Online Public Talk Today

Reminder: I’m giving a public lecture about the Large Hadron Collider today, Saturday, April 28th, 1 p.m. New York time/10 a.m. Pacific, through the MICA Popular Talks series, held online at the Large Auditorium on StellaNova, Second Life.  You’ll need a Second Life viewer to watch it live.  Should you miss it, both the audio and the slides will be posted later for you to look at.

CMS Finds a New (Expected, Composite) Particle

Yes, it’s true what you’ve read; the CMS experiment at the Large Hadron Collider has found a new particle.  However, this isn’t one to get excited about.  Or rather, it’s the particle that’s excited, not the rest of us.  It’s a nice result; a neat result; but this particle is a slightly more massive version of a hadron that we already knew about, a composite object similar to a proton, built out of more fundamental particles we discovered over 30 years ago.  So in the grand scheme of things, this is minor news; no big mysteries to resolve here.  Nevertheless, congratulations to CMS! Finding such particles always involves reconstructing them from their decay products, and since this one decays in a very complicated way, the result represents a technical tour-de-force!

This is a similar story to one from last December, when ATLAS announced that it had found, with confidence, a new particle.  I explained to you then that there are particles and there are particles; Continue reading

Some Good Reads

I’m preparing an article on a very important type of energy that I’ve avoided writing about so far — the energy that comes from the interaction among fields.  I’ve avoided it because it’s tricky to figure out how to explain it.  But it’s important, for this form of energy is responsible for all the structure in the universe, from atoms to galaxies.  The article’s not quite ready yet, so today I’ve just got some good reading material for you, including the heavy, the weird, the amusing, and the optimistic. Continue reading

Is Supersymmetry Ruled Out Yet?

[A Heads Up: I'm giving a public lecture about the LHC on Saturday, April 28th, 1 p.m. New York time/10 a.m. Pacific, through the MICA Popular Talks series, held online at the Large Auditorium on StellaNova, Second Life; should you miss it, both audio and slides will be posted for you to look at later.]

Is supersymmetry, as a symmetry that might explain some of the puzzling aspects of particle physics at the energy scales accessible to the Large Hadron Collider [LHC], ruled out yet? If the only thing you’re interested in is the answer to precisely that question, let me not waste your time: the answer is “not yet”. But a more interesting answer is that many simple variants of supersymmetry are either ruled out or near death.

Still, the problem with supersymmetry — and indeed with any really good idea, such as extra dimensions, or a composite Higgs particle — is that such a basic idea typically can be realized in many different ways. Pizza is a great idea too, but there are a million ways to make one, so you can’t conclude that nobody makes pizza in town just because you can’t smell tomatoes. Similarly, to rule out supersymmetry as an idea, you can’t be satisfied by ruling out the most popular forms of supersymmetry that theorists have invented; you have to rule out all its possible variants. This will take a while, probably a decade.

That said, many of the simplest and popular variants of supersymmetry no longer work very well or at all. This is because of two things: (click here to read the rest of the article.)

Up Another Notch at LHC

A few days back I told you things were going very well so far in 2012 at the Large Hadron Collider [LHC] — that not only had the increase in energy (from last year’s 7 TeV of energy per proton-proton collision up to 8 TeV) gone well but the collision rate (the number of collisions per second) had already been brought back up to last year’s level.  And I pointed out that the current collision rate had been achieved using fewer bunches of protons than last year, which meant it could eventually be increased further, by putting more bunches in.  But I didn’t know when they’d take that step — in particular, whether it would be anytime soon.

The proton beams at the LHC aren’t continuous; as of now, they consist of over a thousand bunches, each containing something like 100,000,000,000 protons.  Two bunches are arranged to hit head on every 50 billionths of a second, and in each bunch crossing occur 10 to 40 virtually simultaneous proton-proton collisions.

Well, they did it the next day!  Since Wednesday the number of bunches per beam has been about 1380, same as late last year, and the collision rate jumped up by over 25%, just like that!  In fact they brought it even a bit higher (not sure exactly how)  to within 15 – 20% of this year’s final target.  And they’ve had some long runs, as long as nearly 10 hours, showing the accelerator remains very stable.

Three cheers for the accelerator physicists!  Now the experimentalists just have to assure they can extract quality data from a firehose.

Dark Matter: Now You See It, Now You Don’t

Two interesting claims about dark matter this week, and on the face of it, completely contradictory, but in fact, not obviously so. Before saying one word more, let me repeat my mantra — something that all physicists know but relatively few non-scientists appreciate — most claims of a radical new result turn out to be largely or completely wrong. This is not because physicists are stupid but because doing science at the forefront of knowledge involves using novel techniques that might have unknown pitfalls, and also because a single small mistake can create a fake effect (as we saw most recently with the OPERA neutrino speed measurement.)  And because nasty statistical accidents can play tricks on you.

Both claims that I’m about to describe use novel techniques, and their analyses have not been repeated by anyone else. At this point you should understand that both are tentative, and (based on the history of radical claims) the odds are against them. Both might be wrong. That said, both analyses look to me as though they’ve been reasonably well done, and if a mistake has been made, it will require someone far more expert in dark matter studies than I am to point it out.

So let me describe them in turn, to the best of my ability. Continue reading