Transcript スライド 1

NuFact02, July 2002, London
Takaaki Kajita ( ICRR, Univ. of Tokyo )
• 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
Present status of oscillation studies by
atmospheric neutrino experiments
Soudan-2
Super-Kamiokande
MACRO
Present status of atmospheric neutrino experiments
Plastic container
Soudan-2 :
stopped data
taking.
Top
Side
Super-Kamiokande
MACRO
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 events,
PC: 39.0)
Zenith angle
L/E distribution
e
μ
Up-going
Down-going
(Final)
MACRO data
νμ→ντ
Δm2 = 2.5×10-3
Consistent with
oscillation.
or
L/E analysis with
momentum measurement
is also consistent with osc.
Super-Kamiokande data
1489day
data have
+ 1678day
upward going muon data
• WholeFC+PC
SK-1 data
been analyzed.
1-ring e-like
1-ring μ-like multi-ring μ-like
up-going μ
stopping
< 1.3GeV
No osc.
Osc.
> 1.3GeV
Up-going
Down-going
Through
going
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
2
Δm12=0
2
2
Δm13 = Δm23 = Δm
Δm2 , θ13, θ23
2
Allowed parameter region
(3 flavor, 1 mass scale dominance, normal mass hierarchy)
Super-K
99%CL
Pure, maximal
νμ→ντ
90%CL
No evidence for non-zero θ13. Consistent with reactor exp.
Oscillation to sterile neutrinos?
Pure νμ→νs oscillation: (1) NC deficit & (2) Matter effect
(1) NC deficit
High E. PC
NC enriched
multi-ring events
Super-K
(2) Matter effect
Vertical / Horizontal
ratio (through going μ)
Super-K 79ktyr
MACRO
Through
going μ
νμ→ντ
νμ→νs
νμ→νs is disfavored > 99%.
Oscillation to sterile neutrinos?
• Use all the SK data (including NC, up-through-going-muons
and High-E PC).
• .nm g cosxnt + sinxn s
pure nm g nt
sin2x
pure nm g ns
Neutrino decay ?
★Scenario
(V.Barger et al., PLB 462 (1999) 109):
νμ=cosθν2 +sinθν3
decay
Δm2→0;
sin2θe-αL/2E)2
X
decay
For
P(ν→ν) = (cos2θ+
Oscillation
α=m/τ
Log10[L/E(km/GeV)]
Decay scenario can explain
the CC data well.
c2min=141.5/152 dof
@sin2q = 0.33
m3/t3=1.0x10-2GeV/km
Neutrino decay vs. NC data
• NC data should also decrease due to decay into sterile state.
FC multi-ring NC enriched sample
Allowed and excluded
parameter regions
Excluded (by NC
data)
Allowed (by
CC data)
Use Up/Down to test
decay scenario
The 99%CL allowed region by FC 1-ring+PC+up-m samples
is almost excluded at 99%CL by the NC enriched sample.
Search for CC ντ events
CC ντ events
Only ～ 1.0 CC ντ
FC events/kton・yr
ντ
τ
ντ
hadrons
● Many hadrons ．．．．
difference with other events ．)
BAD
(But no big
τ- likelihood analysis
● Upward going only
GOOD
(BG (other ν events)
～ 130 ev./kton・yr)
Zenith angle
Tau likelihood analysis
Selection Criteria
 multi-GeV, multi-ring
 most energetic ring is e-like
 log(likelihood) > 0 (multi-ring)
> 1 (single-ring)
Multi-ring
Down-ward
τ-like
total energy
 number of rings
 number of decay electrons
 max(Ei)/ΣEi
 distance between n interaction
point and decay-e point
 max(Pm)
3/4
 Pt/Evis
 PID likelihood of most energetic ring

Multi-ring
Up-ward
τ-like
BG MC
t+BG MC
Tau analysis results
Max. likelihood analysis
Independent analysis by
Neural Network
t+BG
B.G.
Nτ= 145±44+11/-16
Nτ= 99±39+13/-21
Nτexpected=86
Consistent with νμ→ντ.
Future atmospheric neutrino
experiments
Topics
★ Really “oscillation”?
2
2
★ How accurate can sin 2θ23 and Δm23 be
determined ?
★ Is θ13 measurable ?
★ Sign of Δm2 ?
Possible future atmospheric neutrino detectors
Magnetized large
tracking detector
(MONOLITH, ….)
Very large water Cherenkov detector
(UNO, Hyper-Kamiokande, …..)
Really oscillation ?
Use up-going events ⇒ L = 2Rcosθz
Large L ⇒ Need to measure highenergy events
Very large detector
Magnetized detector
0.14 Mton・yr
(MONOLITH)
2.8 Mton・yr
(UNO)
Assume; Δm2=2×10-3eV2
Super-K may not be too small…..
Use only high L/E resolution events
70 year MC (1.6Mtonyr)
First osc. mim.
Accuracy of sin22θ measurement
Standard SK analysis with the
present SK systematics
90%C.L.
0.11 Mton・yr
0.23
0.9
sin22θ
=1+ε
Down
2
Up
Systematic error related to
Up/Down is small (2% @SK)
Precise determination
of sin22θ
(sin22θ) =
δ 90%
3%
Exposre(Mtonyr)
Accuracy of Δm2 measurement
L/E analysis
Magnetized tracking detector
0.14 Mton・yr
(MONOLITH)
First minimum
Δm2
0.14 Mton・yr
δ(Δm2) = 6%
Measurement of θ13 ?
Measurement of θ13 ?
Large water Ch.
detector
(e-like)osc
(e-like)no-osc
2
CosΘ
Down
Water Ch.
0.9 Mton・yr
Up
2
sin θ13=0.026
cosΘ < －0.2
(up going)
1
1
10
Reconstructed momentum (GeV/c)
1
10
Reconstructed momentum (GeV/c)
～4σ effect in 0.9 Mton・yr
Measurement of θ13 and sign of Δm ?
2
Matter effect
Δm2=2.5×10-3
sin2θ 13=0.02
Charge identification
(Magnetized tracking
detector needed)
Determination of sign of
Δm2 at 90%CL.
Summary
Present status
• All the data are consistent with pure νμ→ντ oscillations.
sin22θ > 0.92
Δm2(SK, 90%CL)
= (1.6 – 3.9)×10-3 eV2
• 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
detectors are constructed, our understanding of neutrino
masses and mixing will be improved significantly:
L/E, determination of oscillation parameters (23),
θ13,
sign of Δm , ….
2