Bhabha polarimeter update R Dollan BhabhaPolarimeter Update Ebeam

Bhabha polarimeter update R. Dollan

Bhabha-Polarimeter Update • • Ebeam: after pre acceleration cross section: • • theor. max. asymmetry bei 90°(CMS) example: Pe+= 80%, Pe-= 7% Amax ~ 4. 4 % ~ 400 Me. V Detector Shielding Magnet 22. 01. 2022 • • Magnetized Iron e+ ~ 7/9 ≈ 78 % • ~5 m R. Dollan Mask/shielding selects angular range with max. asymmetry spectrometer -> particle separation, energy selection Polarization measurements -> Asymmetry measurements of opposite polarization states of the target 2

e- produced the target e- distribution • 30 μm magnetized Fe-Foil • Ebeam : 400 Me. V (10 % spread) • Ang. Spread : 0. 5º Pz(Target) = -100% e+, e-, γ e+ asymmetry (analyzing power) Pz(Target) = +100% mask spectrometer ang. range of interest: 0. 03 – 0. 1 rad -> Asymmetry in the ang. range: Ae- ~50 % (Ae+ ~5%, Aγ ~-15%) 22. 01. 2022 R. Dollan 3

“spring” geometry detector 0. 5 m 0. 1 rad magnet: gap: 15 cm 0. 05 rad mask window septum/shielding beampipe target z=0 2. 8 m 3 m 4. 1 m not to scale 22. 01. 2022 R. Dollan 4

Changed geometry Magnet: • Bd. L: 0. 1 Tm • gap: 20 cm • length in z 20 cm • yoke thickn. : 7. 5 cm • coil: ~ 80 000 Amp turns (-> ~100 turns w. 400 A, curr. density ~6. 3/mm 2, water cooling assumed…) 0. 1 rad mask magnet window detector 0. 7 m 0. 05 rad Lead shielding target z=0 22. 01. 2022 4. 7 m 5 m R. Dollan 6 m 5

New geometry in G 4 magnet detector mask shielding 22. 01. 2022 R. Dollan 6

New geometry in G 4 22. 01. 2022 R. Dollan 7

Results (e- only) • 22. 01. 2022 • • • Distribution of electrons and the asymmetry (analyzing power) Target 30 µm Fe Ebeam 400 Me. V New magnet Bd. L 0. 1 Tm P(100%/100%) • • 1. 6 x 109 positrons on target A ~ 51% (RMS 22%) R. Dollan pol. G 4 results 8

Results (e+ and e-) • 22. 01. 2022 • • • Distribution of both, positrons and electrons and the asymmetry (analyzing power) Target 30 µm Fe Ebeam 400 Me. V New magnet Bd. L 0. 1 Tm P(100%/100%) • • 1. 6 x 109 positrons on target A ~ 43% (RMS 21%) R. Dollan pol. G 4 results 9

w. BG (beam pipe interactions) • 22. 01. 2022 • • • Distribution of both, positrons and electrons and the asymmetry (analyzing power) Target 30 µm Fe Ebeam 400 Me. V New magnet Bd. L 0. 1 Tm P(100%/100%) • 1. 6 x 109 positrons on target R. Dollan pol. G 4 results 10

w. BG and Energy cut • 22. 01. 2022 • • • Distribution of both, positrons and electrons and the asymmetry (analyzing power) Target 30 µm Fe Ebeam 400 Me. V New magnet Bd. L 0. 1 Tm P(100%/100%) • • 1. 6 x 109 positrons on target Energy cut: 100 Me. V R. Dollan pol. G 4 results 11

Update Summary • • • 22. 01. 2022 new (adaptive) geometry with a more realistic magnet implemented asymmetries as expected background studies ongoing (shielding of low energy electrons from beampipe interactions – difficult -> not much space) implementation of real beam (much lower background expected) simulation of lower target polarization (Pe-7%) and target inclination is ongoing in parallel (question of computing time and statistics) R. Dollan 12