# Presentation: 890753

## MiniBooNE: Status and Prospects

- Eric Prebys, FNAL/BooNE Collaboration

## The MiniBooNE Collaboration

- Y.Liu, I.Stancu*University of Alabama*
- S.Koutsoliotas*Bucknell University*
- E.Hawker, R.A.Johnson, J.L.Raaf*University of Cincinnati*
- T.Hart, R.H.Nelson, E.D.Zimmerman*University of Colorado*
- A.A.Aguilar-Arevalo, L.Bugel, J.M.Conrad, J.Link, J.Monroe, D.Schmitz, M.H.Shaevitz, M.Sorel, G.P.Zeller*Columbia University*
- D.Smith*Embry Riddle Aeronautical University*
- L.Bartoszek, C.Bhat, S.J.Brice, B.C.Brown, D.A.Finley, R.Ford, F.G.Garcia, P.Kasper, T.Kobilarcik, I.Kourbanis, A.Malensek, W.Marsh, P.Martin, F.Mills, C.Moore, E.Prebys, A.D.Russell, P.Spentzouris, R.Stefanski, T.Williams*Fermi National Accelerator Laboratory*
- D.Cox, A.Green, T.Katori, H.Meyer, R.Tayloe*Indiana University*
- G.T.Garvey, C.Green, W.C.Louis, G.McGregor, S.McKenney, G.B.Mills, H.Ray, V.Sandberg, B.Sapp, R.Schirato, R.Van de Water, N.L.Walbridge, D.H.White*Los Alamos National Laboratory*
- R.Imlay, W.Metcalf, S.Ouedraogo, M.Sung, M.O.Wascko*Louisiana State University*
- J.Cao, Y.Liu, B.P.Roe, H.J.Yang*University of Michigan*
- A.O.Bazarko, P.D.Meyers, R.B.Patterson, F.C.Shoemaker, H.A.Tanaka*Princeton University*
- P.Nienaber*St. Mary's University of Minnesota*
- B.T.Fleming*Yale University*

## Outline

- State of neutrino mixing measurements
- Without LSND
- LSND and Karmen
- Experiment
- Beam
- Detector
- Calibration and cross checks
- Analysis
- Resent Results
- Future Plans and outlook
- Anti-neutrino running
- Path to oscillation results

## Theory of Neutrino Oscillations

- Neutrinos are produced and detected as *weak eigenstates* (e ,, or ).
- These can be represented as *linear combination of mass eigenstates*.
- If the above matrix is not diagonal *and* the masses are not equal, then the net weak flavor content will *oscillate *as the neutrinos propagate.
**Example: **if there is mixing between the e and :then the probability that a e will be detected as a  after a distance *L* is:

- Distance in *km*

- Energy in GeV

- Mass eigenstates

- Flavor eigenstates

- Only measure *magnitude* of the *difference* of the squares of the masses.

## Probing Neutrino Mass Differences

- & Reactors

- Accelerators use  decay to *directly* probe  e

- Reactors use use *disappearance* to probe  e  

- Cerenkov detectors directly measure  and e  content in atmospheric neutrinos. Fit to e mixing hypotheses

- Solar neutrino experiments typically measure the disappearance of e.

- Also probe with “long baseline” accelerator and reactor experiments

## SuperKamiokande Atmospheric Result

- Huge water Cerenkov detector can directly measure and  e  signals.
- Use azimuthal dependence to measure distance traveled (through the Earth)
- Positive result announced in 1998.
- Consistent with  mixing.

- Outer detector

- Inner detector

## SNO Solar Neutrino Result

- Looked for Cerenkov signals in a large detector filled with heavy water.
- Focus on 8B neutrinos
- Used 3 reactions:
* ****e*+*d**p+p+e**-*: only sensitive to ***e*
-  ***x*+*d**p+n+****x*: equally sensitive to ***e *,***** *,****
* ****x*+ *e**-* ***x*+ *e**-*: 6 times more sensitive to ***e *than ***** *,*****d*
- Consistent with initial full SSM flux of ***e*’s mixing to ***** *,******

- Just SNO

- SNO+others

## Reactor Experimental Results

- Single reactor experiments (Chooz, Bugey, etc).  Look for ***e* disappearance: all negative
- KamLAND (single scintillator detector looking at ALL Japanese reactors): ***e* disappearance consistent with mixing.

## K2K

- First “long baseline” accelerator experiment
- Beam from KEK PS to Kamiokande, 250 km away
- Look for  disappearance (atmospheric “problem”)
- Results consistent with mixing

- Best fit

- No mixing

- Allowed Mixing Region

## Three Generation Mixing (Driven by experiments listed)

- General Mixing Parameterization

- CP violating phase

- Almost diagonal
- Third generation weakly coupled to first two
- “Wolfenstein Parameterization”

- Mixing large
- No easy simplification
- Think of mass and weak eigenstates as totally separate

## Best Three Generation Picture

## The LSND Experiment (1993-1998)

- Signature
- Cerenkov ring from electron
- Delayed  from neutron capture

- ~30 m

- Energy 20-50 MeV

- mix

## LSND Result

- (Soudan, Kamiokande,
- MACRO, Super-K)

- (Homestake, SAGE,
- GALLEX, Super-K
- SNO, KamLAND)

- Excess Signal:

- Best fit:

- Only exclusive appearance result to date
- Problem: m2 ~ 1 eV2 not consistent with other results with simple three generation mixing

## Possibilities

- 4 neutrinos?
- We know from Z lineshape there are only 3 active flavors
- Sterile?
- CP or CPT Violation?
- More exotic scenarios?
- LSND Wrong?
- Can’t throw it out just because people don’t like it.

## Karmen II Experiment: not quite enough

- Pulse 800 MeV proton beam (ISIS)
- 17.6 m baseline
- 56 tons of liquid scintillator
- Factor of 7 less statistical reach than LSND
- -> NO SIGNAL
- Combined analysis still leaves an allowed region

- Combined

## Role of MiniBooNE

- Boo(ster) N(eutrino) E(xperiment)
- Full “BooNE” would have two detectors
- Primary Motivation: Absolutely confirm or refute LSND result
- Optimized for L/E ~ 1
- Higher energy beam -> Different systematics than LSND
- Timeline
- Proposed: 12/97
- Began Construction: 10/99
- Completed: 5/02
- First Beam: 8/02
- Began to run concurrently with NuMI: 3/05
- Presently ~7E20 proton on target in neutrino mode
- More protons that all other users in the 35 year history of Fermilab combined!
- Oscillation results: 2006

## MiniBooNE Neutrino Beam (not to scale)

- 8 GeV Protons
- ~ 7E16 p/hr max
- ~ 1 detected neutrino/minute
- L/E ~ 1

**FNAL****Booster**

**Be Target****and Horn**

**“****Little Muon Counter” (LMC): to understand K flux**

**50 m Decay Region**

**500m dirt**

**Detector**

## Detector

- 950,000 l of pure mineral oil
- 1280 PMT’s in inner region
- 240 PMT’s outer veto region
- Light produced by Cerenkov radiation and scintillation

- Light barrier

- Trigger:
- All beam spills
- Cosmic ray triggers
- Laser/pulser triggers
- Supernova trigger

## Neutrino Detection/Particle ID

- Important Background!!!

## Delivering Protons

- Requirements of MiniBooNE greatly exceed the historical performance of the 30+ year old 8 GeV Booster, pushes...
- Average repetition rate
- Above ground radiation
- Radiation damage and activation of accelerator components
- Intense Program to improvethe Booster
- Shielding
- Loss monitoring and analysis
- Lattice improvements (result of Beam Physics involvement)
- Collimation system
- Very challenging to continue to operate 8 GeV line during NuMI/MINOS operation
- Once believed imposible
- Element of lab’s “Proton Plan”
- Goal to continue to deliver roughly 2E20 protons per years to the 8 GeV program for at least the next few years.

## Running MiniBooNE with NuMI

- Note: these projections do *not* take into account the collider turning off in 2009
- NuMI rates would go up at least 20%, possible higher
- Major operational changes could make continued operation of 8 GeV line very difficult

- NuMI/MINOS

- MiniBooNE

## Beam to MiniBooNE

- NuMI Running

- NuMI Problems

- ~7 x 1020 protons

## Analysis: Modeling neutrino flux 

- Analysis: Modeling neutrino flux

- Production
- GEANT4 model of target, horn, and beamline
- MARS for protons and neutrons
- Sanford-Wang fit to production data for  and K
- Mesons allowed to decay in model of decay pipe.
- Retain neutrinos which point at target
- Soon hope to improve model with data from the HARP experiment taken from a target identical to MiniBooNE

##  Interactions

- Cross sections
- Based on NUANCE 3 Monte Carlo
- Use NEUT and NEUEN as cross checks
- Theoretical input:
- Llewellyn-Smith free neucleon cross sections
- Rein-Sehgal resonant and coherent cross-sections
- Bodek-Yang DIS at low-Q2
- Standard DIS parametrization at high Q2
- Fermi-gas model
- Final state interaction model
- Detector
- Full GEANT 3.21 model of detector
- Includes detailed optical model of oil
- Reduced to raw PMT hits and analyzed in the same way as real data

- MiniBooNE

## Background 

- If the LSND best fit is accurate, only about a third of our observed rate will come from oscillations
- Backgrounds come from both intrinsic e and misidentified 

- Energy distribution can help separate

## Blindness

- Given the low signal to background ratio and the inherent difficulty of the analysis, there are many opportunities for unintentional bias
- Therefore, we consider a blind analysis essential
- General philosophy: guilty until proven innocent
- Events go “into the box” unless they are specifically tagged as being non-signal events, e.g
- Muons
- Single -like ring
- Topological cuts
- 0
- No Michel electron
- Clear two-ring fit, both with E>40 MeV
- Will only look at remaining data when we are confident that we model the beam and detector well.
- Note: This still allows us to look at the majority of our data!

## Characterizing the Detector

- Laser Calibration
- Laser pulses illuminate one of 4 flasks which scatter light isotropically
- Used to understand PMT response

- Cosmic Muons
- Muon Tracker used in conjunction with “cubes” to trigger on a particular endpoint (energy)
- Vital in understanding energy scale

## The Detector (cont’d)

- Electrons from muon decay (Michel electrons)
- Vital for understanding signal events.

- 0 Events
- Help to understand higher energy e
- Help fix energy scale

## Selecting Neutrino Events

- Collect data from -5 to +15 usec around each beam spill trigger.
- Identify individual “events” within this window based on PMT hits clustered in time.

- Time (ns)

- Time (ns)

- Time (ns)

- No cuts

- Veto hits < 6

- Veto hits<6tank hits>200

- 1600 ns spill

## Muon Reconstruction

- Muon reconstruction is based on a fit to PMT’s clustered in time
- Position and time of arrival are used to reconstuct the origin, direction and path length of the muon track segment

- Cos of angle of PMT hits relative to beam

## Charged Current Quasi-elastic Events

- Veto hits < 6
- Tank hits > 200
- PMT position/time fit consistent with muon

- Angular distribution

## Recent Results:                                      (CCPiP)*

- Important for understanding backgrounds and nuclear cross sections.

- MiniBooNE

- *analysis by M. Wascko and J. Monroe

## Signature of CCPiP Event

- Look for exactly three events:
- First promptly with the beam
- Second two within the ~15 usec trigger window
- First event consistent with CC muon
- Second two consistent with Michel decays.

- (only charged tracks shown)

- Muon generates Cerenkov ring and stops

- Muon decay (“Michel”) electrons

## CCPiP Results

- CCPiP/CCQE ratio
- Corrected for efficiencies

## Additional Cross-checks: Neutrinos from NuMI beamline*

- NuMI decay pipe extends to almost just below the MiniBooNE detector

- *primarily analysis of A. Aguilar

## Path to “opening the box”

- Our present sample neutrino data is sufficient to release an oscillation result
- We are not yet confident enough in our analysis to do so
- Continue to refine Monte Carlo until open box samples agree within errors
- HARP data on MiniBooNE target an important constraint
- Generate systematic error matrix by varying all important production and optical model parameters (“Unisim Monte Carlo”).
- When confident, practice on a fake oscillation signal.

## Experimental Sensitivity 

- Experimental Sensitivity

- No signal
- Can exclude most of LSND at 5

- Signal
- Can achieve good m2 separation

## Accommodating a Positive Signal

- We know from LEP that there are only 3 active, light neutrino flavors.
- If MiniBooNE confirms the LSND results, it might be evidence for the existence of sterile neutrinos

## Everybody Loves a Mystery

- 3+2 Sterile neutrinos
- Sorel, Conrad, and Shaevitz (hep-ph/0305255)
- MaVaN & 3+1
- Hung (hep-ph/0010126)
- Sterile neutrinos
- Kaplan, Nelson, and Weiner (hep-ph/0401099)
- Explain Dark Energy?
- CPT violation and 3+1 neutrinos
- Barger, Marfatia & Whisnant (hep-ph/0308299)
- Explain matter/antimatter asymmetry
- Lorentz Violation
- Kostelecky & Mewes (hep-ph/0406035)
- Extra Dimensions
- Pas, Pakvasa, & Weiler (hep-ph/0504096)
- Sterile Neutrino Decay
- Palomares-Ruiz, Pascoli & Schwetz (hep-ph/0505216)

## Near Future: MiniBooNE antineutrino running

- Inherently interesting
- Not much anti-neutrino data
- Directly address LSND signal
- Important for understanding our own systematics and those of other experiments
- Problems:
- Cross section not well known
- Lower rate (about 1⁄4)
- Wrong sign background

- Example of new physics:

- As we speak, MiniBooNE is switching the horn polarity to run in antineutrino mode

## Conclusions and Outlook

- MiniBooNE has been running for over three years, and continues to run well in the NuMI era
- The analysis tools are well developed and being refined to achieve the quality necessary to release the result of our blind analysis
- Recent results for CCQE and CCPiP give us confidence on our understanding of the detector and data.
- Look forward to many interesting results in 2006