LHC down until late summer 2009 or early 2010

marcus

Peter Woit provides this link to a talk at CERN
http://indico.cern.ch/getFile.py/acc...s&confId=22937
Slide 46 indicates that restart will not occur until late summer 2009 (Plan A) or sometime in 2010 (Plan B)

The talk was given today by Jörg Wenninger.
Wenninger's slides are well-illustrated with photos and diagrams, including labeled shots of the components where problems developed, and provide the clearest explanation which I have seen so far of the unfortunate event in section 34 of the ring.

By way of summary, here's what slide 46 says:
==quote==
Plans for 2009

Plan A:
• Restart in (late) summer of 2009 beam with beam.
• Beam intensity and energy limited to minimize any risk.

Plan B:
• No beam before a complete ‘upgrade’ of the pressure-relief system is
implemented sectors on all sectors.
• Excludes beam in 2009.

Final decision in February?

46
==endquote==

So we may know in February, if a decision is made about completing the upgrade and scheduling restart.
This and other news/comment here:
http://www.math.columbia.edu/~woit/wordpress/?p=1290

bomanfishwow

The incoming DG has said that the CERN management team are going to give the highest priority to beam in 2009, which means that plan B is out of the window. Of course, this has not been officially ratified, but it does make sense...

humanino

Why does it ? 6 other months matter to whom ?

Vanadium 50

6 months certainly matters to the grad students!

First, "Plan B" never appeared on anything official by CERN. It was a talk at one of the experiment's meetings by someone who works on the accelerator, but not an official statement by the LHC. In fact, on slide 43 of the Wenninger talk, he specifically excludes Plan B himself. Of course, few people paid attention to this aspect.

Second, the experiments have long since crossed the point where cosmic ray commissioning is almost as good as beam commissioning. Both large experiments have demonstrated that they can take look cosmic ray runs, analyze the results, and use them productively. What they haven't been able to do is look at "full" events, nor have they been able to run at full speed.

Third, the Wenninger talk makes it sound like under Plan B there will not be a limit to beam intensity and energy. This is almost certainly not the case. Until there is more experience with the LHC, particularly with unintentional fill terminations, there is likely to be some sort of limit. The first six months are the first six months, no matter where they fall on a calendar.

So it's in everybody's best interest to start as soon as possible.

A run of 100 pb-1 in 2009 would allow some search physics to move past the Tevatron's reach, and some physics to be comparable (for example, the number of top quarks would be about 1/3 of what is seen at CDF or D0). They won't do everything, but this sounds to me like a good start.

humanino

Did it ever matter to submit a PhD topic to grad students entitled "search for the Higgs boson" but which really consisted in calibrating a tiny part of a huge detector, or writing a technical piece of code, or calculating a background... ? It's been years that graduate students wait for it to happen anyway.

bomanfishwow

I don't know how much physics will come out of the first 'x' months. Considering it is quite clear that the beam conditions will not be stable (i.e. variations in bunch structure, energy, luminosity, etc etc) and indeed the detectors have not managed yet to time in all their subsystems to the LHC clock when running (and no, a few beam splash events triggered from beam timing counters does not count).

We have reached as far as we can go with cosmics commissioning really from a physics standpoint (small event sizes, no realistic E/gamma triggers, top / bottom timing differences etc), although there are still clear areas where software needs improving. Anyway, my point is there's a big curve before we get useful physics data out. But, that 100pb would allow us to at least intercalibrate the detectors (you get enough Zs to begin to do useful things), and perform studies of jet multiplicities, pT spectra etc.

I'd like useful physics to come out of the first 100pb as much as the next person, but I think there has to be a reality check at some point.

Vanadium 50

CDF's 1988-1989 run had exactly the same issues you describe, and even less luminosity (4 pb-1). They published at least 15 papers in PRL/PRD.

bomanfishwow

Sure, and if anything we should hopefully perform more efficiently as we don't have antiproton problems (it's just the cooling killing us at the moment... Always the cooling...). But, look at the first CDF papers in PRL:

Measurement of the W-boson mass in 1.8-TeV p̅ p collisions
Measurement of σB(W→eν) and σB(Z0→e+e-) in p̅ p collisions at sqrt[s] =1800 GeV
Measurement of QCD jet broadening in pp̅ collisions at sqrt[s] =1.8 TeV
Topology of three-jet events in p̅ p collisions at sqrt[s] =1.8 TeV
Properties of events with large total transverse energy produced in proton-antiproton collisions at sqrt[s] =1.8 TeV
Limit on the top-quark mass from proton-antiproton collisions at sqrt[s] =1.8 TeV

Which is pretty much 'rediscovery of SM' type stuff, what we expect to be doing too. This fits in with my "and perform studies of jet multiplicities, pT spectra etc." comment. Of course, we can't discovery anything until we rediscover what we (think) we know, so this is a critical step, it's just that I don't think any radical physics will come out of a small* run. Of course, I'd love there to be - my channel of interest, in certain models, is a fantastic first data channel, but one shouldn't get too excited; we have large mounds to climb.

In any case, it's a rather exciting time to be involved.

* Where small is undefined

stevebd1

For anyone interested, here's the timetable to restart-

http://press.web.cern.ch/press/Press...LHCrestart.pdf

and the associated press release dated 5th December-
http://press.web.cern.ch/press/Press.../PR17.08E.html