Search for Leptonic Decays of Dark Photons at NA62.

Dark photons are well motivated hypothetical dark sector particles that could account for observations that cannot be explained by the standard model of particle physics. A search for dark photons that are produced by an electron beam striking a thick tungsten target and subsequently interact in a 3 kiloton-scale neutrino detector in Yemilab, a new underground lab in Korea, is proposed. Dark photons can be produced by “darkstrahlung” or by oscillations from ordinary photons produced in the target and detected by their visible decays, “absorption” or by their oscillation to ordinary photons. By detecting the absorption process or the oscillation-produced photons, a world’s best sensitivity for measurements of the dark-photon kinetic mixing parameter of ϵ2> 1.5 × 10−13(6.1 × 10−13) at the 95% confidence level (C.L.) could be obtained for dark photon masses between 80 eV and 1 MeV in a year-long exposure to a 100 MeV–100 kW electron beam with zero (103) background events. In parallel, the detection of e+e− pairs from decays of dark photons with mass between 1 MeV and ∼86 MeV would have sensitivities of ϵ2> mathcal{O}left({10}^{-17}right)left(mathcal{O}left({10}^{-16}right)right) at the 95% C.L. with zero (103) background events. This is comparable to that of the Super-K experiment under the same zero background assumption.

The NA62 experiment at CERN, designed to study the ultra-rare decay K+ → π+νν¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ u \\overline{\ u} $$\\end{document}, has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to μ+μ− pairs is reported, based on a sample of 1.4 × 1017 protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV/c2.

A coupling of a dark photon A′ from a U(1)A′ with the standard model (SM) particles can be generated through kinetic mixing represented by a parameter ϵ. A non-zero ϵ also induces a mixing between A′ and Z if dark photon mass mA′ is not zero. This mixing can be large when mA′ is close to mZ even if the parameter ϵ is small. Many efforts have been made to constrain the parameter ϵ for a low dark photon mass mA′ compared with the Z boson mass mZ . We study the search for dark photon in e+e− → γA′ → γμ+μ− for a dark photon mass mA′ as large as kinematically allowed at future e+e− colliders. For large mA′, care should be taken to properly treat possible large mixing between A′ and Z. We obtain sensitivities to the parameter ϵ for a wide range of dark photon mass at planed e+e− colliders, such as Circular Electron Positron Collider (CEPC), International Linear Collider (ILC) and Future Circular Collider (FCC-ee). For the dark photon mass 20 GeV ≲ mA′ ≲ 330 GeV, the 2σ exclusion limits on the mixing parameter are ϵ ≲ 10−3-10−2. The CEPC with sqrt{s}=240 GeV and FCC-ee with sqrt{s}=160 GeV are more sensitive than the constraint from current LHCb measurement once the dark photon mass mA′ ≳ 50 GeV. For mA′ ≳ 220 GeV, the sensitivity at the FCC-ee with sqrt{s}=350 GeV and 1.5 ab−1 is better than that at the 13 TeV LHC with 300 fb−1, while the sensitivity at the CEPC with sqrt{s}=240 GeV and 5ab−1 can be even better than that at 13TeV LHC with 3ab−1 for mA′ ≳ 180 GeV. We also comment on sensitivities of e+e− → γA′ with dark photon decay into several other channels at future e+e− colliders.

We present the result of a search for inelastic boosted dark matter using the data corresponding to an exposure of 0.13 kton·year, collected by the ICARUS T-600 detector during its 2012–2013 operational period at the INFN Gran Sasso Underground National Laboratory. The benchmark boosted dark matter model features a multiparticle dark sector with a U(1)′ gauge boson, the dark photon. The kinetic mixing of the dark photon with the Standard Model photon allows for a portal between the dark sector and the visible sector. The inelastic boosted dark matter interaction occurs when a dark matter particle inelastically scatters with an electron in the ICARUS detector, producing an outgoing, heavier dark sector state which subsequently decays back down to the dark matter particle, emitting a dark photon. The dark photon subsequently couples to a Standard Model photon through kinetic mixing. The Standard Model photon then converts to an electron-positron pair in the detector. This interaction process provides a distinct experimental signature that consists of a recoil electron from the primary interaction and an associated electron-positron pair from the secondary vertex. After analyzing 4,134 triggered events, the search results in zero observed events. Exclusion limits are set in the dark photon mass and coupling (mX,ε) parameter space for several selected optimal boosted dark matter mass sets and cover previously unexplored parameter space. Published by the American Physical Society 2025

The NA48/2 and NA62 collaborations report on recent results, current status, and prospects of kaon physics at the CERN-SPS. The NA62 collaborations aims to measure the decay [Formula: see text] with an uncertainty of 10% or better. The NA62 detector and preliminary results from a pilot run in 2014 are presented. In addition, recent results of the NA48/2 collaboration are reported. A search for Dark Photons has been performed in [Formula: see text] decays via the kaon decays [Formula: see text] and [Formula: see text]. No dark photon signal was observed and new upper limits on the mixing parameter [Formula: see text] and the dark photon mass were computed. We also report the first observation of the kaon decay [Formula: see text].

Dark photons that are sufficiently light and/or weakly interacting represent a compelling vision of dark matter. Dark photon decay into three photons, which we call the dark photon trident, can be the dominant channel when the dark photon mass falls below the electron pair threshold and can produce a significant flux of x rays. We use 16 years of data from Interrnational Gamma-Ray Astro Physics Laboratory (INTEGRAL)/Spectrometer of INTEGRAL (SPI) to constrain sub-MeV dark photon decay, producing new worlds-best constraints on the kinetic mixing parameter for dark photon masses between 90 and 1022 keV, and comment on the potential for future x-ray observatories to discover the trident decay process.

Dark photons, hypothesized to be sufficiently light and/or weakly interacting, offer a compelling candidate for dark matter. Their decay into three photons, referred to as the "dark photon trident" process, becomes the dominant channel when the dark photon mass lies below the electron pair production threshold. This decay channel produces a significant flux of x-rays, presenting an opportunity for indirect detection. In this study, we analyze 16 years of x-ray data from INTEGRAL/SPI to investigate sub-MeV dark photon decay. By incorporating state-of-the-art astrophysical background modeling and accounting for the full one-loop decay amplitude, we achieve world-leading constraints on the kinetic mixing parameter for dark photon masses in the range of 61--1022 keV. These results represent a significant improvement over previous constraints, narrowing the parameter space for viable dark photon dark matter models. Furthermore, our findings highlight the potential of x-ray observatories to probe unexplored regions of parameter space and pave the way for future searches using next-generation instruments designed to detect faint astrophysical signals.

The Standard Model (SM) does not provide an information for 26% of dark matter of the universe. In the dark sector, dark matter is supposed to be linked with the hypothetical particles called dark photons that have similar role to photons in electromagnetic interaction in the SM. Besides astronomical observation, there are studies to find dark matter candidates using accelerators. In this paper, we searched for dark photons using future electron-positron colliders, including Circular Electron Positron Collider (CEPC)/CEPC, Future Circular Collider (FCC-ee)/Innovative Detector for Electron-positron Accelerator (IDEA), and International Linear Collider (ILC)/International Large Detector (ILD). Using the parameterized response of the detector simulation of Delphes, we studied the sensitivity of a double dark photon mode at each accelerator/detector. The signal mode is double dark photon decay channel, e+e− → A’A’, where A’ (dark photon with spin 1) decaying into a muon pair. We used MadGraph5 to generate Monte Carlo (MC) events by means of a Simplified Model. We found the dark photon mass at which the cross-sections were the highest for each accelerator to obtain the maximum number of events. In this paper we show the expected number of dark photon signal events and the detector efficiency of each accelerator. The results of this study can facilitate in the dark photon search by future electron-positron accelerators.

A dark sector may exist and interact with the Standard Model (SM) through the $U(1)$ kinetic mixing. Through this portal-type interaction, the dark photon from the dark sector couples to SM fermions, and may explain the discrepancy between experimental data and SM calculations on the muon anomalous magnetic moment, muon $g-2$. However, current searches for the dark photon impose stringent constraints on the mixing parameter $\varepsilon$ for various dark photon masses, excluding the favorite parameter space for muon $g-2$. In this paper, we study the case where a global $U(1)$ in the dark sector is spontaneously broken, resulting in a light pseudo-Goldstone, axion-like particle (ALP) a, which couples to the dark photon and SM photon. Through the dark photon–ALP–photon interaction, the dark photon may decay into a photon and an ALP when this channel is kinematically allowed. As a result, the experimental constraints on the dark photon change significantly, and the dark photon is able to explain the muon $g-2$ anomaly when its mass is heavier than 10 GeV.

The NA62 experiment at CERN Super Proton Synchrotron was designed to measure BR(K+ → π+νv¯) with an in-fight technique, never used before for this measurement. This decay is characterised by a very precise prediction in the Standard Model. Its branching ratio, which is expected to be less than 10−10, is one of the best candidates to indicate indirect effects of new physics beyond SM at the highest mass scales. NA62 result on K+ → π+νv¯ from the full 2016 data set is described.Also a search for an invisible dark photon A′ has been performed, exploiting the efficient photon-veto capability and high resolution tracking of the NA62. The signal stems from the chain K+ → π+π0 followed by π0 → A′γ. No significant statistical excess has been identified. Upper limits on the dark photon coupling to the ordinary photon as a function of the dark photon mass have been set, improving on the previous limits over the mass range 60 - 110 MeV/c2.

Searches for low mass CP-odd Higgs and dark photons at BaBar

One of the explanations for the recent EDGES-LOW band 21 cm measurements of a strong absorption signal around 80 MHz is the presence of an excess radio background to the Cosmic Microwave Background (CMB). Such excess can be produced by the decay of unstable particles into small mass dark photons which have a non-zero mixing angle with electromagnetism. We use the EDGES-LOW band measurements to derive joint constraints on the properties of the early galaxies and the parameters of such a particle physics model for the excess radio background. A Bayesian analysis shows that a high star formation efficiency and X-ray emission of 4–7 × 1048 erg per solar mass in stars are required along with a suppression of star formation in halos with virial temperatures ≲ 2 × 104 K. The same analysis also suggests a 68 percent credible intervals for the mass of the decaying dark matter particles, it's lifetime, dark photon mass and the mixing angle of the dark and ordinary photon oscillation of [10-3.5, 10-2.4] eV, [101.1, 102.7] × 13.8 Gyr, [10-12.2, 10-10] eV and [10-7, 10-5.6] respectively. This implies an excess radio background which is ≈ 5.7 times stronger than the CMB around 80 MHz. This value is a factor ∼ 3 higher than the previous predictions which used a simplified model for the 21 cm signal.

The Heavy Photon Search (HPS) experiment in Hall-B at Jefferson Lab will search for new heavy vector boson(s), aka "heavy photons", in the mass range of 20 MeV/c2 to 1000 MeV/c2 using the scattering of high energy, high intensity electron beams off a high Z target. The proposed measurements will cover the region of parameter space favored by the muon g-2 anomaly, and will explore a significant region of parameter space, not only at large couplings (α′/α > 10−7), but also in the regions of small couplings, down to α′/α∼10−10. The excellent vertexing capability of the Si-tracker uniquely enables HPS to cover the small coupling region. Also, HPS will search for heavy photons in an alternative to the e+e− decay mode, in the heavy photon's decay to μ+μ−.

A search for events with a dark photon produced in association with a dark Higgs boson via rare decays of the standard model Z boson is presented, using 139 fb^{-1} of sqrt[s]=13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron Collider. The dark boson decays into a pair of dark photons, and at least two of the three dark photons must each decay into a pair of electrons or muons, resulting in at least two same-flavor opposite-charge lepton pairs in the final state. The data are found to be consistent with the background prediction, and upper limits are set on the dark photon's coupling to the dark Higgs boson times the kinetic mixing between the standard model photon and the dark photon, α_{D}ϵ^{2}, in the dark photon mass range of [5, 40]GeV except for the ϒ mass window [8.8, 11.1]GeV. This search explores new parameter space not previously excluded by other experiments.

The vector $U$-bosons, or so called 'dark photons', are one of the possible candidates for the dark matter mediators. We present a procedure to derive theoretical constraints on the upper limit of kinetic mixing parameter $\epsilon^2(M_U)$ from heavy-ion as well as $p+p$ and $p+A$ dilepton data from SIS to LHC energies. Our study is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which reproduces the measured dilepton spectra in $p+p$, $p+A$ and $A+A$ collisions well. In addition to the different dilepton channels originating from interactions and decays of ordinary Standard Model matter particles (mesons and baryons), we incorporate in the PHSD the decay of hypothetical $U$-bosons to dileptons, $U \to e^+ e^-$, where the $U$-bosons themselves are produced by the Dalitz decay of pions, $\eta$-mesons, Delta resonances as well as by vector meson and $K^+$ decays. This analysis provides the upper limit on the $\epsilon^2(M_U)$ and can also help to estimate the requested accuracy for future experimental searches of 'light' dark photons by dilepton experiments.