lecture 2...lecture 2 current status of oscillation physics, part ii: solar neutrino experiments...
TRANSCRIPT
Lecture 2
Current status of oscillation physics, part II: Solar neutrino experiments Reactor neutrino experiments Short baseline experimentsWhat's next for oscillation physics: 13
Reactor experiments Long baseline experiments
The Three Signals SOLAR NEUTRINOS
ATMOSPHERIC NEUTRINOS
ACCELERATOR NEUTRINOS
Electron neutrinos from the Sun are disappearing
Muon neutrinos created in cosmic ray showers are disappearing on their way through the Earth
Distance ~ 1013000 km, Energy ~ 0.1100 GeV
Electron antineutrinos appearing in a beam of muon antineutrinos at LSND
Distance ~ 108 km, Energy ~ 0.115 MeV
Distance ~ 30 m, Energy ~ 3050 MeV
x
e
e x
Where we ended up last time: atmospheric 's
SuperK has clean, high statistics atmospheric
disappearance signal; good evidence it's
K2K confirmed the oscillationhypothesis with disappearanceof beam neutrinos
MINOS now has highestprecision m2 measurement
Soon: CNGS experimentsto explicitly see appearance
e x
Next, zoom in on solar neutrinos
Solar Neutrinos: the Classic Puzzle
J. Bahcall
Electron flavor neutrinos generated in solar fusion; spectrum is well understood from weak physics
D. Hahn, Nu2008
Homestake Chlorine Radiochemical Detector
νe + 37Cl → 37Ar + e 600 tons of cleaning fluid
Extract atoms of Ar every few months and count decays (35 day half life): ~ 12 per month!
Threshold: 0.81 MeV
Shortfall: saw about 1/3 of the expected neutrinos1 SNU=interaction/s/1036 atoms
Gallium radiochemical experimentsνe + 71Ga → 71Ge + e
Threshold: 0.23 MeV, 11 day halflifeSensitive to pp neutrinos
The SAGE Experiment
Based on liquid gallium 50 tons
1990present
Caucasus mountains, Russia
Based on
Gallex/GNO (Gallium Neutrino Observatory) at LNGS, Italy: 19912006
Used gallium chloride (30 tons of Ga)
Gallium solar neutrino results
SAGE GALLEX
Again clear shortfall: about 60% of standard solar model expectation (pp neutrinos)
D. Hahn, Nu2008
Water Cherenkov Detectors Observe elastic scattering of ~MeV solar ν's
Pointto Sun!
e, xe−e,xe−
KamiokandeII, 1991
E>~7 MeV
40% ofexpectation
The classic puzzle, end of the 1990's
Experiments: Cl, Ga, H2O have different thresholds
Energydependent suppressionNo known solarmodel could explain: is it νe → ν
?
The MikheyevSmirnovWolfenstein (MSW) Effect a.k.a. "Matter Effects"
Extra forward scattering amplitude modifies the oscillation probability, which depends on:
W
νe
e
e
νe
Z0
e,q
νx
e,q
νx
vs.extra energy √2 GFNe for νe NC only for νµ,τ
vvacuum osc. parametersmatter density profile
vs.
}
log(∆m2)
tan2θ
"Small Mixing Angle"
"Large Mixing Angle"
"Low"
"Vacuum" (or "Just So")
Mattereffectsin Sun apply
"Classic" allowed parameters for solar neutrino oscillations
The "Smoking Guns": oscillation signatures
● Day/night effect: regeneration of νe in Earth due to matter effect enhances νe flux at night for some parameters
● Seasonal variation: variation with L for vacuum oscillation (beyond 7% expected from Earth orbit)
● Spectral distortion
ν2
νe
Looking for smoking guns...
SuperK solar neutrino data: suppression observed
SK I
SK I
Recoil energy spectrum
electron energy
Day/night asymmetry
Seasonal variation
No strong effects(besides suppression) observed at SuperKconstrain parameters
Large mixing favored by SK alone...
But there's another smoking gun...
● Neutral Current Excess: direct evidence for flavor transformation
● Day/night effect: regeneration of νe in Earth due to matter effect enhances νe flux at night for some parameters
● Seasonal variation: variation with L (beyond 7% expected from Earth orbit)
No strongeffects observedat SuperK (constrain parameters)
● Spectral distortion
The Sudbury Neutrino Observatory
1 kton H2O
CC
NC
Elasticscattering(CC, NC)
1.7 kton D2O
Cherenkov light from e
Neutron detection
νe+ d → p + p + e
νx+ d → νx + p + n
νe,x+ e → νe,x+ e
Sudbury, Canada
SNO's unique feature: NC detection
NCνx+ d → νx + p + n
● Phase I: capture on d (D2O)● Phase II: capture on Cl (salt, NaCl)● Phase III: neutron detectors (NCD)
Tag NC via detection of neutron
Oscillation information from SNO
Also look for distortion of CC spectrum night enhancement
φES=φ(νe) + 0.15φ(νµ,τ
)
φNC= φ(νe) + φ(νµ,τ
) ~ total flux
CC
NC
Elastic scattering (CC, NC)
νe+ d → p + p + e
νx+ d → νx + p + n
νe,x+ e → νe,x+ e
specifically tags νe
flavorblind ⇒ measure total active flux
mixture of νe and all with known ratio
φCC
=φ(νe)
component
Phase I SNO Results, 2002
Fit data for CC, NC, ES componentscosθ
Conclusion: νe's are oscillating into active ν's! The solar neutrino problem solved!
φES=φ(νe) + 0.15φ(νµ,τ
) φNC= φ(νe) + φ(ν
µ,τ) ~ total flux
SNO turned off at the end of 2006
Phase III with NCDs (Neutral Current Detectors)
Latest preliminary SNO results H. Robertson, Nu2008
NC
CC
ES
Preliminary SNO NCD results H. Robertson, Nu2008
Final analyses underway
Look at LMAparameter spaceusing reactor antineutrinos
Mozumi, Japan
Sum of reactorfluxes from Japan, KoreaE
~few MeV, L~180 km
The KamLAND experiment
P. Decowski, Nu2008
Inverse Beta Decay (CC)νe + p → e+ + n
Exploit delayed (~180 µs) coincidence of n + p → d + γ as tag against radiactive background
γ
γγe+
n2.2 MeV
0.511 MeV
0.511 MeV
νe
SCINTILLATION DETECTORSLiquid scintillator CnH2n volume surrounded by photomultipliers high light output very low energy threshold possible little directional capability (light is isotropic)
Emeas=Ee−0.8 MeV
KamLAND: 1 kton scintillator
First KamLAND result (2003): observed suppression of reactor νe's selects the LMA region
LMAexpectation
Latest KamLAND spectrum
P. Decowski, Nu2008
KamLAND L/E Results
P. Decowski, Nu2008
Overall fit to the solar neutrino data
KamLANDnarrows them2 range
Global fit shows thatmixing isnot maximal
Next for KamLAND: 'KamLAND lowbg'
Purify the scintillatorto remove radioactivebackgroundfor sensitivity tosolar elasticscattering background
Borexino
LowNU
Gran Sasso, Italy
● 300 ton scintillator● very low radioactivity● <MeV threshold
C. Galbiati, Nu2008
New results from Borexino: 7Be flux, CNO/pp limits
Borexino data can constrain exotic models
Next for solar neutrinos in large detectors:
More from SuperK and Borexino KamLAND lowbg SNO+: SNO acrylic vessel filled with scintillator (more tomorrow) LENA (Europe), HSD (US), ...
Ultralow energy (sub MeV) realtime solar pp ν detectors
can be relatively small (~10 tons) thanks to huge pp flux realtime energy resolution various materials and technologies must be ultraclean to defeat radioactive background
The Frontier:
Vast pp neutrino flux!
K. Abe, TAUP 2007
XMASS:liquid xenon
CLEAN/DEAP: liquid neon (argon)
LENS: indiumloaded scintillator
Summary of solar ν's
Solar ν's
Clean, high statistics signals in many detectors: entering precision measurement era SNO confirms oscillation to active neutrinos with NC signal KamLAND reactor neutrino disappearance confirms LMA New: Borexino sees Be7 at low energy
Coming up: SNO+, KamLANDlowbg Frontier: realtime pp 's XMASS, CLEAN, LENS, ...
Now zoom in on LSND parameter space
LSND e
The LSND Experiment at Los AlamosLiquid Scintillator Neutrino Detector
ν beam: p + target → π+
↳ µ+νµ
↳ e+νµνe
30 m baseline, 167 tons scintillator
π decay at rest: 2060 MeV ν
µ
tag with correlated signals
(No longer see 20200 MeV νµ →νe for decay in flight π+)
Look for νµ νe via
νe + p e+ + n ↳ n + p d + γ
See excess of 87.9 ± 22.4 ± 6.0 beam νe events
The KARMEN experiment at RALKarlsruhe Rutherford Medium Energy Neutrino Experiment
17.5 m from ν source56 tons of scintillator
ISIS source: stopped π+ source but pulsed (50 Hz) ⇒ use time structure to:
● separate νµ (π decay) from νe, νµ
(2.2 µs µ decay) ● reduce cosmic ray bg
Karmen 2: 19972000
Expect: 12.3 ± 0.6 bg, see 11 candidates
NO OSCILLATION SIGNAL
LSNDand KARMENresults KARMEN
rules out some of LSND's allowed region, but not all
MiniBooNE Booster Neutrino Experiment at Fermilab
0.8 kton of mineral oilE
ν~ 1 GeV from 8 GeV booster
L~ 500 m
Test νµ → νe at
same L/E as LSND L↑, E↑ : different systematics
e, µ, π0 PID with scintillator, Ch. light + spectrum measurement
MiniBooNE Results: April 2007
Some excess at low energy: currently under study for possible detector effects or backgrounds
Interpreting as twoflavor oscillation: rules out LSND
No evidence of energydependent excess of e !
S. Brice, Nu2008
Now running with antineutrinos
MicroBOONE: liquid argon TPC to study crosssections in appropriate energy range
Possible future experiments that may help address the issue:
H. Ray, Nu2008
Experiment at the Spallation Neutron Source: LSNDlike beam with MiniBooNElike detector
LSND e
Summary of LSND parameter space
Gone? Still weird stuff?
We'll ignoreit for now!
What Do We Know About the Mixing Parameters?
∆m223, θ23
∆m212, θ12
Two verified examples of twoflavor mixing
P(fg)=sin2 2sin2 1.27m2LE
Atmospheric/beam
Solar/reactor
Allowed parameters getting squeezed down in next generation of experiments
2 mixing angles, 2 ∆m2
Beyond 2flavor: explore neutrino mixing in a 3flavor context
But there's more than just squeezing down 2flavor parameters ...
K
What Do We Know About the Mixing Parameters?
e
=Ue1 Ue2 Ue3
U1 U
2 U3
U1 U
2 U31
2
3
∆m223, θ23
∆m212, θ12
Described by 2 ∆m2
3 mixing angles (θ23,θ12,θ13) CPviolating phase δ
Remaining Questions (that can be answered by oscillation experiments)
What is the mass hierarchy?
What do we still not know?
or∆m12
2
∆m232
{{ ∆m12
2
∆m232
{
{"Normal" hierarchy "Inverted" hierarchy
(solar)
(atm.)
2 ∆m2
3 mixing angles (θ23,θ12,θ13) CPviolating phase δ
maximal?
MNSmixingmatrix
atmospheric solar
1
2
3e
µ
τ1
2
3
eµ
τ1
2
3
e
µ τ1
2
3
eµ
τ
?????? atmosphericsolar
|f>=∑i=1
N
Ufi |i>
U=1 0 00 C23 S23
0 −S23 C23
C13 0 S13e−i
0 1 0−S13e
i 0 C13C12 S12 0−S12 C12 00 0 1
First, θ13: 'the twist in the middle'
1P(νe→νe) ~ sin22θ13
sin2(∆m213L/4E)
Getting at θ13 experimentally: look for disappearance of reactor νe (few MeV,
~ km)
Current best limits for θ13 from CHOOZ
νe → νx
⇒ disappearance amplitude < 510%
New experiments(Double CHOOZ,Daya Bay) are tryingto go further
Matterenhanced ν
µ → νe oscillation
probability for large θ
13
Expect upgoing multiGeV νe excess: not seen
νe enhancement/ deficit
for expected SK events
Can look for signatures of nonzero θ13
in SK atmospheric nus
(Plots by R. Wendell)
Best knowledge so far about 13:
It's small angle, giving small modulation!
Excluded by lack of disappearance of reactor antinus
Allowed: consistent with atmospheric nus
Need <1% systematics!
⇒ resolve ambiguities?
Cancel systematics w/ 2 detectors
Next generation of proposed experiments: improved reactor disappearance search
1P(νe→νe) ~ sin22θ13
sin2(∆m213L/4E)
PNew reactor experiments
Double CHOOZ, France
Daya Bay, China
RENO, South Korea
T. Lasserre, Nu2008
Double Chooz (France)
10 m3 ofGdloaded scintillator
∑ E~8 MeV
n + Gd → Gd*
→ Gd + γ
Double Chooz sensitivity to 13
T. Lasserre, Nu2008start mid2009
Daya Bay, China C. White, Nu2008
Daya Bay detectors (8 total)
Daya Bay sensitivity to 13
start mid2010
One more: RENO in Korea
S. B. Kim
RENO sensitivity to 13
Start ~2010
Another experimental approach: 13signature: look for small νe appearance in a ν
µ beam
Hard to measure... it's a small modulation! Need good statistics, clean sample
For ∆m232 >> ∆m12
2 and Eν~ L∆m23
2 (in vacuum):
P(νµ→νe) = sin22θ13
sin2θ23
sin2(∆m223L/4E)
~ 1/2
atmosphericlikewiggling
small modulation
νµ → ν
µ,τ
νe
Future Long Baseline Beam Projects
T2K: "Tokai to Kamioka" NOνA at NuMi
Existing detector: SuperK295 km, <1 GeV 0.75 MW beam (30 times K2K)Water Cherenkov detector
2009+
Existing beam: NuMi810 km, few GeV beamScintillator detector
Aim for: ~1% on 23 mixing, factor of ~1020 for13 mixing
Detectors will be a few degrees off beam axis
Why are the detectors a few degrees off of the beam axis?
Offaxis, neutrino energy becomes relatively independent of π energy
2body pion decay kinematicsBarenboim et al.hepex/0206025
OffAxis Neutrino Beams
Good forbackground reduction and oscillation fits
Although you get some reduction in flux, get more sharply peaked neutrino energies
OA3°
OA0°OA2°
OA2.5°
September, 2005
T2K: "Tokai to Kamioka" ● SuperK III at 295 km● JPARC 50 GeV PS● <1 GeV 0.75 MW ν beam● 2.5 deg. off axis ● will turn on 2009
Electron appearance signal in SK
Intrinsic beam νe contamination
NC single pionsπ0→γγ
νµ misid
asymmetric decayboth γ boosted forwardone γ near wall
Backgrounds
Expect ~1600 events/year at SK
T2K Near Detectors
Offaxisdetector complexat 280 m tocharacterizeflux forunderstandingof backgroundsat SuperK
T2K sensitivity to 13
I. Kato, Nu2008
NOA
R. Ray, Nu2008
On the US side:
15 kt scintillator Includes NuMI upgrade from 400 to 700 kW 810 km baseline
Liquid scintillator in long cells + optical fiber + avalanche photodiode
R. Ray, Nu2008
NOA sensitivity to 13
Summary of "beyond2flavor" oscillation physicsObservable
Signature Next steps *
Next generationbeams (T2K, NOA)
θ13 Tiny appearance of νe in a beam of ν
µ
Disappearance of νe Reactors
Next: what will be needed to go after mass hierarchy, CP violation
Lecture 3
Finish the oscillation story: CP violation mass hierarchy farther future projects supernova neutrinosKinematic neutrino mass searchesNeutrinoless double beta decayMiscellaneous topics, as time permits