“We hope to detect the largest proportion of the matter in space”

A conversation with Manfred Lindner on the latest results from the Xenon100 detector

April 27, 2011

The underground laboratory at Gran Sasso in Italy is the home of the Xenon100 experiment, which is being conducted as an international collaboration that includes the Heidelberg-based Max Planck Institute for Nuclear Physics to detect the mysterious particles directly. The researchers recently published the evaluations of one hundred days of measurement time. The result: although there is no significant signal for dark matter as yet, the world’s best limits for the masses and interaction strengths of the WIMPs have been obtained, and already noticeably reach into the predicted range.

Could the LHC already be able to detect the theoretically predicted WIMPs?

Trap for dark matter: The Xenon100 experiment is located beneath 1400 metres of rock in the Gran Sasso underground laboratory in Italy to protect it from cosmic radiation. WIMPs can penetrate the earth and reach the detector, which is shielded against radioactivity from the rock with several layers of water, lead, plastic and copper. When a WIMP reacts in the liquid xenon, flashes of light are generated which are registered by photomultipliers (illustration).

© Rice University

Trap for dark matter: The Xenon100 experiment is located beneath 1400 metres of rock in the Gran Sasso underground laboratory in Italy to protect it from cosmic radiation. WIMPs can penetrate the earth and reach the detector, which is shielded against radioactivity from the rock with several layers of water, lead, plastic and copper. When a WIMP reacts in the liquid xenon, flashes of light are generated which are registered by photomultipliers (illustration).

© Rice University

This should be possible with the upcoming data if the WIMPs are present in the mass range predicted.

Couldn’t the WIMPs also be much lighter? In the range below ten gigaelectronvolts, which corresponds to the mass of a carbon atom, Xenon100 is no longer sensitive.

In principle, this cannot be excluded, but the so-called WIMP miracle is then lost. This denotes the fact that new particles, which become necessary because of the shortcomings of the standard model of particle physics, automatically provide the correct quantity of dark matter from the Big Bang. It is easy to see that we are in a way putting together a multi-part puzzle, and it is remarkable how many indications from very different fields fit together consistently. Light or very light WIMPs do not fit into the overall picture nearly as well here. But they cannot be excluded.

What’s the next step?

First of all, we will continue measuring with Xenon100. We have already been able to reduce the interfering krypton background to almost one tenth so that the next series of measurements, which we want to evaluate by the autumn, will already provide even more accurate results. At the same time we are already planning an enlarged version of Xenon100 for the next few years - Xenon1T with 2.5 tonnes of xenon.

When is Xenon1T expected to be completed?

The construction should be completed by the end of 2014, and in 2015 we want to begin with the measurements. A very ambitious schedule, but quite realistic for experiments of this size.

And what happens if you cannot find WIMPs with this either?

Because of the WIMP miracle we hope to of course have a very good chance of seeing a signal and thus directly detect the largest proportion of the matter in the universe. But even if we don’t see anything, this would be extremely interesting because it would make the question as to what dark matter really is even more mysterious.

Interview: Thomas Bührke