Transcript CP-even neutrino beam

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
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Introduction
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If finite value of q13 is NOT found in the next
round neutrino experiments, we need
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More powerful superbeam
Neutrino factory
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Muon-based neutrino factory
Beta-beam
We like to add one more option to neutrino
factory, which would benefit CP phase
measurement.
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Concept of CP-even neutrino beam
Point 1
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Ideal neutrino beam for CP phase (d) measurement:
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Pure beams of neutrino and anti-neutrino.
Mono-energetic.
Flux is known and is composed of neutrino and antineutrino inversely proportional to their cross sections.
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CP phase may be determined just counting the number of m +/-
Point 2
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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.
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Point 3
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Point 1
Oscillation Probability
At the oscillation maximum of 13 
d m132 L


,
4E
2
the oscillation probability at low energy is given by
2
2
P (n e  n m )  s23
sin 2 (2q13 )  c23
sin 2 (2q12 ) sin 2 (12 )  J sin(d )12
J  c13 sin(2q12 ) sin(2q 23 ) sin(2q13 ), 12 
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d m122 L
4E
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.
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Oscillation probability and CP
asymmetry
At the 1st oscillation peak,
E/L=600 MeV/310 km.
Sin22θ13=0.1, 0.05, 0.01
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Point 2
Bound-state β-decay
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 monoenergetic.
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)
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Ratio of bound-to-continuum
beta decay
b

c
n f  Qbb   n (0)
2
2
f ( Z ,W0 )
 n f W0  1
2
 Z 
2
n3 f ( Z ,W0 )
n f : number of free places,
 n (0) : Wave fucntion of atomic state at the nucleus,
f ( Z ,W0 ) : Fermi integral  (W0  1) 7 / 2
W0 : available energy in units of m e
The ratio is bigger for
large Z and small Q.
Bound
beta
ratio
Unfortunately requirement of
short life time means large Q and
contradicts with the large boundto-continuum ratio.
Q value
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Experimental studies
PRL95,052501(2005)
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The first experiment to demonstrate the
bound-state beta decay was done in 1992
at GSI.
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The experiment shown here is to measure
the bound-to-continuum ratio of 207Th.
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For example, fully ionized 187Re (the
galactic chronometer) life time is shorter
more than 109 times than the neutral Re.
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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Point 3
Beta beam & EC beam
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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.
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Merits of beta beam
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Merits of EC beam
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Pure neutrino beam
Known energy spectrum
Known intensity
Mono energetic
Zucchelli:PLB532,166(2002)
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2
He  36 Li   e   n e
18
10

Ne 18
9 F  e n e
148
66
Dy 148
65 Tb * n e
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
10^14 ions /decay ring
Volpe hep-ph/0605033
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Sensitivity to q13
J.E.Campagne et al
Hep-ph/0603172
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Sensitivity to d
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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
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(Pure) CP-even beam
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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
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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.
Examples:122Cd (bb) & 152Yb (EC)
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Property of
EC
2.85%
1484keV,0.26%
１08
47Ag
108Ag
b-decay
97.15% ｔ1/2=2.37 min
1016keV,
1.76%
Neutral 108Ag has both
EC and b-decay modes.
Hydrogen-like 108Ag46+
has bound-state bdecay in addition.
1918keV,2.35%
1649keV, 95.5%
108
46Pd
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108 Cd
48
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Hydrogen-like
108Ag
life 2.37min- 2.36min
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~0.3
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Rate Estimate
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Boosting 108Ag46+ with g=180 produces
(anti)-neutrino beam of En=600-700 MeV.
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This choice of energy is made considering the
cross section and multi-pion production rates..
Reference rate
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1014 ions /ring (same as the beta-beam)
100k ton target at L=310 km.
4 mono-chromatic lines are included.
2 QE events/year: too small !
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Mixed CP-even beam
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For EC beam, better
isotope is 152Yb.
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Life time: 3 sec.
En 4988 keV
g60
EC/(EC+b+)=0.3
Rate=1400 (QE)
events/year
This rate is worth
further study.
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Mixed CP-even beam (2)
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For bb beam,
better isotope is
122Cd.
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Life time: 5.24 sec.
En 3031 keV
bb/(bb+cb)=0.01
Rate=12
events/year
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Some comments
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EC nuclide candidates:
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152Yb;
Life time=3 sec; En 4988 keV; EC/(EC+b+)=0.3
Isotope intensity in the ring
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1014 ions is assumed.
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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
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CP-even neutrino beam
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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.
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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
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Other isotope candidates for pure
CP-even beam
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Bound-state beta-decay、
example 2
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Cosmological
clock
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187Re
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neutral
T=42 Gyear
187Re75+
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T=33 year
PRL77,5190,1996
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