Simulations of Light Collection Efficiency

(JLab Hall C 12 GeV Kaon Aerogel Detector)

Laura Rothgeb

Nuclear Physics Group

Catholic University of America

August 19, 2011

Generalized Parton Distributions (GPD, model of the momenta of quarks within particle) are used to understand the internal structure of nucleons. Using hard scattering meson electroproduction we can construct the GPD of the proton and find the form factor of the kaon. To construct GPDs these data must conform to the model of hard QCD scattering.

Overview:Additional Flavor Degree of Freedom in K+ Production

Kaon Aerogel Cherenkov Detector

Detects kaon particles via Cherenkov radiation

Uses Photomultiplier Tubes (PMTs) to collect the light and convert to electrical signal via the photoelectric effect

Some design considerations• Ideal refractive index of aerogel• Optimum number/placement of PMTs• Effect of light guides on light collection efficiency

SimCherenkov

FORTRAN Monte Carlo simulation written to model the Kaon Aerogel Cherenkov Detector for Jefferson Lab to optimize conceptual design components

Allows for multiple configurations including options for manipulating detector geometry, placement and sizes of PMTs, variety of reflective surfaces and refractive indices of aerogel

Tracks photons emitted by the Cherenkov radiation in the simulated detector and relays the total number of photoelectrons produced based on the characteristics of the detector determined by the user

Experimental SetupImplements extension volume

to study effect of a large, asymmetrical light guide

μ

γ e-

AerogelCasing

LightDiffusion

Box

ExtensionVolume

PMT

Light Guide SimulationsWrote new loop configuration: EXTENSION• Width, length and height of the extension box can be

modified to simulate various light guide geometries• Surface of extension box can be changed to compare

effects of various reflective materials

Aerogel Casing

Light Diffusion Box

PMT

Extension Box Volume

0 5 10 15 20 25 300

0.2

0.4

0.6

0.8

1

1.2

1.4

Distance vs. Photoelectrons

EXTENDW (cm)

# of

Pho

toel

ectr

ons

Maximum: EXTENDW = 0cm Experimental Setup: EXTENDW = 11.6cmEfficiency: 23%

EXTENDH = 11.6EXTENDL = 11.6

μ

γ e-

0 5 10 15 20 25 30 35 40 450

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Height vs. Photoelectrons

EXTENDH (cm)

# of

Pho

toel

ectr

ons

Maximum: EXTENDH = 15cm Experimental Setup: EXTENDH = 11.6Efficiency: 90%

EXTENDW = 11.6EXTENDL = 11.6

Maximum: EXTENDL = 12cm

0 5 10 15 20 25 30 35 400

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Length vs. Photoelectrons

EXTENDL

# of

Pho

toel

ectr

ons

Experimental Setup: EXTENDL = 11.6cmEfficiency: 99%

EXTENDH = 11.6EXTENDW = 11.6

Efficiency:Photon Loss

~37% of the total photons are absorbed in the extension box

Aerogel

123456

Initial Light Guide (0cm)

Light Box (millipore)

Extension Box (mylar)

PMT Window

Returns to Light Box

Aerogel

Light Box

Extension Box

PMT Window

Returns toLight Box

ResultsGeometry of light guides have a drastic effect on

the efficiency of Aerogel Cherenkov detectors: light is lost mainly due to increased surface area in which the photons are absorbed

Decreased efficiency shown empirically with experimental set-up at JLab, confirms simulation results

Next, implementing a model of the detector into a detailed GEANT4 Monte Carlo simulation