Friday, 30 October 2009

Hail to Freedom

Experimental collaborations display vastly different attitudes toward sharing their data. In my previous post I described an extreme approach bordering on schizophrenia. On the other end of the spectrum is the Fermi collaboration (hail to Fermi). After one year of taking and analyzing data they posted on a public website the energy and direction of every gamma-ray photon they had detected. This is of course the standard procedure for all missions funded by NASA (hail to NASA). Now everybody, from a farmer in the Guangxi province to a professor in Harvard, has a chance to search for dark matter using real data.

The release of the Fermi data has already spawned two independent analyses by theorists. One is being widely discussed on blogs (here and here) and in popular magazines, whereas the other paper passed rather unnoticed. Both papers claim to have discovered an effect overlooked by the Fermi collaboration, and both hint to dark matter as the origin.

The first (chronologically, the second) of the two papers provides a new piece of evidence that the center of our galaxy hosts the so-called haze - a population of hard electrons (and/or positrons) whose spectrum is difficult to explain by conventional astrophysical processes. The haze was first observed by Jimi Hendrix ('Scuse me while I kiss the sky). Later, Doug Finkbeiner came across the haze when analyzing maps of cosmic microwave radiation provided by WMAP; in fact, that was also an independent analysis of publicly released data (hail to WMAP). The WMAP haze is supposedly produced by synchrotron radiation of the electrons. But the same electrons should also produce gamma rays when interacting with the interstellar light in the process known as the inverse Compton scattering (Inverse Compton was the younger brother of Arthur), the ICS in short. The claim is that Fermi has detected these ICS photons. You can even see it yourself if you stare long enough into the picture.

The second paper also takes a look at the gamma rays arriving from the the galactic center, but uncovers a completely different signature. There seems to be a bumpy feature around a few GeV that does not fit a simple power-law spectrum expected from the background. The paper says that a dark matter particle of mass around 30 GeV annihilating into b quark pairs can fit the bump. The required annihilation cross section is fairly low, of order $10^{-25} cm^3/s$, only a factor of 3 larger than that needed to explain the observed abundance of dark matter via a thermal relic. That would put this dark matter particle closer to a standard WIMP, as opposed to the recently popular dark matter particles designed to explain the PAMELA positron excess who need a much larger mass and cross section.

Sadly, collider physics has a long way to go before reaching the same level of openness. Although collider experiments are 100% financed by public funds, and although acquired data have no commercial value, the data remains a property of the collaboration without ever being publicly released, not even after the collaboration has dissolved into nothingness. The only logical reason to explain that is inertia - a quick and easy access to data and analysis tools has only quite recently become available to everybody. Another argument raised on that occasion is that only the collaboration who produced the data is able to understand and properly handle them. That is of course irrelevant. Surely, the collaboration can make any analysis ten times better and more reliably. However, some analyses are simply never done either due to lack of manpower or laziness, and others are marred by theoretical prejudices. The LEP experiment is a perfect example here. Several important searches have never been done because, at the time, there was no motivation from popular theories. In particular, it is not excluded that the Higgs boson exist with a mass accessible to LEP (that is less than 115 GeV), but it was missed because some possible decay channels have not been studied. It may well be that ground breaking discoveries are stored on the LEP tapes rotting on dusty shelves in CERN catacombs. That danger could be easily avoided if the LEP data were publicly available in an accessible form.

In the end, what do we have to lose? In the worst case scenario, the unrestricted access to data will just lead to more entries in my blog ;-)

Update: At the FERMI Symposium this week in Washington the collaboration trashed both of the above dark matter claims.


Anonymous said...

Is just accidental coincidence?


Space / Time 3:1

Dark Energy / Dark Matter of the invisible Universe 3:1

Hydrogen / Helium, 99% of the visible Universe 3:1. By the way, Hydrogen atoms - Fermions; Helium- 4 atoms - Bosons.

Stable particles of the Universe (Fermions) spin 1/2 (Proton, Electrons, Neutrinos) -3

Stable particles of the Universe (Bosons) with spin 1 (photon) -1

Is this trivial coincidence?
Why is numerical coincidence container and its contents?

Jester said...

God. This must be it .-)

Anonymous said...

You're mixing a bit data made public with results made public there. Two different things.
Other than this your writing is excellent as always but I wonder whether you're in good health; two posts in four days?! Can you do that more often?

Anonymous said...

Anonymous, my dear cousin, you forgot neutrons in your laundry list of fermions. There are neutron in Helium nuclei, and they are stable.

Jester said...

Yes I was imprecise, I meant data along. Concerning my output, it also depends on the rest of the world to produce interesting results I can write about:-) With the LHC up and running it should get easier.

Anonymous said...

My dear cousin!
neutron non-stable particle, longevity 17min.

Joe B said...

Isn't there a question of size here, though? Aren't the LEP tapes a lot bigger than the data from Fermi?

Not necessarily a reason for not making the data public, but surely a pretty good excuse...

Ervin Goldfain said...


I posed this question before and I am posing it again: how strong is the evidence that the haze comes from processes produced by Dark Matter? Is it possible that we don't understand well enough this particular signature of particle astrophysics and we rush to judgment?


Ervin Goldfain

Jester said...

To my taste the haze would never be the smoking gun, rather one piece of evidence that might fit the bigger picture. It's astrophysics so it's dirty. In fact, there have been already papers trying to explain the haze by pulsars.

Jester said...

Joe B: come on, it's 21st century :-)

Anonymous said...

Actually, Tevatron data (at least for run I, not sure about run II) was really stored on tapes. Yes, in the 1990s...

chris said...

As sad as it sounds, I think your update pretty much gives the reason why e.g. LEP data are not released publicly: it just takes too much of the collaborations efforts to straighten the (typically overambitious or cranky) claims of the reanalyzers.

Gphillip said...

Let the physics community work through the claims. In case anyone has forgoten, that's the way science is supposed to work. Where would we be today if the physics giants of the past had hid their results? I suspect there are many great discoveries hiding in the dusty data of past experiments. Let's be honest. The real reason this data is locked up is greed. The experimenters don't want some grad student working on her/his laptop winning a Nobel Prize with their data. This stinks.