Beyond T2K and NOvA   and reactor experiments

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Aug. 24, 2006. NuFact 06 - Walter Winter. 2. Contents. IntroductionFuture experiment types:Superbeam upgradesBeta beamsNeutrino factoriesDecision making: Which experiment/type?Summary. . . Aug. 24, 2006. NuFact 06 - Walter Winter. 3. Beyond T2K and NOvA: Setting. Beyond T2K and NOvA = beyond

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Beyond T2K and NOvA and reactor experiments

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1. Beyond T2K and NOvA (… and reactor experiments) NuFact 06 UC Irvine, USA August 24, 2006 Walter Winter Universität Würzburg, Germany

2. Aug. 24, 2006 NuFact 06 - Walter Winter 2 Contents Introduction Future experiment types: Superbeam upgrades Beta beams Neutrino factories Decision making: Which experiment/type? Summary

3. Aug. 24, 2006 NuFact 06 - Walter Winter 3 Beyond T2K and NOvA: Setting Beyond T2K and NOvA = beyond 2015?! Specific setups less certain than for the coming ten years q13 discovered if sin22q13 > 0.01

4. Aug. 24, 2006 NuFact 06 - Walter Winter 4 After T2K and NOvA: Status q13 discovered, some hint, or no signal at all Even if q13 is very large and all data are combined: CP violation discovery unlikely Mass hierarchy discovery 50:50 chance (in deltacp) (see, e.g., NOvA proposal, hep-ex/0503053)

5. Aug. 24, 2006 NuFact 06 - Walter Winter 5 What do we still want to know? Discover q13 (if not yet done) Establish CP violation (at high CL) Measure the mass hierarchy (at high CL) Measure q13 precisely, say 5% in log10(sin22q13) Measure dCP precisely, say 20 degrees Measure leading atm. parameters at per cent level Establish deviation from maximal mixing Verify MSW effect, constrain non-standard physics, etc.

6. Aug. 24, 2006 NuFact 06 - Walter Winter 6 Options and representatives Major players: NOvA upgrades Wide band beam FNAL/BNL to DUSEL T2HK/T2KK CERN SPL

7. Superbeam upgrades

8. Aug. 24, 2006 NuFact 06 - Walter Winter 8 Upgrading NOvA Simplest addition: A second detector, possibly liquid argon Main purpose of NOvA: q13, mass hierarchy In principle obtained by matter effects, i.e., long L Originally: Optimization of NOvA-T2K synergy by (Barger, Marfatia, Whisnant, 2002; Huber, Lindner, Winter, 2003; Minakata, Nunokawa, Parke, 2003) Two possibilities for upgrades: Detector at same L/E but different L, i.e., matter effect (similar to above) (Mena, Palomarez-Ruiz, Pascoli, 2005a/b) Detector at 2nd osc. Maximum (possibly at shorter L) (NOvA proposal, hep-ex/0503053)

9. Aug. 24, 2006 NuFact 06 - Walter Winter 9 NOvA+2nd detector Same L/E: Bi-probability ellipses shrink to lines MH discovery for all dCP for sin22q13 > 0.04 More efficient than 2nd osc. maximum for n running only

10. Aug. 24, 2006 NuFact 06 - Walter Winter 10 Broad band beam (1) Idea: Use on-axis beam for the simul- taneous measurement of different oscillation maxima Probably FNAL or BNL to DUSEL (=Homestake/Henderson/…) from FNAL: 1290/1487 km, from BNL: 2540/2770 km Challenge: Backgrounds in a WC detector Compared to NOvA upgrades: New beamline required; therefore: Different timescale?

11. Aug. 24, 2006 NuFact 06 - Walter Winter 11 Broad band beam (2) Baseline does not really matter so much Absolute performance very competitive

12. Aug. 24, 2006 NuFact 06 - Walter Winter 12 T2K upgrades: T2HK, T2KK T2HK: Upgrade of T2K to megaton-size detector + 4 MW beam power T2KK: Split detector mass into two identical detectors in Japan+ Korea (0.27+0.27 Mt) at same OA: Larger matter effects (L=1050 km) Reduce systematics impact

13. Aug. 24, 2006 NuFact 06 - Walter Winter 13 What does the 1050 km baseline help? What does it help that the detectors are identical? T2KK: Key questions

14. Aug. 24, 2006 NuFact 06 - Walter Winter 14 CERN-Memphys (a superbeam-beta beam hybrid) Beta beam (g=100) plus 4MW superbeam to 440 kt WC detector at Frejus site (L=130 km) Effect of systematics smaller and absolute performance better than for T2HK Antineutrino running not necessary because ne to nm (beta beam) and nm to ne (superbeam) channels present

15. Aug. 24, 2006 NuFact 06 - Walter Winter 15 Beta beam Key figure (any beta beam): Useful ion decays/year? “Standard values”: 3 1018 6He decays/year 1 1018 18Ne decays/year Can these be achieved? Typical gamma ~ 100 – 150 (for CERN SPS)

16. Aug. 24, 2006 NuFact 06 - Walter Winter 16 From low to very high gamma “Low” gamma (g<150?) Alternative to superbeam/synergy with superbeam? Originally designed for CERN (SPS) Water Cherenkov detector (see before; also: Volpe, 2003; Campagne, Maltoni, Mezzetto, Schwetz, 2006) “Medium” gamma (150<g<350?) Alternative to superbeam! Possible at upgraded SPS? Water Cherenkov detector (Burguet-Castell et al, 2004+2005; Huber et al, 2005) “High” gamma (g >> 350?) Alternative to neutrino factory? Requires large accelerator Detector technology other than water? (Burguet-Castell et al, 2004; Huber et al, 2005; Agarwalla et al, 2005)

17. Aug. 24, 2006 NuFact 06 - Walter Winter 17 Beta beam vs. Superbeam vs. NuFact? Low/medium g: Can easily compete with superbeam upgrades Higher g: At least theoretically competitive to a neutrino factory Challenges: Can fluxes be reached? Compare completely optimized accelerator strategies? Mass hierarchy measurement for small q13

18. Aug. 24, 2006 NuFact 06 - Walter Winter 18 Neutrino factory Ultimate “high precision” instrument!? Muon decays in straight sections of storage ring Technical challenges: Target power, muon cooling, charge identification, maybe steep decay tunnels

19. Aug. 24, 2006 NuFact 06 - Walter Winter 19 Which baseline(s), which energy? 3000-5000 km good for CP violation 7500 km good for MH, as degeneracy resolver Use two baselines: 4000 km+7500 km, Em > 40 GeV

20. Aug. 24, 2006 NuFact 06 - Walter Winter 20 Why else want a very long baseline? L ~ 6000-9000 km Example: q13 precision Depends on (true) dCP (green band); thick curve: “typical” dCP (median) L ~ 7500 km as risk-minimizer, and for better absolute performance In comb. with short baseline (L=4000 km) less sensitive to L (Gandhi, Winter, in preparation)

21. Aug. 24, 2006 NuFact 06 - Walter Winter 21 More R&D: Detector optimization? Improved detector would increase sensitivity reach significantly In addition: Lower Em = 20 GeV possible (while 50 GeV do not harm)

22. Aug. 24, 2006 NuFact 06 - Walter Winter 22 Additional channels: Silver, Platinum Silver (ne to nt): Standard: 5kt ECC (Autiero et al, 2004) Optimistic: 10kt ECC, 5xSIG, 3xBG Platinum (nm to ne): Standard: 15 kt, 20% efficiency, ~ 7.5 GeV upper threshold (Rubbia, 2001) Optimistic: 50 kt, 40% efficiency, Em upper threshold Large q13: Platinum useful? Medium q13: Both useful? But: Other choices in this range! However: Unitarity tests? (Antusch et al, 2006)

23. Aug. 24, 2006 NuFact 06 - Walter Winter 23 NF optimization potential Optimized NuFact: Excellent q13 reach for both MH and CPV But: For sin22q13 ~ 10-2, g=350 beta beam (L=730 km) better

24. Aug. 24, 2006 NuFact 06 - Walter Winter 24 Decision making: Simplified Do we have enough information to make a decision after T2K and NOvA? Assumptions for this talk: We have to make a decision based on this information There will be no further incremental approach to search for q13 (if not found) = “One more experiment” hypothesis We use the option with the lowest effort if two physically similar Key questions: Superbeam upgrade, beta beam, or neutrino factory? What setup within each class has the best physics performance?

25. Aug. 24, 2006 NuFact 06 - Walter Winter 25 Decision making: Physics cases Possible outcomes after T2K and NOvA q13 discovered Few s hint for q13 q13 not found A possible future strategy based on that (biased): Best possible setup for large q13 with reasonable effort = Superbeam upgrade? But which? Strategy: Max. CP fraction for discoveries for sin22q13 > 0.04? Best possible setup for intermediate q13 = Beta beam with g~350? Other with better MH reach/longer L? Strategy: Max. CP fraction for discoveries for sin22q13 ~ 0.01 Best possible reach in q13 for all performance indicators = Neutrino factory Strategy: Disoveries for q13 as small as possible

26. Aug. 24, 2006 NuFact 06 - Walter Winter 26 Decision making: Example Blue: Superbeam upgrade based upon: lower effort Green: Beta beam based upon: Good CPV reach, MH in most cases Red: Neutrino factory (optimized) based upon: Good q13 reach

27. Aug. 24, 2006 NuFact 06 - Walter Winter 27 Which option for large q13? Based on assumptions before (lowest possible effort): Superbeam? Depends on systematics: Requires more R&D Important selection criterion: Systematics robustness? Depends on what optimized for: MH or CPV Therefore: take two?

28. Aug. 24, 2006 NuFact 06 - Walter Winter 28 Summary What is (more or less) known: Neutrino factory best alternative for small q13 to measure both MH and CPV; a very long baseline is an essential component of that For large q13, a different alternative may be better There may be a separate physics case for a beta beam What is not known: Which setup for large q13? Possibly two, such as T2HK (for CPV) + WBB (MH)? Which has the lowest systematics impact? T2KK? What is the precise physics case for a beta beam? How does that affect the choice of g and L? How far can a neutrino factory be optimized?

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