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Posts Tagged ‘ICHEP’

ICHEP: what to watch for

Wednesday, July 21st, 2010

At long last, the 35th International Conference on High Energy Physics begins tomorrow. It’s the largest particle-physics conference of the year, and the first major conference since the start of LHC operations at 7 TeV, If the US LHC blog has seemed to be a bit quiet lately, it might be because so many bloggers have been working hard to get results ready. Now, it’s highly unlikely that there will be any surprising LHC discoveries announced there; we just don’t have nearly enough data yet. But that doesn’t mean that this conference will be boring! Here are a few things that you might want to be watching for:

  • How well are the experiments keeping up with the LHC? The LHC has now delivered about 350 nb-1 of integrated luminosity to the experiments. What fraction of that data will the experiments show? This is a measure of the operational efficiency of the experiments, and of their ability to get the data through reconstruction and analysis. If the experiments are able to show a large fraction of the delivered data, then we can be optimistic about how quickly results will come out as the collision rates rise.
  • How competitive is the LHC with the Tevatron? The Tevatron experiments have collected a huge amount of data over the past nine years, and have an excellent understanding of how their detectors work. They will still be in the lead on many, many physics topics. (Disclaimer: I also work on one of the Tevatron experiments.) However, because of the LHC’s higher collision energy, there might be a few measurements for which the LHC can produce stronger results, even with a tiny amount of data. Will there be any such results, and what will they be?
  • How competitive is the Tevatron with the LHC? Everyone is eager to hear the latest limits on the standard-model Higgs boson from the Tevatron. The excluded Higgs masses are the ones that would have been the easiest for the LHC to see too. How much harder will new Higgs limits make it to find a Higgs at the LHC?
  • Any surprises from elsewhere? Let’s not forget that this conference covers all of particle physics, and there’s a lot more going on out there than just the LHC!
  • How tired do the presenters look? A lot of that 350 nb-1 came at the last minute — did everyone stay up all night to finish their data analysis?

I won’t be attending the conference, but I’ll try to provide some commentary from lovely Lincoln as events unfold. Good luck to all involved — this is going to be a lot of fun!

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Marathons and sprints

Sunday, March 28th, 2010

I thought it best to write a post now, as I won’t have a chance to during this Tuesday’s excitement — not because I’ll be so wrapped up in first 7 TeV collisions, but because it’s going to be the first day of Passover, which will take me partially offline. (Who exactly thought that this would be a good day for the big event? Well, it had to be on some day or another.) Just like last time, I plan on sleeping through the big event, as I thoroughly expect it to be uneventful.

For instance, don’t expect any radically new science to emerge from the first days of collisions. While it appears that the experiments are really in excellent shape, based on the work done with the December collisions, it will take a long time to accumulate and analyze enough data before we can definitively say that we have observed any new physics. The amount of data we expect to take in these next two years is enough to make the LHC experiments competitive in discovering new phenomena, or constraining what new phenomena might look like, but that’s still two years worth of data. So, as the old saying goes, this is a marathon, not a sprint, and we have to pace ourselves.

But on the other hand, everyone is motivated to get out some kind of result as soon as possible, to demonstrate that the experiments do work and that we’ve got what it takes to complete the marathon. The major milestone is the International Conference on High Energy Physics, which starts on July 22. By then, everyone is hoping to have a bunch of real physics results (even if they are merely confirmation of known phenomena rather than discoveries) that can set the baseline for the performance of the experiments. July 22 is sixteen weeks from this Thursday. To go from having no data at all to high-quality measurements in sixteen weeks is going to be quite a feat. Put on top of that the uncertainty of just how well the LHC will perform over this time — by ICHEP, we definitely expect to have a million times as much data as we recorded in December. But it could turn out to be be ten million times as much! Whether any particular measurement is feasible or not could depend on which end of that range we end up on, and there might be many course corrections to make as we go along as a result.

So even though the real LHC physics program is a marathon, on your marks, get set….

KB

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Today marks the start of the 34th International Conference on High Energy Physics, the biggest particle-physics conference of the year. It is held in even-numbered years, and when the conference started, it was always held at the University of Rochester, and hence some people still refer to it as “the Rochester meeting.” But now it moves from country to country, and this year it is in the United States, jointly hosted by Princeton and Penn in Philadelphia. (I’d be there myself but for some other exciting events going on; see a future post on that.) It’s a big deal; people work hard to produce new science results specifically for this conference. Obviously, at this point the LHC experiments only have so much to say, as we don’t have any LHC data yet. There will be several talks about the status of the machine and detectors, plus presentations on the prospects for various measurements.

But even though a lot of people are focused on the jungle, meanwhile back in the states, there is a lot of physics going on! (See here for this week’s obscure reference.) In particular, the two big experiments at Fermilab’s Tevatron, CDF and D0, continue to put out new results every week. This week there are more results than usual; they were presented in a pair of seminars last Friday. Of particular note (so far) is D0’s observation of pairs of Z bosons. This process is not unexpected, but definitely rare; the fact that the Tevatron experiments can even observe this final state shows that CDF and D0 have enough data that they can think seriously about the possibility of excluding — or observing! — a standard-model Higgs boson.

Increasingly rare processes observed at the Tevatron

OK, so what about that Higgs boson? As of a few months ago, the two experiments together had accumulated enough data to be able to come oh-so-close to being able to exclude some range of Higgs boson masses. Since then, more data has been analyzed, and the experimenters have been working hard to improve their data-analysis techniques to be sensitive to processes with even smaller rates. It’s possible that the analyses to be shown at this conference will actually be able to exclude the Higgs at some masses. If that can be done, it will be the first new direct information about the mass of the Higgs since the end of CERN’s LEP program.

As of this writing, not all the numbers have been crunched yet and not all the results have been approved for release, so we don’t yet know what the answer is! But keep an eye out for news sometime next week, probably. Here is a plot that shows the Higgs results from earlier this year. A new plot will be shown at ICHEP. If the solid black line goes below 1 on the vertical axis, it will indicate that the data do not support the existence of a Higgs boson at the mass values on the horizontal axis. We await the news….

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