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...
Polarimetry Report
Sabine Riemann on behalf of the DESY/HUB groupJanuary 24, 2008
EUROTeV Annual Meeting, Frascati
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
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
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+
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
24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 6
E166 results (preliminary)
E166 publication coming soon...
preliminary
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
24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 8
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
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
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)
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
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
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
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….
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)
24 Jan 2008, EUROTeV Annual Meetiing, Frascati Polarimetry Report 17
Polarized positron source modelling
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
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