MiniBooNE Oscillation Update Mike Shaevitz Columbia University

1
MiniBooNE Oscillation UpdateMike
ShaevitzColumbia University

• XII International Conference on Neutrino
  Telescopes
• March 7, 2007

2
Outline

• Introduction LSND, sterile neutrinos
• MiniBooNE Experiment Setup, reconstruction,
  calibration, particle ID, NuMI offaxis beam
• Systematic Uncertainties for oscillation analysis
• Main backgrounds and Constraints
• Oscillation analysis and sensitivity

3
The LSND Experiment
LSND observed a (3.8s) excess of??e events
87.9 22.4 6.0 events
4
Why Sterile Neutrinos?
Need better measurement in LSND region ?
MiniBooNE

• One of the experimental measurements is wrong
• Additional sterile neutrinos involved in
  oscillations

• (M.Sorel, J.Conrad, M.Shaevitz, PRD
  70(2004)073004 (hep-ph/0305255)
• G. Karagiorgi et al., PRD75(2007)013011
  (hep-ph/0609177)

5
The MiniBooNE Experiment

• Proposed in summer 1997,operating since 2002
• Goal to confirm or exclude the LSND result
• Similar L/E as LSND
• Baseline L 451 meters, x15 LSND
• Neutrino Beam Energy E x(10-20) LSND
• Different systematics event signatures and
  backgrounds different from LSND
• High statistics x5 LSND
• 5.579E20 POT for neutrino mode since 2002.
• Switch horn polarity to run anti-neutrino mode
  since January 2006.

6
The MiniBooNE Collaboration
Y.Liu, D.Perevalov, I.Stancu
University of Alabama
S.Koutsoliotas Bucknell University
R.A.Johnson, J.L.Raaf
University of Cincinnati T.Hart,
R.H.Nelson, M.Tzanov M.Wilking,
E.D.Zimmerman University of Colorado
A.A.Aguilar-Arevalo, L.Bugel L.Coney,
J.M.Conrad, Z. Djurcic, K.B.M.Mahn,
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.J.Stefanski, T.Williams Fermi National
Accelerator Laboratory D.C.Cox, T.Katori,
H.Meyer, C.C.Polly R.Tayloe
Indiana University
G.T.Garvey, A.Green, 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.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 Saint Mary's University of
Minnesota J. M. Link
Virginia Polytechnic Institute
E.Hawker Western Illinois University
A.Curioni,
B.T.Fleming Yale University
7
nm ? ne Oscillation Search

• Beam
• Detector

? ?e / ?? ? 0.5

• 12m diameter tank
• Filled with 900 tons of pure mineral oil
• Optically isolated inner region with 1280 PMTs
• Outer veto region with 240 PMTs.
• Detector Requirements
• Detect and Measure Events Vertex, En
• Separate ?? events from ?e events

8
Oscillation Signal ? An Excess of
ne Events over Expectation

• Understanding the expected events is therefore
  the key
• Need to know the neutrino fluxes
• Electron neutrinos from m, K, and K0 decay
• Muon neutrinos can make background or give the
  signal
• Need to know the nm/e neutrino cross section vs.
  energy
• Events flux cross section
• Need to know the ne reconstruction efficiency vs
  energy
• Observed events efficiency events
• Need to know the probability for nm events to be
  mis-identified as ne events ? Events with single
  EM showers look like ne events
• Neutral current (NC) p0 events are the main
  mis-id background
• NC D production followed by radiative decay, ??N?
• Photons entering from outside detector (Dirt
  background)

9
Event Reconstruction

• Use energy deposition and timing of hits in the
  phototubes
• Prompt Cherenkov light
• Highly directional with respect to particle
  direction
• Used to give particle track direction and length
• Delayed scintillation light
• Amount depends on particle type

10
Calibrations
Spectrum of Michel electrons from stopping muons
p0 Mass Distribution
Michel electron energy (MeV)
Preliminary
15 E resolution at 53 MeV
PRELIMINARY
Preliminary
Energy vs. Range for events stopping in
scintillator cubes
11
Particle ID Algorithms

• Muon id from delayed decay electron signature
  (92 non-capture probability)
• Identify events using
• hit topology
• PID Vars
• Reconstructed physical observables
• Track length, particle production angle relative
  to beam direction
• Auxiliary quantities
• Timing, charge related early/prompt/late hit
  fractions, charge likelihood
• Geometric quantities
• Distance to wall
• Two PID algorithms
• Likelihood based analysis e/m and e/p0
• A boosted decision tree algorithm to separate
  e, m, p0 (See B. Roe et al. NIM A543 (2005))

e candidate
? candidate
?0 candidate
12
NuMI Offaxis ? MiniBooNEs Calibration Beam
Need to verify our PID with ne in the signal
energy range,but cant due to blind analysis.
? Solution use someone elses beam!

100 -200 mr(6 12 deg)
Sitting off axis, we see a beam which is enhanced
in ne flux and is in a useful energy range.
13
Results for Offaxis NuMI Beam in MiniBooNE

• MiniBooNE sees events from the offaxis NuMI beam
• They show up as events during the 8 ms NuMI beam
  window
• These events have a significant ne component that
  can be used to test our PID system

14
MiniBooNE Oscillation Search Method

• Do a combined oscillation fit to the observed nm
  and ne energy distribution for data vs prediction
• Systematic (and statistical) uncertainties in
  (Mij)-1 matrix
• Uncertainties come from analyses of external and
  internal data
• Covariance matrix includes correlations between
  ne and nm events
• Predictions for the various backgrounds are
  directly constrained by actual MiniBooNE
  measurements
• Constraints significantly reduce systematic
  uncertainties
• Combined fit also reduces ne uncertainties using
  high stat nm events

15
Expected Event Numbers
Events with nm Selection Requirements
Simple CutsEn gt 60 MeVVeto Hits gt 6
No Cuts
Events 193,730 (mainly nm CCQE)(Final data
sample for 5.58 1020 pot)
Events with ne Selection Requirements
Events Time (ns)
Events Time (ns)
Total Expected Background 915 events
Example Osc Signal 315 events(Dm2 0.4 eV2 ,
sin22q 0.017)
16
Systematic Uncertainties

• Sources of uncertainty for the ne candidate
  events
• Uncertainties come from modeling the beam,
  neutrino interactions, and the detector
• (These uncertainties will be reduced by using
  MiniBooNE data)
• Uncertainties from external and non-osc internal
  constraints
• Neutrino flux from p decay
• Neutrino flux from K decay
• Neutrino flux from K0 decay
• Neutrino flux from m decay
• n-Xsec uncertainties
• External interactions (Dirt)
• NC p0 Mid-ID
• Radiative ??N?
• Optical Model

Next Few examples of these systematic
uncertainty estimates.
17
Pion and Kaon Production

• pBe Pion production
• pBe production s measured by the HARP
  collaboration at pproton 8.9 GeV
• MiniBooNE uses a parameterization with
  uncertainties set to cover measurements.

• pBe K and K0 production
• Use external pBe cross section measurements for
  beam momenta from 9.5 24 GeV
• MiniBooNE uses a parameterization with
  uncertainties set to cover measurements.

18
n Cross Section Uncertainties

• Differential cross section for quasi-elastic
  scattering determined from MiniBooNE data
• Shape fits are performed to observed data Q2
  distribution using a relativistic-Fermi-gas model
  
• Two parameters (and their uncertainties) are
  determined
• Axial mass parameter, MA
• A Pauli blocking parameter
• Fit also agrees well with neutrino energy
  distributions
• Other cross sections (i.e. CC1p) are determined
  from MiniBooNE data combined with previous
  external measurements

19
Optical Model Uncertainties
Uncertainties on the parameters associatedwith
optical model are used to determine the
uncertainties for the oscillation search

• Light Creation
• Cerenkov well known
• Scintillation
• yield
• spectrum
• decay times
• Light Propagation
• Fluoresence
• rate
• spectrum
• decay times
• Scattering
• Rayleigh
• Particulate (Mie)
• Absorption

• In Situ
• Cosmics muons, Michel electrons, Laser
• External
• Scintillation from p beam (IUCF)
• Scintillation from cosmic m (Cincinnati)
• Fluorescence Spectroscopy (FNAL)
• Time resolved spectroscopy (Princeton, JHU)
• Attenuation (Cincinnati)

20
Backgrounds Constraints from MiniBooNE Data

• All of the major backgrounds for the oscillation
  search can be constrained directly from
  measurements using MiniBooNE data
• NC p0 production
• Largest Mis-ID background is from NC p0
  production where one of the decay photons is
  missed. This background is constrained from the
  large fraction of NC p0 events that are observed
  and measured in MiniBooNE
• External events
• Backgrounds from the events in material outside
  of the MiniBooNE detector are constrained by the
  isolation and measurement of such events.
• Intrinsic kaon decay nes
• Intrinsic ne background from kaon decay can be
  constrained by observed ne events at high energy
  where there are no oscillation events
• Intrinsic muon decay nes
• Largest intrinsic ne background is from muon
  decay and is highly constrained by the observed
  nm events. The constraint is applied by using
  the combined ne/ nm oscillation fit.

21
NC p0 Background Constraint
M?? Mass Distribution for Various p?0 Momentum
Bins

• Using PID variables isolate a very pure sample ?0
  events from nm N ? nm N ?0 (mainly from D
  ? N ?0 )
• Purity 90 or greater
• Measure ?0 production rate as a function of ?0
  momentum and compare to MC prediction to
  calculate a correction factor.
• Correct NC p0 mis-ID rate using this measured
  correction factor(Also can be used to correct
  the D ? N ? radiative background)

22
Constraining External Event (Dirt) Background

• Neutrino beam interacts with material outside of
  MiniBooNE detector creating photons (100 300
  MeV) that come into the tank and produce
  electron-like events.
• Dirt events contribute 10 of background for
  oscillation nue search.
• N_dirt_measured / N_dirt_expected 0.99 0.15

Event Type of Dirt after PID cuts
EnhancedBackgroundCuts
23
Kaon Intrinsic ne Background Constrained by High
Energy Data

• At high energy, candidate ne events are mainly
  from kaon decay
• Small contributions from m-decay and p0 mis-id
• Normalization of the kaon intrinsic background
  can be partially constrained within uncertainties
  by the level of this high energy data

Preliminary
24
Constraining the Intrinsic ne Background from
Muon Decay

• Muon decay is the largest source of ne background
  but is highly constrained by the observed nm
  events.
• MiniBooNE subtends a very small forward solid
  angle for neutrinos from pion decay ? observed
  En ? 0.6 Ep
• So, the measured nm energy spectrum gives both
  the number and energy spectrum of the decaying
  pions
• These decaying pions are the source of the ne
  mu-decay background
• The combined nm/ ne oscillation fit
• Automatically takes this correlation into account
• Effectively constrains the ne background with an
  error that depends primarily on the nm event
  statistics.

25
Summary MiniBooNE Oscillation Analysis Strategy

• Develop a very detailed simulation of the
  neutrino beam and detector using both internal
  and external information
• Constrain the uncertainties associated with the
  simulation using actual MiniBooNE data and
  measurements
• Accomplish the oscillation search by doing a
  combined ne/ nm fit to the observed event
  distribution vs. energy.

90CL
Monte Carlo Sensitivity Estimate
26
Summary

• From the beginning, MiniBooNE decided to do a
  blind analysis
• Candidate ne events in the oscillation energy
  region were sequester (5000 events) (Closed
  Box)
• The other several 100,000 events were open for
  examination (Open Box)
• Collaboration is in the final stages
• Checking the Open Box data including new Side
  Band regions
• Assessing final cuts for enhancing the
  oscillations sensitivity
• Opening the Closed Box is close
• After opening, the result will be presented after
  about two weeks.