vhe cosmic rays: experimental - uniuddeangeli/fismod/cosmiche.pdf · 11/5/13 1 vhe cosmic rays:...
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VHE cosmic rays: experimental
Cosmic Rays
History – 1912: First discovered – 1927: First seen in cloud chambers – 1962: First 1020 eV cosmic ray seen
Low energy cosmic rays from Sun – Solar wind (mainly protons) – Neutrinos
High energy particles from sun, galaxy and perhaps beyond – Primary: Astronomical sources. – Secondary: Interstellar Gas. – Neutrinos pass through atmosphere and earth – Low energy charged particles trapped in Van Allen Belt – High energy particles interact in atmosphere. – Flux at ground level mainly muons
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Cosmic Ray Spectrum
Flux follows power law – E-‐2.7 below knee – E-‐3.2 below ankle
Energies up to 1021 eV
Cosmic Rays at the surface – Mostly muons – Average energy 3 GeV – Integrated Flux 1 per cm2 per minute for a horizontal detector
Ultra High Energy Cosmic Rays
Cosmic rays at the highest energy have galac�c or even extra-‐galac�c origin
The universe is filled with the cosmic microwave background. Remnant of the Big Bang
Photon temperature ~2.7K
Do you believe this result from the AGASA experiment?
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Exercise
Consider a high energy proton interac�on with a photon of the cosmic microwave background. These photons are in thermal equilibrium with T~2.7 K. Find the minimum energy the proton would need for the following reac�on to occur:
p + γ → Δ+ (→ p + π0) Masses: p: 938 MeV, Δ: 1232 MeV =M, π0: 135 MeV Hint: P2 = M2 (P = 4-‐vector), Lorentz invariant Assume head-‐on collisions If the CMB photon density is 420/cm3, and the cross sec�on of the process is 0.6 mb, compute the mean free path.
Taking as a central value for the temperature of the Universe T = 2.7 K, by applying Wien’s one can obtain the peak value for the wavelength, and then and for the energy: Epeak = 1.2 meV
Mean free path
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GZK Cutoff Auger
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Large mean free path… Transparency of the Universe
15 ly
1.5 Mly
500 Mly
Nearest Stars
Nearest Galaxies
Nearest Galaxy Clusters
Milky Way
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E α B R
S. Swordy
Cosmic rays flux vs. Energy
UHECR • one par�cle per century per km2
• many interes�ng ques�ons
(nearly) uniform power-law spectrum spanning 10 orders of magnitude in E and 32 in flux!
structures : ~ 3 – 5 1015 eV: knee change of source? new physics? ~ 3 1018 eV: ankle transition galactic – extragalatic? change in composition?
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Questions
How cosmic rays are accelerated at ? What are the sources? How can they propagate along astronomical distances at such high energies? Are they substan�ally deflected by magne�c fields? Can we do cosmic ray astronomy? What is the mass composi�on of cosmic rays?
eV 1019>E
Detection techniques
Par�cles at ground level • large detector arrays (scin�llators, water Cherenkov tanks, etc) • detects a small sample of secondary par�cles (lateral profile) • 100% duty cicle • aperture: area of array (independent of energy) • results on primary energy and mass composi�on are model dependent (rely on Monte Carlo simula�ons based on extrapola�ons of the hadronic models constrained at low energies by accelerator physics)
ex: AGASA
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Detection techniques
Fluorescence of N2 in the atmosphere • calorimetric energy measurement as func�on of atmospheric depth • only for E > 1017 eV • only for dark nights (10% duty cicle) • requires good knowledge of atmospheric condi�ons • aperture grows with energy, varies with atmosphere
ex: HiRes
The Auger Observatory: Hybrid design A large surface detector array combined with fluorescence detectors results in a unique and powerful design.
Simultaneous shower measurement allows for transfer of the nearly calorimetric energy calibra�on from the fluorescence detector to the event gathering power of the surface array.
A complementary set of mass sensi�ve shower parameters contributes to the iden�fica�on of primary composi�on.
Different measurement techniques force understanding of systema�c uncertain�es in each.
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Loca�on of the Auger experiment
4 fluorescence buildings, each with 6 telescopes 1st 4-‐fold on 20 May 2007 1600 tanks
HYBRID DETECTOR
Pierre Auger South Observatory 3000 km2
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A surface array sta�on
Communica�ons antenna GPS antenna
Electronics enclosure Solar panels
Ba�ery box
3 photomul�plier tubes looking into the water collect light le� by the
par�cles
Plas�c tank with 12 tons of very pure water
The fluorescence detector
Los Leones telescope
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The fluorescence telescope
30 deg x 30 deg view per telescope
20 May 2007 E ~ 1019 eV
First hybrid qudriple event!
Signal in all four FD detectors and 15 SD stations!
First 4-fold hybrid on 20 May 2007
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θ~ 48º, ~ 70 EeV
Flash ADC traces Flash ADC traces
Lateral density distribu�on
Typical flash ADC trace
at about 2 km
Detector signal (VEM) vs �me (µs)
PMT 1
PMT 2
PMT 3
-‐0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 µs
18 detectors triggered
Hybrid Event
longitudinal profile
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θθ = 79 °
Inclined Events offer addi�onal aperture
Energy spectrum from Auger Observatory
Based on fluorescence and surface detector data Model-‐ and mass-‐independent energy spectrum Power of the sta�s�cs and well-‐defined exposure of the surface detector
Hybrid data confirm that SD event trigger is fully efficient above 3x1018 eV for θ<60o
Uses energy scale of the fluorescence detector (nearly calorimetric, model independent energy measurement) to calibrate the SD energy.
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SD parameter S1000: interpolated tank signal at 1000 meters from the lateral distribu�on func�on Determined for each SD event It is propor�onal to the primary energy
Energy calibration
Reduced measurement uncertainty (shower fluctuations dominate) VEM = vertical equivalent muons from self calibration of the tank signal (from
ambient muons)
Energy calibration
Fractional difference between the SD and FD energy for the hybrid events;
Small relative dispersion includes uncertainties in both the FD
energy and the SD signal
S(1000) is intrinsecally a very good energy estimator Reliable energy measurements
when properly calibrated
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The agreement between the spectra derived using three different methods is good
Energy spectra from Auger
Astrophysical models and the Auger spectrum
models assume: an injection spectral index, an exponential cutoff at an energy of Emax times the charge of the nucleus, and a mass composition at the acceleration site as well as a distribution of sources.
Auger data: sharp suppression in the spectrum with a high confidence level!
Expected GZK effect or a limit in the acceleration process?
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Composition from hybrid data
UHECR: observatories detect induced showers in the atmosphere
Nature of primary: look for diferences in the shower development
Showers from heavier nuclei develop earlier in the atm with smaller fluctua�ons – They reach their maximum development
higher in the atmosphere (lower cumulated grammage, Xmax )
Xmax is increasing with energy (more energe�c showers can develop longer before being quenched by atmospheric losses)
Composition from hybrid data
Xmax resolution ~ 20 g/cm2
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composition from hybrid data
The results of all three experiments are compatible within their systematic uncertainties. The statistical precision of Auger data exceeds that of preceding experiments
test of hadronic models
Assump�on: universality of the electromagne�c shower evolu�on
Lateral distribu�on func�on
Longitudinal profile
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Cosmic Rays
Cosmic Rays and LHC
accelerators
satellites, balloons
air shower arrays Auger
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Cosmic Rays and LHC
accelerators Current models tuned here
LHC provides a significant lever arm providing constraints for UHECR simulations !
satellites, balloons
air shower arrays Auger
§ LHC detectors cover all wide rapidity range
§ EAS models bracket accelerator data § no model perfect, but EAS models seem to do be�er than HEP
models
§ HEP High Energy Physics
models
§ EAS Extensive Air Shower
models
Small-‐x region (LHC as a pathfinder for CR, and vice-‐versa)
(Spiering)
η = ln tan ϑ2$
% &
'
( )
$
% &
'
( )
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Cross sec�ons: something not understood in Auger
Shower Maximum Xmax
These suggest high cross sec�on and high mul�plicity at high energy.
Heavy nuclei?
Or protons interac�ng differently than expected?
Informa�on lacking for the EHE (anisotropic?) energy regime!
(Pimenta)
Cosmic Rays and LHC: total cross sec�on
§ Test Glauber model § Tune EAS simula�ons
(Pro
ton-
Prot
on)
[m
b]in
elσ
30
40
50
60
70
80
90
100
110
[GeV]s310 410 510
ATLAS 2011
CMS 2011
ALICE 2011
TOTEM 2011
UA5
CDF/E710
Auger 2012 (Glauber)
QGSJet01
QGSJetII.3
Sibyll2.1
Epos1.99
Pythia 6.115
Phojet
pp inel. cross section at sqrt(s)=57 TeV
If protons, the X-‐sec�on rises at ~100 TeV => A new physics scale?
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§ High-‐mul�plicity cosmic event in ALICE à § Density of ~18 muons/m2 (within the TPC volume)
§ Similar enigmas in underground experiments § Muon numbers in EAS about 50-‐100% higher than MC
predic�ons
§ `
§ à Upgrade EAS experiments with muon counters
Auger
Extreme muon mul�plici�es
N19 ~ Nµ
photon limits
A = Agasa HP = Haverah Park Y = Yakutsk
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Direct hints of cosmic accelerators?
B R E (eV) IGM 10-‐4 µG ISM 3 x 1 µG 100 kpc SNR 30 µG 1 pc 3 x 1016
SMBH 300 µG 104 pc > 1021 GRB 109 G 10-‐3 AU 0.2 x 1021
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!!
E1!PeV
≅B
1!µG×
R1!pc
E1!PeV
≅ 0.2 B1!G
×R
1!AU
Angular resolution Surface detector
Hybrid data: better angular resolution, ~ 0.7o @ 68% c.l. in the EeV energy range
Events with E > 10 EeV : 6 or more SD stations
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Galactic center
Galac�c Center is a “natural” site for cosmic ray accelera�on – Supermassive black hole – Dense clusters of stars – Stellar remnants – SNR (?) Sgr A East
excess should be consistent with a point source
Chandra
Source at the Galactic center AGASA
)4.5( 6.413
506expectedobserved
σ+=
20o scales
1018 – 1018.4 eV
N. Hayashida et al., Astropar�cle Phys. 10 (1999) 303
Significance (σ)
• Cuts are a posteriori • Chance probability is not well defined
22% excess
)280,15(),( °°−=αδ
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Source at Galactic center
J.A. Bellido et al., Astropar�cle Phys. 15 (2001) 167
)2.9( 8.118.21
expectedobserved
σ+=
85% excess
1018 – 1018.4 eV
5.5o cone )274,22(),( °°−=αδ
§ test of AGASA: obs/exp = 2116/2159.5 R = 0.98 ± 0.02 ± 0.01
NOT CONFIRMED (with 3x more stats) § test of SUGAR: obs/exp = 286/289.7
R = 0.98 ± 0.06 ± 0.01 NOT CONFIRMED (with 10x more stats) § Galac�c Center as a point source (σ=1.5°): obs/exp = 53.8/45.8 R = 1.17 ± 0.10 ± 0.01 NO SIGNIFICANT EXCESS § upper limit on the flux of neutrons coming from GC: § Galac�c Plane: NO SIGNIFICANT EXCESS
astro-ph/0607382 (Astropart. Phys., 2007)
Φs < 0.08 ξ km-‐2 yr-‐1 at 95% C.L.
5°, top-hat AGASA SUGAR
G.P.
results for the galactic center
(check proceedings ICRC 07 for an update)
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Overdensity search (galactic center)
Li, Ma ApJ 272, 317-‐324 (1983)
significance
All distribu�ons consistent with isotropy
1 EeV < E <10 EeV
0.1 EeV < E < 1 EeV
anisotropy searches
All-‐sky blind searches for sources: NO EXCESS FOUND Angular coincidences between Auger events and BL Lac objects (as possibly seen by HiRes): see later;
Search for clustering (as seen by AGASA), 1 significant excess observed (Cen A)
Scan in angle and energy: hints of clustering at larger energies and intermediate angular scales – Large scale distribu�on of nearby sources? – Chance probability of such a signal from an isotropic flux ~ 2% (marginally
significant)
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Origin of EHE: the 2007 evidence for the emission of EHE hadrons by AGN almost disappeared (apart from CenA)
The “direct” measurement by AUGER (E > 60 EeV)
Orphan flares in TeV band (?) The produc�on region of gammas from flares in M87 is accompanied by radio ac�vity very close to the BH, where there is abundance of protons – If SNRs O(10 SM) can explain CR at O(1 PeV), BH O(109 SM) “might” explain CR up to O(1023 eV)
27 events as of November 2007 84 events now; 28 correlate with AGN
Correlation significant only around CenA
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One should be careful about astrophysics with CR …
Auger observa�ons confirm
the GZK cutoff
Role of magne�c fields
– Galac�c astrophysics impossible (BMW~1µG)
– Extragalac�c astrophysics very difficult:
Anisotropy
Angular spread
!!
E1!EeV
≅B
1!µG×
R1!kpc
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other physics topics to be explored
Neutrinos Gamma ray burst detec�on Measurement of the primary cosmic ray cross sec�on; and many others ...
Conclusions, perspectives
The EHE CR physics is substan�ally dominated by the Auger experiment No significant correla�on of EHE CR with known sources (apart CenA) Marginal direc�on correla�on with CenA
Hadronic models validated
Something strange might happen around 10^20 eV; change of composi�on does not seem enough to explain it