Have Scientists Found Two Different Higgs Bosons?

[Drakkith]

From here: http://blogs.scientificamerican.com...-scientists-found-two-different-higgs-bosons/

Yesterday researchers at the Atlas experiment finally updated the two-photon results. What they seem to have found is bizarre—so bizarre, in fact, that physicists assume something must be wrong with it. Instead of one clean peak in the data, they have found [STRIKE]two [/STRIKE]an additional peak.* There seems to be a Higgs boson with a mass of 123.5 GeV (gigaelectron volts, the measuring unit that particle physicists most often use for mass), and another Higgs boson at 126.6 GeV—a statistically significant difference of nearly 3 GeV. Apparently, the Atlas scientists have spent the past month trying to figure out if they could be making a mistake in the data analysis, to little avail. Might there be two Higgs bosons?

So how significant would this be if it turns out to be true? I wasn't aware that there had been predictions of more than one Higgs in the first place, but the article says there was.

Also:

But let’s not let this intriguing blip distract us from the original scent of new physics. Back when the preliminary data seemed to show that the Higgs was decaying into two photons more often than it should, I wrote that it could be “a statistical blip that would wash away in the coming flood of data.” But more data has now arrived, and the blip hasn’t gone anywhere. The Higgs boson continues to appear to be decaying into two photons nearly twice as often as it should.

What's the significance of this? I don't know much about particle decay.

 

[K^2]

Could one of these simply be a high energy resonance of one of the mesons? I'm not sure there would be any way to tell what they are detecting from, say, $\small \pi^0$. Of course, if one of these is just a meson resonance, then who's to say the other one isn't also?

Besides energy and $\small 2\gamma$ mode, what are they using to verify that it's actually a Higgs Boson? If somebody has a reference to an actual article, I'd appretiate it.

 

[Bill_K]

The universal belief is that this is just an experimental difficulty. ATLAS sees it, but the other group CMS does not. See the Resonaances blog for a good discussion.

 

[Vanadium 50]

This is shamefully inaccurate blogging. The experiments are not claiming two peaks. It's all noise from the blogosphere.

 

[Bill_K]

V50, I hope you're not knocking the Resonaances blog, which is accurate and well-informed, and IMO one of the top five sources of particle information on the web. He makes clear, I think, that the "two peaks" are the best fits in different channels, 123.5 GeV for the ZZ channel and 126.6 for γγ, undoubtedly due to a calibration error.

 

[ofirg]

undoubtedly due to a calibration error

The statistical significance of this difference is only 2.7$\sigma$, so it could also be mainly a statistical fluctuation (maybe with a little push from a small calibration error)

 

[jim mcnamara]

I particularly like Resonaances third possible cause for the ATLAS problem, speaking of reliable reporting. The one involving ethanol.

 

[mfb]

To quote the ATLAS conference note:

The difference of the mass measurements between the two channels is 3.0 ± 0.8 (stat) +0.7−0.6 (sys) GeV, corresponding to about 2.7 standard deviations, using Gaussian pdfs for systematic uncertainties. A more conservative treatment of the systematic uncertainty related to the mass scale, using rectangular pdfs for parts of the error, reduces the difference to the level of 2.3 standard deviations.

Nothing serious, just bad luck or a calibration problem.@K^2: Other decay channels, their branching fractions (which agree very well with the SM) and the angular distribution to determine its spin (which indicates spin 0).

 

[George Jones]

V50, I hope you're not knocking the Resonaances blog, which is accurate and well-informed, and IMO one of the top five sources of particle information on the web. He makes clear, I think, that the "two peaks" are the best fits in different channels, 123.5 GeV for the ZZ channel and 126.6 for γγ, undoubtedly due to a calibration error.

The Scientific American blog linked in the original post was guilty of "shamefully inaccurate blogging." According to Matt Strassler, this blog entry has been rewritten somewhat,

http://profmattstrassler.com/2012/12/17/two-higgs-bosons-no-evidence-for-that/.

 

[K^2]

@K^2: Other decay channels, their branching fractions (which agree very well with the SM) and the angular distribution to determine its spin (which indicates spin 0).

That certainly makes sense. I've found some theory papers on the decay modes, so I can now sit down and sort through it. Experimental papers ever only make my teeth hurt.