1. NuFact 2012, Williamsburg, VA
RENO
Yeongduk Kim, Sejong University
On behalf of RENO collaboration
NuFact 2012, Williamsburg, VA

2. Contents Q13 measurement with reactor neutrinos Overview of RENO
Data Taking and Data Reduction
Calibration Data of RENO
Background Reduction
Chi2 Analysis & results of Q13
Summary & Perspectives

3. Q13 Measurements with Reactor and Accelerator
- Clean measurement of 13 with no matter effects
* Accelerator
- mass hierarchy + CP violation + matter effects
Two experiments are complementary..

4. Reactor Neutrino Experiment at a Glanceν e + n Gd γ
~30μs
Delayed signal E å ~ 8
MeV g
prompt signal
Inverse Beta Decay
q13 Dominant
sin2(213)=0.04
sin2(213)=0.1
sin2(213)=0.2
E (MeV)
“near”
“far”
q12 Dominant

5. RENO Collaboration (12 institutions and 40 physicists)
Project of Only Korean Institutes
(12 institutions and 40 physicists)
Chonbuk National University
Chonnam National University
Chung-Ang University
Dongshin University
Gyeongsang National University
Kyungpook National University
Pusan National University
Sejong University
Seokyeong University
Seoul National University
Seoyeong University
Sungkyunkwan University
Total cost : $10M
Start of project : 2006
The experiment running with both near & far detectors from Aug. 2011

6. Global fits
Fogli et al., arXiv:

7. RENO Sites
Seoul
RENO
Y2L
Far Detector
Near Detector
1380m
290m

8. Contributions of Reactors to Neutrino Flux
Far ( % )
Near (% ) 1
13.73
6.78 2
15.74
14.93 3
18.09
34.19 4
18.56
27.01 5
17.80
11.50 6
16.08
5.58
Accurate measurement of baseline distances to a precision of 10 cm using GPS and total station.
Accurate determination of reactor neutrino fluxes require small, uncorrelated reactor power uncertainties.

9. RENO Detector 354 10” ID PMTs : 14% surface coverage 67 10” OD PMTs
Both PMTs : HAMAMATSU, R7081
Mu-metal shielding for each PMT. (-5cm)
No special reflector for ID
Tyvek reflector at OD
LAYER D
(cm) H
vessel
Filled with
Mass
(tons)
Target
280
320
Acrylic
Gd(0.1%) +LS
16.5
Gamma catcher
400
440 LS
30.0
Buffer
540
580
SUS
Mineral oil
64.4
Veto
840
880
Concrete
water
352.6

10. Summary of Milestones for RENO
: Start of the RENO project
~ : Civil construction including tunnel excavation
~ : Detector structure & buffer tanks complete.
: Acrylic containers installed
~ : PMT test & installation
: Detector closing/ Electronics hut & control room built
: Installation of DAQ electronics and HV & cabling
~ 07 : Liquid scintillator production & filling
: Start data-taking.

11. Completed RENO Detector (Feb. 2011)
Liquid Scintillator Production System
DAQ Electronics
Calibration System
Control Room

12. Gd Loaded Liquid Scintillator
Recipe of Liquid Scintillator
CnH2n+1-C6H5 (n=10~14)
Aromatic Solvent & Flour
WLS
Gd-compound
LAB
PPO +
Bis-MSB
0.1% Gd+(TMHA)3
(trimethylhexanoic acid)
Gd concentrations in Gd-LS sample measured .
~0.11%, stability ~ year.
FAR
NEAR

13. 10” PMT R7081 [rms/mean] Optimized Mu shielding.
Mu metal shielding up to 5 cm to Top.
All 842 PMTs are working w/o failure for last 1 year.
Relative Light output
[rms/mean]

14. Data-Taking & Data Set
Data-taking efficiency
Data taking began on Aug. 1, 2011 with both near and far detectors.
Data-taking efficiency > 90%.
Trigger rate at the threshold energy of 0.5~0.6 MeV : 80 Hz
Data-taking period : 229 days Aug. 11, 2011 ~ Mar. 26, 2012
2 MeV
6 MeV
40K
10 MeV
208Tl
n capture by Gd
Event rate before reduction
A candidate for a neutron capture by Gd

15. Spectra w/ sources after NPE adjustment
Near Detector
Far Detector
Cs 137
(662 keV)
Ge 68
(1,022 keV)
Co 60
(2,506 keV)
Cf 252
(2.2/7.8 MeV)

16. Energy Calibration w/ source
Near Detector
Far Detector Cf Cf Co Co Cf Cf Ge Ge Cs Cs
~ 250 pe/MeV (sources at center)
Identical energy response (< 0.1%) of ND & FD
Slight non-linearity observed.
“Prompt” energy is calibrated with gamma sources.
Slight difference between (e+ kinetic energy) and (Prompt energy-1.02 MeV) is expected.

18. Long-term Stabilities
Near Detector
Far Detector
Capture Time
Cosmic muon induced neutron’s capture by H
Near Detector
Far Detector
n capture signals (capture on Gd)

19. Cuts for n Events
Reject flashers and external gamma rays : Qmax/Qtot < 0.03
Muon veto cuts : reject events after the following muons
1 ms DEAD time for
E(ID) > 70 MeV
20MeV < E(ID) < 70 MeV & NPMT (OD) > 50
10 ms DEAD time for E(ID) > 1.5 GeV
Coincidence :
Eprompt : 0.7 ~ 12.0 MeV, Edelayed : 6.0 ~ 12.0 MeV
coincidence : 2 ms < Dte+n < 100 ms
Multiplicity cut : reject pairs if there is an any trigger in the preceding ms window.

20. Spectra & capture time of neutrons
Near Detector
Far Detector
Observed spectra of Gd+n capture signal
155Gd
(18.5%)
157Gd
(81.5%)
t = 27.8 ± 0.2 msec
Near Detector
t = 27.6 ± 0.4 msec
Far Detector

21. Backgrounds II – 9Li/8Be
Find prompt-delay pairs after muons, and obtain their time interval distribution with respect to the preceding muon.
Time interval (ms)
9Li time interval distribution
Energy (MeV)
9Li energy spectrum
Near detector :
Far detector :

22. We have tried to extend to lower energy muons, but limited by high rates.
NEAR
FAR
We have extrapolated higher energy data to lower threshold data.
NEAR
FAR

23. Backgrounds III – fast neutrons
Obtain a flat spectrum of fast neutron’s scattering with proton, above that of the prompt signal.
Near detector
Far detector
Near detector :
Far detector :

24. Summary of Final Counts

25. Prompt energy spectra of neutrinos
Near Detector
(BG: 2.7%)
Far Detector
17102 (BG: 5.5%)
Prompt energy spectra shows enhanced rates in 4-6 MeV considering expected neutrino spectra.
Detector response functions are not studied in detail yet.
More calibration work is underway.

26. n Flux estimation Supplied by power plant Daily thermal power
Last Fuel Exchange period
Fission fractions

27. Estimation of n event rates

28. Observed Daily Averaged n Rate

29. Efficiency & Systematic Uncertainties

30. Reactor Antineutrino Disappearance
Clear deficit in rates , consistent with neutrino oscillation with the energy spectra.
E>6 MeV distortion is not understood yet.

31. Results of q13 4.9s significant signal Near detector: 1.2% reduction
Far detector: 8.0% reduction

32. Effect of uncertainty of
For absolute uncertainty of theta13, we have to consider the uncertainty of
Fogli et al., arXiv:

33. Global Picture Exclusion of non-zero 13 A consistent picture
(2010)
2011.6
2012.6
2011.7
2012.6
2012.6
2012.3
(7.7)
2012.4
by S. Jetter
Shown by Jun ICHEP2012

34. Future Efforts for q13 at RENO
Contributions of the systematic errors :
- Background uncertainties :
(far : 5.5%×17.7% = 0.97%, near : 2.7%×27.3% = 0.74%)
- Reactor uncertainty (0.9%) :
- Detection efficiency uncertainty (0.2%) :
- Absolute normalization uncertainty (2.5%) :
Reduce the amound of backgrounds !
Do spectral shape analysis !
More precise calibrations needed.
MC (vertex reconstructions) tuning.
Reactor cycle dependent flux should be included.

35. Summary RENO observed a clear disappearance of reactor antineutrinos.
RENO measured mixing angle q13 unambiguously that was the most elusive puzzle of neutrino oscillations.
Need more detail studies needed to fit L/E analysis.

36. Perspectives A large value of q13 :
Three reactor measurement will strongly promote the next round of neutrino experiments to find the CP phase.
Opens a possibility that mass hierarchy w/o matter effect or CP phase be measured in reactor experiment.
Mass Hierarchy with reactor 50 km

37. Short baseline Reactor Experiment
30MW research Reactor, Small Core size ~ 20x40x60cm
Baseline 6m
50L prototype detector – background study.
500L Main Detector
Location

38. Thank you !

39. Electronics & Trigger Software trigger
QBEE : each channel digitized if over threshold.
All the hits are sorted in time and grouped into an event if number of hits exceeds preset trigger condition. (ID:90, OD:10)
Pedestal hits are collected realtime
Intrinsic charge Injector into each channel for electronics calibration.
Types of Trigger : ID OD
LASER
PEDESTAL
Charge Injector
Data block(20ms)
Software trigger
200ns
“Software”
event
Merge the data
From front-end PCs
Number of hits exceeds the threshold,
Send downstream

40. Trigger Rates NEAR FAR Depth (mwe) 120 450
Distance from Reactor baseline(m)
294
1383
Flux weighted distance (m)
408.56
Muon Rate (Simulation)( /m2 sec)#
5.5
0.85
Average Muon energy (GeV)#
34.3
65.2
Inner Detector (Hz) (NPMT >90)*
~280
~110
Outer Detector (Hz) (NPMT >10)*
~533
~66
* NPMT is counted within 50nsec.
# Simulated for Near (70m), Far(200m) depths.

41. Backgrounds I - Accidentals
Calculation of accidental coincidence
DT = 100 ms time window
Near detector :
Rprompt = 8.8 Hz, Ndelay = 4884/day →
Far detector :
Rprompt = 10.6 Hz, Ndelay = 643/day →

42. c2 Pull Analysis for Rate Only data