Final 19931998 LSND Results

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Final 1993-1998 LSND Results

• Overview of the experiment
• Neutrino sources and processes
• New oscillation analysis

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The LSND Experiment
nm,?nm, ne, (?ne )
Target
800 MeV protons 1 mA 6 duty ratio
CH2
Cu Beam Dump
L 30 meters
167 tons CH2 1220 PMTs Active Veto Shield
Neutrino Targets in CH2 nm, ne
neutrons in 12C electrons ?nm, ,?ne
protons in 12C electrons free protons
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Neutrino Fluxes
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LSND Neutrino Physics

• n interactions on 12C, e, p 20-300 MeV

• Oscillation Search

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Event Time Structure
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Global Fit Parameters
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Fit Results (94-98)
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Oscillation Analysis Strategy

• Search for?nm ? ?ne decay at rest oscillation
  events in the energy range 20-60 MeV
• Search for nm ? ne decay in flight oscillation
  events in the energy range 20-200 MeV
• Use common a primary-event electron selection
  across all neutrino processes
• Simultaneously fit all neutrino processes to
  constrain fluxes and backgrounds
• Identify 20-60 MeV electron events with
  correlated neutron capture ? (?ne p? en ) with
  correlated neutron capture gamma (Rg gt 10)
• Fit 20-200 MeV oscillation signal in
  (E,R,L,cosqn) to determine best oscillation
  parameter values

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Analysis Improvements

• Global fit to all neutrino processes in order to
  constrain backgrounds
• Improved position resolution that gives better
  accidental gamma rejection in decay-at-rest
  analysis
• Correlated gamma efficiency improves from 23 to
  40
• Accidental background efficiency drops from 0.6
  to 0.23
• Combined decay-at-rest decay-in-flight
  treatment when determining oscillation parameters

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Neutrino Oscillations 20-60 MeV

• Rgt10 Selection
• on off ? bkgd excess
• 83 (-)33.7 (-)16.6 32.79.2
• Fit to R distribution
• Oscillation Excess Oscillation Probability
• 83.3 21.2 (0.250.06 0.04)

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Global Oscillation Fit

• Electron selection in energy range of 20-200 MeV
• Fit all backgrounds in (Ee, R?, L?, cos??) and
  calculate likelihood at each (Dm2,sin2q)

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Summary

• LSND observes excess ?ne p? en events which are
  not consistent with conventional neutrino
  processes
• A natural explanation is neutrino appearance due
  to flavor oscillations that have an overall
  probability of (0.250.060.04) with a Dm2 gt 0.2
  eV2
• This is the only appearance evidence of neutrino
  oscillations at the present time

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Fluxes determined from known reactions
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Neutrino Sources
Positive decay chain (88)
Negative decay chain (12)

• All stopped ?- are absorbed
• 88 of stopped m- are captured

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Neutrino Oscillation Search

• Event Selection
• Electron-like events 20-200 MeV
• Distance to PMT surface gt 35 cm
• No prior detector activities within 12 ?s

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Global Fit Parameters
Cross section parameters(6)
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Global Fit Parameters (cont.)
Neutrino flux related parameters(3)
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Global Fit Parameters (cont.)
Detection/selection efficiency related
parameters(4)

• ? efficiency
• e efficiency
• ? efficiency
• ? efficiency

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n 12C Interactions
excited states
excited states
ground state
ground state
12N
12B
17.344 MeV
13.370 MeV
12C
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?nm,e p Interactions

• Cross section determined accurately from neutron
  lifetime
• ?nm p rate constrains number of p- decays

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Global fit to neutrino data

• All neutrino processes included in fit
• Cross sections allowed to vary around theoretical
  values
• Neutrino fluxes allowed to vary within errors
• Detection efficiencies allowed to vary

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Fit Results
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Fit Results(cont.)
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Fit Results(cont.)
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Fit Results (Cont.)
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Neutrino Processes
1. Neutrino-nucleus interactions
2. Neutrino-electron interactions
3. Neutrino-proton interactions
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Neutrino Fluxes at LSND

• 1mA 800 MeV protons on H2O or tungsten
• pp- production is 81
• 2 meter decay distance to Cu beam stop so that
  3(5) of p(p-) decay in flight to produce high
  energy neutrinos
• 95 of p and m decay at rest
• 0.6 of m- decay at rest