Saturday, October 17, 2015

Everything old is new again

I remember when the late Prof. Cline wanted to loft liquid argon time projection chambers in balloons to look for quark nuggets, a hypothetical kind of quark matter with a large fraction of strange quarks in addition to the usual up and down. That's "bare" strange quarks, not the strange/anti-strange pairs that you get all the time in nuclei. I thought the idea was insufficiently motivated to dedicate money to, and so apparently did the funding agencies. (I did some simple simulations/visualizations of a liquid argon TPC for the Icarus experiment, but one kindly scientist pointed out that the program I was using didn't handle slow μ- interactions with nuclei correctly, so I'm not sure how useful it all was.)

At any rate, there had been a fire in the balloon making factory, and so NASA wasn't going to be lofting any balloons for a year or so, so Cline decided to see if he could loft liquid argon detectors in satellites, and maybe piggyback a search for quark nuggets on top of a SDIO project to distinguish (hold your hat) incoming Soviet nuclear missiles from dummy missiles by the prompt radiation you'd get from neutrons emitted by your own nuclear blast in space.

In other words, his SDIO proposal was: you see incoming missiles; fire off your own nuke in space; the neutrons from it make uranium emit gamma rays; you detect the gamma rays in your own detector system in the few milliseconds before the neutrons hit your detector system and blind it; you compute where the gamma rays all come from and tell your anti-missile system which are the real warheads. (Never mind that the EMP pulse knocks our your own communications satellites, the Soviets probably already did that to you anyway.) Ummmm. No. No on several levels: I noticed that the gamma ray pulse from your own nuke would create some slow-decaying atomic states in the argon that would still be glowing like one of those green stickers just at the time when you needed the system to be sensitive.

So much for quark nugget detection.

They're back. This time as dark matter candidates. And, of course, the first thing you ask is how do you detect these quark nugget "macros"? If they're big enough (still way smaller than anything telescopes can see), you could see them streaking through the sky like other meteors or making odd craters--and we don't see anything really anomalous. Yes, if you don't know where you dropped them, you start looking for your missing keys under the lamppost. You ask about big things first. Then you try to figure out how to look for small blobs.

I haven't studied quark nuggets. If wikipedia is an accurate guide (cue the snickering) one theory holds them to have equal numbers of up, down, and strange quarks--which would make them neutral. That would be kind of weird stuff--the normal electromagnetic force fields that make regular matter bounce off other stuff (and that hold you up in the chair) wouldn't be as much of a factor. A macroscopic chunk would act a little like a conductive surface as far as charges are concerned--attractive, but since an electron would be trying to push quarks around (much more massive), the attractive force would be small. I don't know which way W/Z exchange would push--an interesting problem, and one that's actually worth looking at. Somebody must have solved that already for the ordinary nuclear case. The nucleus/chunk bounce is even more complicated: W/Z exchange and pion exchange and maybe a splatter or merge. If I was reasonably familiar with the models I'd guess it would take at least a year to work up a model of the interactions. A year to figure out the interactions of a hypothetical particle that I have no reason to believe exists? Not happening.

Though maybe that's a bit hypocritical--I've spent a lot of odd hours on the mathematical aspects of a model I'm pretty sure isn't useful. The math is kind of interesting, though, and tantalizing--there has to be a pattern in the symmetries.

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