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ºÚÁϲ»´òìÈ physicists, students help prepare precision silicon detector for Switzerland-based international study measuring properties of B meson particles November 12, 2007

Sara Millersemortim@syr.edu

One of the most fragile detectors for the Large Hadron Collider beauty (LHCb) experiment, a particle physics experiment located at the European Organization for Nuclear Research’s (commonly known as CERN) Large Hadron Collider (LHC) in Geneva, Switzerland, has been successfully installed in its final position, and a group of ºÚÁϲ»´òìÈ scientists and graduate students have been an essential part of this achievement.

LHCb is a specialist b-physics experiment aimed at measuring the properties of particles called B mesons, to investigate a physics mystery — why today’s universe is full of matter instead of an equal mix of matter and antimatter. LHCb physicists also study B mesons to search for never before seen particles and physics phenomena. LHCb is one of four large experiments at the LHC in Geneva, the world’s next-generation particle accelerator expected to start up in 2008.

The total LHCb collaboration numbers about 700 scientists from 15 countries. The SU group, headed by SU physics professor Sheldon Stone (above) and with support from the National Science Foundation, joined this international collaboration and has been participating in constructing the LHCb experiment and planning for data analyses.

“When the accelerator starts running in 2008, LHCb will make a series of precise measurements of the asymmetry between matter and antimatter known as CP violation,” says Stone. “The rare decays of B mesons that we will observe will also serve to identify new physics that could be discovered by directly observing new particles by other LHC experiments.”

SU has been deeply involved with many aspects of the LHCb experiment. For example, one member works on electronics configurations and software for the fragile detector, Vertex Locator, or VELO. The VELO is a precise particle-tracking detector that surrounds the proton-proton collision point inside the LHCb experiment. SU scientists made critical test measurements of the VELO detector during its construction and have helped develop software that converts electronic signals from the LHCb experiment to data that researchers will use to probe matter-antimatter asymmetry or search for new phenomena, such as the long-sought Higgs boson and sypersymmetry.

Along with Stone, SU contributors to the project are physics professor Marina Artuso (SU VELO group leader), research assistant professor Raymond Mountain, research assistant professor Jianchun Wang, postdoctoral research associate Gwenaelle Lefeuvre and graduate students Sadia Khalil and Koloina Randrianarivony.

The installation of the VELO into the underground experimental cavern at CERN was a challenging task, and this milestone marks the fruition of the construction phase of the VELO project. The SU group also designed transport modules to move the Vertex Locator detector components safely from the United Kingdom to CERN. “It was a very delicate operation,” says CERN’s Paula Collins, LHCb-VELO project leader. “With its successful completion, the VELO is now in place and ready for physics.”

At the heart of the VELO detector are 84 half-moon-shaped silicon sensors, each one connected to its electronics via a delicate system of more than 5,000 bond wires. These sensors will be located very close to the collision point, where they will play a crucial role in detecting b quarks, to help in understanding tiny but crucial differences in the behavior of matter and antimatter. The sensors are grouped in pairs to make a total of 42 modules, arranged in two halves around the beam line in the VELO vacuum tank. An aluminum sheet just 0.3 mm thick provides a shield between the silicon modules and the primary beam vacuum, with no more than 1 mm of leeway to the silicon modules. Custom-made bellows enable the VELO to retract from its normal position of just 5 mm from the beam line, to a distance of 35 mm. This flexibility is crucial during the commissioning of the beam as it travels around the 27-km ring of the LHC.

“The installation was very tricky, because we were sliding the VELO blindly in the detector,” says Eddy Jans, VELO installation coordinator from NIKHEF. “As these modules are so fragile, we could have damaged them all and not realized it straight away.” However, the verification procedures carried out on the silicon modules after installation indicated that no damage had occurred.

The VELO project has been ongoing for the past 10 years, involving several institutes of the LHCb collaboration, including Nikhef, EPFL Lausanne, Liverpool, Glasgow, CERN, SU and MPI Heidelberg.

CERN is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its member states are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. India, Israel, Japan, the Russian Federation, Turkey, the United States, the European Commission and UNESCO have observer status.

For more information on the LHCb, visit .

Photos of the LHCb experiment can be found at and .