Oct. 22, 2003 - G.Lima 1

Delving Deeper into Geant4

Guilherme Lima

DHCal Meeting

October 22, 2003

Oct. 22, 2003 - G.Lima 2

Updates since last report

• Studied the spikes on the distributions of energy depositions in ECal and HCal absorbers

• Checked materials in subcomponents using geantino scans

Oct. 22, 2003 - G.Lima 3

Spikes at Ecal absorber

Is this a bug?

Oct. 22, 2003 - G.Lima 4

Low energy EM Physics at play

69.5 keV

441 keV

511 keV70 + 441 = 511!!

Eγ = 511 keV in e+e- annihilation

ΦW = 69.5 keV ?(photoelectric effect in tungsten)

Oct. 22, 2003 - G.Lima 5

Why is the Eγ splitted sometimes?

PE happens here

e-γ

PE energy depositionis assigned here in LCDG4

Cell boundary

Oct. 22, 2003 - G.Lima 6

Spikes at Hcal absorber

511 keV

504 keV

MIP peak

7.11 keVzoom in green

Oct. 22, 2003 - G.Lima 7

Geantino scanning

• Purpose: compare radiation lengths (X0) and interaction lengths (λI) to make sure that materials are the same in Mokka and LCDG4

• No φ-dependence (cylindrical symmetry)

• θ- and track-length dependences are shown

Oct. 22, 2003 - G.Lima 8

X0 dependence on θ (SDJan03)

Big discrepancies in the forward regions?

Comparisons so far

Oct. 22, 2003 - G.Lima 9

λI dependence on θ (SDJan03)

Big discrepancies in the forward regions?

Comparisons so far

Oct. 22, 2003 - G.Lima 10

X0, λI along track length at θ= 90°, φ= 90°

HCal

ECal

Tracker

VXD

Muon

Coil

Oct. 22, 2003 - G.Lima 11

X0, λI along track length at θ=5°, φ=90°

Last detectorcomponent

Oct. 22, 2003 - G.Lima 12

X0 differences at θ = 5°, φ = 90°

Differences are quite small

Oct. 22, 2003 - G.Lima 13

Comparing apples to apples…

• Geant version 4.5.2 (new server) • Geometry (SDJan03, projective)• Physics list: identical data files• Range cuts (0.1mm)• Same events are processed in both detector

simulators (single particles: 50 GeV e, μ, π)

input from binary stdhep file: θ = 90°, flat in φ• Geant4 external data files not used• Materials (some minor differences, should never

give significant differences in results)

Oct. 22, 2003 - G.Lima 14

Conclusions

• Peaks at Ecal and HCal absorbers are due to e+e- annihilation in association and photoelectric effect

• Materials in LCDG4 and Mokka are in very good agreement

• Some low-level discrepancies remaining in both ECal and Hcal need to be understood

Should we go for Geant3 cross checks?

Oct. 22, 2003 - G.Lima 15

Next steps

• Fix to energy contributions per cell (lcdg4)

• Further investigation on the origin of discrepancies

• Look at some complex physics processes

• Think about digitization (energies into ADC counts)