How Will We See Leptonic CP Violation? D. Casper University of California, Irvine

Will We See Leptonic CP Violation? Matter asymmetry of the universe likely tied to CP-violation (and baryon number non-conservation) Matter asymmetry of the universe likely tied to CP-violation (and baryon number non-conservation) Hadronic CP violation seems too small to account for matter asymmetry Hadronic CP violation seems too small to account for matter asymmetry Hadronic mixings and CP violation are small Hadronic mixings and CP violation are small Leptonic mixing angles are large… Leptonic mixing angles are large… …maybe leptonic CP violation is also large? …maybe leptonic CP violation is also large?

The Prerequisite:  13 CP violation requires three-flavor mixing CP violation requires three-flavor mixing All three mixing angles enter the CP-violating term All three mixing angles enter the CP-violating term All angles must be non-zero All angles must be non-zero  12 and  23 are large  12 and  23 are large Observing leptonic CP violation requires observing non-zero  13 Observing leptonic CP violation requires observing non-zero  13

The Search for  13 : CHOOZ CHOOZ reactor experiment final results (1999) CHOOZ reactor experiment final results (1999) Limit on  13 ~ 11° Limit on  13 ~ 11° sin 2 2  13 < ~ 0.1 sin 2 2  13 < ~ 0.1 Best current limit in atmospheric mass region Best current limit in atmospheric mass region

The Search for  13 : Atmospheric Super-Kamiokande three-flavor analysis (Little prospect of reaching significantly beyond CHOOZ) Normal hierarchy Inverted hierarchy

The Search for  13 : Reactors Several reactor experiments proposed to search for  13 : Several reactor experiments proposed to search for  13 : Double CHOOZ Double CHOOZ Daya Bay Daya Bay Braidwood Braidwood All hope to improve on CHOOZ (disappearance) sensitivity All hope to improve on CHOOZ (disappearance) sensitivity Typical sensitivities: sin 2 2  13 ~ 0.03 Typical sensitivities: sin 2 2  13 ~ 0.03 Double CHOOZ hopes to reach this by December 2010 Double CHOOZ hopes to reach this by December 2010 No sensitivity to  … No sensitivity to  … Far detector only Far & Near detectors together 05/ /200805/ /2010  sys =2.5%  sys =0.6% Dazeley, NUFACT 2005

The Search for  13 : Superbeams Exploit off-axis “trick” to create narrow-band beam without losing signal Exploit off-axis “trick” to create narrow-band beam without losing signal T2K T2K Approved Approved Funded in Japan Funded in Japan Beam under construction Beam under construction Detector (SuperK) exists Detector (SuperK) exists NO A NO A Approved by PAC Approved by PAC Not yet funded (~$200M?) Not yet funded (~$200M?) Beam exists Beam exists 50 kt liquid scintillator detector design 50 kt liquid scintillator detector design Begin construction in one year? Begin construction in one year? Fully operational July 2011? Fully operational July 2011? Yamada, NUFACT 2005 Nelson, NUFACT 2005

CP Violation in Neutrino Oscillation CP violation is manifest in differences between neutrino and anti-neutrino oscillation probabilities CP violation is manifest in differences between neutrino and anti-neutrino oscillation probabilities Unfortunately matter effects are also CP violating Unfortunately matter effects are also CP violating Matter effects in turn depend on the mass hierarchy Matter effects in turn depend on the mass hierarchy CP violation does not affect disappearance channels CP violation does not affect disappearance channels These differences are typically a few percent These differences are typically a few percent

Detector Challenges Since CP violation causes small changes in probability, large data samples are required to measure them Since CP violation causes small changes in probability, large data samples are required to measure them Big detectors… Big detectors… Expensive detectors… Expensive detectors…

Matter Effects and Degeneracies Observable oscillation probabilities may not uniquely determine the physical parameters Observable oscillation probabilities may not uniquely determine the physical parameters Parameter degeneracies Parameter degeneracies  13 -   13 -  sgn(  m 23 2 ) sgn(  m 23 2 ) octant of  23 octant of  23

Systematics 1% measurements require careful control of systematics 1% measurements require careful control of systematics To find CP violation, must compare neutrinos and anti-neutrinos (different cross-sections) To find CP violation, must compare neutrinos and anti-neutrinos (different cross-sections) Anti-neutrino beams contain significant contamination from neutrino interactions Anti-neutrino beams contain significant contamination from neutrino interactions Conventional neutrino beams difficult to predict accurately Conventional neutrino beams difficult to predict accurately CC interactions and backgrounds are different in near and far detectors, due to oscillation CC interactions and backgrounds are different in near and far detectors, due to oscillation Your near detector cannot easily measure cross- sections for the appearance signal Your near detector cannot easily measure cross- sections for the appearance signal

Superbeams? Nelson, NUFACT 2005

A Neutrino Factory? A neutrino factory (20-50 GeV muon storage ring) is the ultimate tool for studying neutrino oscillation A neutrino factory (20-50 GeV muon storage ring) is the ultimate tool for studying neutrino oscillation Wrong-sign muon appearance Wrong-sign muon appearance Potential step toward muon collider Potential step toward muon collider Serious technical and cost challenges… Serious technical and cost challenges… Important R&D ramping up Important R&D ramping up MICE MICE MUCOOL MUCOOL nTOF11 nTOF11 … P. Huber, NUFACT 2005

A Betabeam? The idea: accelerate and store  -unstable ions to create a pure electron-flavor beam The idea: accelerate and store  -unstable ions to create a pure electron-flavor beam  - : 6 He  - : 6 He  + : 18 Ne  + : 18 Ne Shares many advantages of neutrino factory: Shares many advantages of neutrino factory: Spectrum is ~perfectly known Spectrum is ~perfectly known Flux is ~perfectly known Flux is ~perfectly known Muon appearance Muon appearance Can in principle run neutrinos and anti-neutrinos simultaneously Can in principle run neutrinos and anti-neutrinos simultaneously Near and far spectra nearly identical Near and far spectra nearly identical No secondary beam cooling/reacceleration No secondary beam cooling/reacceleration Technically, a much simpler problem Technically, a much simpler problem P. Zucchelli, Phys.Lett.B 532, (2002)

CERN 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 L ss = 2500 m SPS Acceleration to medium energy RCS PS Acceleration to final energy PS & SPS Experiment Ion acceleration Linac Beam preparation Pulsed ECR Ion productionAccelerationNeutrino source M. Lindroos, NUFACT 2005

Low-Energy Betabeam Initial studies focused on low-  scenario at 150 km baseline Initial studies focused on low-  scenario at 150 km baseline Reduce backgrounds by sitting near  threshold Reduce backgrounds by sitting near  threshold No energy dependence available No energy dependence available Counting experiment Counting experiment Low boost reduces focusing and flux Low boost reduces focusing and flux M. Mezzetto, J.Phys.G 29, (2003) [hep-ex/ ] Sensitivity to distinguish  =0° from  =90° at 99% CL: betabeam and betabeam plus superbeam, compared to NUFACT and and T2K

A Higher-Energy Betabeam New approach: higher energy, longer baseline New approach: higher energy, longer baseline  ~   ~  Exploit energy dependence Exploit energy dependence Increase flux with more focusing Increase flux with more focusing More cross-section at higher energy More cross-section at higher energy NC backgrounds still manageable NC backgrounds still manageable J.Burguet-Castell, D. Casper, J.J. Gomez-Cadenas, P.Hernandez, F. Sanchez, Nucl.Phys.B 695, (2004) [hep-ph/ ] Region where  can be distinguished from  =0 and  =90 at 99% CL  =60/100, 150 km, 400 kt H 2 O  =350/580, 730 km, 400 kt H 2 O  =350/580, 730 km, 40 kt H 2 O

Optimizing the Betabeam Relax baseline and boost constraints to maximize  13 and  sensitivity Relax baseline and boost constraints to maximize  13 and  sensitivity Setup 0: Setup 0: Original Frejus, low-  Original Frejus, low-  Setup 1: Setup 1: Optimal Frejus (  =120) Optimal Frejus (  =120) Setup 2: Setup 2: Optimal SPS (L=350 km,  =150) Optimal SPS (L=350 km,  =150) Setup 3: Setup 3: Optimal betabeam (L=730 km,  =350) Optimal betabeam (L=730 km,  =350) J. Burguet-Castell, D. Casper, E. Couce, J.J. Gomez-Cadenas, P. Hernandez, Nucl.Phys.B 725, (2005) [hep-ph/ ]  13 -  plane where we can Region of the  13 -  plane where we can determine at 99% CL that  13  0

Optimized Betabeam CP Sensitivity For optimal betabeam For optimal betabeam  sensitivity ~ 10°  sensitivity ~ 10°  13 sensitivity ~  13 sensitivity ~ Also sensitive to sgn(  m 2 23 ) and octant of  23 Also sensitive to sgn(  m 2 23 ) and octant of  23 If T2K sees non-zero  13, measure  If T2K sees non-zero  13, measure  If T2K sees no signal, extend  13 sensitivity by another factor of 10 If T2K sees no signal, extend  13 sensitivity by another factor of 10 Proton decay sensitivity ~10 35 years (e +  0 ) Proton decay sensitivity ~10 35 years (e +  0 ) Region of the  13 -  plane where we can distinguish  from  =0 and  =180 at 99% CL for any best-fit value of  13 (i.e. that there is leptonic CP violation)

 TeV? Our optimization studies show that increasing the Lorentz boost optimizes the sensitivity of the beta-beam Our optimization studies show that increasing the Lorentz boost optimizes the sensitivity of the beta-beam Two feasible sites for  ~ few hundred: Two feasible sites for  ~ few hundred: CERN-SPS (possibly with upgrade) CERN-SPS (possibly with upgrade) Tevatron Tevatron Need Fermilab feasibility study to estimate realistic costs Need Fermilab feasibility study to estimate realistic costs Similar to neutrino factory study Similar to neutrino factory study An opportunity for the decisive neutrino oscillation experiment! An opportunity for the decisive neutrino oscillation experiment!

A Mono-energetic Beam? Accelerate an ion that decays by electron capture Accelerate an ion that decays by electron capture Two-body final state Two-body final state Monoenergetic Monoenergetic A challenge A challenge Ions cannot be completely stripped Ions cannot be completely stripped Finite survival time in partially ionized state Finite survival time in partially ionized state Must decay rapidly Must decay rapidly Must have small enough Q value Must have small enough Q value 150 Dy 150 Dy Short decay time (~7 minutes) Short decay time (~7 minutes) 1.4 MeV neutrino in rest frame 1.4 MeV neutrino in rest frame 0.1%  -decay 0.1%  -decay J. Bernabeu, J. Burguet-Castell, C. Espinoza, M. Lindroos, hep-ph/

Conclusion Seems reasonable to expect leptonic CP violation Seems reasonable to expect leptonic CP violation The most challenging neutrino physics measurement ever attempted The most challenging neutrino physics measurement ever attempted A betabeam at Fermilab could be the decisive, complementary follow-on to T2K A betabeam at Fermilab could be the decisive, complementary follow-on to T2K