Posts Tagged ‘physics’

Made in the U.S.A.

September 12, 2008

CMS is on the cover of Newsweek, under a caption that reads “The Biggest Experiment Ever (And It’s European).”  Interestingly enough, the part of CMS they picture is a muon endcap disk, which is a U.S. contribution*.  In general, though, the LHC and the LHC experiments are mostly European.

(* FermiLab, Carnegie Mellon, Florida Tech, University of Florida, Northeastern, Northwestern, Ohio State, Purdue, Rice, Texas A&M, U.C. Davis, UCLA, U.C. Riverside, Wayne State, and Wisconsin.

My “Made in the U.S.A.” subject line isn’t exactly true: two of the four assembly sites were in China (IHEP) and Russia (PNPI).  The Russian contribution was mostly on a different disk than the one shown.)

The LHC is clear!

September 10, 2008

Beams have now circulated in both directions around the LHC (different beam-pipes), so the tubes have been verified to be empty (nothing demonstrates that better than a beam), the magnets are all well aligned and stay cold, and the focusing optics are tuned.  No show-stoppers!

The counter-clockwise direction took a little longer; they had more trouble controlling the beam on the first or second try (it wiggled back and forth around the center of the beamline until they re-tuned the optics), but it has been successfully demonstrated now.  On the whole, it has been a very good day for the storage ring— I don’t think anyone expected it to be so successful so early (6 hours from the first injection to complete success).

If anyone involved is reading this, congratulations!!!


  • time estimates for getting one beam to go in one direction had been as much as 12 hours
  • semi-official date for first collisions is Oct 21 (that can be changed, perhaps earlier)

Beautiful beam-halo tracks in CMS!

September 10, 2008

In posting LHC updates, I want to be careful not to say anything or present anything that is still internal to the collaboration, which usually precludes plots of hours-old data.  However, our first event displays are already available on a publicly-accessible site, so enjoy!

Here’s an annotation of the what I think is the clearest one:

Upstream of our detector, protons from the first LHC beam collided with atomic nuclei of gas atoms and metallic beam collimators (which clip the beam to protect the magnets), producing a “halo” of muons, roughly parallel to the beam in the beampipe.  In the picture above, you’re looking at a reconstruction of one of these muons from detector signals alone.  For clarity, only the subdetectors which saw anything are drawn (they’re the trapezoids hovering in space), and their measurements are presented as intersecting yellow and purple lines.  The yellow and purple are nearly orthogonal measurements, each sensitive to the passing particle’s position in one dimension: where they cross is where the muon passed through.  If you look closely, you’ll see that these points line up.  The software recognized this as a track and fitted a blue line to them, which looks as though it points back to a beam-gas collision in the beamline somewhere to the right of this picture.

The computer-generated image doesn’t give a sense of scale, so I’ve added Big Bird.  It’s also unclear at this level of zooming that the position of the muon as it passes through them is measured with an accuracy of about 300 microns.

Cute event displays are absolutely pouring in on CMS mailing lists.  Meanwhile, it sounds like the LHC is getting close to running protons in the other direction as well (it was delayed due to a cryogenics problem).  As a reminder, they’re not planning to collide them or ramp them up to high energies or high intensities today: that will be a slow, careful process over the next one or two months.  I wonder if they’re going to have festive event like this when the beams actually do collide, or if the media will lose interest by then.

LHC beam through CMS

September 10, 2008

Right now, they’re letting the proton beam stream farther and farther through the LHC, stopping it at intervals with beam-dumps for safety.  Minutes ago, the beam passed half-way around the ring, through the CMS detector (and now beyond CMS).  I hear that the CMS trigger rate is showing something…

The inner CMS tracker has been turned off (no high voltage, no read-out) for protection.  But the outer muon detectors, farther from the beam and less sensitive to radiation, should be on and taking data.  Meanwhile, I’m putting the finishing touches on the software to use these data for alignment.

Happy birthday, Greg!

Update: the beam has gone all the way through!  It all happened much quicker than I would have expected.  They went step-by-step through each sector, saw a little bit of wiggling in the parts that were new territory, dumped the beam, started again, and apparently that was it.

Details for LHC First Beam Day

September 8, 2008

The broadcast will begin at 3 AM in the eastern U.S. timezone on Wednesday morning.  I’ve been quiet recently because I have a project that needs to work when the first data cometh.

First data from GLAST!

August 27, 2008

As interesting or almost as interesting (in my opinion) as the start-up of the LHC is the start-up of another high-energy particle detector, the Gamma-ray Large Area Space Telescope (GLAST).  Now that it has been in space long enough for NASA to be confident that it won’t blow up, they gave it a name: Fermi Gamma-ray Space Telescope (FGST).  It’s more of a high-energy particle detector than a telescope: it sees gamma rays (energetic photons) by letting them convert into electron-positron pairs in a nucleus’s electric field, and then observes the trails left by the electron and the positron from ionizations left on silicon wafers.  This is exactly how the central tracker in CMS will observe particles from LHC collisions.  (We expect to see a lot of gamma-ray to electron-positron pairs ourselves.)  The difference is that GLAST is in space and its gamma rays come from the center of our galaxy, blazars, and gamma ray bursts, rather than man-made collisions.

Here’s the map, and a link to a lot more information and another link to all the news stories.  This four-day exposure has the same sensitivity as 1 year with the previous (first) gamma-ray telescope, EGRET.

(Yes, it makes me jealous.)

Yet further around the LHC

August 24, 2008

The latest beam injection test shows protons making it part-way around the ring in both directions.  They’re getting close to CMS!

Pictures from the Control Room

August 23, 2008

When I was last at CERN (last month), I took some pictures of the CMS Control Room, to give you a sense of the place.  Some control rooms (also called “counting rooms” for historical reasons) show their age and cumulative history, like the CESR control room at Cornell, which has oscilloscope displays next to flat screens, a built-in AM car radio, and an old Macintosh to read all the alarm messages over the intercom in a robotic voice.  I’ve never seen one yet that looks like something from a James Bond movie, but the “CMS Centre” comes close.


More updates from the LHC and CMS

August 21, 2008

Protons have not only entered the LHC, but they have travelled through one of the experiments, ALICE, to a point part-way between ALICE and CMS.  On the first try, the protons threaded through all the dipole magnets and appeared on target at the IP3 beam-dump.

Here’s the spot of protons, as seen by the beam-TV at IP3:

Full details are available on the LHC Injection Test webpage.

Meanwhile, CMS has entered more or less full-time data-taking mode.  Until recently, we had been mostly installing detectors and taking cosmic ray data intermittantly, but now we are primarily taking data and closing up the detector.  This week, we started our fourth major cosmic ray run without a magnetic field, in which charged cosmic ray muons appear as straight tracks through the detector, and soon we will turn on the magnetic field so that the tracks are curved with a radius inversely proportional to their momenta.  In addition to bending muon tracks, it will tug our five-story iron endcaps so strongly that they will bend a few centimeters in the middle, with a force about 5 times their weight.  Therefore, all components must be completely closed and bolted into position, closing off access to the inner detectors.  Half of the detector is already closed.

This is it!  It’s finally happening!  More updates later.

Physics and category theory?

August 11, 2008

This caught my eye on the arXiv blog: the prospect of finding a (physics) theory of everything using category theory. I haven’t followed up on the claims any more than that, but I’d like to point readers (and some authors) of this blog to it: