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February 13, 2008

Purdue scientists, students help create a key piece of one of the world's most powerful cameras

Emily Grace and Brian Kozak
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A team of Purdue University researchers and students built a piece of one of the world's most powerful cameras that will provide information about the universe and physical laws that govern existence.

The camera, called a pixel detector, will take snapshots of the smallest known particles in the universe. The detector will be attached to the Large Hadron Collider, a particle accelerator expected to begin operation later this year.

Purdue professors Daniela Bortoletto and Ian Shipsey, the Julian Schwinger Distinguished Professor of Physics, led a team that included 12 undergraduate students. 

"This was the first time a U.S. university group designed and built a pixel detector for particle physics," Bortoletto said. "The pixel detector is basically a digital camera, but it has silicon that covers an area of 1 square meter and 64 million pixels. A digital camera you could buy at a store has a piece of silicon about the size of a fingernail and only a few million pixels."

Shipsey said the team spent eight years designing and building the camera that will sit within inches of the fireball created when two particle beams collide.

"When the Large Hadron Collider begins operation, beams of billions of high-energy protons traveling at almost the speed of light will collide," he said. "The particles will crash at a rate of almost 1 billion collisions per second."

The collisions may result in particles never before seen.

"In our world, when you collide an orange with an orange you get orange juice," he said. "In the world of particle physics, when you collide an orange with an orange it produces a mango or even a new type of fruit nobody has ever seen before."

The results of the proton collisions could produce dark matter, the mysterious substance discovered by astronomers that appears to account for one-third of all the matter in the universe.

Scientists also will be looking for miniature black holes and Higgs particles, which are believed to explain why tiny subatomic particles have mass and why atoms exist.

The collider is housed at the European Organization for Nuclear Research, or CERN, in Geneva, Switzerland. The Large Hadron Collider is a 16-mile-long ring buried a half mile underground that uses superconducting magnets to circulate and accelerate protons.

This large piece of equipment speeds the tiny particles to an energy eight times greater than has ever been previously achieved.

"The energy, E, of each proton can be transformed into mass, m, by the most famous equation in physics: E = mc2," Bortoletto said. "The new particles we are looking for have large masses and so high-energy protons are needed to create them."

Bortoletto led the camera design team and Shipsey led the assembly team. Both teams collaborated with Fermi National Accelerator Laboratory and other U.S. and European universities to complete the project.

The work began with the design of the silicon chip in 1996, followed by several rounds of prototyping. The final chip was manufactured in 2005. The chip was then attached to sensitive electronics that process the images and to various micro-connectors before being shipped to Fermilab where it was mounted on support structures and sent to CERN.

The camera will be used in the Compact Muon Solenoid experiment - one of four experiments using the Large Hadron Collider.

"The silicon camera built by the Purdue team is essential to the success of the experiment and was a very challenging project," Bortoletto said. "The detector must be very precise in order to distinguish whether particles come from the main collisions or from decays that happen a very small distance away."

The Compact Muon Solenoid houses a massive magnet and is one of the most complex scientific instruments ever constructed. It is the size of a six-story office building and weighs 14,500 tons. More than 2,300 scientists from 40 countries are collaborating on the experiment.

"Although 'C' stands for compact, everything about CMS is large," Shipsey said. "CMS, much like a Russian doll, consists of a nested set of different types of camera. The camera Purdue helped build lies at the heart of CMS."

The camera is capable of recording images within nanoseconds at a resolution finer than that of a human hair. Another, less precise, silicon camera surrounds it. The second-layer camera is made of enough silicon to cover a 25-meter swimming pool.

Outside the silicon layers are 80,000 crystals - weighing the equivalent of 24 elephants - supported by a 400-micron thick carbon fiber support structure that is about the diameter of a piece of dental floss.

The crystals are, in turn, surrounded by another camera made of brass and scintillator, a type of plastic that emits light. The brass was recycled from Russian warships.

The entire system is immersed in a magnetic field 100,000 times stronger than that of Earth and produced by the largest superconducting magnet ever built. The magnet has as much iron as the Eiffel Tower and the stored energy could melt 18 tons of gold.

"This astonishing camera produces data at a prodigious rate," Bortoletto said. "The data flows at 500 gigabits, a rate that matches the entire world's telephone traffic today. In just one second, a data sample equivalent to 10,000 Encyclopedia Britannica is produced."

This data will be analyzed at Purdue and around the world using a distributed array of computers.

In addition to Bortoletto and Shipsey, other physics faculty on the camera project include professors Art Garfinkel and David Miller.

"We have had the privilege of working with a superb engineering, scientific and technical staff at Purdue," Shipsey said. "In particular, research scientists Gino Bolla and Petra Merkel, engineer Kirk Arndt, and technician Gale Lockwood all played key roles in building the pixel detector. We were also very excited to include Purdue's outstanding undergraduates in our research team."

Bortoletto said science and engineering students participated extensively in the project.

"These students now have had the experience of contributing to unique cutting-edge international research," she said. "This experience is exactly what the best graduate schools look for in their incoming students."

Teams from universities around the world, including Purdue, are now hard at work designing the backup camera that will be needed to replace the existing camera a few years from now after the intense radiation from the particle beams has taken its toll.

Bortoletto was recently chosen to coordinate the work of the U.S. universities for the entire Compact Muon Solenoid project. Shipsey chairs the advisory committee of the U.S. data analysis center based at Fermilab.     

As the experiment begins later this year, the Purdue team and many others around the world will sift through the data in search of dark matter, mini black holes and the Higgs particle.

"It could be that the first glimpse of one of these mysterious objects is provided by a piece of silicon assembled by a Purdue undergraduate," Shipsey said.

Writer: Elizabeth Gardner, (765) 494-2081,

Source: Ian Shipsey, (765) 494-0706,

Daniela Bortoletto, (765) 494-5197,

Purdue News Service: (765) 494-2096;

Purdue undergraduate students Emily Grace and Brian Kozak help build a camera that may soon glimpse dark matter, the formation of black holes and Higgs particles at the Large Hadron Collider at CERN, the European Laboratory for Particle Physics, in Geneva Switzerland. (Purdue News Service photograph/David Umberger)

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