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%