E-166 Undulator-Based Production of Polarized Positrons An experiment in the 50
Church, Dennis, Founder and President has reference to this Academic Journal, PHwiki organized this Journal E-166 Undulator-Based Production of Polarized Positrons An experiment in the 50 GeV Beam in the SLAC FFTB K.T. McDonald Princeton University American Linear Collider Workshop Cornell U., July 15, 2003 Undulator-Based Production of Polarized Positrons E-166 Collaboration (45 Collaborators) Undulator-Based Production of Polarized Positrons E-166 Collaborating Institutions (15 Institutions)
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E-166 Experiment E-166 is a demonstration of undulator-based polarized positron production as long as linear colliders – E-166 uses the 50 GeV SLAC beam in conjunction with 1 m-long, helical undulator to make polarized photons in the FFTB. – These photons are converted in a ~0.5 rad. len. thick target into polarized positrons ( in addition to electrons). – The polarization of the positrons in addition to photons will be measured. Balakin in addition to Mikhailichenko (1978) The Need as long as a Demonstration Experiment Production of polarized positrons depends on the fundamental process of polarization transfer in an electromagnetic cascade. While the basic cross sections as long as the QED processes of polarization transfer were derived in the 1950s, experimental verification is still missing The Need as long as a Demonstration Experiment Each approximation in the modeling is well justified in itself. However, the complexity of the polarization transfer makes the comparison with experiment important so that the decision to build a linear collider w/ or w/o a polarized positron source is based on solid ground. Polarimetry precision of 5% is sufficient to prove the principle of undulator based polarized positron production as long as linear colliders.
Physics Motivation as long as Polarized Positrons Polarized e+ in addition to polarized e- is recognized as a highly desirable option by the WW LC community (studies in Asia, Europe, in addition to the US) Having polarized e+ offers: Higher effective polarization -> enhancement of effective luminosity as long as many SM in addition to non-SM processes, Ability to selectively enhance (reduce) contribution from SM processes (better sensitivity to non-SM processes, Access to many non-SM couplings (larger reach as long as non-SM physics searches), Access to physics using transversely polarized beams (only works if both beams are polarized), Improved accuracy in measuring polarization. Physics Motivation: An Example Separation of the selectron pair in with longitudinally polarized beams to test association of chiral quantum numbers to scalar fermions in SUSY trans as long as mations NLC/USLCSG Polarized Positron System Layout 2 Target assembles as long as redundancy
TESLA, NLC/USLCSG, in addition to E-166 Positron Production E-166 Vis-à-vis a Linear Collider Source E-166 is a demonstration of undulator-based production of polarized positrons as long as linear colliders: – Photons are produced in the same energy range in addition to polarization characteristics as as long as a linear collider; -The same target thickness in addition to material are used as in the linear collider; -The polarization of the produced positrons is expected to be in the same range as in a linear collider. -The simulation tools are the same as those being used to design the polarized positron system as long as a linear collider. – However, the intensity per pulse is low by a factor of 2000. E-166 Beamline Schematic 50 GeV, low emittance electron beam 2.4 mm period, K=0.17 helical undulator 0-10 MeV polarized photons 0.5 rad. len. converter target 51%-54% positron polarization
E-166 Helical Undulator Design, l=2.4 mm, K=0.17 PULSED HELICAL UNDULATOR FOR TEST AT SLAC THE POLARIZED POSITRON PRODUCTION SCHEME. BASIC DESCRIPTION. Alex in addition to er A. Mikhailichenko CBN 02-10, LCC-106 Helical Undulator Radiation Circularly Polarized Photons Polarized Positrons from Polarized gs (Olsen & Maximon, 1959) Circular polarization of photon transfers to the longitudinal polarization of the positron. Positron polarization varies with the energy transferred to the positron.
Polarized Positron Production in the FFTB Polarized photons pair produce polarized positrons in a 0.5 r.l. thick target of Ti-alloy with a yield of about 0.5%. Longitudinal polarization of the positrons is 54%, averaged over the full spectrum Polarimeter Overview 1 x 1010 e- 4 x 109 4 x 109 4 x 107 4 x 109 2 x 107 e+ 4 x 105 e+ 1 x 103 2 x 107 e+ 4 x 105 e+ Transmission Polarimetry of Photons Pe = 0.07, P = 0.54, A = 0.62, = 0.027 = Pe P A
Transmission Polarimetry of Positrons 2-step Process: re-convert e+ via brems/annihilation process polarization transfer from e+ to proceeds in well-known manner measure polarization of re-converted photons with the photon transmission methods infer the polarization of the parent positrons from the measured photon polarization Experimental Challenges: large angular distribution of the positrons at the production target: e+ spectrometer collection & transport efficiency background rejection issues angular distribution of the re-converted photons detected signal includes large fraction of Compton scattered photons requires simulations to determine the effective Analyzing Power Formal Procedure: Fronsdahl & Überall; Olson & Maximon; Page; McMaster Positron Polarimeter Layout Positron Transport System e+ transmission (%) through spectrometer photon background fraction reaching CsI-detector
Analyzer Magnets g = 1.919 0.002 as long as pure iron, Scott (1962) Error in e- polarization is dominated by knowledge in effective magnetization M along the photon trajectory: active volume Photon Analyzer Magnet: 50 mm dia. x 150 mm long Positron Analyzer Magnet: 50 mm dia. x 75 mm long Photon Polarimeter Detectors Si-W Calorimeter Threshold Cerenkov (Aerogel) E-144 Designs: CsI Calorimeter Detector Crystals: from BaBar Experiment Number of crystals: 4 x 4 = 16 Typical front face of one crystal: 4.7 cm x 4.7 cm Typical backface of one crystal: 6 cm x 6 cm Typical length: 30 cm Density: 4.53 g/cm³ Rad. Length 8.39 g/cm² = 1.85 cm Mean free path (5 MeV): 27.6 g/cm² = 6.1 cm No. of interaction lengths (5 MeV): 4.92 Long. Leakage (5 MeV): 0.73 % Photodiode Readout (2 per crystal): Hamamatsu S2744-08 with preamps
Expected Positron Polarimeter Per as long as mance Simulation based on modified GEANT code, which correctly describes the spin-dependence of the Compton process Photon Spectrum & Angular Distr. Number- & Energy-Weighted Analyzing Power vs. Energy 10 Million simulated e+ per point & polarity on the re-conversion target Expected Positron Polarimeter Per as long as mance II Table 13 E-166 Beam Measurements Photon flux in addition to polarization as a function of K (Pg ~ 75% as long as Eg > 5 MeV). Positron flux in addition to polarization as long as K=0.17, 0.5 r.l. of Ti vs. energy. (Pe+ ~ 50%). Positron flux in addition to polarization as long as 0.1 r.l. in addition to 0.25 r.l. Ti in addition to 0.1, 0.25, in addition to 0.5 r.l. W targets. Each measurement is expected to take about 20 minutes. A relative polarization measurement of 5% is sufficient to validate the polarized positron production processes.
E-166 Beam Request 6 weeks of activity in the SLAC FFTB: 2 weeks of installation in addition to check-out 1 week of check-out with beam 3 weeks of data taking: roughly 1/3 of time on photon measurements, 2/3 of time on positron measurements. E-166 was approved by SLAC in June, 2003, with proviso as long as a preliminary test run to study backgrounds in the FFTB. E-166 Institutional Responsibilities
Church, Dennis Founder and President
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