Absolute Measurement of Air Fluorescence Yield for Ultra-High Energy Cosmic Rays

1. Fermilab, June 27 2008 Absolute Measurement of Air Fluorescence Yield for Ultra-High Energy Cosmic Rays Paolo Privitera Carlos Hojvat FD SD

2. Auger results Flux suppression Anisotropy < 75 Mpc Astrophysical interpretation GZK horizon

3. Lateral density distribution Auger Energy Calibration Surface Detector The Auger energy scale is based on the FD calorimetric energy. Fluorescence Detector The largest systematic uncertainty is the air fluorescence yield (15%) 10 km

4. 300-400 nm light from de-excitation of atmospheric nitrogen (fluorescence light) • ≈ 4 γ’s / m /electron • 1019 eV 1010 e • Light attenuation in the atmosphere; showers develop in 15 km • Fluorescence spectrum • Dependence on pressure, temperature and humidity • Absolute yield The Auger hybrid detector concept FD SD 20

5. relative band intensities 353.7 nm AIRFLY measurements Pressure dependence 391.4 nm 337.1 nm Temperature and humidity dependence

6. AIRFLY beams Collaboration: Cezch Republic, Germany, Italy, US Beam Test Facility at DAFNE INFN FRASCATI (50-750 MeV) Chemistry Division Van de Graaf (0.6-3 MeV) HEP Division Advanced Wakefield Accelerator (3 MeV-15 MeV) ARGONNE ANL Advanced Photon Source (6-30 KeV)

7. Chamber Lead shielding support Gas system Vacuum pump BTF (Frascati) Argonne Chemistry VdG

8. Fluorescence photons Cherenkov photons Absolute Fluorescence Yield at the Fermilab Meson Test Beam Goal: ≤ 5% uncertainty with the fluorescence/Cherenkov ratio method Tested at Frascati and Argonne 337 nm filter Photon Detector Photon Detector 45° mirror Q.E uncertainty >10% Particle beam Particle beam Normalize to known yield: Q.E cancels (a) (b)

9. Absolute Fluorescence Yield at the Fermilab Meson Test Beam Fluorescence/Cherenkov ratio method + independent laser calibration • High energy (reduce multiple scattering, air as Cherenkov Radiatior) • Well defined beam: single particle trigger and geometry • Wide range of particles type and intensity Integrating sphere Photon Detector Diffuser to be placed for Cherenkov run • Low intensity: Integrating sphere, Ultra Bialkali PMTs (43% QE) Cherenkov dump Acceptance counter Veto counter Particle beam

10. Collaborative Initiative Grant Crucial measurement for Auger (South and North); will have a strong impact in the Auger scientific results and in the UHECR field Use of Fermilab facility: Meson Test Beam University of Chicago and Fermilab have a long history of collaboration in Auger; Auger design Workshop held at Fermilab in 1995 Collaboration well matched for the success of the initiative P. Privitera (Chicago), C. Hojvat (Fermilab), H. Spinka (Argonne), AIRFLY collaborators Some hardware from AIRFLY Funds: 1 postdoc (100% FTE), hardware for new chamber 2 years proposal Tank n. 1600

11. Spherical mirror L.O.T. Oriel MS257 Dl = 0.1 nm Andor CCD DV 420 VdG Beam Optical fiber Air fluorescence spectrum • Argonne 3 MeV electron VdG, DC beam, 10 μA • Spectrograph instead of monochromator: • Insensitive to changes of beam intensity or position

12. Chamber Lead shielding support Gas system Vacuum pump HPD BTF (Frascati)