Neutrino oscillation studies at LAMPF Page: 7 of 11
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33 PMTS a
500 AE/E - 20%
0 --1032a 12.,i
1E c - 191 1 6 ps
Expect 186 p4
3.5o 500 1000 150 2000 2500 3000 300 4000 4500 O
At (ns) x 1
C_ A r-i m
1000
10
o 20 40 60 0O 100 120 140 10 160 200
&r (cm)
Figure 3. A sample of cosmic neutron
events with associated 2.2-MeV ys. (a) The
number of hit phototubes associated with the
. (b) The time difference between the y and
neutron. (c) The distance between the y and
neutron reconstructed positions.
associated activity events 50 ps prior to the
event. The electron selection efficiencies
are given in Table 1; the overall electron
selection efficiency is 26 2%. Eight events
are observed in the 38 < E, < 56 MeV energy
range that are more than can be explained
by conventional processes. This energy
range is chosen because it is above the
v, "C->e- "N background, as seen in
Fig. 2(a). If the electron selection criteria
are relaxed by decreasing the fiducial
volume cut to 50 cm, by allowing up to two in-
time veto shield hits, or by reducing the no-
associated-activity cut to 40 ps, then the
background increases slightly but the event
excess remains.
Table 2 lists all of the backgrounds with
the expected number of background events
in the 38< E, < 56 MeV energy range. The
non-beam-related background is precisely3
S2.5
1e
0.5
0- Beam
Backg o
--
XeIon-off
nd
e0..
Jo
o 10 2 30 40 M0 60 70so
Electron Energy (MeV)
Figure 4. The electron energy distribution,
beam on-off, for events that satisfy the
electron selection criteria and that have an
associated 2.2-MeV y. The histogram is the
data and the dots show the expected back-
ground from known neutrino interactions.
Table 1
The electron selection efficiencies for elec-
trons in the 38< E, <56 MeV energy range
Requirement Efficiency
Event consistent with# -1 0.80 0.04
No veto shield hits 0.67 0.02
No associated activity events 0.49 0.04
Trigger deadtime 0.98 0.01
TOTAL 0.26 0.03
determined from data collected with the
beam off (the 7% duty factor results in 13
times more beam-off data than beam-on
data). A severe limit is obtained for beam-
induced neutrons by looking for a beam on-
off excess for a sample of events consistent#PMTs
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Louis, W. C. & Collaboration, LSND. Neutrino oscillation studies at LAMPF, article, September 1, 1994; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1389287/m1/7/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.