Preliminary Profile Reconstruction of EA Hybrid Showers

1. Preliminary Profile Reconstruction of EA Hybrid Showers Bruce Dawson & Luis Prado Jr thanks to Brian Fick & Paul Sommersand 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 inGAP-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 c” method developed to maximize S/N in flux estimate

7. Light Flux at Camera F(t) (cont.) c=1.9o c=3o • assume track geometry and sky noise measurement • for every 100ns time bin include signal from pixels with centres within c of spot centre. • Try values of c from 0o to 4o. Maximize S/N over entire track

8. Optimum Chi values

9. Camera - Light Collection

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

11. Longitudinal Profile S(X) Received LightF(t) • 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! shower geometry,atmospheric model map t onto slant depth X Light emitted at track L(X) fluorescence efficiency Shower size at track, S(X)

12. Complications - Cherenkov correction Scattered Cherenkov lightRayleigh & aerosol scatteringWorse close to ground (beam stronger, atmosphere denser) Direct Cherenkov • 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

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

14. Cherenkov correction (cont.) Estimate ofS(X) Cherenkov theory, pluselectron energy distrib. as function of age Cherenkov beamstrength as fn of X angular dist of Ch light(direct) and atmosphericmodel (scattered) New estimate of fluorescence lightemitted along track • Iterative procedure

15. Smax number of iterations

16. Xmax number of iterations

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

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 r, T and shower age, s) • can then extract a peak shower size by several methods - we fit a Gaisser-Hillas function with fixed Xo=0 and l=70 g/cm2.

19. E=2.5x1018eV, Smax=1.8x109, Xmax = 650g/cm2 particle number atmospheric depth (g/cm^2)

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 Ecal = calorimetric energyE0 = true energy from C.Song et al. Astropart Phys (2000)

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

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

27. E= 1.3 x 1019eV, Smax= 9.2 x 109, Xmax = 670g/cm2 particle number atmospheric depth (g/cm2)

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

29. Comparison of two methods photons time

30. E= 1.5 x 1019eV, Smax= 1.0 x 1010, Xmax = 746g/cm2 particle number atmospheric depth (g/cm2)

31. Shower profile - two methods number of particles atmospheric depth g/cm2

32. 2 Methods: Compare Nmax

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

34. Nmax distribution

35. Shower Energy

36. Shower Energy dN/dlogE E-2

37. Xmax 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 Nmax assignments • we are continuing our work to check and improve algorithms