Detectors for axion like particle searches – DALPS

DALPS has the ambition to create a new consortium gathering Micromegas, Transition edge sensors (TES), Metallic Magnetic Calorimeters (MMC) and Silicon Drift Detectors (SDD) that will improve the sensitivity of X-ray detectors in the context of the International AXion Observatory (IAXO). IAXO’s main goal is to look for new hypothetical fundamental particles called axions coming from the Sun. The detectors developed in DALPS will be installed in BabyIAXO, an intermediate experimental stage of IAXO, with already relevant physics reach and with potential for discovery.

Axions are one of the most promising solutions in order to explain the absence of Charge-Parity symmetry violation in the strong interaction. More generic axion-like particles (ALPS) are invoked in a number of cosmological and astrophysical scenarios. These neutral, very light particles interact so weakly with ordinary matter that they could contribute to dark matter. A number of long standing astrophysical anomalies could also be solved by the presence of axions.
Most of the axions search techniques rely on their interaction with photons via the conversion of axions into photons (and vice versa) in the presence of electromagnetic fields. Helioscopes search for axions produced in the solar core by the conversion of plasma photons into axions giving rise to a solar axion flux at the Earth surface with a distribution around 1-10 keV.

IAXO will achieve a sensitivity on the axion coupling 1-1.5 orders of magnitude better than the best limits obtained by CAST using a large scale multi-bore superconducting magnet. Each bore will be equipped with X-ray optics coupled to low background detectors. The sensitivity gain is translated into a factor ~20 in terms of the axion-photon coupling. In order to reach that, the required levels of background are extremely challenging: 10-7 counts keV-1 cm-2 s-1, a factor 10 better than current levels. The objective of DALPS is to build high sensitivity, low background X-ray detectors, key components for the sensitivity of a helioscope, for the babyIAXO Technical Design Report.

Micromegas detectors are the baseline technology for the X-ray detectors of babyIAXO. However, other technologies like TES, MMC and SDD show a lower energy threshold and better energy resolution. Yet, their background level in our region of interest has never been studied. The four technologies will be optimized in terms of efficiency, background level, energy resolution and threshold. The SOLEIL synchrotron will be available to evaluate the performance at different energies. The advantages of proposing four technologies are twofold: (i) a sub-keV energy threshold will permit the study of the fine structures in the axion spectrum and will extend the physics case of babyIAXO, allowing axion precision measurements in case of discovery and (ii) if equivalent performances were achieved, the ideal configuration for babyIAXO, and eventually IAXO, would be a combination of them as in case of signal, this configuration would minimize systematic effects and would reinforce the discovery claim. Moreover, a study on how to optimise IAXO sensitivity in the high mass regime (ma~eV) will be carried out taking into account the complementarity of helioscopes and crystal detector searches.

Theoretically motivated axions and ALPS are reachable by current or near future experimental realizations triggering an increasing interest for the detection of such particles and their signatures. A large part of the parameter space explored by IAXO is not attainable by any other experimental technique. DALPS will contribute to the feasibility of babyIAXO and IAXO in a context where 18 worldwide institutions, including CERN and DESY, have shown their support. DALPS will allow to establish a visible French contribution in an experiment that will play a prominent role in the low energy frontier in the next years.