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Jakob Beyer / Jenny List - Beam polarization for EWK precision -------------------------------------------------------------- two advantages: direct access to chiral interactions (shown for future colliders) isolating systematic effects (still open question) looking at EWK fit in different scenarios: both beam polarized (ILC-like) only e- polarized (CLIC-like) no-polarized scenario not yet investigated 2/ab and 10/ab scenarios in fit, polarization and luminosity (the uncertainties?) are free parameters look at e+e- -> Z/G* -> mu+mu- return-to-Z events, and high sqrt(s) polarization-weighed distributions -> toy-fluctuated distributions -> combined log-likelihood fit 6 fit parameters physical parameters (3): total chiral cross section; initial/final fermion chiral asymmetry correction parameters (3): interference correction radiative correction factors (L and R separately) fit results uncertainty drops by factor 2 in high-lumi case about 20% reduction when adding e+ polarization? Ae (the electron - i.e., initial - chiral asymmetry) decreases a lot (factor 4?) when positron beam polarized results on polarization (nuisance parameter) and Ae shows importance of redundancy offered by knowing e+ polarization systematic effects flipping polarization, get different physics, in same detector -> unique global signatures of systematic effects, can be decoupled and reduce their effect looked at some of them: first tested (looked at LEP papers) is muon acceptance (ALEPH, L3, OPAL: muon acceptance was among dominant) used two parameters to describe acceptance: dC and dW (C is acceptance, W is cos\theta\*) acceptance modeled as a box (center, width - C and W) ILD: could be able to ID muons up to 7deg from beamline in fit, dC and dW (size of box) are determined very well beam polarization: uncertainty on C and W halved for this setup, only two parameters affected by letting dC and dW free: KL and KR see that effect is very small, and there is no additional advantage from e+ polarization (mu acceptance is well determined) question: is model too simplified? what is case with unpolarized beams? direct access to chiral part of interactions makes EWK measurements much easier: decouples them from other physical or systematic effects that do not depend on polarization Ayres: Ae determined much less precisely than Af; Af is from AFB, which, at Z pole, is proportional to product of Ae and Af: why one much more precisely than the other? JB: we have access to polarized AFB, and that is directly proportional to Af Ayres: then, would not you need to know polarization well? JB: shall check interpretation of results; all improvement in Ae, Pe-, Pe+ is from redundancy, need to think about that Ayres: what about e+e- -> e+e-? Af becomes Ae, one could do combined fit of the two processes... would that make advantage of positron polarization less important? (one can get Ae from final state) JB: issue is extra term from t-channel, interpretation less direct (but can be done) Ayres: all quantities improve, but need also to keep in mind that polarization comes at price of luminosity in parameterization (slide 5), it is linear in cos\theta; summing the two to get unpolarized cross section, get term proportional to Ae*Af Junping: this is single channel w/ muon, Ae should be better at end if looking at all fermion pairs JB: indeed question is why Ae precision much worse than Af; then, adding all channels, difference goes away? Alberto: unpolarized scenarios? JB: parameter like Ae cannot be determined, fit does not converge, cannot get uncertainty planning to add constraints to parameters that cannot be determined Junping: Ae and Af can be decoupled if one integrates out cos\theta distribution (Af disappears), and Ae is just count of events; is that why Ae limited by knowledge of polarization, while Af is from asymmetry? Ayres: one could go to double-AFB (initial and forward); this depends on Af, but again affected by polarization uncertainties Junping: on systematic uncertainties; how are C and W fixed from data? cut on angular distribution in cos\theta? JB: determining w/ MC what is the influence of cut on C and W (and variations of these cuts) on the differential distributions, then parameterize the bin variations (when varying the cuts on C and W)