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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
e
e
cs
sc
ces
esc
cs
sc
U
100
00
00
0
0
001
0
010
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100
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02/
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
Search for Electron Neutrino Appearance in MINOS 3
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
Mhair Orchanian ([email protected])
Phys.Lett.B466:415-430,1999
2.3210-3
CHOOZ
Search for Electron Neutrino Appearance in MINOS 4
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
Mhair Orchanian ([email protected])
Search for Electron Neutrino Appearance in MINOS 5
How LEM Works•LEM (Library Event Matching) is based on pattern recognition algorithm•Uses raw hit information instead of reconstructed quantities
5
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Original eventMC
Good matchMC
Bad matchMC
planes strips
dnPnP0
21 ,,ln L
Search for Electron Neutrino Appearance in MINOS 6
The LEM PID
Mhair Orchanian ([email protected])
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
Search for Electron Neutrino Appearance in MINOS 7
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
Mhair Orchanian ([email protected])
Search for Electron Neutrino Appearance in MINOS 8
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:
Mhair Orchanian ([email protected])
MCi
MCiData
iPred.i Near
FarNearFar
,
,,,
Search for Electron Neutrino Appearance in MINOS 9
Background Prediction• For component (NC, CC, beam e CC) in
analysis bin i:
Mhair Orchanian ([email protected])
MCi
MCiData
iPred.i Near
FarNearFar
,
,,,
Total data rate in each configuration MC component ratios
between configurations
Different beam configurations
Search for Electron Neutrino Appearance in MINOS 10
Background Prediction• For component (NC, CC, beam e CC) in
analysis bin i:
Mhair Orchanian ([email protected])
MCi
MCiData
iPred.i Near
FarNearFar
,
,,,
Data components in standard configuration
Summing over energy bins:60% NC29% CC11% beam e CC
Search for Electron Neutrino Appearance in MINOS 11
Background Prediction• For component (NC, CC, beam e CC) in
analysis bin i:
Mhair Orchanian ([email protected])
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.
Search for Electron Neutrino Appearance in MINOS 12
Background Prediction• For component (NC, CC, beam e CC) in
analysis bin i:
Mhair Orchanian ([email protected])
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
Search for Electron Neutrino Appearance in MINOS 13
The Far Detector Energy Spectrum
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Search for Electron Neutrino Appearance in MINOS 14
Outside the Signal Region
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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
Search for Electron Neutrino Appearance in MINOS 15
The Far Detector LEM Distribution
Mhair Orchanian ([email protected])
• Above optimal cut of 0.7:
– Predicted background: 49.5 2.8 (syst)7.0 (stat)
– Observed data: 62(1.7 excess)
Search for Electron Neutrino Appearance in MINOS 16
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
Mhair Orchanian ([email protected])
Search for Electron Neutrino Appearance in MINOS 17
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.
Mhair Orchanian ([email protected])
arXiv:1108.0015
Search for Electron Neutrino Appearance in MINOS 18
BACKUP SLIDES
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Search for Electron Neutrino Appearance in MINOS 19
Probability of e Appearance
2
2
122
232
4
23123
23122
2
2
232
1
42
3132131132
132
sin2sincos
,1
1sinsincos2sin2sincos
,1
1sinsinsin2sin2sinsin
,1
1sinsin
where,2sin2sin2sin
:2.02sinFor
x
xT
x
x
x
xT
x
x
x
xT
x
xT
TTTTP e
231
231
231
221
22
4
30
1~
m
ENGx
E
Lm
m
m
eF
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Search for Electron Neutrino Appearance in MINOS 20
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
Mhair Orchanian ([email protected])
Search for Electron Neutrino Appearance in MINOS 21
Far Detector Events in Analysis Region
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Search for Electron Neutrino Appearance in MINOS 22
5-6 GeV Events
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Search for Electron Neutrino Appearance in MINOS 23
Best Fit Shown on Counting Experiment Energy Spectrum
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Search for Electron Neutrino Appearance in MINOS 24
Overlay of MINOS and T2K Allowed Regions
* arXiv:1106.2822
*
NOT a combined fit
Mhair Orchanian ([email protected])