1 CP violation from a combined Beta Beam and Electron Capture neutrino experiment Catalina Espinoza U. Valencia and IFIC NUFACT09 Chicago, July 2009 Work in collaboration with J. Bernabeu, C. Orme, S. Palomares-Ruiz and S. Pascoli based on JHEP 0906:040, 2009

2 Programme  What is known, what is unknown in Neutrino Oscillations  CP Violation without antineutrinos: Energy Dependence  A combined BB and EC experiment for the same ion Ytterbium  Comparison between different baselines and boosts: i) low energy (E p (SPS) ≤ 450 GeV, 130 km and 650 km) i) low energy (E p (SPS) ≤ 450 GeV, 130 km and 650 km) ii) high energy (E p (SPS) ≤ 1000 GeV, 650 km and 1050 km) ii) high energy (E p (SPS) ≤ 1000 GeV, 650 km and 1050 km)  CP-Violation Discovery Potential and Mass Hierarchy Determination  Conclusions

3 Neutrino flavour oscillations ? Majorana neutrinos ?  0: masses and phases Absolute neutrino masses ?  3 H beta, Cosmology Form of the mass spectrum  Matter effect in neutrino propagation What is known, what is unknown, A hint ?

4 The Pontecorvo MNS Matrix  For Flavour oscillations U: 3 mixings, 1 phase Atmospheric  Atmospheric  KEK, MINOS, OPERA OPERA Appearance   e ! Reactors Matter effects Solar KAMLAND Borexino Even if they are Majorana After diagonalization of the neutrino mass matrix,

5 Three Generations of Experiments 0. Only three?  MiniBoone I. Solar Sector, Atmospheric Sector  II. Connection between both Sectors  III. CP-Violating Interference  δ Beta / EC Beams Super-Beams? Beta / EC Beams ? Neutrino Factory? Δ Δm 2 12, θ 12 │Δm 2 23 │, θ 23 Borexino MINOS, OPERA θ θ 13, Sign (Δm 2 23 ) Double CHOOZ, Daya Bay, T2K, NOVA, …

6 European Strategy Plan demands for ~ 2012 a CDR with the alternatives: SuperBeams, Beta/EC Beams, Neutrino Factory. SuperBeam: no pure Flavour, uncertain continuous Spectrum. Beta Beam: pure Flavour, known continuous Spectrum. EC Beam: pure Flavour, known single Monochromatic Beam. Neutrino Factory: pure Flavour iff detector with charge discrimination, known continuous Spectrum. Frejus CP Violation CP Violation can be observed either by an AsymmetryNeutrinosAntineutrinos Asymmetry between Neutrinos and Antineutrinos or Energy Dependence by Energy Dependence (CP phase as a phase shift) both in the Neutrino channel, or both. Third Generation Experiments: CP Violation

7 Why Energy Dependence ? A theorem CP violation : CPT invariance + CP violation = T non-invariance No Absorptive part  Hermitian Hamiltonian  CP odd = T odd = In vacuum neutrino oscillations for relativistic neutrinos  L/E dependence, so CP-even (odd) terms in the appearance probability  Even (odd) functions of energy. Then ENERGY DEPENDENCE disentangles the CP-even and CP-odd terms is an odd function of time = L !

8 Interest of energy dependence in suppressed neutrino oscillations Appearance probability : |Ue3| gives the strength of P(ν e → ν μ ) CP odd term is odd in E/L δ gives the interference pattern: CP odd term is odd in E/L δ acts as a phase shift  This suggests the idea of using either a monochromatic neutrino beam to separate δ and |Ue3| by energy dependence with different boosts, or a combination of channels with different neutrino energies in the same boost CP violationappearanceexperiments CP violation accessible in suppressed appearance experiments, in order to have access to the interference between the atmospheric and solar probability amplitudes

9 Neutrinos from Neutrinos from β + / Electron Capture 3 body decay ● 3 body decay From the well-known β-decay neutrino spectrum, we can get a pure beam by accelerating β-unstable ions β + decay : P. Zucchelli, Phys.Lett.B532: , 2002 Electron capture: J. Bernabeu, et al Z protons N neutrons Z-1 protons N+1 neutrons boostboost Forward direction EνEν EνEν ● 2 body decay! In the CMsingle discrete energy ● 2 body decay!  In the CM, a single discrete energy If a single final nuclear level is populated From the, we can get a From the single energy EC neutrino spectrum, we can get a pure and by and choosing forward ν’s monochromatic beam by accelerating ec-unstable ions and choosing forward ν’s   One can concentrate all the intensity at the most appropriate energy for extracting the neutrino parameters EνEν

10 A combined Beta Beam and EC neutrino experiment ( ) a SINGLE Gamow-Teller resonance. ● The “breakthrough” came thanks to the recent discovery of isotopes with small half-lives of one min or less, which decay in neutrino channels near 100% to a SINGLE Gamow-Teller resonance. Nuclear In proton rich nuclei (to restore the same orbital angular momentum  Superallowed Gamow-Teller transition for protons and neutrons)  Superallowed Gamow-Teller transition DecayDaughterNeutrino Energy (MeV)BR β + EC α 156 Tm * 152 Er * 2.44 (endpoint) % 38 % 10 % Isotopes with favourable decaying properties: Isotopes with favourable decaying properties: Ion Candidate: Ytterbium ( ) The interesting isotopes have to have The interesting isotopes have to have half-life < vacuum half-life ~ few min. half-life: 26.1 sec

11 A combined beta-beam and EC neutrino experiment ( ) Suppressed appearance probabilities for the CERN-Frejus (130 Km, red line) and CERN- Gran Sasso o Canfranc (650 Km, blue line) baselines. The unoscillated neutrino flux is shown for γ=166 Suppressed appearance probabilities for the CERN-Gran Sasso o Canfranc (650 Km, blue line) and CERN-Boulby (1050 Km, red line) baselines. The unoscillated neutrino flux is shown for γ=369

12 Experimental Setups for the combined experiment Appearance Experiment : Electron Neutrino Flux × Oscillation Probability to muon neutrinos × CC Cross Section for muon production. Detectors: LAr or TASD LAr or TASD, 50 kton  Neutrino spectral information from CC muon events Water Cerenkov Water Cerenkov, 0.5 Mton  Neutrino energy from QE events only + inelastic events in a single bin, with 70% efficience The separation between the energy of the EC spike and the end point energy of the beta-spectrum is possible The separation between the energy of the EC spike and the end point energy of the beta-spectrum is possible: if E ν (QE) > 2γE o (β), since E ν (true) > E ν (QE), the event must be attributed to the EC flux and hence, it is not necessary to reconstruct the true energy Number of decaying ions per year : 2 x  10 years Boost with current SPS Boost γ=166 with current SPS I: CERN-Frejus (130 Km) II: CERN-Gran Sasso or Canfranc (650 Km) Boost γ=366 with an upgraded SPS III: and III-WC: CERN-Gran Sasso or Canfranc (650 Km) IV: and IV-WC: CERN-Boulby (1050 Km) Setups:

13 The virtues of combining energies from BB and EC Sensitivity to θ 13 and δ (Setup III : Gran Sasso or Canfranc ) BBEC BB+E C The power of the combination of the two channels is in the difference in phase and in amplitude between the two fake sinusoidal solutions, selecting a narrow allowed region in the parameter space

14 Comparing baselines I and II for the same boost For the combined BB + EC fluxes with θ 13 =1 0 and δ=90 0 The BB channel contributes very little to the overall sensitivity of the setup, due to the γ 2 dependence. The bulk of the sensitivity is due to the EC channel placed on the first oscillation maximum FrejusGran Sasso or Canfranc

15 Comparing boosts II and III with the same baseline Combination of BB and EC fluxes for θ 13 =1 0 and δ=90 0 The sensitivity is better with the upgraded SPS energy The relative role of the two BB and EC components is exchanged when going from II to III γ=166 γ=369

16 Setup III-WC : Disentangling θ 13 and δ Gran Sasso or Canfranc Solutions for Gran Sasso or Canfranc, from discrete degeneracies included, for θ 13 =1 0, 3 0 and for different values of the CP phase The increase in event rates improves the results substantially with respect to those results for Setup III, although not as much as the size factor between the two detectors. The mass ordering can be determined for large values of the mixing angle. The hierarchy degeneracy worsen the ability to measure δ for negative true values of δ.

17 Comparing III-WC and IV-WC Boulby provides a longer baseline than Gran Sasso or Canfranc. This has two contrasting effects on the sensitivity to measure CP violation: i) Sufficient matter effects to resolve the hierarchy degeneracy for small values of θ 13 ; ii) It decreases the available statistics The smaller count rate results in a poorer resolution. The longer baseline allows for a good determination of the mass ordering, eliminating more degenerate solutions. Gran Sasso or CanfrancBoulby

18 CP Discovery Potential for WC Comparing the two locations of the WC detector, the shorter baseline has a significally (slightly) better reach for CP violation at negative (positive) values of δ than the Boulby baseline. Gran Sasso or Canfranc Boulby

19 Mass hierarchy determination Fraction of δ for which the neutrino mass hierarchy can be determinedFraction of δ for which the neutrino mass hierarchy can be determined III-WC with present priors in the known parameters III-WC with negligible errors in the known parameters IV-WC with present priors in the known parameters The Boulby baseline, with its larger matter effect, is better for the determination of the mass hierarchy L=650 km L=1050 km

20 Conclusions The two separate channels BB and EC have a limited overlap of the allowed regions in the (θ 13, δ) plane, resulting in a good resolution on the intrinsic degeneracy. The CP phase sensitivity is obtained by only using neutrinos, thanks to the Energy Dependence of the oscillation probability with the combination of the two BB and EC channels. THE SPS UPGRADE TO HIGHER ENERGY (Ep = 1000 GeV) IS CRUCIAL TO HAVE A BETTER SENSITIVITY TO CP VIOLATION (the main objective of the third generation neutrino oscillation experiments) IFF ACCOMPANIED BY A LONGER BASELINE ( Canfranc, Gran Sasso or Boulby). THE BEST E/L FOR HIGHER SENSITIVITY TO THE MIXING U(e3) IS NOT THE SAME THAN THAT FOR THE CP PHASE. Like the phase- shifts, the effect of δ is easier to observe by going to the region of the second oscillation. HENCE THE IMPORTANCE OF COMBINING DIFFERENT ENERGIES IN THE SAME EXPERIMENT.

21 Conclusions Setups III and III-WC, with the Canfranc or Gran Sasso baselines, have larger counting rates and a better tuning of the beam to the oscillatory pattern, resulting in a very good ability to measure the parameters. These setups provide the best sensitivity to CP violation for positive values of δ. Setups IV and IV-WC, with the Boulby baseline, provide a better determination of the hierarchy and a good reach to CP violation for negative δ, even if the mass ordering is unknown. THE COMBINATION OF THE TWO BB AND EC BEAMS FROM A SINGLE DECAYING ION AND A FIXED BOOST ACHIEVES REMARKABLE RESULTS

22 Acknowledgements Thanks to my collaborators: J. Bernabeu, J. Burguet-Castell, M. Lindroos, C. Orme, S. Palomares-Ruiz and S. Pascoli. Thank you very much for your attention… your attention…

23 Implementation A Facility with an EC channel would require a different approach to acceleration and storage of the ion beam compared to the standard beta-beam, as the atomic electrons of the ions cannot be fully strippedA Facility with an EC channel would require a different approach to acceleration and storage of the ion beam compared to the standard beta-beam, as the atomic electrons of the ions cannot be fully stripped Partly charged ions have a short vacuum life-time against collisions. Partly charged ions have a short vacuum life-time against collisions. The interesting isotopes have to have half-life < vacuum half-life ~ few min. For the rest, setup similar to that of a beta-beam: