Summer 2012

Theta 13 (θ13) Discovery at Daya Bay and the Engineering behind it

A antineutrino detector being lowered into the (empty) water pool.

Located 17 miles southeast of the UW-Madison’s main campus is the Physical Science Laboratory. Daily, people drive by this inconspicuous building without any knowledge of the high tech engineering that takes place here, some of which makes headlines. The most recent headline came from the Daya Bay Project and the UW-Madison’s Professor Karsten Heeger, who along with his U.S. team is trying to find answers to the hard to capture neutrino and θ13. θ13 (pronounced theta one three) is the transformation of electron neutrinos.

Earlier it was believed that during their flight, neutrinos would disappear, but evidence is showing that they are changing their identity.  This finding of θ13 is significant to the world of physics and PSL is proud to be part of the engineering team that participated in helping build the equipment for this highly complex experiment.  Professor Heeger and his team worked closely with PSL engineers, drafters, and machinists to design, build, and create what was needed to make this experiment successful.  Testing was also necessary to ensure that everything would be working correctly. 

Lead Engineer Jeff Cherwinka

Since 2007, PSL Lead Engineer Jeff Cherwinka has spent months at a time in China, working with researchers, collaborators, and team members in the making of this project.  He is largely responsible for managing the assembly and installation activities including work assignments for 10 Chinese speaking technicians, coordination with two Chinese engineers, and organizing the work of graduate students and post docs from the US and China. This work has been done under rigorous Department of Energy documentation and safety standards at a "green field" site in China.

Recently Jeff wrote: The Physical Sciences Lab, working with the UW-Madison’s Physics Department, has made key contributions to the recent measurement of θ13 by the Daya Bay Reactor Neutrino Experiment. The contributions spanned from the design, engineering, fabrication, testing and installation to purchasing, quality control, and shipping.  The key Antineutrino Detector (AD) components including the 4m acrylic vessels, 3m acrylic vessels, acrylic overflow tanks, calibration tubes, PMT cables, and dry boxes to the CAD modeling of these components.

The CAD modeling was deemed of such good quality that PSL became the place for making and maintaining the reference model for the full detector. The shop machined many acrylic parts, stainless steel parts, and over 3000 cable seal plugs for the AD and muon system. Each of the 192 Photo Multiplier Tubes (PMTs) in the experiment have a cable, which was assembled at PSL. The high tech filling system was designed, fabricated and installed in order to pump three liquids simultaneously at controlled flows with no contamination. The system determines the mass of 20,000 kg of target liquid to an accuracy of 1 kg. The manufacturing of the large components was completed in Colorado, California, China, and Taiwan; however the drawings, engineering oversight, problem solving, and quality assurance were administered by PSL.

Jonathan Heise leak testing the cover gas system atop one fo the antineutrino detectors.

Rapidly, the UW became the lead for the entire AD assembly and installation, largely due to PSL's ability to provide good planning and on-site engineering.  In response to the increased role in the project, PSL hired Qiang Xiao, a Chinese speaking engineer, to not only work on the project itself, but also to help in bridging the language and cultural gap.  All the engineers involved along with support staff, worked at their individual tasks with focus on a common goal of building a high functioning detector.

The hope of the Daya Bay collaboration was to make the first measurement of θ13 that shows the value is non-zero. Due to many delays in civil construction and slow initial progress on site it looked like another experiment, RENO, might get the first measurement.

Once the civil construction was completed, PSL led a concerted effort last fall to get a partial six detector system installed by Christmas. The detectors performed better than the goals set out in the technical design report. The first measurement was made with two months of data. The full eight AD system will be completed this summer and Daya Bay will continue to have the world’s best ability to measure the θ13 mixing angle.

PSL is proud to have been able to contribute to this important physics accomplishment.


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