ATLAS observes cosmic-ray events underground!

May 30, 2006 at 6:40 pm 7 comments

Very good news – according to Travis Stewart the ATLAS tile calorimeter has recorded clean cosmic-ray events in the underground cavern. Here is the picture he posted:

Please visit his blog in order to see more information about this.While people are not interested in using ATLAS to do comic-ray physics, this accomplishment is important because it shows an expected signal successfully recorded and understood – the hits are in the right place, there are no garbage hits, the event has the right features, etc. Progress over the next year or two will consist of moving from one modest success (like this one) to the next one, which will be slightly less trivial. So, after a year of comic rays, we will hope to count the number of tracks in minimum-bias events…

(A disclosure: while I am happy about this success, it also makes me slightly nervous and envious, since I am a member of the competing CMS collaboration…)


Entry filed under: Particle Physics.

predictions from Lattice QCD “Discovery for the Sake of Discovery”

7 Comments Add your own

  • 1. Travis  |  May 30, 2006 at 9:11 pm

    Thanks for visiting the blog and for adding me to your blogroll. I will try to post as much about progress being made with ATLAS as I can (I’m not sure how much I actually know, I am new to the experiment). Likewise I hope to hear about progress being made by CMS. Keep up the good work.

  • 2. JR Capablanca  |  May 30, 2006 at 11:19 pm

    Hi michael, thanks for starting this blog – it is on my favourites list and I look forward to following it.
    What event are we looking at here? The final state looks like a fermion pair (?) but what was the incoming cosmic particle?

  • 3. Michael Schmitt  |  May 31, 2006 at 7:17 am

    Travis, I was happy to find your ATLAS blog and I hope you will be able to make many posts about progress there. It is an excellent idea to do so!

    JR, this event display shows a cosmc-ray muon which has passed through many meteres of rock to reach the “cavern” in which the ATLAS detector resides. A muon is an electrically charged particle like the electron, only it is heavier and eventually decays into an electron and two neutrinos. This decay is akin to some kinds of radioactivity. The fact that it is heavy means that it is slow to lose energy as it passes through the rock (in constrast to electrons) and the fact that it is highly energetic means that its decay time is greatly expanded according to the laws of special relativity.

    In general, these CR muons are a nuisance, but experimenters like to use them to check out their appratus. They are omnipresent and cost nothing! The picture that Travis posted shows narrow energy depositions in their calorimeter. A muon will deposit a small and definite energy in a calorimeter, and the ability to measure that deposition is proof that the calorimeter functions correctly. Travis’ event shows a particularly clean even in which the muon appears to pass close to the beam line, so it is formally similar to a di-muon event from a collision. Most cosmic ray events will not look like this, since they come from above with no particular correlation with the center of the detector. The lower picture in Travis’ blog entry shows a CR muon leaving a straight track in the silicon tracker and transition-radiation detector.

    CMS is currently at the surface above their cavern, also using cosmic rays for checking out the hadron calorimeter and muon detectors. A full vertical test is scheduled for June and then the detector sections will be lowered into the cavern.

  • 4. dorigo  |  May 31, 2006 at 6:23 pm

    Michael, don’t worry about CMS – we are seeing cosmic rays in CMS too.
    Data taken during the magnet test have been reconstructed by italian groups working at the muon detectors, and tracks are there too 🙂

  • 5. Michael Schmitt  |  May 31, 2006 at 9:49 pm

    Hi Tommaso, you’re right! In fact, members of the LPC muon group are looking through the “digis” now to make sure they are correct. Of course this leads to long and detailed discussions – as it should! This is how you settle issues, by exercising the whole thing, hardware+software.

    What worries me slightly is the fact that ATLAS sees their muons with major parts of their detector underground, while CMS is getting ready to do the same on the surface. The distinction is slight, I admit, but it is like sprinting in a race and one runner has half a stride ahead of the other. The second one won’t be relaxed, that for sure!

  • 6. dorigo  |  June 2, 2006 at 10:31 am


    thank you for taking your time to “defend” me in Peter’s blog … I read back the comments section of that post only after the heat was gone, and was happy to see that I was not being totally lynched there.

    I’m in Elba now, and the weather sucks! 🙂 But I’ll drink one glass for you.


  • 7. FlientIntitly  |  February 24, 2008 at 1:36 pm

    To me it is necessary to find


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