l. oberauer, paris, june 2004 measurements at reactors neutrino 2004 cdf, paris, june...
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L. Oberauer, Paris, June 2004
Measurements at Reactors
Neutrino 2004
CdF, Paris, June 2004
...chasing the missing mixing angle
L. Oberauer, Paris, June 2004
ex
Why reactors?
The actual best limit is coming from a reactor experiment ! Chooz,
Paolo Verde
sin22
m2 = 2 10-3 eV2
L. Oberauer, Paris, June 2004
Experimental method
nepe
• Nuclear reactors are a powerful source of low energy (up to ~ 8 MeV) electron anti-neutrinos
• Detection via inverse beta decay:
• Q-value ~ 1.8 MeV
• E~ Ee - Q ( spectroscopy)
• suppress background via use delayed coincidence method
L. Oberauer, Paris, June 2004
How to improve the sensitivity?The problem: Reactor exp. = Disappearance exp.
• compare total flux (and spectrum) with the
no- oscillation hypothesis
• one depends on systematic uncertainties, like:
absolute source strength,
cross section,
detection efficiency,
fuel development over time...
L. Oberauer, Paris, June 2004
The basic idea:Use 2 identical detectors
• oscillation frequency basically known
L/2 ~ 1.0 km - 2.0 km
• choose the right distance for the signal with the far detector
• monitor the reactor with the close detector (100m) (cancels also uncertainties like cross section, efficiencies etc.)
m2 = ( 2.0 - 2.5 ) 10-3 eV2
osc.length L
L. Oberauer, Paris, June 2004
The aims:
• Statistics N(far) ~ 5 104
• energy uncertainty (E) < 1%
• normalization uncertainty rel < 1%
number of target protons
efficiencies (positron, neutron) rel
excellent calibrations required...
L. Oberauer, Paris, June 2004
Additional uncertainties:
• shape (~ 2%)
• cross section (~ 1.9%)
should cancel !
• fuel composition (235U, 238U, 239Pu, 241Pu)
should cancel !
Bugey; comparison with spectrum deconvoluted from exp. determined beta spetra
Feilitzsch, Schreckenbach; used for analysis of the Gösgen experiment
Background?• accidental background
determine online not critical
radiopurity experiencies from CTF, Chooz, KamLAND
• correlated background (muon induced)
fast neutrons
beta - neutron cascades
• in Chooz signal/background ~ 25 -> 100 (aim)
• backgrounds in both detectors identical ??
L. Oberauer, Paris, June 2004
Sensitivity ?
• around few 10-2 for sin2 2after ~3 years (20t, 8GW)
• impact of systematics fairly modest
Huber, Lindne
r, Schw
etz & W
inter: hep-ph/0303
232
L. Oberauer, Paris, June 2004
Approach towards an experiment...• 3 workshops on „Future Low Energy -Experiments“
spring 2003 Alabama, USA
fall 2003 Munich, Germany
spring 2004 Niigata, Japan
• White paper
thanks to Maury Goodman.
paper available hep-ex/0402041
(or http://www.hep.anl.gov/minos/reactor13/white.html)
L. Oberauer, Paris, June 2004
Which site for the experiment ?
Diablo Canyon
Byron
Angra
PenlyChoozCruas
Krasnoyarsk
Taiwan
Kashiwasaki
One reactor complexTwo underground cavities @0.1- 1 km & ~1- 2 km
Daya Bay
L. Oberauer, Paris, June 2004
Requirements:
• Strong power plant
• Shielding (300m.w.e. or better) for at least the far detector
• Only one (or two) cores (=sources) preferred
• Support from the power plant responsibles
L. Oberauer, Paris, June 2004
Sites under discussion:
ANGRA, Brazil (reactor II)
BRAIDWOOD, BYRON, LA SALLE, Illinois, USA
CHOOZ, France
DAYA BAY, China
DIABLO CANYON, California, USA
KASHIWAWASAKI, KARIWA, Japan
KRASNOYARSK, Russia (first proposal)
L. Oberauer, Paris, June 2004
The Diablo Canyon site (USA)
• Close to San Francisco (500 km), California • Two cores (2 x 3.1 GWth) • D1 ~ 0.5 – 1 km & D2 ~ 1.5 – 3 km • Overburden: horizontal tunnel 800 mwe Leader Group : Berkeley LBL
L. Oberauer, Paris, June 2004
The Diablo Canyon site (USA)
• Close to San Francisco (500 km), California • Two cores (2 x 3.1 GWth) • D1 ~ 0.5 – 1 km & D2 ~ 1.5 – 3 km • Overburden: horizontal tunnel 800 mwe Leader Group : Berkeley LBL
L. Oberauer, Paris, June 2004
The Kashiwasaki site (Japan)
Kashiwasaki power plant : 24.3 GWth 7 cores 2 near detectors needed ! R&D budget approved 3 identical detector of ~8 tons
shielding 350 - 440 mwe Data taking ~ 2008
Sensitivity (3 years): sin2(213)<0.026 @90% C.L
L. Oberauer, Paris, June 2004
...even SuperK was proposed (Kornoukhov, Starostin)(Phys. Of Atom. Nucl., Vol. 67, 4, (2004) 672)
...with a near detector (KamLAND size) and a russian type 300 MW reactor !
L. Oberauer, Paris, June 2004
Letter of Intent: Double-Chooz
• d~1.05 km
• P~8.4 GW
• 300mwe far detector
• no excavation for far detector
L. Oberauer, Paris, June 2004
L. Oberauer, Paris, June 2004
Chooz (site of far detector)
Detector design, Double-Chooz
-target
Gd-scintillator
-catcher, scintillator
buffer, non-scintillating
Muon Veto, scintillator
2.4m3.6m
5.5m6.7m
)
)
)
)
)
)
PMs 2.8m
Sensitivity ?
• sensitivity between 0.02 and 0.03
for sin2 2 after ~3 years (for m2 = 2.0 10-3 eV2 )
P. Huber et al. hep-ph/0403068
Poster: G. Mention, systematics and sensitivities for Double-Chooz
L. Oberauer, Paris, June 2004
Comparison to LBL-projects?P
. Huber et al. hep-ph/0403068
• D-Chooz: funding French side 2.2 - 2.5 M€ approved
• Aim for start data taking ~ 2008
L. Oberauer, Paris, June 2004
Background studies for Double-Chooz
Correlated background events:
• Monte-Carlo simulation of fast neutrons, generated by cosmic muons
• first check: simulation of the old Chooz experiment
MC - result: 0.8 < bg/day < 4.5 (limited by statistics)
Exp. - result: bg = 1.1 / day
• MC reliable !
L. Oberauer, Paris, June 2004
Background spectrum Double-Chooz
Neutron spectrum - veto off Neutron spectrum - veto on
Shielding 100mwe, t = 33.7 h 1 background event
prelim
inary
L. Oberauer, Paris, June 2004
Background Double-Chooz
• expected rate far detector (300mwe) ~ 0.15 / day
(lower than 0.3 / day at 90% cl)
• signal / background far det. > 100
• expected rate close detector (60mwe) ~ 2 / day
• signal / background close det. > 500
(if distance is ~ 150m)
• spectral shape of background quite flat (unequal to signal spectrum)
L. Oberauer, Paris, June 2004
Example: beta-n from 8He
(generated by cosmic muon on 12C in organic liquid scintillator)
• monitor 8He rate by special beta - alpha delayed coincidence
• data from other candidates (9Li) available from T. Hagner et al. (muon beam @ SPS, CERN), Chooz, CTF, KamLAND
Beta - neutron cascades
L. Oberauer, Paris, June 2004
Spectral information ?Y(‚close‘) - Y(‚far‘)
• ~ 3.5 years
• sin22
m2 = 2 10-3 eV2
very valuable cross-check if one obeserves an effect in the total rates !
L. Oberauer, Paris, June 2004
Conclusions
Search for 13 with a new reactor experiment is very promising
„next future“ experiments
Large expertise available from low energy, low background projects (Chooz, CTF/Borexino, KamLAND)
White paper available
LOI for a new Double-Chooz, France
Poster, A. Ianni, C
TF &
M. Göger, LENA