analysis and background aspects in large water cerenkov detectors
DESCRIPTION
Analysis and Background Aspects in Large Water Cerenkov Detectors. Jessica Dunmore UC, Irvine NNN05, Aussois 8 April 2005. Outline. T2K signal and background rates Water Č erenkov response model Cross-sections and efficiencies Neutrino energy reconstruction Background rejection - PowerPoint PPT PresentationTRANSCRIPT
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Analysis and Background Analysis and Background Aspects in Large Water Aspects in Large Water
Cerenkov DetectorsCerenkov Detectors
Jessica DunmoreJessica DunmoreUC, IrvineUC, Irvine
NNN05, AussoisNNN05, Aussois8 April 20058 April 2005
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OutlineOutline• T2K signal and background
rates
• Water Čerenkov response model– Cross-sections and efficiencies– Neutrino energy reconstruction– Background rejection
• Systematic uncertainties– Near detector(s)– Fast global fit technique
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T2K ExperimentT2K Experiment
Super-KSuper-K
Kamioka
Tokai
JPARCJPARC
40-50 GeV protons create off-axis beam
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Neutrino flux at Super-KNeutrino flux at Super-K
Unoscillated flux
Oscillated flux (sin2223=1.0)
Oscillated e flux (sin2213=0.1)
Energy (GeV)
(2.5° off-axis beam from 0.75 MW, 40 GeV protons,assumes 5 years x 1021 POT)
m2=0.0025
Fl
ux /
cm
2 /
5 y
ears
/ 5
0 M
eV
bin
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CC/NC coherent production: + + 1616O O -- + + 1616O + O +
+ + 1616O O + + 1616O + O + oo
Selection:Selection: Fully contained, Fully contained, single-ring, single-ring,
-like events e-like (showering) no decay electron
Signal:Signal:
Backgrounds:Backgrounds:
Signal and BackgroundsSignal and Backgrounds• From off-axis beam at Super-
KAppearance Appearance ExperimentExperiment
DisappearancDisappearance Experimente Experiment
CCQE: + n + n p + p + -- ee + n + n p + p + ee--
CC single + N + N N’ + N’ + - - + + NC: + N + N N’ + N’ + + +
CC multi’s + N + N N’ + N’ + - - + + ……Beam e
Misidentified muonsNC: + N + N N’ + N’ + + + ...
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Reconstructing Reconstructing Energy EnergyFor T2K disappearance
True Neutrino EnergyTrue Neutrino Energy Reconstructed Reconstructed Energy Energy
Energy (GeV) Reconstructed Energy (GeV)
NCNCCC otherCC other
(1.0,0.0025)
(1.0,0.0025)
NC NC 1100
y-axis: Events / 5 years / 22.5 kton / 50 MeV bin
True True Reconstructed Reconstructed
Transfer MatricesTransfer MatricesCC QECC QE
CC 1CC 1
True Energy (GeV)
True Energy (GeV)
Reco
nst
ruct
ed E
nerg
y
(GeV
)R
eco
nst
ruct
ed E
nerg
y
(GeV
)
Interaction spectrum = Flux x Cross section x Efficiency
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ee Appearance Background Appearance Background
• The 0 fitter (POLfit) finds a second ring by testing:Likelihood(2) vs. Likelihood(1e)
Then fits direction and energy fraction of 2nd ring
500MeV/c 0
true P2 = 55.5MeV/crec.M0 =140.4MeV/c2
12
Standardfitter
Plot fromS. Mine
• Largest background is from NC 0 production
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ee signal vs. background after signal vs. background after 00 fitterfitter
Reconstructed e Energy (GeV)Reconstructed e Energy (GeV)
Events
/ 5
years
/ 2
2.5
kto
n /
50
MeV
bin
(For m2=0.0025 sin2223=1.0 13=9°)
Before 0 fitter:NC background ~ 40 events
After 0 fitter:NC background ~ 10 events
Background estimates by M. Fechner
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Reconstructed e Energy (GeV)
Events
/ 5
years
/ 2
2.5
kto
n /
50
MeV
bin
ee signal for varied signal for varied 1313 values values(For m2=0.0025 sin2223=1.0)
13=9°13=6°13=3° (sin2213=0.10)(sin2213=0.04)(sin2213=0.01)
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Systematic uncertaintiesSystematic uncertainties• Precision measurement
of 23 and m223 and
appearance background subtraction require careful control of systematic uncertainties.– Čerenkov detector
reconstruction:• Energy scale (~3%)• Fiducial volume
(~3%)
– Cross sections• CCQE (~10-20%)• Other (~20-50%)
– Flux normalization and shape
• Hadron production model
• Beam geometry
• Beam e
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Near Detector(s)Near Detector(s)• Systematics may be controlled
by using one or more near detectors.
• Fine-grained detector placed near the target.– Ability to measure relative amounts
of CCQE and nonQE interactions
• Water Cerenkov 2km away from target.– Flux shape matches that at far
detector.– Close to identical response at both
near and far detectors.
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Global oscillation fitGlobal oscillation fit• A fit has been developed to
determine oscillation parameters with the following capabilities:– varying systematic effects– inclusion of near and far detectors– inclusion of both signal and
background – parameterized detector response
(cross-sections, efficiency, reconstruction)A similar approach has been used in the
Super-K atmospheric neutrino oscillation analysis.
References:Y. Ashie et al., Phys.Rev.Lett.93, 101801 (2004)
G. Fogli, et al., Phys. Rev D66, 053010 (2002)Para and Szleper (hep-ex/0110001)
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Example global oscillation fitExample global oscillation fitm2=0.0025 sin2223=0.95 13=0°
“Data”Prediction
Best fit Prediction + Systematics
Fit m2
Fit sin2223
Uncertainty: ~2% on m2
23
~1.2% on sin2223
Preliminary example: no inclusion of 280m detector.
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ConclusionsConclusions• Global fit of oscillation
parameters including systematics, near detectors, and backgrounds is a work in progress.
• Current goals are– Perform sensitivity analysis for
oscillation parameters using different detector configurations.
– Determine effect of systematic uncertainties on T2K sensitivity.
• Method is not limited to Water Cerenkov detectors or to T2K-I experiment