Dark Matter do-si-do

Last week, I had the great pleasure of attending “The Hunt for Dark Matter”, a symposium at Fermi National Accelerator Laboratory. Dark matter hunters, and even a skeptic or two, converged from across the world at Fermilab to discuss the current state-of-the-art in detection, the hopes for future experiments, and reasons why we might be barking up the wrong tree. Most telling was a panel discussion on the second-to-last night of the symposium. It was actually interesting, believe it or not. Luminaries like Case-Western’s Lawrence Krauss and Fermilab’s Rocky Kolb entertained and informed the audience, as well as engaging in issues raised by the audience. Questions like “which technique will find dark matter first” and “is the dark sector as complex as the light sector” were bounced around the audience. Discussions ensued on whether dark matter might really be axionic, making it nearly impossible to detect at the LHC or with nuclear recoil techniques. People even brought up (some dismissively, some seriously) the possibility that changes to gravity at large scales might really be a competative theory, now that it has some aspects that make it falsifiable.

Overall, the experience was great. I didn’t give a talk (but the Belle collaboration did send a member of their trigger group to talk about their invisible Upsilon decay search, which I had been working on last year until they crushed my approach with their own), but I had a great time nonetheless. It was especially engaging to argue with some theorists, to hear from students working on cutting-edge photographic techniques for dark matter bubble chamber experiments, and to learn more than I ever wanted to know about liquid noble gas two-phase experiments. Whoof.

All in all, what it seemed to boil down to was a bet. Do you believe that dark matter will be discovered in the next five years? Going back to the panel question – which technique will find it first – one has to keep in mind the story of the three blind men and the elephant. Three blind men are placed in a room where an elephant is standing. One man stands by the tail, one by a leg, and the other by the trunk. They are asked to reach out and describe what is in the room. The man by the tail says, “Ah! It’s a rope!” The man by the leg says, “No, no! It’s a tree trunk!” The man by the trunk says, “Are you crazy! My goodness, this is a snake!”

Any one of the three men, when asked separately what was in the room, has a different answer. It might be that only once they pool their notes on their experiences that they realize that this might really be an elephant. Asking any one approach – gamma ray telescopes, or solid state nuclear recoil experiments, or collider experiments – whether they have found dark matter is a terrible approach. The collider people might find a heavy neutral particle, but does it really live 13.7 billion years? The astrophysicists might find an excess of gamma rays radiating from the galactic center, or from nearby brown dwarf galaxies, but how can they know it’s due to dark matter annihilation? When all is said and done, it’s going to be super hard to pull all those notes together to say for sure that we’ve actually found dark matter.

Photos to follow.

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