Constraints Experimental on
Shane Squires
13
What is
1 0 0 c 23 0 s23 c13 0 s23 0 c 23 s13e i 0 1 0 s13e 0 c13
i
13
?
s23 0 e i 1 c 23 0 0 0 1 0 0 ei 2 0 0 0 1
Neutrino mixing matrix:
c 23 s23 0
and the CP phase(s) are the only unmeasured neutrino mixing parameters.
13
Four Types of Experiments
Where can you get lots of neutrinos?
The Sun: Homestake, SAGE, GALLEX, SuperKamiokande, SNO, etc. Cosmic rays ("atmospheric neutrinos"): Soudan, IMB, SuperKamiokande, etc. Accelerators: K2K, T2K, NOvA, MINOS, OPERA, etc. Nuclear reactors: KamLAND, Palo Verde, (Double) CHOOZ, Daya Bay, etc.
Physics of the Four Types
Neutrino energy and mass splitting determine oscillation length: E
L0
m
2
The parameter L/E (L=distance to detector) determines range of detectable mass splittings. Advantages of reactor and accelerator expt.s:
Spectrum of neutrino energies is well-understood. Length to detector can be chosen. Neutrino flux is high and can be controlled.
Physics of the Four Types
Type Solar Cosmic Accel. Reactor
E
1
(MeV)
Measures 1-2 mixing 2-3 mixing 1-3 or 2-3 1-3 mixing
L0 (km)
10s 1000 1000 1
( )
1 m 2s
1014 10
3
1000 1000 1
depends
1014
Results for Other Parameters
Solar neutrino experiments: 2 m12 8 10 5 eV 2 34 o 12 Atmospheric neutrino experiments: 2 m23 2 10 3 eV 2 45 o 23 Both have contributed to bounds on 13, but best results come from reactor experiments.
CHOOZ and Palo Verde
CHOOZ: European team, experiment in France. Palo Verde: American experiment in Arizona. Otherwise, the two are very similar. Both were built to rule out the possibility that the atmospheric deficit comes from e. In the process, they created bounds on 13 .
CHOOZ and Palo Verde
Reactor generates a large flux of e. The flux and energy distribution of the antineutrinos can be inferred from reactor operation records. The experiment is designed to observe the reaction + e
+p
e +n
If the reaction count is lower than expected, the missing e must have changed flavor.
CHOOZ and Palo Verde
CHOOZ
Palo Verde
CHOOZ and Palo Verde
Detector: approximately 1 km from source.
CHOOZ and Palo Verde
Detector is filled with liquid scintillator with many free protons. Scintillator fluid is .1% Gadolinium. Positron annihilation is detected promptly. Gd-n cross section is extremely large, and neutron absorption gives a characteristic 8 MeV photon cascade. The neutron is detected within 100 s. Can also see 2.2 MeV cascade from p-n binding. Although positron emission is isotropic, the neutron signal can be used to identify the direction of the antineutrino.
Sample incoming CHOOZ Data
Random error: cosmic ray muons, internal/external radioactivity. Apply cut based on energy, time difference, and location of origin.
Systematic Error in CHOOZ
Results from CHOOZ
Limits on from Chooz (lines, 90%, 95%, 99%, and 3 ), and from Chooz+solar+KamLAND (colored regions).
Current Status
It is now generally accepted that CHOOZ data (together with atmospheric neutrino 2 data to determine m23 ) demonstrates that
< 12 o 13
or
sin 2 (2
13
) < .17
= 0o , 13
at a 90% confidence level. The results so far are consistent with o with a best fit around 13 = 4.4 .
Future Experimental Directions
New reactor experiments measure 13 to high accuracy. If 13 is not too small, accelerator experiments measure CP-violating parameters, etc. Precision neutrino measurements remain important for 20-30 years.
Daya Bay and Double CHOOZ
Daya Bay: US-Chinese collaboration. Experiment will be located east of Hong Kong near Daya Bay and Ling Ao reactors. Broke ground in October. Double CHOOZ: European collaboration. Experiment at old CHOOZ site. Will begin taking data in 2008.
Features of New Experiments
Two detectors (near and far) to reduce uncertainty in antineutrino flux. Larger detectors. "Multiple modules" within each detector. Improved shielding from external radiation. Improved muon detection.
Prospects for New Experiments
After three years of operation, Double CHOOZ will be able to detect
sin (2 sin (2
2
2
13
) > .02 ) > .01
Daya Bay will ultimately b...