1. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK1 Neutrino and Anti-Neutrino Cross Sections and CP Phase Measurement Yoshihisa OBAYASHI (KEK-IPNS) NuInt01, @ KEK (Tsukuba), Dec. 13, 2001

2. Yoshihisa OBAYASHI, NuInt01@KEK2 Introduction MNS Matrix: WHY CP ? –In the Quark Sector, CP is violated. –Then, also in the Lepton Sector? → Leptogenesys –CP Measurement is a final goal of flavor physics

3. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK3 CP Phase Measurement In the case of conventional (super) beam, – –cf: NuFact: Oscillation Probability P(   e ): CPV

4. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK4 Assumed Scenario on physics ~2010  →   oscillation is established by Atm, LBL – sin 2 2 23 ~ 1.0 – m 2 23 ~ 3 x 10 -3 eV 2 LMA solution is established by Sol, KamLAND – sin 2 2 12 ~ 0.8 – m 2 12 ~ 5 x 10 -5 eV 2 Finite  13 is found by JHF1 (, Atm) – sin 2 2 13 ~ 0.03 MiniBooNE excluded LSND result (Still) Unknown parameters: – CP phase  and sign of m 2

5. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK5  → e oscillation probability Asymmetry can be seen at oscillation maximum ~0.7GeV 295km Solid lines: w/ matter, Dashed lines: w/o matter

6. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK6 JHF-Kamioka Experiments Phase I: 2007 (?) ~201x –~1MW 50GeV PS → 22.5kt detector (Super-Kamiokande)  → x disapp.,  → e app., NC measurement Phase II: 201x(?)~202y(??) –~4MW 50GeV PS → ~1Mt detector (Hyper-Kamiokande) CPV search, Proton Decay,... 295km KEK Kamioka Tokai Hyper-K SK JHF

7. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK7 Beams Off Axis Beam Switch and by changing polarity of horn magnets Neutrino Flux is almost the same between and beams  Target Horns Decay Pipe Far Det. -15%@peak 10 21 POT/yr (1st phase)

8. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK8 Cross Sections Quasi elastic interactions dominate below ~1GeV

9. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK9 Expected Neutrino Events (w/o osc.) # of events @ far det. is factor 3 smaller than –Running time of beam need to be longer Wrong sign contribution is 3x3~10 times large for beam –Cause fake CP asymmetry

10. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK10 Selection for e appearance search Select e CCqe interactions –Vertex is in the fiducial volume –Single EM shower ring –No decay electron observed –Evis > 100MeV ( reject NC elastic ) –Tight e/  separation see next slide –Reconstructed E cut 0.4 < E(GeV) < 1.2

11. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK11 Tight e/  separation cose :  from  0 tend to have a forward peak E( 2 )/E( 1 + 2 ): Large for BG Likelihood diff. between 1-ring and 2-rings Invariant mass: Small for e

12. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK12 Expected Signal & Backgrounds By the present tools, –BG level is ~5x larger than expected CP asymmetry. –We need to achieve ~5% precision of BG subtraction if we want to see 3 effect. ~90% of  BG (50~60% of total BG) are from  0 Beam e app. Signal w/o CP Effect of CP Background in Hyper-K total 699-1232412253411510 w/ 0 22313281264 699+120238164342210953 w/ 0 213163028540 m 12 2 = 5x10 -5 eV 2 m 23 2 = 3x10 -3 eV 2 sin 2 2 13 = 0.03 sin 2 2 23 = 1 sin 2 2 12 = 0.8  = 45 deg 5 x 10 21 pot x 450 kt (  ) 1.83 x 10 22 x 450 kt pot () Off axis 2deg beam No matter effect considered

13. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK13 Cross Section (& Efficiency) Difference We want to know Observable Then Asymmetry Parameter Only the difference of r,r between neutrino and anti neutrino appear in the asymmetry

14. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK14 Cross Section Difference CCqe cross section ratio of e /  –Difference between neutrino and anti-neutrino is at most 5% within the energy window ~5%

15. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK15 CP Measurement Matter effect becomes larger for large  13 Black circles represent 3 contour for phase 2 of JHF running

16. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK16 BG subtraction vs Sensitivity Sensitivity strongly depends on systematic uncertainty of BG subtraction. If BG sys. = 2%: –sin 2 2 13 =0.01 → sin>0.55(33 o ) –large  13 → sin>0.25(14 o ) Sensitivity improves with better BG rejection  Better BG rejection and smaller uncertainty in BG subtraction are strongly preferred in the CP measurement Chooz excluded @  m 31 ~3x10 -3 eV 2 JHF1 cannot discover  13 (3)

17. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK17 Items for the Improvement of Sensitivity ~90% of  BG are from  0 –Improve the hardware (Hyper-K) Timing resolution, Light scattering and reflection, Segment... –Improve the software Reconstruction algorithm,... –Measure NC  0 rate@ Front detector Energy scan with Narrow Band Beam ~50% of BG are from e –Measure e /  ratio @ Front detector –Narrower energy window Improvement of energy resolution ~50% of BG are from high energy tail of beam –Tune the beam line and reduce HE tail Measurement of wrong sign contamination –Magnetized detector? –Recoiled neutron detector?

18. Dec. 13, 2001Yoshihisa OBAYASHI, NuInt01@KEK18 Conclusion Phase 2 of JHF-Kamioka experiment aims at measuring CP violation Better BG rejection and smaller uncertainty in BG subtraction are strongly preferred in the CP measurement Let's Complete MNS matrix!