# Presentation: 726858

## MiniBooNE Oscillation UpdateMike ShaevitzColumbia University

- XII International Conference on “Neutrino Telescopes”
- March 7, 2007

## 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

## The LSND Experiment

**The LSND Experiment**

## Why Sterile Neutrinos?

- (M.Sorel, J.Conrad, M.Shaevitz, PRD **70**(2004)073004  (hep-ph/0305255)
-  G. Karagiorgi et al., PRD**75**(2007)013011 (hep-ph/0609177)

- One of the experimental measurements is wrong
- Additional “sterile” neutrinos involved in oscillations

-    Need better measurement in LSND region ******  MiniBooNE**

## 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.

## The MiniBooNE Collaboration

-             ***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***

**The MiniBooNE Collaboration**

## e Oscillation Search

**************e**** 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, E ...
- Separate  events from e events

## Oscillation Signal              An Excess of “e” Events over Expectation

- Understanding the expected events is therefore the key
- Need to know the neutrino fluxes
- Electron neutrinos from , K+, and K0 decay
- Muon neutrinos can make background or give the signal
- Need to know the eneutrino cross section vs. energy
- Events = flux × cross section
- Need to know the e reconstruction efficiency vs energy
- Observed events = efficiency × events
- Need to know the probability for  events to be mis-identified as e events  Events with single EM showers look like e events
- Neutral current (NC)  events are the main mis-id background
- NC  production followed by radiative decay, N
- Photons entering from outside detector (“Dirt” background)

## 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

## Calibrations

**Calibrations**

- Michel electron energy (MeV)

**15% **
**E resolution**
**at 53 MeV**

**PRELIMINARY**

- Preliminary

- Spectrum of Michel electrons from stopping muons

- Energy vs. Range for events stopping in scintillator cubes

-  Mass Distribution

- Preliminary

## 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/ and e/
- A “boosted decision tree” algorithm to separate e, ,  *(See B. Roe et al. NIM A543 (2005))*

- 0 candidate

-  candidate

- e
- candidate

## NuMI Offaxis  MiniBooNE’s Calibration Beam

- Need to verify our PID with e in the signal energy range,but can’t due to blind analysis.
-               Solution: use someone else’s beam!

*Sitting off axis, we see a beam which is enhanced in **e **flux and is in a useful energy range.*

- 100 -200 mr(6 – 12 deg)

## Results for Offaxis NuMI Beam in MiniBooNE

- MiniBooNE sees events from the offaxis NuMI beam
- They show up as events during the 8 s NuMI beam window
- These events have a significant e component that can be used to test our PID system

## MiniBooNE Oscillation Search Method

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

## Expected Event Numbers

**Events with ********e**** Selection Requirements**

**Events with ************ Selection Requirements**

-  Events = 193,730  (mainly  CCQE)(Final data sample for 5.58 × 1020 pot)

- Example Osc Signal = 315 events(m2 = 0.4 eV2 , sin22= 0.017)

- Total Expected Background = 915 events

- Events Time (ns)

- Events Time (ns)

- No Cuts

- Simple Cuts:E > 60 MeVVeto Hits > 6

## Systematic Uncertainties

- Sources of uncertainty for the e 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 + decay
- Neutrino flux from K+ decay
- Neutrino flux from K0 decay
- Neutrino flux from + decay
-  Xsec uncertainties
- External interactions (“Dirt”)
- NC  Mid-ID
- Radiative N
- Optical Model

***Next: Few examples of these systematic uncertainty estimates.***

## Pion and Kaon Production

- pBe Pion production
- pBe production  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.

##  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. CC1) are determined from MiniBooNE data combined with previous external measurements

## Optical Model Uncertainties

- 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  (Cincinnati)
- Fluorescence Spectroscopy (FNAL)
- Time resolved spectroscopy (Princeton, JHU)
- Attenuation (Cincinnati)

***Uncertainties on the parameters associated******with optical model are used to determine the ******uncertainties for the oscillation search***

## Backgrounds Constraints from MiniBooNE Data

**All of the major backgrounds for the oscillation search can be constrained directly from measurements using MiniBooNE data**** **
- NC production
- Largest Mis-ID background is from NC production where one of the decay photons is missed.  This background is constrained from the large fraction of NC 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 e’s
- Intrinsic e background from kaon decay can be constrained by observed e events at high energy where there are no oscillation events
- Intrinsic muon decay e’s
- Largest intrinsic e background is from muon decay and is highly constrained by the observed  events.  The constraint is applied by using the combined e/  oscillation fit.

## NC  Background Constraint

- Using PID variables isolate a very pure sample 0 events from  N   N + 0 (mainly from  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  mis-ID rate using this measured correction factor(Also can be used to correct the  N +  radiative background)

- M Mass Distribution for Various p0 Momentum Bins

## 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

## Kaon Intrinsic e Background Constrained by High Energy Data

- At high energy, candidate e events are mainly from kaon decay
- Small contributions from -decay and 0 mis-id
- Normalization of the kaon intrinsic background can be partially constrained within uncertainties by the level of this high energy data

- Preliminary

## Constraining the Intrinsic e Background from Muon Decay

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

## 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 e/  fit to the observed event distribution vs. energy.

- Monte Carlo Sensitivity Estimate

**90%CL**

## Summary

- From the beginning, MiniBooNE decided to do a “blind analysis”
- Candidate e 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.