Andrew Jaffe: Leaves on the Line

PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) is a Russian-Italian satellite measuring the composition of cosmic rays. One of the motivations for the measurements is the indirect detection of dark matter — the very-weakly-interacting particles that make up about 25% of the matter in the Universe (with, as I’m sure you all know by now) normal matter about 5% and the so-called Dark Energy the remaining 70%. By observing the decay products of the dark matter — with more decay occurring in the densest locations — we can probe the properties of the dark particles. So far, these decays haven’t yet been unequivocally observed. Recently, however, members of the PAMELA collaboration have been out giving talks, carefully labelled “preliminary”, showing the kind of excess cosmic ray flux that dark matter might be expected to produce.

But preliminary data is just that, and there’s a (usually) unwritten rule that the audience certainly shouldn’t rely on the numerical details in talks like these. Cirelli & Strumia have written a paper based on those numbers, “Minimal Dark Matter predictions and the PAMELA positron excess” (arXiv:0808.3867), arguing that the data fits their pet dark-matter model, so-called minimal dark matter (MDM). MDM adds just a single type of particle to those we know about, compared to the generally-favored supersymmetric (SUSY) dark matter model which doubles the number of particle types in the Universe (but has other motivations as well). What do the authors base their results on? As they say in a footnote, “the preliminary data points for positron and antiproton fluxes plotted in our figures have been extracted from a photo of the slides taken during the talk, and can thereby slightly differ from the data that the PAMELA collaboration will officially publish” (originally pointed out to me in the physics arXiv blog).

This makes me very uncomfortable. It would be one thing to write a paper saying that recent presentations from the PAMELA team have hinted at an excess — that’s public knowledge. But a photograph of the slides sounds more like amateur spycraft than legitimate scientific data-sharing.

Indeed, it’s to avoid such inadvertent data-sharing (which has happened in the CMB community in the past) that the Planck Satellite team has come up with its rather draconian communication policy (which is itself located in a password-protected site): essentially, the first rule of Planck is you do not talk about Planck. The second rule of Planck is you do not talk about Planck. And you don’t leave paper in the printer, or plots on your screen. Not always easy in our hot-house academic environments.

Update: Bergstrom, Bringmann, & Edsjo, “New Positron Spectral Features from Supersymmetric Dark Matter - a Way to Explain the PAMELA Data?” (arXiv: 0808.3725) also refers to the unpublished data, but presents a blue swathe in a plot rather than individual points. This seems a slightly more legitimate way to discuss unpublished data. Or am I just quibbling?

Update 2: One of the authors of the MDM paper comments below. He makes one very important point, which I didn’t know about: “Before doing anything with those points we asked the spokeperson of the collaboration at the Conference, who agreed and said that there was no problem”. Essentially, I think that absolves them of any “wrongdoing” — if the owners of the data don’t have a problem with it, then we shouldn’t, either (although absent that I think the situation would still be dicey, despite the arguments below and elsewhere). And so now we should get onto the really interesting question: is this evidence for dark matter, and, if so, for this particular model. (An opportunity for Bayesian model comparison!?)

Welcome to anyone one led here from Physics World’s Blog life column. This is a blog — so comments are encouraged (or you could click on the advertisements)!

It’s making the science-blogging rounds today that Obama has answered the questions posed as Science Debate 2008, questions on education, health care, stem cells and, of course, climate. He supports all the right scientific positions, and says several times that he will increase funding for basic research overall, but most importantly acknowledges and condemns the ideological and political interference that has plagued US research during the Bush administration.

McCain will, apparently, follow with his answers soon.

Meanwhile, here in the UK, the lengthily-named Department for Innovation, University and Skills (DIUS) is holding a consultation on Science and Society where you can answer questions like “How should scientists be rewarded for their efforts to communicate science to the public?” (I’m thinking big wads of cash.)

NASA’s latest space-based telescope has, until now, been known as the Gamma-Ray Large Area Space Telescope (GLAST). Today, they announced the very first results, and renamed it the Fermi Space Telescope, after physicist Enrico Fermi. Fermi was one of the pioneers of modern particle physics, part of the Manhattan Project generation that created the fundamental theories and techniques that we still use today, although he died sadly young before he could see the fruition of his work in today’s standard model of particle physics. He also thought hard about a number of more speculative issues, including wondering why, if life is common in the Universe, we haven’t met any other sentient creatures yet (a question known in fact as the Fermi Paradox) — and worried that the answer might be that civilizations tend to blow themselves up.

Today’s results came in the form of an all-sky map. The band in the center is gamma-ray emission from the Milky Way galaxy, and three of the four bright spots are pulsars — fast-spinning, magnetized neutron stars, and the fourth is a kind of distant active galaxy known as a “Blazar”.

I wonder how long before someone will compare the GLAST (Fermi) maps with the microwave-band maps from WMAP like this one:

The way gamma rays are created is very different from the emission microwaves, but any soup of gas, dust, stars and magnetic fields is likely to produce both.

Just as exciting as these maps is GLAST’s ability to find Gamma-Ray Bursts, some of the most energetic objects in the Universe, whose mechanisms are still poorly understood, and which may let us peer to the epoch of the formation of the very first objects.

(All images courtesy NASA.)

I’ve had this Fermilab-labeled mug ever since I spent the summer working there in 1990 (the picture is from a few years later — ignore the sartorial mis-step of the slouch-shouldered cardigan). Today, sadly, I dropped it fumbling with the keys to my office.

Actually, that was a pretty fun summer. I was working on an idea to detect cosmic axions, with a setup similar to some ongoing experiments but using somewhat odd ferrimagnetic materials. Axions are one of the possibilities for the omnipresent but difficult-to-detect dark matter. For the first and only time in my life, I got to play with superconducting detectors, RF cavities and old-fashioned strip-chart recorders, and not just for some assigned lab project. Alas, the idea didn’t pan out, and axions still haven’t been detected (despite a couple of claims to the contrary).

OK, not a vacation in the true sense of the word: I’ve been in the US, attending meetings (in Berkeley), workshops (in Santa Fe), conferences (in Pasadena) and, because I can’t seem to escape them, teleconferences everywhere and all the time.

Berkeley

In Berkeley, I attended the first all-hands collaboration meeting for PolarBear, an experiment that will measure the polarization of the CMB from a telescope that will eventually be situated on the Atacama desert plain in Chile — one of the highest, driest, least accessible places on the earth, and one of the least contaminated with light or radio interference. (Despite the name of the experiment, there are no polar bears there.) First, we’ll test it at the somewhat less remote White Mountain facility in California, shake out all the bugs. PolarBear is one of a new generation of experiments that will measure the CMB using not just a few tens of detectors, but a few thousand, which brings with it all sorts of technical challenges. In hardware, the first challenge is simply making so many detectors and keeping their properties uniform each to each — these are among the most sensitive microwave detectors ever built, essentially as good as the constraints of quantum mechanics and thermodynamics allow. The second, related to the first, is to pack as many of these into a small space — the focal plane of the telescope — as possible. Traditionally, microwave detectors have used horns to guide the electromagnetic waves from the sky onto the detectors, but those horns are much wider than the detector hardware. For experiments like PolarBear, we put the detectors themselves right at the focus of the telescope and make each of them into a little antenna, receiving directly the focused light after passing through a hemispherical lens. The final hardware challenge is to get the information from these thousands of detectors off of the telescope and into our computers, which the PolarBear designers have solved with a new technique called “frequency-domain multiplexing”. Sort of like the way FM radio manages to convey the full spectrum of sound by modulating at a particular frequency, the very high-tech SQUIDs (Superconducting QUantum Interference Devices) can then amplify these tiny CMB signals into data we can analyze.

In fact, the data analysis and computing challenges are almost as significant as those faced in hardware. With thousands of detectors and a telescope that will run for the better part of several, we have many orders of magnitude more CMB data than we’ve ever dealt with before, combined with a sensitivity goal better than a millionth of a degree. By adding more and more detectors, we can make the raw experiment itself sensitive enough to do this. What we don’t know is whether we can eliminate everything else that can possibly contaminate our results: light may spill over our shield from the 300 degree ground or directly from the atmosphere; dust in our solar system or our galaxy also glows in the bands we want to measure, as do external galaxies millions of light-years away. So our task is to compress the terabytes of data into a few interesting numbers (like the energy scale of inflation) and to simultaneously separate the cosmic signal from the that produced by instrument and from the rest of the Universe (which may be much brighter!). Suffice to say, we have some good ideas but until we’re confronted with real data we won’t know how successful we’ll be.

Plus, I ate bagels (better than London; not as good as New York) and burritos, and bought shoes at cheap American prices (at least when I think in British Pounds).

Next up, Santa Fe…

Thanks to Dave for pointing out that the final results of the STFC programmatic review sweepstakes popularity contest consultation exercise have been released. Following on from the recommendations, which grouped all projects into five projects, the STFC Council has decided where and how the money will flow.

The best news overall is that only the very lowest band of projects will no longer be funded, rather than two lowest as had originally been planned. As expected, Imperial Astrophysics has fared relatively well, with continued support for Planck, Herschel, Scuba II, UKIDSS, LISA Pathfinder and XMM Newton.

Overall, it looks like a relatively small number of projects will be “discontinued” and that STFC “will therefore ramp down funding at an expeditious but appropriate rate in consultation with the PIs/stakeholders. Where possible [they] will look for ways to ensure that there is a return on … previous investments.” In astrophysics, these projects include the UK’s contributions to the gamma-ray observatory VERITAS and the astronomical computing and data-analysis projects AstroGrid and CASU/WFAU, in particle physics the b-physics experiment BaBar, and most of ground-based Solar and Terrestrial physics. On the other hand, despite the panel recommendations which put it into the lowest band, the Mercury mission BepiColombo — which apparently threatens to consume the entire ESA science budget — will continue to be funded, because the UK contribution “is subject to an MOU [memorandum of understanding] with the Agency and will be respected.”

But the dark underside to the entire process remains the assumed 25% cut to the “grants line” — the money to pay for the actual science return on these missions, as well as all of the science that doesn’t come from large projects, mostly in the form of salaries for postdocs: theoretical physics, observations of individual astronomical objects, and just thinking hard and opening up new areas to explore. I’ve just got a big stack of grant applications to referee from STFC — let’s see how many of even the best manage to survive the cut.

[I promise to find something new to talk about, now that this unsavory episode seems to be reaching its conclusion, for now at least. Until then, you’ll just have to follow my twittering, although you’re more likely to learn about my musical tastes than cosmology…]

No time for a full blog post, but I wanted to point out the results of the STFC Consultation, now available.

Some of my favorite projects like AstroGrid seem to have not fared too well (the consultation panel rated it highly, but PPAN, responsible for the final ranks, disagreed). Nonetheless, Imperial Astrophysics projects like Planck, Herschel, Scuba II, UKIDSS, LISA Pathfinder and XMM Newton appear to have survived the cut. However,

It is important to stress that these reports are not the final conclusions of the Programmatic Review. These conclusions will be reached by STFC Council using these reports to inform their decision-making.

Dick Bond, a friend, mentor and longtime collaborator has won the 2008 Gruber Cosmology prize. Dick’s work has been instrumental at bringing us into this age of “precision cosmology”. He has always concentrated on that interface between theory and observation, making predictions for what we would see in the Cosmic Microwave Background, and how we might best extract that information. The present industry in Cosmological Data Analysis is in no small part down to his ongoing work in the field. To quote the Gruber citation itself:

Professor Bond’s work has provided the theoretical framework to interpret the observed inhomogeneities in the fossil radiation left over from the early stages of expansion of the Universe—the Big Bang. Professor Bond’s research has helped us understand the transition from the nearly featureless early Universe to the wonderfully structured world of galaxies, stars and planets today.

Congratulations, Dick!

Today’s obligatory pointer to the latest on the ongoing UK physics-funding crisis: the “Innovation, Universities, Science and Skills” committee has released a pretty scathing report, mostly slamming STFC’s handling of the situation (and refuting most of its arguments for how it got us into this mess to begin with). The BBC’s Today show had interviews confirming these points with Committee Chair Phil Willis MP and Brian Cox.

At this point, the best we could hope for in the short term would be a small amount of emergency funding to close some of the most gaping holes (and as a measure of good faith) and a major change in the STFC management structure. So far, they’ve said they want to “strengthen the management team”, “consult more widely”, and “improve… communication”. We’ll see.

As usual, Paul Crowther collects all the relevant information and news, and Andy Lawrence has good commentary.