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The PADME Experiment on Dark Matter

The Positron Annihilation into Dark Matter Experiment (PADME) is about to begin collecting data at the Frascati Lab of the Italian National Institute for Nuclear Physics to identify dark photons, a hypothetical particle that is similar to the photons of electromagnetic waves but possesses a small mass.

The PADME Experiment is based on the hypothesis that dark matter is sensitive to a new type of force that is not one of the four fundamental forces that we know about (gravitation, electromagnetism, and strong and weak nuclear forces). This new force should be associated with a messenger, the dark photon. This hypothesis is part of some of the theoretical models describing dark matter, which physicists have been trying to identify for years.

“The study of dark matter,” explains Mauro Raggi, experiment spokesperson and a researcher at Sapienza and the National Institute for Nuclear Physics, “is one of the most fascinating frontiers of research in fundamental physics. We do not know what it is made of, but we do know that it is constituted by something other than the particles that compose ordinary matter like protons, neutrons and electrons.”

“Over the coming weeks, PADME will begin gathering data,” points out Paolo Valente, experiment co-spokesperson, “and will immediately begin research on the identification of dark photons.”

PADME will employ a minute, but extremely precise measuring apparatus that will be able to detect the production of dark photons through the collision of electrons and anti-electrons, also known as positrons. The experiment will be conducted in the experimental structure test hall (BTF) at the National INFN Labs in Frascati that will accelerate positrons by “shooting” them against a diamond target. Interacting with atomic electrons, the positrons should produce dark photons together with a visible photon.

In order to function correctly, PADME requires a magnetic field that will be created by a magnet developed by the CERN Super Proton Synchrotron. The synchrotron’s calorimeter, which includes ca. 600 inorganic scintillating crystals, will provide a precise measurement of the characteristics of the visible photon. This will provide precious information on the existence and mass of the dark photon.

The PADME Experiment is an international collaboration that also involves researchers at the MTA Atomki Institute in Debrecen, in Hungary, which has already conducted experiments on dark photons, and the University of Sophia, in Bulgaria, that will be in charge of the bar scintillation detectors. Cornell University, Iowa University and the William and Mary College are also collaborating on the project.


Technology Focus

The PADME target, calorimeter and beam monitors are the result of innovative technologies that have been developed in synergy with industrial and research partners (INFN and Matter Structure Researchers).

The PADME target is constituted by a tenth-of-a-millimetre artificial poly-crystalline diamond membrane, an innovative sensor mechanism that was developed by industrial partners in close collaboration with INFN Labs. Moreover, the collaboration between INFN Researchers and Matter Physicists led to the development of a new technique for the production of electrodes by irradiating the diamond surface with laser light and producing stripes of conductive graphite.

The calorimeter is an example of how technology developed by basic research can have important results in a range of fields with a great social impact. In fact, the calorimeter was produced thanks to a technology developed for Particle Physics, which, thanks to its characteristics (granular, high efficiency and density) was employed in medical diagnostics, such as Positron Emission Tomography (PET).

The beam monitor was developed thanks to a silicon pixel technology known as TimePix, developed at CERN in collaboration with Czech Company Advacam that is applying this technology to industrial applications.


For further information

Mauro Raggi
Department of Physics, Sapienza University