Propagation of photons

The experiment T-1019 team carefully positions the detector for testing. Photo: Toru Iijima

Japan’s high-energy physics laboratory, KEK, is one step closer to completing the SuperKEKB Project, which would increase the KEKB accelerator’s target luminosity to 40 times greater than its current record. To help reach that goal, Fermilab’s Test Beam Facility lent a hand.

The SuperKEKB Project broke ground in November of last year, with a plan for several upgrades to both the KEKB accelerator and the Belle detector. Every upgrade requires thorough testing, and experiment T-1019 was a crucial milestone for this stage. Tested at Fermilab, the research team used the high-energy beam to analyze a new detector concept, the imaging Time Of Propagation detector. SuperKEKB will use this detector to distinguish pions from kaons in the decay products of electron-positron collisions. Kaons contain strange quarks while pions do not. The ability to separate the two is essential for the physics program planned after the full Super B-factory upgrade.

“Evaluation of the full-size detector, finely segmented photodetector, and integrated readout electronics is a crucial step toward finalizing the specifications for the components of the Belle detector upgrade,” said Gary Varner, the experiment T-1019 spokesperson and a professor at the University of Hawaii.

It’s close to impossible to see the pions and kaons without the specially designed Belle II detector. Housed in the center of the detector are time-of-propagation counter arrays, which reflect and magnify the light given off by photons. Called Cherenkov photons, the particles create a ring of light as they decay, making for a more identifiable track. This allows researchers to examine the lifetimes of each particle closely.

To test how well the detector and all of the components are working, the collected data is compared to a Monte Carlo data set. A Monte Carlo simulation makes precise predictions for what the measurements of the experiment should be.

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Ashley WennersHerron