Update (April 25th, 2011) at end.
So I woke up this morning to several emails about a strange “Higgs sighting” at ATLAS. On a Woit’s blog, a commenter named Higgs? shared an abstract purporting observations of some 115 GeV resonance at CERN. It claims to be from an “internal note” from the ATLAS Collaboration.
Report number ATL-COM-PHYS-2011-415
Title Observation of a γγ resonance at a mass in the vicinity of 115 GeV/c2 at ATLAS and its Higgs interpretation
Author(s) Fang, Y (-) ; Flores Castillo, L R (-) ; Wang, H (-) ; Wu, S L (University of Wisconsin-Madison)
Imprint 21 Apr 2011. – mult. p.
Subject category Detectors and Experimental Techniques
Accelerator/Facility, Experiment CERN LHC ; ATLAS
Free keywords Diphoton ; Resonance ; EWEAK ; HIGGS ; SUSY ; EXOTICS ; EGAMMA
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.
Is this a Higgs sighting? Well, the abstract says, “the event rate…is about thirty times larger than the expectation from Higgs to γγ in the standard model” making it certainly not evidence for a Standard Model Higgs. Is it a real observation? That’s a better question at this point. Better still, is this a real note?
I don’t work with CERN, so my login doesn’t give me permission to access internal memos (in fact, I can only read the partial title “Observation of a γγ resonance at a mass”?) although others have told me that the paper is actually there and does claim what the abstract is presenting (although perhaps not convincingly).
One of my favourite ATLAS postdocs, Mark Tibbetts, said,
The line from the management is “This is not an official result of the ATLAS experiment.”
“Not an official result”. Hmm…
Now, the authors are a little interesting because they include Sau Lau Wu. Wu is often associated with her excitement, near the end of the LEP days, when her team thought they had observed a Higgs candidate around 114GeV/c2 (it was basically ruled out later). The energies being so similar here make this curious.
Another important thing to point out is that the CDF has also been focused on the H→γγ search and has seen no 115 GeV bump in their data [see Search for a Standard Model Higgs Boson Decaying Into Photons at CDF Using 7.0 fb-1 of Data [pdf] from April 18th, 2011]. If this sizable 115 GeV bump was being found in ATLAS data, the CDF should also have seen a hint of it, not, nothing.
At this point, I see no reason in speculating on what this [result] means. It’s a rumour. The analysis may be very limited. The data may be non-existent. And it’s not impossible that someone uploaded it to the CERN servers as a joke. If the ATLAS Collaboration were to release it themselves, then we could be excited (and if people want to start throwing around “fourth generation”, “non-Standard Higgs”, “SUSY confirmed/ruled out”, then it might be reasonable). Until there is an official statement from the collaboration, or even one of the co-authors, this is just gossip. Don’t get excited. Seriously.
For more remarks, analysis, and speculation:
Update: April 25th, 2011: “Spokeswoman quashes Higgs particle rumor” in Nature.
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.