Decision for the LHC: 1 Inverse fb at 7 TeV or Bust!

By John Conway | January 29, 2010 10:34 am

Last week in Aspen we learned that this week would be when a major decision was reached by CERN at the annual Chamonix meeting as to how to operate the LHC at high energy. Following the magnet quench incident in September 2008, a year-long shutdown ensued for repairs to the magnets, and retrofitting of the rest of the machine for better quench protection circuitry and helium pressure release valves. Not all sectors were warmed up to room temperature for the retrofit last year, but all magnets were trained to go as high as beam energies of 5 TeV (design energy is 7 TeV per beam).

In November and December the LHC commissioning resumed, and it became the world’s highest energy collider on December 8, eventually delivering about 50,000 collisions at 2.36 TeV to CMS and ATLAS before shutting down for Christmas.

But the question facing the LHC managers this week was whether attempting to operate the LHC at 5 TeV on 5 TeV in 2010 was worth the risk to the machine itself. Clearly another disaster of the scale of the one in 2008 would cripple the program for a long time. In the end the decision is to operate the LHC at 3.5 TeV on 3.5 TeV (7 TeV collision energy, 3.5 times that of the Tevatron) and accumulate a substantial amount of physics-quality data: 1 inverse femtobarn, or stop by the end f 2011, whichever comes first. This corresponds to something like ten trillion proton-proton collisions, of which only a small fraction will yield events interesting enough to record for later analysis by the experiments, and of these, only a tiny fraction yielding data relevant for physics.

After a one to one-and-a-half year shutdown in 2012 to retrofit the rest of the machine and make other preparations, the LHC will attempt to double the energy, to 14 TeV in the center of mass, in 2013 and accumulate substantial physics data. My best guess is that if the Higgs boson is to be discovered, it will be at high energy with this large sample of 14 TeV data. We might be able to rule it out at 95% confidence in certain mass ranges if it’s not there, but we ought not be able to do that if it is, right? Patience, patience!

Nevertheless, there is no question that in a few weeks, when operated at 7 TeV collision energy, the LHC will become an awesome discovery machine. There are many new physics scenarios in which we will be able to see new phenomena with just a fraction of the full 1 fb-1 sample. Will nature give up her secrets so readily though? She may not – we may spend this year and the next rediscovering the Standard Model, building up understanding of the detector, and sharpening our analysis tools in order to discover quite subtle effects. No matter what happens, this is the most exciting time in particle physics in decades.

CATEGORIZED UNDER: Higgs, Miscellany, Science, Technology
  • Sili


    They’re only shutting down for repairs in 2012 in order not to get blamed when the World ends.

  • onymous

    Thanks for posting! Trying to read through slides from Chamonix and figure out what’s going on was getting me nowhere.

  • Mary

    How about some coverage of the upcoming APS Sakurai Prize Award and talks? First time all six founders under one roof (Brout, Englert, Hagen, Higgs, Guralnik, Kibble).

    Award is 02/14 and talks are 02/15 in Washington DC.

  • Xibalba

    yeap no way the world will end in 2012, or this year or 2013, these people dont have any respect for the Mayans. You see, they just want to side with newton:

  • paul mann

    will they do pb-pb collisions at 3.5 tb, if so when? would like to know thanks.

  • Someone at CERN

    Hi John,

    The CERN DG New Year’s presentation talked about 500/pb of data [For all readers: the presentation slides and video recording are available to public]. It wasn’t clear if those 500/pb will be at 7 completely, or mixed with higher energy points. I’d be very careful with making statements about the LHC plans for 2010-2011, as so far there hasn’t been any official notifications from the Directorate yet. You know what — I hastily checked my CERN email inbox if I have missed something.

  • Martin

    I have to agree with Someone at CERN. Please be careful about making these sort of claims before they’re released officially.

    I have a comment on “…there is no question that in a few weeks, when operated at 7 TeV collision energy, the LHC will become an awesome discovery machine.”

    In that sense, the LHC is ALREADY an awesome discovery machine. It’s not just the high energy collision – it’s also how many bunches, luminosity, etc… that one can reach. So even at 7 TeV next week, if you’re not getting many bunches, it is not really colliding to make discoveries just yet. Maybe half a year at least.

  • Andy

    Yup, like I thought… it’s looking good for running the Tevatron until at least 2015! There’s no LHC competition for low mass Higgs until then.

  • LHCfan

    @Paul Mann: Pb-Pb collisions are planned for later in 2010 at the equivalent of 3.5 TeV for protons: 287 TeV/Pb or 1.38 TeV/nucleon.

  • JoAnne

    Mary – I’ll be there. I’m quite excited as I’ve never seen Peter Higgs in person.

  • graviton383

    Take pics JoA!

  • Stanley H. Tweedle

    To bad the Americans cancelled the SSC(Superconducting super Collider).

    A particle accelerator that would’ve been 87 km in length compared to the LHC’s 27 km.
    And it would’ve had a total energy of 40 TeV unlike the LHC’s 14 TeV!

    Sad, isn’t it?

  • marc

    Alternate universe, in which the SSC wasn’t cancelled: SSC began taking data in 1999, and the higher luminosity upgrade finished in 2008. In Europe, no LHC was built, of course, so they concentrated on a linear collider, which began taking data at 1 TeV in 2007. SSC discovers Kaluza-Klein partners of squarks and sleptons, with a warped geometry mass distribution…..


  • Stanley H. Tweedle

    @ marc, #13,

    In which book was that one?

    ‘A hole in Texas’, right?

  • Mandeep Gill

    Sweet — i think this is great and happy news, indicates LHC is starting to hum along steadily if they can make this plan — 1 fb-1 at yes a much lower than design energy, but at at least 3.5*s_Tevatron (s = CM collision energy) is definitely a significant chunk of data that will push the envelope of what we humans have ever seen (the Tevatron appears to be at about 7 fb-1 collected by now between the 2 detectors, and a goal of 12 fb-1 by the end of 2011, i got from this talk: ).

    And yes, if there’s anything *dramatic* at this energy, we should be able to see it within this first dataset. But of course, picking out any SM-like Higgs is going to take much more data (i guess throughout the possible currently allowed energy range, though the requirements for a very low mass Higgs are less stringent, iirc, and a very high mass one is strongly disfavored now by all electroweak precision data, so it’s mostly the intermediate 140 -200ish GeV that will be much harder).

    But i, like everyone else, so very very badly want Nature to give us other hints about what is beyond the SM, and not just a single Higgs, which would clearly make it politically more difficult to build an ILC or anything of this nature anytime soon, i think most folks would agree.

    Also, to Martin above: i’m assuming if they think they can get an fb-1, they believe they can get enough bunches in the beampipe with short enough spacing– you’re not going to get that with only a few!

    To Stanley: sigh — yes, of course, SSC would have beat the pants off LHC. and there are many, many other ways i, and many in the world, would have liked to see history unfold, scientifically, politically, etc. — but we are, where we are. we can learn from the past for how to do things better in the future — but no darn use crying too long over spilt milk. the past is done and over (and yes, the arrow of time *does* have a direction indeed!), and to bring up the SSC only gives many of us sad and miserable memories, doesn’t do much good for helping us get psyched for what LHC *is* going to be capable of getting!!

    So — roll on, ye mighty Large Collider of Hadrons, roll on!


    ps. i finally up and saw Angels and Demons a few weeks ago, mostly to see how CERN was portrayed, and while really it only gets a few min at the start of the film, i have to say, the graphics are damn impressive — better than *any* event display i’ve ever seen! maybe we can adopt *those* for the LHC!! ;->

    Second, the special on the DVD about CERN was *excellent*, i felt, captured most of the essential science and excitement at a lay level, and at the same time clearly stated how much of the fears about collecting enough antimatter to make a “bomb” are entirely fictional for the purposes of the storyline.

    Don’t want to lead this thread too astray (i’m sure the movie was posted on here when it first came out, but not sure if the DVD special has ever been talked about?), but definitely curious what others thought, if you saw this special, too..

  • Count Iblis

    There also exists another alternate universe, in which the SSC wasn’t cancelled. There the new physics that was found is very boring and ugly.

  • Toiski

    An inverse femtobarn at seven tera-elctron-volts sounds so retro-futuristic.

  • John

    It’s quite true there has been no official announcement about the LHC run plan yet, but I can assure you the intertubes were abuzz yesterday with what I wrote in the post. I didn’t quote a source…

    I’d be happy to be wrong about this, too. We’d all like to have as much energy as possible. The difference between 10 TeV and 7 TeV is something like a factor of two in physics sensitivity, and proton synchrotrons deliver higher luminosity at higher energy for the same beam current.

    But I totally understand if the LHC people don’t want to chance another accident, and if that means we get a good chunk of physics data with high reliability, then that’s a good call.

  • eigenvector

    With respect to the statement: “…whether attempting to operate the LHC at 5 TeV on 5 TeV in 2010 was worth the risk to the machine itself.” I submit if the LHC was built to run at 5 & 5 Tev, then run it at 5 & 5! It seems the reluctance is due to the fact that the LHC is so expensive a breakdown is unthinkable. Where is the courage of our convictions?

  • John

    eigenvector, perhaps you are being subtly sarcastic, but I will assume not. The design energy of the LHC is indeed 7 TeV per beam, and they will get there eventually. Superconducting magnets need to be “trained” to attain their design performance, and this means taking them through many cooldown/power up/quench cycles so that the superconducting NbTi filaments in the magnets adjust themselves properly. And, there were design flaws in the machine that still need to be corrected before full energy will be attainable. This will take time and money, and in the mean time we cannot risk damaging the machine. the physics at 3.5+3.5=7 TeV c.m. energy will be quite interesting.

  • Brian137

    Thanks for the update.

  • Martin

    The factor of significance of a particular physics signal can be as great as 4 times between 10 TeV and 7 TeV, so it can indeed be quite a big difference! And the factor between 10 TeV and 14 TeV can be 3 times.

  • Brian137

  • cochrane

    Important to say, that the LHC is pp and the Tevatron is ppbar, so. As long as there is no lucky discovery like a Z’ or t’ (and even then) the cross section for interesting processes at the Tevatron is way higher then at a 7 TeV LHC. W mass, top physics, EW, Higgs searches, all dominated still by the Tevatron….

  • Lac Léman
  • Ralph

    Re post 22 – the increase in cross section with energy appears to be somewhat negated (at least for the short term at the LHC) by machine protection – in the short term, the beam current will be limited by how much total stored energy they are willing to have in the machine, so lower proton energy means more protons.

    Does anyone have figures for production rates v. proton energy at LHC that assumes a fixed total beam energy and takes into account changes in possible optics at different energies?

  • paul mann

    lhc fan ‘latter’ pb-pb collisions means there is no date schedule yet? ive been reading through those papers but couldnt find the info… Do you have more precise information on this detail? i presume they will have to retrain the macchine as all the parameters for pb-pb, mass, charge etc. are different? thanks

  • Martin

    The official announcement was just released minutes ago. While the plans are to run at 7 TeV, the duration to run at this collision energy from this post is misinformed. This is why I feared reporting these plans before they became official.

    It is NOT true that “In the end the decision is to … accumulate a substantial amount of physics-quality data: 1 inverse femtobarn, or stop by the end f 2011, whichever comes first.”

    In fact, the decision is for the LHC to run from 18 months to 24 months at 7 TeV, even through the winter. After that, there will be a long shutdown. There is no mention of a goal for how much integrated luminosity.

    The mistake is minor to the outside world, but there can be real high-energy physicists (who care very much about these details) reading these blogs and it’s important to remain accurate.

  • John

    Here s the official announcement from Steve Myers at CERN. The key here is “18-24 months”. what is the stopping criterion? I am sure someone will ask…

    Better in the long run

    Last week, the Chamonix workshop once again proved its worth as a place where all the stakeholders in the LHC can come together, take difficult decisions and reach a consensus on important issues for the future of particle physics. The most important decision we reached last week is to run the LHC for 18 to 24 months at a collision energy of 7 TeV (3.5 TeV per beam). After that, we’ll go into a long shutdown in which we’ll do all the necessary work to allow us to reach the LHC’s design collision energy of 14 TeV for the next run. This means that when beams go back into the LHC later this month, we’ll be entering the longest phase of accelerator operation in CERN’s history, scheduled to take us into summer or autumn 2011.

    What led us to this conclusion? Firstly, the LHC is unlike any previous CERN machine. Because it is a cryogenic facility, each run is accompanied by lengthy cool-down and warm-up phases. For that reason, CERN’s traditional ‘run through summer and shutdown for winter’ operational model had already been brought into question. Furthermore, we’ve known for some time that work is needed to prepare the LHC for running at energies significantly higher than the 7 TeV collision energy we’ve chosen for the first physics run. The latest data show that while we can run the LHC at 7 TeV without risk to the machine, running it at higher energy would require more work in the tunnel. These facts led us to a simple choice: run for a few months now and programme successive short shutdowns to step up in energy, or run for a long time now and schedule a single long shutdown before allowing 14 TeV (7 TeV per beam).

    A long run now is the right decision for the LHC and for the experiments. It gives the machine people the time necessary to prepare carefully for the work that’s needed before allowing 14 TeV. And for the experiments, 18 to 24 months will bring enough data across all the potential discovery areas to firmly establish the LHC as the world’s foremost facility for high-energy particle physics.

    I’d like to invite you all to the summary of the Chamonix workshop on Friday 5 February at 14:00 in the Main auditorium. See:

    Steve Myers

  • Martin

    Thank you John for posting this, and sorry for being a brick on your back. For interested readers, the news made Yahoo’s front page today:

  • Marco

    Actually Steve Myers said something even scarier in his summary of summaries.
    LHC will run until 1fb-1 of integrated luminosity or until end of 2011, whichever comes first. Then a long shutdown of 18-24 months to fix all the splices (the number of 18-24 months is mentioned around minute 61:46 of the second part
    of the video tape). So no 14 TeV running until late 2013 or 2014.

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