Diapositiva 1

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UHE photons and neutrinos at the Pierre Auger
Observatory Enrique Zas Departamento de Física
de Partículas Instituto Galego de Física de
Altas Enerxías, Universidade de Santiago de
Compostela, SPAIN

• Enrique Zas
• Departamento de Física de Partículas
• Instituto Galego de Física de Altas Enerxías
• Universidad de Santiago de Compostela
• for the Pierre Auger Collaboration

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A Hybrid detector
Two techniques Fluorescence (FD) Particle
detector array (SD) Redundant 10 of events are
observed with both wealth of information about
shower development exploit SD
Fluorescence light
FD
SD
E. Zas
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SD Units
Calibrated online regularly using signals induced
by atmospheric muons
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Rich SD data Useful observables which can be
correlated with hybrid data

• At detector level
• Signal Number of particles
• Start time timing
• Rise time Sperad of particle arrival
• Area over Peak low for single muons
• Structure jumps -gt muon counting ....
• At shower level
• Shower size
• Direction
• Xmax (FD)
• Curvature of particle front

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Slow broad signal produced by EM component
Signal (VEM)
Time (ns)
Fast narrow signal produced by muonic
component
Signal (VEM)
25 ns time resolution allows distinction between
broad and narrow signals
Time (ns)
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Xmax and curvature are related
Xmax
Larger Xmax gt larger curvature (smaller radius)
L C, RAV, AAW, EZ (Ap Phys 2004)
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Apparent for ms in hadronic showers
(ns)
200 150 100 50 0
400 300 200 100 0
Time delay of first muon (curvature) average
600
700
Distance to core
120 80 40 0
80 60 40 20 0
870
800
1000 m
1000 m
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Risetime also related to Xmax
muons travel in straight lines em component
straggles

• Two main reasons
• 1. Z range (production)
• 2. m less delayed than e g Deep showers have
  more em component

Risetime
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Photon Search
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Basis Xmax discrimination
P. Homola for the Auger Collab., ICRC 2009
g-induced showers reach maximum deeper in the
atmosphere than nucleonic ones
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Use Surface Detector data
Astroparticle Physics 29 (2008) 243-256

• Two discriminating observables
• Radius of curvature of shower front
• Time structure of shower front (Risetime)
• (both correlated to Xmax)

50 of integrated signal
Rise time is the time it takes to go from 10 to
50 of the total signal
Signal (VEM)
Time (ns)
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Surface Detector
Principal component analysis
Cut Median of distribution
Deviation of Curvature w.r.t. to mean s units
MC photons
Data
5 Data
Cut
MC photons
Deviation of Risetime w.r.t. to mean s units
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Direct Xmax search Hybrid
Astroparticle Physics 27 (2007) 155 arXiv
0903.1127v2

• Quality cuts
• More than 6 PMTs
• Shower axis distance to highest signal SD station
  lt1.5 km
• Reduced c2 (profile fit) lt6 and ratio to c2 (line
  fit) lt0.9
• Xmax within field of view
• Fiducial volume cuts avoid biasses
• Zenithgt 350 g1(E) 357 _at_ 1019.7
• Distance to telescope lt 24 km g2(E)
• Viewing to shower axis angle gt150 (Cherenkov
  rejection)
• Egt2, 3, 5 and 10 EeV

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• Full simulations made (Corsika, QGSJET01, FLUKA)
  
• Fotons
• Protons
• Iron

Hybrid
Quality cuts
Fiducial volume cuts
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Hybrid search g candidates
E cand p(Fe)
2 EeV 8 30 (0.3)
3 1 12 (0.2)
5 0 4 (0.1)
10 0 1 (0)
Uncertainties s(Xmax) 16 g cm-2 s(E)/E 22
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Deepest event observed
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Limits on g fractions SD Hybrid
P. Homola for the Auger Collab., ICRC 2009
A1, A2 AGASA HP Haverah Park Y Yakutsk
g fraction constrained in Energy - range 2 EeV ?
40 EeV
Strong constraints on Super-Heavy DM
Topological Defect models
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Neutrino Search
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Cosmogenic ns
Cosmic rays at ultra high energy
(neutrino?) V.S. Berezinsky, G.T.
Zatsepin Academy of Sciences of the USSR,
Physical Institute, Moscow, Russia Physics
Letters B Vol. 28, Issue 6, pp. 423-424
(1969) Received 8 November 1968 Published 6
January 1969 Abstract The neutrino spectrum
produced by protons on microwave photons is
calculated. A spectrum of extensive air shower
primaries can have no cut-off at an energy Egt3
1019 eV, if the neutrino-nucleon total
cross-section rises up to the geometrical one of
a nucleon.
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Selected developments in neutrino search with
EAS

• 1969 Inclined showers for neutrino detection
  Berezinsky, Zatsepin
• 1987 n bound with Flys Eye Flys Eye
• 1991-97 n bounds with Tokyo data Halzen, EZ, ...
• 1996 Auger UHE n possibilities shown Capelle,
  Cronin, Parente, EZ
• 1999 Earth skimming nt effect Fargion /
  Lettessier-Selvon Bertou, Billoir
• 2007 First earth skimming experimental bound
  Auger / HiRes

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Inclined showers Protons, nuclei, g Shower gs
es and e-s do not reach ground level Only
muons
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Inclined hadron Air Showers
g
ee-
m
0 2000 4000 6000
8000 10000 12000
Depth (g/cm2)
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Case 1 down-going n
n
Air shower
Detection (deep)gtinclined
Earth
Case 2 Earth-skimming nt
Air shower
nt
t
Upgoing detectiongtinclined)
Earth

• Complex three stage process
• Attenuation through Earth and regeneration NC
• 
  CC t CC
• 
  CC t decay
• CC interaction, t energy loss and no decay
• Exit and t decay in the atmosphere

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Earth skimming nt
Auger results PRL 100 (2008) 211101 Jan 04- Aug
07 PRD 79 (2009) 102001 Jan 04- Apr 08
Low t loss gt large target volume Large density
Earths crust Only sensitivity to nt CC
channel Small zenith angle range (50) (solid
angle)
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Down-going n
Low density target Zenith angle range
750(600?)-900 All channels and flavors. Relative
contributions

• Shower
• EM Hadronic
• Hadronic
• Hadronic
• t decay
• Hadronic
• EM
• NO shower
• t decay

Energy Transfer 100 25 25 40 100 25 50
s x flv 3 x 2 1 x 6 3 x 4 3 x 2 6 x 1 1 x 1 1
x 1 1 x 1

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Searching for n in data general criteria
D. Gora for the Auger Collab., ICRC 2009
(1) Search for Inclined Showers

• Footprint of the shower on ground compatible with
  that of an inclined shower
• Elongated pattern (large Length over Width).
• Speed of propagation of signal along Length,
  close to speed of light.
• Angular reconstruction.

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(2) Search for showers with large electromg
component
Inclined proton/nuclei showers induced high in
the atmosphere (mainly) of muons at ground.
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• Selection for earth skimming neutrinos
• Trace cleaning (remove random muons)
• Inclined
• signal pattern length/widthgt5 (elongated)
• 0.31 m/ns gt ground speed gt 0.29 m/ns (horizontal)
• r.m.s. (ground speed) lt 0.08 m/ns (compatible)
• Electromagnetic
• gt60 of stations satisfy Offline ToT (Time over
  threshod 13 bins above 0.2 VEM)
• Signal over peakgt1.4
• Central trigger condition only to Off Tot
  stations
• Quality trigger (T5)

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• Selection for down going neutrinos
• Only events of 4 or more stations
• Trace cleaning (remove random muons)
• Inclined
• signal pattern length/widthgt3 (elongated)
• 0.313 m/ns gt ground speed gt 0.29 m/ns
  (horizontal)
• r.m.s. (ground speed) lt 0.08 m/ns (compatible)
• Zenith reconstructed lt 750
• Electromagnetic
• Fisher discriminant analysis on ten variables
  (related)

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• Acceptance (Monte Carlo)
• Earth skimming
• Earth conversion of nt to t
• t decay in the atmosphere
• extensive air shower
• Trigger and identification efficiency (Et,
  h10km)
• detector exposure (integration over running
  array)

• Down-going
• Atmospheric interactions

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Down-going neutrino channels
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Fisher discriminant analysis

• Maximise discrimination power using multivariate
  analysis (Fisher discriminant).
• Very simple idea
• Find projection line for maximal hadrons n
  separation

F is a linear combination
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Fisher discriminant analysis
F is the linear combination of discriminating
variables used maximising the ratio
mean of F for HAS and neutrinos maximally
SEPARATED relative to
Variance of F for HAS
Variance of F for neutrinos
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Variables for Fisher method
Exploit that neutrino showers have (1) Broad
signals in the early part (2) Asymmetry in time
spread of signals between early and late parts.
Useful variable AOP integrated signal over
peak signal
Broad signal Large AOP
Narrow signal Small AOP
Signal (VEM)
Training data 01Jan04-31Oct07 (black) and Nu
showers (red)
Area Over Peak of the first T2 tank
AOP Product of the first four T2 tanks
Time (ns)
Time (ns)
Ten discriminating variables First 4 AOPs First
4 (AOPs)2. Product of the first 4 AOPs. An
asymmetry parameter Meanearly AOP - Meanlate
AOP.
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Asymmetry in time spread
Neutrinos interacting deep in the atmosphere
Early region
Late region
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Spread in time of the FADC trace of each station
in an event
Real inclined event
Simulated down-going neutrino
Each dot represents a station in the event
early (broad signals)
Spread in time of the signal ns
Spread in time of the signal ns
late (narrow signals)
early
late
(µs)
(µs)
Attenuation of the EM component of the shower
from the earliest to the latest station
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Example distributions
Inclined real events (black) Simulated nu showers
(red)
AOP of the 1st tank in the event
early late asymmetry parameter of the event
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Blind search for neutrinos

• Data from 01 Jan 04 to 31 Oct 07 used to train
  Fisher method
• Select the best discriminating observables.
• Set cuts in Fisher variable above which an event
  is a n candidate.

Data from 01Nov07 to 28Feb09 to do a blind
search for neutrinos
No neutrino candidates in the search period
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Flux limits for a E-2 neutrino spectrum
AUGER limits Down 01Nov07- 28Feb09 Up 01Jan04-28Feb09
K GeV cm-2 s-1 sr-1 3.2 x 10-7 4.7 x 10-8
J. Tiffenberg for the Auger Collab., ICRC 2009