Solving the Mystery of the Highest Energy Cosmic Rays : 1938 to 2007 cosmic rays: James W. Cronin Inaugural Conference: Institute for Gravitation and the Cosmos Aug 9, 2007 Penn State University
On the way to Solving the Mystery of the Highest Energy Cosmic Rays : 1938 to 2007 cosmic rays: James W. Cronin Inaugural Conference: Institute for Gravitation and the Cosmos Aug 9, 2007 Penn State University
Victor Hess
= 5 sec
Decoherence curve at the Jungfraujoch Auger and collaborators
Pierre Auger at the University of Chicago 1940
Following World War II cosmic ray research resumed with arrays of Geiger counters
Professor Zatsepin in the Pamir mountains
B. Rossi
Volcano Ranch J. Linsley st cosmic ray ~ eV
Two techniques: detect shower particles on the ground detect air fluorescence produced by shower particles
Utah Fly’s Eye Cassiday, Bergeson, Loh, Sokolsky et al.
Instruments for the study of the highest energy cosmic rays operation area exposure period km (m 2 sec sr) Volcano Ranch (?) Haverah Park SUGAR ~ ~2.6 Yakutsk Fly’s Eye (mono) HiRes ~ ~10 (mono) AGASA ~6.0 Auger (~0.8 yr opr.)
10 20 eV proton 16 joules energy Kinetic energy of Andy Roddick’s second serve But momentum of a snail Macroscopic energy in a microscopic particle No known astrophysical sources “seem” able to produce such enormous energies 1/ km 2 / century 3000 km 2 -> 30 events / year Simon Swordy University of Chicago
3 proton + cmb -> + nucleon
4
5
Portugal Netherlands
1438 deployed 1400 filled 1364 taking data ~ 85% All 4 fluorescence buildings complete, each with 6 telescopes 1st 4-fold on 20 May 2007 AIM: 1600 tanks HYBRID DETECTOR
GPS timing precision Cosmic Muon Calibration Surface Detector 7
The Fluorescence Detector 3.4 metre diameter segmented mirror 2.2m diameter aperture stop, corrector lens and optical filter. 440 pixel camera. 24 telescopes in 4 eyes
Can be ~ straight line, but 3 parameters in fit Arrival time at ground provided by the SD, removes degeneracy in the FD geometry fit HYBRID → PRECISE SHOWER GEOMETRY first step towards precise energy, depth of maximum
Arrival time at ground provided by the SD, removes degeneracy in the FD geometry fit HYBRID → PRECISE SHOWER GEOMETRY first step towards precise energy, depth of maximum Get T 0 from SD tank! Geometry uncertainties shrink! (= 90 o - Ψ)
A “perfect” hybrid event: few are as beautiful as this one ! Miguel Mostafa New Mexico/Utah
8 S1000 is Energy parameter
S 38 (1000) vs. E(FD) 387 hybrid events Nagano et al, FY used 4 x eV
JSJS Auger Spectrum 2007 E -2.6 Three spectra combined weighting statistical error in each energy bin. Low energy from Hybrid observation, High energy from SD. ‘ankle’ and ‘steepening’ seen in (nearly) model and mass-independent measurement.
6 sigma deficit from power-law assumption
photons protons Fe Data Energy X max How we try to infer the variation of mass with energy
Elongation Rate measured over two decades of energy Fluctuations in X max to be exploited
Large number of events allows good control and understanding of systematics
Photon limit
Conclusions We are at the point where we have some confidence that the angles and energies of the highest energy cosmic rays can be measured accurately. Good progress is being made for statistical determination of the composition. It remains to make a connection with the cosmic accelerators. This requires patience and the benevolence of Nature.