A concept to generate polarized positrons from polarized undulator-generated photons had been proposed in the 1980ies by Balakin and Mikhailichenko. Twenty years later, Rainer Pitthan and John Sheppard proposed that an experiment should be done at SLAC's FFTB beamline, to demonstrate the feasibility of this concept in view of its application to a future linear collider, ILC. Subsequently, a collaboration ('E-166'), was formed with spokespersons Kirk McDonald of Princeton University, and John Sheppard of SLAC, to perform this experiment. In this experiment the 50 GeV beam of the FFTB (Final Focus Test Beam), passes through a ~ 1m-long, ~1mm-period helical undulator to produce ~10 MeV polarized gammas. The polarized gammas are used in turn on a "thin' (=<0.5 radlength) Ti target to make polarized positrons by pair-production.

In this experiment, one measures the circular polarization of the photons generated by the undulator (by 'transmission Compton polarimetry')and then, the polarization of the generated positrons. (by converting the positrons back to photons, and measuring their polarization as above, by transmission Compton polarimetry. (In 'transmission Compton polarimetry' of photons, the photon beam is sent through a block of iron, which is magnetised either up or down; this aligns the spins of up to 2 of each iron atoms's electron; then measuring the small difference in the number of photons transmitted for each case allows to deduce the photon polarization, as the Compton cross section depends on the relative alignment of the electron and photon spins).

The proposal was approved after the EPAC meeting in June 2003.
Backgrounds (stray particles leaving a trace in our detectors) are of particular concern for this experiment, and studies of such backgrounds in the FFTB beam line had already been performed during the 2003 and 2004 ('parasitically,' that is while other experiments are running). Before the experiment proper could be done, much more work was necessary, such as further detailed design, simulation of all aspects of it, acquiring detectors and their electronics, stringing cables between the accelerator tunnel and the 'counting house,' design and programming of the data acquisition system. The original plan had the experiment performed in two 'runs' of data-taking in October 2004 and January 2005; however, these two runs were postponed, but did eventually happen, in June 2005 and September 2005.

The data acquired show some of the desired asymmetry, but a more detailed analysis was required; this was done and published in Physical Review Letters (Vol. 100, p 210801 (2008)). A longer paper with more detail on the instrumentation and analysis methods had been completed in May, 2009, and is being published as a NIM A article. The publication of this article completes the work of the E-166 collaboration. However, some of us and others will continue to work on making polarized positrons possible at future linear colliders, as the ILC (see also: ILC at SLAC; ILC-Positron Source Links at SLAC )
(Note: The 'internal' web pages directed at collaborators are an internal record of this work [Please don't quote from them].)

News

• Our NIM article, Undulator-Based Production of Polarized Positrons, has been accepted for publication, on July 30, 2009
  doi:10.1016/j.nima.2009.07.091 (Still has uncorrected proof only [Sept.15,2009])
• The report, SLAC-PUB-13605,DESY 09-061, IPPP/09/38, DCPT/09/76 Undulator-Based Production of Polarized Positrons, appeared (~ May 2009), it is also available as arXiv:0905.3066 and was submitted to Nucl. Inst. Methods A.
• Hermann Kolanoski presented the E-166 Results in a talk, The E-166 Experiment: Undulator-Based Production of Polarized Positrons,
  at the 18th International Symposium on Spin Physics, SPIN2008 Charlottesville, Virginia, 6-8 Oct 2008 (Polarized Sources and Targets I) (pdf, 24 p, 2.2M)
• Our article, Observation of Polarized Positrons from an Undulator-Based Source, has been published in
  Physical Review Letters Vol. 100, p 210801 (2008) Abstract (and link to paper; subscription may be required).
• An E-166 Collaboration Meeting will be held in Princeton May 22-23, 2006.
• Karim Laihem gave a review of E-166 at the Linear Collider Workshop LCWS 06, in Bangalore, India
  { LCWS06 Website India | LCWS06 at CERN/Indico | Indico Contributions List ]
  His talk can be found here: [ [pdf, 12p, (2slides/page) 2.4MB | . ]
• Ralph Dollan and Andreas Schaelicke gave E-166 talks at the ECFA Workshop in Vienna, Nov. 15. 2005, and Ralph Dollan gave a talk at the HU-DESY Research Seminar, Nov. 25. 2005.
  All of these are available from the DESY-Zeuthen Positron Polarization Talks Web Page
• A Collaboration Meeting was held at Zeuthen Nov. 7-9 (Mon-Wdn), 2005. ( Web Page )
• The first run of June 2005 and the second run of September 2005 were completed.
• E166 was mentioned in the June 17 issue of SLAC's Newsletter, Interaction Point, entitled E-166: The Sultans of Spin. (Who came up with this title? Does it have unintended meanings?)
• There were several talks of interest at the 2005 International Linear Collider Workshop, LCWS 05 , among them:
  In the Parallel Session on Accelerator Physics Topics
  - Vinod Bhardawaj Polarised positron sources at the ILC, PDF(1 MB)
  - Roman Poeschl, Status of Experiment E166 at SLAC, PDF(1.1MB);
  - Tsunehiko Omori. Polarized Positron Generation Experiment at KEK-ATF, PPT (1.3MB);
  - In the SUSY Parallel Session, Uriel Nauenberg, The Importance of Positron Polarization, and the Deleterious Effects of Beam/Bremmstrahlung on the Measurement of Supersymmetric Particle Masses and other Parameters, PPT(1.2 MB); and
  + Gudrid Moortgat-Pick (CERN): Polarization (Plenary/Summary Talk) pdf.
• Note also the 2005 International Linear Collider Workshop (LCWS 2005) 18-22 Mar 2005, Stanford, California. [Conference Web Site]
• Note the first announcement for a Workshop on positron sources for the ILC, to be held at Daresbury, April 11-13, 2005. [See Workshop Web Site]
• Due to an unfortunate electrical accident on Oct. 11, 2004, all of SLAC is in a Safety Standdown, with no accelerator running (through at least mid-November) nor shop-work being done. This has effectively prevented the planned October run of E-166 from taking place.
• (mid-September 2004) The installation work for the October run is now seriously under way. The undulators have arrived from Cornell; ( Photos taken Friday, 17-Sep-2004 (by Achim W.) of the Undulators in SLAC's Magnetic Measurements Lab, and also some FFTB photos showing where it and other E-166 equipment will go are here (Web page).
• Achim Weidemann submitted a ~8-page review of E-166 to ICHEP04 the 32nd International Conference on High Energy Physics, Beijing, China, 16-22 August 2004, entitled Polarized Positrons at a Future Linear Collider and the Final Focus Test Beam, SLAC-PUB-10581, July 2004, [ ps 1.3MB | pdf 311 kB ]
  to go with a poster [ Power Point, 2.5 MB, 8 by 16 inches (print at 290% magnification on 24x48 paper)] shown there.
• Achim also gave a talk at the 5th Rencontres du Vietnam - Particle Physics and Astrophysics conference (Hanoi, VN, 5-11 August 2004) ( in the Physics at Future Accelerators Parallel Session) [Powerpoint, 2.7 MB] . The conference contribution is also entitled Polarized Positrons at a Future Linear Collider and the Final Focus Test Beam, SLAC-PUB-10842, November 2004, and available here as [ ps 775 kB or pdf 281 kB]
• Note the talks by John Sheppard (E-166 Update) and Yuri Batygin (Positron Capture) at the January 2004 ALCPG Winter Workshop's   Sources session.
• There is also the talk by John Sheppard (E-166 Update) at the December 2003 ISG 11 meeting at KEK: [ PDF at KEK , or PDF at SLAC, 25 p, 2.8MB]
• The E166 Collaboration Meeting & POWER Meeting will take place at SLAC on October 24-27, 2003; see this Web Site for a draft agenda, registered participants etc. Check it out! Do not forget to register (by sending email to Naomi Nagahashi naomi@SLAC.Stanford.EDU)
  Some presentations of that meeting, including a seminar by Gudrid Moortgat-Pick, Beam Polarization at a Future LC: Searches for New Physics, are available at this Collaboration Meeting Talks Page (Note: Reports there are not necessarily official results of the E-166 collaboration).
• There were 3 E-166-related talks at the American Linear Collider Workshop at Cornell, 13-16 July 2003;
  in the parallel sessions of the
  Electroweak Working Group (Achim) and the
  Accelerator/Sources Working Group (Kirk, John).
  and one at the International Europhysics Conference on High Energy Physics EPS (17-23 July 2003) in Aachen, where Gudi Moortgart-Pick's talk can be found as Item 4 in the
  Accelerator R and D Session.
  (The paper for the latter presentation, Gudrid Moortgat-Pick, Prototype for an Undulator-based Source for Polarized Positrons, can be found here [Gzipped PS ps.gz, 230 kB]; submitted 11/11/2003).
• In a meeting with SLAC Director Prof. Dorfan, Profs. Drell, Paterson, and Loew on Wednesday, June 18, 2003, Kirk, Peter (by phone) and John learned that E-166 was approved! But we should demonstrate that backgrounds are reasonable, before the final installation and data-taking run.
• (Updated June 12,2003) Our presentation to the SLAC Experimental Physics Advisory Committee Meeting on June 12, 2003 can be found on the EPAC Meeting Program website here
• Sorry, this web site had not been updating from Friday, May 16, afternoon to Monday, May 19, afternoon [PDT].
  Problem was due to move of web server; it is now fixed.
• Proposal E-166-bis, has been submitted to the SLAC EPAC on Friday, May 16, 2003; see the latest version here [PDF, 1330 kB, 67 p.]
• Proposal-writing for Resubmittal to EPAC continues. (More detail is in the Internal News - for Collaborators)
• Note the ECFA-DESY Linear Collider Workshop in Amsterdam, April 1-4, 2003; Program Overview.
  The Polarization Session has a talk by Peter Schueler on Positron Polarimetry, and other talks of interest, by Torrence, Duncan, Arestov, Desch, Rizzo; including an appeal by G. Moortgart-Pick for a Polarization at a LC write-up.
• (November 22) Our proposal has been presented to the EPAC; The final version of Kirk McDonald's Presentation to the EPAC on Nov. 20 is here as [PDF, 24 p, 1.6MB].
  Our answer to questions of the EPAC is here as [PDF, 5p, 78kB].
• (November 20, 2002)Our proposal will be presented to the SLAC Experimental Physics Advisory Committee (EPAC) Meeting in the Research Office Building on Wednesday, 20 Nov., at 14:30;
  See above for links to our presentation and answers to EPAC questions.
  For reference, the proposal (as a living document, continually updated) is here [pdf, 1.26 MB].
• (October 22,30, 2002)We have completed writing a proposal and sent it to the SLAC PAC (Physics Advisory Committee) this (late) afternoon. The proposal can be found here [pdf, 1.24 MB, 55p]. There will be presentations on this proposal at the up-coming MAC(Machine Advisory Committee) Meeting at SLAC, November 6-8 (J.C. Sheppard's presentation is on Thursday, Nov.9, at 9:00) and, of course, at the next PAC Meeting 20-21 November (E-166 presentation by Kirk McDonald scheduled for Wednesday, Nov. 20, 2:30 p.m).