How Will We See How Will We See Leptonic CP Violation?Leptonic CP Violation?
D. CasperD. CasperUniversity of California, IrvineUniversity of California, Irvine
Will We See Leptonic CP Will We See Leptonic CP Violation?Violation?
Matter asymmetry of the universe Matter asymmetry of the universe likely tied to CP-violation (and baryon likely tied to CP-violation (and baryon number non-conservation)number non-conservation)
Hadronic CP violation seems too small Hadronic CP violation seems too small to account for matter asymmetryto account for matter asymmetry
Hadronic mixings and CP violation are Hadronic mixings and CP violation are smallsmall Leptonic mixing angles are large…Leptonic mixing angles are large… ……maybe leptonic CP violation is also maybe leptonic CP violation is also
large?large?
The Prerequisite: The Prerequisite: 1313
CP violation requires three-flavor CP violation requires three-flavor mixingmixing All three mixing angles enter the CP-All three mixing angles enter the CP-
violating termviolating term All angles must be non-zeroAll angles must be non-zero
1212 and and 2323 are large are large Observing leptonic CP violation Observing leptonic CP violation
requires observing non-zero requires observing non-zero 1313
The Search for The Search for 1313: CHOOZ: CHOOZ CHOOZ reactor CHOOZ reactor
experiment final experiment final results (1999)results (1999)
Limit on Limit on 1313 ~ 11 ~ 11°° sinsin22 2 21313 < ~ 0.1 < ~ 0.1
Best current limit Best current limit in atmospheric in atmospheric mass regionmass region
The Search for The Search for 1313: : AtmosphericAtmospheric
Super-Kamiokande three-flavor analysis(Little prospect of reaching significantly beyond CHOOZ)
Normal hierarchyInverted hierarchy
The Search for The Search for 1313: Reactors: Reactors Several reactor Several reactor
experiments proposed experiments proposed to search for to search for 1313:: Double CHOOZDouble CHOOZ Daya BayDaya Bay BraidwoodBraidwood
All hope to improve All hope to improve on CHOOZ on CHOOZ (disappearance) (disappearance) sensitivitysensitivity
Typical sensitivities:Typical sensitivities:sinsin22 2 2 1313 ~ 0.03 ~ 0.03 Double CHOOZ hopes Double CHOOZ hopes
to reach this by to reach this by December 2010December 2010
No sensitivity to No sensitivity to ……
Far detector only
Far & Near detectorstogether
05/2007 05/2008 05/2009 05/2010
sys=2.5%
sys=0.6%
Dazeley, NUFACT 2005
The Search for The Search for 1313: : SuperbeamsSuperbeams Exploit off-axis “trick” to Exploit off-axis “trick” to
create narrow-band beam create narrow-band beam without losing signalwithout losing signal
T2KT2K ApprovedApproved Funded in JapanFunded in Japan Beam under constructionBeam under construction Detector (SuperK) existsDetector (SuperK) exists
NONOAA Approved by PACApproved by PAC Not yet funded (~$200M?)Not yet funded (~$200M?) Beam existsBeam exists 50 kt liquid scintillator 50 kt liquid scintillator
detector designdetector design Begin construction in one Begin construction in one
year?year? Fully operational July 2011?Fully operational July 2011?
Yamada, NUFACT 2005
Nelson, NUFACT 2005
CP Violation in Neutrino CP Violation in Neutrino OscillationOscillation
CP violation is manifest in differences CP violation is manifest in differences between neutrino and anti-neutrino between neutrino and anti-neutrino oscillation probabilitiesoscillation probabilities Unfortunately matter effects are also CP Unfortunately matter effects are also CP
violatingviolating Matter effects in turn depend on the mass Matter effects in turn depend on the mass
hierarchyhierarchy CP violation does not affect disappearance CP violation does not affect disappearance
channelschannels These differences are typically a few These differences are typically a few
percentpercent
Detector ChallengesDetector Challenges Since CP violation Since CP violation
causes small causes small changes in changes in probability, large probability, large data samples are data samples are required to required to measure themmeasure them Big detectors…Big detectors… Expensive Expensive
detectors…detectors…
Matter Effects and Matter Effects and DegeneraciesDegeneracies
Observable oscillation probabilities Observable oscillation probabilities may not uniquely determine the may not uniquely determine the physical parametersphysical parameters
Parameter degeneraciesParameter degeneracies 1313 - - sgn(sgn(mm2323
22)) octant of octant of 2323
SystematicsSystematics 1% measurements require careful control 1% measurements require careful control
of systematicsof systematics To find CP violation, must compare neutrinos To find CP violation, must compare neutrinos
and anti-neutrinos (different cross-sections)and anti-neutrinos (different cross-sections) Anti-neutrino beams contain significant Anti-neutrino beams contain significant
contamination from neutrino interactionscontamination from neutrino interactions Conventional neutrino beams difficult to Conventional neutrino beams difficult to
predict accuratelypredict accurately CC interactions and backgrounds are different CC interactions and backgrounds are different
in near and far detectors, due to oscillationin near and far detectors, due to oscillation Your near detector cannot easily measure Your near detector cannot easily measure
cross-sections for the appearance signalcross-sections for the appearance signal
A Neutrino Factory?A Neutrino Factory? A neutrino factory (20-50 A neutrino factory (20-50
GeV muon storage ring) is GeV muon storage ring) is the ultimate tool for the ultimate tool for studying neutrino studying neutrino oscillationoscillation Wrong-sign muon Wrong-sign muon
appearanceappearance Potential step toward Potential step toward
muon collidermuon collider Serious technical and cost Serious technical and cost
challenges…challenges… Important R&D ramping upImportant R&D ramping up
MICEMICE MUCOOLMUCOOL nTOF11nTOF11 ……
P. Huber, NUFACT 2005
A Betabeam?A Betabeam? The idea: accelerate and store The idea: accelerate and store -unstable ions to -unstable ions to
create a pure create a pure electron-flavorelectron-flavor beam beam --: : 66HeHe ++: : 1818NeNe
Shares many advantages of neutrino factory:Shares many advantages of neutrino factory: Spectrum is ~perfectly knownSpectrum is ~perfectly known Flux is ~perfectly knownFlux is ~perfectly known Muon appearanceMuon appearance Can in principle run neutrinos and anti-neutrinos Can in principle run neutrinos and anti-neutrinos
simultaneouslysimultaneously Near and far spectra nearly identicalNear and far spectra nearly identical
No secondary beam cooling/reaccelerationNo secondary beam cooling/reacceleration Technically, a much simpler problemTechnically, a much simpler problem
P. Zucchelli, Phys.Lett.B 532, 166-172 (2002)
CERN Betabeam ConceptCERN Betabeam Concept
Neutrino Source
Decay Ring
Ion production ISOL target &
Ion source
Proton Driver SPL
Decay ring
B = 1500 Tm B = 5 T C = 7000 m Lss = 2500 m
SPS
Acceleration to medium energy
RCS
PS
Acceleration to final energy
PS & SPS
Experiment
Ion acceleration Linac
Beam preparation Pulsed ECR
Ion production Acceleration Neutrino source
,
,
M. Lindroos, NUFACT 2005
Low-Energy BetabeamLow-Energy Betabeam Initial studies Initial studies
focused on low-focused on low- scenario at 150 km scenario at 150 km baselinebaseline Reduce backgrounds Reduce backgrounds
by sitting near by sitting near thresholdthreshold
No energy No energy dependence availabledependence available
Counting experimentCounting experiment Low boost reduces Low boost reduces
focusing and fluxfocusing and flux
M. Mezzetto, J.Phys.G 29, 1771-1776 (2003) [hep-ex/0302007]
Sensitivity to distinguish =0° from =90°at 99% CL: betabeam and betabeam plussuperbeam, compared to NUFACT andand T2K
A Higher-Energy BetabeamA Higher-Energy Betabeam New approach: higher New approach: higher
energy, longer energy, longer baselinebaseline
~ ~ Exploit energy Exploit energy
dependencedependence Increase flux with Increase flux with
more focusingmore focusing More cross-section More cross-section
at higher energyat higher energy NC backgrounds NC backgrounds
still manageablestill manageable
J.Burguet-Castell, D. Casper, J.J. Gomez-Cadenas, P.Hernandez, F. Sanchez,Nucl.Phys.B 695, 217-240 (2004) [hep-ph/0312068]
Region where can be distinguished from=0 and =90 at 99% CL
=60/100, 150 km, 400 kt H2O
=350/580, 730 km, 400 kt H2O
=350/580, 730 km, 40 kt H2O
2
20
dN
d dE L
Optimizing the BetabeamOptimizing the Betabeam Relax baseline and Relax baseline and
boost constraints to boost constraints to maximize maximize 1313 and and sensitivitysensitivity
Setup 0:Setup 0: Original Frejus, low-Original Frejus, low-
Setup 1:Setup 1: Optimal Frejus (Optimal Frejus (=120)=120)
Setup 2:Setup 2: Optimal SPSOptimal SPS
(L=350 km, (L=350 km, =150)=150) Setup 3:Setup 3:
Optimal betabeamOptimal betabeam(L=730 km, (L=730 km, =350)=350)
J. Burguet-Castell, D. Casper, E. Couce, J.J. Gomez-Cadenas, P. Hernandez,Nucl.Phys.B 725, 306-326 (2005) [hep-ph/0503021]
Region of the 1313 - - plane where we can plane where we candetermine at 99% CL that determine at 99% CL that 1313 0 0
Optimized Betabeam CP Optimized Betabeam CP SensitivitySensitivity
For optimal betabeamFor optimal betabeam sensitivity ~ 10sensitivity ~ 10°° 1313 sensitivity ~ 10 sensitivity ~ 10-4-4
Also sensitive to Also sensitive to sgn(sgn(mm22
2323) and octant ) and octant of of 2323
If T2K sees non-zero If T2K sees non-zero 1313, measure , measure
If T2K sees no signal, If T2K sees no signal, extend extend 1313 sensitivity by sensitivity by another factor of 10another factor of 10
Proton decay sensitivity Proton decay sensitivity ~10~103535 years (e years (e++ 00))
Region of the 13 - plane where wecan distinguish from =0 and =180at 99% CL for any best-fit value of 13
(i.e. that there is leptonic CP violation)
TeV?TeV? Our optimization studies show that Our optimization studies show that
increasing the Lorentz boost optimizes the increasing the Lorentz boost optimizes the sensitivity of the beta-beamsensitivity of the beta-beam
Two feasible sites for Two feasible sites for ~ few hundred: ~ few hundred: CERN-SPS (possibly with upgrade)CERN-SPS (possibly with upgrade) TevatronTevatron
Need Fermilab feasibility study to estimate Need Fermilab feasibility study to estimate realistic costsrealistic costs Similar to neutrino factory studySimilar to neutrino factory study
An opportunity for the An opportunity for the decisivedecisive neutrino neutrino oscillation experiment!oscillation experiment!
A Mono-energetic Beam?A Mono-energetic Beam? Accelerate an ion that Accelerate an ion that
decays by electron capturedecays by electron capture Two-body final stateTwo-body final state Monoenergetic Monoenergetic
A challengeA challenge Ions cannot be completely Ions cannot be completely
strippedstripped Finite survival time in partially Finite survival time in partially
ionized stateionized state Must decay rapidlyMust decay rapidly Must have small enough Q Must have small enough Q
valuevalue 150150DyDy
Short decay time (~7 Short decay time (~7 minutes)minutes)
1.4 MeV neutrino in rest frame1.4 MeV neutrino in rest frame 0.1% 0.1% -decay-decay
J. Bernabeu, J. Burguet-Castell, C. Espinoza, M. Lindroos, hep-ph/0505054
ConclusionConclusion Seems reasonable to expect leptonic Seems reasonable to expect leptonic
CP violationCP violation The most challenging neutrino The most challenging neutrino
physics measurement ever physics measurement ever attemptedattempted
A betabeam at Fermilab could be the A betabeam at Fermilab could be the decisive, complementary follow-on to decisive, complementary follow-on to T2KT2K