Post on 19-Dec-2015
UHE photons and neutrinos at the Pierre Auger Observatory
Enrique ZasDepartamento de Física de Partículas &
Instituto Galego de Física de Altas Enerxías,Universidade de Santiago de Compostela, SPAIN
Enrique ZasDepartamento de Física de Partículas
Instituto Galego de Física de Altas EnerxíasUniversidad de Santiago de Compostela
for the Pierre Auger Collaboration
A Hybrid detectorTwo techniques:
Fluorescence (FD)
Particle detector array (SD)
Redundant~ 10% of events are observed with both: wealth of information about shower development & exploit SD
SD
Fluorescence light
E. Zas
FD
Digitised signals: FADC
Time [ns]25 ns time bins
Communicationsantenna
Low consumption electronics
Solar panels
Battery box
3 photomultiplier tubes
Rotomolded plastic tank
12 tons of purified water
GPSSD Units
Calibrated online regularly using signals induced by atmospheric muons
• 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 -> muon counting ....
• At shower level– Shower size– Direction– Xmax (FD)– Curvature of particle front
Rich SD data: Useful observables which can be correlated with hybrid data
Sig
nal
(V
EM
)
Time (ns)
“Fast & narrow signal” produced by
muonic component
“Slow & broad signal”
produced by EM component
Time (ns)
25 ns time resolution allows distinction between broad and narrow signals
Sig
nal
(V
EM
)
L C, RAV, AAW, EZ (Ap Phys 2004)
Xmax and curvature are related
Xmax
Larger Xmax => larger curvature(smaller radius)
2
2
2
1
z
rzltc
Time delay of first muon (curvature) & average
400
300
200
100
0
200
150
100
50
0
120
80
40
0
80
60
40
20
0
(ns)
600 700
800 870
Apparent for s in hadronic showers
Distance to core
1000 m 1000 m
Risetime also related to Xmaxmuons travel in straight lines
em component straggles
2
2
2
2
2
1
zz
r
z
rRisetime
zTwo main reasons: 1. Z range (production)
1. 2. less delayed than e & Deep showers have more em component
Photon Search
Basis: Xmax discrimination
-induced showers reach maximum deeper in the atmosphere than nucleonic ones
P. Homola for the Auger Collab., ICRC 2009
Use Surface Detector data
Two discriminating observables
• Radius of curvature of shower front
• Time structure of shower front (Risetime)
(both correlated to Xmax)
Rise time is the time it takes to go from 10% to 50% of the total
signal
Sig
nal
(V
EM
)
Time (ns)
50% of integrated signal
Astroparticle Physics 29 (2008) 243-256
Surface Detector
Deviation of Risetime w.r.t. to mean [ units]
Dev
iati
on
of
Cu
rva
ture
w.r
.t. t
o m
ean
[
un
its]
MC photonsData
MC photons
5% Data
Cut: Median of distribution
Principal component analysis
Cut
Direct Xmax search: HybridAstroparticle Physics 27 (2007) 155 & arXiv 0903.1127v2
Quality cuts• More than 6 PMTs • Shower axis distance to highest signal SD station <1.5 km • Reduced 2 (profile fit) <6 and ratio to 2 (line fit) <0.9 • Xmax within field of view
Fiducial volume cuts avoid biasses:
• Zenith> 350 +g1(E) [35+7 @ 1019.7
• Distance to telescope < 24 km +g2(E)• Viewing to shower axis angle >150 (Cherenkov rejection) • E>2, 3, 5 and 10 EeV
Full simulations made (Corsika, QGSJET01, FLUKA): • Fotons • Protons • Iron
Quality cuts
Hybrid
Fiducial volume cuts
Hybrid search: candidates
Cut: Median of the simulated photon Xmax distribution
5% of protons simulated with QGSJET01 above this line
Uncertainties:
(Xmax) ~ 16 g cm-2
(E)/E ~ 22 %
E cand p(Fe)
2 EeV
8 30 (0.3)
3 1 12 (0.2)
5 0 4 (0.1)
10 0 1 (0)
Deepest event observed
3.8%
2.4%3.5% 2.0%
5.1%
31 %
A1, A2 = AGASA
HP = Haverah Park
Y = Yakutsk
Limits on fractions: SD & HybridP. Homola for the Auger Collab., ICRC 2009
Strong constraints on: Super-Heavy DM & Topological Defect models
fraction constrained in Energy - range2 EeV → 40 EeV
Neutrino Search
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 1968Published: 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 E>3 1019 eV, if the neutrino-nucleon total cross-section rises up to the geometrical one of a nucleon.
Cosmogenic s
• 1969 Inclined showers for neutrino detection Berezinsky, Zatsepin
• 1987 bound with Fly’s Eye Fly’s Eye
• 1991-97 bounds with Tokyo data Halzen, EZ, ...
• 1996 Auger UHE possibilities shown Capelle, Cronin, Parente, EZ
• 1999 Earth skimming effect Fargion / Lettessier-Selvon & Bertou, Billoir
• 2007 First earth skimming experimental bound Auger / HiRes
Selected developments in neutrino search with EAS:
Inclined showers Protons, nuclei, :Shower ’s e+’s and e-’s
do not reach ground level Only muons
vertical atmospheric depth
e+e-
0 2000 4000 6000 8000 10000 12000
Depth (g/cm2)
Inclined hadron Air Showers
Case 2: Earth-skimming
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
Air shower
Earth
Air shower
Earth
Case 1: down-going
Detection (deep)=>inclined
Upgoing: detection=>inclined)
“Earth skimming”
Low loss => large target volume
Large density: Earth’s crust
Only sensitivity to CC channel
Small zenith angle range (50) (solid angle)
Auger results: PRL 100 (2008) 211101 Jan 04- Aug 07PRD 79 (2009) 102001 Jan 04- Apr 08
Shower•EM + Hadronic •Hadronic •Hadronic• decay
•Hadronic•EM•NO shower• decay
Channel
•CC einteractions
•NC interactions
•CC interactions
•CC the decay
•Resonant einteract
• qq• ee
•
•
Energy Transfer100%25%25%40%
100%25%
50%
Low density targetZenith angle range 750(600?)-900
All channels and flavors. Relative contributions:
x flv3 x 21 x 63 x 43 x 2
6 x 11 x 11 x 11 x 1
“Down-going”
Searching for in data: general criteria
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.
(1) Search for Inclined Showers
D. Gora for the Auger Collab., ICRC 2009
Inclined proton/nuclei showers induced high in the atmosphere: (mainly) of muons at ground.
Neutrinos: inclined showers with broad traces
“Slow & broad signal” produced by EM component
“Fast & narrow signal” produced by muonic component
(2) Search for showers with large electromg component
Selection for earth skimming neutrinos• Trace cleaning (remove random muons) • Inclined
• signal pattern length/width>5 (elongated) • 0.31 m/ns > ground speed > 0.29 m/ns (horizontal)• r.m.s. (ground speed) < 0.08 m/ns (compatible)
• Electromagnetic• >60% of stations satisfy “Offline ToT” (Time over threshod: 13 bins
above 0.2 VEM)• Signal over peak>1.4
• Central trigger condition only to Off Tot stations• Quality trigger (T5)
Selection for down going neutrinos• Only events of 4 or more stations
• Trace cleaning (remove random muons) • Inclined
• signal pattern length/width>3 (elongated) • 0.313 m/ns > ground speed > 0.29 m/ns (horizontal)• r.m.s. (ground speed) < 0.08 m/ns (compatible)• Zenith reconstructed < 750
• Electromagnetic• Fisher discriminant analysis on ten variables (related)
Acceptance (Monte Carlo)
Earth skimming • Earth conversion of to • decay in the atmosphere • extensive air shower• Trigger and identification
efficiency (E, h10km)• detector exposure
(integration over running array)
Down-going• Atmospheric interactions
Down-going neutrino channels
F = a1·var1 +a2·var2
Maximise discrimination power using multivariate analysis (Fisher discriminant).
Very simple idea:– Find “projection line” for maximal hadrons & separation
var2
var1
Simple example in 2D
Neutrinos
HAS
Fisher discriminant analysis
F is a linear combination
)(σ(HAS)σ
FFR
2F
2F
νHAS
2)(
“mean” of F for HAS and neutrinos maximally SEPARATED relative to
Variance of F for HAS Variance of F for neutrinos
Fisher discriminant analysis
F is the linear combination of discriminating variables used maximising the ratio:
Ten discriminating variables:First 4 AOPsFirst 4 (AOPs)2. Product of the first 4 AOPs. An asymmetry parameter: “Mean[early AOP] - Mean[late AOP]”.
Variables for Fisher methodExploit that neutrino showers have: (1) Broad signals in the early part(2) Asymmetry in time spread of signals between early and late parts.
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
Useful variable: AOP = integrated signal over peak signal
Sig
nal
(V
EM
)
Broad signal Large AOP
Time (ns) Time (ns)
Narrow signal Small AOP
“Early” region “Late” region
Neutrinos interacting deep in the atmosphere
Asymmetry in time spread:
Spread in time of the FADC trace of each station in an event
Real inclined event Simulated down-going neutrino
Attenuation of the EM component of the shower from the earliest to the latest station
early
early (broad signals)
late (narrow signals) late
Each dot represents a station in the event
(μs) (μs)
Sp
read
in t
ime
of
the
sig
na
l [n
s]
Sp
read
in t
ime
of
the
sig
na
l [n
s]
Example distributions:Inclined real events (black) Simulated nu showers (red)
early – late asymmetry parameter of the event
AOP of the 1st tank in the event
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 candidate.
Data from 01Nov07 to 28Feb09 to do a blind search for neutrinos
No neutrino candidates in the search period
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
COSMOGENIC s