Search

The Positron Annihilation to Dark Matter Experiment (PADME) uses the positron beam of the DA$\Phi$NE Beam-Test Facility, at the Laboratori Nazionali di Frascati (LNF) to search for a Dark Photon $A'$. The search technique studies the missing mass spectrum of single-photon final states in $e^+e^-\rightarrow A'\gamma$ annihilation in a positron-on-thin-target experiment. This approach facilitates searches for new particles such as long lived Axion-Like-Particles, protophobic X bosons and Dark Higgs. This talk illustrated the scientific program of the experiment and its first physics results. In particular, the measurement of the cross-section of the SM process $e^+e^-\rightarrow \gamma\gamma$ at $\sqrt{s}$=21 MeV was shown., Comment: Fixed typos and updated gamma gamma results from preliminary ones to published ones. 6 pages, 6 figures, conference proceedings to be published in SciPost

To search for the production of a dark photon ($A^{\prime} $) in the process ${e}^{+}{e}^{-}\to A^{\prime} \gamma $, the PADME apparatus has been built athe INFN Laboratori Nazionali di Frascati. It is a small-scale detector consisting of an active target, a beam monitor system, a spectrometer to measure charged particle momenta in the range 50–400 MeV, a dipole magnet to deflect the primary positron beam out of the spectrometer and allow charged particle momentum analysis and an electromagnetic calorimetric system to detect signal and background photons produced in the annihilations with high accuracy. Each element has specific requirements that are stringent and sometimes at the limit of present technology. This proceeding will give an overview of each component and a description of the technical solutions implemented to accomplish the experiment needs. Results of the commissioning data taking, performed from October 2018 to February 2019, will be illustrated.

The PADME experiment will search for the $e^{+} e^{-} \rightarrow \gamma A^{\prime }$ process in a positron-on-target experiment, assuming a decay of the $A^{\prime }$ into invisible particles of the hidden sector. The 550-MeV positron beam of the DA $\Phi $ NE beam-test facility (BTF), at Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, will be used. The suppression of the background, due to bremsstrahlung emission from the beam positrons, requires highly efficient charged-particle detectors with optimized geometry. A fine-grained plastic scintillator veto composed of three stations operating in vacuum is proposed. Two stations, placed inside a dipole magnet with 0.6-T magnetic field, will also provide momentum measurement at the percent level. Different prototypes for the design of the detector elements, the photosensor, and the front-end electronics were studied with single electron beam at the DA $\Phi $ NE BTF to choose the optimal technologies and construction solutions. PADME is currently under construction, and it is planned to begin data collection in 2018. The design of the charged-particle vetoes and the test beam performance of the prototypes are reviewed.

The PADME experiment, at the Laboratori Nazionali di Frascati (LNF), in Italy, will search for invisible decays of the hypothetical dark photon via the process $e^+e^-\rightarrow \gamma A'$, where the $A'$ escapes detection. The dark photon mass range sensitivity in a first phase will be 1 to 24 MeV. We report here on measurement and simulation studies of the performance of the Small-Angle Calorimeter, a component of PADME's detector dedicated to rejecting 2- and 3-gamma backgrounds. The crucial requirement is a timing resolution of less than 200 ps, which is satisfied by the choice of PbF$_2$ crystals and the newly released Hamamatsu R13478UV photomultiplier tubes (PMTs). We find a timing resolution of 81 ps (with double-peak separation resolution of 1.8 ns) and a single-crystal energy resolution of 5.7%/$\sqrt{E}$ with light yield of 2.07 photo-electrons per MeV, using 100 to 400 MeV electrons at the Beam Test Facility of LNF. We also propose the investigation of a two-PMT solution coupled to a single PbF$_2$ crystal for higher-energy applications, which has potentially attractive features., Comment: 12 pages, 19 figures. v2: added section on radiation damage studies