Progress with Spin Tracking in GEANT4 Sabine Riemann, DESY ILC-BDIR, European Regional Workshop, RHUL, June 22, 2005 GEANT4 with Polarization: Report on the work of Ralph Dollan, Karim Laihem, Thomas Lohse, Andreas Schälicke and Achim Stahl Plans for the future

Progress with polarization in GEANT4 Motivation MC simulations of spin dependent processes - in the target polarimeter PPMODL PTCD LEPOL June 22, 2005 Progress with polarization in GEANT4

Relevant processes for polarization studies Target Diagnostics Photons: g conversion Compton scattering photoelectric effect  Spin transfer to e+, e- Electrons, positrons: multiple scattering ionization Bremsstrahlung  Polarization tracking spin dependent cross sections: Compton scattering Bhabha scattering Moller scattering Annihilation in flight June 22, 2005 Progress with polarization in GEANT4

Status of Simulation Software GEANT4: - only low energy Compton scattering (linear polarized optical photons on unpolarized e-) - No polarization of the medium - Placeholder for polarization vector (3-vector) exists EGS4: Implementation of Stokes formalism in a seperate extension (K. Flöttmann);  polarization transfer & depolarization included, no asymmetric cross section LEPOL: Need simulation also for asymmetric processes June 22, 2005 Progress with polarization in GEANT4

Progress with polarization in GEANT4 Stokes parameters G.Stokes, Trans. Cambridge Phil. Soc. 9 (1852) 399 Wave function : Jones vector : Spin density matrix : Stokes parameter : June 22, 2005 Progress with polarization in GEANT4

Stokes parameters Stokes parameter Photon observation Fermion observation x1 Plane polarization Spin in z - direction x2 Plane polarization at an angle of p/4 to the right Spin in x - direction x3 Left/Right circular polarization Spin in y - direction Example linear polarized photon: Dollan, Laihem, Lohse, Schälicke, Stahl

Matrix formalism Differential cross section Asymmetry Polarization W.H. McMaster, Rev.Mod.Phys. 33 (1961) 8 Transformation matrix Differential cross section Asymmetry Polarization Depolarization and polarization transfer Dollan, Laihem, Lohse, Schälicke, Stahl

Pair production in field of nucleus Dollan, Laihem, Lohse, Schälicke, Stahl

Compton scattering Independent of electron spin S: (I, A, B, C, D) Dependent on electron spin S: (E, F, Gi, Hi) Dollan, Laihem, Lohse, Schälicke, Stahl

Proposal for the implementation Input: Stokes parameters of the particle (beam) -> G4ThreeVector (bookkeeping already included in GEANT4) Polarization of the Volume -> G4ThreeVector (PolarizationManager) Calculate cross sections (total, differential) -> interaction length Derive polarization transfer from initial to final state Summary of our proposal Output: Stokes parameters of the final states Dollan, Laihem, Lohse, Schälicke, Stahl

Results Compton scattering Polarized: Pe=+1 Pg=+1 Pe=-1 Pg=+1 Unpolarized: Pe= 0 Pg= 0 Eg=10 MeV Dollan, Laihem, Lohse, Schälicke, Stahl

Polarization transfer in the pair production process -1 Conversion target e+ Positron Polarization profile from polarized Undulator photons (creation point) Polarized Photon Beam Stokes Vector Dollan, Laihem, Lohse, Schälicke, Stahl

Polarization transfer in the pair production process Random Conversion target e+ Positron Polarization profile from polarized Undulator photons (creation point) Unpolarized Photon Beam Stokes Vector Dollan, Laihem, Lohse, Schälicke, Stahl

Target studies - results 0.5 X0 W Polarization profile of the first harmonic undulator photons Positron Polarization profile created by the undulator photons (creation point) e+ Energy distribution (inside/outside target) The target may filter positrons with high degree of polarization Dollan, Laihem, Lohse, Schälicke, Stahl

Outlook (GEANT4) Continue the implementation of Polarization in G4 processes Focus on Stokes formalism (describes all polarization states for g, e+, e-) First priority to processes needed for the for polarized positron source Other processes will not be neglected Cross check with other existing simulation packages (EGS4…) Possibility to simulate and cross check with experimental results (E166) Contact and collaborate with other groups (developing polarized Geant4) Coordinate the work and the approach on the implementation. Propose the polarized processes to the G4 collaboration (official release) Dollan, Laihem, Lohse, Schälicke, Stahl

Progress with polarization in GEANT4 e+ Polarimetry at a PPS Peter Schueler in Daresbury: June 22, 2005 Progress with polarization in GEANT4

Progress with polarization in GEANT4 P. Schueler, Daresbury Transmission method: Compton scattering of g’s from re-converted e+ on 3d e- in magnetized iron BUT: huge pair creation background for higher g energies destructive method June 22, 2005 Progress with polarization in GEANT4

e+ Polarimetry at the PPS (LEPOL) Polarimetry at the ILC PPS: where ? E(e+) > 100 MeV after AMD E(e+) ~ 5 GeV at the DR which process? destructive methods? accuracy? Bhabha scattering (~10mm Fe foil, 110K): Alexander, Reinherz-Aronis; Starovoitov, Suarez: could work at ~250 MeV, at ~10 MeV high background; at 5 GeV insensitive more detailed studies needed; analyzing power ? June 22, 2005 Progress with polarization in GEANT4

Progress with polarization in GEANT4 Summary First steps done for G4 with polarization Target modelling with GEANT4 Collaboration with Tel Aviv: - find a process for the LE polarimetry, Collaboration with Minsk (INTAS??) - implementation of polarisation into MC (EGS4) - polarimetry Milestone: E166 June 22, 2005 Progress with polarization in GEANT4

Progress with polarization in GEANT4 June 22, 2005 Progress with polarization in GEANT4