Search for neutrino oscillations at LAMPF Page: 6 of 10
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shield, the scintillator fills only three optically isolated sections:
the cylinder and one endcap, the bottom and the other endcap. The
scintillator is viewed by 360 photomultiplier tubes (EHI 4870-B) to
provide ample redundancy.
The central detector has forty layers, each one consisting of a
scintillator plane followed by vertical and horizontal proportional
drift-chambers (see Figure 2). The liquid scintillator is contained in
horizontal lucite tanks (366 x 30 x 3 cm3) and viewed at both ends by
Hamamatsu R878 phototubes. Particles lose 75X of their energy in the
scintillator, the rest is deposited in the lucite and drift tube walls.
The drift-chamber planes consist of 45 wires assembled 8.1 cm apart.
Drift-time and pulse-height information are recorded for every wire.
Nuclei with loosely bound neutrons, e.g. 27A1 and 13C, provide a target
for vg interactions and are a source of background since we are not able
to distinguish between electrons and positrons (see Table I). Thus, the
drift tubes are constructed of laminated Kraft paper with only a 25-um
aluminum inner layer to shape the electric field.3^ The detector weight
is 20 metric tons, of which 2.3 tons is hydrogen.
Ve must be able to distinguish protons from electrons with high
efficiency in order to eliminate knock-on protons produced in fast
neutron interactions. The granularity of the detector permits such
identification to be made by comparing the particle range to the energy
loss measured in the scintillator. An additional selection can be made
based on the dE/dx measurement in a single scintillator plane. Using
these criteria, protons have been rejected by a factor of 3xl0~4 in a
prototype detector studied in the LAMPF test beam channel. Given the
present estimates of neutron backgrounds (-1000/day) in our detector,
this rejection is adequate to eliminate knock-on protons with kinetic
energies greater than 100 MeV.
The signals from the detector and the shield are digitized with
flash ADC's and stored in cyclic memories containing 150 psec of data.
The positron trigger is flagged by hits in three consecutive planes. At
this point, data are continued to be read into the memories for 100 usee,
so that when the data are eventually transferred to the computer, only 50
usee of information is recorded before the event trigger. The history is
used to tag any signals that might be associated with the trigger, e.g.
a stopping muon. The data recorded after the trigger is needed to help
identify the neutron, which would be present if the event was in fact a
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Harper, R.W.; Ling, T.Y.; Mitchell, J.W.; Romanowski, T.A.; Smith, E.S.; Timko, M. et al. Search for neutrino oscillations at LAMPF, article, January 1, 1986; United States. (https://digital.library.unt.edu/ark:/67531/metadc1102862/m1/6/: accessed March 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.