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Ken Bloom | USLHC | USA

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Higgs seminar live blog from ICHEP

Good afternoon from the Melbourne Convention Centre, where we are all eagerly awaiting the start of the Higgs seminar that will be broadcast from CERN. I’ll be updating this post as we go along, so please stay with me and our other Quantum Diaries bloggers.

17:00: That’s a wrap here! I’ll try to post again soon-ish with some more thoughtful follow-up. Thanks everyone for joining us!

18:58: Not that Higgs is the only one who helped develop this theory…the others are getting their time to make congratulations too.

18:56: A big round of applause here and at CERN for the famous Peter Higgs.

18:52: No questions here! Rolf is right, we want to go to the reception!

18:48: Now questions. I’ll try to transcribe the ones that are coming from this room.

18:47: We’re watching the standing ovation at CERN over the video. Again, so nice to see lots of young people in the room. Then again, maybe they were the ones with the endurance to camp out in front of the auditorium!

18:44: Rolf summarizes by saying that this is a global effort and a global success. It’s only possible because of the extraordinary performance of the accelerators, experiments and computing grid. This is an observation of a new particle consistent of a Higgs boson…but we don’t know which one. It’s an historic milestone, but it is only the beginning, with global implications for the future.

18:41: The conclusion from ATLAS — an excess of events at about 126.5 GeV at 5.0 sigma significance. Fitted signal strength is 1.2 +- 0.3 of the SM expectation. Fabiola says that this is a very lucky mass to have, since it is easy to explore at the LHC in many decay channels.

18:39: Fabiola shows how the signal strength has evolved over time, in the past year — it is really quite striking how much we have advanced!

18:37: ATLAS overall signal strength is a bit higher than SM expectation for 125 GeV Higgs, whereas CMS was a little lower.

18:34: So here comes the combination of the new 2012 analyses with the 2011 results: another 5 sigma excess, and more applause!

18:30: ZZ also shows an excess in the 125 GeV range, 3.4 sigma here, when you’d expect 2.6 sigma from a standard-model Higgs.

18:28: Hmm, the standard-model ZZ rate is coming in bigger than expected. But it has now impact on the low-mass Higgs range.

18:23: Here comes ZZ, with 20-30% increase in sensitivity since December.

18:19: And now the results from the photons channel. Here too, an excess, at the 3.6 sigma level, after accounting for the look-elsewhere effect. 4.5 sigma local.

18:14: Thorough discussion of mass resolution in the photon channel, and the fact that it is independent of pileup. This is quite important, as the pileup is only going to get larger as the LHC luminosity increases.

18:10: Fabiola reviews what the changes are since December, here we go…..

18:09: Fermilab has a press release out too, http://www.fnal.gov/pub/presspass/press_releases/2012/Higgs-Search-LHC-20120704.html

18:07: The CERN press release is out! http://press.web.cern.ch/press/pressreleases/Releases2012/PR17.12E.html

18:04: I’ll admit that I’m finding less to say at the moment, as Fabiola is now covering similar ground to CMS in the preparation of the data, understanding of the detector etc. But it is still all important, of course!

17:57: I think I caught that ATLAS will show 5.9 fb-1 of data? More than CMS has certified.

17:55: Fabiola will show results from 2012 data in the ZZ and gamma gamma channels, but the other channels only for 2011 data. The 2012 results in those channels (which do have less mass resolution) aren’t quite ready yet.

17:53: Rolf congratulates everyone…and now let’s see what ATLAS has!

17:50: We have observed a new boson with a mass of 125.3 +- 0.6 GeV at 4.9 sigma significance. Enthusiastic applause heard on two continents. And then Joe acknowledges all of the theorists, machine physicists, and CMS experimenters who who have gotten us to this point.

17:49: Branching ratios are self-consistent across the decay channels (even with that tau tau result), but Joe emphasizes that it is early yet.

17:48: OK, it looks like there is something there, but is it consistent with a standard-model Higgs? Now we’ll get a first look at that.

17:44: Technical improvements in the tau tau channel have helped improve its sensitivity in the Higgs search. But uh oh, no evidence for a Higgs in that channel, and indeed you nearly exclude a 125 GeV SM Higgs here! It’s low statistics yet, we’ll need a lot more data to understand this.

17:41: Now on to the bb and tau tau channels. Not as much sensitivity to them, but they are important, as a) they actually have bigger branching fractions at ~125 GeV than the WW/ZZ/gammagamma, and b) they are fermions whereas all the others are bosons.

17:38: Unfortunately, the seminar is not over yet — let’s see if that 5.0 stands up with three more decay channels to look at.

17:37: The ZZ and gamma gamma joint significance is 5.0 standard deviations…Joe says that, and it gets applause! 5.0 is considered the threshold for a discovery….

17:33: Joe is now showing how event by event, we can compare the angular separations of the leptons to what would be expected from a Higgs signal or the ZZ background. I’ve always loved that approach, really gets at the physics.

17:30: Now the ZZ mode, with four leptons in the final state — this channel is about as clean as you can get, but very rare, so you need to be super-efficient in selecting the events.

17:28: Slide 43 — A mass bump! Thank goodness that there is a real mass bump. I’ve always said, if we make a discovery that is observed on a plot that runs from 0 to 1 with a slight enhancement at 1, I’ll jump out the window. Maybe I’m safe.

17:22: Now we’re getting into the meat of the Higgs search, with the search for a decay to two photons. CMS paid a lot of money for the lead tungstate crystals that give very good photon energy resolution.

17:17: In fact, Joe is carefully going through all the low-level ingredients that go into these analyses. It’s a lot of work, and that’s why we need thousands of people to get this science done.

17:15: Joe takes a moment to point out the hard work done by the CMS software and computing teams. Yes, we’ve got a fabulous detector, but we can’t get this done without S&C…so I do appreciate the shout-out!

17:11: CMS will show 5.2 fb-1 of certified data today. And again, I’m curious to see how much data ATLAS will show!

17:09: CMS will be showing results from five Higgs decay modes — WW, ZZ, photons, bb, taus. I’m curious to see how many of those ATLAS also has.

17:06: Joe Incandela, for CMS, also starts with standup jokes. And then, on to a discussion of the experimental support for the standard model…except that we haven’t seen the Higgs. Yet.

17:03: Rolf notes that ICHEP is opening with a talk from a different continent — a symbol of how well we collaborate across the world. Then he starts with a standup routine….

17:02: Big round of applause here when Rolf Heuer greets ICHEP!

17:00: Here we go! Watching a very quiet CERN auditorium on video….

16:58: On the video feed from CERN, we can see a lot of young people. I’m glad they were able to get seats, as they are the ones who really make these experiments go.

16:54: Everyone in the hall just laughed at the video feed, which showed someone holding a “Ciao Mamma!” sign.

16:51: Geoff Taylor, the chair of ICHEP2012, is telling us about the timetable. The talks will be running longer than we originally envisioned (45 minutes each), followed by 30 minutes of questions. (We will be able to ask questions from here to CERN.) Hmm, hope everyone can hold out for the reception, which will be at 7 PM now!

16:47: I should say that as a member of CMS, I know the CMS results. Thus, I’m deeply curious about the ATLAS results. Will they agree with CMS or contradict? I’ve been hearing rumors, of course, but it will be interesting to see if they are true.

16:44: While we’re waiting for things to start, let me wish a happy Independence Day to everyone in the US, and also a happy wedding anniversary to my parents and a happy birthday to my colleague Aaron Dominguez, who is watching the proceedings from CERN Filtration Plant conference room.

16:42: I’m now sitting in the auditorium where we will be hearing the talk. Sitting to my left is Joel Butler, the manager of the US CMS operations program (I am also in the program management, as deputy manager of software and computing), and to my right is a reporter from the Australian Associated Press. On the big screen above the stage we can see the video feed from the CERN auditorium, and another panel which I presume will be the slides.

16:24: Just spoke to Pier Oddone and Young-Kee Kim, the director and deputy director of Fermilab. Yes, all of the spotlight is on CERN right now, but the Tevatron experiments have been very important for getting the Higgs search started, and it is also quite possible that CMS and ATLAS will not be able to beat CDF/D0 on the Higgs to bb decay mode anytime soon.

16:16: The registration line is still very long! I have been walking along it and chatting with friends in the hope of entertaining them a little. We’ll see if we can get everyone through in time for the seminar….

15:46: I’ve now picked up my registration materials. There is a long line at the registration desk — no one wants to be late for the start. Right now I’m at a table in the foyer with some of the CMS leadership: Greg Landsberg, the CMS physics coordinator; Chris Hill, a CMS deputy coordinator, and Christoph Paus, one of the leaders of the CMS Higgs group. On the way in, I discovered that the Melbourne Boat Show is also happening in the convention centre. I wonder if we have any buyers at ICHEP….


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