1. Preliminary Profile Reconstruction of EA Hybrid Showers Bruce Dawson & Luis Prado Jr thanks to Brian Fick & Paul Sommers and Stefano Argiro & Andrea de Capoa Malargue, 23 April 2002

2. Introduction we are using –the Flores framework –hybrid geometries from Brian and Paul profile reconstruction scheme described in GAP-2001-16 absolute calibration derived from remote laser shots GAP-2002-10 profiles viewable (December - March) at www.physics.adelaide.edu.au/~bdawson/profile.htm

3. Basic Steps determine light collected at the detector per 100 ns time bin –F(t) (units 370nm-equivalent photons at diaphragm) determine fluorescence light emitted at the track per grammage interval –L(X) (units of photons in 16 wavelength bins) –requires subtraction of Cherenkov contamination determine charged particle number per grammage interval –S(X) (longitudinal profile)

6. Received Light Flux vs time, F(t) Aim: to combine signal from all pixels seeing shower during a given 100ns time slice Avoid: including too much night sky background light Take advantage of good optics –good light collection efficiency –try (first) to avoid assumptions about light spot size (intrinsic shower width, scattering) “variable  ” method developed to maximize S/N in flux estimate

7. Light Flux at Camera F(t) (cont.) assume track geometry and sky noise measurement for every 100ns time bin include signal from pixels with centres within  of spot centre. Try values of  from 0 o to 4 o. Maximize S/N over entire track

8. Optimum Chi values

9. Camera - Light Collection

10. time (100ns bins) photons (equiv 370nm) F(t) 8 photons =1 pe (approx) Event 33 Run 281 (bay 4) January

11. Longitudinal Profile S(X) First guess, assumes –light is emitted isotropically from axis –light is proportional to S(X) at depth X True for fluorescence light, not Cherenkov light! Received Light F(t) Light emitted at track L(X) shower geometry, atmospheric model Shower size at track, S(X) fluorescence efficiency map t onto slant depth X

12. Complications - Cherenkov correction Cherenkov light –intense beam, directed close to shower axis –intensity of beam at depth X depends on shower history –can contribute to measured light if FD views close to shower axis (“direct”) or if Cherenkov light is scattered in direction of detector Scattered Cherenkov light Rayleigh & aerosol scattering Worse close to ground (beam stronger, atmosphere denser) Direct Cherenkov

13. This particular event R p = 7.3km, core distance = 11.8 km, theta = 51 degrees shower FD Event 33, run 281 (bay 4), December

14. Cherenkov correction (cont.) Iterative procedure Estimate of S(X) Cherenkov beam strength as fn of X Cherenkov theory, plus electron energy distrib. as function of age New estimate of fluorescence light emitted along track angular dist of Ch light (direct) and atmospheric model (scattered)

15. S max number of iterations

16. X max number of iterations

17. time (100ns bins) photons (equiv 370nm) Estimate of Cherenkov contamination Total F(t) direct Rayleigh aerosol

18. Finally, the profile S(X) this Cherenkov subtraction iteration converges for most events transform one final time from F(t) to L(X) and S(X) using a parametrization of the fluorescence yield (depends on , T and shower age, s) can then extract a peak shower size by several methods - we fit a Gaisser-Hillas function with fixed X o =0 and =70 g/cm 2.

19. E=2.5x10 18 eV, S max =1.8x10 9, X max = 650g/cm 2 atmospheric depth (g/cm^2) particle number

20. Energy and Depth of Maximum Gaisser-Hillas function Fit this function, and integrate to get an estimate of energy deposition in the atmosphere Apply correction to take account of “missing energy”, carried by high energy muons and neutrinos (from simulations).

21. “Missing energy” correction E cal = calorimetric energy E 0 = true energy from C.Song et al. Astropart Phys (2000)

22. Rp = 10.8km, core distance = 11.1 km, theta = 26 degrees Event 336 Run 236 (bay 4) December

26. time (100ns bins) photons (equiv 370nm) Event 336 Run 236 (bay 4) December

27. atmospheric depth (g/cm 2 ) particle number E= 1.3 x 10 19 eV, S max = 9.2 x 10 9, X max = 670g/cm 2

28. photons (equiv 370nm) time (100ns bins) Event 751 Run 344 (bay 5) March

29. Comparison of two methods photons time

30. E= 1.5 x 10 19 eV, S max = 1.0 x 10 10, X max = 746g/cm 2 particle number atmospheric depth (g/cm 2 )

31. Shower profile - two methods number of particles atmospheric depth g/cm 2

32. 2 Methods: Compare N max

33. Events with “bracketed” X max 57 total events (all bay 4 hybrid events + six bay 5 hybrid events from March) of these 35 had “reasonable” profiles where X max appeared to be bracketed (or close to).

34. N max distribution

35. Shower Energy

36. Shower Energy dN/dlogE E -2

37. X max distribution

41. Conclusions First analysis of hybrid profiles is encouraging, with some beautiful events and the expected near-threshold ratty ones preliminary checks with alternative analysis methods indicate that we are not too far wrong in our N max assignments we are continuing our work to check and improve algorithms