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Discovery, but is it a Higgs? - ePepys

4th Jul 2012

12:52 pm - Discovery, but is it a Higgs?

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After months of equivocation ("hints"), we can finally say that we have discovered something.

It was all very exciting. I'm not used to hearing applause in the middle of a physics presentation. And the second time (ATLAS), they were applauding the number ("5.0σ") that I helped determine.

ATLAS see a 5.0σ excess, and CMS see 4.9σ. Each alone would probably be enough to claim a discovery. (According to particle physics convention, one needs >5σ. It is arguable whether one needs to include the "look-elsewhere effect", which reduces the significance to 4.2σ-ish, but one can either combine ATLAS+CMS (as some blogs are already doing), or use CMS to limit the ATLAS search range (or vice versa) so each doesn't need to look elsewhere.)

There certainly was an observation of a Higgs, but that was Peter Higgs, who attended the presentation. But we can't say that what ATLAS and CMS have discovered is a Standard Model Higgs boson. The observations are compatible with a Higgs (though both ATLAS and CMS see a few more decays to two photons than might be expected, which is what pushed us over the 5σ line), but now we need to measure its properties to see whether it's a SM Higgs, some other sort of Higgs, or something entirely new and different.

Comments:

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From:jackfirecat
Date:4th July 2012 08:51 pm (UTC)
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Well done, you!

As you may not be aware, the twitterverse was consumed by this news this morning. Here's a small selection.

higgs tweets
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From:jackfirecat
Date:4th July 2012 10:03 pm (UTC)
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PS I liked the Telegraph take, in which they seek to cast Peter Higgs as a maverick Einsteinian outsider, as the press will do. (Does it bear any relation to reality?)
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From:e_pepys
Date:4th July 2012 11:47 pm (UTC)
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Not sure (was being born at the time), but it sounds greatly exaggerated. I've heard other people talking about this idea going round soon after, so it didn't take long to go from unpublishable to an interesting idea. Also, there were 3 groups that all published similar ideas at around the same time, so Higgs was hardly a lone maverick. (His first paper was rejected, but that could have been for any number of reasons.)
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From:brixtonbrood
Date:5th July 2012 06:53 am (UTC)
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We are v impressed and have shamelessly name dropped you to the smalls, who saw it on Newsround. "we know someone who helped do the sums on that!" They were also v impressed.
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From:brixtonbrood
Date:5th July 2012 06:55 am (UTC)
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"(and if you work very hard at school maybe you too could grow up to discover fundamental building blocks of the universe and appear on Newsround)". Because there are some things that being a parent just makes you say by reflex.
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From:e_pepys
Date:9th July 2012 01:15 am (UTC)
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Thanks!

"Helped do the sums" is a pretty good description for my role. I did lots and lots of sums on lots and lots of computers to see how much we really saw it. (Or, if you prefer, I ran ensemble simulations to map the probability density function in order to calibrate the significance of the observed signal. Due to the significance of our observation, this needed 16000 computers running flat out to calculate.)
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From:zengineer
Date:5th July 2012 10:47 am (UTC)
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Trouble is if you say you have fairly probably observed something but you're not sure what it is, exactly what it does or if it is useful for anything some politician will probably say "9 BILLION FOR THAT ?!!". Whereas if you say we have made a really complicated discovery that you can't understand but it as fundamental as Newton's laws of motion or Einstein's theory of relativity they will keep quiet to avoid seeming stupid (adding in a Greek symbol always helps). The perennial problem of fundamental science.
Cynicism aside kudos to you as part of the team, for the analysis and for being more accurate rather than repeating the headline.
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From:sharaz_jek
Date:5th July 2012 01:57 pm (UTC)
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Well done!
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From:talking_sock
Date:9th July 2012 12:33 am (UTC)
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Well, congratulations for being there for this historic etc :-) I must say, in the press I read, the fact that Higgs himself got to see it made me tear up a bit. Science, phooey, the human scientist, that's something awesome... (well, not quite how I feel, but close.)
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From:e_pepys
Date:9th July 2012 01:27 am (UTC)
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Nah, I was only there watching the webcast from Oxford. I'm a little disappointed that I wasn't there in person, but being involved in the analysis that produced the result (at least for ATLAS) is better.

It was cool that Peter Higgs got to see the announcement. The news said that he teared up a bit too.
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From:talking_sock
Date:9th July 2012 12:39 pm (UTC)
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Oh totally - I meant "there" in the sense of having been part of doing it. And I agree completely about how awesome that is, to have contributed.
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