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    05-Feb-2016
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Main Slides. Signal region. Isotropic region. Low angle events. p. n e. N. 42 o. n. e +. 25-45 o. μ , π. n. reconstructed angle near 90 o. n (invisible). MC (decay electron channel not shown). SK-I/III combined final data sample. signal region. isotropic region (NC elastic). - PowerPoint PPT Presentation

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  • Main Slides

  • SK-I/III combined final data sampleCherenkov angle distribution degreese CC/ NC elasticlow region(/)isotropic region(NC elastic)signal regionMC (decay electron channel not shown)low region(/)signal regionisotropic region(NC elastic)nee+pn (invisible)Signal region42o, Low angle events25-45oIsotropic regionnNnreconstructedangle near 90o

  • 20-38 degrees38-50 degrees78-90 degreesE (MeV)SK-I/IIIdata CCe CCNC elastic/ > C. thr.all backgroundrelic

  • Combined Fitcombined 90% c.l.: < 5.1 ev / yr / 22.5 ktons interacting < 2.7 /cm2/s (>16 MeV) < 1.9 /cm2/s (scaled to >18 MeV)combined90% c.l.ev/yr interacting in 22.5 ktonslogLikelihoodSK-I/II/IIIcombinedlikelihood

    Comparison to Published/cm2/s >18 MeVPublished limit1.2cross section update to Strumia-Vissani1.2 1.4Gaussian statistics Poissonian statistics in fit1.4 1.9New SK-I Analysis:ETHRESH 18 16 MeV = 52% 78 %(small statistical correlation in samples)improved fitting method takes into account NC1.91.6New SK-I/II/III combined fit1.6 1.9

  • Secondary Slides

  • Final Backgrounds (after all relic cuts)E (MeV)These 3 can be modeled as a combination of other backgrounds, and thus arent considered separatelyCC Backgroundsinvisible decay ee CC > C. threshold

    / CCe CC/NC elastic

  • Combined Fitcombined 90% c.l.: = 5.1 ev / yr / 22.5 ktons interacting = 2.7 /cm2/s (>16 MeV) = 1.9 /cm2/s (scaled to >18 MeV)combined90% c.l.ev/yr interacting in 22.5 ktonslogLikelihoodSK-I/II/IIIcombinedlikelihoodSK-I (~1500 days)SK-II (~790 days)SK-III (~550 days)combined

  • COMPARISON TO PUBLISHED LIMIT/cm2/s >18 MeVPublished limit1.2cross section update to Strumia-Vissani1.2 1.4Gaussian statistics Poissonian statistics in fit1.4 1.9New SK-I Analysis:ETHRESH 18 16 MeV = 52% 78 %(small statistical correlation in samples)improved fitting method takes into account NC1.91.6New SK-I/II/III combined fit1.6 1.9

  • SK-Ibest fit is negativefit shown is 0 relic contribution20-38 degrees38-50 degrees78-90 degreesE (MeV)SK-Idata CCe CCNC elastic/ > C. thr.all backgroundrelicSK-I only 90% c.l. limit:< 2.4 /cm2/s (>16 MeV)< 1.6 /cm2/s (scaled to >18 MeV)

  • SK-IIBest fit (shown):3.5 ev/yr interacting20-38 degrees38-50 degrees78-90 degreesE (MeV)SK-II only 90% c.l. limit:< 7.4 /cm2/s (>16 MeV)< 5.2 /cm2/s (scaled to >18 MeV)

    data CCe CCNC elastic/ > C. thr.all backgroundrelic

  • SK-IIIBest fit (shown) :6.5 ev/yr interacting20-38 degrees38-50 degrees78-90 degreesE (MeV)SK-III only 90% c.l. limit:< 8.1 /cm2/s (>16 MeV)< 5.7 /cm2/s (scaled to >18 MeV)

    data CCe CCNC elastic/ > C. thr.all backgroundrelic

  • Systematics: Inefficiency*Define:r = # relic events we see in dataR = # relic events actually occurring in detector = efficiency (SK-I/II/III dependent)assume follows a probability distribution P()assume P() is shaped like Gaussian w/ width ineffthen we alter likelihood:

    then the 90% c.l. limit R90 is such that ineffSK-I: 3.5%SK-II: 4.5% SK-III: 3.1%

  • Cuts: efficiencies and sys errors* SK-I:effwall : 98% (0.5%)C. angle: 95% (0.4%)pion like: 98% (0.2%)spall+solar: 88% (1%)2-peak, 2-ring: >99%Correlation cut: 99% (0.3%)1st reduction: 99% (2%)(includes: electronic noise cuts, 50 us cut)Total: 78 % SK-II95% (0.3%)88% (0.3%)97% (0.5%)87% (1.4%)>99%99% (0.3%)99% (2%)SK-III96% (0.3%)94% (0.3%)98% (0.5%)89% (1%)>99%99% (0.3%)99% (2%)69%77%