Charm &c.

Three theoretical discussions of the Z(4430) state have shown up on hep-ph in the last couple of days:

• Rosner suggests it’s a rescattering effect in threshold production of D*(2010) D₁(2420);
• Maiani, Polosa, and Riquer suggest it’s a true tetraquark state, the first radial excitation of the X(3872)/X(3876);
• Meng and Chao suggest it’s an actual resonance in D*(2010) D₁(2420).

Belle claims to see a “Z(4430)” as a π^±ψ’ structure in B → Kπ^±ψ’ decays. This joins the X(3872), Y(3940), Y(4260), Y(4350), and Y(4660) in the zoo of incomprehensible things above DD threshold that decay to charmonia. Unlike the other objects, this one is charged, which means it can’t be a hybrid or conventional charmonium state.

At the start of the week, we had a little conference of our own, which went very well, and hopefully this weekend I’ll put up a post on how CLEO sort-of-but-not-really measured the D⁰ mixing parameter y. But first this: the Cornell Cinema early fall calendar is up. Highlights:

• In Case You Missed It: The Namesake, Grindhouse, Aqua Teen Hunger Force Colon Movie Film for Theatres (actually an Ithaca premiere!), Knocked Up, Once, 28 Weeks Later
• In Case You Missed It, Twice: 300, Hot Fuzz
• The Films To Show Us Off To Freshmen: Seven Samurai, The 400 Blows, The Big Lebowski
• Will Anyone Actually Make It All The Way Through This?: Intolerance
• OMG, The Dalai Lama Is Coming: A whole bunch, and you know Kundun is going to be in there. Also apparently Cinemapolis/Fall Creek are also involved.
• With a Name Like This, It’s Gotta Be a Guy Maddin Film: Brand Upon The Brain!

It’s the middle of June, and the Cornell Cinema summer season rapidly approaches — a fantastic time when all the cinema staff work twice as often to provide you with filmic entertainment even more obscure than usual. We reopen on this Sunday (the 17th) and run through the first week of August. Readers who live in Ithaca should come, and those who don’t, well, sorry.

Highlights:

• Cinema under the Stars: Two special outdoor screenings on the Willard Straight terrace — The Triplets of Belleville (June 2 and To Have and Have Not (July 12). A lovely way to spend a languid summer evening. I hear there is some form of cash bar, but bring your own snacks, and arrive early for good seats. Video purists note: these will be video projections, not film. Also, if you deeply care about this fact, you suck.
• Old-ish Things: beyond the aforementioned To Have and Have
  Not, there will be Psycho, Lattuada’s Mafioso, Godard’s Two or Three Things I Know About Her, and, uh, Thelma and Louise.
• In Case You Missed It: Pan’s Labyrinth, Letters From Iwo Jima, 300, Hot Fuzz.
• This Sounds Interesting: Reviewers seem to have gone gaga over Black Snake Moan, and the review has the phrase “cure her hysterical nymphomania.” Red Road is a noir thriller involving the British closed-circuit camera obsession. The Lives of Others makes the point that life wasn’t really all that fantastic in East Germany. Any comedy described as “Jim Jarmusch meets Aki Kaurismaki” (Whiskey) sounds perfect, if you’re into empathetic cringing.

On the strength of totally unverified rumors (propagated by yours truly), Slate tells us that particle physicists are all hoping that the Higgs hasn’t been found at DØ, because otherwise the LHC would have been built for nothing:

That’s why particle physicists, and the EU member states that have spent Nepal’s annual GDP to build this accelerator, are hoping that no one, in Chicago or Switzerland, finds the Higgs. The future of high-energy physics lies with the small chance that the standard model is wrong, and something exotic happens at LHC energies.

Partial credit. In a sense the future of HEP as an experimental science does depend on the Standard Model being wrong. If nothing other than a SM Higgs appears at the TeV energy scale, it will be very difficult to answer the outstanding issues of the model (such as the famous “naturalness” problem of why the Higgs mass would be so low compared to the natural scale of gravity).

However: if the rumors are proven true, then the Standard Model is wrong (and wrong in a deep way, too, unlike the hacks used to add neutrino masses). I can’t say this strongly enough: THE SUPPOSED DØ PARTICLE CAN NOT BE THE STANDARD MODEL HIGGS. The cross section (the rate at which the particles are made) is much too high. All the theoretial interpretations I’ve heard invoke supersymmetry — in particular the so-called Minimal Supersymmetric Standard Model (MSSM) — to increase the production rate for their Higgs equivalent enough that DØ could have detected it. To explain the fact that DØ sees a signal at all, you need non-Standard Model physics.

The Higgs and the MSSM are not incompatible. In fact, in one of its particle-multiplying feats, the MSSM demands five physical Higgs bosons (generally, for each particle we know of, it gives you one or two new ones to look for). Discovering the MSSM, while a little conventional (in the sense that the scenario’s implications have been pored over by lots of theorists for a couple of decades now), would be the opposite of a disaster for particle physics, and the LHC would have a lot to do. It’s actually quite difficult to get rid of the Higgs in reasonable models of any kind, so the mere existence of a Higgs-type particle doesn’t tell you much; you have to look at any candidate carefully to distinguish between models.

Bottom line: If the DØ signal is real, it’s physics beyond the Standard Model. If so, it’s extremely likely that additional phenomena will be revealed by the LHC, and we will get our money’s worth.

(No, not the album.) The scandalous gossip swirling around the collider physics world at the moment is that the DØ experiment at the Tevatron has seen Something Interesting and Statistically Significant, and will announce this Real Soon Now. The 4-bottom-tagged-jets channel keeps getting mentioned, but it’s unclear if the interesting feature is a characteristic of the 4b signal, or of 2 bottom jets within the event. (In other words, it might be a resonance that cascades to 4 bottom quarks, or production of a Higgs and something that decays to 2 bottom quarks, or …) Not being a DØ member, I have no idea whether any of this is true, but it’s sufficient to have excited a number of CDF people into checking if they’ve missed something.

A totally apocryphal metarumor: supposedly the leak was traced back to a young experimentalist’s blog.

Tommaso graciously volunteers to anonymously pass on your leaks here.

UPDATE: if you’ve been linked here from any page involving the word Slate, please take a look at this follow-up post.

I must say I feel a bit cheated by the French elections. Not because of the result (I rooted, in my totally irrelevant way, for the “extreme centrist” candidate François Bayrou, eliminated in the first round), but because on this side of the pond the coverage was over as soon as I tuned in. I was hoping for a nice afternoon of watching trenchant political television, preferably in subtitled French with lots of bickering to fill the gaps between results arriving. Instead, I switch to C-SPAN at 2 pm EDT (only 8 pm Paris!) and get charming English-speaking anchors and graphics screaming “SARKOZY WINS 53%.” Seemingly they have very accurate poll result forecasts in France. What a let down.

The recent local/Scottish Parliament/Welsh Assembly elections in the UK were a good deal more fun to watch. C-SPAN didn’t carry them, unfortunately, so I had to resort to BBC streaming video of much lower resolution. As election night coverage should go, it ran into the not-so-early hours of the morning, with the anchors loudly lusting after full English breakfasts at the end. The results weren’t fully in by the time the show was interrupted by the BBC equivalent of “Good Morning America.”

It’s faintly reassuring to know that the US is not unique in our vaguely messed-up electoral ways. Fog stranded ballot boxes on remote Scottish islands. In the rest of Scotland, electronic ballot counting machines failed to count ballots and huge numbers of votes were rejected due to being wrongly filled out. The ballots were later deemed “confusingly designed.” (The electorate was confronted with three different voting systems at once: one winner-takes-all Parliamentary seat, one proportional representation seat, and finally a rank ordering of local government candidates under single transferable vote.) The commentators rushed to remind the audience that, no matter how bad it was, there were no hanging chads.

We also got to enjoy quaint traditions such as:

• Results announced by Returning Officers with the candidates standing on stage with them
• Only having to listen to acceptance speeches
• Results in Wales given in Welsh
• Breakaway party from Scottish Socialists (“Solidarity”) failing to get anyone elected
• Liberal Democrats explaining that, no matter what else has happened, at least they won Eastbourne
• Conservative councilors in Birmingham declaring that they were elected due to their spectacular record of weekly trash collection
• Representatives of three major parties in the BBC studio, wearing party-color ties, attempting to rebuff nasty questions from the anchor (“This really isn’t a good night for you, is it?”)
• Green spokeswoman declaring that maybe Conservatives pick up the trash every week, but what about the recyclables?
• Welsh nationalist party being beaten back to rural, conservative heartland, where apparently they belong
• Wildly inappropriate graphical metaphors used by BBC statistics people while displaying results: Tony Blair lobbing tennis balls, David Cameron building a townhouse, and Sir Menzies “Ming the Merciless” Campbell trying to earn some, er, bling
• No other politicians wanting to hang out with the Scottish Nationalists

The best part about the election? It doesn’t really affect me! Although if the SNP does manage to achieve an independent Scotland, it’s going to be really weird going through passport control on vacation.

I am incapable of providing timely commentary on things … this has been stewing for a couple of weeks now.

The MiniBooNE collaboration recently released initial results searching for muon neutrinos turning into electron neutrinos. A very nice and detailed discussion of the physics and experiment is here, and I won’t repeat it; instead I’m going to talk a bit about the kind of analysis they did — a “blind analysis.”

“Blind trials,” famous from medical studies, attempt to eliminate biases by keeping the test subjects from knowing whether they’re getting Coke or Pepsi (less frivolously, a treatment or a placebo). Double-blind trials hide this information from the experimenters as well. If the subjects in a taste test know they’re getting Coke or Pepsi, their reactions may have nothing to do with how the drinks actually taste; if doctors treating a patient know if the patient is actually getting a sugar pill, they could (even just subconsciously) affect the patient by behaving differently. Double-blind experiments are critical for good results when living subjects are involved.

Things are a little different for particle physics. Quantum mechanics doesn’t care what we subconscious signals we give out; the first aspect of a double-blind trial - keeping the subject in the dark - is automatically satisfied. However, experimenters can influence how they collect and analyze their data, and so can introduce biases that way: the second aspect is generally not considered.

Experimenter bias has historically been dealt with by consciously trying to be unbiased, but it’s not hard for good intentions to go wrong. Suppose you’re making a measurement of a well-known physical quantity. You find that you are way off. You root around and you find a problem with what you’ve done, which when fixed brings your result into agreement with the “correct” value. Do you stop and declare victory? Well, you shouldn’t necessarily — things that are less obvious, or which compensate each other, may still be incorrect. However, most of us will, in fact, stop. The net effect is a bias towards previous results, which may themselves be wrong (or at least not known to high enough precision), and it’s hard to avoid this.

A related issue arises in searches for new phenomena. If you see a small discrepancy between what you observe and what you expect at some particular value of the Higgs mass, the temptation is to focus on it, see whether the events are special, and so on; but one doesn’t do the same amount of work when the observation and expectation appear to agree. It’s hard to tell how significant such discrepancies are, because there were lots of places you might have seen bumps but didn’t.

To work around these issues, people use “blind analyses.” I first became aware of these when KTeV used one for its analysis of CP violation in kaons. The main idea is to prevent the experimentalist from seeing “the answer,” in whatever form it might take, until the very end. The act of unblinding is supposed to be the last thing you do, and you are stuck with the result you get: if you change it you’ve negated the whole point of doing it blind!

I’ve heard of blinding being done in a couple of ways. If you’re trying to measure a quantity precisely, one way to do it is to arrange for an offset (unknown to you) to be combined with the result you see while you’re preparing your analysis. You can then proceed as you would normally, except that your ability to tweak the real result to agree with previous knowledge is gone.

Alternatively, you can hide the data of interest from yourself — this was the MiniBooNE approach. You choose a class of events that would contain the signal you seek. These selection criteria create a “box” that you keep “closed”: you arrange not to see any passing events. You calibrate your understanding of the detector with data sharing some commonality with what you’re interested in — the same particles detected in a different configuration, for example. You select these “sideband” regions as well as you can to test for all the effects you can imagine would give you the wrong answer. Once you think you understand all the physics going on “around” the box, you have some confidence that you understand what to expect in the box, and then you can “open” it.

You may already have seen the danger with the second kind of blinding: aberrations that show up in the box may not be visible anywhere else. For example, one of the first LIGO results searched for short, bursty gravitational waves; when they opened the box, they found an event, which were almost immediately attributed to an airplane flying over a detector — but following the blinding protocol, they couldn’t remove it from their data sample.

MiniBooNE went through a very involved unblinding procedure to obtain their result. They performed the neutrino oscillation fit, and had the software tell them how consistent the fit was with the observed data (still in the closed box!) without revealing the fit parameters. In short, this told them if they could give a reasonable description of the box, without actually revealing what the description was. In fact, this revealed a problem, and did so before they had committed themselves to a full box-opening. They were able to tighten their selection before going any further. It turns out there is an excess of low energy events (the origin of which, as far as I know, is still unknown, but doesn’t seem to be oscillations), which would have seriously mucked up their result if they hadn’t been able to remove it from their fit. MiniBooNE illustrates the benefits of closed-box analysis (they might have spent a lot of time trying to get the excess to go away and stopped when it looked like a no-oscillation result), the dangers (they didn’t fully understand the box), and an interesting approach to trying to detect such problems beforehand (a sort of non-invasive box examination).

What about me? Strict blind analyses are painfully time- and labor-intensive, and I’ve never actually done one. My current work is sort of blind, in that it is next to impossible to figure out the final answer without running a specific program, and I can avoid doing that (”obscurity through laziness”). However I don’t have protocols that forbid me from fixing an obvious mistake after the program has been run. (I could certainly implement a “χ² consistency check” before I let myself see the fit values, though. I’ll think about it.)

While I’m not necessarily looking forward to seeing Inland Empire (working it tomorrow, as the “early spring snowstorm” moves in) I must admit to liking the trailers for it — if only because I suspect that a long sequence of disconnected images featuring Laura Dern growing progressively more hysterical is probably an excellent summary of the film, and such honesty is rare these days.

21 Apr update: in fact, the Laura Dern hysteria level remains remarkably constant throughout the film.   I don’t think anyone who watches it will ever think quite the same way about screwdrivers, rabbits, or Polish clowns ever again.

Elsewhere, Tommaso Dorigo makes a plea for particle physics experiments to enter the (free) blogging world. I find the argument intriguing but problematic.

A couple of issues are raised. One is whether the data should be made available to the public (in ASCII four-vectors or whatever); after all the taxpayers fund us, shouldn’t they get their money’s worth? I certainly agree that this is desirable, although extremely complicated. Our experimental architectures have not been designed to enable this in a simple manner (it can take literally months for a new collaboration member to learn to access data!), but if this was specified as a requirement from the beginning, as I believe it is for NASA projects, it could probably be done at the expense of a lot of physicist-years. However what is in question is not the data, but the analyses that follow, and even projects that release their data allow that what you extract from the data is your work.

Another is how collaborations communicate their results to a wider audience. Communication can almost always be better, and it’s a fair point that analysis web pages rarely go much beyond a brief technical summary and some plots. At one point, I know CDF was trying to post “plain English” summaries of physics results on the web, though for some reason all the links seem broken now. Regrettably but understandably, in the pressure to get results approved, papers written, and talks put together, the plain English version is seen as a low priority. Blogging might improve this.

[Aside: actually, we tend to communicate directly to specialists, ignoring even other particle physicists. We don't like to admit it, but we, too, get lost and bored very easily by work we don't immediately grasp. Try keeping an average Tevatron physicist's attention through a 30 minute talk about measuring angular distributions in χ_c radiative decays. I dare you.]

Finally, should experiments somehow embrace freer discussion of the data they collect and give up their roles as “sole authoritative commenters of the results they produce”? Are they? The speed of rumor is extremely high in the theoretical community, and (as an example) theorists seem more openly dismissive of the LSND results (because they don’t fit nicely into models) than experimentalists are (they can’t find anything obviously wrong with the experiment). It’s hard to imagine anyone being more authoritative than those who produced a result.

Oh, you mean should experimentalists be free to go “off message,” as they would say? There’s a tricky one. Why shouldn’t a collaboration micromanage how an important result is presented? If I spend a couple of years working on a result, and someone completely unrelated to it is the one who gets to reveal the numbers at a ski resort or be quoted in a popular publication, is it silly to want the right to sign off on what they say? To change this would, I believe, require a fundamental rethink of what a “collaboration” is. In the current model, you are either “in,” in which case you’re generally expected to speak for the collaboration when on record (because you have privileged access to the details and your name is on the papers), or you’re “out,” where you can say whatever you like at the expense of having your opinion discounted. If we atomize into having authors be solely responsible for their analyses, then we will all be able to say what we like, and will lose the ability to report on “our results.”

Incidentally, I’m not sure how an “experiment-approved blog” would address the last point. I think the sticking point is “experiment-approved,” not “blog.” Imagine approving blog entries at physics group meetings, spending hours discussing word choices …