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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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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

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


T2k experiment

T2K Experiment

40-50 GeV protons create off-axis

nm beam

Super-K

Tokai

Kamioka

JPARC


Neutrino flux at super k

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)


Signal and backgrounds

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 eventse-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...


    Reconstructing n m energy

    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)


    N e appearance background

    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


    N e signal vs background after p 0 fitter

    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)


    N e signal for varied q 13 values

    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)


    Systematic uncertainties

    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


    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.


    Global oscillation fit

    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)


    Example global oscillation fit

    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


    Conclusions

    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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