Speaker
Prof.
Patrick Achenbach
(JGU Mainz)
Description
At the MESA accelerator in Mainz, Germany, the parasitic electron beam-dump experiment DarkMESA has a powerful discovery potential for dark sector particles in the light mass range. The possible existence of such light dark matter (LDM) is a candidate explanation for the long-standing dark matter problem.
With 10 000 hours of operation time scheduled for P2 beam experiment at MESA, the dump of the external 150 $\mu$A beam could act as a strong source of a LDM beam. LDM would be produced copiously in the relativistic electron-nucleus collisions taking place in the dump if it couples to electrons via vector mediators, called dark photons. After production, LDM particles could be detected within a shielded detector down-stream of the dump. A large advantage is provided by the boost at which particles are produced by the beam, allowing an improved reach at low masses. Moreover, such a search is unique since it can probe at the same time both the dark photon production and the LDM interaction. DarkMESA will benefit from the beam energy being below pion production threshold, producing very little beam-related backgrounds, and the very stable and continuous beam conditions necessary for the P2 experiment.
The DarkMESA detector will be constructed from total absorbing calorimeters made of high-density Cherenkov radiators. Advantages are their speed and relatively low sensitivity to background neutrons. In order to establish the anticipated performance of such calorimeters experimentally, measurements of detector responses over a range of electron energies relevant for LDM detection down to 5 MeV were performed. PbF$_2$ and SF5 lead glass detectors proofed to be well suited. The first phase of DarkMESA will employ available PbF$_2$ crystals for building a (1 x 1 x 0.13) m$^3$ detector of 1200 kg mass. This calorimeter will be arranged in sub-modules of 5 x 5 crystals. In a 2nd phase, additional calorimeters will be constructed from Pb glass blocks: a first prototype with a volume of 0.15 m$^3$ and a mass of 600 kg is already under construction. The completed Phase-2 calorimeters will comprise 1 m$^3$ volume and a mass of 4100 kg. A final active volume of above 10 m$^3$ is envisaged.
Simulation studies were performed that explored the parameter space of possible dark photon masses and couplings, assuming realistic electron beam energy and angular distributions as well as different detector acceptances and efficiencies. They show that DarkMESA is complementary to experiments at proton beam facilities and reopens the door to regions of the parameter space excluded by searches for dark photon decays into electrons or muons. The studies indicate that DarkMESA has the potential to be sensitive to the LDM thermal relic targets, that are predicted by the annihilation cross sections for reproducing today's dark matter density.
Summary
At the MESA accelerator in Mainz, Germany, the parasitic electron beam-dump experiment DarkMESA is under construction. It has a powerful discovery potential for dark sector particles in the light mass range. The detector will be constructed from calorimeters made of the high-density Cherenkov radiators PbF$_2$ and lead glass.
Primary author
Prof.
Patrick Achenbach
(JGU Mainz)
Co-authors
Prof.
Achim Denig
(JGU Mainz)
Prof.
Frank Maas
(JGU Mainz)
Dr
Harald Merkel
(JGU Mainz)
Dr
Luca Doria
(JGU Mainz)
Mr
Mirco Christmann
(JGU Mainz)
Mr
Paul Burger
(JGU Mainz)
Dr
Sebastian Baunack
(JGU Mainz)
