mini-Chamonix – back on for 10/fb in 2011

The Large Hadron Collider is quickly making its way back to normal physics runs after the technical stop and a power cut that knocked out the cryogenics for an extra couple of days. For a while we will be more interested in new results presented at the EPS conference in just six days time, but first the beams operation groups need to decide how they are going to run the collider for the rest of 2011. A one day “mini-Chamonix” has been organised for today to consider whether and how and by how much luminosity can be further increased. The presentation slides are available here.

There are 107 days remaining for proton physics this year. The most likely means for increasing peak luminosity further now is to increase bunch intensity and decrease emittance (i.e. the transverse spread of the beam over position and momentum space.) This plot shows the statistics so far.

In fact the intensity for the last run at 1380 bunches was 1.25E+11 and the emittance was about 2.8um. How much can this be improved?

Everybody now believes that 4/fb can be delivered to ATLAS and CMS this year and 1/fb to LHCb. This is just by running with present parameters and assuming a reasonable run efficiency, but more is possible.

Present peak luminosity is 1.28/nb/s. CMS and ATLAS would be happy to see that go up to 3/nb/s. Any more would provide more pile-up than they want at this time, but they would still want to go higher near the end of the run to test for ways to deal with high pile-up.

From the injection chain the best bunch intensity with multiple bunches this year is around 1.6E+11 protons per bunch with emittance of 2um. This would double the peak luminosity. Ways to go higher are being studied during MD time, but for next year.

As far as I can tell from all the other slides there are no barriers to these numbers from beam stability or machine protection considerations.

Other ways to increase luminosity such as 25ns bunch spacing and ATS squeeze are still under study. We may see more tests during MD but no real physics runs (with these new features) until at least next year (actually some more squeeze is still a possibility according to the conclusion)

We now just have to wait to see what they decide by the end of today.


The final conclusions are in and it looks promising. This is the table of possibilities they have to discuss.

So increasing intensity and decreasing emittance poses no risk and can be done gradually. A factor of 2.7 is then available. The experiments wont want much more than that so any further increases may result in luminosity leveling.

The increases could be implemented over a 30 day period with 60 day left for running at full luminosity. Looks like 10/fb by the end of the year is back on.

16 Responses to mini-Chamonix – back on for 10/fb in 2011

  1. Luboš Motl says:

    Wow, no physics runs until 2012? That sounds like a dramatic proposal.

    In the long run, the total and peak luminosity should be increasing but the question is “how uniformly” one wants to achieve that.

    I would say that there’s no reason for this to be excessively uniform. In fact, I think that it is very natural to make long breaks for serious updates and to restart the LHC in such a way that in the new “working period”, the integrated luminosity gets multiplied by 5.

    Only when the integrated luminosity gets multiplied by a significant factor like 5 – like from 35/pb to 180/pb, from 180/pb to 900/pb, and so on – you can see “qualitatively new things” in the data because the statistical significance of various signals doubles, so new 3-sigma things grow from the previous 1.5-sigma non-signals and 3-sigma signals may grow to 5-sigma if there were any.

    So this break should have been considered the post-1/fb break and when the LHC is restarted, it should be restarted in such a way that it may accumulate say 4-5/pb, and after the next break, it will get 16-20/pb. That’s what I would recommend. A classic exponential growth formula with the multiplicative factor of 4-5 giving the “waves”.


    • Philip Gibbs says:

      LOL, I had to read the post again to see where you got the idea there would be no more runs this year. I meant no physics runs with 25ns or ATS, my fault for sloppy writing!

    • Luboš Motl says:

      Thank God, Phil. One must be ingenious to figure out that “runs” means “runs with 25 ns or ATS”. 🙂

  2. Leo Vuyk says:

    And What if the Higgs is not there OR has no mass at all.
    At what energy boundary we have to give up? looking for the Higgs?

    • Philip Gibbs says:

      If it is not found in the energy range they are now looking at then the Higgs theory is seriously wrong, but it would still be an amazing result and a success for the LHC.

    • JollyJoker says:

      The energies the LHC is colliding at are far higher than any possible Higgs mass.

    • Luboš Motl says:

      Dear Leo, a massless Higgs would cause new long-range interactions etc. that would seriously influence even everyday life. But even a very light Higgs would have consequences that are incompatible with the known facts. And there’s no known consistent theory of the known electroweak phenomena that would avoid any kind of a Higgs sector (I was just explaining why a B-wedge-F theory of the massive gauge bosons didn’t work).

      But maybe you could have asked what if there were a Higgs with a charge. A totally new innocent US LHC blog entry on systematic uncertainties

      might be a subtle hint that they could actually be seeing something, losing night over comparisons with the background. Otherwise, the huge contrast between the general text about uncertainties and the specific nature of the W- H+ pair from an intermediate top-antitop pair, where H+ decays leptonically and W- decays to quarks, looks like a mind-boggling contrast in a single short text haha.


      • Leo Vuyk says:

        Thanks Lubos, Indeed this idea goes into some interesting direction , however I think there is an alternative FORM changing path
        I wrote:

        It is an interesting challenge to postulate that the FORM and structure of elementary particles is the origin of different FUNCTIONS of these particles.
        Secondly, that all particles are siblings of the mother of all particles the Higgs particle which is supposed to be able to transform by collision.
        If we define mass as the ability of Fermions to change some of the scattered Higgs particles into as much Gravitons, then we may interpret also the “Eigenenergy” of Fermions as the Higgs changing process into different kinds of Photons, without the need for a MASSIVE HIGGS PARTICLE. SO the Higgs could be massless and the same as what is called dark energy.

        Leo Vuyk.

  3. […] Por cierto, más información sobre Mini Chamonix, como no, en Philip Gibbs, “mini-Chamonix – back on for 10/fb in 2011,” viXra log, July 15, 2011. […]

  4. carla says:

    I’m surprised they’re going for a potential increase of 2.7 over 30 days. I thought they might go for for a more modest 1.5 over the next 6 weeks, followed by 2 over the final 8 weeks. 1/fb over a year is a great achievement, 5/fb spectacular, but anything above seems to belong to the realms of fantasy. Yet here we are, considering it a distinct possibility that the LHC may have enough data after combining Atlas and CMS to see a 5-sigma 114Gev 5-sigma Higgs, if it’s there. I think I need to lie down..

    Nice post, by the way. I think you do CERN a favour by publicizing the excitement and talent there, and why it needs to be supported.

  5. carla says:

    They’re having a lot of problems getting an 840 bunch fill to go in, having failed at 6 attempts so far and are now increasing emittance and lowering intensity to see if that will help. I think the road ahead to increasing luminosity is going to be very rocky.

    Were the conclusions those from the seminar, or your own?

    • Philip Gibbs says:

      They finally have a good run for 840 bunches so hopefully they can go back to 1380 next. Getting the luminosity up further is not going to be an easy job if this is anything to go by.

      • carla says:

        This reminds me of the exact same problem they had going from 928b to 1092b, where they had to increase the emittance and reduce the intensity which did the trick after some experimentation. From what the’ve learned from last time, the problem is quickly solved. Perhaps it’s something to do with a sudden change in stress on the beam pipes which causes material to become dislodged

  6. […] Si tot va bé, abans de finalitzar l’any s’assolirien els 4 fb inversos (o fins i tot 10 fb segons les previsions més optimistes). El famós femtobarn invers assolit a mitjan […]

  7. […] Els experiments ATLAS  i CMS de l’LHC  van arribar a la quantitat d’1 femtobarn invers, la qual cosa és un molt bon indicador d’efectivitat relacionada amb el nombre total de col·lisions produïdes (en aquest cas equivaldria al voltant de 70 bilions de col·lisions). Un cop superats els problemes soferts per la infraestructura després de la seva arrencada, l’estiu de 2008, aquesta dada demostraria que el seu funcionament segueix el guió previst. Si tot va bé, abans de finalitzar l’any s’assolirien els 4 fb inversos (o fins i tot 10 fb segons les previsions més optimistes). […]

  8. […] of the beams so there is no increased risk or extra demand on the cryogenics. At the recent mini-chamonix meeting it was predicted that emittance could provide an extra 35% luminosity but now they are 55% […]

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