K. LaihemE166 collaboration LCWS06 Bangalore March 12th 2006 The E166 experiment Development of a polarized positron source for the ILC. Karim Laihem on behalf of the E-166 collaboration

K. LaihemE166 collaboration The goal of the E-166 experiment at SLAC The ATF Compton experiment at KEK Photon transmission polarimetry The helical undulator The E-166 setup Data taking First results on photon and positron asymmetries Outline

K. LaihemE166 collaboration γ e+ e- Undulator Target D1 D2 D3 Gamma Diagnostic Positron Diagnostic e- Dump e- Dump 46.6 GeV 10 MeV 1 m Energy spectrum The goal of the E-166 experiment at SLAC Experimental Demonstration for polarized e + production Final focus test beam (FFTB) at SLAC with 46.6 GeV electrons 1 m long helical undulator produces circular polarized photons Undulator radiation 0-10 MeV (Balakin & Mikhailichenko 1979) Conversion of photons to positrons in 0.2 X 0 W-target Measurement of polarization of photons and positrons by Photon transmission method

K. LaihemE166 collaboration Compton based Pol. e + Generation E = 36±8 MeV 10 4 /bunch E max = 56MeV Pol.  -ray generation: M. Fukuda et al. PRL 91, (2003)

K. LaihemE166 collaboration e + polarization (e + run ) e - spin in Iron e + beam spin non A(R)= ± 0.25% A(L)= ± 0.27% A(0)= ± 0.25% T. Omori et al., arXiv:hep-ex/ Phys. Rev. Lett. accepted ATF-Compton

K. LaihemE166 collaboration Summary of e + Run and e - Run e + Run e - Run abs. A= 0.90 ± 0.18% abs. A=0.89 ± 0.19% Pe + = 73 ± 15(sta) ± 19(sys) Pe - = 72 ± 15(sta) ± 19(sys) T. Omori et al., arXiv:hep-ex/ PRL accepted ATF-Compton

K. LaihemE166 collaboration E166 setup in the FFTB Positron Table Gamma Table TOP VIEW Gamma Analyzing magnet e+ Analyzing magnet helical undulator collimators Positron Table Gamma Table ~30 m Undulator SIDE VIEW Dump magnets e- beam Polarized photons productionphotons collimationPositrons diagphotons diag

K. LaihemE166 collaboration y z x e- beam Undulator photons I1I1 I2I2 I1I1 I2I2 I 1 = - I 2 Helical winding where I 1 and I 2 are in opposite directions. Helical winding: z component of the induced magnetic field cancels remaining magnetic field describes a helical profile The helical undulator

K. LaihemE166 collaboration Undulator photon “Energy and Polarization” Undulator Photon energy spectrumUndulator Photon degree of polarization 1 st Harmonic 2 nd Harmonic

K. LaihemE166 collaboration The Positron production target e+ Energy distribution (in and out the 0.5 X0 W target) Positron Polarization profile created by the undulator photons (creation point) Polarized γ beam From the Helical Undulator e+ e- 0.5 X0 W (Tungsten) -> E166 X0 W (Tungsten) = 3.5 mm Polarization transfer in e+ e- pair creation e+ e-

K. LaihemE166 collaboration

K. LaihemE166 collaboration Positron and Gamma table at the FFTB (SLAC)

K. LaihemE166 collaboration Photon transmission polarimetry Transmission

K. LaihemE166 collaboration Positron Analyzing Power Positron Energy E e + (MeV) Positron Polarisation P e + (%) Positron Asymmetry δ (%) Analyzing Power A e + (%) Expected asymmetries and analyzing power versus positron energy G3 simulation based on the experimental setup of the proposal Most challenging task for E166 was to measure asymmetries ≤1% in the CsI - Calorimeter V. Gharibyan

K. LaihemE166 collaboration What we have achieved in E166 ? (e+ and photon asymmetry) Expected asymmetries [%] (Geant3 Simulation) Measured asymmetries [%] Aerogel AG2 W-Si GCAL Aerogel AG2 W-Si GCAL Peter Schuler, Vahagn Gharibyan DESY William Bugg. University of Tennessee Positron Asymmetry Photon Asymmetry I s = 140 A (1.03 ± 0.08) %

K. LaihemE166 collaboration We still need “A γ “ !!!! The analyzing power Okay !!!! The asymmetry Magnetization of the The Iron core of the analyzing magnet What about the e+ degree of polarization? Transmission

K. LaihemE166 collaboration Field map Measurement at SLAC. Figure 5: By with respect X position and Z position. MERMAID field map calculation. E166 spectrometer magnetic field study

K. LaihemE166 collaboration E166_Geant4_Simulation Figure 1: Synoptic scheme of the E166 e+/e- transportation system.. The present study concerns the region between the target up to the Point A, B and C (entrance of the spectrometer, exit of the spectrometer and reconversion target respectively).

K. LaihemE166 collaboration E166_G4_SIM Reconversion target C Point B Point A Spectrometer Current 180 A as an example

K. LaihemE166 collaboration Summary table of the most relevant parameter for positrons at the reconversion target. Spectrometer current. I S [A] Lens current I L [A] Positron Energy [MeV] , , , , % 68% 61% 53% 44% EGS simulation John Sheppard Qualitative study Covered range.

K. LaihemE166 collaboration Polarized γ beam From the Helical Undulator e+e+ e+e+ e+e+ e-e- e-e- e-e- 0.5 X0 W (Tungsten) -> E166 X0 W (Tungsten) = 3.5 mm TARGET Gammas: GammaConversion ComptonScattering PhotoElectricEffect Electrons and Positrons: MultipleScattering Ionisation Bremsstrahlung Diagnostics (Polarimetry) Cross sections polarization dependent What is needed in Geant4 for polarized Positron/Electrons studies ? Polarization transfer to e-/e+ Polarization traking (depolarization effects ?) MAGNETIC FIELD: Compton Scattering Bhabha Scattering Moller Scattering Positron annihilation in Flight

K. LaihemE166 collaboration Summary and outlook E-166 had two excellent runs (June / September 2005). Asymmetries measured at 6 positron energies. The helical undulator fulfilled its task. The analysis asymmetries in the expected range It still takes some time to come up with a number for the photon and positron polarization More detailed Geant4 E-166 simulation work is in progress The analysis is ongoing….

K. LaihemE166 collaboration Thank you……

K. LaihemE166 collaboration Backup…

K. LaihemE166 collaboration Figure 26. Transmission up to the reconversion target in terms of Signal (or energy) defined by equation 7. Transmission up to the reconversion target (point C). Reconversion target C

K. LaihemE166 collaboration I S = 100 I L = 175 I S = 120 I L = 200 I S = 140 I L = 225 I S = 160 I L = 250 I S = 180 I L = 275 Current [A]

K. LaihemE166 collaboration Figure 33. Positron energy versus spectrometer current. Positron energy versus spectrometer current

K. LaihemE166 collaboration Figure 32 Setting point “Lens current versus spectrometer current”. Comparison between the E166_G4_SIM and September run. Setting points E166_G4_SIM versus E166 September run.

K. LaihemE166 collaboration Summary table of the most relevant parameter for positrons at the reconversion target. Spectrometer current. I S [A] Lens current I L [A] Positron Energy [MeV] Maximum Transmissio n (Statistics) [%] Maximum Transmission (Signal) [%] , , , ,

K. LaihemE166 collaboration Polarimeter setup 4 x 10 9 photons 4 x 10 5 e + 4 x 10 9 photons 4 x 10 7 photons ~ 500 TeV 5 x 10 4 phE 5x10 6 phE 1.6 x 10 3 photons of total ~ 6 GeV 2 x 10 7 e +

K. LaihemE166 collaboration E166 Helical undulator parameters vs. TESLA, NLC parameters

K. LaihemE166 collaboration

K. LaihemE166 collaboration

K. LaihemE166 collaboration Spectrometer current. I S [A] Lens current I L [A] Positron Energy [MeV] Maximum Transmission (Statistics) [%] Maximum Transmission (Signal) [%] , , , ,