Search for ultra-high energy photons and
neutrinos at the Pierre Auger Observatory
Mathieu Tartare1 on behalf of the Pierre Auger Collaboration2
1
Laboratoire de Physique Subatomique et de Cosmologie (LPSC) - Grenoble, France
UMR UJF/INPG/CNRS
2
Observatorio Pierre Auger, Av. San Martı́n Norte 304, (5613) Malargüe, Argentina
Full author list: http://www.auger.org/archive/authors 2013 02.html
Context
The UHECR puzzle
If GZK cutoff : photons and neutrinos expected
Composition ?
Constraints on production models (top-down models)
Origin ?
Neutrinos point directly to sources
GZK cutoff or maximum
acceleration ?
Limits on EeV photon fraction reduce systematic in other
analyses
The Pierre Auger Observatory
Surface Detector (SD)
1600 Cherenkov water tanks with a
1.5 km spacing covering ∼ 3000 km2
61 tanks in 750 m grid (“infill” low
energies)
100 % duty cycle
Fluorescence Detector (FD)
4 sites + 1 HEAT (low energies)
6 fluorescence telescopes per site
Field of view : 30◦ × 30◦
' 14 % duty cycle
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Ultra-high energy neutrinos
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Identifying neutrinos in data
Identify neutrino showers from nucleonic showers background
Regular nucleonic showers :
Neutrinos
Interact high in the atmosphere
At ground : mainly muons, flat
shower front
May interact closer to the ground
level
At ground : EM component, curved
shower front
Discrimination power enhanced at high zenith-angle
Selection criteria : Inclined young (=deep) shower
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Identification criteria : Inclined Showers
Apparent speed along major axis L
Elongated footprint
Vertical Shower
Tij ' 0 → V c
Earth Skimming
Down Going
Elongated event : L/W ≥ 5
m
Apparent speed : 0.29 ns
−1
SD(V ) < 0.08 m.ns
Horizontal Shower
V ∼c
Elongated event : L/W ≥ 3
≤ hV i ≤
m
0.31 ns
m
Apparent speed : hV i ≤ 0.313 ns
SD(V )
V
< 8%
Rec. zenith angle θ ≥ 75◦
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Identification criteria : Inclined Showers
Apparent speed along major axis L
Elongated footprint
Horizontal Shower
V ∼c
Events
Events
Events
Vertical Shower
Tij ' 0 → V c
103
103
103
102
102
102
10
10
10
1
1
1
0
5
10
15
20
25
30
L/ W
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0.2
0.3
0.4
0.5
0.6
<V> (m ns-1)
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0
0.1
0.2
v
0.3
(m ns-1)
4
Identification criteria : Young Showers
Young/Deep Showers = Broad Signal
Signal extented in time
Time over Threshold trigger
Large Area over Peak value
Station trigger
Area over Peak
ToT station
ToT fraction > 0.6
Thr station
ToT station
ToT fraction < 0.6
Thr station
Earth Skimming
Down Going
ToT fraction
Fisher discriminant based on AoP
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Identification criteria : Young Showers
Young/Deep Showers = Broad Signal
Signal extented in time
Time over Threshold trigger
Events
Events
Large Area over Peak value
103
3
10
simulation
102
102
10
Training Data
1
0 0.2 0.4 0.6 0.8 1
ToT stations
10
1
10-1 -10
-5
0
5
10
Fisher discriminant value
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Exposure
Based on detailed dedicated Monte Carlo simulations
1017
Earth-skimming
(3.5 yr of full Auger)
Exposure [cm2 s sr]
1016
1015
Down-going
(2 yr of full Auger)
14
10
Total
CC e
CC µ
CC τ
NC x
CC τ Mountains
1013
1017
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1018
ν energy (eV)
1019
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1020
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Limits to diffuse fluxes
After unblinding : 0 candidates survive the cuts
Assuming a flux φ(E) = k × E −2
k < 3.2 × 10−8 GeV cm−2 s−1 sr−1 in 1.6 × 1017 eV< E < 2 × 1019 eV
k < 1.7 × 10−7 GeV cm−2 s−1 sr−1 in 1 × 1017 eV< E < 1 × 1020 eV
Single flavour neutrino limits (90% CL)
10-6
k=
10-7
Search sample :
Earth skimming :
Jan. 04 - May 10
10-9
10-10
-11
10
Nup
R Emax
φ(E)EdE
E
min
10-8
k = Eν2 Φ(Eν)
[ GeV cm-2 s-1 sr -1 ]
10-5
Down going :
Nov. 07 - May 10
ν limits
Auger downward-going
Auger Earth-skimming
IceCube-40 (333.5 days)
Anita-II (28.5 days)
1017
1018
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Eν [eV]
Cosmogenic models
Ahlers 2010
Kotera 2010
1019
1020
1021
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Limits to point sources
Search for point-like sources of UHEν over a broad range of declinations :
[north -65◦ , south +55◦ ]
Single flavour neutrino limits (90% CL)
Auger downward-going
[GeV cm-2 s-1]
10-6
kPS = E2ν F(Eν)
10-5
10-7
Auger Earth-skimming
-80
-60
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-40
-20
0
20
40
Source declination δ [deg]
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60
80
8
Ultra-high energy photons
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Identifying UHE photons
Fluorescence Detector
Deeper development of the air showers.
→ larger Xmax
Surface Detector
Smaller signal at a given distance & same energy
Fewer triggered stations
Sb =
X
Si
i
Ri
1000
4
→ smaller Sb
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Identifying UHE photons
Xmax (g cm-2)
FD : Deeper Xmax
1200
SD : Smaller Sb
18 < log (E /eV) < 18.5
Monte Carlo Simulations
10
photon
Photon-like events
1000
800
proton
600
-3
-2
-1
0
1
2
3
log (S )
10
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Photon selection
Data selection
Reconstruction Level :
Quality cuts :
Good geometry and longitudinal profile
Zenith angle <
60◦
Xmax within the field of view
Time periods with clouds rejected
Active station within 2 km from the
shower axis ≥ 4
Fisher analysis
3 separate energy intervals (1-3 EeV,
3-10 EeV, > 10 EeV)
Background : proton QGSJET-II-03
Event are tagged as photon candidates for
X > Xcut
Proton background . 1%
Photon selection efficiency = 50%
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Photon candidates
Using hybrid data from Jan. 2005 to Sep. 2010 :
6, 0, 0, 0 and 0 candidates above 1, 2, 3, 5 and 10 EeV
Compatible with the expected nuclear background
4
3.5
E [EeV] =1.18 ±0.09
Xmax [gcm-2] =1023 ±10
log10(Sb) =1.16 ±0.27
2/Ndf=
93.8/95
3
Xmax (g cm-2)
dE/dX [PeV/(g cm-2)]
Example of a selected candidate
1200
1100
900
1.5
800
1
700
0.5
700
800
900
1000 1100 1200 1300
slant depth [g cm-2]
selected candidate
photon-like events
1000
2.5
2
~ 2% of protons are marked as candidates
600
-1
proton
simulations
-0.5
0
0.5
1
1.5
2
2.5
log10(Sb)
Dedicated proton simulations : same energy, arrival direction, core position and detector
configuration of this selected candidate
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Hybrid exposure
Upper Limit to the Integral Photon Flux :
Nγ95CL : Number of photon candidates
(at 95% C.L.) with energy Eγ above the
threshold E0 .
Nuclear background not subtracted
(conservative approach)
Eγ,min : Minimum hybrid exposure for
photons.
Time dependent simulations
Nγ95CL (Eγ > E0 )
Eγ,min
Hybrid Exposure for photons [km2 sr yr]
Φ95CL
=
γ
103
102
Photon candidate level
10
Realistic and time dependent simulations
J anuary
2005
- September
January
2005
- September2010
2010
1
Photon candidate level
Photon
candidate
-1
10
17.5
18
18.5
(method according to Astrop. Phys. 34, 2011)
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19.5
log (Energy/eV)
10
14
SHDM
SHDM’
TD
Z-burst
GZK
upper limits 95% C.L.
1
0
Integral Flux E>E [km-2 sr -1 y-1]
Limits on photon flux
Y
Auger Hyb 2009
Y
Exposure, ∆Xmax , ∆Sb ,
Energy scale, hadronic
interaction model and mass
composition assumptions :
A
10-1
A
Auger Hyb 2011
TA 2011
10-2
Auger SD
10-3
1018
1019
Systematic uncertainties
+20%
(E0
−64%
= 1 EeV)
+15%
(E0
−36%
> 1 EeV)
1020
Energy[eV]
Upper limit on the integral photon fraction assuming the Auger spectrum :
0.4%, 0.5%, 1.0%, 2.6% and 8.9% at E > 1, 2, 3, 5 and 10 EeV
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Conclusions
Neutrino search using surface detector
Earth skimming (sensitive to ντ ) :
k < 3.2 × 10−8 GeV cm−2 s−1 sr−1 in 1.6 × 1017 eV< E < 2 × 1019 eV
Down going (sensitive to all flavors) :
k < 1.7 × 10−7 GeV cm−2 s−1 sr−1 in 1 × 1017 eV< E < 1 × 1020 eV
The surface detector of the Pierre Auger Observatory is sensitive to potential point sources of
UHE neutrinos in a broad range in declination.
Photon search using hybrid data
6, 0, 0, 0 and 0 candidates above 1, 2, 3, 5 and 10 EeV
Upper limit to the integral photon flux :
8.2 × 10−2 km−2 sr−1 year−1 above 1 EeV
2.0 × 10−2 km−2 sr−1 year−1 above 2, 3, 5 and 10 EeV
Corresponding to photon fractions limit of :
0.4%, 0.5%, 1.0%, 2.6% and 8.9% at E > 1, 2, 3, 5 and 10 EeV
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Perspective & Outlook
GZK within reach in the next few years
Photon & neutrino limits provide severe constraints on top-down models.
Photon limits allow to reduce systematic uncertainties on mass composition, energy
spectrum & cross section measurements
Earth skimming and Downgoing combination in progress.
Directional search for UHE photons in progress
Search for UHE photons and neutrinos
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Perspective & Outlook
GZK within reach in the next few years
Photon & neutrino limits provide severe constraints on top-down models.
Photon limits allow to reduce systematic uncertainties on mass composition, energy
spectrum & cross section measurements
Earth skimming and Downgoing combination in progress.
Directional search for UHE photons in progress
Search for UHE photons and neutrinos a postdoctoral position
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Backup slides
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General neutrino search strategy
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Limits to point-like sources
10-5
Single flavour neutrino limits (90% CL)
Fixed energy range
Down-going (2yr)
E2 g(E) [GeV cm-2 s-1]
1017 eV < E < 1020 eV
10-6
1.6 1017 eV < E < 2 1019 eV
Earth-skimming (3.5yr)
10-7
Energy range
depends on declination
Below 1017 eV
Cen A
10-8
10-9
-80
-60
-40
IceCube-40 (375.5 days)
-20
0
20
40
Source declination [deg]
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60
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80
20
Limits to CenA
Centaurus A - Single flavour neutrino limits (90% CL)
[GeV cm-2 s-1]
10-4
10-5
10-6
Auger Earth-skimming
10-7
kPS = Eν2 F(Eν)
LUNASKA 2008
Auger Downward-going
IceCube 2011b
Cuoco 2008
10-8
10-9
Kachelriess 2009
-10
10
1015
1016
1017
1018
1019
1020
1021
1022
1023
Eν [eV]
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Point source as seen by Auger
1
1
Source at δ = -43o
Source at δ = -80o
0.5
0.5
θ = 75
θ = 90o
0
cosθ
cosθ
θ = 75
o
-0.5
o
θ = 90o
0
-0.5
-1
-1
0
0.2
0.4
0.6
0.8
1
0
Time t [sidereal days]
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0.2
0.4
0.6
0.8
1
Time [sidereal days]
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“safe” cut on Fisher value such that expected background <1 event / 20 years of Auger data
11
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Down- going: estimation of background
Assume an exponential
shape for the tail of
background distribution
of F
extrapolation to find
the value of F_cut
corresponding to 1
background event in a
given time
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Expected number of events
Model & reference
Cosmogenic (Fermi) [40]
BBR (AGNs) [41]
Exotic (SH relics) [42]
Earth-skimming
Downward-going
∼ 0.6
∼ 5.1
∼ 3.0
∼ 0.1
∼ 0.8
∼ 1.0
Table 4: Number of expected events for several theoretical models of UHE
neutrino production, given the exposure of the surface detector of the Pierre
Auger Observatory to Earth-skimming and downward-going neutrinos (Table 3).
Integrated limit
The limits indicate the level of the diffuse neutrino flux needed to detect Nup events with a
Poisson probability of ∼ 90% given the exposure accumulated during the 3.5 years for
Earth-skimming (2.0 years for downward-going) of equivalent time of a full SD
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-2
<Xmax> (g cm )
Elongation rate
1200
Fly´s Eye
HiRes-MIA
HiRes 2004
Yakutsk 2001
Yakutsk 2005
CASA-BLANCA
HEGRA-AIROBICC
SPASE-VULCAN
DICE
TUNKA
1100
1000
900
800
photon
with preshower
photon
proton
700
600
iron
QGSJET 01
500
QGSJET II
SIBYLL 2.1
400
10
14
10
15
10
16
10
17
10
18
10
19
10
20
10
21
Elab (eV)
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Systematics
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Phot on candidat es
Hybrid data J an 2005 - Sep 2010
(~ a factor 2 more events compared to previous analysis)
6, 0, 0, 0 and 0 candidates above 1, 2, 3, 5 and 10 EeV
E (EeV)
Xmax (gcm-2)
log10(Sb)
1.18 ±0.09
1023 ±10
1.16 ±0.27
Xmax (g cm-2)
compatible with the expected nuclear background
1200
Photon candidates
Jan 2005 - Sept 2010
1150
1.59 ±0.19
981 ±16
1.35 ±0.09
1.20 ±0.09
952 ±17
1.17 ±0.07
1100
1.25 ±0.16
958 ±27
1.08 ±0.24
1050
1.13 ±0.17
1119 ±29
1.56 ±0.21
1000
1.42 ±0.19
959 ±22
1.08 ±0.55
1.13 EeV
1.18 EeV
1.59 EeV
1.25 EeV
950
1.20 EeV
1.42 EeV
900
850
0.8
1
1.2
1.4
1.6
1.8
log (S )
10
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