search for electron neutrino appearance in minos

Search for Electron Neutrino Appearance in MINOS

Mhair OrchanianCalifornia Institute of Technology

On behalf of the MINOS Collaboration

DPF 2011 Meeting – Providence, RIAugust 8-13, 2011

Search for Electron Neutrino Appearance in MINOS 2

Basics of Neutrino Oscillation• 3 weak eigenstates 3 mass eigenstates

– Related by the unitary leptonic mixing matrix U

• Can compute the transition probability in the usual way:

ijijijijii

i scvUv sin,cos *

Majorana

i

i

cAtmospheriMixingCross

i

i

Solar

ee

cssc

ces

esccssc

U

1000000

00

001

0010

0

10000

2/

2/

2323

2323

1313

1313

1212

1212

2

1

iii

i UU PropAmp *

ELimi 2expProp 2i

ELmUUUU

ELmUUUU

P

ijji

jjii

ijji

jjii

2**

22**

2

54.2sin2

27.1sin4

Amp

atmospheric

atmospheric

Mhair Orchanian ([email protected])

ELmP e /27.1sinsin2sin 232

223

213

2


Motivation – Why Study 13?• Sufficiently large 13 provides

access to mass hierarchy and through P(e)

• Finding CP-violation in the lepton sector may help explain baryon asymmetry in the universe

• Finding 13 = 0 may point to a new symmetry

PhysRevD.82.051102

MINOS 2010


Phys.Lett.B466:415-430,1999

2.3210-3

CHOOZ


How Do We Do It?• MINOS designed and optimized to study disappearance• Challenging to distinguish EM showers from hadronic showers

• Need strong(er) event selection algorithm to improve 13 sensitivity

EM Showers in MINOS Detector Parameters

Radiation length: 1.76 cm Steel thickness: 2.54 cm

Molière radius: 3.7 cm Strip width: 4.12 cm



How LEM Works•LEM (Library Event Matching) is based on pattern recognition algorithm•Uses raw hit information instead of reconstructed quantities

5


Original eventMC

Good matchMC

Bad matchMC

planes strips

dnPnP0

21 ,,ln L


The LEM PID


Reconstructed Energy Distributions

for Signal and Background

Neural Net

•Optimal cut: LEM > 0.7•Optimal binning for PID shape fit:

0.6 < LEM < 0.70.7 < LEM < 0.80.8 < LEM < 1.0


CHOOZ upper limit

2010-style analysis with new data

Counting expt with LEM

Shape fit with LEM

Since 2010 result: ● 1.21020 PoT (17%) more data● Improved event selection variable (LEM): 15% sensitivity gain● Shape fit: 12% sensitivity gain

Improvements to the Analysis



Background Prediction• Each background component (NC, CC, beam

e CC) “extrapolates” differently from Near Detector to Far Detector must make prediction component-by-component

• For component in analysis bin i:


MCi

MCiData

iPred.i Near

FarNearFar

,

,,,


Background Prediction• For component (NC, CC, beam e CC) in

analysis bin i:


MCi

MCiData

iPred.i Near

FarNearFar

,

,,,

Total data rate in each configuration MC component ratios

between configurations

Different beam configurations



analysis bin i:


MCi

MCiData

iPred.i Near

FarNearFar

,

,,,

Data components in standard configuration

Summing over energy bins:60% NC29% CC11% beam e CC



analysis bin i:


MCi

MCiData

iPred.i Near

FarNearFar

,

,,,

Use ratio to extrapolate from Near to Far:

•Flux (1/R2, acceptance, decay kinematics, focusing)

•Fiducial volume•Energy smearing• disappearance•Detector effects

Note: Error bars are systematic.



analysis bin i:


MCi

MCiData

iPred.i Near

FarNearFar

,

,,,

Event Classsin2 (213)

0 0.1NC 34.1 34.1

CC 6.7 6.7e CC 6.4 6.2 CC 2.2 2.1

Total Background 49.4 49.1 e CC 0.2 19.1

Note: Predictions assume CP = 0, 23 = /4, normal mass hierarchy.

Arise from oscillations base prediction on measured Near CC spectrum


The Far Detector Energy Spectrum



Outside the Signal Region


Expect negligible signal for LEM < 0.5 use as test of entire analysis chain• Predicted background

(i.e., event count if13 = 0): 370 19 (stat)

• Observed data: 377


The Far Detector LEM Distribution


• Above optimal cut of 0.7:

– Predicted background: 49.5 2.8 (syst)7.0 (stat)

– Observed data: 62(1.7 excess)


Best Fit• Official fit performed in 3 PID

bins 5 reconstructed energy bins

• Assuming CP = 0, 23 = /4, and normal mass hierarchy, best fit is sin2213 = 0.041



Official Result• Feldman-Cousins contours• Uncertainties in other

oscillation parameters accounted for

• Assuming CP = 0, 23 = /4, and normal (inverted) mass hierarchy:– sin2(213) < 0.12 (0.20) [90% C.L.]– sin2(213) = 0.041 (0.079) [Best Fit]

• sin2(213) = 0 excluded at 89% C.L.


arXiv:1108.0015


BACKUP SLIDES



Probability of e Appearance

2

2

122

232

4

23123

23122

2

2

232

1

42

3132131132

132

sin2sincos

,11sinsincos2sin2sincos

,11sinsinsin2sin2sinsin

,1

1sinsin

where,2sin2sin2sin

:2.02sinFor

xxT

xx

xxT

xx

xxT

xxT

TTTTP e

231

231

231

221

224

301~

mENGx

ELm

mm

eF



LEM LibraryLibrary consists of 50 million Far Detector Monte Carlo Events

● 20M e CC and 30M NC● Optimal library = large library with a fraction of 0.3 – 0.4 e CC● NC is sufficient to represent the background – CC events are either cut

by preselection, or look very similar to NC hadronic showers.

Measure of sensitivity

Total library size

Fraction of library that is signal events



Far Detector Events in Analysis Region



5-6 GeV Events



Best Fit Shown on Counting Experiment Energy Spectrum



Overlay of MINOS and T2K Allowed Regions

* arXiv:1106.2822

*

NOT a combined fit


search for electron neutrino appearance in minos

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