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Neutrino and Anti-Neutrino Cross Sections and CP Phase Measurement

NuInt01, @ KEK (Tsukuba), Dec. 13, 2001. Neutrino and Anti-Neutrino Cross Sections and CP Phase Measurement. Yoshihisa OBAYASHI (KEK-IPNS). Introduction. MNS Matrix: WHY CP ? In the Quark Sector, CP is violated. Then, also in the Lepton Sector? → Leptogenesys

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Neutrino and Anti-Neutrino Cross Sections and CP Phase Measurement

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

  2. 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 Yoshihisa OBAYASHI, NuInt01@KEK

  3. CP Phase Measurement CPV • In the case of conventional (super) beam, • cf: NuFact: • Oscillation Probability P(nmgne): Yoshihisa OBAYASHI, NuInt01@KEK

  4. Assumed Scenario on n physics ~2010 • nm → nt oscillation is established by Atmn, LBLn • sin22q23 ~ 1.0 • Dm223 ~ 3 x 10-3eV2 • LMA solution is established by Soln, KamLAND • sin22q12 ~ 0.8 • Dm212 ~ 5 x 10-5eV2 • Finite q13 is found by JHF1 (, Atmn) • sin22q13 ~ 0.03 • MiniBooNE excluded LSND result • (Still) Unknown parameters: • CP phase d and sign of Dm2 Yoshihisa OBAYASHI, NuInt01@KEK

  5. nm→ne oscillation probability 295km • Asymmetry can be seen at oscillation maximum ~0.7GeV Solid lines: w/ matter, Dashed lines: w/o matter Yoshihisa OBAYASHI, NuInt01@KEK

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

  7. Beams Off Axis Beam Switch and by changing polarity of horn magnets Neutrino Flux is almost the same between and beams -15%@peak 1021POT/yr (1st phase) Far Det. Decay Pipe Horns Target q Yoshihisa OBAYASHI, NuInt01@KEK

  8. Cross Sections Quasi elastic interactions dominate below ~1GeV Yoshihisa OBAYASHI, NuInt01@KEK

  9. 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 Yoshihisa OBAYASHI, NuInt01@KEK

  10. Selection for ne appearance search • Select ne CCqe interactions • Vertex is in the fiducial volume • Single EM shower ring • No decay electron observed • Evis > 100MeV ( reject NC elastic ) • Tight e/p0 separation • see next slide • Reconstructed En cut • 0.4 < En(GeV) < 1.2 Yoshihisa OBAYASHI, NuInt01@KEK

  11. Tight e/p0 separation • cosqne: g from p0 tend to have a forward peak • E(g2)/E(g1+g2): Large for BG • Likelihood diff. between 1-ring and 2-rings • Invariant mass: Small for ne Yoshihisa OBAYASHI, NuInt01@KEK

  12. 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 3s effect. • ~90% of nm BG (50~60% of total BG) are from p0 • Dm122 = 5x10-5eV2 • Dm232 = 3x10-3eV2 • sin22q13 = 0.03 • sin22q23 = 1 • sin22q12 = 0.8 • d = 45 deg • 5 x 1021 pot x 450 kt (nm) • 1.83 x 1022 x 450 kt pot () • Off axis 2deg beam • No matter effect considered Yoshihisa OBAYASHI, NuInt01@KEK

  13. Cross Section (& Efficiency) Difference • We want to know • Observable • Then Asymmetry Parameter • Only the difference of rs,re between neutrino and anti neutrino appear in the asymmetry Yoshihisa OBAYASHI, NuInt01@KEK

  14. Cross Section Difference • CCqe cross section ratio of ne/nm • Difference between neutrino and anti-neutrino is at most 5% within the energy window ~5% Yoshihisa OBAYASHI, NuInt01@KEK

  15. CP Measurement • Matter effect becomes larger for large q13 • Black circles represent 3s contour for phase 2 of JHF running Yoshihisa OBAYASHI, NuInt01@KEK

  16. BG subtraction vs Sensitivity Chooz excluded @Dm31~3x10-3eV2 JHF1 cannot discover q13 (3s) • Sensitivity strongly depends on systematic uncertainty of BG subtraction. • If BG sys. = 2%: • sin22q13=0.01→sind>0.55(33o) • large q13→sind>0.25(14o) • Sensitivity improves with better BG rejection • Better BG rejection and smaller uncertainty in BG subtraction are strongly preferred in the CP measurement Yoshihisa OBAYASHI, NuInt01@KEK

  17. Items for the Improvement of Sensitivity • ~90% of nm BG are from p0 • Improve the hardware (Hyper-K) • Timing resolution, Light scattering and reflection, Segment . . . • Improve the software • Reconstruction algorithm, . . . • Measure NC p0 rate@ Front detector • Energy scan with Narrow Band Beam • ~50% of BG are from ne • Measure ne/nmratio @ 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? Yoshihisa OBAYASHI, NuInt01@KEK

  18. 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! Yoshihisa OBAYASHI, NuInt01@KEK

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