Search for neutrino oscillations at LAMPF Page: 5 of 10
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Intermediate-energy proton accelerators provide neutrino sources in
the energy range 10-50 MeV, which are ideal for oscillation searches in
the mass region $m2 - .leV2. In addition, the available beams are very
intense, allowing the experiments to be sensitive to mixing parameters as
low as sin2 29 - 10-3 . The distance of the detector from the beam stop
(L) and neutrino energy (E^) set a topical oscillation scale of
L/Ev - .6 m/MeV, a value intermediate to that which can be obtained in
reactors and high energy experiments.
The Los Alamos Meson Physics Facility (LAMPF) provides a 670 yA
proton beam with a kinetic energy of 800 MeV. The beam is absorbed in a
copper beam stop, producing on the average 0.09 pions for every proton.1 ^
Although both positive and negative pions are produced, n- quickly fall
into' atomic orbitals and are absorbed into the nucleus by strong
processes. The n+ come to rest and decay, producing the beam-stop
neutrino spectra via the decay sequence n+ -* y+vJJ, y+ -» e+vev]J. These
decays provide a clean point source of vg, and v^.
The LAMPF experiment E-645 is located 24 m from the beam stop at a
polar angle of 17° from the main proton beam. The liquid scintillator
detector is the target for the inverse beta decay reaction vgp -» e+n
which, if seen, would provide a signature for the appearance of The
construction phase of the experiment is complete. Calibration and
cosmic-ray background studies are currently under way. The first data
run is expected to begin in July of 1986.
The design and construction of the experiment is dictated by the
expected backgrounds rather than by the signal of a single isolated
positron. Due to the long accelerator duty cycle (-9%), cosmic rays
constitute a serious background, since Los Alamos is 2100 m above sea
level. The detector will operate inside a tunnel with an overburden of
3000 g/cm2, enough passive material to eliminate the hadronic component
in the cosmic-ray flux (see Figure 1). The estimated integrated muon
flux inside the tunnel is 8 kHz. In addition, the central detector is
covered by a 4n cylindrical cosmic-ray shield,2) which contains a 15.2 cm
outer layer of liquid scintillator and an inner layer of lead (12.7 cm)
and iron (5.1 cm). The outer layer is used to veto charged particles.
The passive layer is designed, in particular, to eliminate the background
of muons stopping outside the active layer, where an electron from the
decay radiates a photon that can pass through the scintillator undetected
before it converts inside the shield. To minimize inefficiencies in the
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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/m1/5/: accessed March 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.