1. 2012

    New type of matter?

    Phys.org has picked up on the results from the LHC pilot pA run showing the formation of The Ridge in high-multiplicity collisions. I wrote about this last month, when it was first presented at the High-pT LHC Physics Workshop in Wuhan, and at that time, the sentiment at the conference seemed to be that it wasn’t clear what could be causing the ridge.

    Now, people are starting to lean toward the color glass condensate (CGC) as an explanation. The CGC has been called a new state of matter, which probably isn’t the worst description, but I think that makes it sound like more than it is. It’s a model that predicts the behavior of gluons within a proton or nucleus, under conditions in which the gluons are so numerous that they regularly “bump into” each other and fuse, or “recombine” to use the technical term. (That’s an extreme oversimplification, of course; perhaps someday I’ll do a post explaining this in more detail.) This model predicts some correlations among gluons which might be able to explain the ridge. But it’s not at all clear yet that that is the case. The LHC didn’t …

  2. 2012

    Results from HPT 2012

    One unexpected perk of being in China: I woke up before 7:30 this morning. That would never happen without jet lag.

    Unfortunately, even waking up at 7:30 every day hasn’t given me any time to write up a mid-conference blog post. Talks have been running from 8:30-6:30, with the rest of the time mostly taken up by meals and discussions. So I’ll just post this “teaser” of some of the more interesting results that were presented.

    Of the presentations that gave new results, most of them are based the September proton-lead run at the LHC. This was just a pilot run, meant to ensure that there wouldn’t be any unexpected problems with colliding two different types of particles, so there wasn’t a lot of data collected — only 2 million collisions — but it was already enough to start shedding some light on the underlying physics.

    No initial state effects

    Ion-ion collisions have already been extensively studied at both RHIC and the LHC, and as you might imagine, when you smash a blob of a hundred blobs of particles into another blob of a hundred blobs of particles, what you get is a mess …

  3. 2012

    A smorgasboard of major experiment results

    We’re now halfway into Quark Matter 2012, and many of the presentation slots (at least the ones I’ve looked at) have been devoted to the experimental groups presenting their new results. In heavy ion physics, the major groups are the STAR and PHENIX collaborations at RHIC, and ATLAS, CMS, and ALICE (which I’ve learned is pronounced “ah-LEES,” not “AL-iss”) at the LHC.

    Naturally, the experts who are interested in these things will just go straight to the conference page and look at the presentations — heck, they’re pretty much all here in Washington anyway. So I’m going to try to explain some of these results in a way that makes them comprehensible for non-experts (although, apparently unlike some of my fellow conferencegoers, I’ll give you enough credit to assume you know what atoms are).

    What Quark Matter is all about

    The main focus of the Quark Matter conference is, of course, quarks, and also gluons: the most fundamental particles that make up atomic nuclei. How do they organize themselves into protons and neutrons and then into nuclei? How do the properties of those atomic nuclei emerge from their internal structure? And what really happens when …