Fluorescence from Air in Showers (FLASH) J. Belz 1, Z. Cao 2, P. Chen 3*, C. Field 3, P. Huentemeyer 2, W-Y. P. Hwang 4, R. Iverson 3, C.C.H. Jui 2, T. Kamae 3, G.-L. Lin 4, E.C. Loh 2, K. Martens 2, J.N. Matthews 2, W.R. Nelson 3, J.S.T. Ng 3, A. Odian 3, K. Reil 3, J.D. Smith 2, P. Sokolsky 2*, R.W. Springer 2, S.B. Thomas 2, G.B. Thomson 5, D. Walz 3 1 University of Montana, Missoula, Montana 2 University of Utah, Salt Lake City, Utah 3 Stanford Linear Accelerator Center, Stanford University, CA 4 Center for Cosmology and Particle Astrophysics (CosPA), Taiwan 5 Rutgers University, Piscataway, New Jersey * Collaboration Spokespersons Proposal E-165

Cosmic Rays have been observed with energies at up to ~10 20 eV: The flux (events per unit area per unit time) follows roughly a power law ~E -3 Changes of power-law index at “knee” and “ankle”. Onset of different origins/compositions? Where does the spectrum stop?

Discrepancy Between Two UHECR Experiments AGASA HiRes AGASA

UHECR From Source to Detector CMB γ

Greisen-Kuzmin-Zatsepin (GZK) Cut-off (protons) 3×10 20 eV 50 Mpc ~ Size of local cluster Protons above 6×10 19 eV will loose sizable energy through CMB Super-GZK events have been found with no identifiable local sources

Extensive Air Showers Zoom on next slide

Extensive Air Shower Development êHadronic shower initiated by primary  Electromagnetic Shower produced by γ’s from  0 decays…

Observation of Cosmic Ray with Fluorescence Technique The two detector sites are located 12 km apart Geometry of an air shower is determined by triangulation. Energy of primary cosmic ray calculated from amount of light collected.

Other Proposed Fluorescence Experiments Carlos Escobar (Campinas, Italy) Andrea Santangelo (Palermo, Italy) - Lab. measurements induced by hard-x-ray photons Paolo Privitera (Rome, Italy) - similar approach to Kakimoto and Nagano Hans Klages (Karlsruhe, Germany) - Karlsruhe activities on Air Shower Light Pierre Colin (LAPP, France) - MacFLY Photons Philippe Gorodetzky (College de France) - Measurements planned at CERN

UNIQUE LABORATORY ASTROPHYSICS OPPORTUNITY High intensity e - /e + beams ultra-fast (< 50 fsec), high energy (~30GeV/e) ultra-high intensity (~ W/cm 2 ) very high repetition rate (10 Hz) High fluence photon beams 1. X-ray from undulator (~ 10 9 γ/pulse at 1.5 Å) 2. Terawatt laser (at ~ 1 μm) 3. Gamma-ray (up to ~ 15 GeV) through laser-particle beam Compton- backscattering * Experiments can be performed with different combinations of these beams

MEASURING FLUORESCENCE AT SLAC Extensive Air Showers (EAS) are predominantly a superposition of EM sub- showers. Important N 2 transition (2P) not accessible by proton excitation; only e-beam can do it. FFTB beam-line provides energy equivalent showers from ~10 15 to ~10 20 eV. – electrons/pulse at 28.5 GeV. –2% of electron pulse bremsstrahlung option.

FLASH useful for future UHECR Experiments Ground-Based: The Pierre Auger Observatory Hybrid detection 1600 Cherenkov detectors 1.5 km grid in 3000 km 2 4 fluorescence eyes – Comparable to HiRes 65 km

è Space-Based: EUSO, OWL/AirWatch