Nitrogen fluorescence yield in dependence on atmospheric conditions

1. Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft Nitrogen fluorescence yield in dependence on atmospheric conditions • B. Keilhauer1, J. Blümer1,2, R. Engel2, H. O. Klages2 • Universität Karlsruhe, Institut für Experimentelle Kernphysik • Forschungszentrum Karlsruhe, Institut für Kernphysik • Fluorescence Efficiency - measurements and calculations • Fluorescence Yield at sea level • dependence on altitude • dependence on relative humidity

2. efficiency at each wavelength λ without collisional quenching • measurements - interpolation to zero pressure (e.g. Bunner, 1967) • relative calculations - combination of • radiative transition probabilities • radiative life times • apparent exitation cross sections Fluorescence Efficiency needs

3. with air taken to be a two-component gas Fluorescence Efficiency

4. Results for 2P system (only excerpt) Relative calculations are scaled to the strongest emission of measurements.

5. Fluorescence Light • mainly e± of EAS excites N2 molecules in air • 18 strong emission bands in 2P system between 300 and 400 nm • 1 strong emission band in 1N system between 300 and 400 nm • only contributions < 1% from Argon • even less from Oxygen • Fluorescence Yield with assumption

6. Fluorescence Yield at sea level (only excerpt) • p and T at sea level of US Standard atmosphere • air with 78.8 % N2 and 21.1 % O2 • 0.85 MeV electron as exciting particle⇒dE/dX= 0.1677 MeV/kg·m-2

7. Fluorescence Yield at sea level

8. Relative comparison of 19 band systems

10. non-wavelength dependent results • Kakimoto et al. (1996) FY (300-400nm) at sea level = 3.275 • HiRes Coll. (2005) FY (300-400nm) per charged particle in EAS = 5.0 assumes average dE/dX of 0.22 MeV/kg m-2⇒ FY at sea level = 3.811 ⇒ with altitude-dependence ≈ 3.6 - 3.7

11. Altitude dependence • this work: with • Nagano et al. (2004): • Kakimoto et al. (1996):

12. Altitude dependence for some wavelengths

13. Altitude dependence

14. Seasonal and Altitude dependence for Auger

15. Seasonal and Altitude dependence- rel. difference to US-StdA -

16. Humidity dependence • US-StdA withrelative humidity = 100 % • Morozov et al. (2005) measured collisional cross-section for 2P, ν' = 0, 1 • reduction of FY337nm by about 20 % at sea level • 5 % at 4 km a.s.l. • 0.3 % at 8 km a.s.l. • Waldenmaier (2006) measured collisional cross-section for 2P , ν' = 0, 1 and 1N, ν' = 0 at 20 °C • reduction at sea level by 21.7 % for 2P, ν' = 0 19.6 % for 2P, ν' = 1 10.0 % for 1N, ν' = 0 • for realistic conditions reduction by about 5 - 10 % at ground 1 - 3 % at 4 km a.s.l.

17. Summary • FY-calculations agree quite well with measurements from Davidson & O‘Neil (1964), Nagano (2004), and Waldenmaier (2006) • results from Bunner (1967) and Kakimoto (1996) are lower by 18 % and 11 %, respectively • value used by HiRes collab. (2005) slightly higher (4 %) if no altitude dependence is applied • parameterizations for altitude dependence for wavelength range 300 – 400 nm agree well with calculations • increase of FY (photons/m) from 0 km to 8 km a.s.l. by 7 % • seasonal dependence in the order of 3 % • water vapor reduces FY due to additional quenching • paper published in Astropart. Phys. 25, pp. 259-268, (2006), or astro-ph/0511153