Polarimetry Report Sabine Riemann on behalf of the DESY/HUB group January 24, 2008 EUROTeV Annual...
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Transcript of Polarimetry Report Sabine Riemann on behalf of the DESY/HUB group January 24, 2008 EUROTeV Annual...
![Page 1: Polarimetry Report Sabine Riemann on behalf of the DESY/HUB group January 24, 2008 EUROTeV Annual Meeting, Frascati.](https://reader035.fdocuments.us/reader035/viewer/2022062519/5697bfbd1a28abf838ca1e17/html5/thumbnails/1.jpg)
Polarimetry Report
Sabine Riemann on behalf of the DESY/HUB groupJanuary 24, 2008
EUROTeV Annual Meeting, Frascati
![Page 2: Polarimetry Report Sabine Riemann on behalf of the DESY/HUB group January 24, 2008 EUROTeV Annual Meeting, Frascati.](https://reader035.fdocuments.us/reader035/viewer/2022062519/5697bfbd1a28abf838ca1e17/html5/thumbnails/2.jpg)
24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 2
Outline
ILC Positron Polarization: Pe+ ≈ 30% (baseline design)
Pe+ ≈ 60% (update)
E166 Proof of principle polarimetry at low energies
Status G4 with polarization Polarimetry at low ILC energies (LEPOL)
Update of Bhabha polarimeter studies Compton polarimetry after DR?
Polarized e+ source modeling Summary
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 3
E166 @ SLAC
Helical undulator:
energy and polarization of photons
Simulation of• Conversion into e+ e- pairs in thin W target, • polarization transfer to high energetic leptons
46.6 GeV e- beam
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 4
e+ polarimetry at low energies
• Mott polarimeter rotate longitudinal spin to transverse
• Bhabha (Moller) polarimetry (E(e+) > 100 MeV)
• Compton polarimeter need small beam size
• E166:Compton transmission polarimeter ( and e+)– Reconversion of e+ to polarized photons (bremsstrahlung,
annihilation)
– Transmission of photons through magnetized iron ( and ) Measurement of transmission with CsI calorimeter
– Polarization dependent Compton cross section asymmetry
– Method suitable for E(e+) ≤ few tens MeV
reconversion magnetized transmitted detector
target iron photons
e+
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 5
E166: Compton transmission polarimetry
• Measurement of transmission in CsI calorimeter (3x3 crystals)
good signal-background separation
» Asymmetry for parallel / antiparallel polarized iron
• e+ polarization• (PFe = 7%)
• Analyzing power Ae+ from simulation Geant4 with polarized prozesses
ii
iii
EE
EE
eFe
eAP
P
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 6
E166 results (preliminary)
E166 publication coming soon...
preliminary
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 7
Geant4 with polarized processes• Polarization is taken into account for
– Pair-production– Bremsstrahlung– Compton scattering– Moller/Bhabha scattering– Positron annihilation into 2 photons
• Included since Geant4 release 8.2 (Dec 06)– Main focus: longitudinal (or circular) polarization (extension to
transversal is foreseen)– Energy range of interest: MeV … ~5 GeV
• Applications:– Polarization transfer (target, E166)– Polarimetry (Bhabha/Moller, Compton transmission – e.g.
E166)– ILC polarized positron source
• Cross checks with EGS, WHIZARD/O’mega
Authors: A. Schälicke, K. Laihem, P. Starovoitov
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 8
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 9
Polarimetry at/near the e+ source(LEPOL)
• Requirements:– Suitable for low energy range– Suitable for large positron beam size– Fast– Non-destructive– Accuracy O(few %)
• Possibilities:– Bhabha polarimeter (125-500 MeV)– Compton – after DR (beamsize!)– Compton transmission (~E166): after capture section but only
for few bunches
• People:– DESY/HUB: R. Dollan, T. Lohse, S. Riemann, A. Schälicke, P. Schuler, A. Ushakov
Minsk: P. Starovoitov, Tel Aviv U: G. Alexander
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 10
Bhabha Polarimetry• As Møller polarimeter already widely used
• Cross section:
• e+ and e- must be polarized• maximal asymmetry at 90°(CMS) ~ 7/9 ≈ 78 %
Example: Pe+= 80%, Pe-= 7% Amax ~ 4.4 %
42422
42
20 coscos67coscos69
sin16
cos1
ee
PPrd
d
e+
MagnetizedIron
Detector
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 11
Bhabha Polarimetry Centre-of-mass system Lab system
Position for Bhabha polarimeter:– After pre-acceleration and beam separation: 400 MeV– Studies done for Ee+ = 400 MeV – Target foil heating (<30 m) is in acceptable limit (simulation)
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 12
Example: e- distribution and e- asymmetry
angular range of interest: 0.03 – 0.1 rad Asymmetry in the angular range: Ae- ~50 % (Ae+ ~5%, Aγ ~-15%)
Pz(Target) = -100%
Pz(Target) = +100%
• 30 μm magnetized Fe foil• Ebeam: 400 MeV (10 % spread)• Angular spread: 0.5º• 100% e+ and e- polarisation assumed
e- asymmetry (analyzing power)
e- distribution
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 13
scattered e- in detector plane
(beam: 1*109 e+, E: 400 MeV (10 % spread), ang spread: 0.5º, int. B-gield 0.1 Tm
asymmetry (analyzing power)
e- distribution
e- distribution
- run
+ run
Distance analyzing magnet – detector ~ 5m
Optimization is ongoing
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 14
Compton Polarimetry after DRLarge e+ beam size no Compton polarimetry before the DRAfter DR: small beam size, 5GeV, transverse polarization (DR…Turnaround) ~longitudinal polarization (spin rotation after turnaround) taking into account earth curvature
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 15
Compton Polarimetry after DRPossible option:
– Compton polarimetry after turnaround (5GeV)
• First considerations for (5 GeV): – see G. Alexander, P. Starovoitov, LC-M-2007-014
• Use laser of laser wireLaser wire:
• /2 crossing angle between e and • e beam size larger than laser beam waist
– Compton:• ~ crossing angle between e and • small e beam size for high rate
– Discussions with ‘instrumentation’ WP leader of former EDR started….
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 16
Polarized positron source modeling
• Activation and radiation damage studies(A. Ushakov et al., EPAC06: EUROTEV-REPORT-2006-052,
ILC07: arXiv:0712.2343)
• Production and tracking of polarized e+ at the source:– Use G4 (spin tracking) and FLUKA, ASTRA (acc.)– PAC07: PAC07-THPMN0– Optimization of capture efficiency and polarization
(see next slide)
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 17
Polarized positron source modelling
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 18
Polarized positron source modeling
• Recent study of beam displacement with photon collimator polarization is ‘robust’
• up to now `ideal’ undulator spectrum as input used• Fast helicity reversal
– RDR design not sufficient, – need helicity flip with frequency as for electrons
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24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 19
Summary & Conclusion• Lessons from E166 for low energy polarimetry
– Detailed simulations are essential – but time consuming
• Tools for design/performance studies:– G4 with polarization extension:
• Ongoing: validation, spin tracking, transverse pol.• e+ polarimeter:
– Compton transmission (few bunches, E < 50 MeV)– Bhabha (~400 MeV)
• Ongoing simulation studies for polarimeter layout – Compton (5GeV, longitudinal polarization)
• Further studies only in cooperation with machine and Lw people – Report on LEPOL will be delivered end of 2008– No prototype
• Source modeling – status report will be delivered end of 2008• Fast helicity flip to match the experimental precision for physics
– Design exists (seeSLAC-TN-05-045), work on alternatives is planned