News From the LHC

Just saw this from Tommaso Dorigo, which made me realize that I should get to work and write a blog posting before the CERN press office people wake up. The big news today is that the first collisions at a record energy higher than that of the Tevatron have occurred, marking a first step into new territory past what has been the energy frontier in HEP for a very long time. Two beams of two bunches each were successfully ramped up to 1.18 TeV, and although one of the beams was lost after a while, before that point some collisions at a total energy of 2.36 TeV were observed. An event display from ATLAS is here.

Over the next few days, the main objective of the beam commissioning team is to try and increase the intensity per bunch and provide a large number of collisions at 450 GeV/beam to the experiments. They’ll also continue tests in which they ramp up the energy to 1.18 TeV/beam, and if all goes well should be able to provide the experiments with an equally large number of collisions at that energy. The experimenters are gleeful about finally having real data to play with. CMS has publicly announced the re-discovery of the pi-zero, and I assume that by now they’re working their way through the 1950s, already rediscovering kaons and other particles with strange quarks. If they manage to get a significant amount of data at 2.36 TeV, there must be some sort of cross-section they can measure at an energy that just beats out the Tevatron, although with this size of a collision sample, it won’t be one that anyone cares much about…

Beam commissioning work for 2009 should end on December 16, and the accelerator complex will be shut down over the holidays, re-starting January 4. During January the LHC will go back into hardware commissioning mode, with a month-long plan to commission the new quench protection system in all sectors, allowing operation at 3.5 TeV/beam. The injectors are supposed to restart on February 5, LHC beam commissioning restarting on February 8. The way things have been going, they may have at least some 7 TeV collisions happening quite quickly after that.

Update: This morning again a pair of 1.18 TeV beams were stored and brought into collision at the LHC. This time CMS as well as ATLAS is publicly saying that collisions were seen, with event displays here. CERN’s twitter feed is saying over a million collisions at 900 GeV, 50,000 at 2.36 TeV. Still no press release from CERN gloating about how they now are doing physics at higher energy than Fermilab.

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9 Responses to News From the LHC

  1. Steve says:

    Hi, Peter. Could you explain what it means for a beam to be “lost”? I’ve heard that term used few times, but I don’t understand the relation between that and just dumping the beam. Is there some sense in which the beam is “lost” but still circulating and waiting to be shunted to the dump system?


  2. Peter Woit says:


    I think in this context “lost” means more “lost control”, presumably the operators could tell you what happened to the beam particles. When a beam is “dumped”, that’s a controlled shutdown of the beam, by directing its particles to a safe location to be stopped.

    There are all sorts of instabilities than can disrupt a particle beam and lots of complex mechanisms for stabilizing the beam and controlling it. When it’s “lost” I think this normally means that there was some sort of failure leading to a destabilization and loss of control of the beam.

  3. Nobody says:

    It appears that the beams were never declared as “stable” (neither they were intended to collide); does this mean that ATLAS keeps his detector switched on even when the beam is not under complete control and can do weird things?

  4. Peter Woit says:


    My understanding is that in this situation the detector is not fully operational, with some parts switched off for protection. But enough of the detector is working to see the evidence of a collision that ATLAS showed.

  5. jks says:

    Vistars Op comments at 02:01:01 on 11-12-2009: “FIRST HIGH INTENSITY STABLE BEAMS”. Looks like five bunches each in B1 & B2 (@ 450 GeV) with the FBCT (fast beam current transformer) intensity saying about 6e+10 with a slow rolloff to 4e+10 and hour and 1/2 later. Nice.

  6. Hi Peter,

    thanks for the link 🙂
    Yes, you assume well. Atlas and CMS are working their way through the fifties, literally.

    By the way, when the beam is lost it is indeed what you explained. There are so many components in a proton synchrotron that may cause the beam to get progressively out of sync and lost, there is not much to explain.
    As for stable beam: LHC is indeed producing stable beams, and in fact the data that ATLAS and CMS are analyzing come from those short periods of time when machine operators take their hands off the controls and go for a coffee. Normally, they try to study the beams and by doing so the conditions are not suitable for data taking.


  7. Oh, and just before I forget: you might want to read my latest posting on the events of this week. Not really releasing any insider information, but I hope I have given the flavour of what is going on at CERN these days.


  8. Mehmet Tezgel says:

    Hey it’s 2.36 TeV not GeV . Greetings from Darmstadt, Germany 😀

  9. Peter Woit says:

    Thanks Mehmet!


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