D0 Decides to be Debbie Downers

By Sean Carroll | June 10, 2011 9:40 am

Alliterative title stolen shamelessly from the lovely and understanding Jennifer Ouellette, who blogs background about the hunt for new particles at Discovery News.

So here we have science, marching on. Just last week we heard that CDF, one of the big experiments at the Tevatron at Fermilab, had collected more data relevant to a mysterious bump they had previously reported around 150 GeV in collisions that produced a W boson and two jets. The new data (7.3 inverse femtobarns, up from 4.3 fb-1 previously) made the bump look even more prominent, rather than watching it regress back down to the mean. The discrepancy is now more than 4 sigma, giving license to get just a wee bit excited that new physics might be on the loose.

Now D0, the other big experiment at the Tevatron, is ready to weigh in — and the “D” stands for “damper,” it appears. Here’s a blog post at symmetry, a link to the technical paper, and a webcast for a talk that will happen this afternoon at 4:00pm Central Time. You knew that Jester would be on the case, and he is.

But this picture tells you all you need to know.

With 4.3 fb-1 of data analyzed, the CDF bump should be just barely visible, as indicated by the dotted line labeled “Gaussian.” But there doesn’t seem to be anything there. And it’s not just you; the collaboration estimates that the probability that there is really a bump there is less than 10-5. Not very encouraging, really.

But still — it does seem to be there in the CDF data. So what’s going on? At this point, it’s not clear. Both experiments are extremely mature and well-understood, and the collaborations are good at what they do, so it is likely to be something very subtle at work. It still could be new physics, that is somehow playing games with us, but certainly the prospects don’t look as good today as they did yesterday. Look like science is going to have to march on a bit more before everything is clear.

  • Phil

    The Tevatron DID find something. They discovered a new Fund-on particle.

  • uncleMonty

    I know this bump wasn’t supposed to be the Higgs boson. But can someone explain something to me? I’m trying to make sense of the Higgs thing, and I know without the maths I’m doomed to remain at the level of the analogy, but sometimes that can still make you feel like you understand a little about something. So: the Higgs field is compared to molasses, slowing down everything with mass. The way it slows massive things down is by interacting with the Higgs bosons that are an integral part of everything massive. Higgs bosons are very difficult to detect because it takes incredibly high energies to separate them from whatever they are bound to, and they disappear very quickly after that.

    Is that kind of right, is the Higgs field just sort of *there*, everywhere, hanging out slowing down anything with mass? And there’s no way to detect the field directly? Correct me if I’m wrong. But if I’m right-ish: how is this preferable to eliminating the field altogether, and just saying the Higgs boson itself *is* the mass?


  • Low Math, Meekly Interacting

    Are there some other good examples of such a significant bump being completely absent in another experiment’s results? The obvious culprit appears to be mis-modeled backgrounds, but even the blogospheric nay-sayers seem to be at a loss for what could account for such a discrepancy, given the reputation of both groups and their corresponding instruments.

  • Rien

    No, the Higgs bosons aren’t part of everything massive. One has to make a difference between the Higgs field and the Higgs particle. The Higgs field is everywhere, and interacts with everything massive so that it is slowed down. This looks like a mass, and if it looks like a mass it is a mass. The Higgs bosons on the other hand are excitations of the Higgs field. That is what all particles are: they are excitations of an underlying quantum field.

  • Wolowitz

    Maybe someone can explain something else about the Higgs field. If it had an average value of zero at the time of the big bang (or shortly afterwards), wouldn’t that mean that the singularity — and the universe — had zero mass? That would make it easier to understand how the entire universe could fit into an infinitely small size, but it also seems to contradict the idea of the singularity having infinitely high gravity. Maybe I don’t understand the timeline correctly.

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  • http://washparkprophet.blogspot.com ohwilleke

    Is it appropriate to pool data in this case?

    The D Zero results, after all, do show a bump where CDF finds one, just at not nearly the same intensity or statistical significance.

    Were one to split the difference, one wouldn’t get the 4 something sigma result that CDF announced, but surely would end up somewhere in the 2 sigmas. Not a “discovery” but not necessarily “nothing” either.

    It does suggest that a very comprehensive and detailed comparison of the methods used by the two experiements is in order, however.

  • Brian137

    Even if CDF’s bump is the result of some error, we need to discover the source of that error. This matter needs to be thoroughly resolved in any case.

  • http://www.anadish.com/ Anadish Kumar Pal

    Sure, Higgs boson never explained the whole. But attempted to explain the oldest concepts of modern physics in quantum framework, which was given a raw demonstration by Galileo in 1589 by dropping objects from the Leaning Tower of Pisa. We start learning Physics with his laws of force and friction but never learn more than that ever during our whole tenure as students. A quantum explanation of mass and gravity thus will give a body to the 100 year old painting of quantum mechanics.

    However, it’s not Higgs boson, but unnamed particles of two origins, which create gravity between ‘masses’. The discovery already took place in 2010 and has now been reported as a USPTO application which will be officially published by the US Patent Office. Some general landmarks are on my site http://www.anadish.com/. I have refrained from giving details, as the details are already under publication.

  • Alan

    A standard statistical quibble: it is not that “the probability that there is really a bump there is less than 10^-5.” Instead, the p-value describes the probability that the standard model + 4pb bump would produce this data or something “less bumpy” (measured by LLR). It’s P(data|bump), not P(bump|data).

  • JPH

    @Wolowitz: Without getting technical, probably the best way to clear up your confusion is to point out that General Relativity says that gravitational effects are due to energy and momentum (technically the stress-energy tensor) unlike Newtonian Gravity which says gravity is due to mass. Massless particles, like photons, can have a very large gravitational effect. In fact, the early universe was dominated by gravitational effects of massless (or effectively massless) particles because they had most of the energy.

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  • KWK

    So this particular bump went away, but I’m curious what you (Sean) have to say about another bump that’s in the news of late…the DAMA/LIBRA “Dark Matter” annual modulation that is now sort of confirmed by CoGeNT.

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  • http://webmohan.wordpress.com/ Manmohan

    I think CDF and Dzero need to check their MC for exactness eg the list of decay modes that were studied in MC in Dzero and in CDF need to be same atleast the ones that were reconstructed.. is it possible that Dzero missed a mode or a particular branching of that mode. Very likely. suppose one intermittent resonance is missing in case of one mode (or more) from the topography, at the generator or reconstructed level then this could be the most likely case. The topography of all modes of both analysis needs to be matched…(and the modes that were reconstructed in the data). This list of modes needs to be same…and their topography at the generator and reconstruction need to be exctly same for both analysis…

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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .


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