Absolute Measurement of Air Fluorescence Yield for Ultra-

High Energy Cosmic Rays

Paolo Privitera

Carlos Hojvat

Fermilab, June 27 2008

FD

SD

Auger results

Flux suppression

Anisotropy < 75 Mpc

Astrophysical interpretation GZK horizon

Auger Energy Calibration

Lateral density distribution

Fluorescence Detector

Surface Detector

The largest systematic uncertainty is the air fluorescence yield (15%)

The Auger energy scale is based on the FD calorimetric energy.

10 km

The Auger hybrid detector concept

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 20

FD

SD

AIRFLY measurements

391.4 nm337.1 nm

353.7 nmrelative band intensities

Temperature and humidity dependence

Pressure dependence

Chemistry Division Van de Graaf (0.6-3 MeV)

Advanced Photon Source (6-30 KeV)

HEP Division Advanced Wakefield Accelerator

(3 MeV-15 MeV)

AIRFLY beams

Beam Test Facility at DANE INFN FRASCATI (50-750 MeV)

ARGONNEANL

Collaboration: Cezch Republic, Germany, Italy, US

Chamber

Gas system

Vacuum pump

Lead shielding support

BTF (Frascati)

Argonne Chemistry VdG

Absolute Fluorescence Yield at the Fermilab Meson Test Beam

Goal: ≤ 5% uncertainty with the fluorescence/Cherenkov ratio method

Photon Detector

Particle beam

Fluorescence photons

Cherenkov photons

Photon Detector

Particle beam

45° mirror

(a) (b)

337 nm filter

Q.E uncertainty >10% Normalize to known yield: Q.E cancels

Tested at Frascati and Argonne

Absolute Fluorescence Yield at the Fermilab Meson Test Beam

Fluorescence/Cherenkov ratio method + independent laser calibration

• Low intensity: Integrating sphere, Ultra Bialkali PMTs (43% QE)

Particle beam

Photon Detector

Integrating sphere

Diffuser to be placed for Cherenkov run

Cherenkovdump

Acceptance counter

Veto counter

• High energy (reduce multiple scattering, air as Cherenkov Radiatior)

• Well defined beam: single particle trigger and geometry

• Wide range of particles type and intensity

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

Air fluorescence spectrum

• Argonne 3 MeV electron VdG, DC beam, 10 μA• Spectrograph instead of monochromator:Insensitive to changes of beam intensity or position

VdG Beam

Sphericalmirror

Optical fiber

L.O.T. Oriel MS257 = 0.1 nm

Andor CCD DV 420

Chamber

Gas system

Vacuum pump

Lead shielding support

BTF (Frascati)

HPD