Dark Matter. Its existence is still not 100% certain, but if it exists, it is exceedingly dark, both in the usual sense — it doesn’t emit light or reflect light or scatter light — and in a more general sense — it
Dark Matter. Its existence is still not 100% certain, but if it exists, it is exceedingly dark, both in the usual sense — it doesn’t emit light or reflect light or scatter light — and in a more general sense — it doesn’t interact much, in any way, with ordinary stuff, like tables or floors or planets or humans. So not only is it invisible (air is too, after all, so that’s not so remarkable), it’s actually extremely difficult to detect, even with the best scientific instruments. How difficult? We don’t even know, but certainly more difficult than neutrinos, the most elusive of the known particles. The only way we’ve been able to detect dark matter so far is through the pull it exerts via gravity, which is big only because there’s so much dark matter out there, and because it has slow but inexorable and remarkable effects on things that we can see, such as stars, interstellar gas, and even light itself.
About a week ago, the mainstream press was reporting, inaccurately, that the leading aim of the Large Hadron Collider [LHC], after its two-year upgrade, is to discover dark matter. [By the way, on Friday the LHC operators made the first beams with energy-per-proton of 6.5 TeV, a new record and a major milestone in the LHC’s restart.] There are many problems with such a statement, as I commented in my last post, but let’s leave all that aside today… because it is true that the LHC can look for dark matter. How?
When people suggest that the LHC can discover dark matter, they are implicitly assuming
- that dark matter exists (very likely, but perhaps still with some loopholes),
- that dark matter is made from particles (which isn’t established yet) and
- that dark matter particles can be commonly produced by the LHC’s proton-proton collisions (which need not be the case).
You can question these assumptions, but let’s accept them for now. The question for today is this: since dark matter barely interacts with ordinary matter, how can scientists at an LHC experiment like ATLAS or CMS, which is made from ordinary matter of course, have any hope of figuring out that they’ve made dark matter particles? What would have to happen before we could see a BBC or New York Times headline that reads, “Large Hadron Collider Scientists Claim Discovery of Dark Matter”?
Well, to address this issue, I’m writing an article in three stages. Each stage answers one of the following questions:
- How can scientists working at ATLAS or CMS be confident that an LHC proton-proton collision has produced an undetected particle — whether this be simply a neutrino or something unfamiliar?
- How can ATLAS or CMS scientists tell whether they are making something new and Nobel-Prizeworthy, such as dark matter particles, as opposed to making neutrinos, which they do every day, many times a second?
- How can we be sure, if ATLAS or CMS discovers they are making undetected particles through a new and unknown process, that they are actually makin