last lecture: the quest for the two remaining unknowns in ... · last lecture: the quest for the...
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CP Violation and the Mass Hierarchy Last lecture: the quest for the two remaining unknowns in our understanding of 3-neutrino mixing
Aside: Other Unknowns Important Neutrino Physics Goals
• Majorana or Dirac nature of neutrinos – double beta decay
• absolute scale of neutrino mass – direct neutrino mass measurements and cosmology
• are there only 3 active neutrino states? • any evidence for sterile neutrinos?
Neutrino CP Violation • is as “simple” as conducting two experiments and measuring
• this is a direct test of CP symmetry • could imagine this starting with electron neutrinos and electron
antineutrinos, but: • these have to be appearance experiments – survival probabilities for
disappearance experiments don’t depend δCP • it is possible to make energetic electron neutrino and antineutrino
beams that could then search for muon appearance • e.g. beta beams
• but muon neutrino and antineutrino beams are the current leading technology (DAR: LSND, DIF: MINOS, T2K, NOνA, MiniBooNE, CNGS, LBNE)
• don’t even bother thinking about tau neutrino beams except to entertain yourself with thought experiments
Pνµ→νe– Pνµ→νe
T Violation • by the way, CP violation for neutrino oscillations was first
discussed in 1978 • N. Cabibbo, Phys. Lett. B 72, 333-335 (1978)
“Time Reversal Violation in Neutrino Oscillation”
• short paper pointing out that if you have 3 (or more) neutrino states, non-degenerate masses (e.g. so both Δm2 have to be non-zero), the unitary mixing matrix can be complex and can lead to T (or CP) violation
• note: CPT tells us that CP violation is the same as T violation • that’s why a disappearance experiment doesn’t work for CP
Pνe→νe time reversed experiment would be the same
T Violation cont’d • for appearance experiments, it can work to search for
• mathematically, the same quantities will be involved
• technical note: Nunokawa, Parke and Valle point out in arXiv:0710.0554 (review published in Prog. Part. Nucl. Phys.) that does contain cosδ and thus by doing a disappearance experiment you can determine sinδ (up to a sign) since the other angles can be determined
Pνµ→νe= Pνe→νu
?
Pνµ→νµ= Pνµ→νµ
this bothers me greatly!
Neutrinos and Antineutrinos
Right-Handed
Giunti
PMNS Neutrino Mixing Matrix ν f = U fi ν ii∑
CP Violation
2Re [Uαk* UβkUα jUβ j
*
k> j∑ −UαkUβk
* Uα j* Uβ j ]exp(−i
Δmkj2L
2E)
= 4Re i Im[Uαk* UβkUα jUβ j
*
k> j∑ ]exp(−i
Δmkj2L
2E)
= 4 Im[Uαk* UβkUα jUβ j
*
k> j∑ ]sin(
Δmkj2L
2E)
Pνµ→νe– Pνµ→νe
=
Jarlskog Invariant • this quantity is called a Jarlskog invariant, from the quark
CKM unitarity triangle J = c12 s12 c23 s23 c13
2 s13 sin δ =
J = Im[Uαk* UβkUα jUβ j
* ]
= 4 Im[Uαk* UβkUα jUβ j
*
k> j∑ ]sin(
Δmkj2 L
2E)
= sinδ sin2θ12 sin2θ23 sinθ13 cos2θ13 sin(
Δm312 L
2E)
−sinδ sin2θ12 sin2θ23 sinθ13 cos2θ13 sin(
Δm322 L2E
)
−sinδ sin2θ12 sin2θ23 sinθ13 cos2θ13 sin(
Δm212 L
2E)
if any angle is zero, ΔP=0; if any Δm2=0, ΔP=0
18sin2θ12 sin2θ23 sin2θ13 cosθ13 sinδ
Properties of Jarlskog Permutations
AαβCP = 4J sαβ ;kj sin(
Δmkj2 L
2E)
k> j∑
• s for 31 is –1 • s for 32 is +1 • s for 21 is +1
J = c12 s12 c23 s23 c132 s13 sin δ =
e→ µ,µ→τ ,τ → eIs positive and the sign flips if flavours flip
Pνe→νµ− Pνe→νµ
= AµeCP = −Aeµ
CP
18sin2θ12 sin2θ23 sin2θ13 cosθ13 sinδ
Search for CP Violation
• all angles should be large! • should place detector at correct L for neutrino beam E • Δm21 solar is small compared to Δm31
• the mass hierarchy can matter
• NH • IH
• |J| ≤ 0.039 from present knowledge of all 3 mixing angles
AαβCP = 4J sαβ ;kj sin(
Δmkj2 L
2E)
k> j∑
Δm312 = Δm21
2 + Δm322
Δm322 = Δm21
2 + Δm312
J = 18sin2θ12 sin2θ23 sin2θ13 cosθ13 sinδ
compare J for CKM quarks = 3 × 10–5
Accelerator Neutrino Beams for CP Violation
figure from H. Ray
T2K as an Example The!T2K!Experiment!
~500 Collaborators / 340 Authors / 59 Institutions / 11 Countries (Canada / France / Germany / Italy / Japan / Poland / Russia / Spain / Switzerland / UK / USA)
30 GeV Tunnel
06/04/2014! Chris!Walter!9!Results!from!T2K!9!Neutrino2014! 2!
T2K slides from C. Walter talk at Neutrino 2014
The T2K Off-Axis Beam
0
50
100
150
200
250
300
350
400
0En (GeV)
at 295 km
2ºAll
1 2 3 4 5
High$energy$$tail$causes$$backgrounds$
At$1$GeV$an$off5axis$$beam$has$a$higher$$and$narrower$flux$peak.$
Super9Kamiokande!Off!Axis!(2.5°)!Neutrino$Source$
π
120m 0m 280m 295 km
on-axis off-axis
monitor
Proton$Beam$ Neutrino$Beam$
The$kinemaQcs$of$pion$decay$allow$$us$to$make$a$narrower$neutrino$$beam.$$
06/04/2014! Chris!Walter!9!Results!from!T2K!9!Neutrino2014!
Epion!(GeV)!
E ν!(G
eV)!
7!
ND280!Near!Detector!
Example Off-axis Spectra
Eν (MeV) (GeV)
your homework: make this plot
Electron Appearance Probability
and then there are matter effects on top of this! in an experiment, DIF beam has some intrinsic νe contamination
• Comparing!with!the!external!reactor!constraint!the!best!overlap!is!for!the!normal!hierarchy!with!δcp=–π/2.!
• This!is!a!lucky$point!!• You!also!need!to!increase!the!θ23!mixing!angle!to!account!for!the!number!of!observed!events.!
06/04/2014! 15!Chris!Walter!9!Results!from!T2K!9!Neutrino2014!
Let’s!think!about!these!regions!!
Note: Marginalized over θ23 and Δm2
32
T2K Recent Results • narrow band is reactor θ13
measurement • use theta13 reactor results to
help constrain (break degeneracies)
• use second expt (e.g. T2K-NOνA) to break degeneracies • especially different baselines with
both at different oscillation maxima • must correct for/exploit different
matter effects for different baselines of beam traversing the Earth
Future!SensiQvity!to!CPV!using!T2K!
06/04/2014! Chris!Walter!9!Results!from!T2K!9!Neutrino2014! 23!
No systematics 5% error on signal, 10% on background
T2K!studies!indicate!our!best!sensiQvity!will!be!for!50%!ν/50%!anQ9ν!!running.!AnQ9nu!running!also!opens!a!large!new!physics!program.!!
50%!ν/50%!anQ9ν!(true!NH)!100%!ν!(true!NH)!
50%!ν/50%!anQ9ν!(true!NH)!w/!Reactor!constraint!
100%!ν!(true!NH)!w/!Reactor!constraint!
“Lucky! (+: Sin22θ=0.1, δCP=-90)”
NH$
T2K:!50%!ν/50%!anQ9ν!
Precision Reactor Neutrino Disappearance
• could break degeneracy with other experiments that can determine the hierarchy • precision atmospheric neutrino (e.g. PINGU, ICAL) • in principle could have something to say about δCP (I showed that
yesterday when we looked at recent Super-K atmospheric results)
• one class of experiments is precision reactor neutrino disappearance (e.g. JUNO, RENO-50)
Future Long Baseline Neutrino Experiments plans for LBNE, Hyper-K feature: - intense neutrino beams for higher statistics - ideally both neutrino and antineutrino beams - large far detectors to accumulate statistics
- how to break the hierarchy degeneracy? - exploit matter effects
- over long baseline, beams traverse greater distance underground - we know matter effects care about the sign of the hierarchy
Future Long Baseline Neutrino Experiments plans for LBNE, Hyper-K feature: - intense neutrino beams for higher statistics - ideally both neutrino and antineutrino beams - large far detectors to accumulate statistics
- how to break the hierarchy degeneracy? - exploit matter effects
- over long baseline, beams traverse greater distance underground - we know matter effects care about the sign of the hierarchy
Neutrino Mass Hierarchy • Large T13 open doors to MH
– Utilize matter effects ¾e-Q CC interactions in the earth
modulate the oscillation probability at long baselines (LBNE, LBNO, T2HK)
2
Precision Reactor Neutrino Disappearance
• could break degeneracy with other experiments that can determine the hierarchy • precision atmospheric neutrino (e.g. PINGU, ICAL) • in principle could have something to say about δCP (I showed that
yesterday when we looked at recent Super-K atmospheric results)
• one class of experiments is precision reactor neutrino disappearance (e.g. JUNO, RENO-50)
JUNO • Jiangmen Underground Neutrino Observatory • 20 kton liquid scintillator with 3%/√E energy resolution
Daya Bay ~60 km JUNO
JUNO Experiment
5
� Jiangmen Underground Neutrino Observatory (was Daya Bay II) slides from L. Wed talk at Neutrino 2014
Location of JUNO NPP Daya Bay Huizhou Lufeng Yangjiang Taishan Status Operational Planned Planned Under construction Under construction Power 17.4 GW 17.4 GW 17.4 GW 17.4 GW 18.4 GW
Yangjiang NPP
Taishan NPP
Daya Bay NPP
Huizhou NPP
Lufeng NPP
53 km 53 km
Hong Kong
Macau
Guang Zhou
Shen Zhen
Zhu Hai 700 m underground
2.5 h drive
JUNO
6
Previous site candidate
JUNO Detector Concept Challenge: high-precision, giant LS detector
11
20 kt LS
Acrylic tank: )a34.5m Stainless Steel tank: )a39.0m
~1500 20” VETO PMTs
coverage: ~77% ~18000 20” PMTs
Muon detector
Steel Tank
5m
~6kt MO
~20kt water
JUNO RENO-50
Mass Hierarchy from Precision Reactor Spectrum • need high statistics and excellent energy resolution
Phys.Rev.D78:111103,2008
Neutrino Mass Hierarchy • Large T13 open doors to MH
– Exploit L/E spectrum with reactors
3
S.T. Petcov et al., PLB533(2002)94 S.Choubey et al., PRD68(2003)113006 J. Learned et al., PRD78, 071302 (2008) L. Zhan, Y. Wang, J. Cao, L. Wen, PRD78:111103, 2008, PRD79:073007, 2009 J. Learned et al., arXiv:0810.2580 … Realistic requirements about determining MH with reactors will be discussed later
Vision&of&the&Future&for&Neutrino&Oscilla3ons&• from%puzzle%
– to%discoveries%• to%complete%determina3on%of%mixing%parameters%in%the%lepton%sector%
– CP%viola3on%(Majorana%nature%of%neutrinos)%
• probing&neutrino&mass&and&mixing&will&guide&us&to&the&correct&extensions&of&the&Standard&Model&at&higher&energy&scales&