At the center of one of the largest experimental particle physics detectors, CMS, located at the CERN collider, protons collide with each other and create blasts of 100s of particles 40 million times a second. These created particles are tracked using detectors made of silicon and electronic circuitry and a snapshot is created much like how your camera takes a picture. This “pixel” tracking detector is a small detector (about the size of bobsled) at the heart of the larger CMS detector which is over 5 stories high. Since CMS started collecting data in 2009, it has been using a 64 million pixel inner tracking chamber. That detector was extracted a month ago and a brand new 124 million pixel replacement detector was inserted into CMS last week. Some are dubbing this as a heart transplant as the installation is a tricky procedure with the amount of clearance available of the order of millimeters. You can find out more about that here.
After about 10 years of planning, construction, through the work of dedicated physicists, technicians, engineers, and students, we are now ready to commission this brand new device. We expect to start taking proton beam data in a couple of months to see what will happen. So how did this heart get built? Each pixel in the larger pixel tracking detector is about the same diameter as that of a human hair and is made using silicon. Then, there is a custom designed integrated circuit built for every 4160 pixels that amplifies the electronic signals and has memory to store the pictures. As we can’t keep all pictures from each of the 40 million crossings a second, smart circuitry throws away most of the data. Then we have to figure out how to get these pictures out of the detector and 60 meters away to an off detector computer to store them. This is done by using low mass electronic cables as well as fiber optics. We also have to figure out how to get the power into the detector efficiently, and the heat created by the electronics out of the detector. So the design and construction of this detector was non-trivial and took a few years by the international collaboration. Then we started building it a couple of years ago. The U.S. team was responsible for the construction of half of the detector called the forward disks. The costs were supported by grants from the National Science Foundation and the Department of Energy. You can see what one of these disks looks like in the picture shown as it was installed into CMS. Our University of Kansas students, as well as those at Univ. of Illinois-Chicago, helped to x-ray over 600 modules, each with 66560 pixels each in them to test whether the electronic circuitry was working as expected and could keep up with the data rate. We were part of a larger team of over 100 people at several institutions. The modules were assembled at Univ. of Nebraska, Lincoln and Purdue and the final assembly of the detector took place at Fermilab (near Chicago) before people flew with the detectors (which had their own seats on the planes) to Geneva, Switzerland last fall. Other U.S. institutions who also worked on the project included: Vanderbilt, SUNY Buffalo, Rice Univ, Cornell, UC Davis, Johns Hopkins, Purdue/Northwest, Kansas State Univ, Univ of Puerto Rico Mayaguez, Univ. of Mississippi, Rutgers Univ, Ohio State Univ, Catholic Univ. of America, UC Riverside, Univ. of Colorado-Boulder, Wayne State Univ, and Univ. of Tennessee. Students, postdoctoral researchers, and other scientists and technicians have been running shifts 24 hours a day to check whether all of the plumbing, power supplies, and computer infrastructure needed to read out the detector is working as planned and they will continue to do this until beam data arrives. Our students are excited to participate in this scientific enterprise where they are trained to solve problems, create new technology, and work alongside of international partners seeking to understand how the universe works.