messing family picture

Our Trip To Cern

Thursday, May 24, 2007

We arrived in Geneva early in the morning after an overnight flight from Newark. After resting at our hotel for awhile, we joined the rest of our group for an afternoon walking tour of the city. When you think of visiting Europe, one thing you look forward to is seeing all the beautiful churches. This is not the case in Geneva. Geneva was the home of strict Calvinism, and all of the churches had their interior decorations painted over during the Reformation. The insides are quite stark, though they did leave the stained glass windows. It was interesting to see in places where xrays were being used to get under the paint and find the pre-existing Catholic artwork. Also, our tourguide must have been quite religious herself, as she dwelled at great length on the Reformation.

Her discussion of the neutrality of Switzerland was quite interesting as well. I did not realize how financially beneficial it was to them to always be neutral. I did take a bit of offense at her indignation that at the end of WWII, just before the cease fire, the US bombed 3 Swiss factories that were supplying munitions to the Nazis. That is not exactly my definition of 'neutrality'.

In the evening, we had a nice sea food meal at a local restaurant while getting to know the rest of our group.

Friday, May 25

The day started with a lecture from Jerry Friedman on the history of particle physics. It was interesting, as, of course, the physics is so intertwined with the development of the accelerators and detectors themselves. He told us about both. It was immediately apparent that Jerry's enthusiasm and excitement would be a major part of the trip. He is so energetic and infectious in how he presented the material and got us to ask questions. This continued both in the formal sessions and whenever there was a spare moment on the bus or at a restaurant, etc.

As the lecture continued, Jerry was careful to tell us the dates and scientists involved in all the major discoveries, like Rutherford and the nuclear atom, and Chadwick and the neutron. However, after introducing us to quarks, all he said was that their existence was confirmed in 1968. Someone in the audience had to interject, "Jerry, tell us who did that". It was of course Jerry himself, and was the work for which he received the Nobel Prize in 1990. His modesty was genuine. As we toured CERN it gradually became obvious how well known he was there, and how many important committees he served on over the years.

One final comment about Jerry: he became almost wistful when discussing the aborted construction of the US Supercollider in the early 90's. He had put a lot of energy and effort and threw his name into the effort to get it built (which was occurring just as he was receiving the Nobel Prize); he testified in Congress and spent his summers traveling the country advocating for it. It would have been several times larger than the one we are here to see at CERN, and would have been completed 15 years earlier. He seemed quite upset at Congress and their attitude about science, particularly as it was abandoned when 1/3 done after $2,000,000,000 was spent.

After the lecture, we visited the UN Geneva headquarters. It was interesting, and our Italian tourguide did a nice job, but having been to the UN in NYC, we already knew much about how the UN operated. The building and grounds themselves were pretty, particularly those that had been constructed as part of the League of Nations. On the drive there we passed an interesting sculpture, a huge 3 legged chair...meant to symbolize the Anti-Landmine treaty. Originally planned to be up for only 6 months while the treaty was being negotiated and signed, it has been there for over a decade as several nations, unfortunately including the U.S., have not yet signed.

In the afternoon, Colleen was tired and rested at the hotel. Lauren, Sam and I took a walk down to Lake Geneva, saw their magnificent fountain, had some gelatto, and in the evening went to a simple pizza style Italian restaurant. There was also another lecture by Jerry, specifically describing what we were to see at CERN the next day.

Saturday, May 26

We arrived at CERN headquarters and were greeted by Christoph Paus. He is an Assistant Professor at MIT, currently working at CERN who had made most of the detailed arrangements for our trip and would serve as our host and coordinator. There was a 30 minutes slide presentation giving an overview of CERN, showing where things were and what was done there. (Although we were there to see the Large Hadron Collider(LHC), there is a whole lot more they do). The grounds are quite large, and not all on one campus. The LHC tunnel itself is 27km (17 miles) in circumference with farms, homes, plus other CERN facilities in the center. The two main detectors, Atlas and CMS, are on diametrically opposite points around the ring.

What is the LHC? It is a machine for accelerating two beams of protons in opposite directions using superconducting magnets to guide them and then bringing the beams together to collide inside detectors where the results can be observed. The LHC will accelerate each proton to an energy level of 7 TEV (7,000,000,000,000 electron volts of energy! A typical battery gives an electron 1 electron volt of energy). The energy of each collision is enormous, approaching that not seen since the Big Bang. The total energy of the beams is also enormous, approaching that of two railroad locomotives hitting each other at 120km/h, contained in 2 beams about 1cm in diameter at the collision point. They have to be quite careful how this is constructed, as the beam will poke a hole in almost anything in its path. (In fact, just to turn it off, the beam has to be 'dumped' into a specially prepared mass of concrete and graphite to absorb the energy).

We were all anxious to actually see something; we were not disappointed by our first stop. We headed to the magnet facility, where the dipole magnets (for bending the beam) and the quadrapole magnets (for focusing the beam), were assembled, tested and lowered into place. There are around 1,600 of these 15m long magnets (6,700 magnets of all kinds total), that consist of two small tubes for the beams surrounded by coils and other tubes for carrying liquid helium, all in a blue pipe. The engineering is amazing. The liquid helium is to keep the magnets superconducting, and building what is in effect a 27km long refrigerator that operates at just a few degrees above absolute zero was quite the challenge. In addition, the tunnel is not that big and maneuvering the magnets into place by hand would have been impossible. We saw how a specially constructed robot lowered the magnets 50-100m through a delivery hole, onto another robot that crawled mostly autonomously through the tunnel to the installation point.

Testing the magnets was also of critical importance. Liquid helium is very hard to contain and quite expensive (especially in the quantities needed by the LHC). The cooling process takes a long time (several days). Access to the magnets in place is difficult. All of this caused CERN to develop a rigorous testing methodology with several huge test rigs to test all the magnets. The work involved was enormous and the time pressure huge. (There are so many different pieces that are necessary for the LHC to work, and each group does not want to be responsible for holding it up).

Our next stop was the CERN control room. While each detector in the LHC has its own control room, there is one overall facility for the LHC and the other CERN experiments. It was recently reconstructed. A lot of emphasis was placed on ergonomics, understanding that accidents often happen through human factors that could be obviated by appropriate design. It was exciting to see the master video display, that shows the current status of the LHC over time including its power level, etc. This is going to be echoed all over CERN so that even in the cafeteria, the physicists can keep an eye on what is going on.

As opposed to the old style NASA control rooms we've seen on TV with analog racks and lots of video monitors, this one consisted almost completely of banks of PCs and their flat panel displays. There was only one non-PC rack, a panel that seemed to contain rows of what appeared from a distance to be rotary knobs. It turns out that they were not knobs, but rather were keys. For the LHC beam to be on, all of the keys must be in place. If a key is withdrawn then the beam automatically gets dumped and the LHC shutdown. When in operation, these keys will in fact be the only keys to the doors that allow access to the LHC tunnel and the detectors. The LHC is not a safe place to be when on, and this is their way of assuring that no one can be inside when it is working.

As a further failsafe, there are a couple of copies of the control room at remote locations around the world. Designed as a backup in case of failure, it is also their hope that eventually they will avoid the need of their ever having to be a large night shift at CERN, as it can be operated from a different location.

We had lunch in the CERN cafeteria (not a very memorable one...the only poor meal we had on the entire trip), and then headed off to the Atlas detector.

We arrived at a large building at the Atlas detector site. Christoph warned us that it was a working site, and that we should be careful where we walked. It was amazing to me on our whole tour of CERN how much freedom we were given to wander...I think again a sign of the fact that this was not a regular tour, and our guides were physicists not tour guides. We each had to put on hard hats and be given security cards that enabled us to enter through security gates. An elevator took us down approximately 100 meters into an enormous cavern completely filled with the Atlas detector. It is hard to describe just how big the detector is. Pictures don't do it justice. It is a bunch of rings making a cylinder lying on its side, with the beams going in the ends and colliding in the middle. The diameter is 35m (10 stories!) and the length is 55m. It is not easy to see how it all fits together. In the center is a tracker...the device that records the paths of particles formed by the collisions. It is like a bubble chamber, only made out of more modern technology. Surrounding the tracker is an enormous magnet, which bends the particle paths so that you can see if they are charged or not. (Straight path = no charge, curve one way for + charge, and the other way for - charge). Surrounding this are calorimeters, which figure out the energy of the particles. And surrounding that are muon detectors. Some of the collisions produce many particles, which then possibly decay causing a huge cascade of things to track. The length and position of the path helps identify the particle, e.g. some don't make it out of the tracker, some don't make it out of the calorimeter. Muons (similar to an electron but 200 times as massive) are produced in abundance and penetrate fairly far, hence the surrounding muon detector. In addition there is at least one particle, the neutrino, that passes through everything and is detected only by noting that the energies and masses of the collision don't add up.

At each end of the hall were giant green 'caps' that could be swung into place fairly quickly to block the beams if something went wrong. The energy of the beams being so huge, if they are misaligned just a bit, they will ruin the detector and at $500,000,000 and 4 years to construct that would be a problem.

We spent about an hour gawking at the workings of the detector and asking lots of questions. The complexity of the project is not to be under estimated. Everything has to be aligned around the center where the actual collisions take place with incredible precision. Around the cavern at various points are markers that have been carefully surveyed (& I understand that surveying underground to the precision needed is difficult).

One of the systems in the cavern was described to us, but not demonstrated. In the case of fire, the entire space can be filled with foam in 20 minutes (which is actually breathable). They had done a test run some time ago and we saw pictures of the cavern 2/3 filled with foam.

After visiting Atlas, we boarded the bus and returned to our hotel.

That evening, we travelled to France for one of the best meals I have ever had at a very nice restaurant. Some of the physicists accompanied us. I sat next to an MIT graduate student, who has come over to help out and begin work on his thesis. It was interesting to hear his enthusiastic description of his life; particularly the international, cooperative effort that the LHC has become.

Sunday, May 27

This morning, we went to see the other major detector, the CMS (Compact Muon Solenoid). This visit was quite a bit more interesting than the ATLAS, as the bulk of MIT's faculty and students are involved with this project. The detector is not quite as big as Atlas, though it is still huge. However, it uses the most powerful magnet in the world to bend the particle paths (hence the solenoid in the name). Another difference revolved around how the detector was constructed. The Atlas was built in place. The CMS was built, ring by ring, in an enormous building and then lowered into place. Hence we could really get up close to the detector parts that we couldn't quite get to on the Atlas.

We were greeted by Steven Nahn, an MIT professor whose specialty is building silicon particle detectors. The entire center of the CMS will be filled with a detector of his design, that will be the largest of its kind ever constructed. It works kind of like a bubble chamber. Particles speeding through ionize the silicon, and the loose electrons are then counted. (In a bubble chamber, the particles cause nucleation of water drops and leave a visible path). He and his staff were excited, as they had turned on the detector for the first time a couple of days prior to this and were seeing the paths of cosmic ray particles as a test. We saw a full scale mockup of the detector that was used to check out positioning and size and how to maneuver it into place. The real detector was in a clean room, beneath some protective plastic.

After Steve gave us an introductory lecture on how the detector worked, he also showed us these huge perfectly clear crystals that were enormously heavy. They were basically very leaded glass (hence the weight). While quite expensive and difficult to manufacture, they have the property of fluorescing along the track of particles. Surrounding the detector, these crystals are themselves surrounded by photomultipliers that see and record the flashes.

After the lecture, we went upstairs to the computer facility for the CMS. Not completed, we could see hundreds and hundreds of PC's ready to be installed in racks. Each second the LHC will be on, there will be approximately 600,000,000 collisions! (And it will be on about 18 hours a day for 9 or 10 months a year for 10 to 15 years!) There is no way anything meaningful could be determined and saved about all of these. Out of these 600,000,000 collisions, approximately 1,000 will be deemed interesting and recorded for study at leisure. The computation to decide what is interesting has to be done in real time, and hence the number of computers that run in parallel has to be huge. Not seen by us is the computer room underground right by the detector. The initial sifting has to be done very close to the detector. The speed of light is an important parameter and running all the signals above ground would make the signals take too long. In addition, just figuring out which recordings from various parts of the detector potentially 10's of meters apart belong to which collision is an enormous task.

After the data is saved, it can be studied, but even at the reduced rate of 1,000 per second the amount of data involved is huge, petabytes or more. They are putting into place a network of computers distributed around the world to do the initial analysis. (And eventually something like Einstein @ Home will be set up to help out).

After the computer facility, we again donned hard hats and descended by elevator to see the CMS. There is a confusing warren of passages to walk through leading to all the auxiliary rooms and facilities. In addition, for safeties sake it is designed so that every place that people might be in when the LHC is on has a massive amount of concrete between them and the beam. No straight corridors. This detector is about half in place, and it was interesting to see how they are maneuvering the pieces down a huge shaft and into place. It looks very much like the Atlas, just a tad smaller.

After viewing the detector, we ventured into the actual tunnel ring of the LHC. It is not very big. While a person can easily walk in it, you can see how it gets tight with a lot of equipment in place. Hence the need for autonomous robots to move the magnets around. The part of the tunnel we were in was just outside the CMS detector so it was relatively straight, but you could see far down the tunnel a slight curve. 17 miles is a long way. The entire ring has to be bathed in liquid helium. Preventing leaks is a challenge.

As I was standing there, one of the physicists reminded me that once the beams are turned on, it will not be safe to be standing anywhere near. Any charged particle that is accelerated or curved produces radiation (synchrotron radiation it is called), and the amount there would be a fatal dose. As he put it, "5 minutes in here when it is on and you will be dead in 3 months".

Our final stop at CERN was a lecture by Christoph, mostly about what they hoped to achieve. The biggest part of the answer was that they don't know, but they are sure it will be interesting. At 7 times more powerful than the next most powerful detector, new physics is sure to appear. In particular, there is hope that a particle called the Higgs boson will be observed. The Standard Model developed by physicists over the last 40 years has proved to be very accurate in predicting what particles exist and how they interact, but it has no explanation for what the mass of particles should be. The most favored theory for accounting for mass posits a new scalar field, the Higgs field that fills all of space and interacts with particles to cause them to have mass. Associated with this field is a particle. There is reason to believe that the LHC has the right energy to see it. (The Higgs boson is believed to itself be heaver than any of the particles so far observed and you need a powerful beam to see a heavy particle). If found, it will confirm the theory. If not the physicists will have to go back to the drawing board. Christoph himself hopes that several kinds of Higgs boson will be observed confirming the basic theory but leading to more research to be done. (Incidentally, I asked Jerry Friedman if he thought they would observe the Higgs boson. He thought it was 50-50.) There is also great hope that other basic mysteries of both atomic physics and cosmology can be elucidated by the LHC. (Supersymmetry, dark matter, where did all the antimatter go, etc.)

That ended our visit to CERN. It was remarkable. We learned an incredible amount about physics and accelerators and saw what is clearly the largest machine in the world. Seeing how literally thousands of physicists are working together in search of knowledge about the basic components of the world was inspiring. And feeling the enthusiasm and excitement in the air was amazing.

After leaving CERN, we made a stop in Lausanne and had a meal with some MIT alumni who live in the area. It was an opportunity to meet some Swiss citizens and was fun. Nice people. In Lausanne, we dropped Sam off at the train station. He took a train from there to Florence, where he is joining his girlfriend for a one month summer program. (Tough life for a 19 year old, huh?) We then made our way to Zurich.

In Zurich, we stayed at the Hotel Righof. It was not very nice (cigarette smoke everywhere), but the architecture was fascinating. Built in the 1930's, it was designed to be and always exhibited as a prototypical Bauhaus design. It must have appeared supermodern when first built.

Monday, May 28

We took a walking tour of Zurich in the morning in the rain. A pretty city, I'm glad there are not tall buildings. Two points of interest: the home where Lenin lived till he was transported secretly at the German's request to Russia to create 'trouble'. The other was a church, which though as starkly decorated as other Swiss churches did have these magnificent stained glass windows of biblical scenes done by Chagall. I thought it was wonderful that a Jewish artist had done this for a Christian church. That evening we had dinner with Zurich area MIT alumni. I was seated next to Alex, an MIT graduate originally from Serbia who absolutely hated it in Zurich. Single and 35 years old he seemed quite lonely. I imagine he will soon seek a job in either London or NYC, places he indicated he felt he would be happier.

Tuesday, May 29

This was the day we were to go by bus and boat and cog railway to see Lucerne and some of the Alps. Sadly it was still raining. We went anyway. The ceiling was high enough that we could see somewhat and the mountain tops being shrouded in clouds did have their own appeal. The boat trip was pleasant. At one point a Swiss aerobatics team passed low over the boat, practicing from a nearby airfield...that was exciting to see.

When we got to the cog railway at Mt. Pilatus (the steepest in the world), it had stopped raining, but was still quite cloudy. As lunch was reserved at the top, we had no choice but to ascend. About half way up it became obvious we were going to have quite an adventure, as the driver stopped the train, and said that he would not proceed until a snow plow arrived to lead us up! And indeed the higher we got the more snow there was. About 3/4 of the way up we entered white out conditions. At the very top we got out into a sightseeing/souvenir shop building and the guide pointed outside and said we had to walk to the restaurant, about 150 yards away. Lauren started laughing, assuming it was a the wind was about 40mph and the snow was coming down furiously and none of us were dressed for the weather. (And we had some elderly folks in the group as well). But they were serious, and we walked through the whiteout snowstorm to the restaurant....I got some amazing pictures of Colleen in the snow and Lauren fighting with an umbrella.

Afterwards, we returned to Lucerne for some shopping before returning to Zurich. I don't like to shop, but I enjoyed getting a watch for Lauren.

Wednesday, May 30

In the morning we went to visit the Uetliberg Tunnel, part of the Zurich Beltway being constructed. We had some civil and mechanical engineers in the group and they were quite interested to see how this very long traffic tunnel was being constructed. I enjoyed the visit, but having been on tours of the Big Dig in Boston, some of it was a bit redundant for Lauren and I.

Our last afternoon in Zurich was spent wandering around the city, eating lunch in a nice cafe, and doing some shopping.