At 10:00 on December 21st, the third data collection period of the PADME experiment came to an end.
The goal of PADME is to search for signals of new particles responsible for dark matter, the enormous amount of matter that is observed on a cosmic scale, but whose nature is still unknown. The search is carried out among the products of the annihilations of positrons (the antiparticles of electrons) produced by the Frascati linear accelerator, with the electrons of the atoms of a very thin diamond target. In comparison to previous PADME data taking, Run III was conceived to verify the existence of a new particle with a mass of approximately 17 MeV/c2 which was introduced to explain some anomalies highlighted by a nuclear physics experiment conducted at the ATOMKI laboratory of Debrecem, Hungary.
The particle, labelled X17, would be a metastable state decaying into an electron-positron pair (e+e−). If this particle exists, it should be possible to produce it in the annihilations of a positron beam with electrons from a target.
This is the goal of 2022 PADME data taking. After some modifications to the experimental apparatus made at the beginning of 2022, in July the beam configuration was studied. In fact, the measurement strategy envisages acquiring the data by varying the energy of the incident particles to “excite” the resonant production of the X17 particle. Together with colleagues from the accelerator division, we worked on the linear accelerator of the laboratory to establish the sequence of necessary operations. In early October, the collection of data useful for the analysis began. Overall, about 10 billion annihilation events were acquired for each of the 51 different positron energy values explored.
The amount of data collected is huge, and the data analysis will take several months, also because, given the stakes, it will have to be conducted with special care.
If PADME will observe signals from the X17 particle, these will finally be the first incontrovertible evidence of new phenomena that cannot be explained by the Standard Model of particle physics.