Energy Dependence and Physics
Reach in regard to Beta/EC
Beams
J. Bernabeu
U. Valencia and IFIC
B. Pontecorvo School
September 2007
Energy Dependence and Physics potential
in regard to Beta/EC Beams
 Third generation proposals for the CP phase δ
 ß Beams: combination 6He ()- 18Ne() at the same γ
 EC Beams: combination of two energies for the same ion 150Dy
 Comparison between ( low energy Ep(SPS) ≤ 450 GeV, Frejus)
and (high energy Ep(SPS) ≤ 1000 GeV, Canfranc )
The Pontecorvo MNS Matrix
After diagonalization of the neutrino mass matrix,
 e 
 1 
 
   For Flavour oscillations
U: 3 mixings, 1 phase
    U  2 
 
 
 
 3
Even if they
are Majorana
i 
0   c13
0 s13e   c12 s12 0
1 0





U  0 c23 s23   0
1
0    s12 c12 0
i

0  s23 c23    s13e 0 c13   0
0 1
Appearance e!
Atmospheric
Solar
Reactor
KEK
KAMLAND
More LBL-beams Matter in Atmospheric…
Beta Beam Concept
P. Zuchelli
Design and performance: M. Benedikt, M. Lindroos, M. Mezzetto…
Neutrino Oscillation Physics
• After atmospheric and solar discoveries and accelerator and
reactor measurements → θ13 , δ
Appearance probability:
m132 L
P ( e    )  s sin 213 sin (
)
4 E


2
23
2
2
Atmospheric
2

m
L
2
c23
sin 2 212 sin 2 ( 12 ) 
4 E


Solar
m132 L m122 L
m132 L
~
J cos( 
)
sin(
)
E
4E
E
4
4
Interferen ce
For Beta Beams,
• 6He antineutrino beam
combined with
18Ne neutrino beam
• 5 years each
• Intensity of 2.9x1018 6He and
1.1x1018 18Ne decays per year
• Detection by charged-current
event with a muon in the final
state  440 Kton fiducial mass
water Cherenkov detector
Beta Beams
• Neutrino Continuous Spectrum implies the need of the reconstruction
of the energy in the detector for each event, based on the quasi elastic
channel
6
He
18
Ne
Fixing the CERN-Frejus baseline

Is the sensitivity to CP
Violation and θ13 changing
with energy?
For γ > 80, the sensitivity
changes rather slowly
because the flux at low
energies does not reduce
significantly.
• Then it is not advantageous
to increase the energy if
the baseline is not
correspondingly scaled to
remain closed to the
atmospheric oscillation
maximum: remember L/E !
•
J. Burguet-Castell et al.
Fixing γ
•
The maximum energy reachable with the present SPS is γ=150.
• Is the sensitivity to θ13 and δ changing with the baseline?
•
L = 300 Km is clearly favoured, but …
Comparison of two set-ups



Setups with the same
γ for both ions
Set up I : γ =120,
L=130 Km (Frejus)
Set up II : γ =330,
L=650 Km (Canfranc)
Set up II needs the
upgrade of SPS until
Ep=1000 GeV
Conclusion: Set up II is clearly better. It provides better
precision and resolves the degeneracies.
J. Burguet - Castell et al.
Comparison of two set-ups
CP violation exclusion plot at
99% CL.
Exclusion plot for θ13 at
99 % CL.
Outlook: R & D effort to design Beta-beams for the
upgraded CERN-SPS (Ep=1000 GeV) appears justified.
Interest of energy dependence in
suppressed neutrino oscillations
•
Appearance probability:
2

m
L
2
P ( e    )  s23
sin 2 213 sin 2 ( 13 ) 
4 E


Atmospheric
m122 L
c sin 212 sin (
)
4 E


2
23
2
2
Solar
m132 L m122 L
m132 L
~
J cos( 
)
sin(
)
E
4E
E
4
4
Interferen ce
|Ue3| gives the strength
of P(ne→νμ)
• δ gives the interference
pattern: CP odd term is odd in
E/L
• This result is a consequence
of a theorem under the
assumptions of CPT invariance
and absence of absorptive
parts
•
This suggests the idea of a monochromatic neutrino
beam to separate δ and |Ue3| by energy dependence!
δ acts as a phase shift
Interest of energy dependence in
suppressed neutrino oscillations
Canfranc
Frejus
Neutrinos from electron capture
How can we obtain a monochromatic neutrino beam?
Electron capture:
Z protons
N neutrons
J. Bernabeu et al
Z-1 protons
N+1 neutrons
boost
Forward direction
2 body decay!  a single discrete energy if
a single final nuclear level is populated
From the single energy e--capture neutrino spectrum,
we can get a pure and monochromatic beam by
accelerating ec-unstable ions  No need to reconstruct
the neutrino energy in the detector !
An idea whose time has arrived !
In heavy nuclei (rate proportional to square wave function at
the origin) and 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 half-lives
of a few minutes or less,
which decay in neutrino
channels near 100%
through electron
capture to
a single Gamow-Teller
resonance.
Implementation
The facility 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. The isotope we
discuss ( 150Dy) has a half-life ≤ vacuum half-life ~ few minutes.
●
For the rest, setup similar to that of
a beta-beam. Due to possible
problems with space charge if we
want to accumulate 1018 decaying
ions per year  Look for an isotope
with all the nice properties pointed
out before and a half- life near 1 sec.
Electron neutrino flux
●
Notice the proportionality with γ2
and the monochromaticity

• Strategy:
Put all the intensity at the energy in which the sensitivity to
Physics is higher !
Experimental set-up for EC
• Combine two different energies for the same ion and baseline
●
1018 decaying ions/year
●
440 kton water ckov detector
Appearance &
Disappearance
• Set up I (low energy, Frejus):

5 years  90 (close to minimum energy to avoid background)
5 years = 195 (maximum achievable at present SPS)
Versus 10 years for each γ  the virtues of two energies
L = 130 km (CERN-Frejus)
• Set up II (high energy, Canfranc):

5 years 95 (maximum achievable at present SPS)
5 years = 440 (maximum achievable at upgraded SPS)
L = 650 km (CERN - Canfranc)
Set up I - Disentangling θ13 and δ
Access to
measure
the CP phase
as a phaseshift
Much better
separation for
two different
energies, even
with lower
statistics
The virtues of two energies
130 km
Set up I: Fit of 13 , 
from statistical distribution
The principle of an energy dependent measurement is working
and a window is open to the discovery of CP violation
Set up I:
Exclusion plot: 13  0 sensitivity
Total running time: 10 years... Significant below 1o
Set up I:
Exclusion plot: CP sensitivity
Total running time: 10 years... Significant for θ13 > 40
Set up II: The virtues of
combining two energies
650 km
Conclusion: the separation between 13 and  is much better
than that for set up I
Set up II: Fit of 13 , 
from statistical distribution
δ
θ13
Conclusion: the precision reachable for the CP phase is better
than that for set up I <-> WITH NEUTRINOS ONLY,
AT TWO SELECTED DIFFERENT ENERGIES
Set up II: θ13 sensitivity
0.1 – 0.4 degrees, depending on δ
Set up II:
Exclusion plot: CP sensitivity
Without any previous information on θ13 …
Set up II: δ sensitivity
δ sensitivity < 45º for θ13 ≥ 3 º.
Asymptotically, a δ sensitivity of ± 18º
δ
99 % C L
θ13
Set up II:
Exclusion plot: CP sensitivity
If θ13 previously known …
IMPRESSIVE !!!
Set up II: δ sensitivity
δ sensitivity < 45º for θ13 ≥ 0.4 º.
Asymptotically, a δ sensitivity of ± 8º
50
δ
-50
99 % C L
1
3
θ13
Conclusions




The simulations of the Physics Output for both Beta and EC beams indicate:
THE 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.
THE BEST E/L FOR HIGHER SENSITIVITY TO THE MIXING U(e3) IS NOT THE SAME
THAN THAT FOR THE CP PHASE. Like the phase-shifts, the presence of δ is easier to
observe in the region of the second oscillation: Set up II in EC beams has an impressive
sensitivity to CPV, particularly if the mixing is previously known. The mixing is better seen
around the first oscillation maximum, instead.
Besides the feasibility studies for the machine, MOST IMPORTANT FOR PHYSICS IS THE
STUDY OF THE OPTIMAL CONFIGURATION BY COMBINING
- Low energy ( < 2017(?)) with high energy (> 2017(?))
- Frejus (L=130 Km) with Canfranc (L=650 Km) , i.e., the decay “ring” should be a triangle and
not a rectangle.
- EC monochromatic neutrinos with 6He beta- antineutrinos.
MUST DEFINE A PROGRAM TO DETERMINE INDEPENDENTLY THE RELEVANT CROSS
SECTION
Outlook

The result of the synergy of
Neutrino Oscillation Physics
with LHC- Physics (SPS
upgrade) and, in the case of
Beta/EC Beams, with Nuclear
Physics (EURISOL) for the
Facility at CERN, could be
completed with the synergy
with Astroparticle Physics for a
Multipurpose Detector, common
to neutrino oscillation studies
with terrestrial beams,
Atmospheric Neutrinos
(neutrino mass hierarchy),
supernova neutrinos and Proton
decay!!!
MUCHAS GRACIAS!