• Present status of oscillation studies by atmospheric neutrino experiments
νμ→ντ 2 flavor oscillations 3 flavor analysis Non-standard explanations
Search for CC ντ events• Future prospects Possible detectors Physics• Summary
NuFact02, July 2002, London
Takaaki Kajita ( ICRR, Univ. of Tokyo )
Present status of oscillation studies by atmospheric neutrino experiments
Super-Kamiokande
Soudan-2
MACRO
Present status of atmospheric neutrino experiments
Super-Kamiokande
Soudan-2 : stopped data taking.
MACRO
Plastic container
Top
Side
New (almost final) data from Soudan-2• 5.9 kton ・ yr exposure• Partially contained events included.• L/E analysis with a “high resolution” sample• Total number of events: 403.6 (high resolution sample: 245.5 event
s, PC: 39.0)
Zenith angle L/E distribution
e
μ
Down-goingUp-going
(Final) MACRO data
or
νμ→ντ
Δm2 = 2.5×10-3
Consistent with oscillation.
L/E analysis with momentum measurement is also consistent with osc.
Super-Kamiokande data
• Whole SK-1 data have been analyzed.1489day FC+PC data + 1678day upward going muon data
1-ring e-like 1-ring μ-like multi-ring μ-like up-going μ
Up-going Down-going
No osc.
Osc.
stopping
Through going
< 1.3GeV
> 1.3GeV
νμ→ντ oscillation results
Kamiokande
Soudan-2
MACRO
Super-K
sin22θ> 0.92 Δm2=(1.6 – 3.9)×10-3eV2
3 flavor analysis
●Assumption / Approximation
mν3
mν2
mν1
Δm12=02
Δm13 = Δm23 = Δm2 2 2
Δm , θ13, θ232
Matter effect !
Allowed parameter region
Pure, maximal νμ→ντ
90%CL
99%CL
No evidence for non-zero θ13. Consistent with reactor exp.
Super-K
(3 flavor, 1 mass scale dominance, normal mass hierarchy)
Oscillation to sterile neutrinos?Pure νμ→νs oscillation: (1) NC deficit & (2) Matter effect
NC enriched multi-ring events
Super-K 79ktyr
High E. PC
Through going μ
Super-K
Vertical / Horizontal ratio (through going μ)
MACRO
νμ→ντ
νμ→νs
νμ→νs is disfavored > 99%.
(1) NC deficit (2) Matter effect
Oscillation to sterile neutrinos?• Use all the SK data (including NC, up-through-going-muons
and High-E PC).• . cossin
s
pure pure s sin2
Neutrino decay ?
Decay scenario can explain the CC data well. 2
min=141.5/152 dof @sin2= 0.33 m3/3=1.0x10-2GeV/km
Oscillation
decay
Log10[L/E(km/GeV)]
★Scenario (V.Barger et al., PLB 462 (1999) 109):
νμ=cosθν2 +sinθν3
decay X For Δm2→0; P(ν→ν) = (cos2θ+ sin2θe-αL/2E)2
α=m/τ
Neutrino decay vs. NC data• NC data should also decrease due to decay into sterile state.
FC multi-ring NC enriched sample
The 99%CL allowed region by FC 1-ring+PC+up- samplesis almost excluded at 99%CL by the NC enriched sample.
Allowed and excluded parameter regions
Allowed (by CC data)
Excluded (by NC data)
Use Up/Down to test decay scenario
Search for CC ντ events
CC ντ events
ντ
ντ
τ
hadrons
● Many hadrons .... (But no big difference with other events . )
BAD τ- likelihood analysis
● Upward going only
GOOD Zenith angle
Only ~ 1.0 CC ντ FC events/kton ・ yr
(BG (other ν events) ~ 130 ev./kton ・ yr)
Tau likelihood analysis
Multi-ring Down-ward
Multi-ringUp-ward BG MC
+BG MC
Selection Criteria multi-GeV, multi-ring most energetic ring is e-like log(likelihood) > 0 (multi-ring) > 1 (single-ring)
total energy number of rings number of decay electrons max(Ei)/ΣEi distance between interaction point and decay-e point max(P) Pt/Evis3/4 PID likelihood of most energetic ring
τ-like τ-like
Tau analysis results
B.G.
+BG
Independent analysis by Neural Network
Nτ= 145±44+11/-16
Nτexpected=86
Nτ= 99±39+13/-21
Consistent with νμ→ντ.
Max. likelihood analysis
Future atmospheric neutrino experiments
★ Really “oscillation”?
★ How accurate can sin 2θ23 and Δm23 be determined ?
★ Is θ13 measurable ?
★ Sign of Δm2 ?
Topics
2 2
Possible future atmospheric neutrino detectors
Magnetized large tracking detector (MONOLITH, ….)
Very large water Cherenkov detector (UNO, Hyper-Kamiokande, …..)
Really oscillation ?
Assume; Δm2=2×10-3eV2
2.8 Mton ・yr (UNO)
0.14 Mton ・yr (MONOLIT
H)
Use up-going events L = 2Rcosθ⇒ z
Large L Need to measure high-⇒energy events
Magnetized detectorVery large detector
Super-K may not be too small…..
70 year MC (1.6Mtonyr)
First osc. mim.
Use only high L/E resolution events
Accuracy of sin22θ measurement
Standard SK analysis with the present SK systematics
0.11 Mton ・yr 0.23
0.9
90%C.L.
δ (sin22θ) = 3% Exposre(Mt
onyr)
Up sin22θ
Down 2= 1 - +ε
Systematic error related to Up/Down is small (2% @SK)
Precise determination of
sin22θ 90%
Accuracy of Δm2 measurement
L/E analysis
0.14 Mton ・yr
0.14 Mton ・ yr (MONOLITH)
Magnetized tracking detector
First minimum Δm2
δ(Δm2) = 6%
Measurement of θ13 ?
Matter effect !
Measurement of θ13 ?
Matter effect !
Reconstructed momentum (GeV/c)
CosΘ
Up
Down 2
1
(e-like)osc
(e-like)no-osc
1 10
Water Ch.
Reconstructed momentum (GeV/c)
0.9 Mton ・ yr
cosΘ < - 0.2 (up going)
sin θ13=0.0262
~ 4σ effect in 0.9 Mton ・ yr
1 10
Large water Ch. detector
Measurement of θ13 and sign of Δm ?
Matter effect
2
Charge identification (Magnetized tracking detector needed)
Determination of sign of Δm2 at 90%CL.
Δm2=2.5×10-3 sin2θ =0.0213
SummaryPresent status • All the data are consistent with pure νμ→ντ oscillations.
• No evidence for θ13.• No evidence for physics beyond standard neutrino osci.• Hint of τ appearance.
Future prospects• If much larger detectors and/or magnetized tracking dete
ctors are constructed, our understanding of neutrino masses and mixing will be improved significantly:
L/E, determination of oscillation parameters (23), θ13, sign of Δm , ….
sin22θ > 0.92 Δm2 = (1.6 – 3.9)×10-3 eV2
(SK, 90%CL)
2
Top Related