# Presentation: 711021

## Final 1993-1998 LSND Results

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

## The LSND Experiment

- 800 MeV protons
- 1 mA
- 6% duty ratio

- L = 30 meters

- CH2

- ee )

- _Neutrino Targets in  CH__2__ :_
- 	  e  :   neutrons in 12C  +  electrons
- e  :   protons  in 12C  +  electrons  +  free protons

- 167 tons CH2
- 1220 PMT’s
- Active Veto Shield

- Cu Beam Dump

- Target

## Neutrino Fluxes

## LSND Neutrino Physics

-   interactions on 12C, e, p: 20-300 MeV

-  Oscillation Search:

## Event Time Structure

## Global Fit Parameters

## Fit Results (94-98)

## Slide 8

## Oscillation Analysis Strategy

- Search for  e decay at rest oscillation events in the energy range 20-60 MeV
- Search for   e 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    (e p e+n ) with correlated neutron capture gamma (R> 10)
- Fit 20-200 MeV oscillation signal in (E,R,L,cos) to determine best oscillation parameter values

## 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

## Neutrino Oscillations 20-60 MeV

- _R>10 Selection:_
- _on__	__off__	__	____ bkgd__	__	__excess_
- 83	(-)33.7		(-)16.6		32.7±9.2
- _Fit to R distribution:_
- _Oscillation Excess__	__ Oscillation Probability_
- 83.3 ± 21.2		(0.25±0.06 ± 0.04)%

## 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 (m2,sin2)

## Summary

- LSND observes excess e p e+n  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 (0.25±0.06±0.04)% with a m2 > 0.2  eV2
- This is the only appearance evidence of neutrino oscillations at the present time

## Fluxes determined from known reactions:

## Neutrino Sources

- _Positive decay chain (88%)_

- _Negative decay chain (12%)_

- All stopped - are absorbed
- 88% of stopped - are captured

## Neutrino Oscillation Search

- Event Selection:
- Electron-like events 20-200 MeV
- Distance to PMT surface > 35 cm
- No prior detector activities within 12 s

## Global Fit Parameters

- _Cross section parameters(6):_

## Global Fit Parameters (cont.)

## Global Fit Parameters (cont.)

-    efficiency
-   e efficiency
-    efficiency
-    efficiency

##   12C Interactions

- 12B

- 12N

- 12C

- 13.370 MeV

- 17.344 MeV

- ground state

- ground state

- excited states

- excited states

## ep  Interactions

-  Cross section determined accurately from neutron lifetime
-  p  rate constrains number of - decays

## 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

## Fit Results:

| Process | Events fit
dist>-10 | Events calc
dist>-10 | <fit> 
(10-40cm2) | <calculated> (10-40cm2) |
| --- | --- | --- | --- | --- |
| DAR |  |  |  |  |
| e12C(ex.) | 3000 | 3062 | 0.037 | 0.041 |
|  e12C(g.s.) | 6961 | 7111 | 0.091 | 0.093 |
| e p | 112 | 108 | 0.719 | 0.734 |
| e | 2491 | 2520 | 0.0040 | 0.0040 |
| e13C(incl.) | 344 | 461 | 0.041 | 0.53 |

## Fit Results(cont.)

| Process | Events fit
dist>-10 | Events calc
dist>-10 | <fit> 
(10-40cm2) | <calculated> (10-40cm2) |
| --- | --- | --- | --- | --- |
| DIF |  |  |  |  |
| 12C(inc..) | 12797 | 17378 | 11.0 | 13.9 |
| 12C(g.s.) | 663 | 730 | 0.62 | 0.63 |
| p | 1393 | 1339 | 4.48 | 4.57 |
| C(inc.) | 565 | 661 | 4.85 | 6.14 |
| C(g.s.) | 59 | 55.9 | 0.51 | 0.52 |

## Fit Results(cont.)

| Fluxes Parameters |  |
| --- | --- |
| DIF flux | 0.933 |
| DAR flux | 0.97 |
| -/+ ratio | 1.10 |

## Fit Results (Cont.)

| Efficiencies |  |
| --- | --- |
| e- | 0.99 |
|  | 1.00 |
|  | 1.01 |
|  | 1.10 |

## Neutrino Processes

- _1. Neutrino-nucleus interactions:_

- _2. Neutrino-electron interactions:_

- _3. Neutrino-proton interactions:_

## Neutrino Fluxes at LSND

- 1mA 800 MeV protons on H2O or tungsten
- production is 8:1
- 2 meter decay distance to Cu beam stop so that 3%(5%) of  decay in flight to produce high energy neutrinos
- 95% of and decay at rest
- 0.6% of  decay at rest