Connect through Zoom: https://pitt.zoom.us/j/98556040471
Meeting ID: 985 5604 0471
Swagato: question about Belle II results AF: depends on Z->tautau type of result; if Belle can measure EWK physics through taus, we would be interested SB: presenting polarization here, covers e.g. AFB and mixing angle, but there is full program of tau physics (e.g., BR, Vus, ...), will have white paper AF: probably rare processes / precision physics frontier is interested; if they were unclear, we can help mediate Richard Ruiz - Weak Boson Scattering with Weak Boson PDFs --------------------------------------------------------- LOI question: how does EWK theory behave at very high energies, when momentum transfer is >>mZ? can explore in many ways: EW boson scattering/fusion; EW boson PDF; EW parton showers; spin correlation and interference in parton showers; muon collider physics exactly one year ago: exploring polarized matrix elements in MG5: this was done EW VBF w/ multi-TeV muon colliders (effectively EW boson colliders) NEW: explore validity of W/Z PDFs -> just added support for polarized W/Z PDF in MG5 (https://arxiv.org/abs/2111.02442) what was done in MG? mumu -> F+X = f * f * sigma + power-law and log correction fully differential events for VV' -> F at LO V is polarized vector boson F can be anything, up to 5-6 legs W/Z depends on helicity; added also polarized photon PDF (Weizsacker-Williams) spent lots of time understanding when factorization works necessary when m(V)/m(VV) ~< 0.1, just like heavy quark factorization e mu -> H H nu nu see effective-W approximation vs full matrix element: see disagreement for di-H masses <1TeV: highly not trivial disagreement due to W and Z having large mass -> see that reducing vev by factor of ten you get agreement between EWA and full ME really see that disagreement are power corrections depending on W mass e mu -> G G G nu nu uncertainty band due to mu_F factor again, if one reduces vev, can get better agreement looked at multiple processes: 2H, 4H, tt, ttG, ttH, ttZ, VVV... table with m5amc notation for each process summary: LOI question is how EW theory behaves looked at polarized matrix elements, seeing clear picture that these PDFs are valid Ayres: studying how to simulate EW processes at muon collider, what about tests of anomalous couplings? plans? large uncertainties could probably limit ability to set limits on anomalies? RR: EW VBF: different work by Antonio Constantini and Luca about EFT; my side and Olivier's: our question is how EW fundamentally works at high energy, from theoretical point how factorization itself works in broken gauge theory; even if new collider constructed, there is question about whether tools we have at LHC are rigorous enough to discuss my question is what are the uncertainties, and how do they go together (slide 7) AF: this shows that LHC tools not work, and new tools still need some work; any idea about next step in improvement? RR: parton shower is next part; machinery is there in MG5 (code to do matching, do DGLAP...), whether it can be done by March, that is the big question Michael Roney - Electroweak precision at Belle II ------------------------------------------------- upgrade of SuperKEKB w/ polarized electrons: high precision EW program; probe dark sector Michel parameters of tau; EDM; magnetic form factor... upgrades to provide x40 luminosity plan for precision neutral current EW measurements: ALR for beauty, charm, tau, muon, electron (only place where you can do these independently) Chiral Belle ALR: shall choose electron helicity randomly pulse-by-pulse, to get reduce systematic effects (need to measure it, though - will use tau pairs at IP?) existing tension in data at Z pole: 3.2 sigma between ALR SLC and ALR LEP: now Chiral Belle can measure this slide w/ SMPO fit, one exception to everything in place international collaboration of accelerator and particle physicists theorists working on SM EW calculations: ee->mumu, ALR vs mixing angle, ee->ee (this is new development: see asymmetry w.r.t. mumu flips, due to effect of t channel) new generator: ReneSANCe: new generator with beam polarization capable to produce Bhabhas comparison between theory calculations and ReneSANCe, ALR vs angle w.r.t. e- direction: good agreement one could use ReneSANCe to estimate uncertainties on ALR and mixing angle vs variations of W mass Belle II paper w/ Bhabha acceptance in central part of detector: major development assuming 70% polarized beam at IP one gets impressive precision on ALR for b, c, tau, muon, electron (barrel): relative uncertainties between 0.5 to 2.4% (b and tau), with dataset of 40/ab note that luminosity 20/ab or 40/ab gives small improvement: hitting systematic limit Chiral Belle combined leptons w/ 40/ab should have uncertainty comparable to world average precision probe of running of mixing angle when moving from pole: get sensitivity to new physics away from pole beam polarization cancels in ratios: highest precision test of universality of fermion couplings 2D plots of vector vs axial couplings show that Chiral Belle can get 4-7 times improvements in bottom and charm cases in an nutshell, Chiral Belle probes both high and low energy scales unique sensitivity to dark sector w/ parity-violating light neutral gauge bosons, especially when Z' is off-shell or couples more to 3rd generation Moller experiment at JLAB will measure mixing angle electron below 100MeV w/ similar precision EIC can measure mixing angle in similar kinematic region as Belle, but lower precision Chiral Belle can also provide tau Michel parameters, EDM, magnetic form factor F2 electron beam polarization reduces backgrounds on tau decays EFT interactions between tau and photon: F1, F2 (anomalous magnetic moment) enter picture angular polarizations of tau sensitive to EDM conclusion: can get tau EDM limit to <1e-20 (stat only); if unpolarized, <5e-19 magnetic form factor: get limit on real part of F2(10GeV): up to 2e-6 (stat only, but usually systematics are under control) hardware: lots of work here, low-emittance polarized source, spin rotators (lots of work here), Compton polarimeter (will reach absolute precision of longitudinal polarization of order <1%) spin rotators: success in having them not mess up luminosity summary: e- polarization upgrade opening a unique discovery window w/ precision EW competitive measurements with those at Z pole, complementary to Moller and low-energy PV (test running couplings) Junping: what is expected measurement uncertainty on beam polarization? MR: assuming 0.5% in studies, study using BaBar, expect statistical uncertainty to 0.3% Ayres: showed LR measurements can be interpreted as measurements of vector couplings, but in principle ALR would include also axial coupling; assuming that axial coupling is the LEP/SLD one? formula in slide 5 has an axial coupling in denominator too? one could also do AFB to get info about axial couplings MR: assuming LEP values; AFB: not competitive; also have dependence on acceptance, one could in principle have sensitivity to axial by changing acceptance (angular cut) or doing 2D AFB vs ALR measurement Ayres: table 13, some efficiencies seem ~low? MR: b quark selection to get high purity sample, acceptance plays big role; these numbers are realistic, but would require people to work (tau and muon solid; electron based on Belle; b and c seem small, but realistic, need dedicated studies to identify them) Ayres: LEP results in terms of effective mixing angles; here have results vs mu? which final form of results? MR: probably prefer to publish vector coupling ;-) calculations (such as slide 11) use effective on-shell case focus is precision Junping: does ISR play a role in ALR? it would change effective center-of-mass energy MR: it does, and it is incorporated in the studies shown (e.g., slide 9, points are from KKMC, which includes it; ReneSANCe also does); could be interesting to do measurement vs c.o.m. energy in case of very hard ISR (but it would be low-statistics study...) Ayres: slide 16, impact of axial vector couplings; they appear in that formula, and in case of charm uncertainty seems large; was this uncertainty included? it should be overall scaling effect? MR: interesting point, worth taking a look at how sensitive we are to overall normalization