takaaki kajita, icrr, univ. of tokyo
DESCRIPTION
NuFact04, Osaka, July 2004. Atmospheric Neutrinos; - Present and future -. Takaaki Kajita, ICRR, Univ. of Tokyo. Outline. Atmospheric neutrino beam Atmospheric neutrinos: Present L/E analysis Atmospheric neutrinos: Future sub-dominant oscillations ? - PowerPoint PPT PresentationTRANSCRIPT
Takaaki Kajita, ICRR, Univ. of Tokyo
NuFact04, Osaka, July 2004
Outline
• Atmospheric neutrino beam
• Atmospheric neutrinos: Present
L/E analysis
• Atmospheric neutrinos: Future
sub-dominant oscillations ?
• Summary
Only 2 and 3 flavor neutrino oscillations
Atmospheric neutrinos Cosmic Ray
, K
e
e
Atmosphere μ
Neutrinos from the other side of the Earth.
e
Atmospheric neutrino beam
Zenith angle:F
lux
× E2
E(GeV)
Measured cosmic ray proton flux
e
Total flux
Event classificationFully Contained (FC) (E ~1GeV)
Partially Contained (PC) (E ~10GeV)
Through-going (E~100GeV)
Stopping (E~10GeV)
Super-Kamiokande (50,000ton water C
h. Detector)
Soudan-2 (1kton tracking detector)
MACRO (large muon detector)
76m
12m
9.3m
Super-K atmospheric neutrino data
1489day FC+PC data + 1646day upward going mu
on data
CC e CC
Soudan2
Reconstructed Lν/ Eν dist.
No osc. osc.
Phys.Rev. D68 (2003) 113004
• 5.9 kton ・ yr exposure• Partially contained events included.• L/E analysis with the “high resolution” sample
Zenith angle
e
μDown-going
Up-going
e μ
or
MACRO
OscillationΔm2 =2.5×10-3
Upward horizontal
L /E
Multiple scattering
E
E
PLB 566 (2003) 35
Neutrino oscillation parameters
Soudan-2
MACRO
Super-K
92.02sin
)(104.35.1
23
2
23223
eVm
90%CL
oscillation
decoherence
decay
Further evidence for oscillations Strong constraint on oscillation parameters, especially m2
-like multi-GeV + PC
Should observe this dip!
New !
SK collab. hep-ex/0404034
Selection criteria
Following events are not used:
★horizontally going events
★low energy events
Select events with high L/E resolution
((L/E) < 70%)
FC single-ring -like
Full oscillation 1/2
oscillation
(L/E)=70%
Similar cut for: FC multi-ring -like,
OD stopping PC, and
OD through-going PC
2121 FC -like and
605 PC
L/E distribution
MC (no osc.)
1489 days FC+PC (Super-K)
Evidence for oscillatory signature
Mostly down-going
Mostly up-going
Osc.
Decay
Decoh.
Decay and decoherence disfavored at 3.4 and 3.8 level, respectively.
Allowed neutrino oscillation parameters
2min=37.9/40 d.o.f
@ m2=2.4x10-3,sin22=1.00(sin22=1.02, 2
min=37.8/40 d.o.f)
1.9x10-3 < m232 < 3.0x10-3 eV2
0.90 < sin2223 (90% C.L.)
Stronger constraint on m2
Consistent with that of the standard zenith angle analysis
SK L/E analysis
90% CL
SK Zenith angle analysis
K2K
Soudan2
MACRO
Kam.
Search for non-zero 13
Electron appearance in the 5 – 10GeV upward going events.
E
LmP e
2232
13
2
23
2 27.1sinsinsin)(
s213=0.05 s213=0.00 null oscillation
MC, SK 20yrs
Electron appearance
1+multi-ring, e-like, 2.5 - 5 GeV
cosE(GeV)
cos
)( eP
Matter effect
(m122=0 assumed)
Super-K e-like data
Multi-GeV, single-ring e-like Multi-GeV, multi-ring e-like(special)
No evidence for excess of upward-going e-like events
3 flavor analysis from Super-K
Normal
Inverted
3
21
3
21
prelim.
Present: Study of dominant oscillation channel ( )
Future: Study of sub-dominant oscillations
ν m
ass
23
2
)13(23
m
12
2
12 (small)m
(small)13
2
)23(13
m
e
Normal mass hierarchy is assumed.
★ 13?
★Mass hierarchy?
★Solar oscillation effects?
Possible future atmospheric detectors
Magnetized large tracking detector
Hyper-K (1Mton)
Very large water Cherenkov detector
MONOLITH,
INO (India-based Neutrino Observatory, …
Mton class detector at Frejus
UNO
Water Cherenkov detector 450 kton ・ yr (SK 20 years)
3 3 3
Importance of s223>0.5; S.Pascoli et al., hep-ph/0305152
TK noon2004
2 ∝ ~ exposure) ~ Present bound on sin213
Multi-GeV electron appearance
Sensitivity to non-zero 13
SK 20yr MC
How can we discriminate positive and negative m2 ?
Real m232 = positive
assumed
(No resonance for anti-neutrinos)
Real m232 = negative
assumed
(No resonance for neutrinos)
E(GeV)
cos
P(e)
E(GeV)
cos
P(e)
Sign of m23(13)2 ?
3
21
3
21
Measurement of sign of m2
in large magnetized detectors
Determination of sign of Δm2 at 90%CL.
Δm2=2.5×10-3 sin2θ =0.0213
NPB (proc suppl) 91 (2001) 147, hep-ex/0106252
Measurement of sign of m2
in water Cherenkov detectors ?
3 3 3
m2: fixed, 23: free, 13: free, positive m2
Exposure: 1.8Mtonyr (SK 80yr or HK ~ 3.3 yr)
Use differences in and d/dy
TK NOON2004
Solar oscillation effectsSolar neutrino oscillation: LMA (m12
2 = 7×10-5eV2) Expected number of sub-GeV e-like events in SK.
Peres, Smirnov NPB 680 (2004) 479
The number of e-like events changes as a function of sin223 (NOT sin2223).
Discrimination of >45 and <45 might be possible. (However, the effect is very small for s2223=1.00.)
P.Lipari NOON2004
10
1
• Atmospheric neutrinos have been playing major role in the neutrino oscillation studies.
• The present data are nicely explained by oscillations with;
m2=1.9 – 3.0 × 10-3 eV2
sin22 > 0.90 (SK L/E analysis)• Recent L/E analysis has shown evidence for “oscillatory”
signature.• Future atmospheric neutrino experiments is likely to conti
nue to contribute to the neutrino oscillation physics (13, sign of m23
2 ….)
(If (a) much larger detector, (b) relatively large 13.)
End
Specials in L/E analysis
1.5m from top & bottom
1m from barrel
22.5kt
→26.4ktExpand fiducial volume
More statistics for high energy muons
Classify PC events using OD charge
I. OD stoppingII. OD through going
Different L/E resolution
FC single-ring, multi-ring -like
PC
observed charge / expectation from through-going
OD stopping
OD through-going
OD through-going MC
OD stopping MC
Energy and angular resolution of neutrinos
L/E cuts
Full osc.
Half osc.
Sensitivity to other models (determination of L/E resolution cut)
70% 80%
80%70%
decay decay
decoherence decoherence
decay
decoherence
L/E resolution cut at 70%
Event summary of L/E analysis
Fractions of FC and PC samples in L/E distribution
1619 2105.8 (98.3%)
502 813.0 (94.2%)
114 137.0 (95.4%)
491 670.4 (99.1%)
single-ring
multi-ring
stopping
through-going
FC
PC
Data MC CC
Check of the observed dip in L/E distribution (1)
Other L/E resolution cuts
Check of the observed dip in L/E distribution (2)
FC e-like
(Flat L/E distribution is expected.)
Check of the observed dip in L/E distribution (3)
zenith angle : cos-cos
(Zenith angle of each event is inverted. Because of the wrong assignment of L, no dip is expected.)
Sensitivities to alternative models and the data
decay
decoherence
L/E resolution cut at 70%
obtained2
Neutrino decay and decoherence models ?
Oscillation
Decay
Decoherence
2min=37.9/40 d.o.f
2min=49.1/40 d.o.f 2 =11.3
2min=52.4/40 d.o.f 2 =14.5
decay disfavored at 3.4
decoherence at 3.8
First dip observed in the data cannot be explained by alternative hypotheses
Evidence for oscillatory signature
2 as a function of sin213
Normal Inverted
How can we discriminate neutrino and anti-neutrino interactions ?
Simple answer: No. It is not possible to discriminate event by event in water Cherenkov experiments.
However, (total) and d/dy are different.
Try to discriminate positive and negative m2 using these events.
CC e
CC e
CC e
CC e
Others Others
Single-ring e-like Multi-ring e-like
Electron appearance for positive and negative m2 in a water
Chrenkov detector
Single-ring e-like Multi-ring e-like
Positive m2
Negative m2
null oscillation
cos cos
Relatively high anti-e fraction
Lower anti-e fraction
m2=0.002eV2
s223 = 0.5 s213 = 0.05(SK 20yrs)
2 difference (inverted-normal)
m2: fixed, 23: free, 13: free
Exposure: 1.8Mtonyr (SK 80yr or HK ~ 3.3 yr)
3 3 3
True= normal mass hierarchy assumed.
2 difference (normal – inverted)
m2: fixed, 23: free, 13: free
Exposure: 1.8Mtonyr (SK 80yr or HK ~ 3.3 yr)
3 3 3
True= inverted mass hierarchy assumed.