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We address the radio frequency (RF) cavity experiment for probing dark photons, which is a modification of the light-shining-through-thin-wall (LSthinW) setup with a relatively thin conducting barrier between a cylindrical emitter and a hollow receiver. The experimental facility allows for the effective probing of dark photons even in the off-shell regime, i.e., when the dark photon mass exceeds the driving frequency of the emitter cavity, which is pumped by an electromagnetic mode. We compare the sensitivity of two specific setup configurations: (i) two adjacent cylindrical cavities placed end-to-end with an end-cap separating them, and (ii) a nested geometry in which the cylindrical receiver is encapsulated within the emitter. We demonstrate that, for a certain range of dark photon masses, the nested configuration with the TM 010 pump mode can provide enhanced sensitivity compared to an adjacent emitter setup. Remarkably, for the TE 011 pump mode, both the nested and adjacent cavity configurations can yield comparable expected reaches for the specific geometry type.

A bstract We address production of massive axion-like particles by two electromagnetic modes inside a superconducting radio-frequency (SRF) cylindrical cavity. We discuss in detail the choice of pump modes and cavity design. We numerically compute time-averaged energy density of produced axion field for various cavity modes and wide range of axion masses. This allows us to estimate optimal conditions for axion production within a cavity. In addition, we consider photon regeneration process initiated by produced axion field in a screened radio-frequency cavity and derive constraints in parameter space ( g aγγ , m a ) for different choice of pump modes.

We report the results of a search for a new vector boson (A′) decaying into two dark matter particles χ1χ2 of different mass. The heavier χ2 particle subsequently decays to χ1 and an off-shell Dark Photon A′∗→e+e-. For a sufficiently large mass splitting, this model can explain in terms of new physics the recently confirmed discrepancy observed in the muon anomalous magnetic moment at Fermilab. Remarkably, it also predicts the observed yield of thermal dark matter relic abundance. A detailed Monte-Carlo simulation was used to determine the signal yield and detection efficiency for this channel in the NA64 setup. The results were obtained re-analyzing the previous NA64 searches for an invisible decay A′→χχ¯ and axion-like or pseudo-scalar particles a→γγ. With this method, we exclude a significant portion of the parameter space justifying the muon g-2 anomaly and being compatible with the observed dark matter relic density for A′ masses from 2me up to 390 MeV and mixing parameter ε between 3×10-5 and 2×10-2.

Recently, the ATOMKI experiment has reported new evidence for the excess of e + e - events with a mass ∼ 17 MeV in the nuclear transitions of 4 He, that they previously observed in measurements with 8 Be. These observations could be explained by the existence of a new vector X 17 boson. So far, the search for the decay X 17 → e + e - with the NA64 experiment at the CERN SPS gave negative results. Here, we present a new technique that could be implemented in NA64 aiming to improve the sensitivity and to cover the remaining X 17 parameter space. If a signal-like event is detected, an unambiguous observation is achieved by reconstructing the invariant mass of the X 17 decay with the proposed method. To reach this goal an optimization of the X 17 production target, as well as an efficient and accurate reconstruction of two close decay tracks, is required. A dedicated analysis of the available experimental data making use of the trackers information is presented. This method provides independent confirmation of the NA64 published results [ 1 ], validating the tracking procedure. The detailed Monte Carlo study of the proposed setup and the background estimate show that the goal of the proposed search is feasible.

A bstract In light of the Higgs boson discovery and other results of the LHC we re-consider generation of the baryon asymmetry in the split Supersymmetry model with an additional singlet superfield in the Higgs sector (non-minimal split SUSY). We find that successful baryogenesis during the first order electroweak phase transition is possible within a phenomenologically viable part of the model parameter space. We discuss several phenomenological consequences of this scenario, namely, predictions for the electric dipole moments of electron and neutron and collider signatures of light charginos and neutralinos.

A bstract Thermal light dark matter (LDM) with particle masses in the 1 MeV–1 GeV range could successfully explain the observed dark matter abundance as a relic from the primordial Universe. In this picture, a new feeble interaction acts as a “portal” between the Standard Model and LDM particles, allowing for the exploration of this paradigm at accelerator experiments. In the last years, the “missing energy” experiment NA64 e at CERN SPS (Super Proton Synchrotron) has set world-leading constraints in the vector-mediated LDM parameter space, by exploiting a 100 GeV electron beam impinging on an electromagnetic calorimeter, acting as an active target. In this paper, we report a detailed description of the analysis of a preliminary measurement with a 70 GeV/c positron beam at NA64 e , performed during summer 2023 with an accumulated statistics of 1 . 596 × 10 10 positrons on target (hereafter referred to as e + OT). This data set was analyzed with the primary aim of evaluating the performance of the NA64 e detector with a lower energy positron beam, towards the realization of the post-LS3 program. The analysis results, other than additionally probing unexplored regions in the LDM parameter space, provide valuable information towards the future NA64 e positron campaign.

Decays of light pseudoscalar mesons play an important role in the search for dark matter signals in fixed-target experiments. The intermediate vector meson state is shown to be of importance in the analysis of dark photon physics in the decays of neutral mesons. Constraints on the dark photon model for the optimistic statistics of the NA64 experiment with a beam of negative pions are presented.

Millicharged particles emerge as compelling candidates in numerous theoretically well-motivated extensions of the Standard Model. These hypothetical particles, characterized by an electric charge that is a small fraction of the elementary charge, have attracted significant attention in contemporary experimental physics. Their potential existence motivates dedicated search strategies across multiple experimental platforms, leveraging their distinctive electromagnetic interactions while evading conventional detection methods. In the present paper we estimated the projected sensitivity of fixed-target experiments, specifically NA64 μ and LDMX, to the parameter space of millicharged particles. For the NA64 μ experiment, with an anticipated muon flux of MOT ≲ 10 14 , our analysis reveals a detectable mass window of 10 MeV ≲ m χ ≲ 150 MeV and charge parameter range 10 - 4 ≲ ϵ ≲ 7 × 10 - 4 . This sensitivity arises from the bremsstrahlung-like missing energy signature μ N → μ N γ ∗ ( → χ χ ¯ ) . Furthermore, we evaluate the discovery potential of the LDMX facility, considering its projected electron beam statistics, EOT ≲ 2 × 10 16 , and energy, E e ≃ 8 GeV . Our results demonstrate that LDMX can probe heavier MCPs in the mass range 250 MeV ≲ m χ ≲ 400 MeV , with sensitivities reaching 10 - 3 ≲ ϵ ≲ 1.5 × 10 - 3 . This parametric window can be accessible through the distinctive invisible decay channel ρ → χ χ ¯ , where ρ -meson photo-production γ N → N ρ plays a pivotal role.

We address the radio frequency (RF) cavity experiment for probing dark photons, which is a modification of the light-shining-through-thin-wall (LSthinW) setup with a relatively thin conducting barrier between cylindrical emitter and hollow We address the radio frequency (RF) cavity experiment for probing dark photons, which is a modification of the light-shining-through-thin-wall (LSthinW) setup with a relatively thin conducting barrier between a cylindrical emitter and a hollow receiver. The experimental facility allows for the effective probing of dark photons even in the off-shell regime, i.e., when the dark photon mass exceeds the driving frequency of the emitter cavity, which is pumped by an electromagnetic mode. We compare the sensitivity of two specific setup configurations: (i) two adjacent cylindrical cavities placed end-to-end with an end-cap separating them, and (ii) a nested geometry in which the cylindrical receiver is encapsulated within the emitter. We demonstrate that, for a certain range of dark photon masses, the nested configuration with the \\(TM_010\\) pump mode can provide enhanced sensitivity compared to an adjacent emitter setup. Remarkably, for the \\(TE_011\\) pump mode, both the nested and adjacent cavity configurations can yield comparable expected reaches for the specific geometry type.