CP violation from a combined
Beta Beam and Electron Capture
neutrino experiment
Catalina Espinoza
U. Valencia and IFIC
NUFACT09
Chicago, July 2009
Work in collaboration with
J. Bernabeu, C. Orme,
S. Palomares-Ruiz and S. Pascoli
based on JHEP 0906:040, 2009 1
Programme
 What is known, what is unknown in Neutrino Oscillations
 CP Violation without antineutrinos: Energy Dependence
 A combined BB and EC experiment for the same ion Ytterbium
 Comparison between different baselines and boosts:
i) low energy (Ep(SPS) ≤ 450 GeV, 130 km and 650 km)
ii) high energy (Ep(SPS) ≤ 1000 GeV, 650 km and 1050 km)
 CP-Violation Discovery Potential and Mass Hierarchy
Determination
 Conclusions
2
What is known, what is unknown
Neutrino flavour oscillations
 m 23  2.4  10 eV

 m 212  7.65  10 5 eV 2
 13  10o , A hint ?

2
3
2
sin  23  0.50
2
sin 12  0.304
2
 ?
Absolute neutrino masses ?  3 H beta, Cosmology
Form of the mass spectrum
 Matter effect in neutrino
propagation
Majorana neutrinos?  0: masses and phases
3
The Pontecorvo MNS Matrix
 e 
 1 
 
 
    U  2 
 
 
 
 3
After diagonalization of the neutrino mass matrix,
Even if they
are Majorana
 For Flavour oscillations
U: 3 mixings, 1 phase
0   c13
1 0


U  0 c23 s23   0
i

0  s23 c23    s13e
 Atmospheric
 KEK, MINOS,
OPERA
i 
0 s13e   c12 s12 0


1
0    s12 c12 0
0 c13   0
0 1
•Appearance e!
•Reactors
•Matter effects
Solar
KAMLAND
Borexino
4
Three Generations of Experiments
• 0. Only three?  MiniBoone
• I. Solar Sector, Atmospheric Sector 
Δ
Δm212, θ12
│Δm223│, θ23
Borexino
MINOS, OPERA
• II. Connection between both Sectors 
θ13,
θ
Double CHOOZ, Daya Bay, T2K, NOVA, …
Sign (Δm223)
• III. CP-Violating Interference  δ
Super-Beams? Beta / EC Beams? Neutrino Factory?
5
Third Generation Experiments:
CP Violation
• European Strategy Plan demands
for ~ 2012 a CDR with the
alternatives: SuperBeams,
Beta/EC Beams, Neutrino Factory.
• SuperBeam: no pure Flavour,
uncertain continuous Spectrum.
• Beta Beam: pure Flavour, known
continuous Spectrum.
• EC Beam: pure Flavour, known
single Monochromatic Beam.
• Neutrino Factory: pure Flavour
iff detector with charge
discrimination, known continuous
Spectrum.
Frejus
• CP Violation can be observed either by an
Asymmetry between Neutrinos and Antineutrinos or
by Energy Dependence (CP phase as a phase shift)
in the Neutrino channel, or both.
6
Why Energy Dependence ?
A theorem
CP violation:
P( e    )  P( e    )
CPT invariance + CP violation = T non-invariance
P( e    )  P(    e )
No Absorptive part  Hermitian Hamiltonian 
CP odd = T odd = P(   )  P(   )
e

e

is an odd function of time = L !
• In vacuum neutrino oscillations for relativistic neutrinos
 L/E dependence, so
CP-even (odd) terms in the appearance probability
 Even (odd) functions of energy. Then ENERGY
DEPENDENCE disentangles the CP-even and CP-odd terms7
Interest of energy dependence in
suppressed neutrino oscillations
• CP violation accessible in suppressed appearance experiments,
in order to have access to the interference between the
atmospheric and solar probability amplitudes
• Appearance probability:
m L
P ( e    )  s sin 213 sin (
)
4
E


2
23
2
2
2
13
Atmospheric
m L
2
c23
sin 2 212 sin 2 (
)
4 E


2
12
Solar
2
2
2
m13
L m12
m13
L
L
~
J cos( 
)
sin(
)
E
4E
E
4
4
|Ue3| gives the
strength of P(νe→νμ)
•
δ gives the interference
pattern: CP odd term is
odd in E/L
•
•
δ acts as a phase shift
Interferen ce
This suggests the idea of using either a monochromatic
neutrino beam to separate δ and |Ue3| by energy dependence
with different boosts, or a combination of channels with
8
different neutrino energies in the same boost

Neutrinos from β+/ Electron Capture
β+ decay:
P. Zucchelli, Phys.Lett.B532:166-172, 2002
boost
●
Forward direction
3 body decay
Eν
From the well-known β-decay neutrino spectrum,
we can get a pure beam by accelerating β-unstable ions
•
Electron capture:
d 2 N N iones  2

y 2 (1  y ) (1  y ) 2  y e2
2
dSdE
L g ( y e )
J. Bernabeu, et al
boost
Z protons
N neutrons
●
Z-1 protons
N+1 neutrons
Forward direction
2 body decay!  In the CM , a single discrete energy
If a single final nuclear level is populated
•
Eν
Eν
From the single energy EC neutrino spectrum, we can get a pure and
monochromatic beam by accelerating ec-unstable ions and choosing forward ν’s
 One can concentrate all the intensity at the most appropriate energy
9
for extracting the neutrino parameters
A combined Beta Beam and EC
156
neutrino experiment ( 70Yb)
Isotopes with favourable decaying properties:
• In proton rich nuclei (to restore the same orbital angular momentum
for protons and neutrons)  Superallowed Gamow-Teller transition
The “breakthrough” came thanks to the recent
discovery of isotopes with small half-lives of one
min or less, which decay in neutrino channels
near 100% to a SINGLE Gamow-Teller resonance.
●
• The interesting isotopes have to have
half-life < vacuum half-life ~ few min.
Nuclear
Ion Candidate: Ytterbium ( 156
70Yb )
half-life: 26.1 sec
Decay
Daughter
Neutrino Energy (MeV)
BR
β+
EC
α
156Tm*
2.44 (endpoint)
3.46
52 %
38 %
10 %
156Tm*
152Er*
10
A combined beta-beam and EC
156
neutrino experiment ( 70Yb)
• Suppressed appearance probabilities
for the CERN-Frejus (130 Km, red line)
and CERN- Gran Sasso o Canfranc
(650 Km, blue line) baselines. The
unoscillated neutrino flux is shown for
γ=166
• Suppressed appearance probabilities
for the CERN-Gran Sasso o Canfranc
(650 Km, blue line) and CERN-Boulby
(1050 Km, red line) baselines. The
unoscillated neutrino flux is shown for
11
γ=369
Experimental Setups
for the combined experiment
•
Appearance Experiment : Electron Neutrino Flux × Oscillation
Probability to muon neutrinos × CC Cross Section for muon production.
Setups:
• Boost γ=166 with current SPS
I: CERN-Frejus (130 Km)
II: CERN-Gran Sasso or Canfranc (650 Km)
• Boost γ=366 with an upgraded SPS
III: and III-WC: CERN-Gran Sasso or Canfranc (650 Km)
IV: and IV-WC: CERN-Boulby (1050 Km)
Detectors:
• LAr or TASD, 50 kton
 Neutrino spectral information from CC muon events
• Water Cerenkov, 0.5 Mton  Neutrino energy from QE events only + inelastic events
in a single bin, with 70% efficience
• Number of decaying ions per year: 2 x 1018  10 years
• The separation between the energy of the EC spike and the end point
energy of the beta-spectrum is possible: if Eν(QE) > 2γEo(β),
since Eν(true) > Eν(QE), the event must be attributed to the EC flux and
hence, it is not necessary to reconstruct the true energy
12
The virtues of combining energies
from BB and EC
•
Sensitivity to θ13 and δ (Setup III: Gran Sasso or Canfranc )
BB
EC
BB+E
C
• The power of the combination of the two channels is in the difference
in phase and in amplitude between the two fake sinusoidal solutions,
selecting a narrow allowed region in the parameter space
13
Comparing baselines I and II
for the same boost
• For the combined BB + EC fluxes with θ13=10 and δ=900
Frejus
Gran Sasso or Canfranc
• The BB channel contributes very little to the overall sensitivity of the
setup, due to the γ2 dependence. The bulk of the sensitivity is due to the EC
14
channel placed on the first oscillation maximum
Comparing boosts II and III with
the same baseline
• Combination of BB and EC fluxes for θ13=10 and δ=900
γ=166
γ=369
The sensitivity is better with the upgraded SPS energy
• The relative role of the two BB and EC components is
exchanged when going from II to III
•
15
Setup III-WC : Disentangling θ13 and δ
• Solutions for Gran Sasso or Canfranc, from discrete degeneracies
included, for θ13=10 , 30 and for different values of the CP phase
•
• The increase in event rates improves the results substantially with respect to
those results for Setup III, although not as much as the size factor between
the two detectors.
• The mass ordering can be determined for large values of the mixing angle.
• The hierarchy degeneracy worsen the ability to measure δ for negative
16
true values of δ.
Comparing III-WC and IV-WC
•
Boulby provides a longer baseline than Gran Sasso or Canfranc.
This has two contrasting effects on the sensitivity to measure
CP violation: i) Sufficient matter effects to resolve the hierarchy
degeneracy for small values of θ13; ii) It decreases the available
statistics
Gran Sasso or Canfranc
Boulby
• The smaller count rate results in a poorer resolution.
• The longer baseline allows for a good determination of the mass
ordering, eliminating more degenerate solutions.
17
CP Discovery Potential for WC
Gran Sasso or Canfranc
Boulby
• Comparing the two locations of the WC detector,
the shorter baseline has a significally (slightly) better
reach for CP violation at negative (positive) values of δ
than the Boulby baseline.
18
Mass hierarchy determination
• Fraction of δ for which the neutrino mass hierarchy can
be determined
L=650 km
• III-WC with
present priors
in the known
parameters
• The
L=650 km
• III-WC with
negligible errors
in the known
parameters
L=1050 km
• IV-WC with
present priors
in the known
parameters
Boulby baseline, with its larger matter effect, is better
19
for the determination of the mass hierarchy
Conclusions
•
The two separate channels BB and EC have a limited overlap of the
allowed regions in the (θ13, δ) plane, resulting in a good resolution on
the intrinsic degeneracy.
•
The CP phase sensitivity is obtained by only using neutrinos, thanks to
the Energy Dependence of the oscillation probability with the
combination of the two BB and EC channels.
•
THE SPS UPGRADE TO HIGHER ENERGY (Ep = 1000 GeV) IS CRUCIAL
TO HAVE A BETTER SENSITIVITY TO CP VIOLATION (the main
objective of the third generation neutrino oscillation experiments) IFF
ACCOMPANIED BY A LONGER BASELINE ( Canfranc, Gran Sasso or
Boulby).
•
THE BEST E/L FOR HIGHER SENSITIVITY TO THE MIXING U(e3)
IS NOT THE SAME THAN THAT FOR THE CP PHASE. Like the phaseshifts, the effect of δ is easier to observe by going to the region of
the second oscillation. HENCE THE IMPORTANCE OF COMBINING
DIFFERENT ENERGIES IN THE SAME EXPERIMENT.
20
Conclusions
• Setups III and III-WC, with the Canfranc or Gran
Sasso baselines, have larger counting rates and a better tuning
of the beam to the oscillatory pattern, resulting in a very good
ability to measure the parameters. These setups provide
the best sensitivity to CP violation for positive values of δ.
• Setups IV and IV-WC, with the Boulby baseline, provide a
better determination of the hierarchy and a good reach to CP
violation for negative δ, even if the mass ordering is unknown.
THE COMBINATION OF THE TWO BB AND EC
BEAMS FROM A SINGLE DECAYING ION AND A
FIXED BOOST ACHIEVES REMARKABLE RESULTS
21
Acknowledgements
• Thanks to my collaborators:
J. Bernabeu, J. Burguet-Castell, M. Lindroos,
C. Orme, S. Palomares-Ruiz and S. Pascoli.
Thank you very much for
your attention…
22
Implementation
•
A Facility with an EC channel would require a different approach to
acceleration and storage of the ion beam compared to the standard
beta-beam, as the atomic electrons of the ions cannot be fully stripped
• Partly charged ions have a short vacuum life-time against collisions.
The interesting isotopes have to have
half-life < vacuum half-life ~ few min.
For the rest, setup similar to that of a beta-beam:
23