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
absolute calibration derived from remote laser shots GAP
profiles viewable (December - March) at

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

11. Longitudinal Profile S(X)
Received Light F(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 light Rayleigh & aerosol scattering Worse 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 Event 33, run 281 (bay 4), December
shower FD
Rp = 7.3km, core distance = 11.8 km, theta = 51 degrees

14. Cherenkov correction (cont.)
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)
Iterative procedure

15. Smax
number of iterations

16. Xmax
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 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 energy E0 = 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

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