Cern, and the LCH

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Main Question or Discussion Point

Does anyone know specific dates on when the first experiments (particularly thos involving finding the Higgsparticle) will start in the LCH?
 

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  • #2
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So far as I know, even the people working at CERN don't know exactly for sure when they'll start taking data. First, they have to get the beams running and make sure everything involved with them is working right and well characterized. Last I heard, the beams are supposed to turn on next month. So, I wouldn't expect any data collection to start before some time in July at the earliest. And then, it will be some time after that before they have collected enough statistics to really say they've detected anything.
 
  • #3
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A good thing to do here is follow the updates at the USLHC blogs, maintained by people actually at the LHC.

Although Parlyne is right that they can't say for certain (it's all very unpredictable), there is a constantly updated best-guess schedule which is sometimes shown to the public, and this can maybe be a good indicator of what to expect. A http://uslhc.us/blogs/?p=159#comments:

there are some major announcements worth noting. First the current schedule plans that the machine will be cold (to superconducting temperatures) by mid-June. And that we could expect single beam in July. The first physics run in 2008 will be at an energy of 10TeV. (The machine design is 14TeV and for comparison the Tevatron accelerator in Chicago is 1.96 TeV).
Note that when they say they're turning the beam on in July, they just mean for testing purposes-- they need both beams to do physics.

So, when do they start doing physics? Well, One analysis (by a third party) of the "single beam in July" news cited in the USLHC above said:

Their nominal beam commissioning plan refers to taking 30 days of work on the beam to get ready for physics, with likely down-time meaning it would take on average two calendar days for each day of work. So, this puts them with a physics run starting in September. Maybe it will go more quickly, maybe they’ll run into problems, we’ll see.
So that's for first collisions. Note the amount of time between first collisions and publication could be very long, though, as explained in the USLHC post above:

There are many factors which determine the time from turn-on to publication. As Seth points out, one of those factors is the number of collisions. The fewer collisions, the longer we must run to gather decent statistics. Additionally before reaching the publication stage we have to have a good understanding of the detector calibration. And how long this takes depends on how smoothly each of the steps along the way go. There are two many unknown factors right now, such as how stable the beam will be in the beginning, how straightforward the calibration will be, to really be able to predict the time to publication.
Between comments here and http://uslhc.us/blogs/?p=163 they seem to be suggesting a good guide would be to look at how things went with CDF/D0, which would suggest time from first physics collisions to first real-world publication could be as long as two years!
 
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There are certainly very different time scales between the time beam is first injected and the time that the first papers on search physics are written.

The experiments have been told that they need to be ready to go on July 15th. Single beam collisions will happen immediately after that, and collisions some number of weeks later. How many weeks depends on how many problems they run into. There will be problems. There always are with something this complex. The question is how many problems, and how serious they will be. I am optimistic, as many of the difficulties the Tevatron had to face and solve involved the antiprotons, and the LHC collides only protons.

The first beam will be of lower energy, lower luminosity and almost certainly with a lower duty cycle than they will ultimately achieve. This substantially reduces the sensitivity to new physics, but it's perfectly fine for detector commissioning. All the subdetectors can work separately, and they can work together at the low rates typical of cosmic rays, but the experiments need beam to make sure all the subdetectors work together at the high event rates of the LHC. This isn't like turning on a light switch, and once again, there will be problems.
 
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I suspect that many papers are already written, maybe even internally reviewed, covering ranges from "We found it" to "We put upper limits on it". Publication of physics results will happen within one year after the first collision, whatever the results will be at this point.
 
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I disagree.

I know for a fact that one of the two general purpose detectors has not written the papers in advance, deliberately so. Part of the rationale is that the data taking during the commissioning period will be, by definition, before the detector is fully commissioned. That means a significant fraction of the early papers will need to be on what data is included and what data is not, and how this was decided.

Also, the amount of data obtained in 2008 will be really tiny, for the reasons I outlined above. In very few cases will limits from 2008 data be beyond the present limits. Of course the experiments will try to squeeze every last drop of science out of this run, but the purpose of this run really is more commissioning than science.
 
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Also, the amount of data obtained in 2008 will be really tiny,
To say the least :) SUSY will be discovered first, but if the higgs really is at 115 GeV, then FermiLab will discover it before LHC sees it, or so I've been told. As I understand it, light higgs favored decay mode is to two photons, a signature that needs a lot of statistics.
 
  • #8
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To say the least :) SUSY will be discovered first, but if the higgs really is at 115 GeV, then FermiLab will discover it before LHC sees it, or so I've been told. As I understand it, light higgs favored decay mode is to two photons, a signature that needs a lot of statistics.
Hm,

Could you clarify on this? I had been told that there was some reason why one should expect the "Lightest Supersymmetric Particle" is heavier than the Higgs. Is this incorrect?
 

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