1 accelerator neutrino oscillations results and prospects koichiro nishikawa institute for particle...
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Accelerator Neutrino Oscillations Results and Prospects
Koichiro NishikawaInstitute for Particle and Nuclear Studies
KEK
III International Pontecorvo Neutrino Physics School 16-26 September, 2006
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• The present observations are good at discovering a surprise (if it is a large effect) for which small scale (controlled) experiments do not have enough sensitivity.
– Long baseline (100 – 108 km) size of earth, Sun size by luck
• They are however not good at measuring underlying parameters very precisely.
• Inherent uncertainties exist in calculation of various observables:
– Fluxes of solar neutrinos on Earth
• Nuclear reaction cross sections, chemical compositions, opacity, etc.
– Fluxes of atmospheric neutrinos
• Primary cosmic ray flux, nuclear interactions, etc.
• Find model-independent observables
– Solar neutrinos:
• Comparison of NC and CC interactions
• Spectral shape, day/night effect, etc
– Atmospheric neutrinos
• /e ratio
• Zenith angle distribution
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Accelerator experiment• Neutrinos can be measured more than once
– Relative change of spectrum
• Effect of oscillation depend only on neutrino energy (fixed distance)
• Beam energy can be chosen – Type of detector– Neutrino energy determination method can be chosen
)E
Lm27.1(sin2sin.prob
222
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Critical issues
• Only the product F(Ei) x (Ei) are measurable– Flux times cross section as a function of E
• The P(→ must be determined by minimizing the followings– (E) poorly known at low-medium energy
• Two measurements at different distances can reduce the the effect of ambiguities of cross sections
– Fnear(E) , Ffar(Edifferent from 1/r2 unless decay at rest• Different spectrum due to finite decay length and acceptanc
e at two distances – decay volume and distance– PID and Edetermination of observed events
• background processes (eps. NC, etc.) different in near, far
)E()(P)E(F)E(N
)E()E(F)E(Nfarfar
obs
nearnearobs
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Neutrino beams from accelerator with existing technologies
Produce mesons by strong int. and let them decay in weak int.
1. Neutrinos from stopping ’s and ’s
(LSND KARMEN) unique spectrum of e
no problem of Far/Near, cross section, energy determination
2. Neutrinos from in-flight decays
• Wide Band Beam - sign selected by horn system but wide p band accepted, the highest intensity of CHORUS, NOMAD,K2K, MiniBooNE, MINOS, CGSN…..)
– Off-axis beam
• Dichromatic beam-momentum selected by B and Q mangets
– clean but the acceptance beam line limits intensity
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Decay at Rest (DAR)
Small intrinsic e contaminationfew x 10-4
decay in flight contamination ?
Inverse beta decay well known
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LSND/KARMEN Experiments
• 800MeV LINAC– 1mA – 600 sec width – 10msec rep.
• Mineral oil (Cherenkov pattern)
• prompt e and (2.2 MeV) p(n,)d
• 800MeV Rapid cycling syn– 200A– 200 nsec width– 20msec rep.
• Gd loaded scintillator
• prompt e and 7.8MeV) Gd(n,
•single measurement at one position•Ee+ from anti-e + p→e+ +n •unique spectrum for anti-e
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Signal and Background
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Gamma Ray Distribution
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LSND Final Results
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KARMEN Distributions
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With NOMAD and reactor experiments
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sin2 2
m2 (
eV2 )It is impossible to have only 3 neutrinos
involved if all of the effects are the result of neutrino oscillations. Either some of the data are not due to oscillations,
or there must be at least one undiscovered “sterile” neutrino
or there must be CPT violation in the neutrino sector.
or exotic processes
‘Evidence’ of oscillations
e
e
31
23
22
23
21
22
213
232
221
mmmmmm
0mmm
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Experimental issue
• ‘MiniBooNE’ single detector
– compare the results with MC only
• signal = no muon, shower like events, not • Backgrounds = NC production, e in the beam
• PID e,
• Hadron production knowledge
– production by 8 GeV proton →normalization and HE components to interact with NC
– K to give Ke3 decay (K→e+ e)
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A neutrino interaction model/E (10-38cm2/GeV)
Total (NC+CC)
CC Total
CC quasi-elastic
DIS
CC single
NC single 0
E (GeV)
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Intrinsic Intrinsic ννee (from K& (from K&μμ decay) decay) : 236 events: 236 events
OtherOtherννμμ mis-ID: 140 eventsmis-ID: 140 events
ππ00 mis-ID: 294 events mis-ID: 294 events(Neutral Current Interaction)(Neutral Current Interaction)
LSND-like e signal: 300 events
Approximate number of events Approximate number of events and Background expected in Mand Background expected in M
iniBooNEiniBooNE
Charged Current, Quasi-elasticCharged Current, Quasi-elastic 500,000 events500,000 events
Bac
kgro
und
Signal
~10-3 of total neutrino events
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SignalMis-IDIntrinsic νe
Δm2 = 1 ev2
Δm2 = 0.4 ev2
Sensitivity to a SignalSensitivity to a Signal
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PID e seperation e-seperation
NUANCE adjustment
photon propagationin oil simulation
HARP data on K
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Checking the reproducibilityof ’s, detector sim.
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~10-3 of total neutrino events
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Accelerator-based Long Baseline Neutrino Oscillation Experiments
Long = distance>>decay region
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Wide Band Beam• Maximum available neutrino intensity
• Protons hit target
• Pions produced at wide range of angles
• Magnetic horn to focus • Rock shield range out • beam travels through earth to the experiment
• decay / decay ~10-2 ,, Ke3→~1% e contamination
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Horn in K2K
200m
p+Al + + +
HELE
Need measurements of high energy (muon monitor)and low energy (neutrino events at near detector)secondary particle direction
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Neutrino Beam
22
2
22
22
cm
cmcml
cmcmt
1
)0(E)(E
E5.0Em
mm)0(E
MeV35~m2
mmp,
m
E
)(cospp
sinpp
pt~35MeV/c
Typical characteristics
edecay vol.)• lifetime of ~ 0.01• production cross sectionof K/
~ 0.1 and Ke3 ~0.01 divergence ~ 10mrad/E(GeV)• Horn focuses to about a few mrad• Far/near is not scale as 1/r2
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Neutrino event vertex distribution at 300m from target
Width
HE-LE
LE 0.5<EGeV HE 1<EGeV
cm
FWHM4m/300m~ 10 mrad
FWHM2m/300m~ 6 mrad
divergence is dominated by decay angle at these energies
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Critical issues (reminder)
• Only the product F(Ei) x (Ei) are measurable– Flux times cross section as a function of E
• The P(→ must be determined by minimizing the followings– (E) poorly known at low-medium energy
• Two measurements at different distances can reduce the the effect of ambiguities of cross sections
– Fnear(E) , Ffar(Edifferent from 1/r2 unless decay at rest• Different spectrum due to finite decay length and acceptanc
e at two distances – decay volume and distance– PID and Edetermination of observed events
• background processes (eps. NC, etc.) different in near,far
)E()(P)E(F)E(N
)E()E(F)E(Nfarfar
obs
nearnearobs
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Critical issues-1
• (E) poorly known at low-medium energy– Nuclear physics at GeV region
– Pauli blocking
– Nucleon Form factor
– Final state interaction inside nucleus
For several 100~1000km baseline
SciBooNEMinerva
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Quasi-elastic scattering cross-sections
• Two form factors
•MV fixed by e.m. (CVC)
•Axial V form factor
magenta Old MCred new MC
Cross-section ()
10-3
8 cm
2
/Ecm2/GeV)
1 10 100 GeV
n
pW 2
2V,A
2VA
M
q1
1f,f
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Data on charged current processes
• Not well known
• Especially 2~3 GeV
→SciBooNE
→Minerva
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Neutrino spectrum and the far/near ratio (in K2K)
beam
10-6
1.0 2.0
Far/Near Ratio
E(GeV)
beam MC w/PION Monitor Angular acceptance
(well collimated for HE)
Finite decay volume length (shorter for HE, Near better accep. for MH )
300m 250km
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Accelerator NeutrinosPresent Status
K2K (1999-2005 Completed)
MINOS (2005-)
OPERA (2006-)
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• 1995– Proposed to study neutrino oscillation for atmospheric neutrinos anomaly.
• 1999– Started taking data.
• 2000 – Detected the less number of neutrinos than the expectation at a distance of
250 km. Disfavored null oscillation at the 2 level.• 2002
– Observed indications of neutrino oscillation. The probability of null oscillation is less than 1%.
• 2004– Confirm neutrino oscillation at the Confirm neutrino oscillation at the level with both a deficit of level with both a deficit of and and
the distortion of the Ethe distortion of the E spectrum. spectrum.
• 2004 Nov.6– Terminated K2K due to horn trouble and high residual radiation level
Brief history of K2K
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K2K experiment
monitormonitor
Near detectors(ND)
+
Target+Horn200m
decay pipe
SK
100m ~250km
12GeV protons
~1011/2.2sec(/10m10m)
~106/2.2sec(/40m40m)
~1 event/2 days
Signal of oscillation at K2K Reduction of events Distortion of energy spectrum
(monitor the beam center)
E
LmP
22 27.1
sin2sin
E
~105 /2 days
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Particle detection at 250km away
(BG: 1.6 events within 500s 2.4×10-3 events in 1.5s)
TSKTspill
GPS
SKTOF=0.83msec
112 events
Decay electron cut.
20MeV Deposited Energy
No Activity in Outer DetectorEvent Vertex in Fiducial VolumeMore than 30MeV Deposited Energy
Analysis Time Window
500sec
5sec
TDIFF. (s)
-0.2TSK-Tspill-TOF1.3sec
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Analysis Overview
Observation #, p and
interaction MCMeasurement(E), int.
KEK
Far/Near Ratio (beam MC with mon.+ HARP )
Observation# and E
rec.
Expectation# and E
rec.
(sin22, m2)
SK
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Overall normalization error on Nsk for Nov99~
(Event)
Stat 0.28 0.37%
KT 3.32 4.37%
SK 2.28 3.00%
Flux +2.81
-2.59
F/N +4.26
-5.55
NC/CC +0.15
-0.23
nQE/QE +0.38
-0.61
CT 0.46 0.60%
Total +6.53
-7.37
5.34%
KT: dominated by FV errorSK: also.
Errors
HARP~1 %
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Pion Monitor: pion distribution after horn
Measure Momentum / Angle Dist. of π’s Just after Horn/Target
+Well known π Decay Kinematics +Well Defined Decay Volume Geometry
⇒Predict νμ Energy Spectrum at Near Site Far Site
Ring Image Gas Cherenkov Detector (Index of Refraction is Changeable)
To Avoid Severe Proton Beam Background,νμ Energy Information above 1GeV is Available(β of 12GeV Proton ~ β of 2GeV π)
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Good agreement with old data. (Cho et.al.)
Beam MC based on Cho et al.
Error assignment based on this measurements
p
w1 w2 w3 w4 …..: :
: :p, gives two C-light peaksfit withwi • C-light)
index of refraction : p thresholdposition of ring :
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Thin target data need assumption of secondary interaction in targetTotal cross section of p-AlHorn magnetic field ambiguityProton beam profile
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spectrum shape
HARP, Pion monitor and MC comparison
Far/Near ratio vs E
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NEUT: K2K Neutrino interaction MC
• CC quasi elastic (CCQE)
– Smith and Moniz with MA=1.1GeV
• CC (resonance) single (CC-1)
– Rein and Sehgal’s with MA=1.1GeV
• DIS
– GRV94 + JETSET with Bodek and Yan
g correction.• CC coherent
– Rein&Sehgal with the cross section rescale by J. Marteau
• NC
+ Nuclear Effects
/E (10-38cm2/GeV)
Total (NC+CC)
CC Total
CC quasi-elastic
DISCC single
NC single 0
E (GeV)
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Near detector measurements
• 1KT Water Cherenkov Detector (1KT)
• Scintillating-fiber/Water sandwich Detector (SciFi)
• Lead Glass calorimeter (LG) before 2002
• Scintillator Bar Detector (SciBar) after 2003
• Muon Range Detector (MRD)
Muon range detector
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1KT Flux measurement• The same detector technology as Super-K.
– Sensitive to low energy neutrinos.
– Sensitive for NC
KT
SK
KT
SK
KT
SKobsKTSK M
M
dEEE
dEEENN
)()(
)()(exp
Far/Near Ratio (by MC)~1×10-6
M: Fiducial mass MSK=22,500ton, MKT=25ton: efficiency SK-I(II)=77.0(78.2)%, KT=74.5%
NSKexp=158.4 NSK
obs=112+11.6 -10.0
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Near Detector Spectrum Measurements
• 1KT– Fully Contained 1 ring (FC1R) sample.
• SciBar– 1 track, 2 track QE (p≤25), 2 track nQE (2 track nQE (pp>25>25)) wher
e one track is • SciFi
– 1 track, 2 track QE (p≤25), 2 track nQE (p>30) where one track is
(p) for 1track, 2trackQE and 2track nQE samples
(E), nQE/QE
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0-0.5 GeV
0.5-0.75GeV
0.75-1.0GeV
1.0-1.5GeV
••
••
E QE (MC) nQE(MC)
MC templatesKT data
P (MeV/c)
(
MeV
/c)
• flux KEK(E) (8 bins)• interaction (nQE/QE)
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Flux measurements2=638.1 for 609 d.o.f
– ( E< 500) = 0.78 0.36– ( 500 E < 750) = 1.01 0.09– ( 750 E <1000) = 1.12 0.07– (1000 E <1500) = 1.00 (1500 E <2000) = 0.90 0.04– (2000 E <2500) = 1.07 0.06– (2500 E <3000) = 1.33 0.17– (3000 E ) = 1.04 0.18– nQE/QE = 1.02 0.10
The nQE/QE error of 10% is assigned based on the sensitivity of thefitted nonQE/QE value by varying the fit criteria.
>10(20 ) cut: nQE/QE=0.95 0.04• standard(CC-1 low q2 corr.): nQE/QE=1.02 0.03
• No coherent: =nQE/QE=1.06 0.03
(E) at KEK
E
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Super-K oscillation analysis
• Total Number of events
• Erec spectrum shape of FC-1ring- events
• Systematic error term
)(),2sin,(),2sin,(
),2sin,(22
2
xsyst
xshape
xnorm
x
fLfmLfmL
fmL
f x : Systematic error parameters
Normalization, Flux, and nQE/QE ratio are in fx
Near Detector measurements, Beam constraint, beam MC estimation, and Super-K systematic uncertainties.
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Log Likelihood difference from the minimum.
sin22m2[eV2]
lnL lnL- 68%- 90%- 99%
- 68%- 90%- 99%
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disappearance versus E shape distortion
sin22sin22
m2[e
V2]
m2[e
V2]
NSK (#) E shape
Both disappearance of Both disappearance of and the distortion of and the distortion of EE spectrum have the consistent result. spectrum have the consistent result.
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sin22
0.002
0.004
0.006
0.0 0.2 0.4 0.6 0.8 1.0
Normalized by area
Nobs=112 Nexp=158.4
+9.4-8.7
Distortion of the neutrino spectrum
Rate
Best fitsin22=1m2 =2.77 x 10-3
Allowed region
Null oscillation hypothesis excluded at 4.4
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K2K upper bounds on →e
limitlimit
sensitivitysensitivity
K2K-I+II (#obs.=1, #B.G.=1.70)K2K-I+II (#obs.=1, #B.G.=1.70)upper limit (90% CL)upper limit (90% CL) sinsin2222ee=0.13 =0.13 @2.8e-3 [email protected] eV22
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Conclusion
• K2K Oscillation analysis on June99 ~November 6 , 05 full data
1. Long Baseline experiment can be done!
2. Both SK rate reduction and Erec shape distortion has been
observed3. Null oscillation hypothesis has been excluded by 4.41 m2=1.88~3.48x10-3eV2 for sin22=1 @ 90%CL5. sin22, m2 are consistent with atmospheric neutrino results6. e-appearance search is limited by statistics, upper limit (9upper limit (9
0% CL)0% CL) sinsin2222ee=0.13 @2.8=0.13 @2.8 xx 1010-3-3 eV eV22
7. Many studies on low energy neutrino interaction continue
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MINOS experiment
• Two neutrino detectors• Long baseline neutrino oscillation exp
eriment• Fermilab’s NuMI beamline
735 km
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Neutrino beamline
• 120 GeV protons hit graphite target• Two magnetic horns focus positive pions and kaons • Mesons decay in flight in evacuated decay pipe giving rise to almost pure υμ beam• Adjustable neutrino beam energy
νμTarget
HornsDecay Pipe
Absorber
Hadron Monitor
Muon Monitors
Rock
μ+π+
10 m 30 m675 m
5 m 12 m 18 m
Z. Pavlovic
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Adjustable beam energy
• Changing target position changes neutrino beam energy
• 10 cm most favorable for oscillation analysis
• Data in other configurations used for systematic studies
• LE event composition: – 92.9% υμ
– 5.8% υμ
– 1.3% υe / υe
• After target replacement run at 9cm
- 10 cm
- 100 cm
- 250 cm
Target position:
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MINOS Detectors
• Functionally identical– 2.54cm thick steel planes– 4.1×1cm scintillator strips– Multianode PMT readout– Magnetized B~1.3T
Coil
Near Detector
Far Detector
• Near Detector:– 1 km from target– 1 kton– 282 steel and 153 scintillator pla
nes
• Far Detector:– 735 km from target– 5.4 kton– 484 steel/scinitllator planes
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Neutrino interactions
CC Event NC Event
•long track + hadronic activity at vertex
•short event, often diffuse
3.5m 1.8m
Monte CarloMonte Carlo
υμ μ
X X
υ υ • Likelihood procedure used to differentiate between NC and CC events
• NC contaminations in lowest energy bins
Eυ = Eshower+Pμ
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Event classification
• Good agreement between data and MC for input variables
y=E shw/E υ
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Event Classification
Event Classification Parameter
rejected asNC like
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Tuning hadron production MC for ND data
• Fit ND data from all beam configurations : various Target-horn configuration
• Simultaneously fit νμ and νμ spectra(Use MIPP data in future)
υμ LE010/185kALE010/185kA LE100/200kA LE250/200kA
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Beam matrix method
• Construct beam matrix using MC
• Use Near Detector data to predict the “unoscillated” spectrum at the Far detector
• Spectrum known at 2-4% level
X
=
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Observed FD events
• Energy dependant deficit
Data SampleFD
Data
Expected(MC)
Data/Prediction(Matrix Method)
All 563 738±30 0.76 (4.4 )
(<10 GeV) 310 496±20 0.62 (6.2 )
(<5 GeV) 198 350 ±14 0.57 (6.5
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Far Detector Data timing to spill time
• Time stamping of the neutrino events is provided by two GPS units
• Timing of neutrino candidates consistent with spill signal
• Easy to separate cosmic muons (0.5Hz)
• Time distribution is as expected
NuM
I onl
y m
ode
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Systematic errors
• Systematic shifts in the fitted parameters are computed using MC “data samples” (at best fit point)
UncertaintyShift in Δm2
(10-3 eV2)
Shift in
sin2(2θ)
Near/Far normalization 4% 0.065 <0.005
Absolute hadronic energy scale 10% 0.075 <0.005
NC contamination 50% 0.010 0.008
All other systematic uncertainties 0.041 <0.005
Total systematic (summed in quadrature) 0.11 0.008
Statistical error (data) 0.17 0.080
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Far spectrum
• Best fit for 2.5x1020 POT
423200160
232 c/eV1038.2||
..Δm
080232 00.1)2(sin .
2 /n.d.f = 41.2/34 = 1.2
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Allowed region
• Fit is constrained to physical region: sin2(223)≤1
080232 00.1)2(sin .
423200160
232 c/eV1038.2||
..Δm
2 /n.d.f = 41.2/34 = 1.2
)3.2( 2min
)61.4( 2min
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Unconstrained fit
2-32 eV10 26.2 Δm
07.12sin2 2 /n.d.f = 40.9/34 = 1.2
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Summary
• Analyzed data using 2.5×1020 POT
• Systematic errors well under control
• MINOS disfavors no disappearance hypothesis by 6.2σ (<10GeV)
• Best fit to oscillation hypothesis yields:
• Forthcoming results:
– υμ → υe search
– υμ → υs search
423200160
232 c/eV1038.2||
..Δm
080232 00.1)2(sin .
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Forthcoming improvements • Use antineutrinos + neut
rinos• Expanded FD fiducial v
olume• Improved event reconstr
uction + selection• 3.5×1020POT through 8/
07• Next year significant pr
oton accelerator improvements– 4.6×1020ppp (demons
trated in MI)
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K2K and MINOS have established neutrino oscillation in muon-neutrino disappearance
as observed in atmospheric neutrino observation in Super-Kamiokande
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Collaboration :
13countries 37 Institutes
An Emulsion-Counter Hybrid experiment for Tau neutrino Appearance
Detection.
OPERA
OPERA Detector
CNGS Beam
730km
CNGS First Neutrino to Gran Sasso at 2006 August
Current phase: Installation of Emulsion target (ECC Bricks)
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Expected signal and background in OPERA in 5 years
mrad
I.P.=5-20m
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Beam events:~horizontal tracksBeam angle:3.35° from below
Cosmic rays muons
Tracks zenith angle (no beam timing requirement)
319 on-spill events are observed
¾ muons coming from the rock¼ neutrino interactions in the detector (CC+NC)
The observed numbers are consistent with the expectation
Detector live-time ~95%
First neutrino : Muons from Neutrino Interactions 2006 August
Recorded "Rock Muon" event
CERN
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Summary• First CNGS Neutino in 2006: total 8.2x1017 pot
– Electric detector's performance was confirmed.– Succeeded to connect tagged muons from the Electric detect
or to the Emulsion target (CS and ECC).
• Current status in Gran Sasso: ECC brick production and installation is going on.– Current production and insertion Speed ~300ECC/day about
1/3 of planned. Need speed up 700ECC/day. – until the end of April 2007
• CNGS 2007 run is planned in this Autumn.– OPERA will start the Physics RUN with 60,000ECC bricks.– ~300 neutrino interaction ~10 charm events for decay det
ection and analysis. And <1 Tau neutrino event.
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Three generation neutrinos
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Current status of neutrino mass and mixingsAnything new?
Solar + KamLAND
J.W.F. Valle, hep-ph/0410103J.W.F. Valle, hep-ph/0410103
12, m122 23, m32
2 13, m312
Only upper limit on 13
No info. on AtmosphericMINOS、 K2K
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Three Flavor Mixing in Lepton Sector
3
2
1CPMMNSVU
e
100
0
0
0
010
0
0
0
001
U 1212
1212
1313
1313
2323
2323PMNS cs
sc
ces
esc
cs
sci
i
e
Weak eigenstates m1
m2
m3
mass eigenstates
100
0e0
00e
V 2
1
i
i
CPM
12, 23, 13
+ (+2 Majorana phase)
m122, m23
2, m132
cij = cosij, sij=sinij
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Present Knowledge
solar neutrino (SK,SNO), reactor (KamLAND) Matter effect fix the sign of m2 12
07.00.842sin 122 0meV103.8m 2
12252
12
atm. neutrino (SK), long-baseline (K2K,MINOS)Oscillation probability sqaured is measured
545
00.196.02sin
23
232
reactor neutrino exp.(CHOOZ), K2K, MINOS
limit)(upper 16.02sin 132
to be the larger component in e
to be the larger component in e unkowneV105.2m 232
13
unkowneV105.2m 23223
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Three ambiguities
232 2sin 2323 (( octantoctant ) ) and and
2 fold ambiguity for 2 fold ambiguity for
MNS13 , undeterminedundetermined
213m sign of m2
1 3
2 fold ambiguity for mass
“best fit” 23 =45 : no octant ambiguity
11
22
33
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Regardless of ‘ambiguities,only the measurements of can open the
next phases of progress