After breakfast at 8:30 this morning, we took a bus to the CMS headquarters. CMS is one of the four detectors on the LHC; the acronym stands for Compact Muon Solenoid, because the detector is half the size of the largest detector (hence, it’s “Compact”); it has special Muon detectors; and, like all the detectors, it’s a huge Solenoid. Interestingly, the largest detector, Atlas, would float if you wrapped it in a plastic bag and threw it into a river, but CMS would sink because although it’s half the size, it weighs twice as much.
In a large conference room at the CMS headquarters, we met with Dr. Tejinder Virdee, who is essentially the “CEO” of CMS, although his official title is “spokes person.” Last year, he was the main speaker at Intel ISEF! He’s also a professor at Imperial College in London. He started his fabulous talk by giving us a basic overview of the physics related to CERN, and then he moved on to more complicated and specific information about the CMS detector. His talk was one of the most understandable and informative I’ve heard.
We then stood directly above the CMS detector. A few years ago, the detector was lowered about 100 meters below ground onto the LHC. Below is a suspenseful time-lapse video of one piece lowering; we stood directly above where this happened.
After touring this landmark, we visited the CCC, or CERN Control Center. We met in a conference room with large windows overlooking about 25 people working on computers. Dr. Django Manglunki talked to us. He was in charge of building this control center, and the two computer science enthusiasts in our group especially appreciated his informal lecture.
We then ate lunch at a restaurant in France near CERN. Everyday, Wolfgang invited the scientists who spoke with us to join us for lunch/dinner. This way, we can ask them more questions, learn more about CERN, and discuss physics over every meal. It was a terrific idea.
Today at lunch, Jennifer, Zaren and I sat with Filippo Costa, the Italian computer scientists/physicist who spoke to us yesterday and showed us the ALICE control rooms. He’s been working at CERN for two years. After working here for five years, a committee meets and decides whether that person will stay and get promoted, or leave.
Wolfgang ordered dessert for us too (another great idea of his)! I had a delicious crème brûlée.
After lunch, Dr. Alberto Pace (who was a judge at Intel ISEF) spoke to us about computing for the LHC. Alberto is head of the data and storage system for the LHC. His talk was most intriguing. I learned that after processing the data on CPUs (processors), they store it on disks or magnetic tape like in a cassette. Also, the data is simultaneously distributed to eleven large data centers around the world, which keep a second copy of the data.
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CERN computing is performed in three “tiers” described below, with 85% of the process preformed outside CERN.
- Tier 0 is CERN, which collects the data and is responsible for its long-term storage.
- Tier 1 is comprised of 11 separate computer centers around the world; there are two in the United States, one in Canada, seven in Europe, and one in Taiwan. These centers enable CERN’s “grid service,” which is the network that transfers data from CERN to scientists everywhere.
- Tier 2 is the end user, the university physicists around the world who look for interesting patterns in the data. This tier provides more than 50% of CERN’s processing power.
Although it would be more efficient and cost effective to centralize these tiers into one computer center, the tier system prevails because it’s easier for a hundred or so universities to contribute about 100 computers each on their campus, than for CERN to fundraise hundreds of millions of dollars for a centralized computer center.
After Alberto’s fascinating talk, Wolfgang gave us a tour of CERN’s main computing facility, where there are thousands of CPUs, or disk drives, stacked up in a cold room. Each CPU has little blue and green lights flashing endlessly in seemingly random patterns. I asked Wolfgang if these blinking lights were really necessary; he said no. A computer does all the checking regardless of the lights, although when someone has to come down here to fix something, it’s convenient that a flashing red light indicates what’s broken.
Wolfgang also talked about CERN Open Lab, which is a collaboration between CERN and major information technology companies, such as Intel, Siemens, HP, and Oracle. These companies fund young scientists to work jointly with CERN and industry experts to improve their systems by finding bugs. For this reason, CERN Open Lab’s motto is “you make it; we break it.”
Finally, we toured the ATLAS detector control room, which had a very nice museum-like educational display. They also showed us a 3D movie about ATLAS!
- ATLAS control room
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Wolfgang then gave us all nice laptop bags with the CERN logo, CERN mugs, a set of adapters, an Intel pen, and CERN magazines; it felt like Christmas! This was just one of the many nice things he’s done for us. I’m going to use the bag at MIT next year. Interestingly, all the lecturers we’ve heard put only their first and last names on the slides, leaving out titles such as “Dr.,” “PhD,” etc. Also, the scientists introduce themselves to us by their first name. This possibly indicates several things: 1) They don’t feel the need to show-off their title; 2) They’re not treating us as students; and/or 3) They want everyone to have an equal status. Anyway, it’s different from many of my experiences. Also, today there was much talk of Angels and Demons, the fictional book by Dan Brown and action movie starring Tom Hanks. I’ve neither seen the movie nor read the book, but I understand the plot is centered on CERN research. I’m now curious see the movie, although the physicists here are amused by the book/movie’s fictional adaptation. When Tom Hanks and Ron Howard (the movie’s director) visited CERN, they presented one of the “antimatter generators” used in the movie. It’s a cool-looking device that Wolfgang said he will show us on Thursday. Afterward, we ate dinner in the cafeteria and chatted in Building 40, which is near the hostel. I believe most people sat in the lounge downstairs, but I accompanied Zaren to a meeting with a Turkish physicist. Unfortunately, they both only spoke Turkish together, so I politely excused myself from the meeting after about 15 minutes to play cards with the other students downstairs.