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

Superbeams?Superbeams?

Nelson, NUFACT 2005

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