Transmission and Reflection of Electrons using GEANT3

Angus Comrie (University of Cape Town, SA-CERN)

Supervisor: Karel Safarik

Kinetic Energies of 100keV to 1MeV, Aluminium & Beryllium foils of thickness <500 micron

Background• Heavy flavour mesons (D0 etc) have small (100μm)

impact parameters• Produced δ-rays may interfere with pixel detector’s

cluster algorithm, produce “charm candidates” by fake impact parameter

• Many more tracks than real charm events

Expected δ-ray energy distribution

1GeV Pion in 500μm Foil

Δ-ray Kinetic Energy (T0)

# of δ-rays with T>T0 (per track)

Emission Angle

Range in Beryllium

Range in Aluminium

0.1 MeV 7×10 -3 70° 90μm 70μm

1.0 MeV 7 ×10 -2 45° 3mm 2mm

•Non-negligible range in both Be & Al

Simulation Setup

• ROOT VirtualMC• GEANT3 (GEANT4 comparison soon)

Z<0: Reflected

Z>0: Transmitted

Calculated Quantities

• Transmission/Reflection Number Coefficients TN, RN

– TN can rise above 1 (additional e- knocked on by δ-rays)

• Energy Spectra, Eav , Ep

• Transmission/Reflection Energy Coefficients TE, RE

• Angular Distribution• Plot in (z/r0) for energy-independent results (where

r0 is mean electron range in medium)

Reference Results

Transmission Coefficients (Al)Errors are not show as they are smaller than points (1%)

Transmission Coefficients (Be)

Reflection Coefficients (Al)

•Closer to theoretical approximation•Agrees for small (z/r0)

<cos

(θ)>

Conclusion

• TN similar to MC results – Deviates at larger (z/r0)– Differs by up to 20% for Be & 15% for Al

• RN totally off below 1MeV– Possibly fixed in later version of GEANT4

Further Work

• Short Term (Next week):– Compare with GEANT4 simulation– Tweak simulation parameters

• Long Term:– Full simulation of production and propagation of

δ-rays in detector– Simulate detector response