Cherenkov and Scintillation Separation

The CheSS benchtop experiment will demonstrate the separation of Cherenkov and scintillation light in different pure scintillator cocktels and in WbLS. In addition, it will characterize the newly developed WbLS by measuring the light yield and scintillation time constants. The so-called timing setup will account on the first task, while the light setup will be in charge of the second.

The timing setup consists of a plane of several 1 inch PMTs distributed in a cross shape facing upwards to a small acrylic target filled with scintillator. Thanks to cosmic tags, we can trigger the acquisition when a vertical cosmic muon passes through the target creating both: a Cherenkov ring and isotropic scintillation light. These PMTs as well as our state-of-the-art electronics provide a great timing precision of 100ps making the time separation of the prompt Cherenkov and delayed scintillation lights possible.

The light setup is made up of 6 10 inches PMTs surrounding the target and facing towards it, providing ~15% coverage of the light produced by the scintillation medium. The aim is to collect as much light as possible to perfectly understand the light yield and time characteristics of different scintillator cocktels, like WbLS.

Admixtures of linear-alkybencene (LAB) mixed with water at different loading levels (1%, 5%, 10% and pure LAB) provided by the Minfang Yeh group at Brookhaven are being tested and characterized at Berkeley.

Water-based liquid scintillator (WBLS)

Scintillator materials are very well known and broadly used in particle physics to detect and measure the energy of charged particles as they transform the deposited energy in visible photons. Although they provide low energy threshold measurement, they are not very efficient in big detectors due to the poor optical properties such as the attenuation and the scattering length. Moreover, Cherenkov light is also produced but it is pushed into the background due to the high light yield of the scintillation light. Then, it is very difficult to detect and to distinguish from the scintillation light.

The new scintillators water-like rather than oil-like are a mixture of small amounts of liquid scintillator in water. By changing the loaded fraction of scintillation, we obtain a medium with a custom light yield adapted to any specific situation. In addition, it provides water-like optical properties and the possibility of separating between scintillation and Cherenkov light, opening a new window of applications for optical detectors.

LAPPD

The Large Area Picosecond PhotoDetectors are the future generation of photon detection. They are single photon counting devices with a very fast timing response that provide a superb timing and spatial resolution: ~10ps and ~1cm precision, respectively. All of that in a flat device of ~3cm thickness and ~30cm length.

They are made under a stripped pattern to provide spatial resolution in one of the axis. When one of the strips sees light, it produces photons that travel to each of the ends where the electronics precisely monitor the timing and hence, it is possible to estimate where the hit took place by measuring the difference in time between both signals. This provides full XY pixelation. The principle is somehow similar to the time projection chambers (TPC) and this is why these devices are also known as optical TPCs.