Exploring the Universe at the highest energies with the Pierre...
Transcript of Exploring the Universe at the highest energies with the Pierre...
Exploring the Universeat the highest energies with the Pierre Auger ObservatoryKarl-Heinz KampertUniversity Wuppertal
OBSERVATORY
1 Photo by Steven SaffiOdense (Denmark), May 19-22, 2014
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 20142
1 event per m2 and sec
γ≈ 2.7 - 3.0
„ankle“(1 per km2-year)
log(energy/eV)
log(
flux)
32 o
rder
s of
mag
n.
„Knee“(1 per m2-year)
Satellite <1 m2
Balloons <5 m2
0.1 km2
Air Shower Exps
3000 km2
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 20145
courtesy R. Engel
Particle Energy (eV)
1310 1410 1510 1610 1710 1810 1910 2010
)1.
5 e
V-1
sr
-1 s
ec-2
J(E
) (m
2.5
Scal
ed fl
ux
E
1310
1410
1510
1610
1710
1810
1910
(GeV)ppsEquivalent c.m. energy 210 310 410 510 610
RHIC (p-p)-p)eHERA (
Tevatron (p-p)LHC (p-p)
ATICPROTONRUNJOB
KASCADE (QGSJET 01)KASCADE (SIBYLL 2.1)KASCADE-Grande (prel.)Tibet ASg (SIBYLL 2.1)
HiRes-MIAHiRes IHiRes IIAuger SD 2008
SNR?
Diffusion lossesfrom Galaxis ?
SNR ?
Galactic CRs?
magn. confinement➠ Emax ~ Z
Features of CR spectrum
Fe-knee
p,He-knee
AGN ?
Extragal. CRs?
pFe
? extragal.component
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Lamor radii at 1020 eV compared to Milky-Way
E18 ≤ Z·BµG·Rkpc
Conjecture:Extragalactic
origin
Size × B-Field needsto be very large …
Interesting feature:Can do astronomy with cosmic rays !
1020 eV CRs in our Galaxy ?
6
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Cosmic Magnetic Fields
Halo B?
Extra-galactic B < nG ?
γ, ν
weak deflection
RL = kpc Z-1 (E / EeV) (B / μG)-1
RL = Mpc Z-1 (E / EeV) (B / nG)-1
strong deflection
Milky wayB ~ μG
E > 1019eV
E < 1018eV
�(E,Z) ⇥ 0.8��
1020 eVE
⇥ ⇤L
10 Mpc
⇤Lcoh
1 Mpc
�B
1 nG
⇥· Z
UHECR Astronomy
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Active GalacticNuclei (AGN)
LHC
GRB
AGN-Jets
SNR
Colliding Galaxies
Potential Sources of 1020 eV particles
8
Neutron Stars
white dwarfts
Active Galactic Nuclei ?
jets from radioInterplanetary
Space
Galact.disk
halo
eV proton
galaxies
GalacticClusters
Size
Mag
net
ic F
ield
stre
ng
th (G
auß
)
1AU
SNR
1012
10 6
1
10 –6
1km 10 6 km 1pc 1kpc 1Mpc
IGM
10 20
{
LHC
GRB ?Emax ~ βs·z·B·L
Fe
Hillas Diagramm
Realistic constraints more severe
• small acceleration efficiency• synchrotron & adiabatic losses• interactions in source region
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Cas A(3.4 kpc)
Cygnus A(250 Mpc)
Fornax A (20 Mpc)
NRAO/AUI
1.4 , 5, & 8.4 GHz
Supernova RemnantsAccreting
Supermassive Black Holes
E < 1016 eV
E ~ 1020 eV ?
Radio Images of Cosmic Accelerators
9
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201410
• Where do they come from?
• What are they made of ?
• How do their accelerators work?
• Is there a maximum limit to their energy ?
• What can can they tell us aboutfundamental and particle physics?
Key Questions aboutUltra High-Energy Cosmic Rays
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Hybrid Observation of Extensive Air Showers
11
Particle-density and-composition at ground
light traceat night-sky(calorimetric)
Also:Detection of Radio- & Microwave-Signals
Fluorescence light
Concept pioneered by thePierre Auger Collaboration(Fully operational since 06/2008)
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Pierre Auger Observatory
12
3000 km2
~65 km
~65 k
m
CoihuecoHEAT
BLS
CLF
XLF
Loma Amarilla
Los Morados
Los Leones
1660 detector stationson 1.5 km grid
27 fluores. telescopesat periphery
130 radio antennas...Province Mendoza, Argentina
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
SANTIAGO
A R G E N T I N A
Pampa AmarillaProvince of Mendoza1400 m a.s.l.35° South, 69° West3000 km2
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201414
3000 km2 area, Argentina27 fluorescence telescopes plus
...1660 Water Cherenkov tanks
Auger Hybrid Observatory
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Pierre Auger Collaboration~500 Collaborators; 90 Institutions, 18 Countries:Argentina Poland UK
Australia Portugal USA
Brasil Romania
Czech Republic Slovenia Bolivia*
France Spain Vietnam*
Germany
Italy USA
Mexico
Netherlands
16
*Associated
OBSERVATORY
☀
Full membersAssociate members
☀
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201417
Event Example in Auger Observatory
12 km
~ 20 km
OBSERVATORY
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201418
Event Example in Auger Observatory
12 km
~ 20 km
E = 68 EeVXmax=770 g/cm2
dE/
dx
(PeV
/g c
m2 )
Slant Depth (g cm2)
0
40
400 600 800 1000 2000
80
120
160Longitudinal Profile
Lateral Profile
1000
S(1000)
S(1000)=222 VEMθ = 54°S38=343 VEME = 71 EeV
10
100
1000
Sign
al (V
EM)
Distance to Shower Core (m)
12000 3000
OBSERVATORY
Cross Correlation
Infill
Standard
inclined
calorimetric meas.
µ+e measurement
17.5 18.0 18.5 19.0 19.5 20.0 20.5log10( E /eV )
1036
1037
1038
E3J(E)
eV2km
−2sr
−1yr
−1
1035
863
1736
5622
0112
9532
4226
2720
1514
1052
202
2968
421
413
1301
486
2458
0739
8427
0017
0111
1667
642
718
890
457
31
1018 1019 1020E [eV ]
Auger 2013 preliminary
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201419
OBSERVATORY
End of the CR-Spectrum
γ1=3.23±0.07 γ2=2.63±0.04
Eankle=5·1018 eV
* *E50% =4·1019 eV
130 000 events
J(E;E > Ea) µ E�g2
1+ exp
✓ log10 E � log10 E1/2
log10 Wc
◆��1
g g
29
Is this the GZK-effect... ?
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
threshold: EpEγ > (mΔ2 - mp2)
⇒ EGZK ≈ 6·1019 eV100
101
102
103
104
1018 1019 1020 1021 1022
Ener
gy L
oss
Path
leng
th (M
pc)
Energy (eV)
Expansion
CMBRz = 0
Photopion, p
Photopair, p
Total, p
Photopair,Fe
Photopion,Fe
ePhotodisintegration, F
20
Greisen-Zatsepin-Kuz‘min (1966)
GZK-Effect: Energy losses in CMB
p
CMB
pπ
A
CMB
➙ GZK-Horizon ~ 60 Mpc
p+ �CMB ! � ! p+ ⇡0photo-pion production
A+ �CMB ! (A� 1) + n...photo disintegration
17.5 18.0 18.5 19.0 19.5 20.0 20.5log10(E/eV)
1036
1037
1038
E3 J
(E)[e
V2
km-
2sr
-1
yr-
1 ] �E/E = 14 %
Proton, Ecut = 1020 eVProton, Ecut = 1020.5 eVIron, Ecut = 1020 eVIron, Ecut = 1020.5 eV
1018 1019 1020E [eV]
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201421
Data compared to GZK-effect
(Phys. Rev. Lett., 2008, updated)
p-sources
Fe-sources
lg (E [eV])18 18.5 19 19.5 20 20.5
]-1
yr
-1 s
r-2
km
2 [e
V3
diff
flux
X E
3710
3810
all
p
He
=3-12obsZ
=12-26obsZ
primary p
Auger ICRC2013
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201422
Protons Emax,p = 1018.9 eV
Model inspired by Allard, Astropart. Phys. 39-40, 2012
Limiting Energy of Sources (Emax~Z) + GZK
Simulations done with CRPropa 2.0
m=0; γ=1.55In this case GZK-effect isnot responsible for cut-off!
Iron Emax, Fe = 26 Emax,p = 1020.3 eV
]2slant depth [g/cm200 400 600 800 1000 1200 1400 1600
)]2 e
nerg
y de
posi
t [Pe
V/(g
/cm
0
10
20
30
40
50 Auger event
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Longitudinal Shower Development ➙ Primary Mass
23
OBSERVATORY
Example of a 3·1019 eV EAS event in FD
KHK, Unger, APP 35 (2012)EPOS 1.99 Simulations
<Xmax>
RMS(Xmax)
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Xmax and RMS(Xmax) as a fct of E
24
Updated Measurement of hXmax
i and �(Xmax
)
comparison to air shower simulations
E [eV]1810 1910 2010
]2 [g
/cm
〉m
axX〈
660
680
700
720
740
760
780
800
820
840
proton
iron
EPOS-LHC QGSJetII-04 Sibyll2.1
E [eV]1810 1910 2010
]2) [
g/cm
max
(Xσ
0
10
20
30
40
50
60
70
80
90 Auger 2013 preliminary
proton
iron
[8 of 15]
OBSERVATORY
OBSERVATORY
Auger data show a smooth changeto a heavier composition above 5 EeV
using post LHC interaction models:
3844
64
96
129
174
246
324
431
lg(E [eV])18 18.5 19 19.5 20 20.
]-1
yea
r-1
sr
-2 k
m2
[eV
3di
ff flu
x * E
3710
3810
Auger ICRC2013
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Composition compared with astrophys. scenarios
25
]2>
[g/c
mm
ax<X
650
700
750
800
850
900Proton
Iron
proton source
iron source
Auger ICRC2013
lg(E [eV])18 18.2 18.4 18.6 18.8 19 19.2 19.4 19.6 19.8 20 20.2
]2) [
g/cm
max
(Xσ
0
10
20
30
40
50
60
70Proton
Iron
Auger ICRC2013
proton source
iron source
p
FeGCR sourcecomposition
GCR sourcecomposition
]2>
[g/c
mm
ax<X
650
700
750
800
850
900Proton
Iron
proton source
iron source
Auger ICRC2013
lg(E [eV])18 18.2 18.4 18.6 18.8 19 19.2 19.4 19.6 19.8 20 20.2
]2) [
g/cm
max
(Xσ
0
10
20
30
40
50
60
70Proton
Iron
Auger ICRC2013
proton source
iron source
lg (E [eV])18 18.5 19 19.5 20 20.5
]-1
yr
-1 s
r-2
km
2 [e
V3
diff
flux
X E
3710
3810
all
p
He
=3-12obsZ
=12-26obsZ
primary p
Auger ICRC2013
Limiting energy of sources combined with
GZK describes composition data best
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201426
Mass Fractions from Xmax DistributionsSlide removed (data not yet public)
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Implications of a heavy composition
27
Extragalactic propagation of ultrahigh energy cosmic-rays q
Denis Allard
Laboratoire Astroparticule et Cosmologie (APC), Université Paris 7/CNRS, 10 rue A. Domon et L. Duquet, 75205 Paris Cedex 13, France
a r t i c l e i n f o
Article history:
Available online 10 November 2011
a b s t r a c t
In this paper we review the extragalactic propagation of ultrahigh energy cosmic-ray (UHECR). We pres-
ent the different energy loss processes of protons and nuclei, and their expected influence on energy evo-
lution of the UHECR spectrum and composition. We discuss the possible implications of the recent
composition analyses provided by the Pierre Auger Observatory. The production of secondary cosmogenic
neutrinos and photons and the constraints their observation would imply for the UHECRs origin are also
addressed. Finally, we conclude by briefly discussing the relevance of a multi messenger approach for
solving the mystery of UHECRs. ! 2011 Elsevier B.V. All rights reserved.
1. Introduction
After more than 50 yr of experimental efforts, the origin of ultra-
high energy cosmic-rays (UHECRs, e.g., cosmic-rays above
!1018 eV) remains a mystery. The understanding of the production
of these particles, the most energetic particles in the universe, is
one of the most intense research field of high energy astrophysics.
Since the pioneering experiment at Volcano Ranch and the observa-
tion of the first cosmic-ray event above 1020 eV (see [1] for a com-
plete review of the early experiments), large statistics have been
accumulated above 1018 eV. High resolution measurements of the
UHECR spectrum, composition and arrival direction have been al-
lowed by recent experiments like AGASA [2], HiRes [3], the Pierre
Auger Observatory [4] and Telescope Array [5]. Among the most
interesting recent results, one can cite (see [6]) the evidence for a
suppression of the UHECR flux above 3–5 " 1019 eV observed by
HiRes [7] and Auger [8] with a large significance. Furthermore,
the recent analyses at the Pierre Auger Observatory seem to indi-
cate an evolution of the composition toward heavier elements
above the ankle [9] as well as hints for an anisotropic distribution
of the arrival directions of the highest energy events [10] and in par-
ticular a possible diffuse excess in the direction of the Centaurus
constellation[11]. Since the statistics above !3 " 1019 eV are quite
low, and the consistency between the results of different experi-
ments is still a matter of debate, these trends remain to be con-
firmed and understood with future data.
The extragalactic origin of UHECRs (at least above the ankle of
the cosmic-ray spectrum) is widely accepted. As a consequence
the measured cosmic-ray spectrum on Earth has to be shaped by
the effect of the propagation of the particles in the extragalactic
medium. During their journey from the source to the Earth the in-
jected cosmic-ray spectrum and composition can be modified by
interactions with photon backgrounds and cosmic magnetic fields.
A detailed modeling of the extragalactic propagation of UHECRs is
then a necessary ingredient for the astrophysical interpretation of
the data. One of the most important features due to UHECRs extra-
galactic propagation is the prediction of a cut-off in the observed
spectrum above a few 1019 eV due to interactions of UHE protons
or nuclei with photons of the Cosmic Microwave Background
(CMB). This prediction [12,13] of the so-called GZK cut-off (named
after the authors of the original studies Greisen, Zatsepin and Kuz-
min) was made in 1966, closely following the discovery of the
CMB. This prediction started a long series of studies on the extra-
galactic propagation of UHECRs including the production of sec-
ondary neutrinos and photons.
In this paper, we review the main aspects of the extragalactic
propagation of UHECR protons and nuclei. It will be organized as
follows. In the next section, we will review the main interaction
channels of protons and nuclei and discuss their influence on the
energy and mass losses. In Section 3., we show some propagated
spectra, allowing us to discuss expectations concerning the evolu-
tion of the composition from the source to the Earth and the pro-
duction of secondary protons. We discuss, in particular, the
possible implications of the composition trend suggested by the
recent analyses of the Pierre Auger Observatory. In Section 4 we
discuss discuss the production of secondary messengers (neutrinos
and photons) and the possible constraints their observation could
bring for the understanding of the UHECR origin. in Section 5.,
we finally conclude by briefly discussing the prospects for improv-
ing our understanding of the UHECR phenomenon and the ex-
pected contributions of current and planed experiments in
cosmic-rays, gamma-rays and neutrinos.
0927-6505/$ - see front matter ! 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.astropartphys.2011.10.011
q (A section discussing the influence of extragalactic magnetic fields and the
possible 14 departures from the rectilinear case is available in an extended version
of the present review available from: <arXiv:1111.3290>.)
E-mail address: [email protected]
Astroparticle Physics 39–40 (2012) 33–43
Contents lists available at SciVerse ScienceDirect
Astroparticle Physics
journal homepage: www.elsevier .com/ locate/ast ropart
UHECR composition models
Andrew M. Taylor⇑
Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
a r t i c l e i n f o
Article history:
Received 11 July 2013
Received in revised form 4 November 2013
Accepted 8 November 2013
Available online 16 November 2013
Keywords:
UHECR
Composition
a b s t r a c t
In light of the increasingly heavy UHECR composition at the highest energies, as observed by the Pierre
Auger Observatory, the implications of these results on the actual source composition and spectra are
investigated. Depending on the maximum energy of the particles accelerated, sources producing hard
spectra and/or containing a considerably enhanced heavy component appear a necessary requirement.
Consideration is made of two archetypal models compatible with these results. The secondary signatures
expected, following the propagation of the nuclear species from source to Earth, are determined for these
two example cases. Finally, the effect introduced by the presence of nG extragalactic magnetic fields in
collaboration with a large (80 Mpc) distance to the nearest source is discussed.
! 2013 Elsevier B.V. All rights reserved.
1. Introduction
During the last decade the field of UHECR research has under-
gone considerable developments with the completion of extremely
large detector facilities. The data from these instruments has lead
to a notable improvement in both the quantity and quality of
UHECR measurements. Following the digestion of this new infor-
mation, a revision of the UHECR model working hypothesis may
be due. In particular, measurements sensitive to the UHECR com-
position have improved dramatically with a coherent picture start-
ing to emerge from the ensemble of different composition sensitive
measurements the Pierre Auger Observatory (PAO) has made [1]. It
should be noted that this picture is obscured somewhat when
additional observational data from the TA experiment are included.
The statistical significance of this disagreement, however, remains
unclear. In this study, such additional observational data sets are
neglected.
2. Monte Carlo modeling
In order to test different hypothesis models, a Monte Carlo
description of UHECR propagation is used, as first described in
[2]. In this description, UHECR protons and nuclei are propagated
through the cosmic microwave background (CMB) and cosmic
infrared background (CIB) radiation fields, undergoing photo-disin-
tegration, photo-pion, pair production, and redshift losses as they
do so. Though the cross-sections and target photon spectral distri-
butions relevant for the proton related energy loss processes are
well understood, some uncertainty still remains in both the
photo-disintegration cross-sections and the CIB spectral distribu-
tion relevant for nuclei propagation. In the present study, the
description of these adopted are [3,4] for the cross-sections and
CIB spectral distribution respectively. In Sections 3–5, extragalactic
magnetic field (EGMF) effects are neglected. The effects introduced
by such fields on the main results are discussed in Section 6. In or-
der to take account of EGMF effects, the ‘‘delta-approximation’’
prescription provided in [5] is implemented.
To perform a comparison with the PAO measurements, the
predicted values of the composition sensitive shower profile
parameters, Xmax and RMSðXmaxÞ, were determined for each model.
In order to encapsulate the uncertainty in the hadronic model
description for these values, the spread in predicted values from
four different models [6–9] was determined.
The Monte Carlo description was applied to an ensemble of dis-
tributed sources whose redshift evolution scaled as ð1þ zÞm , with
m ¼ 3 from zmin (with corresponding nearest source distance
Lmin) up to zmax ¼ 1:5. An energy spectrum output by each source,
of the form dN=dE / E%ae%ðE=Emax;ZÞ , with Emax;Z ¼ ðZ=26ÞEmax;Fe, was
adopted.1 Source spectral indices in the range 1 < a < 3, and 3-com-
ponent compositions were scanned over for both the cutoff energy
cases of Emax;Fe ¼ 1020 eV and Emax;Fe ¼ 1020:5 eV. Only spectral and
composition data points with energies above 1018:6 eV were used
in the analysis. The systematic errors for the energy resolution,
Xmax, and RMSðXmaxÞ, were also included in the v2 determination.
The regions of parameter space for which good fits to both the
spectral and composition data were found are shown in Fig. 1.
From each of the two cutoff energy results, two example models
0927-6505/$ - see front matter ! 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.astropartphys.2013.11.006
⇑ Tel.: +353 16621333x337.
E-mail address: [email protected]
1 Such a parameterisation should be considered to provide ‘‘effective parameters’’,
which broadly encapsulate the true emission spectrum properties.
Astroparticle Physics 54 (2014) 48–53
Contents lists available at ScienceDirect
Astroparticle Physics
journal homepage: www.elsevier .com/ locate/ast ropart
Needfor a
localsourc
e of ultrahi
gh-energy c
osmic-raynucle
i
Andrew M. Tayl
or,1 Markus
Ahlers,2 and Felix
A. Aharonia
n3,4
1 ISDC, Che
min d’Ecogia 16, Ve
rsoix,CH-1
290, SWITZER
LAND
2C. N.Yang
Institute for
Theoretical
Physics, SU
NY at Stony Br
ook, Stony B
rook,New York
11794-3840
, USA
3Dublin Institu
te forAdvan
ced Studies, 5 Merrion
Square, Du
blin 2, IRELAND
4Max-Planck-
Institut fur K
ernphysik,
Postfach 10398
0, D-69029
Heidelberg,
GERMANY
(Received 11 July 2011;
published 7 Nove
mber 2011)
Recent resu
lts of the PierreAuge
r (Auger) fluore
scence detec
tors indicate an increa
singlyheavy
composition of ult
ra-high energ
y (UHE) co
smic rays (CR
s). Assuming th
at thistrend
continues u
p to the
highest ene
rgiesobser
ved by the
Auger surf
ace detector
s, wederive
the constrai
nts this pla
ces onthe lo
cal
source distrib
utionof UH
E CR nuclei. Uti
lizingan analy
tic description
of UHE CR propa
gation, we
derivethe expec
ted spectra and compositi
on for awide
rangeof sou
rce emissionspectr
a. We find that
sources of
intermediate
-to-heavy nucle
i areconsi
stentwith
the observed spectr
a and composition data
abovethe an
kle. This co
nsistency re
quiresthe pr
esence of n
earbysourc
es within 60
Mpc and 80 M
pc for
silicon and iron-o
nly sources, re
spectively.
The necessity of the
se localsourc
es becomes even
more
compelling in the pr
esence nan
o-Gauss loc
al extragala
ctic magnet
ic fields.
DOI:10.11
03/PhysRev
D.84.10500
7
PACSnumbers:
13.85.Tp, 9
8.70.Sa
I. INTRODUC
TION
Ultra-high
energy CRs
withenerg
ies above10
19 eV
arriveat Ea
rth witha frequ
encyof les
s thanone event
per square-kilo
meter-year (i.e.
withan energ
y fluxof
30 eV cm!2 s!
1 ) in ! steradian. T
he recently completed
PierreAuge
r observator
y [1]with a
surface dete
ctor cover-
ing an area of abou
t 3000km
2 is thus able
to detect up to
several hund
red UHE CR event
s peryear.
However, d
ue to
the steeply
falling CR
spectrum the ar
rival freque
ncy drops
by about2 order
s of magnitu
de aswe go
up in energy by
one decade
, leaving only a few
events per
year detecta
ble
at energies
around 10
20 eV. Hence,
the statistical u
ncer-
taintyassoc
iatedwith t
he upper en
d of the spec
trumis stil
l
large,limiting
our knowledge
of UHECR compositi
on
and origin.
Before thei
r arrival, UH
E CRs must pr
opagate acr
oss the
astronomical d
istance betw
een their so
urce and Ea
rth. The
relevant inte
ractions of
UHECR nucle
i during pro
pagation
are Bethe-H
eitlerpair p
roduction a
nd photo-d
isintegratio
n
in collision
s withphoto
ns ofthe co
smic backgrou
nd radia-
tion. The cro
ss sections
of both thes
e processes
rise quickly
abovethe thresh
old values of a
bout1 MeV and 10 MeV,
respectivel
y, inthe nucle
i’s rest-frame. At
evenhighe
r
energies above
150 MeV pionprodu
ctionturns
on and
becomes the
dominantenerg
y loss proces
s. However
, for
the UHE CR cutoff
energies an
d compositi
on weconsi
der,
whichare m
otivated by
the most re
cent Auger r
esults, this
process never
playsa dominant
role and may be safely
neglected.
Provided the propa
gationtime from
theirsourc
es to
Earthis greate
r thantheir
energy loss time, UH
E CRs
invariably
undergo these
energy loss
interactions
. The
breakup of nu
clei via pho
to-disintegr
ationprodu
ces lower
mass nuclei with
the same Lorentz factor
. For heavy
nuclei, the most dominant
transitions
are one-nucleo
n
and two-nucleo
n losses. Sec
ondary heavy
nuclei rem
ain
closeto the photo
-disintegrat
ion resonance
and quickly
disintegrate
further to li
ghternucle
i. Hence, on
resonance,
the initialmass compositi
on of the sources is quick
ly
shifted to lower
atomic number values and in gener
al
showsa strong
dependence
on CR energy.
The arrivin
g fluxfrom
an ensemble of
UHECR sourc
es
can be exp
ectedto con
tain suppre
ssionfeatur
es at the hig
h
energies at
whichthe photo
-disintegrat
ion processes t
urn
on and the nuclei part
icle’sattenu
ationlength
decreases.
Most prominentl
y, for the caseof a proto
n-dominated
spectrum, the
flux is expected to be suppr
essedby the
Greisen-Za
tsepin-Kuz’
min (GZK)
cutoff[2,3]
due toreso-
nantpion
photo-prod
uctionintera
ctionswith
the cosmic
microwave ba
ckground (C
MB). Intrigui
ngly,a supp
ression
of theCR spectr
um at about 5
" 1019 eV has been
ob-
servedat a statist
icallysignifi
cant level [
4,5].Howe
ver,
sincea similar fe
aturemay also appea
r in the spectrum
fromnucle
i primaries,
the observation
of such a featur
e
provides litt
le clue as to
the underlyi
ng compositi
on. Such a
suppression
feature becom
es a cutoffin the arrivi
ng flux
if theattenu
ationlength
dropsbelow
the distance to the
nearest UH
ECR source. Thu
s, theshape
of thesuppr
ession/
cutofffeatur
e doesconta
in information
aboutthe sourc
e
distribution,
as hasbeen i
nvestigated
already for t
he case of
UHECR proto
ns [6–8].
On theirarriva
l at Earth,
UHECRs i
nteract with
mole-
culesin the atmosphe
re and deposit the
ir energy in the
formof ext
ensiveair sh
owers. The
characteris
tics of thes
e
showers alo
ng theshowe
r depth X (in g=
cm2 ) cont
ain vital
UHECR compositi
on information.
On average, p
roton-
induced showe
rs reachtheir
maximum development,
hXmaxi, deeper i
n the atmosphere than do showe
rs ofthe
same energy gener
ated by heavier nu
clei. Accom
panying
this effect,
the shower
to shower fl
uctuation of Xmax
about
PHYSICAL
REVIEW D 84, 10
5007(2011
)
1550-7998=
2011=84(10
)=105007(1
0)
105007-1
! 2011American
Physical So
ciety
On the heavy chemical composition of the ultra-high energy cosmic rays
Dan Hooper a,b, Andrew M. Taylor c,d,*
a Fermi National Accelerator Laboratory, Theoretical Astrophysics, Batavia, IL 60510, USA
b University of Chicago, Department of Astronomy and Astrophysics, Chicago, IL 60637, USA
c Max-Planck-Institut für Kernphysik, Postfach 103980, D-69029 Heidelberg, Germany
d ISDC, Chemin d’Ecogia 16, Versoix, CH-1290, Switzerland
a r t i c l e i n f o
Article history:
Received 11 October 2009
Received in revised form 10 December 2009
Accepted 10 January 2010
Available online 18 January 2010
Keywords:
UHECRComposition
a b s t r a c t
The Pierre Auger Observatory’s (PAO) shower profile measurements can be used to constrain the chem-
ical composition of the ultra-high energy cosmic ray (UHECR) spectrum. In particular, the PAO’s measure-
ments of the average depth of shower maximum and the fluctuations of the depth of shower maximum
indicate that the cosmic ray spectrum is dominated by a fairly narrow distribution (in charge) of heavy or
intermediate mass nuclei at the highest measured energies ðE J 1019 eVÞ, and contains mostly lighter
nuclei or protons at lower energies ðE # 1018 eVÞ. In this article, we study the propagation of UHECR
nuclei with the goal of using these measurements, along with those of the shape of the spectrum, to con-
strain the chemical composition of the particles accelerated by the sources of the UHECRs. We find that
with modest intergalactic magnetic fields, 0.3 nG in strength with 1 Mpc coherent lengths, good fits to the
combined PAO data can be found for the case in which the sources accelerate primarily intermediate
mass nuclei (such as nitrogen or silicon). Without intergalactic magnetic fields, we do not find any com-
position scenarios that can accommodate the PAO data. For a spectrum dominated by heavy or interme-
diate mass nuclei, the Galactic (and intergalactic) magnetic fields are expected to erase any significant
angular correlation between the sources and arrival directions of UHECRs.! 2010 Published by Elsevier B.V.
1. Introduction
The chemical composition of the ultra-high energy cosmic ray
(UHECR) spectrum has long been a topic of great interest [1–6].
Until recently, however, very little was known about the nature
of these particles. On one side of the debate, the so called Hillas cri-
terion [7] gives a preference for the electromagnetic fields of cos-
mic ray sources to accelerate heavy nuclei to higher energies
than protons or light nuclei. On the other side, it has been argued
that the angular correlations reported by the Pierre Auger Observa-
tory (PAO) [8], as well as features in the shape of the UHECR spec-
trum [9], suggest that these particles consist largely of protons.
None of these arguments, however, has yet settled the question
of what types of particles make up the UHECR spectrum.
Data from the Pierre Auger Observatory (PAO), however, is
offering increasingly powerful insights into this question. Firstly,
the spectral shape predicted for the UHECR all-particle spectrum
depends not only on the injected spectrum and spatial distribution
of the sources, but also on the chemical composition that is in-
jected from the sources of the highest energy cosmic rays. As the
PAO measures the UHECR spectrum with increasing precision
[10], this information can be used to constrain the chemical com-
position of these particles [11]. Furthermore, the PAO is capable
of performing several measurements that can be used to directly
or indirectly determine the chemical composition of UHECRs as
they enter the Earth’s atmosphere. Among these empirical tools
are the measurements of the average depth of shower maximum,
hXmaxi, and the RMS variation of this quantity, RMSðXmaxÞ. On aver-
age, proton-induced showers reach their maximum development,
hXmaxi, deeper in the Earth’s atmosphere than do showers of the
same energy generated by heavier nuclei. Accompanying this re-
sult, the shower to shower fluctuation of Xmax about the mean,
RMSðXmaxÞ, is larger for proton-induced showers than for iron-in-
duced showers of the same energy. As a result, measurements of
both hXmaxi and RMSðXmaxÞ can be used to infer the average chem-
ical composition of the UHECRs as a function energy.
Very recently, the PAO collaboration has announced their first
measurements of RMSðXmaxÞ [12,13]. These measurements, along
with those of hXmaxi, imply that the UHECR spectrum contains a
large fraction of heavy or intermediate mass nuclei, especially at
the highest energies measured. Furthermore, the small values of
RMSðXmaxÞ measured by the PAO also imply that the composition
of the UHECR spectrum is relatively narrowly distributed at the
highest measured energies, containing little or no protons or light
0927-6505/$ - see front matter ! 2010 Published by Elsevier B.V.
doi:10.1016/j.astropartphys.2010.01.003
* Corresponding author. Address: Max-Planck-Institut für Kernphysik, Postfach
103980, D-69029 Heidelberg, Germany.
E-mail address: [email protected] (A.M. Taylor).
Astroparticle Physics 33 (2010) 151–159
Contents lists available at ScienceDirect
Astroparticle Physics
journal homepage: www.elsevier .com/ locate/ast ropart
arX
iv:1
312.
7459
v1 [
astro
-ph.
HE]
28
Dec
201
3
Prepared for submission to JCAP
Ultra high energy cosmic rays:implications of Auger data for sourcespectra and chemical composition
R. Aloisio1,2, V. Berezinsky2,3 and P. Blasi1,2
1INAF/Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5 - 50125 Firenze, Italy2Gran Sasso Science Institute (INFN), viale F. Crispi 7, 67100 L’Aquila, Italy3INFN/Laboratori Nazionali Gran Sasso, ss 17bis km 18+910, 67100 Assergi, Italy
E-mail: [email protected],[email protected], [email protected]
Abstract. We use a kinetic-equation approach to propagation of ultra high energy cosmicray protons and nuclei to infer possible implications of the data on spectrum and chemicalcomposition collected by the Pierre Auger Observatory. Using a homogeneous source dis-tribution, we show that a simultaneous fit to the spectrum, elongation rate Xmax(E) anddispersion σ(Xmax) implies the injection of nuclei with very hard spectra. This leads howeverto underestimate the flux at energies E ≤ 5× 1018 eV, thereby implying that an additionalcosmic ray component is required, which needs to be of extragalactic origin. We discuss thenature of this additional component in terms of the recent findings of KASCADE-Grandeon fluxes and chemical composition, which allows to describe the transition from Galactic toextragalactic cosmic rays.
Astroparticle Physics 54, 48 (2014)
Astroparticle Physics 39–40 (2012) 33–43
Astroparticle Physics 33 (2010) 151–159
Subm. to JCAP 2013
...and many more papers of this type
all require very hard injection spectra unless
a nearby source (population) is assumed
E [eV]1810 1910 2010
]-1
y-1
sr
-2in
tegr
al fl
ux [k
m
-510
-410
-310
-210
-110
1
10 SHDM GZK pTD GZK FeZ-burst
AGASAYakutskAuger SDAuger HybridTA SD
Cosmogenic+neutrinos+
4+
Detec?on+in+EeV+range+may+provide+complementary+informa?on+to+direct+UHECR+detec?on+on:++UHECR+nature+(p,+mixed,+Fe),+origin+(evolu?on+of+the+sources,+maximum+energy+a^ainable,…)+
[eV]νE1710 1810 1910 2010 2110
]-1
sr
-1 s
-2 d
N/d
E [
GeV
cm
2E
-1010
-910
-810
-710
-610
-510
-410Single flavour
p, best fit with Fermi-LAT bound (Ahlers)
eV (B. Sarkar)20=10maxp, FRII & SFR, E
eV (B. Sarkar)20=26 x 10maxFe, FRII & SFR, E
eV (Kotera)21.5 - 1020=Z x 10maxp & mixed, SFR & GRB, E
p+ �CMB ! � ! p+ ⇡0
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Smoking Gun of GZK-effect
28
! p+ ⇡0! �EeV! n+ ⇡+! ⌫EeV
cosmogenic neutrinos and photons– a guaranteed signal –
GZK-p
GZK-Fe
GZK-p
GZK-Fe
TopDown models
Energy[eV]1810 1910 2010
]-1
y-1
sr
-2 [k
m0
Inte
gral
Flu
x E>
E
-310
-210
-110
1upper limits 95% C.L.
SD
Hyb 2011
Hyb 2009A
A
YY
TA
SHDMSHDM'TDZ-burstGZK
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201429
Diffuse Photon Limits
GZK
Photon upper limits rule out Top-Down Modelsand get close to expected GZK-fluxes
OBSERVATORY
Sensi?vity+to+all+flavours+&+channels+
��������
��������� ��� ��������
�������� ��� ��������
���� �� ���� ��
����������� �������� �� ��������
�� �� ����������������
�� �� ���������
����������������� �� ��������
�
��������������� �� ������
�������������������� �� ��������
�
������������������
� �������������
������������������������������� ���������������
��!���������!� ������"� �#�$���!����������� ������"%�$� �#���
10+
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201430
Sensitivity to all ν flavors and channels
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Differential diffuse ν flux limits
31
[eV]E1710 1810 1910 2010 2110
]-1
sr
-1 s
-2 d
N/d
E [
GeV
cm
2 E
-1010
-910
-810
-710
-610
-510
-410Single flavour (90% CL)
Pierre AugerPRELIMINARY
[eV]E1710 1810 1910 2010 2110
]-1
sr
-1 s
-2 d
N/d
E [
GeV
cm
2 E
-1010
-910
-810
-710
-610
-510
-410 limits
Full IceCube (2 yr)Auger (6 yr)ANITA-II (28.5 days)
modelsCosmogenic p, Fermi-LAT boundFe, FRII & SFR evol.p & mixed
Astrophysical sourcesAGN Waxman-Bahcall
All limits converted to single flavour and given per half a decade of energy
GZK
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201432
Taking Profit fromthe extreme energies... (1)
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Tests of Lorentz Invariance Violation
33
Galaverni & SiglPRL 100, 021102 (2008) and many others
cascading of UHEphotons suppressed
LIV ➙ may modify photon dispersion relation
⇥2 = k2 + m2 + �nk2(k/MPl)n
➙ affect the threshold for e+e– pair production
➙↳ �� � e+e�
expect significant photonfraction above ~ 1019 eV
γ-fractionif LIV
no LIV
p + �CMB � �� p + ⇥0
�1 ⇥ 2.4� 10�15
7 orders of magnitudesbetter than previous limits!CPT tests possible as well
�2 ⇤ �2.4⇥ 10�7
Auger upper limits
Auger:Astropart. Phys. 29 (2008) 234
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Bounds on LIV and Smoothness of Class. Space-Time
34
Klinkhamer/Risse; PRD77 (2008) 016002; 117901; Klinkhamer, AIP Conf.Proc.977:181-201,2008
• Conservative limit on any small-scale structure of space:LEP/LHC: ℓ≤10-19 m ≈ ℏc/(1 TeV).
• Use published 27 Auger events + 1 AGASA + 1 Fly‘s-Eye
↪ single scale classical space-time foam at
UHECRs: b ≤ 10-26 m ≈ ℏc/(2·1010 GeV)
• Conjecture: fundamental length scale of quantum space time may be different from Planck length and may be linked to cosmological constant
Observation of 1020 eV eventsproofs absence of Vacuum Cherenkov-Radiation➙ Provides limits on smoothness of space & LIV-effects
by far best (3 to 8 orders of magn.!) existing bounds of Standard Model Extension parameters of nonbirefringent modified Maxwell theory
Results complemented by TeV γ-rays
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201435
Taking Profit fromthe extreme energies... (2)
]2 [g/cmmaxX500 600 700 800 900 1000 1100 1200
/g]
2 [
cmm
axdN
/dX
-110
1
10
2 g/cm+2.4-2.3 = 55.8 fR
dPdX1
= 1�int
e�X1/�int
�p�Air = hmAiri�int
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201436
p-Air Cross-Section from Xmax distribution
Data: 1018 eV < E < 1018.5 eV
In practice: σp-Air by tuning models to describe Λ seen in data
X1: point of 1st interactionΔX1
ΔXmax ≈ X1
Difficulties:• mass composition can alter Λ• fluctuations in Xmax
• experimental resolution ~ 20 g/cm2
Λint
top of atmosphere
Inelastic Proton-Proton Cross-Section
Standard Glauber conversion + propagation of modeling uncertainties
(Pro
ton-
Prot
on)
[m
b]in
elσ
30
40
50
60
70
80
90
100
110
[GeV]s310 410 510
ATLAS 2011CMS 2011ALICE 2011TOTEM 2011UA5CDF/E710Auger ICRC 2011
QGSJet01QGSJetII.3Sibyll2.1Epos1.99Pythia 6.115Phojet
σinelpp =
!
90 ± 7stat (+9−11)sys ± 1.5Glauber
"
mb√spp = [57 ± 6] TeV
The 1.5mb do not reflect the total theoretical uncertainty, since there are other
models available for the conversion.Ralf Ulrich ([email protected]) Measurement of the Proton-Air Cross-Section with the Pierre Auger Observatory 12 / 19
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
p-Air and pp Cross section @ √s=57 TeV
37
(Energy/eV)10
log11 12 13 14 15 16 17 18 19 20
Cro
ss s
ectio
n (p
roto
n-ai
r)
[mb]
200
300
400
500
600
700
QGSJet01cQGSJetII.3Sibyll 2.1Epos 1.99
Energy [eV]1110 1210 1310 1410 1510 1610 1710 1810 1910 2010
[TeV]ppsEquivalent c.m. energy -110 1 10 210
Nam et al. 1975Siohan et al. 1978Baltrusaitis et al. 1984Mielke et al. 1994Honda et al. 1999Knurenko et al. 1999ICRC07 HiResAglietta et al. 2009Aielli et al. 2009This work
0.9TeV 2.36TeV 7TeV 14TeV
LHC
Conversion from p-airto p-p cross section by Glauber-approach
σp-Air= (505 ± 22stat (+26)sys ) mb –34
σpp = [92 ± 7stat (+9 )sys ± 7.0Glauber] mb –11
LHC OBSERVATORY
OBSERVATORY
inel
prod
σpp = [133 ± 13stat (+17 )sys ± 16Glauber] mb –20
tot
Auger
Auger Collabora,on, PRL 109, 062002 (2012)
0
200
400
600
800
1000
1200
1400
1e-07 1e-06 1e-05 0.0001 0.001 0.01 0.1 1 10 100 1000
σp-
Air [
mb]
Energy [EeV]
σp-Air vs. Energy
QII-04EPOS-LHCTo Fit RMS
AugerQII-04 (π-Air)
EPOS-LHC (π-Air)
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Disentangling Int.-Models from Composition
38
17.5 18.0 18.5 19.0 19.5 20.0 20.5log10(E/eV)
600
650
700
750
800
850
900
hXm
axi[
gcm
-2 ]
Post-LHC modelsProtonIron
17.5 18.0 18.5 19.0 19.5 20.0 20.5log10(E/eV)
0
20
40
60
80
100
�( X
max
)[g
cm-
2 ]
Post-LHC modelsProtonIron
If the composition would be protons at all energies, Xmax and RMS(Xmax) could only be described by a rapidly rising cross section above LHC energies
G. Farrar, priv. comm.
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201439
⟨ρµ⟩ and RMS(ρµ) in a mixed composition changes distinctively different with Xmax
as compared to models of a pure p-composition
Disentangling Int.-Models from Composition
0.5
1
1.5
2
2.5
3
600 700 800 900 1000 1100 1200
l µ [m
-2]
Xmax [g/cm2]
EPOS-LHC pEPOS-LHC He
EPOS-LHC N
Models of new physics33RD INTERNATIONAL COSMIC RAY CONFERENCE, RIO DE JANEIRO 2013
2.4
2.6
2.8
3
3.2
650 700 750 800 850 900
ρ µ(1
000)
[m-2
]
Xmax [g/cm2]
CSRPDSPPS
PPS-HE
Figure 5: The density of muons at 1000 m as a functionof Xmax for the four template models. The error bars showthe variance in samples of 800 hybrid events, which is anumber achievable at the PAO and TA.
or decay and, thus, have different correlation strengths be-tween Nµ and Xmax. Fig. 5 shows the average Nµ as a func-tion of Xmax and its variance in ensembles of 800 simu-lated events, for 10 EeV showers at a zenith angle of 38o,for each of the four schematic models. These simulationswere done at a fixed zenith angle and energy, but the samestatistical power could be achieved by normalizing show-ers to a fiducial energy and angle. The negative correla-tion between Nµ and Xmax is strongest when the modifica-tion is made at all energies, and weaker when the modifica-tion is applied only at high energy. The PPS and PPS-HEmodels show a negative correlation while the CSR modelshows almost no correlation. Finally, the PDS model actu-ally shows a positive correlation: showers with a shallowXmax produce fewer muons than showers with a deep Xmax.Thus the models can be discriminated at high significancewith presently realizable datasets.The behavior of the PDS and PPS models demonstrates
that the correlation is sensitive to the energy threshold ofthe pion modifications. This is made explicit in Fig. 6,which compares the average Nµ and Xmax of iron, carbon,and proton initiated showers, for different degrees of pionproduction suppression at high energy. As pion productionsuppression is increased, the relative difference betweenthe mean Nµ in iron and proton showers decreases.
5 ConclusionWe argue that the muon deficit in simulations of air show-ers indicates that the hadronic models are incorrectly pre-dicting the fraction of energy which is transfered to theelectromagnetic sub shower. Changing the π0 energy frac-tion or suppressing pion decay are the only modificationswhich can be used to increase the number of muons atground without coming into conflict with the Xmax obser-vations.We have developed four schematic models of hadronic
interactions, all of which are capable of correctly describ-ing the Xmax distributions and number of muons at ground.They utilize both pure proton and mixed primary composi-tions, which demonstrates the need for models to correctlydescribe all air shower observables before they are used tointerpret the primary mass composition.The fourmodels can be distinguished by observations of
the correlation between the number of muonsNµ and Xmax,
0.9
1
1.1
1.2
1.3
1.4
1.5
660 680 700 720 740 760 780 800 820
ρ µ / ρ µ
(p)
Xmax [g/cm2]
p, EPOS 1.99C, EPOS 1.99
Fe, EPOS 1.9920% π -> B,K45% π -> B,K
Figure 6: The dependence of the density of muons at 1000m, relative to protons, on pion production at high energy.
for an ensemble of hybrid events. This correlation providesa crucial new observable for determining the nature ofUHE air showers. Existing hybrid datasets may already belarge enough to rule out some explanations of the muonexcess.Acknowledgements: The authors are members of thePierre Auger Collaboration and acknowledge with grat-itude innumerable valuable discussions with colleagues.This research was supported by NSF-PHY-1212538.
References[1] T. Abu-Zayyad et al., HiRes-MIA Collab., Astrophys.J. 557 (2001) 686.
[2] J. Allen, for PAO, Proc. 32nd ICRC, Beijing, China 2(2011) 83, arxiv:1107.4804
[3] G. Rodriguez, for PAO, Proc. 32nd ICRC, Beijing,China, 2 (2011) 95, arxiv:1107.4809
[4] B. Kegl, for PAO, ICRC 2013 arxiv:1307.5059.[5] I. Valino, for PAO, ICRC 2013 arxiv:1307.5059.[6] The Pierre Auger Collaboration, Phys. Rev. Lett. 104(2010) 091101.
[7] The Pierre Auger Collaboration, JCAP 02 (2013) 026.[8] The TA Collaboration, Proc. 32nd ICRC, Beijing,China, 2 (246) .
[9] The HiRES Collaboration, Phys. Rev. Lett. 104(2010) 161101.
[10] J. Matthews, Astroparticle Physics 22 (2005) 387.[11] R. Ulrich et al, Phys. Rev. D 83 (2011) 054026.[12] T. Pierog and K. Werner, Phys. Rev. Lett. 101 (2008)171101.
[13] H.-J. Drescher and G. Farrar, Phys. Rev. D 67 (2003)116001.
[14] K. Werner et al, Phys. Rev. C 74 (2006) 044902.[15] G. Farrar and J. Allen, Proc. UHECR 2012, CERN;arXiv:1307.2322
[16] G. Farrar and G. Veneziano, in prep.[17] S. Ostapchenko, Nucl. Phys. B - Proc. Supp. 151(2006) 143.
[18] E.-J. Ahn et al., Phys. Rev. D 80 (2009) 094003.[19] J. Alvarez-Muniz et al., arxiv:1209.6474.[20] R. Engel, D. Heck, and T. Pierog, Annu. Rev. Nucl.Part. Sci. 61 (2011) 467.
[21] P. Younk and M. Risse, Astroparticle Phys, 35(2012) 807.
Allen, Farrar ICRC2013, arXiv:1307.7131
CSR: Chiral Symmetry RestorationPDS: Pion Decay SuppressionPPS: Pion Production Suppression
10 EeV, θ=38°
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Same measured Eventwith predicted signals for p and Fe
Interaction Models underestimate Muon-numbers
40
Models underestimate µ-content of EAS by 30-60%
models
independent tests e.g. using showeruniversality yield the same results
Measured event with matching p and Fe-simulations
G.R. Farrar et al., Muon content of hybrid PAO CRs33RD INTERNATIONAL COSMIC RAY CONFERENCE, RIO DE JANEIRO 2013
0
10
20
30
40
50
1 1.2 1.4 1.6 1.8 2
S [V
EM]
sec(θ)
TotalPure Muon
Pure EMEM from µ DecayEM from Had. Jetµ from Photprod.
Figure 4: The contributions of different components to theaverage signal as a function of zenith angle, for stations at 1km from the shower core, in simulated 10 EeV proton airshowers illustrated for QGSJET-II-04. The signal size ismeasured in units of vertical equivalent muons (VEM), thecalibrated unit of SD signal size [18].
where a is the energy scaling of the muonic signal; it has thevalue 0.89 in both the EPOS and QGSJET-II simulations,independent of composition [19].
Finally, the variance of S(1000) with respect to Sresc mustbe estimated for each event. Contributions to the varianceare of two types: the intrinsic shower-to-shower variance inthe ground signal for a given LP, sshwr, and the variance dueto limitations in reconstructing and simulating the shower,srec and ssim. The total variance for event i and primarytype j, is s
2i, j = s
2rec,i +s
2sim,i, j +s
2shwr,i, j.
sshwr is the variance in the ground signals of showerswith matching LPs. This arises due to shower-to-showerfluctuations in the shower development which result invarying amounts of energy being transferred to the EM andhadronic shower components, even for showers with fixedXmax and energy. sshwr is irreducible, as it is independentfrom the detector resolution and statistics of the simulatedshowers. It is determined by calculating the variance in theground signals of the simulated events from their respectivemeans, for each primary type and HEG; it is typically⇡ 16% of Sresc for proton initiated showers and 5% for ironinitiated showers.
srec contains i) the uncertainty in the reconstruction ofS(1000), ii) the uncertainty in Sresc due to the uncertaintyin the calorimetric energy measurement, and iii) the uncer-tainty in Sresc due to the uncertainty in Xmax; srec is typi-cally 12% of Sresc. ssim contains the uncertainty in Sresc dueto the uncertainty in S
µ
and SEM from the S(1000)�wµ
fitand to the limited statistics from having only three simu-lated events; ssim is typically 10% of Sresc for proton initi-ated showers and 4% for iron initated showers.
The resultant model of si, j is checked using the 59 events,of the 411, which are observed with two FD eyes whoseindividual reconstructions pass all required selection cutsfor this analysis. The variance in the Sresc of each eye iscompared to the model for the ensemble of events. Allthe contributions to si, j are present in this comparisonexcept for sshwr and the uncertainty in the reconstructedS(1000). The variance of Sresc in multi-eye events is wellrepresented by the estimated uncertainties using the model.In addition, the maximum-likelihood fit is also performedwhere sshwr is a free parameter rather than taken from the
0.4 0.6 0.8
1 1.2 1.4 1.6 1.8
2
0.7 0.8 0.9 1 1.1 1.2 1.3
R µ
RE
Systematic Uncert.QII-04 p
QII-04 MixedEPOS-LHC p
EPOS-LHC Mixed
Figure 5: The best-fit values of RE and Rµ
for QGSJET-II-04 and EPOS-LHC, for mixed and pure proton composi-tions. The ellipses show the one-sigma statistical uncertain-ties. The grey boxes show the estimated systematic uncer-tainties as described in the text; these will be refined in aforthcoming journal paper.
models; no significant difference is found between the valueof sshwr from the models, and that recovered when it is a fitparameter.
The results of the fit for RE and Rµ
are shown in Fig.5 and Table 1 for each HEG. The ellipses show the one-sigma statistical uncertainty region in the RE � R
µ
plane.The systematic uncertainties in the event reconstructionof Xmax, EFD and S(1000) are propagated through theanalysis by shifting the reconstructed central values by theirone-sigma systematic uncertainties; this is shown by thegrey rectangles.1 As a benchmark, the results for a purelyprotonic composition are given as well2.
The signal deficit is smallest (the best-fit Rµ
is the closestto unity) in the mixed composition case with EPOS. Asshown in Fig. 6, the primary difference between the groundsignals predicted by the two models is the size of the muonicsignal, which is ⇡15(20)% larger for EPOS-LHC thanQGSJET-II-04, in the pure proton (mixed composition)cases respectively. EPOS benefits more than QGSJET-IIwhen using a mixed composition because the mean primarymass determined from the Xmax data is larger in EPOS thanin QGSJET-II [20].
4 Discussion and SummaryIn this work, we have used hybrid showers of the PierreAuger Observatory to quantify the disparity between state-of-the-art hadronic interaction modeling and observed at-mospheric air showers of UHECRs. The most important ad-vance with respect to earlier versions of this analysis[21], inaddition to now having a much larger hybrid dataset and im-proved shower reconstruction, is the extension of the anal-
1. The values of ssim, srec and sshwr and the treatment of system-atic errors used here will be refined with higher statistics MonteCarlo simulations and using the updated Auger energy and Xmaxuncertainties, for the journal version of this analysis.
2. Respecting the observed Xmax distribution is essential for evalu-ating shower modeling discrepancies, since atmospheric attenu-ation depends on the distance-to-ground. This is automatic inthe present analysis, but the simulated LPs – which are selectedto match hybrid events – is a biased subset of all simulatedevents for a pure proton composition since with these HEGspure proton does not give the observed Xmax distribution.
54
Req
. res
calin
g of
µ-s
igna
l
Required rescaling of ground signals
The muon content of UHECR air showers observed by the Pierre Auger Observatory
The Pierre Auger Collaboration(Dated: January 17, 2014)
The hybrid events of the Pierre Auger Observatory are used to test the leading, LHC-tuned,hadronic interaction models. For each of 411 well-reconstructed hybrid events collected at theAuger Observatory with energy 1018.8
− 1019.2 eV, simulated events with a matching longitudinalprofile have been produced using QGSJET-II-04 and EPOS-LHC, for proton, He, N, and Fe pri-maries. The ground signals of simulated events have a factor 1.3-1.6 deficit of hadronically-producedmuons relative to observed showers, depending on which high energy event generator is used, andwhether the composition mix is chosen to reproduce the observed Xmax distribution or a pure protoncomposition is assumed. The analysis allows for a possible overall rescaling of the energy, howeverit proves not to be needed.
PACS numbers: Pierre Auger Observatory, ultra-high energy cosmic rays, muons, hadronic interactions
INTRODUCTION
The ground-level muonic component of ultra-high en-ergy (UHE) air showers is sensitive to hadronic parti-cle interactions at all stages in the air shower cascade,and to many properties of hadronic interactions suchas the multiplicity, elasticity, fraction of secondary pi-ons which are neutral, and the baryon-to-pion ratio [1].Air shower simulations rely upon hadronic event gener-ators (HEGs), such as QGSJET-II [2], EPOS [3], andSIBYLL [4]. The HEGs are tuned on accelerator exper-iments, but when applied to air showers they must beextrapolated to energies inaccessible to accelerators andto phase-space regions not well-covered by existing ac-celerator experiments. These extrapolations result in alarge spread in the predictions of the various HEGs forthe muon production in air showers [5].
The hybrid nature of the Pierre Auger Observatory,combining both fluorescence telescopes (FD) [6] and sur-face detector array (SD) [7], provides an excellent experi-mental setup for testing and constraining models of high-energy hadronic interactions. Thousands of air showershave been collected which have a reconstructed energyestimator in both the SD and FD. The measurement ofthe longitudinal profile (LP) constrains the shower devel-opment and thus the signal predicted for the SD, at theindividual event level.
PRODUCTION OF SIMULATED EVENTS
In the present study, we compare the observed groundsignal of individual hybrid events to the ground signalof simulated showers with matching LPs. The datawe use for this study are the 411 hybrid events with1018.8 < E < 1019.2 eV recorded between 1 January 2004and 31 December 2012 and satisfying the event qualityselection cuts in [8, 9]. This energy range is sufficient tohave adequate statistics while being small enough thatthe primary cosmic ray mass composition does not evolvesignificantly.
For each event in this data set we generate Monte Carlo
0
5
10
15
20
0 200 400 600 800 1000 1200
dE/d
X [P
eV/g
/cm
2 ]
Depth [g/cm2]
Energy: 8.8 ± 0.5 EeVZenith: 34.7 ± 0.4o
Xmax: 697 ± 7 g/cm2χ2/d.o.f. (p): 0.75χ2/d.o.f. (Fe): 0.76
DataQII−04 Fe
QII−04 p
1
10
100
500 1000 1500 2000
S [V
EM]
Radius [m]
DataQII−04 Fe
QII−04 p
FIG. 1. Top: The measured longitudinal profile of a typicalair shower with two of its matching simulated air showers, fora proton and an iron primary, simulated using QGSJET-II-04. Bottom: The observed and simulated ground signals forthe same event.
(MC) simulated events with a matching LP, as follows:• Generate a set of showers with the same geometry andenergy, until 12 of them have an Xmax value within the1-σ reconstruction uncertainty of the real event.• Among those 12 generated showers select, based on theχ2-fit, the 3 which best reproduce the observed longitu-dinal profile (LP).• For each of those 3 showers do a full detector simu-lation and generate SD signals for comparison with thedata. We produce three simulated showers to adequately
The muon content of UHECR air showers observed by the Pierre Auger Observatory
The Pierre Auger Collaboration(Dated: January 17, 2014)
The hybrid events of the Pierre Auger Observatory are used to test the leading, LHC-tuned,hadronic interaction models. For each of 411 well-reconstructed hybrid events collected at theAuger Observatory with energy 1018.8
− 1019.2 eV, simulated events with a matching longitudinalprofile have been produced using QGSJET-II-04 and EPOS-LHC, for proton, He, N, and Fe pri-maries. The ground signals of simulated events have a factor 1.3-1.6 deficit of hadronically-producedmuons relative to observed showers, depending on which high energy event generator is used, andwhether the composition mix is chosen to reproduce the observed Xmax distribution or a pure protoncomposition is assumed. The analysis allows for a possible overall rescaling of the energy, howeverit proves not to be needed.
PACS numbers: Pierre Auger Observatory, ultra-high energy cosmic rays, muons, hadronic interactions
INTRODUCTION
The ground-level muonic component of ultra-high en-ergy (UHE) air showers is sensitive to hadronic parti-cle interactions at all stages in the air shower cascade,and to many properties of hadronic interactions suchas the multiplicity, elasticity, fraction of secondary pi-ons which are neutral, and the baryon-to-pion ratio [1].Air shower simulations rely upon hadronic event gener-ators (HEGs), such as QGSJET-II [2], EPOS [3], andSIBYLL [4]. The HEGs are tuned on accelerator exper-iments, but when applied to air showers they must beextrapolated to energies inaccessible to accelerators andto phase-space regions not well-covered by existing ac-celerator experiments. These extrapolations result in alarge spread in the predictions of the various HEGs forthe muon production in air showers [5].
The hybrid nature of the Pierre Auger Observatory,combining both fluorescence telescopes (FD) [6] and sur-face detector array (SD) [7], provides an excellent experi-mental setup for testing and constraining models of high-energy hadronic interactions. Thousands of air showershave been collected which have a reconstructed energyestimator in both the SD and FD. The measurement ofthe longitudinal profile (LP) constrains the shower devel-opment and thus the signal predicted for the SD, at theindividual event level.
PRODUCTION OF SIMULATED EVENTS
In the present study, we compare the observed groundsignal of individual hybrid events to the ground signalof simulated showers with matching LPs. The datawe use for this study are the 411 hybrid events with1018.8 < E < 1019.2 eV recorded between 1 January 2004and 31 December 2012 and satisfying the event qualityselection cuts in [8, 9]. This energy range is sufficient tohave adequate statistics while being small enough thatthe primary cosmic ray mass composition does not evolvesignificantly.
For each event in this data set we generate Monte Carlo
0
5
10
15
20
0 200 400 600 800 1000 1200
dE/d
X [P
eV/g
/cm
2 ]
Depth [g/cm2]
Energy: 8.8 ± 0.5 EeVZenith: 34.7 ± 0.4o
Xmax: 697 ± 7 g/cm2χ2/d.o.f. (p): 0.75χ2/d.o.f. (Fe): 0.76
DataQII−04 Fe
QII−04 p
1
10
100
500 1000 1500 2000S
[VEM
]Radius [m]
DataQII−04 Fe
QII−04 p
FIG. 1. Top: The measured longitudinal profile of a typicalair shower with two of its matching simulated air showers, fora proton and an iron primary, simulated using QGSJET-II-04. Bottom: The observed and simulated ground signals forthe same event.
(MC) simulated events with a matching LP, as follows:• Generate a set of showers with the same geometry andenergy, until 12 of them have an Xmax value within the1-σ reconstruction uncertainty of the real event.• Among those 12 generated showers select, based on theχ2-fit, the 3 which best reproduce the observed longitu-dinal profile (LP).• For each of those 3 showers do a full detector simu-lation and generate SD signals for comparison with thedata. We produce three simulated showers to adequately
Distance from core [m]
data
Ready to be submi?ed
p-assumpt.
Fe-assumpt.
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
•Clear observation of flux suppression
• Strongest existing bounds on EeV ν and γ• Strongest existing bounds on large scale anisotropies
• First hints on directional correlations to nearby matter
• Increasingly heavier composition above ankle
• pp cross section at ~10*ELHC, LIV-bounds, ...
•muon deficit in models at highest energies
• geophysics (elfes, solar physics, aerosols...)
Major Achievementsin the first 6 years of operation
41
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Science Goals of Auger Upgrade
43
1. Elucidate the origin of the flux suppression, i.e. GZK vs. maximum energy scenario- fundamental constraints on UHECR sources- galactic vs extragalactic origin- reliable prediction of GZK ν- and -γ fluxes
2. Search for a flux contribution of protons up to the highest energies at a level of ~ 10%- proton astronomy up to highest energies- prospects of future UHECR experiments
3. Study of extensive air showers and hadronic multiparticle production above √s=70 TeV- particle physics beyond man-made accelerators- derivation of constraints on new physics phenomena
measure composition intoflux suppression region...
... and do so event-by- event
do good muon counting}improve muon counting in surface detector array:factor of 10 in event statistics
]2 [g/cmmaxX600 700 800 900 1000
)m
axµ
(N10
log
8.4
8.5
8.6 p QGSjetII.04
He QGSjetII.04
N QGSjetII.04
Fe QGSjetII.04
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 2014
Nµmax vs Xmax
44
Xmax (g/cm2)
lg (N
µ )
p
FeN
He
E = 5·1019 eVQGSJet II.04
Muons may even outperform Xmax
at highest energies !
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201445
Five different realisations under test in the field • segmented tank • scintillators or RPCs beneath tanks or buried in ground • scintillators on top
muonic signals
EM signals
Selection will be done this summerbased on performance, reliability, readiness, cost, risk
Different Upgrade Options under StudyNeed to improve on em/mu separation in EAS
Karl-Heinz Kampert - Pierre Auger Observatory Mass 2014, Odense (Denmark), May 19-22, 201446
UHECRBoost in understanding UHECRs
Auger data ➙ change of paradigm at GZK energies:seem to see maximum energy of cosmic accelerator(s)
Precise data and modelling required!UHECR ⇔ LHC: mutual benefits
The True High-Energy Frontier of Physicsmost stringent tests on LIV, Space-Time Structure...
Upgrades of present observatories and
Preparation for Next Generation Observatories in Space and at Ground