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Archive for December, 2008

Curveballs are Fun

Friday, December 19th, 2008

We’re not big fans of rigid hierarchy in academia, not even on big experiments like ATLAS with multifarious coordinators and project leaders.  On the one hand, this means that nobody ever gives me orders — but on the other hand, it does mean that there are a lot of people who can give me “strong suggestions.”  And sometimes one of those people decides to throw me a curveball…

Friday was a day of two work days.  First I worked a pretty normal eight hours debugging code, then spent the evening at a few holiday parties before heading to the ATLAS Control Room at 11 PM for an eight hour shift.  After I arrived, while waiting for the expert running things to let me do my shift so he could go home and get some sleep, I found an email in my inbox which had been sent only that evening.  It asked me to give a talk at the ATLAS Inner Detector-wide meeting about the activities of the Pixel group over the previous week.  All of the work to be discussed had done by others rather than me, and some of it I hadn’t even been aware of — and the talk was on Monday.

I had never received a request like that before, but believe it or not, I’m not complaining.  Yes, it was rather short notice, but it wasn’t even a strong suggestion, really — I was allowed to opt out if I didn’t have time.  But more importantly, after I thought about it, I decided that giving the talk was entirely a good thing for me.  There are a couple of reasons I can think of to give an inexperienced person the responsibility of summarizing the work of the whole Pixel Collaboration.  One is to give everyone who’s done work on the Pixel Detector a turn to make their participation visible to the wider Inner Detector community, even if their work contributed only indirectly to the material being presented.  (In my case, the contributions were taking shifts and writing tools for analyzing calibration scans.)  Another is to give the person giving the talk the opportunity to learn more about the broader work on the detector.

In my case, it was an opportunity I had to take quickly, so I sprung into action: I checked the agenda for Monday, found that the meeting wasn’t until 3 PM, and decided I could delay the writing of the talk itself until Monday morning.  I did look at the list of topics to cover during my shift, and asked a few questions; then I printed out all the supporting material on Sunday night.  But otherwise I continued with my weekend as scheduled.  This required Monday to be a very productive day: I got up at 6:30 AM to start reading everything I had printed out, then got intto work by 8:30 am and started writing.

Most of the slides were summarized from elsewhere, or even provided for me.  The most important part of what I had to do was to understand what was on them, so that I could provide context for the work and avoid sounding like an idiot if I had to go “off script.”  The way I think about it was that the people who had done the studies had given me intermediate-level information to present, and nobody would expect me to answer really hard stuff during a summary talk, but that I absolutely had to have a command of the basic way in which the material I was presenting fit into the broader picture.  I needed some help with that, and got plenty of it, from the experts who did the original work as well as from the person who asked me to give the talk.

By 3PM, I was ready, but also nervous about talking in a new venue and in front of new people.  I hadn’t given myself time to be nervous up until that point, but I had plenty of it while watching the other four talks ahead of mine.  My strategy during the talk itself was to try to sound confident that I understood everything, unless I actually didn’t know something and had to punt questions to the other pixel people in the room — which it turned out I never did.  In the end, in fact, I was told the talk was clear and went well.   So I suppose I managed to hit the curveball, and it definitely made for a more exciting Monday than usual!


When the LHC gives you lemons…

Friday, December 12th, 2008

This week was one of the quarterly big CMS collaboration meetings.  I didn’t go, as it’s the last week of classes here, but I’ve been following it as much as I can from here.  What we’re seeing is some impressive work with real CMS data.  “But wait,” you are saying, “the accelerator broke three months ago, what real data are you talking about?”  Ah, but I said CMS data, not LHC data.  Cosmic rays are still raining down on CMS, and the collaboration spent several weeks this fall recording data from muons that came through the detector.  This took a lot of operational effort, and it really seems to be paying off in our understanding of how the detector works, and how our software interprets the data that come out of it.

There are a lot of questions you can answer with these data.  In any given cosmic-ray event, you expect to see one and only one muon come through.  Do you see only one, or do you reconstruct additional fake charged particles?  You can measure the muon momentum in either the muon system or the silicon-based tracker.  Do the two measurements agree?  There should be very little activity elsewhere in the detector.  Is that so?  If not, we’d better understand it; many searches for new physics will revolve around looking for energy imbalances in the detector, and if the energy is already imbalanced when there is nothing happening, we’re in trouble.

And then you can also do some studies related to the cosmic rays themselves.  Do you observe the right ratio of positive and negative muons?  Do they have the right angular distribution (predominantly from directly above, but falling off with the square of the cosine of the angle from vertical)?  Can you see the shadow of the moon when it is overhead?  These are harder to do (that last one in particular is tricky, but appears to be worth trying), but they could show that we really are getting a grasp on how this detector, in the making for years, actually works.  We’d rather have collision data, of course, but my colleagues are really making the most of the data we have.

Lemonade, anyone?


Chu to be Nominated Secretary of Energy

Thursday, December 11th, 2008

We learned yesterday — or overnight, for those of us on the other side of Atlantic and asleep for the wrong part of the American news cycle — that President-elect Barack Obama’s choice for Secretary of Energy will be Steve Chu.  This is very exciting news.  Not only is Dr. Chu a Nobel Prize-winning physicist — rather unusual for an Energy Secretary, since after all the Department of Energy has far more under its purview than just the Office of Science — he’s also the director of my lab, Lawrence Berkeley National Laboratory.  I can imagine that the atmosphere back in Berkeley today will be electric.

I hope I can be forgiven, with the nomination so “close to home” on so many levels, for thinking a little bit in particular about how my field of research will be affected.  Of course, Sean Carroll is right when he says that “just because Chu is an accomplished physicist, this doesn’t mean that researchers should expect a bonanza of new funds.”  Certainly there’s no reason to anticipate such a bonanza for particle physics.   Although Berkeley Lab’s founding project was particle accelerator research, and we still have quite a number of excellent particle physicists (if I do say so myself), over the decades it has developed a very diverse research program and a focus on bringing together different disciplines to solve real-world problems.  This interdisciplinary environment has been expanded during Dr. Chu’s tenure as Lab Director, and his particular focus has been on the development of technology to address energy resources and climate change.  His interest and expertise in this area is doubtless one of the key reasons that he has been selected for the new job.

This past January, during the Lawrence Berkeley National Laboratory ATLAS group’s annual “back to the mothership” group meeting in Berkeley, Director Chu joined us for dinner one evening and gave a brief, informal talk.  Of course, he couldn’t say what he might like to say to every group at the Lab, that our research was his top priority, because that wasn’t true.  But what he did say is that fundamental research, including fundamental particle physics research, is a critical part of any long-term effort to address concrete problems.  He was very aware of the ongoing funding difficulties that our field is having, both in terms of the complexities on the political side and of the effects that uncertain and diminished funding have on the operation of our experiments and laboratories.  I came away with a sense that, although he had many things to focus on beyond my own area of research, he knew a lot about our work and had an extraordinary understanding of how it fit into the big picture.

For Dr. Chu, the picture is now getting far larger.  His nomination comes along with several other officials who will be dedicated to environmental and energy issues, and we can expect his first priority as Secretary of Energy to be working with them and with the President on a new national policy in those areas.  I hope he will also be able to work with the Congress on stabilizing funding for particle physics and preserving what he calls the “intellectual capital” of our scientists, engineers, and technicians working at places like Fermilab.  From what I’ve seen, he has the knowledge and perspective necessary to keep pace with the many tasks that will require his attention as Secretary of Energy, and to balance our nation’s urgent needs in terms of energy policy with our long-term interest in continued excellence in fundamental science.


I don’t think any real scientist would ever make a statement like “this is impossible”, or “this will never happen” — it is always “this is extremely unlikely”, with a qualifying “if current knowledge and theory holds”. It seems to be a fundamental property of science that we can never prove that something is true, but can only falsify hypotheses.

So, what is this “no conceivable danger” conclusion in the 22-page “Review of the Safety of LHC Collisions” November 2008 publication by the LHC Safety Assessment Group? How does one make any claims at all about what will not happen in an unexplored regime of experiment/theory?

The fine print that resolves the dilemma is that “unexplored regime” is not true. Homo sapiens may be patting ourselves on our backs for finally anticipating life at 10 TeV center-of-mass energy, but the universe has been ahead for some number of years equal to 1031 LHC experiments — and at a rate of 1013 LHC’s per second. Now we note that the universe still exists (as far as we can tell), planets and stars don’t spontaneously turn into black holes (as far as we can tell), and even the Earth has apparently survived 100 000 LHC-like experiments i.e. all those cosmic rays that the cosmos bestows upon us.

Could the 100 001-st time be particularly unlucky? It’s not impossible, but we probably have to work much harder to increase our ratings as a threat to reality.

This post was inspired by an interesting comment from a reader, who asked “when will the experiment finish?” After getting all excited about the lifetime of CMS and proposed Super-LHC upgrades — and hitting the “send” button — I suddenly realized that the concern was probably “hey, when will you stop gambling with all our lives?”, and not so much “hey, how long does a cool experiment like this take?”

I was going to mention that I believe politicians and military to be more active threats to humanity than the unbounded (but not unregulated) curiosity of scientists. But then, it can be argued that destroying an ecosystem is still a lesser crime than annihilating the planet and perhaps the universe too, while we’re at it.


CERN confirms 2009 LHC restart

Friday, December 5th, 2008

OK, for once I’m going to be the first blogger out there with news on the LHC schedule.  Today CERN put out a press release affirming that the LHC will restart in 2009, thus squashing the rumors that Adam mentioned in his post.  The release includes phrases like “ready for physics by summer” and “provide collision data for the experiments as soon as reasonably possible,” which I hope means that this is not just circulating single beams, but colliding beams.  It’s an encouraging statement.

Attached to the release is a report with more information about the analysis of the incident, and details of the repair plan, with what needs to be done with how many magnets etc.  One thing I know that people had been worried about was whether soot and/or debris had found its way into the beampipe at distances far from the original problem, which could have led to a major effort to clean many meters of pipe.  This appears not to be so bad; soot is limited to the pieces that are being repaired and replaced anyway, and other bits of debris seem to be easily removable.

Since I’m writing, has anyone noticed that they are still counting ballots in Minnesota?  Election officials now appear to be limited by systematic uncertainties associated with their methods.  Maybe it is time to flip a coin!


I’ve been meaning to write a quick note thanking people for their comments on last week’s post about tracking.  When I spend a lot of time on making sure a post really explains something well, it means a lot to me to know that my effort succeeded.  (A note to readers who happen to be my advisor: I didn’t spend too long on it, I swear.  And anyway I was waiting for my code to compile.)  So, thanks!  While I’m here, I figure I might as well share an observation that occured to me while reading the comments, and then answer a question that was asked.

First the observation.  In my experience, if you go to a baseball game and point out that the people on the other side of the stadium “look like” a particle tracker for the ball, your friends stare at you as if you’re crazy.  And yet, if you write about particle physics and manage to compare it to baseball, then it goes over rather well as a feat of science explication.  I conclude from this that the trick to being a tremendous nerd while still being cool is to manage expectations; get your audience to expect you to be an even bigger nerd than you actually are, and they’ll be impressed.

Second, the question: Didi Mouse asked who gets to name any new particles we find.  The answer is that we don’t actually know yet, but it depends on what’s out there.  Many particles — for example, the Higgs boson — have been named already; if we make a discovery that looks more or less like a Higgs boson, we’ll call it a Higgs boson.  There are also theories that predict lots of new particles; often those particles are all named, but according to some regular rule.  For example, Supersymmetry predicts a new particle for every known fundamental particle.  The superpartners have the same name as the original, but with an “s” in front for some spins, and an “ino” at the end for others; electron becomes selectron, quark becomes squark, photon becomes photino, gluon becomes gluino, and (my favorite) W becomes Wino.  If we were sure we’d found Supersymmetry, we’d probably keep those names, but we won’t be sure at first what new theory the particles we’ve found fit into — so what will we do?  I expect the decision will be made as part of the experimental collaborations’ processes for writing and approving papers, because the name for a new particle usually comes from the paper that announces the discovery.  As far as I know, nobody has specific plans for how to handle the naming, but it is a problem we will be delighted to have.


LHC update

Monday, December 1st, 2008

In addition to the information contained in Seth’s post, there was another interesting LHC update today at the ATLAS Week. Last week, there was a talk that caused a lot of conversation among the physicists that implied the CERN management was considering the possibility of not having any beam at all in the LHC in 2009.  During the talk today, the statement was made that there are definitely no plans being considered to not try for collisions in 2009.

The schedule in this talk calls for the machine to be cold at the end of July.  Of course, something could go wrong with the repairs, but every effort is being made to have collisions next year.  The collision energy next year would be at a maximum of 10 TeV (14 TeV is the design) and possibly lower.

Some other interesting points in the talk:

  • Approximately 100 people from CERN (and contractors) are already working on the repairs.
  • 39 dipoles & 14 “short straight sections” in the incident area and in the buffer zone around it will be removed and repaired or replaced.  About 20 new dipoles will be installed before the end of the year.
  • 12 dipoles and 6 SSSs have already been transported to the surface.  The first replacement dipole was transported underground on Saturday.  Some neat pictures here.
  • Techniques have been developed to spot resistive splices, the original cause of the disaster.
  • The anchoring of some of the cryostats will be reinforced, so they wouldn’t be able to move in future incidents.

On Friday, CERN Director-General Robert Aymar gave a talk on CERN activities at the 84th Plenary Meeting of the European Committee for Future Accelerators.  One major focus of the talk was of course the status of the LHC, and of particular interest are two pictures of the damage done to the accelerator during the incident on September 19.  They are the first publicly-available pictures of the damage that I am aware of.

The pictures of the damage are on pages 17 and 18.  Page 18 in particular illustrates that the consequences when one of LHC’s multi-ton magnets is shifted by a significant distance.

Many thanks to Director-General Aymar and to CERN for making these updates and pictures available to the public.

Update (5:10PM CET / 11:10AM EST): Access to the talk has been restricted over the past hour or so.  I will send an inquiry to the CERN Press Office to ask about this change in access.  In the meantime, the pictures from the talk may be seen here and here.

Update (December 4): The slides are publicly accessible again.

Update (December 5): I have received a reply to my inquiry from the Press Office: “Sorry for not replying to your mail about the LHC pictures sooner. I believe that the [Director General] was concerned that the CERN community should receive the news from him before it was made more widely available, that’s why the link to the talk was temporarily restricted. As you’ve noted, it’s now back up, as is a more comprehensive report on the status of the LHC: http://press.web.cern.ch/press/PressReleases/Releases2008/PR17.08E.html.”