The Pierre Auger Observatory II Inclined Showers and
The Pierre Auger Observatory (II): Inclined Showers and neutrino limits R. A. Vázquez, University of Santiago, Spain for the Pierre Auger Collaboration Santiago, 3 rd June 1
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 2
Vertical showers: h ~ 10 km Inclined Showers: E ~ 1 -10 Ge. V h ~ 100 km X ~ 1000 gr/cm 2 E ~ 100 Ge. V E. M. and Muons X ~ 30000 gr/cm 2 Atmosphere Earth Only muons survive (plus an E. M. halo) 3
Longitudinal development of showers Dashed lines: E. M. component Full lines: Muons 4
Correlation E versus r Average muon energy as a function of the distance to the shower axis Very high energetic muons! 5
Total number of muons as a function of Primary Energy scales as Eγ with γ~ 0. 94 Production Distance to the ground 6
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Muon maps -Shape is ~ composition independent Normalization is - Hadronic model dependent - Composition dependet 60 degrees 80 degrees Perpendicular Plane 88 degrees 9
53 Triggered Stations 10
63 Triggered Stations 11
Selection T 3 triggers Compacity/time consistency T 4 T 5 Has* Station nearest to the core surrounded by 6 active stations *Slightly different from T 5 vertical Data selection from 1/2004 to 12/2008 Aperture ~30% of the vertical ~0. 29* 12790 km 2 s sr Over 80000 T 5 Has inclined events with 60 < Θ < 80 deg 12
Reconstruction Angular reconstruction: shower front is fitted using the start time Angular resolution of order of 1 deg. Energy reconstruction: 1. Electromagnetic component is subtracted 2. Muon Maps and the Tank response is used to calculate the Maximum Likelihood 3. A “Muon Shower size” is estimated : N 19 4. Hybrid events provide the absolute energy correlation between N 19 and the Shower Energy The whole procedure was implemented in two independent reconstruction programs A and B. 13
Reconstruction The electromagnetic signal is subtracted from the total Signal by using a parameterization EM Signal Fraction 14
Ratio of tracklength Dependence on Energy Zenith angle Tank response: 15
Energy Calibration is done using high quality hybrid events Surface Detector (SD) cuts Fluorescence Detector (FD) cuts Cherenkov fraction < 50 % 60 < Θ < 80 deg. Largest signal tank < 750 m from core T 5 Has Uncertainty on the reconstructed energy < 40% Chi 2/ndof <4 for Gaisser Hillas fit Uncertainty on the reconstructed Energy < 40 % Chi 2 of the linear fit must exceed 4 the Gaisser Hillas fit. 16
Elliptical cut Calibration fit 145 events log(N 19)= a + b log(E) a = -0. 72 +/- 0. 02 b= 0. 94 +/- 0. 02 a The number of muons measured is larger by a factor of ~ 2 than model predictions for proton b Reconstruction A 17
Statistical < 20% Zenith angle < 6% Shower fluctuations ~ 18% Systematic ~ 5% Uncertainty ESD 18
Uncertainty on the energy Reconstruction Compatible with estimated uncertainties Comparison ESD - EFD 19
Systematic uncertainty due to different reconstruction algorithms Relative energy difference between reconstruction A and reconstruction B Mean ~ 0. 01 RMS ~ 0. 07 20
Constant Intensity cut Array Is fully efficient Above N 19 > 1 E > 6. 3 Ee. V 21
Black: Inclined A Red: Inclined B Blue: Raw Vertical Suppression observed in the Inclined spectrum 22
Example Event Θ~ 48º, ~ 70 Ee. V 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 23
Surface Detector Event Θ~ 60º, ~ 86 Ee. V Flash ADC Trace for detector late in the shower Lateral density distribution PMT 1 PMT 2 PMT 3 Flash ADC traces 24
SD search a real vertical event (20 deg) Noise ! doublet 25
a real horizontal event (80 deg) “single” peaks : fast rise + exp. light decay (t ~ 70 ns) accidental background signals are similar 26
Simulated t p+ (5. 1) p 0(16. 1) n 1800 m above ground 27
Downgoing showers EM signal in shower plane [VEM] Xinjection ρ, ε → Sμ, EM 3035 g/cm 2 y shower plane [m] 3167 g/cm 2 3306 g/cm 2 3438 g/cm 2 3570 g/cm 2 3703 g/cm 2 3968 g/cm 2 4100 g/cm 2 4238 g/cm 2 4371 g/cm 2 4503 g/cm 2 4636 g/cm 2 4768 g/cm 2 4901 g/cm 2 Proton 1 Ee. V θ = 80 deg J. Alvarez-Muniz x shower plane [m] 28
Risetime/Falltime S [VEM] 10% 50% 90% • Risetime is defined as the time from 10% - 50% of the integrated pulse. 29 • Falltime from 50% - 90%
Falltime vs Risetime (2 cuts) S ≥ 15 VEM & r ≥ 500 m θ ≤ 45 deg. Neutrino candidates should have θ ≥ 70 deg and should show up here. θ ≥ 70 deg. No events up to now! 32
footprint analysis Variables defined from the footprint (in any configuration, even aligned) • length L and width W (major and minor axis of the ellipsoid of inertia) • “speed” for each pair of stations (distance/difference of time) ti d tj ij xis a r o j ma 33
n 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 no real event survived… r. m. s. < 0. 08 34
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Limits on neutrino fluxes 37
Summary Inclined events are detected 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 38
- Slides: 36