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Archive for November, 2010

All stat mech and no play…

Thursday, November 11th, 2010

It’s pretty late in the night, and I’m still working my way through several statistical mechanics homework problems. This reminded me of one of the funniest (and most depressing) paragraphs that I’ve ever found in a physics textbook.

Without further ado, I give you the first paragraph of page 1 of chapter 1 of David Goodstein’s book “States of matter”

Ludwig Boltzmann, who spent much of his life studying statistical
mechanics, died in 1906, by his own hand. Paul Ehrenfest, carrying on the
work, died similarly in 1933. Now it is our turn to study statistical
mechanics. Perhaps it will be wise to approach the subject cautiously…

David Goodstein (States of Matter)

Isn’t that a great intro? I’ll be back soon with something more enthusiastic to say about physics!


Live event displays

Wednesday, November 10th, 2010

You can see live event displays from ALICE here.  Perhaps you can identify the different detectors in the event display from the description of the ALICE detector.  And here’s an event display with our Time Projection Chamber in:

What you’re looking at is the charged particles we’ve seen in ALICE.  I’d tell you roughly how many we see except that I’m afraid that some theorists in our field would mistake that for a measurement.  (You know who you are!)

There’s more information about ALICE and more event displays here.

(ATLAS and CMS also have event displays.)


Collisions of Lead ions in the ALICE Detector's central barrel

Collisions of Lead ions in the ALICE Detector's central barrel

The moment the ALICE Collaboration have been waiting for has arrived. Today, the LHC announced that collisions of Lead ions are finally underway. We can at last begin studies on the curious quark gluon plasma, as our “mini-bang” factory recreates the extreme environment of the early universe in 10^-22 second microcosms. I cannot begin to describe the excitement it has generated in the community. We are thrilled.

The image above shows the tracks from one of the collisions propagating the detector, reconstructed using the High Level Trigger as the data was being taken. As you can see, the analysis challenge is much greater with Lead than with protons, if only for the density of tracks that need to be identified. It is here that the ALICE detector gets to shine – nearly 20 subsystems will work together to measure and unravel information from the events, so that we can know as much as possible about what is happening. This is what ALICE was built for.

My own journey with ALICE is drawing to a close, as my thesis nears completion and I prepare for the next stage in my life. However, for those that remain involved with ALICE, the story is just beginning. I feel so lucky to have had the opportunity to play a small part in such an exciting piece of history. I look forward to reading the papers that will come from this unique data, and that could change the face of science, for years to come.

Keep your eyes on the ALICE website for more images and any further news.


Very early this morning we got the first lead-lead collisions at the LHC!  I am all a twitter.  This is a very exciting time.  I just arrived at CERN today and I am very, very jet-lagged, so I’ll keep this short.

Pictures.  What you all want to see is pictures.

Here are some event displays with the first Pb+Pb collisions seen by ALICE.  This is an example:

These event displays only show information with the Inner Tracking System (ITS).  Our main tracking detector, the Time Projection Chamber (TPC), was off for these collisions.  The reason is that the beams were not perfectly stable for the first collisions and we did not want to damage our TPC.

And check out this video of an event display (the original video is here):

And now that we have lead-lead data, we have a lot of work to do.  Expect the first lead-lead paper soon.  It will be a multiplicity paper like ALICE’s first few proton-proton papers.  We will just measure the number of charged particles in an event.  This information alone will tell us a lot about heavy ion collisions – the first estimates for how many particles we should see in an event varied by a factor of 4, from 2000-8000 tracks.


Coming and Going

Saturday, November 6th, 2010

Hi, all!

It’s 6am, and I am just entering the night shift doldrums. (Again.) I won’t lie: Lady Gaga is the only thing keeping me awake right now. Ra ra, ah ah ah. Roma, roma ma.

I had thought to write about the LHC’s big switch from proton-proton to heavy ion collisions, but another blogger beat me to it. Kudos, Ken. I’m tempted to write about how I’m spending my weekend — 3D pixel sensors, and the R&D thereof — but at this point in my shift, I’m trying very hard not to think about it. So… here’s a human interest (fluff) piece instead. 🙂

I moved to CERN 1 year ago, and I mean to stay for another one, at least. (I celebrated my anniversary by working until 9pm. Very fitting.) By CERN standards, I believe this makes me a long-term resident, since the community here has such a high turnover rate: physicists are constantly coming and going! Short stays for meetings, conferences, shifts, testbeams, “the experience,” cleverly-disguised European vacations, etc. are common and easily worked into a busy schedule. Longer-term stays, on the other hand, require a certain degree of independence from one’s institution or employment at CERN itself, but of course these eventually come to an end. All good things do.

Let’s take my university, Stony Brook, as an example. This 3D pixel testbeam (still going…) brought out a pair of grad students for two weeks, but they’ve already left. Last week an e/gamma workshop near Marseilles, France drew an SBU friend (and former US LHC blogger!) to CERN, but she’s only here for a few days — zut! This fall, four professors have been or will soon be here, but only briefly. And my advisor often shows up unexpectedly; not long ago we actually crossed paths at the Geneva airport going in opposite directions. Now multiply this by the (five?) hundreds of institutions doing work here. It gets a little intense.

To accommodate the transient physicist population, CERN operates three hostels on-site. When I first moved here, I stayed in one for a couple weeks; I could see my office from my bedroom. Yikes. For medium-term visitors, there’s the St. Genis “Aparthotel,” an unfortunate hybrid located kitty-corner from the only bar in town. This is, I think, a necessary convenience. And for longer-term CERNois like me, there are apartments all around, as far as the eye can see. Although the housing market can be quite competitive in the vicinity of Geneva, we have our own CERN Market that provides international movers a much-needed leg up. It’s a great source of apartments-for-rent, used cars, ski equipment, and of course, cheap Swedish-made furniture. (I love you, Ikea, but please don’t make me lecture on the sustainability of disposable furniture.)

Now, finally, I arrive at the point of my post: This constant flow of people from all around the world results in a diverse mix of cultures and experience that enriches and informs our scientific research. There’s a CERN Market for ideas, too. I think this goes to the heart of having a global laboratory: All together, it’s much more than the sum of its parts.

Well, my shift is over, and I’m overdue for some much-needed sleep — followed by the weekend! Gaga give me strength.

— Burton


This morning, the LHC ended proton-proton collisions for 2010. What an exciting year! Seven months ago, there had never been particle collisions at a center of mass energy of 7 TeV in an accelerator. Now, LHC physicists are busy combing through the mountains of data that have been accumulated since. True, the collisions are still a factor of two below design energy, and a factor of a hundred below design collision rate — we have a long way to go. However, the improvements we have seen this year have been very encouraging and show that we are well on our way to getting there. We have seen the instantaneous collision rate (luminosity, really, for those who want the right techical term) increase by a factor of 100,000 over the past seven months. As a result, the bulk of the collision data has actually arrived within the past month. Everyone has had to be on their toes to keep up with it.

Today thus marks the end of at least one era. With the heavy-ion run about to start and then an extended technical stop to begin in early December, we don’t expect proton collisions again until late February 2011. This break of at least three months gives everyone a chance to chew on the data that we do have in hand. This dataset is thus going to be the basis for a raft of papers that are going to be published in 2011. At the very least, this data will be used to re-establish a variety of standard-model processes at this energy scale, and will be able to exclude a number of theories of new phenomena. (Or, if we are very lucky, discover some new phenomena!) On top of that is another intriguing possibility: it is possible (but certainly not yet confirmed!) that in 2011 the LHC will run at a collision energy of 8 TeV rather than 7 TeV. This decision will likely be made at the Chamonix workshop in January, where CERN will set the run plan for the year. A move to 8 TeV will increase the production rate of a variety of particles, including the much-sought Higgs boson (if such a thing actually exists). If this happens, then it is likely that 7 TeV collisions will never be done again, in which case the data we have collected this year, and the measurements done with them, will be something unique in the history of particle physics.

Your LHC physicists will be hard at work over the next few months to fully explore the 2010 data. Watch this space for more news about the science that will come out of it!


As I was writing a talk for a conference, I ran into a bunch of pictures of ALICE that I thought y’all might like to see.  In my last post I gave an overview of ALICE and described each of the subsystems in ALICE.  I don’t have a picture of every subsystem, but to give you an idea of what these pieces look like:

This is the ALICE magnet (which used to be the L3 magnet) in 2001, before any of the detectors were installed inside of it.

This is the hole inside the TPC where the ITS sits now

This is the whole ITS when it was being installed

Here you can see the PMD team in front of the PMD

This shows the PMD after it was installed in ALICE

Here you can see piece of the TRD right before it was installed

This is the HMPID right before it was installed

This is one of the trays of the TOF

And here you can see one of the EMCal supermodels right before it was installed

And this is the ALICE collaboration in front of ALICE

(Note to ALICE collaborators – if you didn’t see a picture of your favorite subsystem, email it to me.  If I get enough cool ALICE pictures for another post, I’ll do a follow up with more gratuitous cool pictures of ALICE.)