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Question

I heard from a friend recently that a new 'type' of matter has been detected at CERN: neutralinos. Is that true?
Asked by: Elizabeth

Answer

As a member of the particle physics community I can only say that I wish the rumors were true!

The LEP electron/positron collider at CERN has been slowly increasing its energy over the past two or three years, searching for any number of 'new' particles: Higgs bosons, new quarks, new gauge bosons, supersymmetric particles (such as neutralinos), etc.. Over the past 18 months there have been occasional flurries of excitement in the particle physics community -- and articles in the New York Times -- announcing the possible discovery of some new particle. Unfortunately each of these exciting rumors has proven to be premature.

Recently an Italian collaboration named DAMA has published data suggesting what might be a signature for dark matter. While none of the other worldwide experiments looking for dark matter has been able to confirm these results, the data is consistent with the hypothesis that much of the dark matter in the universe is made up of neutralinos. Perhaps this is the new experimental data (recently described in the New York Times) to which your friend refers. Despite experimentalists crying 'wolf' several times in the last few years, this recent evidence is creating a bit of excitement. You can download a postscript version of their publication at: http://mercury.lngs.infn.it/lngs/preprint/preprint36.ps but this report isn't exactly written for the lay-person.

Another possibility is that your friend is thinking of an experiment at CERN which claims to have found a new *state* of matter known as a quark-gluon plasma. This doesn't involve any new types of matter (it's the same particles we've known about for a while -- no neutralinos here!). However, it does involve quarks that are not bound up into protons and neutrons but are instead temporarily free to propagate on their own. This experiment received a good deal of press lately as well and you can find a fairly readable account of what's going on at the CERN website: http://www.cern.ch/CERN/Announcements/2000/NewStateMatter/.

So unless your friend actually knows someone who works at CERN and has let you in on a big secret, the experiment you're interested in is one of these two. I hope this helps.
Answered by: Brent Nelson, M.A. Physics, Ph.D. Student, UC Berkeley


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