1. High density detectors to exploit the technology of the Beta Beams High density detectors are the key technology for a Neutrino Factory. Are they an option for the Beta Beams? What constraints they impose to the Beta Beam technology? In what range of parameters they represent an optimal option for the study of leptonic mixing? F.Terranova INFN-LNF, in collaboration with A. Donini, E. Fernandez Martinez, P. Migliozzi, S. Rigolin, L. Scotto Lavina, T. Tabarelli de Fatis

2. 2009 2012 T2K – No a?   discovery ? 2007 2012 LHC and Double CHOOZ startup End of CNGS Phase I 2022 Beam upgrade and HK construction Data taking... 2015 2022 “Phase 2” lumi upgrade of the LHC LHC Energy upgrade? Phase II 2014 “The investigation and comparison of the physics potential of future neutrino oscillation facilities has by now become an industry...” (T.Schwetz, hep-ph/0612223) The reasons: The ratio of  m sol /  m atm is small but not too small (about 1/30): an ENORMOUS opportunity for accelerator based neutrinos Cost, complexity and physics case strongly depend on the size of the subdominant oscillation at atm scale (magnitude of  13 ) -> (too) many options still open

3. Two different worlds  13 is large and we study the feature of a “large”  - e transitions at the atmospheric scale: We can allow systematic uncertainties in the initial flavor composition. We want energy resolution and matter effects to see fine structures of the amplitude It is the realm of intense neutrino beams produced traditionally from  decays ( Superbeams ). The detectors work in e appearance mode: low density detectors  13 is small. We cannot sustain anymore the intrinsic background of traditional (super)beams Use of high energy muons as parent neutrino particles Observe e   transition in a background bulk of anti(num) It is the realm of the Neutrino Factories High density detectors (muon id) with superior charge identification

4. A technology that mixes the two realms: the Beta Beam proton target isotope isotope* + e + + e Ion sourceAccelerationStorage e Works in  appearance mode but only one flavor is present in the initial state: Ideal condition at t=0 !! It makes estensive use of current technologies (ISOL technique for ion production, existing accelerators at CERN or Fermilab) Main drawback: q/m << q/m  … we mainly work with low-energy neutrinos (sub GeV if we use 18 Ne, 6 He and the SPS as terminal booster) e

5. The smallnes of the energy is a serious drawback [see J.Burguet et al., Nucl.Phys. B695 (2004) 217] Outstanding beam purity (no contamination from other flavors) Possibility to work in  appearance mode (  CC are an easier channel than e CC and allows for dense detectors) No need to distinguish  from anti-  (sign of the muon) Additional information from event kinematics At peak of oscillation maximum, statistics increase ~E Exploited in present design NOT fully exploited NOT exploited Exploited There is growing consensus on the fact that working in the multi-GeV is a feature that should be preserved. Otherwise the performance of the BB (even with a 1Mton water Cherenkov detector) are too close to that of a Superbeam to embrace the risk of a new accelerator technology

6. The route to multi-GeV A novel last-stage booster: expensive but synergical with the upgrades of the LHC. Fast cycling magnets up to 4-5T to allow injection at 1 TeV, reduces the dynamic effects of persistent currents and increase the peak luminosity. Mandatory for DLHC + the decay ring Present design lenght: 6880 m useful decays: 36% 5 T magnets S-SPS based design lenght: 6880 m useful decays: 23% 8.3 T magnets (LHC) M. Benedikt et al., CERN-AB-2006-019

7. High Q 2 ions The possibility of producing 8 B ions at high flues is fascinating because: It offers a way out to the “ 18 Ne crisis” (yields seem too low) It has a large Q 2 that brings neutrinos in the multi-GeV even for moderate boosters (see e.g. Rubbia’s exercise with the FNAL Main Injector: hep-ph/0609235) HOWEVER: this is not equivalent as increasing  because, for P osc =1, the events at the far detector scale as  /E max CM (the flux scale as  2, not as Q 2 !!, hence the increase of Q does NOT fully compensate the L -2 flux reduction due to the increase of baseline) The route to multi-GeV brings an additional advantage: it makes the average muon range much greater than the pion interaction length in dense materials. Dense detectors come into play C. Rubbia et al., NIM A568 (2006) 475

8. A Fe/RPC detector at 730 km (CERN-Gran Sasso) 40 kton iron (4 cm thickness) and glass RPC Digital readout (2x2 cm 2 pads) No magnetic field Full GEANT3 simulation but event selection based on inclusive variables only (n. hits, layers etc.)  can be improved with pattern recognition See e.g. T.Tabarelli @ LCWS05

9. Signal efficiency and background mis-identification as a function of the neutrino energy Neutrino Antineutrino

10. Discovery potential vs Flux Minimum  13 can be discovered, assuming  = 90° Minimum  can be discovered, assuming  13 = 3° Black curves:  ( 18 Ne)=350,  ( 6 He)=350, 10y with “nominal” flux (F 0 ), 99% C.L. Red curves:  ( 18 Ne)=580,  ( 6 He)=350, 10y with “nominal” flux (F 0 ), 99% C.L.

11.  discovery potential Left curves:  ( 18 Ne)=350,  ( 6 He)=350, 10y run, 99% C.L. Right curves:  ( 18 Ne)=580,  ( 6 He)=350, 10y run, 99% C.L. F 0 x2 F0F0 F 0 /2 F 0 is the “nominal” flux For comparison: SPS-based Beta Beam with Mton-size water Cherenkov detector [Or double the masses: hall B and C of LNGS…]  ( 18 Ne)=350,  ( 6 He)=350  ( 18 Ne)=580,  ( 6 He)=350

12. Neutrino hierarchy Blind region for low mass experiments (sensitivity mainly relies on differential distributions). NOvA A.Donini et al., EPJ C48 (2006) 787

13. Atmospheric neutrinos Multi-GeV atmospheric neutrinos are particularly effective to test the neutrino hierarchy: The range 3-6 GeV offers the highest sensitivity to sign(  m 32 ): Positive sign: depletion of  survival probability Negative sign: depletion of anti(  ) survival probability Moreover: Sensitivity is highly enhanced by the a-priori (i.e. external) knowledge of  m 32 and  13 The observables are nearly blind to delta

14. 40 kton x 10 y exposure 99% CL PRELIMINARY Magnetized iron detector

15. Conclusions Working in the multi-GeV range is a special opportunity for the Beta Beam to enhance its physics case well beyond the intrinsic limitations of SuperBeams As a by-product, it opens up the possibility of exploiting high density detectors Given the enormous costs, setups should have sensitivity to close-up the PMNS and hierarchy for any value of  13 that give positive signals at any “phase I” experiment (T2K, Nova, Reactors) A coarse grain iron detector (40 kton, L=CERN→LNGS) can do the job; 100 kton (two instrumented halls) would be ideal for nominal BB fluxes Magnetization offers a serious advantage: exploitation of atm neutrinos to (partially) cover the blind region at negative delta. (+  background reduction of ~2)