Dark-matter detector

A European research team has prototyped a ‘scintillating bolometer’, a device that will be used to detect dark matter of the universe.



The prototype was developed by researchers from the University of Zaragoza (UNIZAR) in Spain and the Institut d’Astrophysique Spatiale (IAS) in France, and tested at the Canfranc Underground Laboratory in Huesca, Spain.



It forms part of the ROSEBUD project (Rare Objects SEarch with Bolometers UndergrounD), a collaborative initiative between the UNIZAR and the IAS to hunt for dark matter, a material that exerts gravitational force but does not emit light or radiation.



The scientists have been working for the past decade on this mission in Huesca, where they have developed various cryogenic detectors that operate at temperatures close to absolute zero (-273.15°C). Their latest device is a ‘scintillating bolometer’, a 46g device that contains a crystal scintillator made up of bismuth, germinate and oxygen and acts as a dark-matter detector.



Eduardo García Abancéns, a researcher from the UNIZAR’s Laboratory of Nuclear Physics and Astroparticles, said: ‘This detection technique is based on the simultaneous measurement of the light and heat produced by the interaction between the detector and the hypothetical WIMPs (Weakly Interacting Massive Particles), which, according to various theoretical models, explain the existence of dark matter.’



He explained that the difference in the scintillation of the various particles enables this method to differentiate between the signals that the WIMPs would produce and those produced by various elements of background radiation such as alpha, beta or gamma particles.



In order to measure the miniscule amount of heat produced, the detector must be cooled to temperatures close to absolute zero. The detector is housed in a cryogenic facility reinforced with lead and polyethylene bricks and protected from cosmic radiation under the Tobazo mountain.



García Abancéns said early tests show the scintillating bolometer performs well as a dark-matter detector and gamma spectrometer.



The scintillating bolometer is currently at the Orsay University Centre in France where the team is working to optimise the device’s light gathering. The team is also carrying out trials with other BGO crystals.



There are direct and indirect detection methods for detecting dark matter, which cannot be directly observed since it does not emit radiation. The former include simultaneous light and heat detection such as the technique used by the scintillating bolometers, simultaneous heat and ionisation detection and simultaneous light and ionisation detection.



With indirect detection methods, researchers would avoid looking for dark matter and instead focus on identifying particles such as neutrinos and photons produced when the universe’s dark-matter particles are destroyed.



García Abancéns said: ‘One of the biggest challenges in physics today is to discover the true nature of dark matter, which cannot be directly observed – even though it seems to make up one-quarter of the matter of the universe. So we have to attempt to detect it using prototypes such as the one we have developed.’