The Neutrino Detector at the Far Site

A schematic of the two instrumented cryostats that make up a 34-kiloton Liquid Argon Far Detector to be located 4,850 feet below the surface at the Sanford Underground Research Facility (SURF) in Lead, SD.

A neutrino can travel through the Earth without interacting with a single atom, therefore most leave no trace of their passage. To observe even just a few of the extremely rare interactions of neutrinos with matter, physicists build detectors with massive amounts of target material and run the experiments for several years. The detectors record signals from the detectable particles that have emerged from these rare collisions of neutrinos with atoms of the target material. LBNE plans to construct a neutrino detector known as a Liquid Argon Time Projection Chamber (LArTPC), in which liquified argon is the target material. It will be placed in the path of the neutrino beam coming from Fermilab.

Argon, a gas at room temperature, condenses to a liquid when cooled to cryogenic temperatures. LArTPC technology uses liquid argon (LAr) as a target material. The detection method is based on the collection of ionization electrons, resulting from particle interactions in the liquid argon, onto wire planes immersed in the fluid. Under the influence of an electric field, the electrons drift to the wire planes, thereby creating a signal. Three planes of wires allow 3D reconstruction of the electron's track. The LArTPC is planned for installation at 4850 feet below the surface. Such underground placement of the detector will shield it from cosmic rays, which are abundant and would generate signals in the detector that serve only to complicate the data analysis. Most cosmic rays will get absorbed by the matter above the detector. A predecessor experiment at Fermilab, MicroBoone, is building a 100 (metric) ton LArTPC.

The largest neutrino detector to date is a 50,000-ton water Cherenkov detector in Japan called Super-Kamiokande. In a water Cherenkov detector, charged particles are created in collisions of neutrinos with water molecules and light is emitted. Super-Kamiokande is placed 3300 feet underground in a cylindrical cavern about 130 feet in both height and width. The cavern is filled with water and on its walls is an array of light-sensitive devices called photomultiplier tubes (PMTs) that collect the emitted light.

The largest existing LArTPC neutrino experiment is ICARUS, located at the Gran Sasso National Laboratory in Italy. It uses a detector containing 600 tons of liquid argon target material to detect the arrival of neutrinos sent through 730 km of rock from the CERN laboratory in Switzerland. The ICARUS detector is composed of two symmetric, LAr-filled, instrumented modules seated inside of vacuum-tight cryostats roughly 3.5m by 4m by 20m in size. It is also located underground to reduce unwanted signals from cosmic rays.

The water Cerenkov neutrino detector of the Super-Kamiokande experiment in Japan comprises a tank filled with 50,000 tons of water and lined with more than 11,000 photomultiplier tubes. Credit: Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo
The MicroBooNE experiment at Fermilab will detect neutrinos with a time projection chamber that holds about 100 tons of liquid argon cooled to minus 187 degrees Celsius. The TPC will be 12 meters long and have a width and height of 2.5 meters. Credit: Fermilab
This event display shows the interaction of a muon neutrino inside the Super-Kamiokande detector. Credit: Super-Kamiokande Collaboration
In Spring 2009, the Argon Neutrino Test detector at Fermilab recorded the first interaction of a neutrino. Credit: ArgoNeuT Collaboration
Last modified: 12/13/2013 |