1 Probing CP violation in neutrino oscillations with neutrino telescopes Kfir Blum, Yosef Nir, Eli Waxman arXiv: [hep-ph]

2 Why hunt CPV? (in Lepton sector) CP structure in Quark sector well known. CP structure in Quark sector well known. Completely unknown in Lepton sector Leptogenesis may explain baryon asymmetry, provided large CPV in lepton sector Leptogenesis may explain baryon asymmetry, provided large CPV in lepton sector

3 Probing CP violation with ν telescopes Propagate flavor composition from source to detector Astrophysical distances - P αβ is CP conserving depends on CP phase δ via cosδ only Establish CPV Exclude |cosδ|=1

4 Flavor ratios Avoid normalization uncertainty – consider flux ratios S only becomes available at >PeV energies T may be measured at GR ~ 6.4PeV

5 Astrophysical sources Extragalactic: GRBs ε ν > TeV High energy primaries mesons π ± typically dominate Standard pion source At high energies muons cool off prior to decay. Pion source becomes a muon-damped source

6 More than one type of source More than one ratio Reactor: sin 2 2θ 13 =0.09±0.01 R π : ΔR/R=5% Rμ,Sμ: ΔR/R, ΔS/S=10% S π : ΔS/S=10% 90%CL (1dof)

7 Challenges \ Requirements Mixing angles Mixing angles θ 13 must be large, and well measured θ 13 must be large, and well measured Precision data on θ 12 and θ 23 Precision data on θ 12 and θ 23 Source mechanism Source mechanism Good handle on flavor ratios at the source Good handle on flavor ratios at the source Transition to muon-damped regime must be observed Transition to muon-damped regime must be observed Challenges at neutrino telescopes Challenges at neutrino telescopes Flavor identification! Flavor identification! High energy reach High energy reach

8 Conclusions Neutrino telescopes may be able to probe CPV provided some favorable conditions Muon-damped regime, with sufficient statistics (O(100)) Muon-damped regime, with sufficient statistics (O(100)) in addition to pion flux Precision theoretical predictions for flavor at source Precision theoretical predictions for flavor at source Large θ 13 (D-CHOOZ,…) Large θ 13 (D-CHOOZ,…) Improved θ 12, θ 23 (KamLAND, SBs,…) Improved θ 12, θ 23 (KamLAND, SBs,…) Last requirements Global analysis

9 Thank you! Thank you!*

10 Mixing angles: θ 13 Constraints on δ from oscillation experiments generically break down if θ 13 too small. Constraints on δ from oscillation experiments generically break down if θ 13 too small. IF θ 13 large (~0.15) reactor experiments can detect it within ~ 10 years (D-CHOOZ: hep-ex/ )

11 With vanishing uncertainties With current uncertainties With reduced uncertainties Mixing angles: θ 12, θ 23

12 Source mechanism Theoretical knowledge of flavor ratios at the source Standard pion source Standard pion source ~10% corrections are likely. Systematics when considering a specific source; Spread when integrating over a population Muon-damped regime Muon-damped regime Transition to muon-damped regime is a robust prediction. However, transition threshold is model dependent

13 Challenges at neutrino telescopes Flavor id Study errors. Is 10% feasible? Study errors. Is 10% feasible? Disentangle ν e - from ν τ -originated events Disentangle ν e - from ν τ -originated events (below transition: S π !) Energy reach Reach for the muon-damped regime! Reach for the muon-damped regime! ν τ –originated event topology emerges ν τ –originated event topology emerges