VHE cosmic rays: experimental Cosmic Rays History 1912: First discovered 1927: First seen in cloud chambers 1962: First 10 20 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 1
Cosmic Ray Spectrum Flux follows power law E - 2.7 below knee E - 3.2 below ankle Energies up to 10 21 ev Cosmic Rays at the surface Mostly muons Average energy 3 GeV Integrated Flux 1 per cm 2 per minute for a horizontal detector Ultra High Energy Cosmic Rays Cosmic rays at the highest energy have galacc or even extra- galacc 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? 2
Exercise Consider a high energy proton interacon 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 reacon to occur: p + γ Δ + ( p + π 0 ) Masses: p: 938 MeV, Δ: 1232 MeV =M, π 0 : 135 MeV Hint: P 2 = M 2 (P = 4- vector), Lorentz invariant Assume head- on collisions If the CMB photon density is 420/cm 3, and the cross secon 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: E peak = 1.2 mev Mean free path 3
GZK Cutoff Auger Large mean free path Transparency of the Universe Nearest Galaxies Nearest Stars 1.5 Mly Nearest Galaxy Clusters Milky Way 15 ly 500 Mly 8 4
E α B R Cosmic rays flux vs. Energy (nearly) uniform power-law spectrum spanning 10 orders of magnitude in E and 32 in flux! structures : ~ 3 5 10 15 ev: knee change of source? new physics? ~ 3 10 18 ev: ankle transition galactic extragalatic? change in composition? S. Swordy UHECR one parcle per century per km 2 many interesng quesons 5
Questions How cosmic rays are accelerated at E >10 19 ev? What are the sources? How can they propagate along astronomical distances at such high energies? Are they substanally deflected by magnec fields? Can we do cosmic ray astronomy? What is the mass composion of cosmic rays? Detection techniques Parcles at ground level large detector arrays (scinllators, water Cherenkov tanks, etc) detects a small sample of secondary parcles (lateral profile) 100% duty cicle aperture: area of array (independent of energy) results on primary energy and mass composion are model dependent (rely on Monte Carlo simulaons based on extrapolaons of the hadronic models constrained at low energies by accelerator physics) ex: AGASA 6
Detection techniques Fluorescence of N 2 in the atmosphere calorimetric energy measurement as funcon of atmospheric depth only for E > 10 17 ev only for dark nights (10% duty cicle) requires good knowledge of atmospheric condions 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 calibraon from the fluorescence detector to the event gathering power of the surface array. A complementary set of mass sensive shower parameters contributes to the idenficaon of primary composion. Different measurement techniques force understanding of systemac uncertaines in each. 7
Locaon of the Auger experiment Pierre Auger South Observatory 3000 km 2 4 fluorescence buildings, each with 6 telescopes 1st 4- fold on 20 May 2007 1600 tanks HYBRID DETECTOR 8
A surface array staon Communicaons antenna GPS antenna Electronics enclosure Solar panels Baery box 3 photomulplier tubes looking into the water collect light le by the parcles Plasc tank with 12 tons of very pure water The fluorescence detector Los Leones telescope 9
The fluorescence telescope 30 deg x 30 deg view per telescope First 4-fold hybrid on 20 May 2007 First hybrid qudriple event! Signal in all four FD detectors and 15 SD stations! 20 May 2007 E ~ 10 19 ev 10
θ~ 48º, ~ 70 EeV 18 detectors triggered Typical flash ADC trace at about 2 km Detector signal (VEM) vs me (µs) PMT 1 PMT 2 PMT 3 Lateral density distribuon Flash ADC traces Flash ADC traces - 0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 µs Hybrid Event longitudinal profile 11
Inclined Events offer addional aperture θ = 79 Energy spectrum from Auger Observatory Based on fluorescence and surface detector data Model- and mass- independent energy spectrum Power of the stascs and well- defined exposure of the surface detector Hybrid data confirm that SD event trigger is fully efficient above 3x10 18 ev for θ<60 o Uses energy scale of the fluorescence detector (nearly calorimetric, model independent energy measurement) to calibrate the SD energy. 12
Energy calibration SD parameter S1000: interpolated tank signal at 1000 meters from the lateral distribuon funcon Determined for each SD event It is proporonal to the primary energy 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 13
Energy spectra from Auger The agreement between the spectra derived using three different methods is good 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? 14
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 fluctuaons They reach their maximum development higher in the atmosphere (lower cumulated grammage, X max ) X max is increasing with energy (more energec showers can develop longer before being quenched by atmospheric losses) Composition from hybrid data X max resolution ~ 20 g/cm 2 15
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 Lateral distribuon funcon Longitudinal profile Assumpon: universality of the electromagnec shower evoluon 16
Cosmic Rays Cosmic Rays and LHC accelerators satellites, balloons air shower arrays Auger 17
Cosmic Rays and LHC accelerators LHC provides a significant lever arm providing constraints for UHECR simulations! Current models tuned here satellites, balloons air shower arrays Auger Small- x region (LHC as a pathfinder for CR, and vice- versa) $ $ η = ln tan ϑ '' & & )) % % 2 (( LHC detectors cover all wide rapidity range EAS models bracket accelerator data no model perfect, but EAS models seem to do beer than HEP models HEP High Energy Physics models EAS Extensive Air Shower models (Spiering) 18
Cross secons: something not understood in Auger Shower Maximum X max (Pimenta) These suggest high cross secon and high mulplicity at high energy. Heavy nuclei? Or protons interacng differently than expected? Informaon lacking for the EHE (anisotropic?) energy regime! 37 Cosmic Rays and LHC: total cross secon pp inel. cross section at sqrt(s)=57 TeV (Proton-Proton) [mb] σ inel 110 100 90 80 70 60 50 40 30 Auger 2012 (Glauber) ATLAS 2011 CMS 2011 ALICE 2011 TOTEM 2011 UA5 CDF/E710 3 10 10 [GeV] Test Glauber model Tune EAS simulaons s 4 QGSJet01 QGSJetII.3 Sibyll2.1 Epos1.99 Pythia 6.115 Phojet 5 10 If protons, the X- secon rises at ~100 TeV => A new physics scale? 19
Extreme muon mulplicies High- mulplicity cosmic event in ALICE à Density of ~18 muons/m 2 (within the TPC volume) Similar enigmas in underground experiments Muon numbers in EAS about 50-100% higher than MC predicons N 19 ~ N µ ` Auger à Upgrade EAS experiments with muon counters photon limits A = Agasa HP = Haverah Park Y = Yakutsk 20
Direct hints of cosmic accelerators? E 1!PeV B 1!µG R 1!pc E!! 1!PeV 0.2 B 1!G R 1!AU B R E (ev) IGM 10-4 µg ISM 3 x 1 µg 100 kpc SNR 30 µg 1 pc 3 x 10 16 SMBH 300 µg 10 4 pc > 10 21 GRB 10 9 G 10-3 AU 0.2 x 10 21 41 Angular resolution Surface detector Hybrid data: better angular resolution, ~ 0.7 o @ 68% c.l. in the EeV energy range Events with E > 10 EeV : 6 or more SD stations 21
Galactic center Galacc Center is a natural site for cosmic ray acceleraon 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 Significance (σ) 20 o scales ( δ, α) = ( 15,280 ) 10 18 10 18.4 ev observed expected = 506 413.6 ( + 4.5σ ) 22% excess Cuts are a posteriori Chance probability is not well defined N. Hayashida et al., Astroparcle Phys. 10 (1999) 303 22
Source at Galactic center 5.5 o cone ( δ, α) = ( 22,274 ) 10 18 10 18.4 ev observed expected = 21.8 11.8 ( + 2.9σ ) 85% excess J.A. Bellido et al., Astroparcle Phys. 15 (2001) 167 results for the galactic center test of AGASA: obs/exp = 2116/2159.5 R = 0.98 ± 0.02 ± 0.01 NOT CONFIRMED (with 3x more stats) SUGAR G.P. AGASA 5, top-hat test of SUGAR: obs/exp = 286/289.7 R = 0.98 ± 0.06 ± 0.01 NOT CONFIRMED (with 10x more stats) Galacc 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: Galacc Plane: Φ s < 0.08 NO ξ SIGNIFICANT km - 2 yr - 1 at EXCESS 95% C.L. astro-ph/0607382 (Astropart. Phys., 2007) (check proceedings ICRC 07 for an update) 23
Overdensity search (galactic center) 1 EeV < E <10 EeV 0.1 EeV < E < 1 EeV significance Li, Ma ApJ 272, 317-324 (1983) All distribuons consistent with isotropy 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 distribuon of nearby sources? Chance probability of such a signal from an isotropic flux ~ 2% (marginally significant) 24
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) 27 events as of November 2007 84 events now; 28 correlate with AGN Correlation significant only around CenA Orphan flares in TeV band (?) The producon region of gammas from flares in M87 is accompanied by radio acvity 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(10 9 SM) might explain CR up to O(10 23 ev) 49 One should be careful about astrophysics with CR Auger observaons confirm the GZK cutoff E!! 1!EeV B 1!µG R 1!kpc Role of magnec fields Galacc astrophysics impossible (B MW ~1µG) Extragalacc astrophysics very difficult: Angular spread Anisotropy 50 25
other physics topics to be explored Neutrinos Gamma ray burst detecon Measurement of the primary cosmic ray cross secon; and many others... Conclusions, perspectives The EHE CR physics is substanally dominated by the Auger experiment No significant correlaon of EHE CR with known sources (apart CenA) Marginal direcon correlaon with CenA Hadronic models validated Something strange might happen around 10^20 ev; change of composion does not seem enough to explain it 26