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Meeting ID: 985 5604 0471
Takahiro Mizuno - Study of A_LR using radiative return events at ILC250 ----------------------------------------------------------------------- primary physics goal of ILC250: Higgs couplings, and whether they deviate from SM values corrections are of order a*mH^2/M^2: a coefficient order 1, M mass of new particle -> need measurements with 1% precision SMEFT: Lorentz-invariant, SU(2)xU(1) dim-6 operators conserving CP: there are only 10 useful observables: Higgs processes, but also W/Z boson EWPO, e.g., ALR at Z pole deviation of ALR from SM contains three terms one can write gL and gR coupling constants (they are different), and that gives rise to ALR current best measurement has ~1% precision; need full detector simulation to figure out uncertainty at ILC250 generating 900/fb for each of the two polarization combinations, mixing angle set to 0.22225 (correspond to ALR=0.219298) signal is e+e- -> Z gamma -> 2jets + gamma signal event: radiative return w/ photon escaping into beam pipe: cosine polar angle of photon is >0.999; m(Z) between 80 and 120GeV backgrounds: 4-fermion single-W, 4-fermion single-Z, WW... suppress backgrounds with cut on number of photons >50GeV (require 0), on visible energy (between 120 and 160GeV), di-jet mass (between 50 and 160GeV) require also cosine angle between two jets and photon (i.e., all tracks that form the 2 jets?) to be >0.95 photon is very forward, expected to be in opposite region w.r.t. the two jets from Z S/B~1/0.02 for e- -0.8 and e+ +0.3 polarization S/B~1/0.006 for e- +0.8 and e+ -0.3 polarization efficiency is 75% in both cases, very similar plots of m(2jet) signal and background: indeed see mostly signal LR precision: L and R in asymmetry are defined for 100% polarization; rewrite formula when polarizations are not 100%, get additional factor ALR precision gets contribution from ALR_observed and uncertainty on additional factor assume uncertainty on polarizations of e+ and e- are independent to calculate uncertainty on additional factor ALR_observed uncertainty: get formula for uncertainty (note that correlated parts of uncertainties cancel in the ratio) final conclusion: can get uncertainty of order 10 better than SLC if uncorrelated part of uncertainties (on product of efficiency and luminosity) remains below 0.006% other uncertainty contributions: polarization error: assume 0.1% luminosity, efficiency: assume negligible Ayres: nice to see progress with full simulation! two questions: is target of 0.006% realistic? stability of luminosity over time will be important? luminosity will need to be monitored when one changes polarization; any sense on how well we can monitor that? TM: mostly expect that to be in correlated part Junping Tian: number does look challenging; at the end care for ratio; suggest to calculate uncertainty if one achieves 0.1% Jurgen Reuter: question on event selection; cut broad window on dijet mass; is S/B good enough, or one could optimize? (slide 12, see picking up more background than signal on left plot) Jacob Beyer: I am working on the same samples on something similar, nice to see this; have question on this mass range: to which extent it makes sense to integrate ALR over such a big mass region (50-160GeV)? ALR varies a lot around Z pole; is this useful from theoretical point of view? TM: if we integrate over full range, deviation of ALR is expected to be small Junping: now mentioned average, but useful part is as close as possible to Z pole; other parts affected by photon, and symmetry disappears there Ayres: theoretically, in principle well defined, whether one uses effective operators (as here) or effective coupling; question is what is goal and strategy: ALR, when one puts in photon, changes sign: if one integrates over wide window, partially washing out asymmetry; binned analysis could be more powerful Junping: when going too far from pole, also get effect of 4-fermion operators Ayres: related to my second question: background small, estimated with SM, and subtracted; would be good to have data-driven estimate, if possible; slide 12: shape of signal and background very different, one could do differential analysis of mass and do model-independent background subtraction Jurgen Reuter: note that 4-fermion operators give flat distribution; one could also add events that are not-radiative returns and compare: 4-fermion would contribute in same way to both (use to constrain 4-fermion contribution) Ayres: ZZ background is the only one that gives a real peak too, would need to look at visible part of the other Z Jurgen: also H Ayres: indeed, decay to invisible small in SM, but shall be complete Junping Tian - Status of global SMEFT fits for Snowmass ------------------------------------------------------- goal of white paper: coherent projections on precision EW/top/Higgs couplings at future colliders ongoing (and completed) work: chapter 4 contains individual directions: this is done (Jiayin) chapter 5: 4-fermion operators: Yong Du will report in next talk chapter 7: top quark operators: yesterday presentation at EF03 photon and muon colliders not in original plan, but could add if there is interest important part: need to update the inputs (responsibility of topical groups) recent progress: independent fitting codes exist in group, need to agree on conventions and operator basis: go for original Warsaw, w/ same assumptions and inputs (nominal inputs from ESG, statistically consistent, not so much the systematic part) flavor assumptions: complicate discussion, lots to assume; however, seems can relax lepton flavor universality (LFU) and get some promising results fit is split in different sectors: EWK/Higgs fit updated (w.r.t. ESG), working on low-energy stage of future e+e- global fit for 4-fermion operators; top inclusion Fit-1: EWK and Higgs: slide with summary of operator basis, observable (alpha, GF, mZ; e+e- -> WW optimal observable; Higgs cross sections; Drell-Yan), assumptions (no 4- fermion; flavor diagonal; CP even; w/ and w/o LFU and Higgs exotic decays) tables with EWPO inputs needed, from ILC and FCC-ee discussion about uncertainty on Ab: FCC-ee much worse than ILC; GigaZ option could help here? Ae can be determined using tau polarization (hence small uncertainty) tables with Higgs input plots with preliminary bounds using ILC250 four flavors of fit for now assuming U(2) on quark generation 1 and 2, likely to be completely eased four operators for each generation, using Gamma(Z->f) and Gamma(W->f) Ruc: EWK charge of u and d different, can use to calculate asymmetry ALR suggestion to use AFB at LHC as additional input plot with bounds on effective couplings, based on partial widths (Z, W, H) plot for ILC250, HL-LHC + LEP, and FCC 240GeV (also add HL-LHC to ILC250 and FCC Jurgen: chapter 9.4, impact of photon collider, what about e-e- option? could that add anything? goal is lepton flavor violation; wondering if it were useful to add JT: there is some interest, but no follow up? shall investigate CP-odd: one of them already studied experimentally, but not so much others: would need help to study Yong Du - Global fit for 4-fermion operators & operators at Z-pole ------------------------------------------------------------------ framework: turns out that in 4-fermion case, Higgs basis is more convenient for calculations than the Warsaw one currently using only flavor-conserving operators there are 3 operators for one flavor (x3), and 6 for two flavors (x3) list of Z-pole observables and W-pole observables: BR, asymmetries, widths, cross sections in Z case: axial-vector terms; not including in fit some Z BR more observables: cross section e+e- -> mu-mu+ / tau+tau- differential Bhabha cross section (vs cos\theta) GF from tau decay Michel parameters from polarized muon decays updates: Michel parameters from EF04 meeting differential Bhabha: there was problem, fixed strategy: keep only linear order in EFT, and do chi2 fit optimistic scenario: one operator at a time conservative scenario: use full correlation among observables general conclusion from fit: if one only considers one operator at a time, get much stronger constraint than when considering all operators some exception: Z->tautau coupling and Michel parameters from polarized tau decays (very weak correlation with other operators; expect situation to improve when Michel parameters from polarized tau will be available) future colliders as precision machines: projections for inputs on EWPO used inputs in table, from de Blas, Durieux, Grojean, Gu, Paul, JHEP 2019 summary of results delta-g: see that FCC will be slightly better than CEPC, but situation will change when some updates will be included CLIC and ILC very similar; in general circular colliders seem to perform better than linear ones see in some cases that optimistic and conservative are the same, or only optimistic due to correlations among operators slide with table of correlations among correlators final slide: comment: C1133 and 3311: can break degeneracy using beam polarization (missing projections; good to include them to lift degeneracy) no constraints on C2222: muon collider or muon-nu_mu scattering? Junping: fit now includes W and Z poles, there is good assumption that there are no 4-fermion at W and Z pole; suggest to fit data with only 4-fermion and both, to see if Z pole part is constrained well enough YD: plan to do Ayres: plan to look at boson production at future colliders? YD: yes Ayres: Junping's comment: no need to float all operators, can make life easier; one can also break some degeneracies of 4-fermion can be broken by looking at Z pole vs somewhere else Jakob Beyer: confused by one thing: circular colliders achieve same precision in optimistic case, then they perform better than linear colliders when one includes correlations; is not usually the other way around? circular more lumi -> higher precision; linear beam polarization -> reduce correlations updates to table with observables: difficult (quite late) now know luminosity and energies: could ask for at least update of statistical uncertainty Junping: some of the numbers could be updated really want to expand to 4-fermion operators, so this is very important input Jurgen Reuter: there also some new studies, definitely not included in this document Junping: those are probably included in EF03, we need here all flavors some new updates in projections for C2222, and top?