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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 (2005-2006)
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 eliminatedp’(air) = 16.89 ±0.33 hPa (stat. unc.)P’(N) = 103.6±2.7 hPa (stat. unc.)
Pressure dependence of the spectrum
BeamSpectrometer
Sphericalmirror
Optical fiber
Spectrum linesIntegral of line (some
contamination expected)
Spectrum lines
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”
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 0.92 334 nm 1.03 365 nm 1.03 404 nm 1. 407 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 nm1% Argon air
1000 hPa
Energy dependence
• A very precise energy scan has been performed at AWA
GEANT4simulation
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
N337(fluor.) = FLY x Geomfluor x Tfilterx QE337 x Nelectr.
N337(cher.) = CHY x Geomcher x Tfilterx QE337 x Nelectr.
measured MC
PMT PMT
450 mirror
relative meas.~ cancel!known
Systematic error potentially ≤ 5%