Fermi Lab's New Particle Discovery in Question

"Back in April physicists at Fermilab speculated that they may have discovered a new force or particle. But now another team has analyzed data from the collider and come to the exact opposite conclusion. From the article: 'But now, a rival team performing an independent analysis of Tevatron data has turned up no sign of the bump. It is using the same amount of data as CDF reported in April, but this data was collected at a different detector at the collider called DZero. "Nope, nothing here – sorry," says Dmitri Denisov, a spokesman for DZero.'"

Comments

Data sharing

[symes]

I think more than anything, this demonstrates why sharing data openly is such a good thing. Sure, not great news for those at Fermi Lab, but if scientists generally (especially those in the behavioural sciences...) were encouraged (or forced?) to allow others free access to their data then I'm sure a few surprising claims might be rewritten and a few interesting blips otherwise missed might be found.

Re:Data sharing

[The_Wilschon]

These experiments do not share their data openly (while the experiment is still taking data) because if they did, there would not be any data. The only way to get enough physicists to work on the experiment to make it run well enough to get any data is to restrict data access to those who do service work on the experiment. After the end of data taking, the data may be released, but I don't know the time table on which that typically occurs.

Re:Data sharing

[Anonymous Coward]

Ex particles guy writing here --- the reason that data isn't immediately shared is that data acquisition and first pass analysis have to be done before you even *think* about looking for new physics. Moreover, the detector systems are complex enough, that it is really hard to be sure the analysis works correctly when you were the one who built the bleedin' thing. Then there's the other half -- almost no detector has complete coverage -- certainly none of the detectors at FNAL or CERN do so you are at the mercy of Monte Carlo simulations to work out the corrections. So you have to do the experiment twice; once is the physical world and once in a virtual world. Mismatches between the worlds can easily lead to spurious signals. Not saying that astronomy is any easier -- at least as its practiced now a days. And WMAP, for example, doesn't seem to be giving away the raw data. There is some turf protection -- "we invested blood sweat and tears as well as years of our lives to build the detector -- we get first crack at the data" -- I don't think that's a bad thing.

The particle physics community does have the equivalent of a star map it's the Review of Particle Properties (RPP).

Re:Data sharing

[chissg]

[Re-post non-AC] Star catalogs aren't data: they're the results of decades of observations, corroborations, corrections and debates over just exactly what that particular black spot on the white plate was. You want the raw telemetry from every telescope that isn't read out with a Mark I eyeball, and every plate ever taken and scientist's observation note from those that were? You want all the calibration data from WMAP, and all the histograms that were plotted to analyze them and turn them into corrections for the main data so they actually *mean* something? Particle physics, "data" is the 1s and 0s from every piece of sensory equipment in the detector hall, beam area and points between: often millions of readout channels, each of which means something and has its own quirks and problems that need to be measured and understood with more and different types of data (calibration, cosmic rays, etc). And, these readings are taken at frequencies between thousands and millions of times per second. We often have to analyze the data to a preliminary level just to decide whether they're worth keeping to analyze properly later because there's neither the bandwidth nor the storage space nor the computing power -- even now -- to keep them all. The LHC experiments store petabytes of data per month, and storage, access and transfer costs are significant: you pay for access to those data by contributing to the experiment. OK, now let's assume you get the raw data. Now what? Good luck with that. There's a reason scientist groups and expert contractors spend years and sometimes decades writing the reconstruction and analysis software for particle physics experiments: teasing useful results from the data are hard. If we were to spend our timing pointing out the rookie mistakes of every schmo who fiddled with the data for a while and thought he'd found something new, the work would never be done. "Heisenberg's Uncertainty Principle Untenable [icaap.org]," anyone?

Already known?

[MurukeshM]

What about this comment on the original /. post: D0 has done this same sort of analysis, and they do not see this bump. But, their background modeling procedure involves reweighting the expected distributions (from Monte Carlo) in delta R between the jets (sort of an angular separation between the jets), which is a variable that is strongly correlated with the dijet mass. That is, their background model would be expected to have a strong tendency to fill in a bump like this. Now, which model is more correct is open to question, but it is certainly true that whether or not this bump turns out to be from real new physics (unlikely, in my professional opinion), their procedure is almost guaranteed not to find it.

Re:Already known?

[The_Wilschon]

That was me. In the analysis released on Friday, D0 does not perform the delta R reweighting (this was a specific criticism that they sought to address). In spite of no delta R reweighting, they still do not see the bump. There are some systematic errors that they handle differently from CDF which are quite likely to explain the result. Some of my colleagues at CDF are investigating (and were investigating before this D0 release, because of a suggestion by a D0 physicist at the release of the original bump paper) these systematics and their effect on our ability to model the data well. I can't really comment further until results are released, however.