cp-even neutrino beam

2007/3/8 Sasao @ Neutrino Telescope 1

CP-even neutrino beamN. 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


Introduction If finite value of 13 is NOT found in the next ro

und 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.


Concept of CP-even neutrino beam

Ideal neutrino beam for CP phase () 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

+/-

We propose to use bound-state beta-decay (b) 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 1

Point 3


Oscillation Probability

Appearance experiment is needed to observe CP. Matter effect is negligible at low energy. For anti-neutrino, the 3rd term reverses its sign. P (e)+P (e) is sensitive to while P (e)-P (e) t

o CP phase

213

13

2 2 2 2 223 13 23 12 12 12

13 12 23

At the oscillation maximum of ,4 2

the oscillation probability at low energy is given by

( ) sin (2 ) sin (2 )sin ( ) sin( )

sin(2 )sin(2 )sin

e

m LE

P s c J

J c

212

13 12(2 ), 4m LE

Point 1


Oscillation probability and CP asymmetry

Sin22θ13=0.1, 0.05, 0.01

At the 1st oscillation peak,E/L=600 MeV/310 km.


Bound-state β-decayIf 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.

Point 2

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)

2007/3/8 Sasao @ Neutrino Telescope 7Q value

Bound beta ratioThe ratio is bigger for

large Z and small Q.

Ratio of bound-to-continuum beta decay

2 2 2

20 3

0 0

7 / 20 0

0 e

(0)1

( , ) ( , ): number of free places,

(0) : Wave fucntion of atomic state at the nucleus,

( , ) : Fermi integral ( 1) : available energy in units of m

f b nbf

c

f

n

n Q Zn W

f Z W n f Z Wn

f Z W WW

Unfortunately requirement of short life time means large Q andcontradicts with the large bound-to-continuum ratio.


Experimental studies 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.

PRL95,052501(2005)


Bound Decay BranchingThe result agrees very well with the theoretical expectation.


Beta beam & EC beam 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

6 62 3

18 1810 9

e

e

He Li e

Ne F e

148 14866 65 * eDy Tb

J. Sato: PRL95,131804(2005)J. Bernabeu et al: hep-ph/0605132;J. Bernabeu et al: JHEP0512,14(2005)

Zucchelli:PLB532,166(2002)

Point 3


CERN scheme for beta & EC beam

10^14 ions /decay ringVolpe hep-ph/0605033


Sensitivity to 13

J.E.Campagne et alHep-ph/0603172


Sensitivity to The red

dashed curve is when beta intensity is ½ of the design.

Thus the intensity is the key parameter.


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 +/- discrimination. Examples: 108Ag, 110Ag, 114In, 104Rh

Mixed CP-even beam Two separate isotopes, with EC or bound-state bet

a decay. Need to store both beams simultaneously in a ring

or store them in a time-sharing mode. Examples:122Cd (b) & 152Yb (EC)


Property of 108Ag

１ 0847Ag

10848Cd

10846Pd

1016keV, 1.76%

1649keV, 95.5%

1484keV,0.26%

1918keV,2.35%

97.15%2.85% ｔ 1/2=2.37 min

-decayECNeutral 108Ag has bothEC and -decay modes.Hydrogen-like 108Ag46+ has bound-state -decay in addition.


Hydrogen-like 108Ag

life 2.37min- 2.36min

2007/3/8 Sasao @ Neutrino Telescope 17~0.3


Rate Estimate Boosting 108Ag46+ with =180 produces (ant

i)-neutrino beam of E=600-700 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 L=310 km. 4 mono-chromatic lines are included. 2 QE events/year: too small !


Mixed CP-even beam For EC beam, better

isotope is 152Yb. Life time: 3 sec. EkeV EC/(EC++)=0.3 Rate=1400 (QE) eve

nts/year This rate is worth fur

ther study.


Mixed CP-even beam (2) For b beam, better

isotope is 122Cd. Life time: 5.24 sec. EkeV b/(b+c)=0.01 Rate=12 events/ye

ar


Some comments EC nuclide candidates:

152Yb; Life time=3 sec; EkeV; EC/(EC++)=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 r

ejection.

Bernabea et al. hep-ph/0510278


Summary CP-even neutrino beam

Pure mono-energetic e and e beam; suited to determine CP phase.

Bound-sate beta-decay is employed to produce e in addition to EC for e.

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.


Back Slides


Other isotope candidates for pure CP-even beam


Bound-state beta-decay、example 2

Cosmological clock 187Re neutral

T=42 Gyear 187Re75+

T=33 year

PRL77,5190,1996

cp-even neutrino beam

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