CPeven neutrino beam

1
CP-even neutrino beam

• N. Sasao Kyoto University
• The talk is based on hep-ex/0612047
• done in collaboration with
• A. Fukumi, I. Nakano, H. Nanjo,
• S. Sato, M. Yoshimura

2
Introduction

• If finite value of q13 is NOT found in the next
  round neutrino experiments, we need
• More powerful superbeam
• Neutrino factory
• Muon-based neutrino factory
• Beta-beam
• We like to add one more option to neutrino
  factory, which would benefit CP phase measurement.

3
Concept of CP-even neutrino beam
Point 1

• Ideal neutrino beam for CP phase (d) measurement
• Pure beams of neutrino and anti-neutrino.
• Mono-energetic.
• Flux is known and is composed of neutrino and
  anti-neutrino inversely proportional to their
  cross sections.
• CP phase may be determined just counting the
  number of m /-
• We propose to use bound-state beta-decay (bb) to
  generate mono-energetic anti-neutrino in addition
  to electron capture (EC) neutrino.
• This idea is an extension of beta-beam and EC
  beam.

Point 2
Point 3
4
Oscillation Probability
Point 1

• Appearance experiment is needed to observe CP.
• Matter effect is negligible at low energy.
• For anti-neutrino, the 3rd term reverses its
  sign.
• P (ne)P (ne) is sensitive to q13 while P (ne)-P
  (ne) to CP phase d.

5
Oscillation probability and CP asymmetry
At the 1st oscillation peak, E/L600 MeV/310 km.
Sin22?130.1, 0.05, 0.01
6
Bound-state ß-decay
Point 2

• If the parent atoms are (fully or partially)
  ionized, electrons emitted from ordinary beta
  decay may be captured in available atomic orbits.
  
• In this case, anti-neutrino becomes
  mono-energetic.
• Bound-state beta-decay has been studied
  theoretically for long time, but experimentally
  it was proven rather recently.

Theoretical studies by R.Daude et al Comptes.
Rend. 224,1427 (1947) R.M.Shrk Phy.Rev.84,
591(1949) J.H.Bahcall Phy.Rev.124, 495(1961)
7
Ratio of bound-to-continuum beta decay
Bound beta ratio
The ratio is bigger for large Z and small Q.
Unfortunately requirement of short life time
means large Q and contradicts with the large
bound-to-continuum ratio.
Q value
8
Experimental studies
PRL95,052501(2005)

• The first experiment to demonstrate the
  bound-state beta decay was done in 1992 at GSI.
• For example, fully ionized 187Re (the galactic
  chronometer) life time is shorter more than 109
  times than the neutral Re.
• The experiment shown here is to measure the
  bound-to-continuum ratio of 207Th.
• 208Pb from the heavy ion synchrotron (SIS) hit a
  production target 208Tl was selected by the
  fragments separator (FRS), and stored in the
  experimental storage ring (ESR) the daughter
  nuclei was identified by the Fourier analysis of
  the frequency change.

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Bound Decay Branching
The result agrees very well with the theoretical
expectation.
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Beta beam EC beam
Point 3

• The basic idea of beta beam is to accelerate and
  store beta unstable nuclides. Then sharply
  focused high energy neutrinos are obtained in
  the forward direction.
• Merits of beta beam
• Pure neutrino beam
• Known energy spectrum
• Known intensity
• Merits of EC beam
• Mono energetic

ZucchelliPLB532,166(2002)
J. Sato PRL95,131804(2005) J. Bernabeu et al
hep-ph/0605132 J. Bernabeu et al
JHEP0512,14(2005)
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CERN scheme for beta EC beam
1014 ions /decay ring
Volpe hep-ph/0605033
12
Sensitivity to q13
J.E.Campagne et al Hep-ph/0603172
13
Sensitivity to d

• The red dashed curve is when beta intensity is ½
  of the design.
• Thus the intensity is the key parameter.

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CP-even beam and its variants

• (Pure) CP-even beam
• Consists of single isotope which has both EC and
  bound-state beta decay channels.
• Need a detector capable of m/m- discrimination.
• Examples 108Ag, 110Ag, 114In, 104Rh
• Mixed CP-even beam
• Two separate isotopes, with EC or bound-state
  beta decay.
• Need to store both beams simultaneously in a ring
  or store them in a time-sharing mode.
• Examples122Cd (bb) 152Yb (EC)

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Property of 108Ag
Neutral 108Ag has both EC and b-decay
modes. Hydrogen-like 108Ag46 has bound-state
b-decay in addition.
EC
b-decay
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Hydrogen-like 108Ag
life 2.37min-? 2.36min
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0.3
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Rate Estimate

• Boosting 108Ag46 with g180 produces
  (anti)-neutrino beam of En600-700 MeV.
• This choice of energy is made considering the
  cross section and multi-pion production rates..
• Reference rate
• 1014 ions /ring (same as the beta-beam)
• 100k ton target at L310 km.
• 4 mono-chromatic lines are included.
• 2 QE events/year too small !

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Mixed CP-even beam

• For EC beam, better isotope is 152Yb.
• Life time 3 sec.
• En 4988 keV
• g60
• EC/(ECb)0.3
• Rate1400 (QE) events/year
• This rate is worth further study.

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Mixed CP-even beam (2)

• For bb beam, better isotope is 122Cd.
• Life time 5.24 sec.
• En 3031 keV
• bb/(bbcb)0.01
• Rate12 events/year

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Some comments

• EC nuclide candidates
• 152Yb Life time3 sec En 4988 keV
  EC/(ECb)0.3
• Isotope intensity in the ring
• 1014 ions is assumed.
• Limit comes from space charge and production
  rate.
• Space charge limit is severer for highly charged
  ions.
• Duty factor limit may be relaxed because of
  better background rejection.

Bernabea et al. hep-ph/0510278
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Summary

• CP-even neutrino beam
• Pure mono-energetic ne and ne beam suited to
  determine CP phase.
• Bound-sate beta-decay is employed to produce ne
  in addition to EC for ne.
• 108Ag for pure CP-even beam
• 122Cd and 158Yb for mixed beam.
• Feasibility very much depends on production rate
  of these isotopes as well as accelerator
  technology to store high current beams.
• Hope RI factory may find better isotopes.
• The option of CP-even beam should be kept in mind
  for further study.

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Back Slides
24
Other isotope candidates for pure CP-even beam
25
Bound-state beta-decay?example 2

• Cosmological clock
• 187Re neutral
• T42 Gyear
• 187Re75
• T33 year

PRL77,5190,1996