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John Felde | University of Maryland | USA

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Fast Photosensors for Neutrino Physics

Last week we hosted Matthew Wetstein from Argonne National Lab for a High Energy Physics Seminar.  Matthew has been working on a project of great interest to me: the development of fast, large area photo sensors.  For a little background, a lot of neutrino (and indeed other) detectors, rely on detecting photons (light) that are produced from energetic particles. Currently, the most economical devices are photomultiplier tubes (PMTs). There are some practical limitations to these devices, including size, performance in a magnetic field, and timing.

The “Large-Area Picosecond Timing Project,” a group primarily from The University of Chicago, Argonne, Fermilab and Berkeley, are working to develop large (~8in^2), flat, fast, and cheap particle detectors for use in physics, medical, and industry applications.  The photosensors are designed as Micro-Channel Plates (MCP), but fabricated in a different, cheaper, way.  The timing resolution (how well you can tell when your signal came) is currently around 100 pico-seconds, or about 10 times better than typical large area PMTs.

Detectors such as these (above) could have real potential in neutrino physics. Many neutrino detectors function by detecting either direct Cherenkov light, and/or scintillation light produced in the detection medium. Our goal is always to maximize the detection of this light by having as many sensors as possible, hence we like things cheap.  Knowing exactly when the light reaches the sensitive part of our detector is how we determine where in the detector the interaction took place, hence we like things fast. Knowing exactly where on the wall of our detector the light hit helps constrain the geometry and type of event, hence we like lots of pixels.

As an example, one area where these sensors might be useful is in large water Cherenkov detectors.  A primary background for these detectors is distinguishing electrons from neutral pion decays.  An electron appears as a single fuzzy ring on the wall of the detector. A neutral pion will decay and appear as two separate electron like rings.  A major background come about because sometimes your detector simply can not tell distinguish two rings from one.  With highly pixelated and fast photosensors, one could better distinguish these two types of events by either both being more sensitive to seeing two rings, or separating the rings in time.

A great deal of work has been done by this group to understand the potential impact of these devices on the field, and we never get tired of thinking how we could get the most out of our detectors.

EDIT: For more info see here.




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