\ell }$$ , as well as longitudinal polarization fraction $$F_\mathrm{{L}}^{\ell }$$ .

Yin-Long Yang

Fang-Ping Peng

Yan-Ting Yang

Hai-Bing Fu

Sheng-Quan Wang

Non-perturbative effects for the isoscalar light vector $$\omega $$ -meson in charmed meson semileptonic decays

The density of ultralight dark matter can be modified in the vicinity of macroscopic bodies when the dark matter possesses quadratic couplings to the Standard Model. If these couplings are sufficiently strong, Earth’s atmosphere acts to shield the dark matter, thereby limiting the effectiveness of laboratory-based experiments. Experiments performed at altitudes exceeding the dark matter de Broglie wavelength experience the same orbit-averaged field amplitude as in the absence of scattering. Quantum clocks are capable of detecting variations in fundamental parameters due to the dark matter background. If based on the International Space Station, they are therefore well-suited to probe dark matter masses $\textit{m}$ ≳ 10 eV. Moreover, when the dark matter de Broglie wavelength is smaller than Earth’s radius ($\textit{m}$ ≳ 10 eV), the dark matter profile around Earth exhibits a dipole feature. In Low Earth Orbits this dipole temporally modulates potential dark matter signals. This provides a powerful cross-check of the orbit-averaged effect and can enhance the sensitivity of these experiments. We find optical clocks could give rise to world-leading constraints in some cases. Orbiting nuclear clocks could probe even more of the parameter space inaccessible to ground-based experiments.

Dawid Brzeminski

Aaron Pierce

Searching for ultralight scalar dark matter with clocks in Low Earth Orbit

The Galactic Center is potentially hosting the largest indirect signal from particle dark matter (DM), which in many well-motivated models would produce gamma rays as their final states. However, this region has often been dismissed for DM studies because of the evidence for an unexpected gamma-ray component over astrophysical backgrounds at GeV energies, firstly discovered in the data of the Fermi Large Area Telescope (LAT), the so-called Galactic Center excess (GCE). While this was initially considered to hint at GeV thermal relics, recent work supports a GCE interpretation in terms of a stellar population of millisecond pulsarlike sources in the Galactic bulge. Building on this preference, we reevaluate the Galactic Center as a powerful target for indirect DM searches via gamma rays. This is achieved by combining adaptive template fitting and photon-count statistical methods to assess the role of subthreshold point sources in the observed Fermi-LAT gamma-ray counts while minimizing the mismodeling of Galactic diffuse-emission backgrounds. In a fully self-consistent way, the gamma-ray data are fitted with a mixed model comprising a DM signal and a stellar bulge, both potentially contributing to the GCE. The space left for signals from weak-scale DM particle annihilations is quantified by extracting 95% confidence level upper limits on the annihilation cross section, which, depending on the DM density profile, result in stringent limits for masses <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo>≲</mo><mn>300</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>. The robustness of our results is supported by tests on simulated data.

France

Silvia Manconi

Slovenia

Christopher Eckner

Francesca Calore

Italy

Fiorenza Donato

Stellarlike Galactic Center excess challenges particle dark matter

We investigate Schouten–Nijenhuis brackets of Killing–Yano tensors for Kimura IIC metric showing that Killing–Yano tensors form a Lie algebra.

Romania

Florian Popa

Schouten–Nijenhuis bracket of Killing–Yano tensors for Kimura IIC metric

We present an implementation of Higgs-boson production in association with a hard, isolated photon via vector-boson fusion in the framework of the for the consistent matching of next-to-leading order QCD corrections with parton showers. The impact of parton-shower settings and non-perturbative effects on Higgs observables is studied and found to be small, while larger corrections are found for distributions of the sub-leading jets. Various approaches for the isolation of the photon are explored. For typical setups, the isolation strategy is found to have little impact on even the most sensitive observables.

Germany

Barbara Jäger

Simon Reinhardt

NLO QCD and parton-shower effects for Higgs-boson production in association with a hard photon via vector-boson fusion