Ultra-High Energy Cosmic Ray Ultra-High Energy Cosmic Ray Research with the Research with the

Pierre Auger ObservatoryPierre Auger Observatory

Methods, Results, What We Learn,Methods, Results, What We Learn,

and expansion to Coloradoand expansion to Colorado

Bill RobinsonBill Robinson

Mysteries of Ultra-High Energy Cosmic RaysMysteries of Ultra-High Energy Cosmic Rays

• What are they made of through the range of energies?

• What accelerates them?

• How energetic can they get?

• Why do we detect UHECRs that are too energetic to be allowed by current theory?

• Where do they come from? And why do different detectors get different results?

(S. Swordy, AUGER design report)

power law E-2.8Above knee:supernova remnant shocksBelow knee; where from?Upper limit;GZK cutoff atankle, mostenergetic yet3 E 20 eV or 300 EeV

[1 EeV = 10 E18,Exaelectron Volt]

(from http://www.mpi-hd.mpg.de/hfm/CosmicRay/Showers.html)

Simulated Longitudinal development of 50 1 EeV CascadesSimulated Longitudinal development of 50 1 EeV Cascades

M. Ambrosio et. al., Astroparticle Physics 24, 355-371 (2005).

Interaction Depth of shower maximum Interaction Depth of shower maximum (PAO ~ 850 g/cm^2; sea level = 1000 = interstellar space 10^8 LY)(PAO ~ 850 g/cm^2; sea level = 1000 = interstellar space 10^8 LY)

1 EeV Anisotropy from Akeno1 EeV Anisotropy from AkenoRatio of # of observed events to expected ones in equatorial coordinate. Solid line = Galactic Plane, G.C. is galactic center. Amplitude: ~ 4%

Galactic region of excess (Akeno)Galactic region of excess (Akeno)Ion gyroradius [cgs];

73.4 10 cmR eVZ

m = mass in proton unitsZ = ionizationE = energy in eV Galactic B = 3 microgauss

R for 1 EeV proton = ~300 pc

102 cmR EBZ

Anisotropies in HE Arrival DirectionAnisotropies in HE Arrival Direction

But there’s a lot of controversy about this…..

From the Japanese Akeno observatory, above 40 EeV, 1990—2002

ProblemsProblems• Shaded circles show clustering within 2.5 degrees;

chance probability of 0.9% for just one triple event• BUT this is not corroborated by other observatories;

when they show anisotropies they are in other directions• No sources in arrival directions away from galaxy*• Neutrons of 10 EeV have gamma ~ 10 E9, so a range of

about 10 kpc; galactic center within range. Immune to field deflections. No anisotropies below 10 E17.9

• Impossible to detect directly if neutrons are primaries• Only Akeno shows galactic center and Cygnus clustering• Extremely low flux and contradictory results are good

arguments for more observatories using multiple detection methods in different regions

• Have to separate gamma ray showers from nuclei

PAO fails to find excess…PAO fails to find excess…10 E17.9 < E < 10 E 18.5, 5 degree windows, GC at cross, line is galactic plane;2.3 years of Auger data, no abnormally over-dense regions, cannot resolve probable source at GC (must use gamma rays to investigate)

GZK Cutoff? (2003, pre-PAO)GZK Cutoff? (2003, pre-PAO)

arXiv:hep-ph/o206217 v5 27 Feb 2003, “Has the GZK suppression been discovered?”

PAO (south); near completionPAO (south); near completion

PAO Hybrid DetectorPAO Hybrid Detector

Lonesome Water Tank and the AndesLonesome Water Tank and the Andes

Fluorescence telescope enclosureFluorescence telescope enclosure

2

em em[MeV cm / g]2.2 N ( )E x dx

Energy loss in the shower; Energy loss in the shower;

Energy loss in the shower;UHECR Energy loss and calibration;UHECR Energy loss and calibration;

with Nem = particle density along shower

direction x, Nph = photons reaching fluorescence detector, R(x) = distance from shower point x and FD, T(x) = atmospheric transmission (<1)

Calibration with Lidar

2ph

em

( )( )

( )

N R xN x

T x

Night atmosphere assumed horizontallyInvariant; only steered through zenithangle, probes to 30 km tracing lossesto molecular and aerosol scattering. Requires clear moonless nights; 14% duty cycle.

Auger fluorescence telescopeAuger fluorescence telescope

Diameter: 2.2 metersAperture: 3.8 sq. m.440 photomultiplier tubesSchematic shows positions of diffusers for optical calibrations

Central Laser Facility (PAO South)Central Laser Facility (PAO South)

• UV laser (355 nm) fires 7 ns, 7 mJ pulse every 15 minutes to calibrate FDs; scattered luminosity approx. same as strong shower

• Located equidistant from 3 of the 4 FD eyes• Polarization randomized (better than circular)• Can fire in any direction• Weather checked by instruments every 5 minutes

PAO proposed initial Colorado sitePAO proposed initial Colorado site

(Middle of Nowhere)

ConclusionConclusion

• More detectors needed!

• Colorado site ideal; funding on order of $100 million; room for huge expansion

• Primary questions remain unresolved

• Existing PAO works both physically and politically as a model of international cooperation

ReferencesReferencesWebsites:History of the Air Fluorescence Technique, www.cosmic-ray.org/reading/fluor.htmlPierre Auger Observatory; www.auger.org and www.augernorth.orgAGASA; www-akeno.icrr.u-tokyo.ac.jp/AGASA/Interaction Depth

www.lbl.gov/abc/cosmic/SKliewer/Cosmic_Rays/Interaction.htm

Journals: M. Ambrosio et. al., Astroparticle Physics 24, 355-371 (2005). Pierre Auger Collaboration, arXiv:astro-ph 3, 0607382 (2006). N. Hayashitda et al., Astroparticle Physics 10, 310 (1999). J. Bahcall and Eli Waxman, arXiv:hep-ph 5, 0206217 (27 Feb 2003). A. Filipcic et. al., Astroparticle Physics 18, 502 (2003).Optical Relative Calibration for Auger Fluorescence Detector, and

Performance of the PAO Surface Array, Pune (2005) 00, 101-106The Central Laser Facility at the PAO, Subm. To Nucl. Inst. Meth. ‘06