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
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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
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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
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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)
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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
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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
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Optimum Chi values
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Camera - Light Collection
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time (100ns bins)
phot
ons
(equ
iv 3
70nm
)
F(t)
8 photons =1 pe(approx)
Event 33 Run 281 (bay 4) January
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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
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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
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This particular event
Rp = 7.3km, core distance = 11.8 km, theta = 51 degrees
showerFD
Event 33, run 281 (bay 4), December
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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)
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Smax
number of iterations
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Xmax
number of iterations
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time (100ns bins)
phot
ons
(equ
iv 3
70nm
)Estimate of Cherenkov contamination
Total F(t)
directRayleigh
aerosol
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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.
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E=2.5x1018eV, Smax=1.8x109, Xmax = 650g/cm2
atmospheric depth (g/cm^2)
part
icle
num
ber
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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
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“Missing energy” correction
Ecal = calorimetric energy
E0 = true energy
from C.Song et al. Astropart Phys (2000)
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Rp = 10.8km, core distance = 11.1 km, theta = 26 degrees
Event 336 Run 236 (bay 4) December
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time (100ns bins)
phot
ons
(equ
iv 3
70nm
)Event 336 Run 236 (bay 4) December
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atmospheric depth (g/cm2)
part
icle
num
ber
E= 1.3 x 1019eV, Smax= 9.2 x 109, Xmax = 670g/cm2
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phot
ons
(equ
iv 3
70nm
)
time (100ns bins)
Event 751 Run 344 (bay 5) March
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Comparison of two methods
phot
ons
time
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E= 1.5 x 1019eV, Smax= 1.0 x 1010, Xmax = 746g/cm2pa
rtic
le n
umbe
r
atmospheric depth (g/cm2)
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Shower profile - two methods
num
ber
of p
artic
les
atmospheric depth g/cm2
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2 Methods: Compare Nmax
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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).
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Nmax distribution
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Shower Energy
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Shower Energy dN/dlogE
E-2
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Xmax distribution
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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
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