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