preliminary profile reconstruction of ea hybrid showers
DESCRIPTION
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. Introduction. we are using the Flores framework hybrid geometries from Brian and Paul - PowerPoint PPT PresentationTRANSCRIPT
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
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
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)
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
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 0o to 4o. Maximize S/N over
entire track
=1.9o
=3o
Optimum Chi values
Camera - Light Collection
time (100ns bins)
phot
ons
(equ
iv 3
70nm
)
F(t)
8 photons =1 pe(approx)
Event 33 Run 281 (bay 4) January
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 LightF(t)
Light emittedat track L(X)
shower geometry,atmospheric model
Shower sizeat track, S(X)
fluorescenceefficiency
map t onto slantdepth X
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 lightRayleigh & aerosol scatteringWorse close to ground (beam stronger, atmosphere denser)
Direct Cherenkov
This particular event
Rp = 7.3km, core distance = 11.8 km, theta = 51 degrees
showerFD
Event 33, run 281 (bay 4), December
Cherenkov correction (cont.)
• Iterative procedure
Estimate ofS(X)
Cherenkov beamstrength as fn of X
Cherenkov theory, pluselectron energy distrib.as function of age
New estimate offluorescence lightemitted along track
angular dist of Ch light(direct) and atmosphericmodel (scattered)
Smax
number of iterations
Xmax
number of iterations
time (100ns bins)
phot
ons
(equ
iv 3
70nm
)Estimate of Cherenkov contamination
Total F(t)
directRayleigh
aerosol
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 Xo=0 and =70 g/cm2.
E=2.5x1018eV, Smax=1.8x109, Xmax = 650g/cm2
atmospheric depth (g/cm^2)
part
icle
num
ber
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).
/)max(0max /)(
0max
0max)(
XX
eXX
XXSXS
XX
“Missing energy” correction
Ecal = calorimetric energy
E0 = true energy
from C.Song et al. Astropart Phys (2000)
Rp = 10.8km, core distance = 11.1 km, theta = 26 degrees
Event 336 Run 236 (bay 4) December
time (100ns bins)
phot
ons
(equ
iv 3
70nm
)Event 336 Run 236 (bay 4) December
atmospheric depth (g/cm2)
part
icle
num
ber
E= 1.3 x 1019eV, Smax= 9.2 x 109, Xmax = 670g/cm2
phot
ons
(equ
iv 3
70nm
)
time (100ns bins)
Event 751 Run 344 (bay 5) March
Comparison of two methods
phot
ons
time
E= 1.5 x 1019eV, Smax= 1.0 x 1010, Xmax = 746g/cm2pa
rtic
le n
umbe
r
atmospheric depth (g/cm2)
Shower profile - two methods
num
ber
of p
artic
les
atmospheric depth g/cm2
2 Methods: Compare Nmax
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).
Nmax distribution
Shower Energy
Shower Energy dN/dlogE
E-2
Xmax distribution
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