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

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

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 : 6 - 11 GeV include Fermi motion Beithe-Heitler cross section HepEvtInterface is used to link the Generator ouput file to Geant4

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

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

Kinem. variables

Event distribution in (Q2,x) plane

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

Effect of Fermi Motion on nucleon momentum

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 150 strips

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

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…