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Polarimetry at NLC How Precise? e - e - 99 Workshop, UC Santa Cruz Dec. 10-12, 1999

Polarimetry at NLC How Precise? e - e - 99 Workshop, UC Santa Cruz Dec. 10-12, 1999. Mike Woods SLAC. Standard Model asymmetries in e + e - and e - e - testing for physics beyond SM polarimetry from SM asymmetries running at Z 0 resonance

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Polarimetry at NLC How Precise? e - e - 99 Workshop, UC Santa Cruz Dec. 10-12, 1999

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  1. Polarimetry at NLC How Precise? e-e- 99 Workshop, UC Santa Cruz Dec. 10-12, 1999 Mike Woods SLAC • Standard Model asymmetries in e+e- and e-e- • testing for physics beyond SM • polarimetry from SM asymmetries • running at Z0 resonance • Other considerations for precision polarimetry • background suppression of W pairs in e+e- • depolarization in beam-beam interaction • design of extraction line and beam losses

  2. Assumptions for Machine Performance Parameter e+e-e-e- 500 GeV 500 GeV 80 fb-1 25 fb-1 P1 0 90% P2 90% 90%

  3. SM Asymmetries in e+e- From Snowmass ‘96 study, Consider, Final State #events ALR W+W - 560K 100% q q 250K 45% 0.005 l+l- 120K 10% 0.032

  4. SM Asymmetries in e+e- From Snowmass ‘96 study, Consider, Final State #events ALR W+W - 560K 100% q q 250K 45% 0.005 l+l- 120K 10% 0.032

  5. e- W- n W+ e+ SM Asymmetries in e+e-(cont.) • Notes: • 1. Better than 1% polarimetry is needed to fully exploit • these measurements for SM tests. • 2. Can we use asymmetry in forward W pairs as a polarimeter? • Yes, if can achieve backgrounds below 1%. • (This level of backgrounds is achieved for LEP200 W mass • measurements, if require one W to decay to ee or mm.) • advantage wrt Compton polarimetry is that any • depolarization in beam-beam interaction is properly • accounted for • disadvantage wrt Compton polarimetry is Compton can • achieve 1% accuracy in a few minutes

  6. SM Asymmetries in e-e- e-e- to determine: From F. Cuypers and P. Gambino, Phys. Lett. B388: 211-218, 1996, Measure 3 asymmetries: Consider, For comparison, i) SLD has achieved ii) E158 at SLAC will achieve (at Q2=0.02 GeV2)

  7. SM Asymmetries in e-e- (cont.) Notes: 1. Achieves better than 1% polarimetry using a SM physics asymmetry. Again, has advantage wrt Compton polarimetry that it properly takes into account any depolarization due to beam-beam effects. But disadvantage is that Compton can achieve 1% accuracy in a few minutes.

  8. The Linear Collider Z-factory option Some anomalies remain from the LEP/SLC era (sin2qWeff, Ab, Nn) May be very desirable to accumulate a large Z sample (>>10M) with polarized beam(s) (ex. Monig and Hawkings, DESY-99-157) Ideally the positron beam has P+=0.6, and can then use Blondel scheme for polarimetry from the measured physics asymmetries in the detector. However, if positron beam is unpolarized then will want a very precise Compton polarimeter, better than the 0.5% accuracy achieved with SLD’s Compton. And will want the Compton to measure any beam-beam polarization effects.

  9. Other Considerations for Precision Polarimetry 0 2.4% 1% 2.6% 2% 3.1% • Background suppression of W pairs in e+e- • most important is to achieve high polarization; • increasing P from 80% to 90% allows for a • factor 2 further background reduction • need more precise polarimetry as P increases An example P =90% Observe 400 events -- after analysis cuts, but no polarization cut Observe 40 events -- after additional requirement on polarization state An excess of 20 events is observed above the expected W pair background. Would like 1% polarimetry in order to achieve a 4s signal.

  10. Depolarization in beam-beam interaction • need Compton polarimeter in extraction line to measure • polarization with and without collisions, or • polarization measured from a physics asymmetry • need to emphasize that depolarization should be included in • parameter tables for the Interaction Region • need to encourage the simulation programs Guinea-Pig and • CAIN to include polarization effects

  11. But • Design of Extraction Line; effect of beam losses • ideally, want to have a large number of diagnostic devices for • measuring and optimizing luminosity, • polarization and energy measurements • in practice, need to balance this with cleanly transporting the • beams to the dumps. Want to minimize beam losses • and backgrounds for the detector. • ZDR approach allowed for a Compton polarimeter, a wire scanner and • other devices • Increased disruption effects in higher luminosity schemes or e-e- option, • may lead to elimination of some extraction line diagnostics • important to point out how this may limit the physics capability • important to still try to incorporate polarization and energy diagnostics • in the extraction line

  12. Summary Standard Model asymmetries - better than 1% polarimetry is needed for testing SM and probing for new physics - SM asymmetries in e-e-e-e- and in e+e-W+W- should achieve better than 1% polarimetry (very good detector coverage and capability needed for forward angles) Other considerations for precision polarimetry - should have a Compton polarimeter in the extraction line - depolarization effects should be calculated in beam-beam simulations and tabulated in IR paramater tables - high luminosity scenarios and e-e- option significantly complicate the design for a Compton polarimeter in the extraction line, and could make it impractical

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