On December 2, the PADME run 2 completed the data taking session at the LNF accelerators complex.

PADME (Positron Annihilation into Dark Matter Experiment) is an INFN experiment searching for dark matter and in particular the dark photon. Some theoretical models allow the existence of a force bridging our world and dark matter. This so-called “fifth force” would be associated to a mediator particle named dark photon, a particle similar to the ordinary photon, mediator of the electromagnetic force, but with a non-zero mass.

To produce dark photons PADME uses the annihilation between positrons, created and accelerated up to 500 MeV (an energy approximately 1000 times their mass) by the LINAC and the electrons in a thin diamond target (1/10 mm thick).

During the 79 days of data taking 5*1012 positrons impinged on the diamond target.

Many of these positrons passed through the target with no interactions whereas a part of them smashed the electrons of carbon atoms that form diamond producing electrons, positrons and photons. The dark photon could hide in these interactions.

The data analysis is now starting and will shed light on the evidence (or exclusion) of dark photons existence at these energies. In particular data will allow to define constraints on the dark photon mass and on its capability to interact with the known particles and forces.

Run 2 results will enrich the data set available in literature in this energy range derived from alternative methods used in other experiments to produce the dark photon that are via electron-positron beams collision and mesons decays.

Paolo Valente, co-spokesperson of the experiment: “We are very proud for having completed this data taking during this pandemic, thanks to the effort of the Italian groups of the collaboration and the commitment of our young students, Phd student and Post docs”.

Even in Physics the concept of circular economy works: particle collisions are mines where to study different subnuclear physics areas. This is applies to PADME. The data collected during the past months will provide precious information also related to another field, quantum electrodynamics QED. The same collisions between electrons and positrons that could create the dark photon, produce final states populated by 2 or 3 photons as well. These processes are known and studied in a theoretical framework but either no data exist at these energies or are very scarce. Run 2 data will help in the comprehension of these processes in an unexplored regime.

The hunt for dark matter at LNF is not yet over. The collaboration is already looking to the future of PADME with a project that will exploit the possibility of having a more intense positron beam, extracted from one of the DAFNE ring.

The PADME collaboration is composed of researchers from LNF, INFN Lecce unit, INFN Torino unit and Politecnico di Torino, INFN Roma 1 e Roma 2 units, University of Sofia, MTA Atomki, Debrecen, Cornell University and College of William and Mary, Williamsburg.