ATLAS Higgs Interpretation

Question

I came across this abstract, and I am curious as to what the ATLAS Team has actually discovered:

Abstract Motivated by the result of the Higgs boson candidates at LEP with a mass of about 115~GeV/c2, the observation given in ATLAS note ATL-COM-PHYS-2010-935 (November 18, 2010) and the publication “Production of isolated Higgs particle at the Large Hadron Collider Physics” (Letters B 683 2010 354-357), we studied the γγ invariant mass distribution over the range of 80 to 150 GeV/c2. With 37.5~pb−1 data from 2010 and 26.0~pb−1 from 2011, we observe a γγ resonance around 115~GeV/c2 with a significance of 4σ. The event rate for this resonance is about thirty times larger than the expectation from Higgs to γγ in the standard model. This channel H→γγ is of great importance because the presence of new heavy particles can enhance strongly both the Higgs production cross section and the decay branching ratio. This large enhancement over the standard model rate implies that the present result is the first definitive observation of physics beyond the standard model. Exciting new physics, including new particles, may be expected to be found in the very near future.

The abstract seems to be from a restricted web site (CERN Log-in required), however I have been able to track down a PDF that seems to be discussing the same phenomenon, however the abstracts are not the same.

Currently, as I understand it, there is a lot of skepticism about the initial Higgs candidate. If this isn't the Higgs, then what part of the standard model is actually being represented? Or is this an entirely new phenomenon?

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Comments

Could you link to the paper?

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@Joe I will try, I had a hard time digging this abstract up (I only re-found it on a blog).

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For instance, the one link I have requires a CERN account... http://cdsweb.cern.ch/record/1346326?

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Have you seen this? http://blogs.plos.org/badphysics/2011/04/22/115gev/ The update at the end makes it look like this is not a real paper.

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@Joe, no I had not! :) Well, that sort of makes my question moot... Darn it.

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$4\sigma$ would certainly be enough to be evidence of something, but most of the stuff you here about is $2\sigma$ and as they are measuring across a big range you get these kind of hits simply from sampling error. The number of events recorded tends to be very low. That said, I'm not a HEP person, so you might get a better answer from someone else.

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Rather than leaving the question answerless, if you consider my comments an answer, would it be ok for me to turn them into one?

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@Joe please do. :)

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I'm not sure on the idea of discussing theoretical implications unpublished experimental rumors. Meta for this discussion: http://meta.theoreticalphysics.stackexchange.com/questions/57/should-we-allow-discussion-of-unpublished-rumors

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Answer 1

The abstract you refer to seems not to actually be a real paper. It excited the blogosphere last april, but from what I can see it is not actually a real result. A CERN spokesperson talking to Nature pretty much quashed the rumour:

ATLAS’ spokeswoman Fabiola Gianotti stops short of disowning the leaked document, but tells Nature signals of the kind reported in the memo show up quite frequently in the course of data analysis and are later falsified after more detailed scrutiny. “Only official ATLAS results, i.e. results that have undergone all the necessary scientific checks by the Collaboration, should be taken seriously,” she says.

A $4\sigma$ result would certainly be something to be taken seriously, though still short of the $5\sigma$ level which is usually taken as a discovery. However, most of the bumps that appear tend to be more around the $2\sigma$ range, and with good reason. These kind of events are very rare, and it can take many years to build up enough recorded events to sufficiently decrease the sampling error. The reason for these kind of bumps often turns out to be sampling error. While naively one would think that a $2\sigma$ event is already a rare event and so should signal something, you have to keep in mind that they are searching across a large range, and so some small bumps are to be expected. These don't necessarily correspond to anything other than sampling error.

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Answer 2

As Joe said, that was an old rumor that turned out to be nothing. You can see more recent Higgs to two photon results from ATLAS here and CMS here. There are no hints of a signal so far in this channel.

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