Hidden charm in South Carolina

This last week I've been enjoying the hospitality of the University of South Carolina, where the The Eighth International Conference on Hyperons, Charm and Beauty Hadrons, a.k.a. "BEACH 2008", has just concluded. I presented an invited review of the new "hidden charm" states, focussing on results from my experiment, Belle: we have taken the lead in finding, and trying to characterise, a number of these new mesons, so called because they have both a charm quark and charm antiquark in their makeup, and thus have no charm (!) overall. Some of these particles just don't fit. Known mesons are built from a quark and an antiquark, and this structure gives rise to certain expected properties, different from those of the new states. So, we believe, these particles are put together in some other way.

The slides from my talk can be found here. The key result comes at the end: we see evidence for two more hidden-charm states that carry electric charge, something it's impossible for a conventional charm-anticharm meson (a "charmonium" state) to do. We found evidence for the first such state last year: this article from CERN Courier gives a brief description. Our paper on the latest results, which we'll submit to the Physical Review soon, can be found at arXiv:0806.4098 [hep-ex].

The early slides of my talk cover a quite different topic: charm mixing, previously mentioned on this blog. There's an historical and personal reason for this. I was supposed to present a review of mixing at the seventh BEACH meeting in Lancaster two years ago, but got very unpleasantly sick after a visit to Beijing, and ended up stuck in a hospital bed "back home" in Japan. (The glamour of international work and travel can be over-stated.) So it felt only right to include a brief update, in lieu of the review I couldn't give in '06. And it was nice to actually make it this time.

Mongolia via Taiwan, with assistance from Iran and Poland

I've recently been in Taipei for the Flavor Physics and CP Violation conference, the highlight of which was the ominously named "cultural activity" ... a trip to a local auditorium to hear the Mongolian singer Urna perform together with the Chemirani Trio on zarb drums (and other percussion), and the wonderful Jerzy Bawol. (I will never say a bad word about the accordian again, I swear it.)

This was splendidly accessible, serious, light-hearted, joyful music, without a trace of irony. Terrific stuff. There are samples on the Urna website I linked, but sadly none from the particular collaboration that I saw on the 6th.

It's somehow appropriate that one could find so impeccably international a collaboration in a place that does not even belong to the United Nations ...

[The slides of my presentation at FPCP, a review of "Quantum entanglement at the ψ(3770) and Υ(4S)", can be downloaded from the conference site. Regular readers of this blog may recognise the principal result, which was previously remarked under "Tangled up in (quantum) blue". Particle physicists (and some other physicists) should have no trouble with the slides, but I guess they'll be somewhat heavy going for anyone else. The writeup for the conference proceedings will, I hope, be a bit more accessible. I will link it here when it's done.]

The NYT deep-sixes Ice Nine

In recent days my friends --- including several physicists --- have been tormenting me with the news about the court case in Hawaii attempting to stop the turn-on of the Large Hadron Collider at CERN. I would like to think that I have a sense of humour about my work, but I do not have a sense of humour about relentless focus on the spectacular (as opposed to the central, or the important); nor do I have much time for the current conviction that crackpots and obsessives, for some mysterious reason, deserve to be given cultural space.

Ahem.

I was pleased to see an editorial in the New York Times today, dismissing the concern while having fun with it at the same time. I may not have a sense of humour in this matter, but at least I can appreciate it in other people.

[I have previously posted on the LHC, and on the ATLAS experiment, which I am joining this year.]

If the facts do not conform to the theory ...

... what do you do?

Over the last five years or so there has been a test case for this in particle physics, where experimental results and the expectation from theory were completely at odds: qualitatively different, and (where they could be compared numerically) out by a factor of ten or more.

My review of the experimental situation, Double ccbar production in e+e- annihilations at high energy, is now available on the web as arXiv:0712.3138 [hep-ex]. If you want the short version: theory fought experiment, and experiment won. In principle this always happens, but the trick is to get it to work out in practice. And the short version is of course prejudicial: it was always possible that something had been neglected in the analysis (there were some ingenious suggestions), or that some mistake had been made. The rhetoric about a theory being thrown out the moment you see a piece of contrary data sounds unlikely --- or just plain wrong --- and indeed it is. If you want to get a feel for how this sort of thing really plays out, at least in my field, read on. I can't claim that it'll be accessible unless you have some particle physics, however.

(This paper is the long-overdue writeup of a review I presented at the International Workshop on Charm Physics, a meeting I helped organise at Cornell in August. I posted earlier concerning the future of charm physics, the panel discussion that closed the workshop.)

The future of charm physics

It was my privilege, back in August, to chair the panel discussion that closed the International Workshop on Charm Physics at Cornell University.

My writeup for the conference proceedings, The future of charm physics: a discussion, is available on the web as arXiv:0711.1636 [hep-ex].

Tangled up in (quantum) blue

An object goes "bang" in the middle of a room and two pieces go flying off, one to the left and one to the right. Each one follows the laws of physics just by itself, and is influenced only by things that touch it (and gravity etc.^[1]). To know what the left piece will do, you needn't bother about the right piece in any special way: no more than you'd bother about the influence of your shoes, the ceiling, or the planet Jupiter.

Sorry: not true, so far as we understand.

If you believe quantum mechanics, those two pieces are in a certain sense still a single object ... even if the two pieces are on opposite sides of the room, or in separate towns many kilometres apart. It's called entanglement, a.k.a. "spooky action at a distance", a.k.a. "weird quantum s***".

I mention this because our paper on quantum entanglement at the Belle experiment has been published in Physical Review Letters.^[2] The theory does just fine at predicting our data --- that's not unexpected, since it's done just fine on all the data it's been confronted with. The real interest in this kind of measurement is to see if one can go beyond testing quantum predictions, and test entanglement itself: to show that entanglement is just-a-fact-about-how-the-world-is-put-together which we'll always be stuck with, even if we eventually improve on quantum mechanics in some way.^[3]

The gold standard for proving entanglement is a theorem by the late John Bell (no relation): our experiment couldn't meet this standard, even if our equipment were perfect (for rather technical reasons). What we can do is put other specific models --- other ways of explaining the data that don't involve entanglement --- to the test. The ones we have been able to try, fail; quantum mechanics succeeds. So entanglement wins this round, yet again, but some alternatives still live to fight another day ...

Here ends the lesson. It's not usually my aim to post such pedagogical material on this site, but there is no end to the flaky silliness on these topics doing the rounds in popular culture, so I feel some kind of duty to fly the flag when I've been a part of the work. What the bleep do we know? Um, well, quite a bit actually.

^[1]Gravitational and electromagnetic forces act "at a distance" but their influence is not instantaneous: it's bound by the speed of light. For everyday purposes that's so fast that the influence might as well be instantaneous, but a lot hangs on the distinction. You can think of it this way: it's the gravitational and electromagnetic fields right where you are ("touching" you) that affect you, and they take time to catch up on what's going on elsewhere, the same as you do. These forces are still local in this sense.
The "spooky" part about quantum entanglement is that the connection between the parts of an entangled system works without any regard to distance whatsoever --- with no speed limit --- yet it turns out that you still can't use the thing to send a signal faster than the speed of light. Put like that, it seems somewhat contrived, and this is one of the things behind the intuition that it's our assumption of separability that's the problem, not the assumption of locality: it's not that relativity doesn't describe spacetime, it's that things really can't be divided up into "parts" the way we tend to think they can.

^[2] It's also publicly available on the arXiv preprint server as quant-ph/0702267.

^[3] Like many people (physicists included) I have my doubts about quantum mechanics: I suspect that there's something more going on. However, I also suspect that the "something more" will still leave us stuck with entanglement: that the weirdness is real.

Australian Research Fellowship

On Wednesday the Australian Research Council announced the "outcomes" for the 2008 round of Discovery Project applications.

I've received an Australian Research Fellowship for the next five years, and some additional funding: not as much as I asked for, but hey. I'll still be based at the University of Sydney, but with a proper job --- who knows, maybe even a proper office --- and will once again be doing work at CERN, the Jerusalem of particle physics. [Sigh.] I have been away for too long.

Some colleagues from Melbourne were also successful in this round: Prof. Geoff Taylor (overboss of particle physics in Australia) has received a Professorial Fellowship, freeing him from other duties over the next five years, as ATLAS starts taking data; and A/Prof. Martin Sevior and Dr Glenn Moloney received a grant to use the (computing) Grid to support particle physics work. Congratulations, guys.

Oh, and an old schoolfriend who is working on the theory of freedom of expression, in the law faculty at U.Melbourne, also received a grant. The DP process funds all sorts of things, medical research excepted ...

ATLAS under construction

There are time-lapse movies of the ATLAS detector under construction on YouTube here, in one minute and two minute versions. They give a better idea of the sheer scale and complexity of the thing, than mere description does.

ATLAS, and the Large Hadron Collider project more generally, was discussed in an earlier post

Charm mixing in Physical Review Letters

My experimental collaboration, Belle, has a paper presenting evidence for the mixing of charm mesons (D⁰ and anti-D⁰) in the current issue of Physical Review Letters.

This is an example of matter turning into antimatter, and vice versa. There are four known mesons for which this can occur without "breaking the rules", and the D⁰ system is the last of the four in which the effect has been observed. A related phenomenon may, or may not, occur among the neutrinos. (Mixing is known to occur between different neutrino types [called "flavours"], a process usually known as neutrino oscillation due to its characteristic signature. It's still unresolved whether neutrinos and anti-neutrinos mix.) It's a pretty big deal in any case, especially for those of us who've devoted time to studying the charm sector. Mixing is one of the principal concerns of the research group I founded at Belle (and ran for many years), and so finding it is a milestone for us. And personally, when a paper has taken a large fraction of your life for a year or more, it's very satisfying for it to be completed.

A semi-technical summary of the work is available in the news section of the CERN Courier. Our paper is PRL 98, 211803, also available as a preprint at arXiv:hep-ex/0703036. The competing experiment, BaBar, presents a different kind of evidence for the same phenomenon in a paper published back-to-back with ours. These results were the talk of the conference at the electroweak session of this year's Rencontres de Moriond in March, when they were first announced, and have provoked a lot of theoretical discussion since.

The LHC in the news

The Large Hadron Collider has been in the news lately, with half a page in the SMH a few weeks ago, and big articles in the current New Yorker, and the New York Times science pages.

The LHC is the world's next big particle physics endeavour, and due to switch on soon; my colleagues in the particle physics groups at the Universities of Sydney and Melbourne are working on one of the experiments there, ATLAS.

The NYT article is quite ambitious, skating over a lot of ground; it also manages to be quite jaunty. And in the spirit of a picture telling a thousand words, it links to a beautiful interactive graphic that clearly distinguishes the general-purpose experiments (ATLAS and CMS) from the specialist ones (LHCb and ALICE), and explains what the detectors are doing.

The New Yorker article misses out on things like this, giving the impression (for example) that there are four experiments doing basically the same thing. I actually have a bunch of gripes with the New Yorker article: it disses the CERN cafeteria; it canvasses the idea that the LHC could destroy the world in an ice-nine-type catastrophe (it seems we'll never be free of that one); and it indulges a theoretical particle physicist in a theorist-as-performance-artist act, which is getting a little old. But if that's the worst I can say about a seven-page article in my own field, then it is clearly doing something right. The writer is engaged with the subject; she has talked to a variety of people; she is thinking.

There are, however, some bad thoughts expressed in memorable language, that seem destined to live forever. The New Yorker repeats the dread line that all science is either physics or stamp-collecting: an idea utterly without merit, but still in circulation. But what goes around can come around. Today's (Thursday's) NYT editorial on the LHC contemplates a scenario where the project fails, putting another nail in the coffin of the Age of Physics, in favour of the Age of Biology.

Yeah, right. Physicists, like everyone, are a menace when they get arrogant. So what should we do about it? Hey! I know! Let's replace them with arrogant biologists ...

I shall call him MiniBooNE

On email today with a colleague, I've been discussing the somewhat surprising/frustrating/tantalising result posted at arXiv:0704.1500 [hep-ex] by the BooNE neutrino experiment. Well, actually, the current experiment is called MiniBooNE, which is a bit unfortunate. (In their defence, I think their idea pre-dates Mike Myers'.)

MiniBooNE was set up to test the results of the LSND experiment, which <short version>found evidence for neutrino oscillations, but evidence that didn't fit with all of the other positive neutrino-oscillation results we've been seeing; and over the years, the disconnect has been getting worse</short version>. The idea of MiniBooNE was to come at the same physics using a different approach, and either reach the same conclusion or not --- let the data decide.

Trouble is, the MiniBooNE data (for which we have waited for a long time) are confusing. The simplest explanation of LSND will not wash, but we already knew that; some convoluted explanations of LSND are still hard to rule out, which we probably suspected; and there is an unexpected anomaly in the MiniBooNE data which looks like either (a) they have missed something, or (b) something very interesting is going on.

It has been difficult to have a sensible conversation about LSND for a long time. MiniBooNE was supposed to make it easier, whereas for now, it has made it more difficult. I for one am waiting for their next paper, and the one after that, and hoping they shed some light.