# Presentation: 470696

## A Search for e Oscillation with MiniBooNE

- A Search for e Oscillation with MiniBooNE

- Hai-Jun Yang
- University of Michigan, Ann Arbor
- (on behalf of MiniBooNE Collaboration)
- The 6th KEK Topical Conference
- Frontiers in Particle Physics and Cosmology
-  KEK, Tsukuba, Japan, February 6-8, 2007

## Outline

- Physics Motivation
- The MiniBooNE Experiment
- Neutrino Beam Flux
- Event Reconstruction & Identification
- NuMI / MiniBooNE Data vs. MC
- Measurement of Dirt Events
- Expected Neutrino Oscillation Result

- H.J. Yang - MiniBooNE

- 2/6/2007

## The LSND Experiment

***Oscillations?***

- Signal:    p  e+ n
- 			 n p  d (2.2MeV)

- LSND took data from 1993-98
- Nearly 49000 Coulombs of
- protons on target
- Baseline: 30 meters
- Neutrino Energy: 20-55 MeV
- LSND Detector:
-   -- 1280 phototubes
-   -- 167 tons Liquid Scintillator
- Observe an excess ofe :  -- 87.9 ± 22.4 ± 6.0 events.

- H.J. Yang - MiniBooNE

- 2/6/2007

## The LSND Experiment

- H.J. Yang - MiniBooNE

- 2/6/2007

## Physics Motivation

-  If the LSND signal does exist, it will imply new physics beyond SM.
-  The MiniBooNE is designed to confirm or refute LSND oscillation
-      result at m2 ~ 1.0 eV2 .

- m2atm + m2sol ≠ m2lsnd

**K2K, Minos**

- H.J. Yang - MiniBooNE

- 2/6/2007

## How can there be 3 distinct m2 ?

**Mass Difference Equation: **
**	****(m****1****2 ****–m****2****2****) + (m****2****2****-m****3****2****) = (m****1****2 ****–m****3****2****)**
- One of the experimental measurements is wrong
- One of the experimental measurements is not neutrino oscillations:
-   Neutrino decay
-   Neutrino production from flavor violating decays
- Additional “sterile” neutrinos involved in oscillation
- CPT violation or CP violation + sterile ’s allows different mixing for ’s and  bars.

- H.J. Yang - MiniBooNE

- 2/6/2007

## The MiniBooNE Experiment

- Proposed in summer 1997,operating since 2002
**The goal**** of the MiniBooNE Expriment****: **** ****to confirm or exclude the LSND result and extend the explored oscillation parameter space**
- 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
- Expected ~ 90% C.L. for most of LSND allowed region

- H.J. Yang - MiniBooNE

- 2/6/2007

## The MiniBooNE Collaboration

-             _[University of Alabama](http://ua1vm.ua.edu/~physics/)_
-                   S.Koutsoliotas
-              _[Bucknell](http://www.eg.bucknell.edu/physics/)__[ University](http://www.eg.bucknell.edu/physics/)_
-           R.A.Johnson, J.L.Raaf          _[University of Cincinnati](http://nimrod.phy.uc.edu/)_
-       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 and State University*__    _
-                            E.Hawker  *Western Illinois University*
-                            A.Curioni, B.T.Fleming  *Yale University*

- H.J. Yang - MiniBooNE

- 2/6/2007

## Fermilab Booster

- MiniBooNE

- H.J. Yang - MiniBooNE

- 2/6/2007

## The MiniBooNE Experiment

- The FNAL Booster delivers 8 GeV protons to the MiniBooNE beamline.
- The protons hit a 71cm beryllium target producing pions and kaons.
- The magnetic horn focuses the secondary particles towards the detector.
- The mesons decay into neutrinos, and the neutrinos fly to the detector, all other secondary particles are absorbed by absorber and 450 m dirt.
- 5.579E20 POT for neutrino mode since 2002.
- Switch horn polarity to run anti-neutrino mode since January 2006.

- H.J. Yang - MiniBooNE

- 2/6/2007

## MiniBooNE Flux

- The intrinsic *e* , ~0.5% of the
- neutrino flux, are one of the major
- backgrounds for   e search.

* **L(m), E(MeV), ****m**2**(eV**2**)*

- H.J. Yang - MiniBooNE

- 2/6/2007

## Understanding Neutrino Flux (I)

- E910 @ BNL + previous world data fits
- Basis of current MiniBooNE  production model
- HARP @ CERN, 8 GeV Proton Beam
- MiniBooNE target slug - thin target (5, 50, 100 %)
- Measure production

- H.J. Yang - MiniBooNE

- 2/6/2007

## Understanding Neutrino Flux (II)

- Little Muon Counter (LMC)
- Scintillating fibre tracker 7 degrees off axis
- K decays produce wider angle  than  decays
- K production is deduced by measuring off-axis 

- H.J. Yang - MiniBooNE

- 2/6/2007

## The MiniBooNE Detector

- 12m diameter tank
- Filled with 800 tons of pure
-       mineral oil
- Optically isolated inner region with 1280 PMTs
- Outer veto region with 240 PMTs.

- H.J. Yang - MiniBooNE

- 2/6/2007

## PMT

- Delayed Scintillation

- H.J. Yang - MiniBooNE

- 2/6/2007

## Energy Calibration

-  Michel e  from  decay:  low energy 52.8 MeV.

- cosmic ray  + tracker + cubes: calibrate 
-     energy ranging from 100 ~ 800 MeV

- 0 mass peak: calibrate medium energy,
-      photons decay from 0 ranging 50 ~ 400 MeV

- Michel e: E~15%

- 0: m0~20 MeV/c2

- H.J. Yang - MiniBooNE

- 2/6/2007

## Neutrino Candidates

- DAQ triggered on beam from Booster
- Detector read out for 19.2 s
- Neutrino pulse through detector lasts 1.6 s
- 1.09 neutrino candidates / 1E15 POT
- With a few very simple cuts (time window, tank/veto hits) to obtain pure neutrino events.

- H.J. Yang - MiniBooNE

- 2/6/2007

## Event Topology

- H.J. Yang - MiniBooNE

- 2/6/2007

## Event Reconstruction

- To reconstruct event position, direction, time, energy and invariant mass etc.
- Cerenkov light – prompt, directional
- Scintillation light – delayed, isotropic
- Using time likelihood and charge likelihood method to determine the optimal event parameters.
- Two parallel reconstruction packages
- S-Fitter is based on a simple, point-like light source model;
- P-Fitter differs from S-Fitter by using more 0th approximation tries, adding e/ tracks with longitudinally varying light source term, wavelength-dependent light propagation and detection, non-point-like PMTs and photon scattering, fluorescence and reflection.

- H.J. Yang - MiniBooNE

- 2/6/2007

## Particle Identification

- Two complementary and parallel methods:
- Log-likelihood technique:
- simple to understand, widely used in HEP data analysis
- Boosted Decision Trees:
- Non-linear combination of input variables
- Great performance for large number of input variables (about two hundred variables)
- Powerful and stable by combining many decision trees to make a “majority vote”

- H.J. Yang - MiniBooNE

- 2/6/2007

## Boosted Decision Trees

-           How to build a decision tree ?
- For each node, try to find the best variable and splitting
- point which gives the best separation based on Gini index.
- Gini_node = Weight_total*P*(1-P), P is weighted purity
- Criterion = Gini_father – Gini_left_son – Gini_right_son
- Variable is selected as splitter by maximizing the criterion.

-           How to boost the decision trees?
- Weights of misclassified events in current tree are increased, the
- next tree is built using the same events but with new weights,
- Typically, one may build few hundred to thousand trees.

-           How to calculate the event score ?
- For a given event, if it lands on the signal leaf in one tree, it is
- given a score of 1, otherwise, -1. The sum (probably weighted)
- of scores from all trees is the final score of the event.

- H.J. Yang - MiniBooNE

- 2/6/2007

## Performance vs Number of Trees

-  Boosted decision trees focus on the misclassified events which usually have high weights after hundreds of tree iterations. An individual tree has a very weak discriminating power; the weighted misclassified event rate errm is about 0.4-0.45.

- The advantage of using boosted decision trees is that it combines many decision trees,  “weak” classifiers, to make a powerful classifier. The performance of boosted decision trees is stable after a few hundred tree iterations.

- Ref1: H.J.Yang, B.P. Roe, J. Zhu, “Studies of Boosted Decision Trees for MiniBooNE Particle Identification”,
-           Physics/0508045, Nucl. Instrum. & Meth. A 555(2005) 370-385.
- Ref2: B.P. Roe, H.J. Yang, J. Zhu, Y. Liu, I. Stancu, G. McGregor, ”Boosted decision trees as an alternative to
-           artificial neural networks for particle identification”, physics/0408124, NIMA 543 (2005) 577-584.

- H.J. Yang - MiniBooNE

- 2/6/2007

## Blindness Analysis

- We do not look into the data region where the e oscillation candidates are expected.
- We are allowed to use part sample to check the goodness of Monte Carlo modeling
- Some of the information in all of the data
- All of the information in some of the data
- To use NuMI sample as an useful cross check
- To use  background events to study the agreement of Data and Monte Carlo events.

- H.J. Yang - MiniBooNE

- 2/6/2007

## NuMI Sample

- H.J. Yang - MiniBooNE

- 2/6/2007

## NuMI Sample

- H.J. Yang - MiniBooNE

- 2/6/2007

## NuMI Sample

- H.J. Yang - MiniBooNE

- 2/6/2007

## MiniBooNE Data VS. Monte Carlo

- Outputs of Boosted Decision Trees

- Visible Energy, Tank Hits, Radius

- H.J. Yang - MiniBooNE

- 2/6/2007

## MiniBooNE Event Rates

-   events currently “on-tape”
- 5.6E20 protons-on-target (POT)

- H.J. Yang - MiniBooNE

- 2/6/2007

## Measurement of Dirt Events

- Neutrino beam interacts with dirt outside of tank, the high energy photons
-     (100 ~ 300 MeV) sneak into the tank to produce electron-like Cerenkov ring.
- N_dirt_measured / N_dirt_expected = 0.99 ± 0.15
- Dirt events contribute ~10% of background for oscillation nue search.

**Event Type of Dirt after PID cuts**

- H.J. Yang - MiniBooNE

- 2/6/2007

## Expected Nue Oscillation Events

- N_oscnue ~ 239 (m2=1.0 eV2, sin22=0.004), N_background ~ 702, N_dirt ~ 80

- + HE box data

- H.J. Yang - MiniBooNE

- 2/6/2007

## Nue Oscillation Sensitivity

- MiniBooNE aims to cover most of
-     LSND allowed region at 90% CL.
- We are currently finalizing systematic error matrix from beam flux, cross sections, detector modeling, optical modeling etc.
- We are finalizing analysis program.
- We anticipate to open box shortly.

- H.J. Yang - MiniBooNE

- 2/6/2007