Neutrino and Anti-Neutrino Cross Sections and CP Phase Measurement

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

• Yoshihisa OBAYASHI
• (KEK-IPNS)

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

3
CP Phase Measurement

• In the case of conventional (super) beam,
• cf NuFact
• Oscillation Probability P(nmgne)

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

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nm?ne oscillation probability
295km
Solid lines w/ matter, Dashed lines w/o matter

• Asymmetry can be seen at oscillation maximum
  0.7GeV

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, . . .

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Beams
Far Det.
Decay Pipe
Target
Horns
q

• Off Axis Beam
• Switch and by changing polarity of horn
  magnets
• Neutrino Flux is almost the same between and
  beams

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Cross Sections

• Quasi elastic interactions dominate below 1GeV

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Expected Neutrino Events (w/o osc.)

• of events _at_ far det.

• is factor 3 smaller than
• Running time of beam need to be longer
• Wrong sign contribution is 3x310 times large
  for beam
• Cause fake CP asymmetry

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Selection for ne appearance search

• Select ne CCqe interactions
• Vertex is in the fiducial volume
• Single EM shower ring
• No decay electron observed
• Evis gt 100MeV ( reject NC elastic )
• Tight e/p0 separation
• see next slide
• Reconstructed En cut
• 0.4 lt En(GeV) lt 1.2

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Tight e/p0 separation

• cosqne g from p0 tend to have a forward peak
• E(g2)/E(g1g2) Large for BG
• Likelihood diff. between 1-ring and 2-rings
• Invariant mass Small for ne

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Expected Signal Backgrounds
Beam ne app. Signal w/o CP Effect of CP Background in Hyper-K Background in Hyper-K Background in Hyper-K Background in Hyper-K Background in Hyper-K
Beam ne app. Signal w/o CP Effect of CP total
699 -123 241 225 34 11 510
w/p0 223 13 28 1 264
699 120 238 164 342 210 953
w/p0 213 16 302 8 540

• 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 (5060 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

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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

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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
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CP Measurement

• Matter effect becomes larger for large q13
• Black circles represent 3s contour for phase 2 of
  JHF running

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BG subtraction vs Sensitivity
(3s)

• Sensitivity strongly depends on systematic
  uncertainty of BG subtraction.
• If BG sys. 2
• sin22q130.01?sindgt0.55(33o)
• large q13?sindgt0.25(14o)
• Sensitivity improves with better BG rejection
• Better BG rejection and smaller uncertainty in BG
  subtraction are strongly preferred in the CP
  measurement

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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_at_ Front detector
• Energy scan with Narrow Band Beam
• 50 of BG are from ne
• Measure ne/nm ratio _at_ 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?

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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!