Hadron-hadron interactions, being nonperturbative in nature, play a significant role in addressing phenomenological questions in particle physics. Femtoscopy is a powerful tool in heavy-ion collision experiments, enabling the extraction of hadron-hadron interactions via momentum-correlation functions (CFs). These CFs are typically expressed as a convolution of source functions and hadron-hadron wave functions, with the latter encoding information about the interactions. However, source functions remain poorly constrained and are commonly approximated by a Gaussian form. Reconstructing source functions from experimental correlation data constitutes an 'inverse problem.' To address this, we propose a toy model based on Tikhonov regularization. Using a square-well potential with four distinct strengths, we calculate the CFs for inputs of single Gaussian source functions and mixed Gaussian source functions. The resulting CFs are then used to reconstruct the source functions via Tikhonov regularization. Our results show that the Gaussian source function can be successfully reconstructed, highlighting the potential of this approach for extracting realistic source functions from hadron pairs of interest.

China

Ao-Sheng Xiong

Qi-Wei Yuan

Ming-Zhu Liu

Fu-Sheng Yu

Zhi-Wei Liu

Li-Sheng Geng

Solving the inverse source problem in femtoscopy with a toy model * Supported in part by the Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM204) and the National Natural Science Foundation of China (W2543006, 12435007). Ming-Zhu Liu acknowledges support from the National Natural Science Foundation of China (12575086). Zhi-Wei Liu acknowledges support from the National Natural Science Foundation of China (12405133) and from the Shenzhen Science and Technology Program (ZDSYS20230626091501002). Fu-Sheng Yu and Ao-Sheng Xiong acknowledge support from the Scientific Research Innovation Capability Support Project for Young Faculty (ZYGXQNJSKYCXNLZCXM-P2) and from the Fundamental Research Funds for the Central Universities (lzujbky-2023-stlt01, lzujbky-2024-oy02, lzujbky-2025-eyt01)

We give an extensive discussion of the displaced signals of heavy Majorana neutrino production at future electron-positron colliders operating at various proposed energies in the context of the Left-Right symmetric model. A comprehensive collection of channels is taken into account, ranging from those featuring $\textit{W}$ and $\textit{W}$ mediation to those induced by scalar mixing and gauge/scalar boson fusion, with connections to the mechanism of neutrino mass origin. The emerging signatures feature possibly multiple displaced heavy neutrinos that are in some cases accompanied by prompt activity and forward leptons. We derive the corresponding total production rates and differential distributions, which allow us to differentiate the channels and have analytical estimates of the signal yield. We then develop realistic estimates of the selection efficiencies using a dedicated vertexing algorithm which establishes the displaced decay positions and supplies a reliable proxy for reconstructing the full four-momenta of long-lived particles. This allows us to determine the realistic reaches in the parameter space of the Left-Right symmetric model across the various channels, and we show that these can strongly surpass the LHC ones, demonstrating that future lepton colliders are sensitive to left-right symmetry breaking scales in the deep multi-TeV regime.

France

Benjamin Fuks

Slovenia

Jonathan Kriewald

Miha Nemevšek

Italy

Fabrizio Nesti

Long-lived left-right signals at the FCC-ee

Long-baseline neutrino oscillation experiments require external constraints on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>sin</mi><mn>2</mn></msup><msub><mi>θ</mi><mn>12</mn></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Δ</mi><msubsup><mi>m</mi><mn>21</mn><mn>2</mn></msubsup></math> to make precision measurements of the leptonic mixing matrix. These constraints come from measurements of the Mikheyev-Smirnov-Wolfenstein (MSW) mixing in solar neutrinos. Here we develop an adiabatic MSW approximation in the presence of heavy neutral leptons; it adds, to leading order, a single new parameter (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>α</mi><mn>11</mn></msub></math>) representing the magnitude of the mixing between the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>e</mi></msub></math> state and the heavy sector. We use data from the Borexino, SNO, and KamLAND Collaborations to find a solar constraint appropriate for heavy neutral lepton searches in long-baseline oscillation experiments. Solar data yields a strongly correlated constraint on the solar mass splitting and the magnitude of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>e</mi></msub></math> nonunitary mixing, limiting the magnitude of the nonunitary parameter to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><mn>1</mn><mo>−</mo><msub><mi>α</mi><mn>11</mn></msub><mo stretchy="false">)</mo><mo>&lt;</mo><mn>0.046</mn></math> at the 99% credible region.

Andrés López Moreno

Nonunitary solar constraint for long-baseline neutrino experiments

The determination of the neutrino mass ordering is one of the flagship goals in particle physics. A well-known and powerful synergy emerges when combining high-precision measurements of the effective atmospheric mass-squared splitting from electron antineutrino disappearance in reactor experiments with that from muon (anti)neutrino disappearance in accelerator-based long-baseline experiments. To fully exploit this synergy, percent-level precision in the atmospheric mass splitting is required—a target that JUNO is expected to achieve within a few months of data taking. This motivated the formulation of a mass ordering sum rule for neutrino disappearance channels, which shows that by combining data from T2K and NOvA with JUNO after one year of operation, the neutrino mass ordering can be determined at the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3</mn><mi>σ</mi></math> confidence level. Since JUNO has recently started taking data, it is timely to ask whether this sum rule remains robust in the presence of new physics. We identify the necessary conditions for new physics to affect the sum rule and demonstrate that, in some cases, such effects could lead to an incorrect inference of the mass ordering. As concrete examples, we consider scalar nonstandard interactions (SNSI) and neutrinos coupled to an ultralight scalar field. We find that, for SNSI, current constraints render any modification of the sum rule negligible, whereas in the latter case, the inference of the ordering requires caution. Nevertheless, these effects can be disentangled, illustrating how the sum rule can also be used to search for new physics.

United States

Brazil

Gustavo F.S. Alves

Hiroshi Nunokawa

Renata Zukanovich Funchal

Impact of new physics on the JUNO-long-baseline synergy in the neutrino mass ordering determination

Violations of classicality can be probed through measurements performed on a system at different times, as proposed by Leggett and Garg. Specifically, violations of Leggett-Garg inequalities suggest the presence of quantum effects in macroscopic systems. Long-baseline neutrino experiments provide some of the longest available propagation distances over which such tests can be performed. Previous studies of Leggett-Garg tests in the neutrino sector have largely focused on showing that the oscillation probabilities can violate classical bounds for certain parameter choices. In this work, we develop a more complete and data-driven framework that treats both the distributions representing the classical and quantum behavior, as well as the experimental uncertainties. We consider MINOS, T2K, NOvA, as well as the upcoming DUNE, and present the respective statistical significance for distinguishing quantum behavior from classical scenarios at these long-baseline neutrino experiments. Among them, we find that T2K yields the most significant violation of classicality, at the level of ∼ 14$\textit{σ}$, with NOvA and projections for DUNE also resulting in a significance of more than 5$\textit{σ}$.

Murshed Alam

Vedran Brdar

Dibya Chattopadhyay

Exploring quantumness at long-baseline neutrino experiments

We study a dark gauge boson $\textit{Z′}$ that exclusively couples to the QCD gluons through higher dimensional operators. These operators are generated from integrating out of heavy ultraviolet resonances carrying both QCD and dark gauge charges. With $\textit{SU}$(3) gauge invariance, charge and parity symmetries preserved, we find that the leading effective operators are restricted to have the form of $\textit{Z′GGG}$ and $\textit{Z′Z′GG}$ at dimension-eight, which can naturally render the $\textit{Z′}$ particle long-lived, and serve as a viable dark matter candidate. We investigate the phenomenology of these operators with both collider experiments and cosmological observation, without and with the assumption that this dark gauge boson plays the role of the dominant dark matter component. For an unstable $\textit{Z′}$, we show that depending on its lifetime, it can be probed by various observables up to ultraviolet physics scale around 10 GeV. For $\textit{Z′}$ being dark matter, we find that $$ {m}_{Z^{\prime }}\gtrsim 1 $$ TeV is consistent with the thermal freeze-out scenario. In contrast, in the freeze-in scenario, the extremely small couplings leave the relevant parameter space largely unconstrained by current experiments.

Xiaoyong Chu

Qiyuan Gao

Hongkai Liu

Teng Ma

Chengjie Yang

Heavy long-lived dark vector via a gluonic portal

Germany

Marzieh Bahmani

Alessandro Guida

Maral Khandan

Heiko Lacker

Anupama Reghunath

Erratum to: Techniques for mass peak reconstruction in searches for long-lived heavy neutral leptons decaying to a lepton and a $$\rho $$ meson

In this work, we compute the graviton mediated scattering amplitude of a massive spin-2 Fierz-Pauli field with various other massive spin fields, and in the nonrelativistic limit, find out the corresponding two-body gravitational potentials. The massive spin-2 field does not represent gravity here. The theory of gravity is taken to be the usual massless general relativity, and the massive spin-2 field is taken as a test quantum field coupled to gravity via the standard minimal prescription. We first compute the tree level 2-2 scattering of a massive spin-2 field with massive scalar, spin-1, and spin-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></math> fields with one graviton exchange. Leading Newton potential, as well as the subleading spin or polarization dependent terms at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mi>G</mi><mo stretchy="false">)</mo></math> have been computed. We also consider the next to the leading order [<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mi>G</mi><mn>2</mn></msup><mo stretchy="false">)</mo></math>] scattering of the massive spin-2 field with a massive scalar, and demonstrate the spin independent, spherically symmetric leading part of the two body gravitational potential. The present paper can be considered as an attempt to compute the gravitational potential in the context of a higher spin field theory.

India

Avijit Sen Majumder

Sourav Bhattacharya

Scattering of massive spin-2 field via graviton exchanges with different spin fields and the long range gravitational potential

A new measurement of the $^{65}$Cu($\textit{γ}$, $\textit{n}$)$^{64}$Cu photoneutron cross section is performed using quasi-monoenergetic, tunable $\textit{γ}$-ray beams produced at the Shanghai Laser Electron Gamma Source (SLEGS). The energy spectrum of the SLEGS $\textit{γ}$-ray beams incident on the isotopically enriched $^{65}$Cu target is monitored using a BGO detector, while the photoneutron yields are determined with a moderated $^{3}$He detection array with high and flat efficiency. Within the energy range of $10.1 \le E_\gamma \le 17.6$ MeV, the measured $\sigma(E_\gamma)$ data have an uncertainty of $\lesssim 4$ %, and a pronounced giant-dipole peak is observed at $E_\gamma \simeq 16.65$ MeV with a maximal cross section of $\sigma_{\text{max}} \simeq 137$ mb. These photoneutron data are compared with previous experimental results and are employed to extract the $\textit{γ}$-ray strength function of $^{65}$Cu above the neutron threshold. Furthermore, we calculate the radiative neutron capture cross sections and astrophysical reaction rates for $^{64}$Cu, which is a short-lived intermediate nucleus whose reaction rate controls the local abundance distribution in the weak $\textit{s}$-process. It is found that the calculated $^{64}$Cu($\textit{n,}$ $\textit{γ}$)$^{65}$Cu data have an overall agreement with ENDF/B-VIII.0, JEFF-3.3, and TENDL-2023 evaluations, and the corresponding astrophysical reaction rates are consistent with those reported in the JINA REACLIB database.

Yu-Long Shen

Zi-Rui Hao

Qian-kun Sun

Hong-Wei Wang

Long-Xiang Liu

Hang-Hua Xu

Yue Zhang

Sheng Jin

Kai-Jie Chen

Meng-Die Zhou

Zhen-Wei Wang

Meng-Ke Xu

Xiang-Fei Wang

Chang Yang

Pu Jiao

Chun-Wang Ma

Gong-Tao Fan

Zhi-Cai Li

Wen Luo

Photoneutron cross section measurements on $^{65}$Cu: toward understanding ($\textit{n,}$ $\textit{γ}$) cross sections relevant to weak $\textit{s}$-process nucleosynthesis * This work was supported by the National Key Research and Development Program (2023YFA1606901), and the National Natural Science Foundation of China (12575133, 12505144)

In the type-I two-Higgs-doublet model, the pseudoscalar $\textit{A}$ can act as a long-lived particle (LLP) for sufficiently large values of tan $\textit{β}$. At the LHC, the $\textit{A}$ particles are predominantly produced in pairs through $\textit{pp}$ → $\textit{W}$ /$\textit{Z}$ → $\textit{H}$ /$\textit{H A}$, with subsequent decays $\textit{H}$ /$\textit{H}$ → $\textit{W}$ /$\textit{Z A}$. For the mass range of our interest, 10 GeV ≲ $\textit{m}$ ≲ 100 GeV, the pseudoscalar $\textit{A}$ typically decays into a pair of bottom quarks after traveling a macroscopic distance from its production point, giving rise to displaced-vertex (DV) signatures inside the inner detector. We perform Monte Carlo simulations of signal events with DVs plus jets, and assess the discovery prospects of $\textit{A}$ as an LLP at the ATLAS and CMS experiments. Our findings show that a substantial portion of the parameter space with $\textit{m}$ > 10 GeV has already been excluded by LHC Run-2 data, while the high-luminosity LHC will be able to probe broader regions.

Lei Wang

Zeren Wang

Haotian Xu

Probing a long-lived pseudoscalar in type-I 2HDM with displaced vertices and jets at the LHC