CRESST

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CRESST ( acronym for C ryogenic R are E vent S earch with S uperconducting T hermometers , mutatis mutandis: Low-temperature searching for rare events by means of superconducting thermometers) is a European experiment to directly search for dark matter . It is located in the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, the largest underground laboratory in the world. Participating institutions are the Max Planck Institute for Physics (Munich), the Technical University of Munich , the University of Tübingen , the University of Oxford (Great Britain), the Institute for High Energy Physics HEPHY (Vienna) and the Istituto Nazionale di Fisica Nucleare (INFN, Italy).

The CRESST experiment in Hall A of the Laboratori Nazionali del Gran Sasso . The actual detector is located on the ground floor, the maintenance access and measuring electronics are on the first floor. The office and a small laboratory are located on the second floor.

Detection principle

CRESST uses low temperature calorimeters to detect the recoil energy of dark matter particles ( WIMPs ) in an absorber crystal at temperatures close to absolute zero (operating temperature ≈15 mK). The impact of a WIMP deposits energy in the crystal, which leads to a tiny change in temperature. A superconducting thermometer is converted from the superconducting to the normally conducting phase. The associated change in resistance is amplified and read out via SQUIDs .

Since the recoils we are looking for are processes of weak interaction, the expected rates are extremely low (approx. 5 to 10 events per kilogram over several years, depending on the model). In order to be able to measure this at all, all underground events must either be suppressed by a shield or be identifiable by data analysis. Attempts are also made to increase the detector mass to up to one ton.

Project phases

CRESST I

The first stage of CRESST used four 262 g heavy sapphire crystals (Al 2 O 3 ) as absorber material. The first measurements were made in 1999; the limit obtained for the WIMP cross section was published in 2003.

CRESST II

Several fundamental changes were made in the second expansion stage:

  • 300 g calcium tungstate crystals (CaWO 4 ) were used as absorbers
  • Introduction of double detectors for the simultaneous measurement of recoil energy and scintillation light. This allows the distinction between photon / electron events and nuclear recoil
  • Installation of a bracket for up to 33 double detector modules including SQUID system

In September 2011 the CRESST collaboration published the analysis of the measurement period from 2009 to the beginning of 2011. After subtracting the known interfering signals, there was an inexplicable signal excess, which can be interpreted as an indication of a light dark matter particle. This result contradicts the results of the XENON and CDMS experiments. Since the CoGeNT and DAMA collaborations have also published indications of a light WIMP with slightly different masses and scattering cross-sections, the result is currently being discussed controversially.

Since August 2013, 18 absorber modules have been used in the 33 places.

In the last few months (as of April 2020) new modules were installed and the measurements were last started when they had to be canceled again due to the measures taken in the course of the corona pandemic .

EURECA

The long-term goal of astroparticle physicists is to build a detector with one ton of detector mass. For this purpose, it is planned to combine and expand the existing experiments CRESST, EDELWEISS and ROSEBUD under the name EURECA ( European Underground Rare Event Calorimeter Array ). The location will be the Laboratoire Souterrain de Modane (LSM).

Similar projects

Web links

Individual evidence

  1. J. Jochum et al .: Limits on WIMP dark matter using sapphire cryogenic detectors. In: Nuclear Physics B - Proceedings Supplements. Volume 124, 2003, pp. 189-192.
  2. J. Schmaler et al .: Results from 730 kg days of the CRESST-II Dark Matter Search , arxiv : 1109.0702
  3. Hints of dark matter reported, again (Science News)
  4. ↑ Everyday researcher: Standstill in the orf.at underground laboratory, April 19, 2020, accessed April 19, 2020.