Prospects of J-PARC Neutrino Program

1. Prospects of J-PARC Neutrino Program Changgen Yang Institute of High Energy Physics Beijing

2. Overview of J-PARCexpect to start in 2007 approved ~1GeV n beam Super-K: 22.5 kt Hyper-K: 1000 kt 0.77MW 50 GeV PS 4MW 50 GeV PS ( conventional n beam) Phase-I (0.77MW + Super-K) Phase-II (4MW+Hyper-K) ~ Phase-I  200

3. J-PARC AERI@Tokai-mura (60km N.EJ. of KEK) Construction 2001～2006 (280m from target) (Approved in Dec.2000)

4. JHFnu: K2K as an example nm ＳＫ p+ FD m+ Target+Horn 200m decay pipe 100m ~250km FD Pion monitor (PIMON) MUMON

5. 2horns Far Det. Decay Pipe q Horns Three Beams • Intense • Wide sensitivity in Dm2 • BG from HE tail • Syst. err from spectrum extrapolation Wide Band Beam Narrow Band Beam • Less HE tail • Less sys err from spectrum “counting experiment” • Easy to tune En momentum selected p Off Axis Beam • High int. narrow band beam • More HE tail than NBB • Hard to tune En

6. Far Det. q Decay Pipe Horns Target Off Axis Beam

7. Comparision of Spectra Peak @ 800MeV~1GeV Sharp peak for NBB/OAB OAB produce very intense “NBB” WBB:5200 CC int./22.5kt/yr NBB: 620 CC int./22.5kt/yr (2GeV/c p tune) OAB: 2200 CC int./22.5kt/yr (2degree)

8. ne contamination NBB (LE2p) OAB (2degree) m-decay m-decay K-decay K-decay 0.73% (0.15%@peak) 1.0% (0.21%@peak) Very small ne/nm ratio at nm spectrum peak: 1~2x10-3

9. Requirement of Near Detector: • Measure the quality of neutrino beam • Estimate the neutrino flux and the energy spectrum at Super-K • Study neutrino interactions to estimate b.g. for oscillation analysis Measurements of the neutrino beam: • Direction; • Flux/spectrum for  and e • Profile • Stability • Event types(QE, single  ,NC pi0 etc…)

10. One example of Near Detector

11. Far/Near ratio (OA 2 deg)

12. Intermediate Detector

13. A tool: Pion Monitor(PIMON) nm disappearance F/N extrapolation (incl. HE tail) Kaon production(p/K ratio)  HE tail ne appearance BG : NCp0: ne~1:1, half of p0 BG from HE tail F/N extrapolation  HE tail Kaon production(p/K ratio)  HE tail  ne contamination Neutrino int. study at 280m Precise spectrum information

14. Far detector: Super-Kamiokande

15. Physics Goal of JHFnu(Phase I) L=295km, En=0.5~2GeV(Match the WCD) Precise determination of neutrino oscillation parameters: sin22231% m2321×10-4eV2 at (sin22q=1.0, Dm2=3.2×10-3eV2) sin2213< 1% Physics Goal of JHFnu(Phase II) CP violation measurement Proton decay

16. nl + n → l + p l- (El , pl) ql n p Neutrino Energy Reconstruction Assume CC quasi elastic (CCQE) reaction

17. Neutrino Energy Reconstruction Quasi-elastic s=80MeV En(reconstruct) En (True) En(reconstruct) – En (True) (MeV) QE dominate at ～1GeV

18. Dm232 andq23 measurement P(nm→nm)=1 - cos4q13sin22q23sin2(1.27 Dm232 L/E) ~1 P(nm→ nm) sin22q Dm2 En (GeV)

19. nm disappearance 1ring FC m-like Ratio after BG subtraction (linear) Dm2=3×10-3 sin22q=1.0 Oscillation with Dm2=3×10-3 sin22q=1.0 Non-QE (log) No oscillation ~3% Reconstructed En (MeV) Fit with 1-sin22q・sin2(1.27Dm2L/E)

20. q13 measurement • A mixing angle between 1st and 3rd generation , q13may be not very small • A discovery of nm→ne can open the new window to study CP violation in this mode • May be a source of baryogenesis in the universe P(nm→ne)=sin22q13sin2q23sin2(1.27 Dm232 L/E)

21. ne appearance Background rejection against NC p0 is improved. sin22qme=0.05 (sin22qme 0.5sin22q13) Dm2 CHOOZ ×20 improvement 3 5 ×10-3 sin22qme

22. Non standard n oscillation • A sterile neutrino (LSND result? 3 or 4 n’s) with nmnm /ne measure: nmnt (/ ns) • non standard CP violation of nm→nt . • Any other unexpected phenomena

23. OAB nmnt #p0 + #e-like D=390±44 nmns 3.510-3 Dm232 nm →nt confirmation • NC p0 interaction (n + N →　n + N + p0) • nmne CC + NC(~0.5CC) ~0 (sin22qme~0) nm CC + NC(~0.5CC) ~0 (maximum oscillation)nt NC #p0 is sensitive to nt flux.

24. ndetector Phase-II: Hyper-K 1,000 kt • Far n detectors Phase-I: Suker-K 22.5kt (50kt)

25. Search for nmne sin22qme sensitivity 310-3 Phase-II Phase-I ~310-4 102 Exposure/(22.5kt1021pot) p0 background has to be understood with 2% level. (n physics at a front detector)

26. CP violation in n oscillation L=295km : small MSW En~1 GeV : large CP asym. • If LSND is true, CP violation may be much larger than expect.

27. CP Violation Study Dm122=5×10-5eV2 , Dm232=3×10-3eV2 sin22q13 = 0.01 q23 = p/4, q12 = p/8 • Compare nmne withnmne N(e+) NO CP violation w/o matter effect. |d|>20 (3s discovery) 3s discovery 90% C.L. N(e-)

28. Analysis for discovery of p→e+π0 Tight momentum cut ⇒ target is mainly free protons efficiency=17.4%, 0.15BG/Mtyr free proton bound proton Small systematic uncertainty of efficiency High detection efficiency Perfectly known proton mass and momentum No Fermi momentum No binding energy No nuclear effect

29. How the signal looks like Proton mass peak can be observed ! τp/B(p→e+π0) = 1×1035 yrs S/N = 4 for 1×1035 years ↓ S/N = 1 for 4×1035 years τp/B(p→e+π0) = several×1035 yrs is reachable by a large water Cherenkov det.

30. Physics Reach • Phase-I (0.77MW + 22.5kt): • NC interaction:Establish nmnt and limit on nmns • nmnm :dsin22q23 < 0.01 nmne :sin22q13 < 6×10-3 (90% CL) nmnm :dDm232< 1×10-4eV2 at (sin22q=1.0, Dm2=3.2×10-3eV2) • Phase-II (4MW + 1000kt): nmne :sin22q13 < 1×10-3 (90% CL) nmne vs nmne : |d|>20 (3s discovery) at (Dm122=5×10-5eV2 , Dm232=3×10-3eV2)

31. q13 measurement:superbeams vs. reactor P. Huber et al., hep-ph/0303232 400 tGWy 8000 tGWy Systematics Correlations Degeneracies

32. To get funding for the 2 km Detector? To get additional funding for the Experimental hall + Detector (from KEK for JPY 2004?) The availability of the candidate site for the 2 km detector Realistic design and cost estimation of the detector hall

33. Schedule (4 year plan)  KEK(~163 M$) • MEXT(Ministry of Education,Science and Technology) • Council for Science and Technology Policy  Ministry of Finance • Need re-consideration for JFY 2004