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The PADME experiment, at the Laboratori Nazionali di Frascati (LNF) of INFN, is designed to be sensitive to the production of a low mass gauge boson A ′ of a new U ( 1 ) symmetry holding for dark particles. The DA Φ NE Beam-Test Facility of LNF is providing a high intensity, mono-energetic positron beam impacting on a low Z target to provide e + e − annihilations, where the dark photon can be produced along with an ordinary photon. Simulation studies predict a sensitivity on the interaction strength ( e 2 parameter) down to 10−6, in the mass region 1 MeV/ c 2 M A ′ 23.7 MeV/ c 2 , for one year of data taking with a 550 MeV beam. In 2018 the first run will take place, and early data will give the opportunity to compare the detector performance with the design parameters. Right now, an intense activity is taking place to install and commission the PADME experimental apparatus on site.

The PADME experiment is under construction at the Frascati National Laboratories of INFN to explore the coupling between ordinary and dark matter. This will be done through the detection of Standard Model photons produced in the reaction e + e − → γ A ′ . The measurement of the photons 4-momentum allows to reconstruct the missing mass spectrum of this process, where the A ′ could appear as a peak. To this purpose, two independent electromagnetic calorimeters are used. The layout of the two detectors, and their expected performance measured during prototypes tests, are here presented.

PADME (Positron Annihilation into Dark Matter Experiment) is an experiment that will search for the production of a dark photon A ′ from the annihilation of a positron beam on a thin diamond target. It will use the 550 MeV positron beam of the Beam Test Facility (BTF) of the Laboratori Nazionali di Frascati (LNF) of INFN. According to the PADME design, the region of sensitivity is M A ′ ≤ 23.7 MeV/c 2 and ϵ 2 > 1 0 − 6 , where M A ′ and ϵ are the dark photon mass and the A ′ γ mixing parameter. This paper presents the status of the active diamond target, in particular the assembly of two 32 channel targets of polycrystalline Chemical Vapor Deposition (CVD) diamond, one with graphitic strips and another with traditional CrAu strips.

The PADME (Positron Annihilation into Dark Matter Experiment) will search for the production of a dark photon from positron–electron annihilation e + e − → γ A ′ using the positron beam of the Beam Test Facility (BTF) of the DA Φ NE Linac at Laboratori Nazionali di Frascati (LNF). This paper presents the status of the charged particle veto system which is necessary to tag bremsstrahlung processes which are the main source of background events.

The PADME charged particle detector system should detect positrons and electrons with efficiency better than 99 {\%} and time resolution below 1 ns. The system hosts about 200 readout electronics channels whose operation has to be verified and commissioned. A custom based test system allowing to perform qualitative check of the produced frontend electronics has been developed and was used to test a total of 256 channels. The obtained time resolution was found to be consistent with the requirements and better than 500 ps for all the channels.

The PADME experiment at the Laboratori Nazionali di Frascati of the INFN searches for a hypothetical dark photon A ′ , produced in the annihilation between a positron of a beam with an electron of a target. The target is an active component of the experiment; it consists of a thin and large size diamond detector with a pattern of graphitic strips on both sides acting as ohmic electrodes for detector polarization and signal readout. In this paper the operation and performance of the active diamond target, as observed in the first PADME physics run, are reported.

Deposition of Au nanoparticles (NPs) through UV ultra-short-pulse laser ablation in vacuum is a methodology suitable for obtaining high purity supported plasmonic NPs with a superb adherence to both planar and patterned substrates. Furthermore, the peculiarity that upon sub-picosecond laser irradiation NPs form directly within the target leads to narrow and controlled size-distribution. While extensive literature theoretically models phase changes and pressure relaxation of metal targets under sub-picosecond irradiation, the evolution of the nanostructured deposit through different ablation regimes is poorly documented experimentally. In this paper, besides modeling the temporal evolution of electron and lattice temperature following sub-picosecond laser pulse irradiation of Au bulk at the threshold ablation fluence (0.1 J/cm2), we report an accurate statistical, morphological and structural characterization of the AuNP distributions as a function of the laser fluence tuned from 0.1 to 3 J/cm2 to drive the target through two ablation regimes. The occurrence of photomechanical spallation and phase explosion at low and high fluence, respectively, is correlated with the evolution of the NP deposits, which are discussed by providing a physical insight in the interplay between fluence-driven ablation regimes of the target, arrangement kinetics of the deposited species (NPs and vapour species) and (crystalline or amorphous) phase of the NPs. This knowledge is key for controlling the surface plasmon resonance response of AuNPs depending on the designed application.

The ablation of a metal target at laser energy densities in the range of 1–10 TW/cm2 leads to the generation of nanoparticles (NP) of the ablated material. This aspect is of particular interest if the immobilization of NPs on three-dimensional (3D) substrates is necessary as for example in sensing applications. In this work the deposition of Au NP by irradiation of a Au bulk target with a sub-picosecond laser beam (500 fs; 248 nm; 10 Hz) on 2D (silica and Si(100)) and 3D substrates (silica nanowire forests) is reported for different number of laser pulses (500, 1000, 1500, 2000, 2500). A uniform coverage of small Au NPs (with a diameter of few nm) on both kinds of substrates has been obtained using a suitable number of laser pulses. The presence of spherical droplets, with a diameter ranging from tens of nm up to few μm was also detected on the substrate surface and their presence can be explained by the weak electron-phonon coupling of Au. The optical characterization of the samples on 2D and 3D substrates evidenced the surface plasmon resonance peak characteristic of the Au NPs although further improvements of the size-distribution are necessary for future applications in sensing devices.

In this paper, we report on the current status of the different configurations that have been suggested for the preparation of metallic and superconducting photocathodes (MPs and SCPs, respectively) by pulsed laser deposition. These strategic devices are used in the new generation of free-electron lasers and in research and development into plasma-based accelerators. To date, three different types of photocathodes have been used: conventional, hybrid and non-conventional configurations. In the case of the conventional configuration, the photocathode consists of a metallic bulk, typically Cu for normal conducting radio-frequency guns and Nb for superconducting radio-frequency guns. In the hybrid configuration, a thin emitting film with high photoemission performance, like Y or Mg, is located in the centre of the Cu flange of the photoinjector. For hybrid SCPs, the emitting material is a thin film of Pb, which has a quantum efficiency higher than that of Nb. Non-conventional configurations of MPs and SCPs have recently been engineered that consist respectively of a Y disc partially covered by a film of Cu and a Pb disc partially covered by a film of Nb. The central surfaces of the Y and Pb discs are not coated, thus providing an emitting area of the materials with higher quantum efficiency. These last devices inserted into a RF gun offer both the photoemission properties and work function of Y and the advantages of Cu in the case of MPs. In the case of SCPs, this new approach offers the relatively high photo-emissive properties of Pb and at the same time preserves all the advantages of Nb as a superconducting material.