Status of AIRFLY fluorescence yield measurements Paolo Privitera Università di Roma Tor Vergata, INFN Prague, May 19, 2006

The AIRFLY experiment Rome, Aquila, Frascati, Karlsruhe, Munich, Prague, Olomuc, Argonne, Chicago Precise measurement of the fluorescence yield (< 10%) over a wide energy range (keV to GeV). Measurement of the pressure, temperature and humidity dependence of the fluorescence spectrum. Beam Test Facility at the Laboratori Nazionali di Frascati (2004), Argonne Accelerator Facilities ( )

AIRFLY at Argonne Chemistry Division Van de Graaf (0.6-3 MeV) Advanced Photon Source (6-30 KeV) HEP Division Advanced Wakefield Accelerator (3 MeV-15 MeV)

Measurement of the pressure dependence of the fluorescence spectrum Precise measurement of p’ at 337 nm with PMT (AWA) Pressure dependence of the spectrum with spectrophotometer. p’(line) from Signal(line)/Signal(337) vs pressure (Van der Graaf, 3 MeV, 10 μA DC beam)

Pressure dependence of the 337 nm line Contamination from closeby lines only 1.7% of 2P(0,0) Nitrogen 180 hPa Bkg. AWA running mode with large fluctuations of beam charge: accurate slope measurement (no dependence on pedestal shifts). Small bkg.!

Pressure dependence of the 337 nm line Argon has negligible contribution to quenching Nitrogen/air Signal ratio Bias from secondary electrons escaping the field of view is eliminated p’(air) = ±0.33 hPa (stat. unc.) P’(N) = 103.6±2.7 hPa (stat. unc.)

Pressure dependence of the spectrum Beam Spectrometer Spherical mirror Optical fiber

Spectrum lines Integral of line (some contamination expected)

Spectrum lines

p’ of different spectrum “lines” 1% Argon air 2P(0,1)2P(1,0)

p’ of different spectrum “lines” 1% Argon air 1N(0,0)

p’ of different spectrum “lines” 1% Argon air 2P(0,i) 2P(1,i) 2P(2,i) 2P(3,i) 1N(0,i) Within each band p’ values are consistent

air no Argon p’ of different spectrum “lines”

1% Argon air 2P(0,i) 2P(1,i) 2P(2,i) 2P(3,i) 1N(0,i) Stability: 4 independent scans (different day, gas, beam)

Relative spectrum “lines” intensities Spectrometer calibration is not necessary for the p’ measurements, but it is needed for the relative intensities. Absolutely calibrated Oriel Source (2% unc.)

Relative spectrum “lines” intensities Cross-check with a Hg source (Reader et al., use as absolute calibration source with 15% uncertainty, relative line uncertainty 4- 15%) 313 nm nm nm nm nm 1.12 measured/nominal

Relative spectrum “lines” intensities Preliminary, current syst. uncertainty ~5%. Spectrum at APS (6 keV) is consistent Bunner AIRFLY Large uncertainty below 300 nm For smaller lines, a crude subtraction of neighbouring lines was performed 297 nm

Humidity dependence Analysis is under way, analogous to pressure dependence 337 nm 315 nm 1% Argon air 1000 hPa

Energy dependence A very precise energy scan has been performed at AWA GEANT4 simulation

Energy dependence First measurements at Van der Graaf are promising

Absolute measurement of fluorescence yield at ~12 MeV Use the fluorescence/cherenkov ratio method at AWA We need a higher index of refraction (threshold in air is 21 MeV) First tests were performed with Freon 12. Measurement look feasible Two different beam energies

Outlook Absolute measurement at 300 MeV paper Spectrum relative intensities and pressure dependence paper Measurement program still rich: - Temperature measurement for all lines: this year at Argonne (VdG) - Absolute measurement at 12 MeV (AWA) - Energy scan and Spectrum at APS (keV range), first tests performed, beam time this year - final checks in Frascati to link the energy scans in the full range

New method for absolute measurement of fluorescence yield with AIRFLY  IDEA: normalize to well known process (cherenkov emission) to cancel detector systematics N 337 (fluor.) = FLY x Geom fluor x T filter x QE 337 x N electr. N 337 (cher.) = CHY x Geom cher x T filter x QE 337 x N electr. measured MC PMT 45 0 mirror relative meas.~ cancel! known  Systematic error potentially ≤ 5%