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Analysis and Background Aspects in Large Water Cerenkov Detectors

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

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Analysis and Background Aspects in Large Water Cerenkov Detectors

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  1. Analysis and Background Aspects in Large Water Cerenkov Detectors Jessica Dunmore UC, Irvine NNN05, Aussois 8 April 2005

  2. Outline • 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

  3. T2K Experiment 40-50 GeV protons create off-axis nm beam Super-K Tokai Kamioka JPARC

  4. Neutrino flux at Super-K (2.5° off-axis beam from 0.75 MW, 40 GeV protons, assumes 5 years x 1021 POT) n Flux / cm2 / 5 years / 50 MeV bin Unoscillated nm flux Dm2=0.0025 Oscillated nm flux (sin22q23=1.0) Oscillated ne flux (sin22q13=0.1) n Energy (GeV)

  5. Signal and Backgrounds • From off-axis nm beam at Super-K Appearance Experiment Disappearance Experiment Selection: Fully contained, Fully contained, single-ring, single-ring, m-like events e-like (showering) no decay electron Signal: Backgrounds: CCQE: nm + n  p + m- nm ne+ n  p + e- CC singlep: nm + N  N’ + m- + p NC: n + N  N’ + n+ p0 Beam ne Misidentified muons CC multip’s: nm + N  N’ + m- + p… • CC/NC coherent p production: • nm + 16O m- + 16O + p+ • nm + 16O nm + 16O + po NC: n + N  N’ + n+ p...

  6. Reconstructing nm Energy For T2K disappearance True  Reconstructed Transfer Matrices True Neutrino Energy Reconstructed nm Energy Reconstructed Energy (GeV) (1.0,0.0025) (1.0,0.0025) CC QE Interaction spectrum = Flux x Cross section x Efficiency True nm Energy (GeV) Reconstructed Energy (GeV) CC other NC CC 1p y-axis: Events / 5 years / 22.5 kton / 50 MeV bin NC 1p0 Reconstructed nm Energy (GeV) nm Energy (GeV) True nm Energy (GeV)

  7. ne Appearance Background g2 g1 Standard fitter 500MeV/c p0 true Pg2 = 55.5MeV/c rec.Mp0 =140.4MeV/c2 • The p0 fitter (POLfit) finds a second ring by testing: Likelihood(2g) vs. Likelihood(1e) Then fits direction and energy fraction of 2nd ring • Largest background is from NC p0 production Plot from S. Mine

  8. ne signal vs. background after p0 fitter (For Dm2=0.0025 sin22q23=1.0 q13=9°) Background estimates by M. Fechner Before p0 fitter: NC background ~ 40 events After p0 fitter: NC background ~ 10 events Events / 5 years / 22.5 kton / 50 MeV bin Reconstructed ne Energy (GeV) Reconstructed ne Energy (GeV)

  9. ne signal for varied q13 values Events / 5 years / 22.5 kton / 50 MeV bin Reconstructed ne Energy (GeV) (For Dm2=0.0025 sin22q23=1.0) q13=6° q13=3° q13=9° (sin22q13=0.10) (sin22q13=0.04) (sin22q13=0.01)

  10. Systematic uncertainties  • Precision measurement of q23 and Dm223 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 ne

  11. 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.

  12. Global 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)

  13. Example global oscillation fit Dm2=0.0025 sin22q23=0.95 q13=0° “Data” Prediction Best fit Prediction + Systematics Fit Dm2 Uncertainty: ~2% on Dm223 ~1.2% on sin22q23 Preliminary example: no inclusion of 280m detector. Fit sin22q23

  14. Conclusions • 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

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