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LSND Neutrino Oscillation Results and Implications
William C. Louis, representing the LSND Collaboration [1]
Los Alamos National Laboratory, Los Alamos, NM 87545, USA
The LSND experiment at Los Alamos has conducted searches for P. -+ ve oscilla-
tions using v. from /+ decay at rest and for vg -+ ve oscillations using v from 7r+
decay in flight. For the , - Pe search, a total excess of 51.8+1 8.0 events is
observed with e+ energy between 20 and 60 MeV, while for the v, , ve search, a
total excess of 18.1 6.6 t 4.0 events is observed with e- energy between 60 and
200 MeV. If attributed to neutrino oscillations, these excesses correspond to oscilla-
tion probabilities (averaged over the experimental energies and spatial acceptances)
of (0.31 0.12 0.05)% and (0.26 0.10 i 0.05)%, respectively. For the future,
the BooNE experiment at Fermilab could prove that neutrino oscillations occur and
make precision measurements of Am2 and sin2 20.
1 Introduction
One of the only ways to probe small neutrino masses is to search for neutrino oscillations, where a
neutrino of one type (e.g. 0,) spontaneously transforms into a neutrino of another type (e.g. pe). For
this phenomenon to occur, neutrinos must be massive and the apparent conservation law of lepton
families must be violated. In 1995 the LSND experiment [1] published data showing candidate events
that are consistent with P, -+ Pe oscillations. [2] Additional data are reported here that provide
stronger evidence for ,, -+ ie oscillations [3] as well as evidence for v, -+ ve oscillations. [4] The two
oscillation searches have completely different backgrounds and systematics from each other.
2 Detector
The Liquid Scintillator Neutrino Detector (LSND) experiment at Los Alamos [5] was designed to
search with high sensitivity for i2, -+ Pe oscillations from + decay at rest. The LANSCE accelerator
is a most intense source of low energy neutrinos due to its 1 mA proton intensity and 800 MeV energy.
The neutrino source is well understood because almost all neutrinos arise from 7r+ or + decay; Tr
and p- are readily captured in the Fe of the shielding and Cu of the beam stop. [6] The production of
kaons and heavier mesons is negligible at these energies. The ve rate is calculated to be only 4 x 10'
relative to v,, in the 36 < E~ < 52.8 MeV energy range, so that the observation of a significant Pe rate
would be evidence for D, -+ Pe oscillations.
The LSND detector consists of an approximately cylindrical tank 8.3 m long by 5.7 m in diameter.
The center of the detector is 30 m from the neutrino source. On the inside surface of the tank
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Louis, W.C. & Collaboration, LSND. LSND neutrino oscillation results and implications, article, March 1, 1998; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc702230/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.