neutrinos in the standard model, and why the standard model is …oser/llwi1.pdf · 2006. 2....
TRANSCRIPT
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1
Neutrino Physics, Part 1
Neutrinos in the
Standard Model, and
Why The Standard
Model is Wrong
Scott Oser
UBC
Lake Louise Winter Institute
February 2006
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2
Outline
1. Neutrinos In The Standard Model
2. Neutrino Mixing And Oscillation
3. The Solar Neutrino Problem, With Solution
4. Atmospheric Neutrino Oscillations
5. Results from Long Baseline Neutrino
Experiments
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3
Neutrinos in the Standard Model
A neutrino is a neutral cousin of the
electron and the other charged leptons.
νe
νe
νe
νe
e
e
W
e
e
Z
Only weak interactions — carried by very
heavy W, Z particles with short ranges
In the Standard Model, mν ≡ 0. (The
current limit on the sum of the three
masses is ∼ 0.6 eV). Neutrinos are
many orders of magnitude lighter than the
other fermions.
Why are ν ’s so light? Why 3 kinds?
What’s the relationship between leptons and quarks?
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4
Different Kinds of Neutrinos: “Flavours”
Each charged lepton (e, µ, τ ) has its own kind of neutrino. For example,
in these reactions you get:
p + e− → νe + n
p + µ− → νµ + n
Note that the number of particles of each flavour type seems to be
conserved in each reaction.
Flavour is also conserved in the other direction:
νe + n → p + e−
νµ + n → p + µ−
In the Standard Model lepton flavour is rigorously conserved, but is not
protected by any symmetry of the Lagrangian.
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5
The Left and the Right of the Matter
spin
momentum
ANTINEUTRINO
spin
momentum
NEUTRINO
Weak interactions only couple to left-handed ν ’s, or right-handed ν ’s
This is a pure V-A interaction (maximally parity violating). Weak current has the form:
jµ = ψγµ(1 − γ5)ψ
Right-handed ν ’s either don’t exist, or are sterile (don’t interact).
A plausible, but wrong, argument ...
1. Ockham’s Razor: the simplest solution is if right-handed ν ’s don’t exist.
2. In Standard Model, mass couples left-handed and right-handed states.
3. Therefore, to avoid right-handed states, neutrinos should have no mass.
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Neutrino Flavour Mixing
In Standard Model, neutrinos are rather boring ... they have
no mass, and only seem to be there to conserve lepton
number, flavour number, and energy/momenta/spin.
In 1962, Maki, Nakagawa, and Sakata proposed, on the
basis of zero experimental evidence, a new phenomenon
called neutrino oscillation.
To understand what led MNS to this, let’s look at quark
mixing first.
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Weak Interactions with Quarks
The simple version: W particle couples u ↔ d, c ↔ s, t ↔ b,
W
u
d
W
c
s
W
t
b
But this can’t be complete, since we see weak decays such as:
Λ(uds) → p(uud) + π−(du)
Somehow the strange quark in the Λ gets turned into an up quark!
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Quark Flavour Mixing
In reality, W particle couplings mix quark generations:
W
u
d’
We say that flavour eigenstates
(eg. d,s,b) are rotated with respect
to weak eigenstates (d’,s’,b’)
u
d′
c
s′
t
b′
d′
s′
b′
=
Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb
d
s
b
This allows generation-mixing decays such as Λ(uds) → pπ−
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Neutrino Mixing
W
e
νe
Since ν ’s have only weak
interactions, flavour eigenstates
are defined as those states that
couple to W
What if the flavour eigenstates are rotated relative to the mass
eigenstates (eigenstates of Hamiltonian with well-defined mass)?
νe
νµ
ντ
=
Ue1 Ue2 Ue3
Uµ1 Uµ2 Uµ3
Uτ1 Uτ3 Uτ3
ν1
ν2
ν3
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How does superposition of mass eigenstates evolve in vacuum?
|νe〉 = cos θ |ν1〉 + sin θ |ν2〉
|νµ〉 = − sin θ |ν1〉 + cos θ |ν2〉
Each term evolves with a phase factor of ei(px−Et)
If m1 6= m2, then arguments of exponential will be different! For
example, if we consider p to be fixed, then
E =√
p2 + m2 = p√
1 + m2/p2 ≈ p + m2/(2p)
As neutrino propagates, a phase difference develops between terms!
|ν(t)〉 ∝ cos θ |ν1〉 + eiφ sin θ |ν2〉
with
φ =
(
m21
2p−
m22
2p
)
t
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Neutrino Oscillation
Net result: at some later time, |ν(t)〉 6= |νe〉.
Probability that the original νe is detected as a νµ at some later time:
P (νe → νµ) = |〈νµ|ν(t)〉|2 = sin2 2θ sin2
(1.27∆m2L
E
)
Energy (MeV)
Osc
illat
ion
Prob
abili
ty
00.10.20.30.40.50.60.70.80.9
1
1 10
θ = neutrino mixing angle
∆m2 = m21 −m2
2 (in eV2)
L = distance ν has travelled (in km)
E = neutrino energy (in GeV)
Neutrino oscillation:
• requires at least one non-zero neutrino mass
• requires non-zero mixing elements
• results from the QM of the propagation, not from an interaction
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Matter Effects On Neutrino Oscillation
Surprisingly the oscillation formula can be dramatically altered in matter!
id
dt
(
νe
νµ
)
=
(
−∆m2
4Ecos 2θ+
√2GF Ne
∆m2
4Esin 2θ
∆m2
4Esin 2θ ∆m2
4Ecos 2θ
)(
νe
νµ
)
The relevant process is forward scattering, in
which no momentum is exchanged. In matter,
νe ’s have a different forward scattering
amplitude than the other flavours:
e- e- e-
e-
νe
νeνx νx
WZ +
All neutrino flavors
0
Only electron neutrinos
AT SOLAR NEUTRINO ENERGIES:
This produces a matter-induced potential that
is different for νe. Effectively νe ’s have a
different “index of refraction” in matter.
The size of the potential is proportional to the
electron density Ne.
For solar ν ’s, matter effects are dominant.
Average survival probability in vacuum
Actual solar neutrino survival probability
Neutrino Energy (MeV)
Ele
ctro
n N
eutr
ino
Surv
ival
Pro
babi
lity
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10 12 14 16 18 20
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Solar Neutrinos
The Sun is an intense source of MeV neutrinos!
4p + 2e− →4He + 2νe + 26.731 MeV
Shape of Spectra Determined By Nuclear Physics.
Solar Models Only Affect Normalization.
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The pp Chain
99.6% 0.4%
85% 15%
99.9% 0.1%
<< 1%
p + e− + p →2H + νe
2 3He →4He + 2p 3He + p →
4He + e+ + νe
(hep)
2H + p →3He + γ
3He + 4He →7Be + γ
(7Be)
7Be + e− →7Li + νe
7Be + p →8B + γ
8B →8Be
∗
+ e+ + νe
7Li + p → 24He
8Be∗
→ 2 4He
p + p →2H + e+ + νe
(pep)
(8B)
(pp)
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15
The Pioneers
The 37Cl experiment
started in the 1960’s
Ray Davis and John
Bahcall with the
tetrachloroethylene tank.
100,000 gallons of
cleaning fluid!
νe+37Cl → e−+37Ar
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A setback ...
Predicted rate: 7.6+1.3−1.1 SNU’s
Measured rate: 2.56 ± 0.23 SNU’s
Most people reacted in two ways ...
• Experiment must be wrong. No one can look for 50 Ar atoms in 600
tons of cleaning fluid and expect to find them all!
• Theory must be wrong. The solar models are too complicated to
take seriously. The flux changes with solar temperature by T 25.
Even a tiny mistake could change fluxes greatly!
Ray Davis checked and rechecked his experiment. John Bahcall refined
astrophysical calculations. Both stuck to their guns.
Others began planning new experiments ...
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17
Super-Kamiokande
Detector hall Access tunnel
1,000m
Control room
Inner Detector
Outer Detector
Photo multipliers
41m
39m
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18
Water Cherenkov Detectors
ν
Neutrino-electron scattering
e
ν
e
Elastic scattering of electrons by ν ’s
Scattered electron can move faster than
light in water (since water has slowed
down light).
Get Cherenkov light—an electromagnetic
sonic boom!
• Light is blue
• Comes out in cone
• More energy→ more light!
Cherenkov cone
electron
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Super-Kamiokande
νx + e− → νx + e−
Rate ∝ φ(νe) + 1
6φ(νµτ )
Rexp = 0.465 ± 0.005+0.014−0.012× SSM
(hep-ex/0106064, hep-ex/0206075)
z
SKDayNight Man 1Man 2Man 3Man 3 Man 4Man
4 Man 5M
an 5
CoreCore
No SKData
InnerCore
All Day
Night
Man
1
Man
2
Man
3
Man
4
Man
5
Cor
e
cosθz
Dat
a/S
SM
0.4
0.45
0.5
0.55
-1 -0.5 0 0.5
Clear directional ν signal from Sun!
0
0.1
0.2
-1 -0.5 0 0.5 1cosθsun
Eve
nt/d
ay/k
ton/
bin
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20
Solar Neutrino Flux Measurements
Two Classes of Experiment (so far)
• Radiochemical
– νe interactions convert target nuclei
– Radioactive products extracted and
counted after exposure time
• Water Cerenkov
– Real-time detection of scattered
atomic e− ’s
– Mixed CC and NC sensitivity
0 1 10ENERGY (MeV)
0.00
0.50
1.00
RA
TIO
TO
SS
M P
RE
DIC
TIO
N
Ga
Cl
SK
Experiment Detection Reaction Threshold Primary Sources
Homestake νe+37Cl → e−+
37Ar 0.8 MeV 7Be,8B
Kamiokande νe,(µ,τ) + e → νe,(µ,τ) + e 7.3 MeV 8B
SAGE, GALLEX/GNO νe+71Ga → e+
+71Ge 0.23 MeV pp,7Be,8B
Super-K νe,(µ,τ) + e → νe,(µ,τ) + e 5 MeV 8B
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21
The Solar Neutrino Problem
• Standard Solar Model Predictions:
• Measurements:
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Sudbury Neutrino Observatory
2092 m to Surface
1700 Tonnes InnerShielding H2O
1000 Tonnes D2O
5300 Tonnes Outer Shield H2O
12 m DiameterAcrylic Vessel
18 m DiameterSupport Structurefor 9500 PMTs,60% coverage
Urylon Liner andRadon Seal
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Event Display–Neutrino Event
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Solar ν Interactions in SNO
SNO measures primarily8B neutrinos by three
interactions:
Charged Current:
νe + d → p + p + e−
Neutral Current:
νx + d → p + n + νx
Elastic Scattering:
νx + e → νx + e−
SNO CC threshold
SNO NC threshold
For the Large Mixing Angle (LMA) solution to solar neutrino problem:
|Ue2|2 ≈ sin2 θ12 ≈
φCC
φNC
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25
Three Phases of the SNO Experiment
D2O Phase
(pure D20)
Nov 1999 - May 2001
n + d → t + γ
(σ = 0.0005 b)
Detect a Compton-
scattered electron from a
6.25 MeV γ
Salt Phase
(D2O + 0.2% NaCl)
July 2001 - Sept 2003
n+35Cl →36Cl +γ ’s
(σ = 44 b)
Detect Compton-scattered
electrons from multiple γ ’s
totalling 8.6 MeV
NCD Phase
(3He counters)
Dec 2004 - Dec 2006
n+3He → p + t
(σ = 5330 b)
Detect 764 keV of
ionization from the
charged particles in 3He
proportional counters
PRL 87, 071301 (2001)
PRL 89, 011301 (2002)
PRL 89, 011302 (2002)
PRD 70, 093014 (2004)
PRL 92, 181301 (2004)
PRL 92, 102004 (2004)
PRC 72, 055502 (2005)
PRD 72, 052010 (2005)
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Signal Probability Distributions
CC ES NC
Angle
Isotropy
Radius
Energy
Fit the PDFs to the data to determine fluxes. Leave out the energy
PDFs to fit for the spectral shapes.
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Results for the full 391-day Salt Phase
14β-0.2 0 0.2 0.4 0.6 0.8
Eve
nts/
(0.0
107)
0
20
40
60
80
100
120
140
160 DataFit result Neutrons CC ES External neutrons
(a)
θcos -1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 1
Eve
nts/
(0.0
2)
0
20
40
60
80
100
120
DataFit result Neutrons CC ES External neutrons
(b)
ρ0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Eve
nts/
(0.0
5)
0
50
100
150
200
250
300
350
Fit ResultAV bkgPMT+H2O bkgd. External neutrons
DataNeutrons CC ES
(c)
=55
0 cm
R
(MeV) effT6 7 8 9 10 11 12 13 20
Eve
nts/
(0.5
MeV
)
0
100
200
300
400
500
600
700
800
900
DataFit resultNeutrons CC ES External neutrons
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Evidence for Solar Neutrino OscillationN
eutr
ino
Flux
(×
106 c
m-2
sec
-1)
Frac
tion
of S
SM
SSM Prediction (BPB 2000)
0
1
2
3
4
5
6
7
CC ES NC0.0
0.5
1.0
SNO: Direct evidence that
φ(νe) < φ(νtot)
Phys Rev C 72, 055502 (2005)
(MeV) effT6 7 8 9 10 11 12 13
Eve
nts/
(0.5
MeV
)
0
50
100
150
200
250
300Data
Systematic uncertainties
B model shape8SSM
B model shape8LMA
No evidence of spectral distortion.
ADN = 0.037 ± 0.040
Self-consistent picture of results from
Homestake, SAGE/GALLEX/GNO, and
Super-K.
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29
Evidence for Reactor Neutrino Oscillations
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Nob
s/N
exp
101 102 103 104 105
Distance to Reactor (m)
ILL Savannah River Bugey Rovno Goesgen Krasnoyarsk Palo Verde Chooz
KamLAND
KamLAND: Observation of reactor
neutrino disappearance at L/E value
where solar neutrino effect occurs.
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30
Evidence for Reactor Neutrino Oscillations
(PRL 94, 081801, 2005)
(M
eV)
dela
yed
E 2
3
4
5
Fri Jun 11 11:43:30 2004 (MeV)promptE0 1 2 3 4 5 6 7 8
Eve
nts
/ 0.4
25 M
eV
0
20
40
60
80
no-oscillation
best-fit oscillation
accidentals
KamLAND data
Spectral distortion seen inreactor neutrino energy spectrum
Solar data constrains θ12, while reactor
data constrains ∆m2—extreme
complementarity!
)2 e
V-5
(10
2 m∆
5
10
15
20(a)
θ2tan
)2 e
V-5
(10
2 m∆
5
10
15
20
0 0.2 0.4 0.6 0.8 1
68% CL
95% CL
99.73% CL
(b)
ONLYSOLAR DATA
SOLAR DATA + KamLAND
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31
Future Solar Neutrino Experiments
There are various ideas for precision
measurement of 7Be and pep neutrinos by
low-background scintillator detectors:
• Borexino
• KamLAND
• SNO+
• liquid noble gas detectors
Barger et al, hep-ph/0502196
Possible Motivations:
• Observe turn-up in LMA survival
probability
• Constrain solar models
• Test exotic scenarios
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32
Atmospheric Neutrinos
π µ + νµ
e ν ν+ eµ+
ν
π
µ
e
ν
ν
atmosphere, making pionIncident proton strikes
p
Two muon neutrinos
electron neutrino!produced for each
Super−Kamiokandedetector
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33
Super-Kamiokande Event Display
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34
Super-Kamiokande Atmospheric ν Results
050
100150200250300350400450
-1 -0.5 0 0.5 1cosθ
Num
ber
of E
vent
s Sub-GeV e-like
050
100150200250300350400450
-1 -0.5 0 0.5 1cosθ
Num
ber
of E
vent
s Sub-GeV µ-like
0
20
40
60
80
100
120
140
-1 -0.5 0 0.5 1cosθ
Num
ber
of E
vent
s Multi-GeV e-like
0
50
100
150
200
250
300
350
-1 -0.5 0 0.5 1cosθ
Num
ber
of E
vent
s Multi-GeV µ-like + PC
0
0.5
1
1.5
2
2.5
3
3.5
4
-1 -0.8 -0.6 -0.4 -0.2 0cosθ
Flu
x(10
-13 cm
-2s-1
sr-1
) Upward Through Going µ
0
0.2
0.4
0.6
0.8
1
1.2
1.4
-1 -0.8 -0.6 -0.4 -0.2 0cosθ
Upward Stopping µ
0
0.001
0.002
0.003
0.004
0.005
0.8 0.85 0.9 0.95 1
sin22θ
∆m2 (
eV2 )
Zenith angle analysis
L/E analysis
0.8 0.85 0.9 0.95 1.00.0
1.0
2.0
3.0
4.0
5.0
× 10-3
PRD 71, 112005 (2005)
Super-K sees suppression of νµ flux at
large zenith angles (distances).
νe flux is unaffected.
Looks to be νµ → ντ oscillations
First clear evidence for neutrino oscillations (1998)!
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35
Neutrino Mass Hierarchy
∆m2
∆m2
∆m
2
12
3
3
12solar {
} solar
atm
osph
eric
mas
s
νe νµ τν
NORMAL INVERTEDHIERARCHYHIERARCHY
∆m2atm ≈ 2.5 × 10−3 eV2 ∆m2
sol ≈ 8 × 10−5 eV2
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36
Neutrino Mixing Matrix
Adjust L/E to view oscillations at different ∆m2’s
U =
1 0 0
0 c23 s23
0 −s23 c23
︸ ︷︷ ︸
c13 0 eiδs13
0 1 0
−e−iδs13 0 c13
︸ ︷︷ ︸
c12 s12 0
−s12 c12 0
0 0 1
︸ ︷︷ ︸
Atmospheric ν ’s: Short baseline reactor ν ’s: Solar ν ’s:
θ23 ≈ π/4 θ13 < π/20 θ12 ≈ π/6
Maximal mixing! (?) Small, quark-like mixing Large, non-maximal mixing
Compare to identical parameterization of CKM matrix ...
θ23 ≈ π/76 θ13 ≈ π/870 θ12 ≈ π/14
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37
Physics of Long Baseline ν Experiments
295km(Tokai)
JAERISuper Kamiokande
KEKTokyo
K2K: KEK to Kamioka
T2K: J-PARC to Kamioka
(×50 stats.)
Far detector: Super-K
Basic idea: shoot a
man-made neutrino beam
through the Earth, and study
neutrino oscillations in
controlled way
Measure Determine
P (νµ → νµ) ∆m223, θ23
P (νµ → νe) θ13
P (νµ → νµ ) CPT
P (νµ → νe ) δCP , sign(∆m223)
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38
K2K: KEK to Kamiokande
250 km baseline, wide-band beam
Beam
νµ 98.2%
νe 1.3%
νµ 0.5%
K2K-I: March 1999 - July 2001
Super-K accident, reconstruction
K2K-II: December 2002 - November 2004
The first long baseline ν experiment
Goal: measure νµ disappearance at atmospheric ∆m2
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39
Anatomy of a Long Baseline Experiment
10 /2.2 sec11ν 10 /2.2 sec
6 ν
ν
µπAl target
+ horns MuonMonitor
NearDetectorsDecay Pipe
PionMonitor
200 meter
300 meters
12 GeV protons
250 kilometers
SK
Target: 3cm dia × 66cm long Al cylinder
Horns: toroidal B fields, pulsed at 250 kA
Pion monitor: gas Cherenkov detector
Muon monitor: segmented ionization
chamber + array of silicon pad detectors
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40
12 GeV PS Beamline
FrontDetectors
Decay pipe Horn and target station
12 GeV PS
100m0
Magnetic horns focus π’s, which decay in pipe to produce νµ
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41
K2K Beam Statistics
µ1.1 sec
120 nsec
∼ 6 × 1012 p.o.t. in 9 bunches
-101234567
Jan/99Jan/99 Jan/00Jan/00 Jan/01Jan/01 Jan/02Jan/02 Jan/03Jan/03 Jan/04Jan/04
Pro
tons
/Pul
se (
10^1
2)
Date
-20
0
20
40
60
80
100
120
Acc
umul
ated
PO
T (
10^1
8)
89.1 × 1018 POT usable data
Eν
Neutrino Energy Spectrum at KEK
0 1 2 3 4 5
Measurement
Beam MC
integrated
GeV
arb
itra
ry u
nit
On-axis beamRelatively wide energy
spectrum
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42
K2K Near Detectors
Scibar
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43
Kiloton Water Cherenkov Detector
8.6 m diameter × 8.6 m high
cylinder
680 Super-K PMTs with
electronics—a miniature Super-K
1 kton water Cherenkov detector
normalizes beam interactions on
water target.
Measure ν spectrum and
backgrounds before oscillation
Used to predict event rate at
Super-K
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44
Scibar Detector
14848 extruded scintillator strips
Read out by 1.5mm diameter WLS fibres
with multi-anode PMTs
Θµ
∆Θp
µ
p
νµ
Compare measured proton recoil
direction to quasielastic prediction to
identify or reject CCQE events
(νµ + n→ µ+ p).
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45
Analysis Flowchart
NeutrinoInteractionMC
∆ 2 2m , sin 2 Θ
Beam MC
# of νpµ µ, Θ distribs
Observed:
EνΦ( )
Derived:ν xsec ratios
# of νE spectrumν
rec
Observed:# of ν
E spectrumνrec
Expectation:
AT KEK ND:
AT SK:
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46
Main Interaction Types
Processes modelled with the NEUT Monte Carlo
CC Quasi-Elastic (CCQE)
• Smith & Moniz with MA = 1.1 GeV
CC Resonant Single Pion (CC-1π)
• Rein & Sehgal with MA = 1.1 GeV
CC Multiple Pion (DIS)
• GRV94 + JETSET with Bodek & Yang
correction
CC Coherent Pion
• Rein & Sehgal with cross-section
rescaling by J. Marteau
NC
+ Nuclear Effects
σ/E (10−38 cm2/GeV)
Eν (GeV)
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47
Low q2 Anomaly
K2K observes a deficit of
forward-going µ relative to MC in
all near detectors
• Seen in non-QE events
Two possible explanations:
• Suppression of CC-1π at
q2 < 0.1 GeV2
• Absence of CC coherent π
production
Significant nuclear effects (poorly
understood).
Scibar data
0
50
100
150
200
250
300
350
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Entries 1726
q2
2 track non-QE
GeV2
Co
un
ts /
0.05
GeV
2
DataNCCC multi πCC coherent πCC 1πCC QE
Data favours coherent pion
suppression (PRL 95, 252301
(2005)).
Oscillation analysis is insensitive
to how q2 deficit is modelled.
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48
Flux measurement with the kiloton detector
The kiloton near detector, like SK, is water Cherenkov detector. So
cross-section systematics cancel in far-near ratio.
N expSK = N obs
KT ·
[∫
dEνΦSK(Eν)σ(Eν)∫
dEνΦKT (Eν)σ(Eν)·
]
MSK
MKT
·εSK
εKT
[Far-near ratio (from MC) ≈ 1 × 10−6]
N obsSK = 107 N exp
SK = 150.9+11.5−10.1
Null oscillation probability: P = 0.0025 (3.02σ)
(PRL 94, 081802 (2005))
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Reconstructed Neutrino Spectrum at Super-K
Reconstructed energy spectrum from 1-ring µ events
Eνrec
0
2
4
6
8
10
12
14
16
18
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5[GeV]
even
ts/0
.2[G
eV]
Kolgomorov-Smirnov test probability (no oscillation): 0.08%
Kolgomorov-Smirnov test probability (best-fit oscillation): 36%
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50
Allowed K2K Mixing Parameters
Consistency with null oscillation
hypothesis:
Normalization only 0.26%
Spectrum only 0.74%
Spectrum + normalization 0.005%
Favored mixing parameters:
∆m2 = 2.8 × 10−3 eV2
sin2 2θ = 1
90% CL at sin2 2θ = 1:
1.9 − 3.6 × 10−3 eV2
K2K-I & K2K-II
10-4
10-3
10-2
10-1
0 0.2 0.4 0.6 0.8 1sin2(2θ)
∆m2
[eV
2 ]
68%90%99%
Null oscillation hypothesis rejected at 4.0σ level
(PRL 94, 081802 (2005))
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The MINOS Experiment
A beam from Fermilab’s Main Injector to
the Soudan mine located 720 km away
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Expected MINOS Sensitivity
Goals of MINOS;
• precise measurement of ∆m2
• test alternatives of oscillation model (eg. neutrino decay)
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Conclusions• Neutrinos have mass and oscillate. Compelling evidence from four different kinds
of experiments
1. solar neutrinos
2. reactor neutrinos
3. atmospheric neutrinos
4. long baseline neutrino beams
• Neutrino mixing opens a whole new area of lepton flavour physics. This is new
physics beyond the Standard Model, involving new fields and new fundamental
constants!
• Next time:
1. How many neutrinos are there really?
2. What are the theoretical implications?
3. How do we complete our map of the neutrino mixing matrix?
4. How might we determine the absolute mass of neutrinos?
5. Are neutrinos the reason we’re all here?