Nucifer Experiment at Osiris
Yo KATOThe University of Tokyo
7 December 2013
7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

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Nucifer Collaboration

7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

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Reactor Monitoring
Reactor monitoring using antineutrino detectors-- Neutrinos cannot be shielded -> can be detected outside a reactor building-- There’s no alternative source of antineutrino -> cannot hide reactor operation-> Suitable for IAEA’s inspection!

Reactor Neutrino- 6 antineutrinos- 200MeV
emitted per fission
Previous experiments-- ROVNO experiment (Ukraine, 1984)-- SONGS experiment (California, 2006)-- KASKA Prototype experiment (Japan, 2007)
7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

3PANDA

7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

4Nucifer
4π plastic scintillator muon veto (30 PMTs)

N2 blanket

16 8’ low background PMTs

2.5 m

25 cm width acrylic buffer
Bore doped polyethylene(neutron background shielding)Calibration guide tube
Target: 850 L Gd-LS (0.2 %)Stainless steel vessel: double
containment
4π 10 cm lead shielding + additional 10 cm thick wall on thereactor side (against g-ray background)
7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

Total weight:  50 t
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Osiris-- Located at CEA Saclay (FR)-- Experimental nuclear reactor-- 70 MWth, enriched 235U fuel (20%)-- Operating cycle: 3 weeks ON + 10 days OFF-- Distance between core and detector: 7 m-- 11 m underground, 10 m.w.e. overburden
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Neutrino Frontier Seminar @ Fuchu

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Backgrounds
Accidental background-- Natural radioactivity (gamma)-- Thermal neutrons-> Can be estimated using shifted time window
Correlated background-- Fast neutrons(prompt-like event : proton recoil)-- Double neutron capture (caused by muon spallation)-- Long-lived cosmic ray activation product (9Li, 8He)-> Can be estimated using reactor off data

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Neutrino Frontier Seminar @ Fuchu

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Selection Cuts
Energy Cut

PSD Cut

Prompt Qtot

2 – 6 MeV

Delayed Qtot

6 – 10 MeV

Qtail/Qtot

0.18 – 0.26

Time Cut
Delta T5 – 45 s

Clean Before Window> 50 s

Clean After Window> 100 s

7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

8Preliminary Results

Reactor State

Accidental Rate [/day]Correlated Rate [/day]

On4372 ± 6

251 ± 17

Off35.3 ± 0.3

123 ± 6𝟏𝟐𝟖 ± 𝟏𝟖

On - OffGood agreement with expected rate 132 events/day (12% efficiency)
7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

9Preliminary Results

Rejected

7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

10Preliminary Results

Rejected

Proton recoil region:
does not change
between reactor Onand Off

7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

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Preliminary Results

Rejected
Gamma & e+/- region:
Neutrino signalProton recoil region:
does not change
between reactor Onand Off

7 Dec 2013

Neutrino Frontier Seminar @ Fuchu

12New Cuts
Energy Cut

PSD Cut
Old cut

New cut

Prompt Qtot

2 – 6 MeV

2.0 – 7.1 MeVDelayed Qtot

6 – 10 MeV

4.2 – 9.6 MeVTime Cut
Old cut

New cut

Delta T5 – 45 s

5 – 40 s

Clean Before Window> 50 s> 50 s

Clean After Window> 100 s> 100 s
Old cut

New cut

Expected rate: 272 events/day

Low cut

QQ>0.18

QQ>0.18(Old cut: 132 events/day)High cut

QQ<0.26

QQ<0.282-1.77e-05Qtot

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Neutrino Frontier Seminar @ Fuchu

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Summary• First neutrinos were detected by Nucifer inApril-May 2013.
• Good agreement of measured neutrino signalwith simulations.
• New selection cuts have been optimized.
• New data are being taken since November 2013.
• Study of detector systematics is now on-going.

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