1. nDVCS MC generator @ clas12
Ahmed El Alaoui
GDR Nucleon, Saclay, 8-9 April, 2007
Outline:
- Introduction
- nDVCS MC generator
- Conclusion
Laboratoire de Physique
Subatomique et de Cosmologie

2. DVCS & GPDs σ(eN→eNγ) = + hard soft
DVCS process provides a new tool to study both the intrinsic motion of the partons and their transverse spatial distributions inside the nucleon
hard
soft
These informations are accessed through the measurement of the GPDs:
Both DVCS and BH processes contribute to the experimental cross section +
σ(eN→eNγ) = 2

3. DVCS MC generator
The generator aim is to provide a study of the reaction
e(k) + N(P)
e(k’) + N(P’) + γ(q’)
Beam Energy : GeV
include Fermi motion
Beithe-Heitler cross section
HepEvtInterface is used to link the Generator
ouput file to Geant4

4. e-, N, and γ momenta - Ebeam = 11GeV - -t < 2 GeV2 - Q2 >1GeV2
- W2 > 4 GeV2

5. e-, N, and γ polar angles - Ebeam = 11GeV - -t < 2 GeV2
- Q2 >1GeV2
- W2 > 4 GeV2
The scat. Electron & real photon are emitted at small angles while the neutron is emitted at large angle

6. Kinem. variables

7. Event distribution in (Q2,x) plane

8. Event distribution in (x,t) & (Q2,t) plane

9. Effect of Fermi Motion on nucleon momentum

10. Generator + Geant4
The generator output is used as input to Geant4 neutron detector simulation provided by silvia z
50 cm long cylinder with RIN=24 cm and ROUT=39 cm made of PbWO4
The detector is segmented into 5 by 30 along r and φ directions respectively strips

11. Photon-Neutron multiplicities
Neutron beam
Photon beam
- Energy : 0.5 GeV
- Direction : θ=90°, φ=27°
- Energy : 1 GeV
- Direction : θ=60°, φ=27°
Neutron beam from MC output

12. Conclusion The DVCS Monte Carlo generator was presented
GPD models to be included…
Angular distribution of Neutrons is in satisfactory with the desired neutron detector layout (35-70) [deg]
Photon/neutron separation work in progress…