Status of AIRFLY fluorescence yield measurements Paolo Privitera Università di Roma Tor Vergata,...
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Transcript of Status of AIRFLY fluorescence yield measurements Paolo Privitera Università di Roma Tor Vergata,...
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%