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The Pierre Auger Observatory (II): Inclined Showers and neutrino limits

The Pierre Auger Observatory (II): Inclined Showers and neutrino limits. R.A. Vázquez, University of Santiago, Spain for the Pierre Auger Collaboration. Santiago, 3rd June. Introduction. Inclined showers are made basically by muons Due to the magnetic field the ground profile is deformed

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The Pierre Auger Observatory (II): Inclined Showers and neutrino limits

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  1. The Pierre Auger Observatory (II):Inclined Showers and neutrino limits R.A. Vázquez, University of Santiago, Spain for the Pierre Auger Collaboration Santiago, 3rd June

  2. Introduction Inclined showers are made basically by muons Due to the magnetic field the ground profile is deformed and the cylindrical symmetry is lost Inclined events can give information on the hadronic processes and composition at high energies They give an increased aperture of ~30 % They are the background for neutrino detection

  3. Vertical showers: h ~ 10 km E ~ 1-10 GeV X ~ 1000 gr/cm2 E.M. and Muons Inclined Showers: h ~ 100 km E ~ 100 GeV X ~ 30000 gr/cm2 Only muons survive (plus an E.M. halo) Atmosphere Earth

  4. Longitudinal development of showers Dashed lines: E.M. component Full lines: Muons

  5. Correlation E versus r Average muon energy as a function of the distance to the shower axis Very high energetic muons!

  6. Total number of muons as a function of Primary Energy scales as Eγwith γ~ 0.94 Production Distance to the ground

  7. Muon maps • Shape is ~ composition • independent • Normalization is • - Hadronic model dependent • - Composition dependet 60 degrees 80 degrees 88 degrees Perpendicular Plane

  8. 53 Triggered Stations

  9. 63 Triggered Stations

  10. Selection T3 triggers Compacity/time consistency T4 T5Has* Station nearest to the core surrounded by 6 active stations *Slightly different from T5 vertical Data selection from 1/2004 to 12/2008 Aperture ~30% of the vertical ~0.29* 12790 km2 s sr Over 80000 T5Has inclined events with 60 < Θ < 80 deg

  11. Reconstruction Angular reconstruction: shower front is fitted using the start time Angular resolution of order of 1 deg. • Energy reconstruction: • Electromagnetic component is subtracted • Muon Maps and the Tank response is used to calculate the Maximum Likelihood • A “Muon Shower size” is estimated : N19 • Hybrid events provide the absolute energy correlation between N19 and the Shower Energy The whole procedure was implemented in two independent reconstruction programs A and B.

  12. Reconstruction The electromagnetic signal is subtracted from the total Signal by using a parameterization EM Signal Fraction

  13. Ratio of tracklength Dependence on Energy Zenith angle Tank response:

  14. Energy Calibration is done using high quality hybrid events Fluorescence Detector (FD) cuts Cherenkov fraction < 50 % Largest signal tank < 750 m from core Uncertainty on the reconstructed energy < 40% Chi2/ndof <4 for Gaisser Hillas fit Chi2 of the linear fit must exceed 4 the Gaisser Hillas fit. Surface Detector (SD) cuts 60 < Θ< 80 deg. T5Has Uncertainty on the reconstructed Energy < 40 %

  15. Elliptical cut Calibration fit 145 events log(N19)= a + b log(E) a = -0.72 +/- 0.02 b= 0.94 +/- 0.02 a b The number of muons measured is larger by a factor of ~ 2 than model predictions for proton Reconstruction A

  16. Statistical < 20% Zenith angle < 6% Shower fluctuations ~ 18% Systematic ~ 5% Uncertainty ESD Uncertainty ESD

  17. Uncertainty on the energy Reconstruction Compatible with estimated uncertainties Comparison ESD - EFD

  18. Systematic uncertainty due to different reconstruction algorithms Relative energy difference between reconstruction A and reconstruction B Mean ~ 0.01 RMS ~ 0.07

  19. Constant Intensity cut Array Is fully efficient Above N19 > 1 E > 6.3 EeV

  20. Black: Inclined A Blue: Raw Vertical Red: Inclined B Suppression observed in the Inclined spectrum

  21. Example Event Θ~ 48º, ~ 70 EeV Neutrino search in the Pierre Auger observatory Typical flash ADC trace Detector signal (VEM) vs time (ns) Lateral density distribution PMT 1 PMT 2 PMT 3 Flash ADC traces Flash ADC traces

  22. Flash ADC Trace for detector late in the shower Lateral density distribution PMT 1 PMT 2 PMT 3 Flash ADC traces Surface Detector Event Θ~ 60º, ~ 86 EeV

  23. a real vertical event (20 deg) SD search Noise ! doublet

  24. a real horizontal event (80 deg) “single” peaks : fast rise + exp. light decay (t ~ 70 ns) accidental background signals are similar

  25. Simulated t • p+ (5.1) p0(16.1)n • 1800 m above ground

  26. Downgoing showers EM signal in shower plane [VEM] Xinjection ρ, ε→ Sμ,EM 3035 g/cm2 3167 g/cm2 3306 g/cm2 3438 g/cm2 3570 g/cm2 y shower plane [m] 3703 g/cm2 3968 g/cm2 4100 g/cm2 4238 g/cm2 4371 g/cm2 4503 g/cm2 4636 g/cm2 4768 g/cm2 Proton 1 EeV θ = 80 deg 4901 g/cm2 x shower plane [m] J. Alvarez-Muniz

  27. Risetime/Falltime S [VEM] 10% 50% 90% • Risetime is defined as the time from 10% - 50% of the integrated pulse. • Falltime time from 50% - 90%

  28. Falltime vs Risetime (2 cuts) S ≥ 15 VEM & r ≥500 m Neutrino candidates should have θ≥ 70deg and should show up here. θ≤ 45 deg. θ≥ 70 deg. No events up to now!

  29. footprint analysis • Variables defined from the footprint • (in any configuration, even aligned) • lengthL and width W • (major and minor axis of the ellipsoid of inertia) • “speed” for each pair of stations • (distance/difference of time) tj ti dij major axis

  30. candidate selection 2. Discriminating variables Search for long shaped configurations, compatible with a front moving horizontally at speed c, well contained inside the array (background: vertical or inclined showers, d/Dt > c ) cuts: L/W > 5 0.29 < av. Speed < 0.31 r.m.s. < 0.08 no real event survived…

  31. Limits on neutrino fluxes

  32. Summary Inclined events are detected and analyzed in a regular basis in Auger They provide an increase on the aperture They could give a hint on the mass/hadronic model The Pierre Auger observatory could be used as a neutrino detector

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