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Seth Zenz | Imperial College London | UK

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Liveblog: New ATLAS Higgs Results

In a short while, starting at 11:00 CEST / 10:00 BST, ATLAS will announce some new Higgs results:

“New Higgs physics results from the ATLAS experiment using the full Run-1 LHC dataset, corresponding to an integrated luminosity of approximately 25 fb-1, of proton-proton collisions at 7 TeV and 8 TeV, will be presented.” [seminar link]

I don’t expect anything earth-shattering, because ATLAS already has preliminary analyses for all the major Higgs channels. They have also submitted final publications for LHC Run I on Higgs decaying to two photons, two b quarks, two Z bosons – so it’s reasonable to guess that Higgs decaying to taus or W’s is going to be covered today.

(Parenthetically, CMS has already published final results for all of the major Higgs decays, because we are faster, stronger, smarter, better looking, and more fun at parties.)

I know folks on ATLAS who are working on things that might be shown today, and they promise they have some new tricks, so I’m hoping things will be fairly interesting. But again, nothing earth-shattering.

I’ll update this very page during the seminar. You should also be able to watch it on the Webcast Service.

10:55 I have a front row seat in the CERN Council Chamber, which is smaller than the main auditorium that you might be more familiar with. Looks like it will be very, very full.

11:00 Here we go! (Now’s a good time to click the webcast, if you plan to.)

11:03 Yes, it turns out it will be taus and W’s.

11:06 As an entree, look how fabulously successful the Standard Model, including the Higgs, has been:

11:10 Good overview right now over overall Higgs production and decay and the framework we used to understand it. Have any questions I can answer during the seminar? Put them in the comments or write something at me on Twitter.

11:18 We’re learning about the already-released results for Higgs to photons and ZZ first.

11:24 Higgs to bb, the channel I worked on for CMS during Run I. These ATLAS results are quite new and have a lot of nice improvements from their preliminary analysis. Very pretty plot of improved Higgs mass resolution when corrections are made for muons produced inside b-jets.

11:30 Now to Higgs to tau tau, a new result!

11:35 Developments since preliminary analysis include detailed validation of techniques for estimating from data how isolated the taus should be from other things in the detector.

11:36 I hope that doesn’t sound too boring, but this stuff’s important. It’s what we do all day, not just counting sigmas.

11:37 4.5 sigma evidence (only 3.5 expected) for the Higgs coupling to the tau lepton!

11:39 Their signal is a bit bigger than the SM predicts, but still very consistent with it. And now on to WW, also new.

11:41 In other news, the Nobel Prize in Physics will be announced in 4 minutes: It’s very unlikely to be for anything in this talk.

11:44 Fixed last comment: “likely” –> “unlikely”. Heh.

11:48 When the W’s decay to a lepton and an invisible neutrino, you can’t measure a “Higgs peak” like we do when it decays to photons or Z’s. So you have to do very careful work to make sure that a misunderstanding of you background (i.e. non-Higgs processes) produces what looks like a Higgs signal.

11:50 Background-subtracted result does show a clear Higgs excess over the SM backgrounds. This will be a pretty strong result.

11:51 6.1 sigma for H –> WW –> lvlv. 3.2 sigma for VBF production mechanism. Very consistent with the SM again.

11:52 Lots of very nice, detailed work here. But the universe has no surprises for us today.

11:54 We can still look forward to the final ATLAS combination of all Higgs channels, but we know it’s going to look an awful lot like the Standard Model. Congratulations to my ATLAS colleagues on their hard work.

11:56 By the way, you can read the slides on the seminar link.

12:02 The most significant result here might actually be the single-channel observation of the Vector Boson Fusion production mechanism. The Higgs boson really is behaving the way the Standard Model says it should! Signing off here, time for lunch

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