Tau.Neutrino said:
Can a superfluid helium detector help us finally find dark matter?
Although it makes up everything we see and touch around us, ordinary matter only accounts for about 15 percent of the mass of the universe. The other 85 percent is believed to be dark matter, a theoretical substance that doesn’t interact with ordinary matter and has so far eluded our best efforts to directly detect it. Now, physicists from Brown University have proposed a new way to find dark matter, using a huge tub of helium in a superfluid state.d
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> To do so, the new system would use a tank of superfluid helium instead of xenon. The thinking goes that if the nucleus of the atoms in the tank is bigger than the incoming dark matter particles, then the dark matter would just bounce off without disturbing the detector particle. Since the nucleus of xenon is about 100 proton masses, that limits how light an incoming particle can be and still be detected. Helium, however, has a nuclear mass of just four proton masses, extending its sensitivity to lighter particles. In fact, the Brown researchers say their design will be able to detect particles between 1,000 and 10,000 times lighter than previous experiments could pick up. Using helium is only part of the improvement, too: the instrument has been cleverly designed to amplify a signal from just a single atom.
Interesting, but does anyone expect to see dark matter particles smaller than 10 proton masses?
It’s perhaps a good time to look at where the xenon detectors are at. These are the most sensitive dark matter detectors that I know. They’ve been getting bigger and much more sensitive. Starting from XENON10, we’ve progressed to XENON100 and XENON1T. The XENON10 detector contained 15 kg of liquid xenon. The XENON100, contains 165 kg of liquid xenon. The XENON1T detector contains 3.5 tons of liquid Xenon, it started in 2014. The first results from XENON1T were announced on May 18, 2017, based on 34 days of data-taking between November 2016 and January 2017. No WIMPs or dark matter candidate signals were detected.
Here’s a chart of WIMP mass vs sensitivity.
A proton has a mass on 0.938 GeV/c, so is well off the chart which has a lower limit of 5 GeV/c. Which is where the new superfluid helium detector comes in, at energies below 5 GeV/c. Looks sensible to me.
At very much lower masses (2 μeV to 20 μeV) we have the https://en.wikipedia.org/wiki/Axion_Dark_Matter_Experiment which uses a SQUID cooled by liquid helium-3.