From IPNL: “First Results of the EDELWEISS III experiment”


Institut de Physique Nucleaire de Lyon

13 May, 2016 [I just found these guys]
Cazes Antoine

EDELWEISS bolometers before installation. No image credit

The EDELWEISS experiment aims to detect WIMPs, a candidate for dark matter particles. It is located in the Modane Underground Laboratory. The experiment operates bolometers cooled to tens of Millikelvin where a WIMP might collide with a germanium nucleus and produce its recoil. This recoil is then measured by the resulting temperature rise (few microkelvin) and ionisation production (Germanium is a semiconductor material). This double measurment allow to identify nuclear recoils and thus eliminating much of the background due to gamma rays from natural radioactivity.

For the third phase of the EDELWEISS experiment, the bolometers have been greatly improved and the cryostat was redesigned to reduce background noise and to accommodate a larger mass of detector. The experiment ran from July 2014 to April 2015. The data, equivalent to 582 kg.days were blindly analyzed and the background rejection was performed using a Boosted Decision Tree. This results in a lack of detection of WIMP and an improvement, by a factor varying between 12 to 41, compared to the previous limit EDELWEISS II: for a WIMP 5 GeV / c2, the collision cross sections WIMP -nucléon above 4.3×10-40 cm2 are excluded and those above 9.4×10-44 cm2 for WIMPs 20 GeV / c2.

The EDELWEISS experiment is now working on a major R & D with the aim of lowering bolometers detection thresholds to explore collisions with low-mass WIMP (below 5 GeV / c2). This work is carried out in particular with the IOL cryostat installed IPNL.

Science paper:
Constraints on low-mass WIMPs from the EDELWEISS-III dark matter search

See the full article here .