Life on the lattice

Thoughts on lattice QCD, particle physics and the world at large.

Thursday, July 02, 2009

LATTICE 2009 programme online

The programme for the LATTICE 2009 conference in Beijing is up on the Web (here). This gives me the opportunity to remind my readers of the need for guest bloggers to cover the conference, since I will not attend this year.

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Sunday, June 14, 2009

我不去 LATTICE 2009 北京

I hope I didn't maltreat the 汉字 above too badly in my ignorance -- in any case, what I'm trying to say is that I am not going to the Lattice conference this year. Yes, that means no conference blog from me.

"But how are we going to survive without the annual conference blog?" I hear a reader exclaim. To which I reply, without so much as batting an eyelid: "You will have to write it yourself." Okay, I admit that imaginary exchange is just silly, but the reality is that I'd still like to cover the Lattice meeting in Beijing, but obviously can't do the reporting myself. So I would like to encourage my readers to volunteer as guest bloggers and cover a session or two from their own point of view. Any conference reports (except for those of a libelous, pornographic or defamatory nature) submitted as comments or by email will be published, with or without attribution as desired by their respective authors.

To make this a more tempting offer I will add a prize for the most productive (by number of sessions covered, by words in case of equal numbers of sessions) guest blogger, who will win my Lattice 2008 Williamsburg baseball cap (autographed or unautographed at the winner's discretion).

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Tuesday, May 19, 2009

Austria will not leave CERN

Public pressure has been successful: Austrian chancellor Faymann has decided to veto the pull-out from CERN that his science minister had announced. Over 32,000 people have signed the online petition against the proposed withdrawal, and together with open letters by Nobel laureates and other public figures, this seems to have been enough to convince the Austrian government that leaving CERN would have been bad PR. I suppose that's another example of "yes, we can!"

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Sunday, May 17, 2009

Openness >> fraud

In the most recent edition of PhysicsWorld, there are two articles that on the face of it have little to do with each other: one is about Jan Hendrik Schön, the physicist formerly famous for creating the first organic superconductor and the first single-molecule transistor, and now most famous for having simply made up all of those results out of thin air, the greatest kind of scientific fraud in physics. The other article, by Michael Nielsen, is about how the internet is transforming scientific communications, looking at which new means of scientific communication failed (such as Physics Comments and scientists contributing to Wikipedia -- although Scholarpedia is taking off quickly at the moment, probably because its signed and peer-reviewed authorship model is more in line with academic customs than Wikipedia's semi-anarchistic one) and which succeeded (the arXiv, of course) in making the dissemination of scientific results quicker and more transparent.

At first glance these two topics appear to have little to do with each other. At second glance, however, they are closely intertwined.

Schön's deception was only possible because the researchers who tried and failed to replicate his results didn't have access to his primary data. Once doubts had been raised over the appearance of two completely identical graphs supposedly representing two completely different sets of experimental data, Schön's primary data were subjected to close scrutiny and were found to be non-existent -- his labbooks had been destroyed, and his samples were damaged beyond recovery. This raises the question whether it would have been possible to even contemplate such a fraud in an environment where scientists are genuinely expected to hide nothing, and in particular to make their primary data publicly available after publication.

The more radically open schemes, where raw data are being made public before publication, are unlikely to take off largely because of concerns over the enormous plagiarism potential. But once results have been published and priority has thus been established by the original authors, there is no immediately obvious reason not to allow other researchers to perform their own analyses of the primary data, either to confirm (or possibly to refute) the original analysis, or to use their own methods to obtain results from the data that the original authors didn't (either because they weren't interested or because they didn't have the relevant analysis methods at their disposal). Some access controls are needed, of course, in order to ensure that the later researchers will duly acknowledge the use of the original group's datasets.

It is hard to see how a fraud like the Schön case could have occurred under a scheme like this; the groups who wasted years on trying to replicate his results to no avail would likely have realised the fraud if they had had access to Schön's lab books.

Just like with the arXiv (which after all started out as a specialised High Energy Physics preprint server and now has revolutionised publishing in most of physics and mathematics, plus assorted other areas), particle physicists are pushing ahead with schemes to open access to raw data, and lattice QCD is right at the forefront of the movement: since the most expensive step in unquenched simulations is the actual generation of the gauge configurations, using those just once for whatever analysis or analyses interests one specific group would be an irresponsible waste of computer resources, postdocs' lifetime and taxpayers' money.

It has therefore been common for a long time now for lattice theorists to form larger collaborations that pool their resources to generate their configurations and then perform different analyses on them (policies differ: some collaborations publish all of their papers as a collaboration, some break up into smaller groups for most analyses). But with the huge effort needed for unquenched simulations on large ultrafine lattices with very light quarks, even that becomes inefficient; in particular, groups that don't belong to any of the major collaborations would be left out in the quenched darkness. Therefore, it is becoming an increasingly common policy to make gauge configurations available to the larger lattice community after performing some initial analyses that the collaboration generating the ensemble is particularly keen on doing (generally, that includes the hadron spectrum, plus some other stuff).

Configurations have been available for a while at NERSC's Gauge Connection, and are now quickly beginning to be available on the International Lattice Data Grid (ILDG). This way the many CPU cycles that have been invested in generating these ensembles are put to even better use by enabling other groups to run their analyses on them.

Just like in the case of the arXiv, it may take a while for other disciplines to follow suit, but it appears likely that if and when more and more scientists choose to make their raw data public after publication (and those that don't therefore become increasingly subject to suspicion by their peers), a fraud case like that of Jan Hendrik Schön will become quite impossible at some point in the future.

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Tuesday, May 12, 2009

Austria to leave CERN?

Austria's Science Minister Johannes Hahn has announced that Austria is to pull out of CERN. The reason given is that the 20 M$/year that Austria contributes to CERN is too much in these economically difficult times. Given the amounts handed out to bankrupt banks these days, that seems like an odd argument against participating in the greatest international endeavour of our time, an endeavour whose spinoffs include among others the WWW, no less. Maybe the crackpots convinced Mr Hahn that the LHC was going to end the world? Or maybe the Austrian government just wants to reap the global benefits of international research without contributing anything to it? You can sign a petition against this piece of political silliness here.

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Thursday, April 09, 2009

arXiv goes Facebook

Remember my slightly tongue-in-cheek question when we'd see a "My arXiv papers" application for Facebook? Well, it has happened, and apparently not on April Fool's Day. In fact, it is a part of the new author identifiers system introduced by the arXiv, which will help identify papers by the same author (since not everyone has the advantage of having a name that is unique within his field).

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Saturday, April 04, 2009

MAMI and beyond, Day Five

Today's first talk was by Savely G. Karshenboim (Garching and St Petersburg) who spoke about hadron physics' impact on precision in atomic physics. Atomic physics is famously precise in its measurements, with relative precisions of order 10-12 now being achieved for some quantities. The largest uncertainty in theoretical predictions there now comes from uncertainty about the effects of nuclear and proton structure.

The second speaker was Wolfgang Gradl (Mainz) with a talk on hadronic uncertainties in flavour physics. Flavour physics is about quark-level quantities (CKM matrix elements), but only hadronic decay and oscillation processes are experimentally accessible; thus one needs good control of QCD effects contained in form factors, decay constants and the B meson bag parameter. Lattice QCD is an important ingredient here, in particular when coupled with effective field theories such as HQET.

This was followed by discussion sessions about the prospects for MAMI, about the prospects for an electron-nucleon collider, and about the impact of hadronic physics on high-energy physics. The good news for lattice theorists is that there is a high demand for precise lattice predictions by experimentalists. The not so good news is that most of that demand is in areas where the lattice is not in a position to make accurate predictions in the near future, such as resonances, hadronic scattering lengths or hadronic light-by-light scattering amplitudes.

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Thursday, April 02, 2009

MAMI and beyond, Day Four

Today's first talk was Fabio Ambrosino (INFN Napoli) speaking about flavour physics at the 1 GeV scale. Of course, flavour physics here does not mean charm or B-physics -- the topic was instead the accurate determination of |Vud| and |Vus| from nuclear transitions and Kaon decays. The very accurate results obtained there confirm the unitarity of the first row of the CKM matrix to great accuracy, as well as confirming universality (via a comparison of Gμ and GF).

The next talk was by Christoph Hanhart (Forschungszentrum Jülich), who spoke about QCD exotics such as hybrids, glueballs, tetraquarks and hadronic molecules. Here I learned what the physical difference between a tetraquark and a mesonic molecule (who after all both consist of two quarks and two antiquarks) is: since hadrons (as opposed to quarks) can go on-shell, the S-matrix elements for a hadronic molecule (but not a tetraquark state) would contain non-analyticities.

The remainder of the day had talks mostly about hypernuclear physics (hypernuclei are nuclei with a nucleon replaced by a strange baryon), which I feel unable to summarise (I only remember that hypernuclei are smaller and more tightly bound than normal nuclei), and accelerator physics, which I skipped in order to look after my email and a couple of papers that are in the final pre-arXiv stages of the pipeline.

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MAMI and beyond, Day Three

Today's morning session was filled with experimental talks making the case for an electron-nucleon collider to study the structure of the nucleon.

The short afternoon session had a talk by Akaki Rusetsky (Bonn) about the determination of resonance properties from finite-volume spectroscopy using a combination of Lüscher's formula and heavy-baryon chiral perturbation theory applied to lattice simulations near (or ideally at) the physical quark masses.

After that there was an excursion to Kloster Eberbach, a nearby former Cistercian monastery, where a guided tour was combined with a wine tasting. After that, the conference dinner took place in a castle hotel on the Rhine.

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