LHC back to physics runs with 50ns bunch spacing

The Large Hadron Collider today returned to physics runs. Over the last few days they had been filling the collider for scrubbing runs in an effort to remove the e-cloud problem. In fact they only did a few hours of scrubbing runs before surprisingly returning to physics with 50ns bunch spacing.

On the face of it this is great news because it suggests that they have concluded that the problems are not too severe and physics with 50ns spacing will be the norm for this year. However I have heard no official word so I can’t confirm that they wont change back to 75ns spacing.

With the 50ns spacing they will be able to get 1400 bunches into the collider. This is half the design limit of the machine which may only be achievable when they move to the higher energy of 14 TeV in 2014. During the scrubbing runs they were already able to circulate 1020 bunches, so perhaps it will not be long before they reach similar numbers with colliding beams. It is very impressive that they have reached this point so quickly.

For today they have been running with 228 bunches providing a luminosity of 250/ub/s just below the records of a few weeks ago. They need three runs and 20 hours of stable beams before they can go to the next step at about 300 bunches. Just one more runs of about 5 hours should do it. Today’s runs have already added about 10/pb to the total integrated luminosity delivered to each of ATLAS and CMS.

Update 16-Apr-2011: The next step is set as 336 bunches and still with 50ns spacing. Expected peak luminosity is about 360/ub/s which will be a new record, fingers crossed. Total luminosity delivered for 2011 has passed the 40/pb delivered in 2010.

Update 17-Apr-2011: After a few false starts a good long run with 336 bunches is now in progress. It started with a peak luminosity of 380/ub/s in ATLAS and 360/ub/s for CMS. After 9 hours the integrated luminosity has passed 10/pb, the highest yet for a single run. This may be a good moment to speculate about how much data they can collect before the “Physics at LHC” conference to be held in Italy from 6-11 June. The answer depends on many things but I don’t think 0.5/fb is overly optimistic at this stage assuming they proceed with continuous physics runs and increasing luminosity according to the plan which has six weeks of running before the conference. To give some meaning to that amount of data here is the expected Higgs limits for ATLAS.

0.5/fb would exclude the Higgs between 140GeV and 180GeV, unless it is there. Of course even if they do collect 0.5/fb before the conference they would have to do the analysis very quickly to be able to report it in time and I don’t expect that to be possible. Other results are more likely to be shown and the Higgs limit should just be taken as an indication of how much progress has been made when these landmarks are reached.

15 Responses to LHC back to physics runs with 50ns bunch spacing

  1. Bornerdogge says:

    There it is: ~370/µb/s in ATLAS…. But apparently they had to switch from 72b injections to 36b!

  2. Bill K says:

    I’ve determined what is the real cause of the numerous minor glitches we’ve been seeing. Not UFOs. Because German folklore, and Swiss folklore too, tells of mischievous spirits called kobolds. They are subterranean in nature and known to frequently inhabit mines, where they have earned a reputation for causing caveins and otherwise making themselves a general nuisance. Did you know, Snow White and the Seven Dwarfs was originally Snow White and the Seven Kobolds.

    Kobolds would surely find the tunnels of the LHC an ideal environment.

    • Philip Gibbs says:


    • Bill K says:

      The little guys have been unusually active this week. First a flashover in the kicker magnet for B2, which was predicted to happen only once in 20 years. Now cryogenics trouble at the same point, IP8. Possibly these are related issues? Maybe they should leave out a plate of bratwurst, or whatever it is that kobolds eat.

      Does anyone know who the VIPs are, scheduled for tomorrow?

  3. OhRight says:

    Where can I see the total integrated luminosity delivered in 2011? Thanks.

  4. [...] cada mañana. Muchos blogueros se han hecho eco de este nuevo récord, como Philip Gibbs, “LHC back to physics runs with 50ns bunch spacing,” viXra log, 15 Apr 2011 (updated 6 Apr [...]

  5. tpqr13 says:

    thanks Bornerdogge, I was looking for that !

  6. Luboš Motl says:

    Hi Phil, I hope you will quickly find some new data about the new ATLAS’ 4-sigma diphoton 115 GeV Higgs boson:


    I am not going to pretend that the mass of 115 GeV would be any surprise for me. ;-)

    • Philip Gibbs says:

      Yes, I am going to try to make a suitably uninformed comment about it even though I am still on hols. :)

  7. [...] LHC cada mañana. Muchos blogueros se han hecho eco de este nuevo récord, como Philip Gibbs, “LHC back to physics runs with 50ns bunch spacing,” viXra log, 15 Apr 2011 (updated 6 Apr [...]

  8. [...] LHC cada mañana. Muchos blogueros se han hecho eco de este nuevo récord, como Philip Gibbs, “LHC back to physics runs with 50ns bunch spacing,” viXra log, 15 Apr 2011 (updated 6 Apr [...]

  9. [...] can add last years 40/pb as well to make nearly 240/pb. I will also be tracking this number above. Two weeks ago I upped the estimate to 500/pb for the conference but even that is looking a little unambitious [...]


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