Month: July 2010

This was originally posted in the SMU CERN blog (http://blog.smu.edu/smucern). It’s reproduced here because I am the author! 🙂

10:45 p.m., a cluster of massive buildings marking the location of the Point 1 Control Room for the ATLAS Experiment. ATLAS is itself 90 meters below the earth.

It’s 10:40 p.m. when I leave building 1, cut through a parking lot, and head for CERN Entrance B. It’s only been 6 hours since I woke up; I’ve rotated my schedule to put myself on a night-cycle. This is not easy for a human being. We’re adapted to the sun, and we run our lives by it. The gentle rhythms of our biological clocks crave the day-night cycle. But here I am, a physicist in Switzerland standing at a crosswalk, waiting to step into the distant dark and down to the Point 1 Control Room.

The ATLAS Control Room, or ACR, is located in the back of a cluster of large surface buildings. I say “surface buildings” because these structures mark the top hat of ATLAS, covering the large shaft that descends down to the ATLAS cavern, 90 meters (295 feet) below the earth. Approaching the buildings in the dark is an eerie experience. You walk from the intersection of Route de Meyrin and CERN Entrance B, up a tree-shaded, unlit driveway to a long security gate. A wave of your CERN ID in front of the gate sensor starts the gate on a slow slide to the left, allowing you to squeeze through. The cluster of lighted buildings then sits in the distance, perhaps another 100 feet away.

We gather at the Run Control desk to discuss committing some configuration changes to a database. The LHC is currently down, addressing some issues with the CMS experiment.

The ACR itself is abuzz with activity, even at 11pm. I relieve the previous shifter at the Trigger Desk. We exchange information about the day’s activities. The Run Control shifter, an old colleague of mine from Scotland, comes over and asks for my approval of the current set of trigger configurations and then about committing some changes to a database. Despite the fact that there are no beams in the LHC, it’s a busy night. I had been told by the previous trigger shifter not to expect colliding beams until at least 5 am.

There is a routine to a shift that I like very much. Most of it involves checking dozens of windows, each which displays some nuanced aspect of the ATLAS trigger system. The “trigger” is a computer hardware and software system whose sole job is to decide if a particular proton-proton collision is interesting enough to write to disk for further investigation. If the trigger isn’t running correctly, physics can be tossed aside and wasted. In addition to the technical routine, there is the job of interacting with colleagues in related systems, like the Data Acquisition Shifter who sits next to me, or the Shift Leader. It’s important to keep exchanging information while on shift, and work together to solve problems. There are always problems, and that’s the real fun of taking shifts.

The two coffee machines that serve the ACR. The Nespresso machine on the right is my favorite.

To survive a night shift, even after rotating your schedule, you need coffee. Or, at least, I need coffee. Two floors up from the ACR is a pair of coffee machines that make decent espresso. I’m a big fan of these two machines; they’re really the unsung heroes of the ATLAS experiment. On the floor between the ACR and the coffee, painted on the wall along the staircase, is a mural of the ATLAS detector depicting different particles interacting in the equipment. The painting is 1:1 scale, meaning that as you walk up the stairs and follow an electron back along its illustrated path, you are getting a sense of the immense journey that this high-energy subatomic particle is making from the proton-proton collision that birthed it.

Whenever I am on night shift, I think about my mother-in-law. She’s been working in a bakery for decades, and that means she’s up between midnight and 3 am, in time to go in and do all the prep work and baking for the day. It’s a hard life, and she’s been doing it a long time. She does it because the job demands it – people want their baked goods first thing in the morning, when they get up to do their “normal” jobs at “normal” hours. For physicists on a major experiment like ATLAS, the data demands to be taken at all hours of the day. In fact, night is the most stable time to take data – the people that like to tweak the collider are home for the day, leaving a shift crew behind who are ready and eager to have stable operating conditions through the late hours of the night. On the experimental side, we welcome such conditions – stable beams mean steady data. ATLAS, and the other LHC experiments, will run 24 hours a day for most months of the year. a crew of hundreds of people per experiment is needed to maintain the detector. It’s not just the people in the ACR – the “seen” – it’s those who work in the satellite control room, in distant homes and offices doing remote shifts, and on-call experts who commit themselves to this task 24-hours a day for months at a time. Those are the “unseen”, the people without whom the experiment fails but who don’t get to be on the ACR webcam.

A 1:1 scale mural of a segment of the ATLAS detector, depicting in life-size the journey of different subatomic particles.

It’s 12:30 am. My shift is just beginning, and it’s starting to quiet in the ACR. The LHC is promising beams in the machine in 30 minutes or so. They aren’t messing with the collider settings too much, which means we may get steady data tonight. It occurs to me that I am almost on Dallas time, here in this distant control room for a global experiment. It’s dark outside, but I feel alive. There is a deep and substantial pleasure in committing yourself to an experiment like this, one which cannot be explained but through weak analogy to pride of place and service. We are subatomic shepherds, here in the ACR, looking to bring the data home.

This was originally posted in the SMU CERN blog (http://blog.smu.edu/smucern). It’s reproduced here because I am the author! 🙂

What DOES a professor do during the summer months? I found it amusing – and, to be fair, a bit reminiscent of my own beliefs when I was a student – that several undergraduates at SMU thought I took the summer off. So, just what DOES a professor do during the summer?

It depends on the professor, but many of us devote ourselves to teaching classes and many devote ourselves to research. Of course, we mingle the disciplines a lot – just because you’re teaching doesn’t mean you aren’t thinking deep thoughts about physics, and just because you’re doing research doesn’t mean you aren’t ready to teach at a moment’s notice.

Tingting (left) and Aidan (right) discuss particle accelerator beam structure next to a full-scale model of the Large Hadron Collider.

For my own case, it’s been a lot of both. I am joined this summer by an SMU graduate student, Tingting Cao (featured recently in [1]). She has never worked on an experiment like ATLAS before. The sheer magnitude of things you need to learn to make sense of day-to-day ATLAS physics and activities is immense. Tingting’s devotion and enthusiasm have so far carried her a long way in this regard. However, as a professor it is incumbent upon me to insure that TIngting has all the tools she needs not only to answer questions, but to know how to ask lots of questions.

My post-doc, Aidan, has been instrumental in working with Tingting to discuss physics and to teach her how to write analysis software (using C++, the language du jour of big collider physics). One of the great traps of software is that you can spend so much time learning just how to do it, you forget why you’re doing it. In collider physics, there is an ever-present tension between making progress (by writing analysis code) and seeing “the big picture” (why you are writing code in the first place). Aidan and I have been working hard, with a lot of help from Tingting’s curiosity, to keep that tension at bay.

In the foreground, a “warm” quadrupole magnet (meaning it operates at room temperature, rather than the superconducting temperatures needed by the Large Hadron Collider). In the background, Tingting and I discuss how such magnets act to focus charged particles.

We recently used the Microcosm, a teaching and learning center at CERN (which Aidan will discuss in a separate post) to learn about particle physics hardware. For instance, we discussed how magnets are to electrically charged particles as lenses are to light: they steer and focus the beams so that they are right where you want them. Shown below is a quadrupole magnet – a magnet with two pairs of North and South Poles – which act to focus charged particles. You need a long sequence of these to control the size of the beam, and the care and skill that goes into building and coordinating such magnets is incredible.

It’s not always about the hardware. Sometimes, you just want to understand why subatomic particles like quarks lead not to single particles in your detector, but “jets” – cone-like sprays containing dozens of particles smashing into your tracking system, your energy readout system (“calorimeters”), and your muon system (needed to detect the less-interacting, heavy cousin of the electron – the muon). Tingting asked for a lecture about how you go from simple diagrams of quarks and leptons – “Feynman Diagrams” – to the complex signatures of particles in the ATLAS detector. Aidan and I spent over an hour going step-by-step through an example diagram, discussing all the physics we could. In fact, veterans of my “Modern Physics” class from last semester may recall a problem involving whether or not top quarks can bind together via the strong force [2]. Tingting asked about just that process, in the context of other kinds of quarks, and we discussed that very problem as part of the lecture.

Tingting and I discuss what different kinds of particles will look like in an ATLAS-like detector (photo by Aidan Randle-Conde).

Teaching doesn’t stop when the summer starts for those of us who do research in the summer, just as new ideas for physics papers and projects don’t stop when the teaching starts. Being a physicist sometimes demands both, and it makes the enterprise all the sweeter to know that it’s impossible to separate the doing from the learning.

[1] “Knowing the Hardware”, by Aidan Randle-Conde, SMU CERN Blog (http://blog.smu.edu/smucern/2010/07/knowing_the_hardware_1.html)

[2] Problem SS-13: “Top Mesons” (PHY 3305, Spring 2010) http://www.physics.smu.edu/sekula/phy3305/homeworksolutions010.pdf

This was originally posted in the SMU CERN blog (http://blog.smu.edu/smucern). It’s reproduced here because I am the author! 🙂

I made some promises to myself for the summer: not too much eating out, regular food shopping, and home-cooked meals. Switzerland and France are expensive places; for instance, a shopping bag containing some vegetables (a few peppers and tomatoes), fruit (apples and bananas), some cheese, milk, yogurt, baguette, and pasta runs close to 30-40 Swiss Franc (about $25-$35 U.S.). However, a single meal at a restaurant often runs AT LEAST this much.

Whipping this into something resembling a tasty meal takes some extra effort. Air conditioning is not common in Switzerland, unless the building is for business; running the stove for 30 minutes to make dinner means sweating through your clothes, with temperatures in the 80s and humidity at uncomfortable levels.

I’ve managed to stick close to my promise. My host and I have shared cooking duties over the past two weeks, including the meal shown below:

From top to bottom: artichokes (cooked in some oil and tomato); beans cooked with peppers, onions, garlic, and cream; and chicken paprikash (chicken sauteed in cream, onion, pepper, paprika, and garlic).

Of course, food means gathering – not just eating alone. A few of the SMU graduate students organized a Fourth of July cookout at a park near CERN and Meyrin, a residential community by the laboratory. There were burgers and sausages, pickles and condiments and even American chips (Doritos!). We were joined not only by SMU folk, but by friends and colleagues from other Universities, including nearby UT Arlington and far-flung New York University (NYU). Kids were present, too, which made the whole thing feel a lot more like a family gathering on the 4th and less like a bunch of work colleagues hanging out and tossing a frisbee.

Of course, sometimes you do eat out. It’s unavoidable. There is a budding tradition in the SMU CERN group of picking a new place on Friday night, someplace preferably where you can dine for less than 20-30 CHF and which can be added to the list of affordable but tasty restaurants in Geneva. This past Friday evening, we found ourselves at a small local chain of chicken restaurants with a limited but delicious menu. The most popular item at our table? The half-chicken, roasted, with fries and salade (demi-poulet avec pommes frites et salade).