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Meeting ID: 985 5604 0471
Intro ----- muon collider 30TeV was considered one of benchmark points, proposal to collect 10/ab -> not yet finalized FCC-ee 100TeV: 30/ab https://arxiv.org/abs/1511.06495 Siqi Yang - AFB measurement at hadron colliders & weak mixing angle at CEPC --------------------------------------------------------------------------- two independent activities: measurement of AFB at hadron colliders; effective weak mixing angle at CePC AFB theta originally angle between incoming and outcoming fermions, but at hadron collider get effect from gluons, need recalculation historical review of AFB best precision from LEP, SLC, Tevatron expectation from LHC: expect statistical to go down, but PDF > 0.0002 (roughly order of uncertainties at LEP/SLC/Tevatron) future LHC (>1/ab): statistical < 0.0001 (becomes negligible), but PDF uncertainty still large, hard to reduce note: theoretical uncertainty based on 2-loop corrections is 0.00005: small, need to improve experimental precision significantly to compare with theory LHC measurement dominated by light-quark initial state in future, high-precision measurement from single experiment will give higher precision than LHC combination combinations will require to make assumptions most important issue: AFB dilution, need to know direction of quark and anti-quark that is problem for AFB, but makes AFB usable as tool to look into proton structure in novel way, not covered by other experiments (it is measurement of quark vs anti-quark PDF difference for Q=100GeV) using AFB in PDF global fitting reduces uncertainties on ubar/u_valence and dbar/d_valence issue: correlation between proton structure and weak mixing angle slide with reduced uncertainties used weak mixing angle fixed (see that central value did not change) if one uses AFB w/ weak mixing angle fixed to different value from the one used in PDF global fitting theory, get big biases (0.2315 vs 0.2324) there is a lot of work to do to include weak mixing angle as floating parameter to study its correlations with AFB one could try and reduce that correlation at experimental level: Z region: sensitive to AFB/weak mixing angle sideband region: sensitive to AFB/dilution --> use AFB vs M: weak mixing angle gives global shift, dilution works as a shape rotation -> use shape only to reduce correlation https://arxiv.org/abs/2108.06550 look at slope of AFB vs M see effect of using sideband-AFB only in PDF fit, and using Z-pole data with AFB slope correction: correlation reduced, central value gets back to before weak mixing angle has worst precision among EWK fundamental parameters! essential to get improvements in its precision Ayres: systematics: got reduced or improved robustness? SY: no major changes, updated to current CePC detectors Junping: invariant mass can be determined with beam energy; effect of ISR? considered effects? SY: very small, less than statistical uncertainty Ayres: if no separate input from lepton colliders, are there estimates on how LHC can measure AFB and constrain PDF? SY: spectrum itself will be worth studying, lots of stats, possibility of data-driven estimates Ayres: plan is to have updated estimate soon and quantitative estimates that can be included in report? Jurgen Reuter: recent work Paolo Nason and Giulia (Zanderighi) about LuxPDF and lepton content in PDF; any idea to work about it in ATLAS/CMS? could look at lepton-initiated state Zhijun Liang - R_b in hadronic Z decays at CEPC ----------------------------------------------- look at BR(Z->bb)/BE(Z->had) studying systematics at LEP measurements, and seeing what can be done in future experiments to improve b tagging hemisphere correlations is major systematics some theory systematics: CERN-EP/98-23 details some QCD-related syst (high order QCD corrections impact hemisphere correlations; impact on AFB) see linear behavior of correlation vs b-tag efficiency, extrapolate LEP uncertainty to CEPC b-tagging ROC curve alignment systematics: already small at LEP, seem to almost disappear? hit efficiency, lepton efficiency: expect improvement of factor 2-6 w.r.t. LEP, and their effect on Rb measurement was already negligible charm modeling and lepton ID: dependent on input of flavor experiment (BELLE...) need more study to check D mesons at FCC-ee gluon splitting: estimated comparing data and simulation in the past, did data-driven study, looking at Z->4b and at eta of third jet in 4b, 2b, and charm events expect that also input from theory has improved goal: use Rb/Rc measurements as benchmarks to optimize detectors need some external inputs: charm modeling, higher-order QCD calculations, gluon-splitting modeling Ayres: b-tag hemisphere correlation: in previous talk, mentioned will try to use CEPC simulation instead of OPAL? ZL: this is ongoing; basically have two approaches: seeing if one can reproduce OPAL plot using two different b-tagging schemes; expect to be done with this in time for Snowmass report Jurgen Reuter: ILC group in Valencia working a lot on Rb and bbbar mass measurements, any contact with them (e.g., look at ILC vs CEPC systematics)? ZL: please put us in contact! JR: Adrian will give talk next week at ILC workshop Junping: effect of gluon splitting: are events categorized? efficiencies should be different according to number of hard gluons once event categorized, one can calculate contribution w/ and w/o hard gluon, and reduce some theoretical uncertainties Ayres: on time scale of CEPC running, expect improvements on HO QCD theory: suggest to keep them separate, it is job of theorists to reduce them ;-) Chilufya Mwewa - Longitudinal VBS at 100 TeV -------------------------------------------- test EWKSB w/ longitudinal VBS, search aQGC look at same-sign-WW+jj leptonic channel primary goal: measure sensitivity (anomalous couplings if there is time/manpower) generated signal MC, validating will use centrally-produced background samples analysis will use BNL framework (currently doing validation with RIVET) signal samples: Madgraph5 3.1.0 + Pythia8 inclusive sample, longitudinal/transverse and mixed polarizations issue with mixed polarizations and taus: need to separate them (link to discussion) using NNPDF 3.0 LO, 100TeV c.m.e., 10k events per sample comparing inclusive sample with sum of polarized samples: cross sections are ok, jet distribution different (fewer jets in inclusive sample), but close enough? leading jet pT: seems ok validation of background samples: looking at ttbar compare snowmass samples (MCProd, on collab/project/) to fcc-hh samples (on /eos/experiment/fcc/hh) at truth level both samples converted to hepmc differences: MadGraph version some cuts dilepton mass cut applied on FCC-hh sample only, introduces large difference in cross section (effectively, snowmass sample is inclusive, fcc-hh is di-lepton) summary: exercised and validated setup for signal sample production started validation of background samples to do: adjustments of analysis framework baseline is sensitivity, on time scale of two months Junping: outcome scattering cross section measurement, hard to interpret in lobal fit? Marc-Andre: unclear how to translate cross section to aQGC couplings Tao Han: TT dominant contribution, how we separate LL? Marc-Andre: basically do template fit to extract the fractions Jurgen Reuter: cuts on slide 6 done only for MC validation, or optimized for BSM signal search? CM: for the moment, just for validation Yang Ma - QCD fragmentation at muC ---------------------------------- background: PDF of a lepton equivalent-photon approximation (EPA): treat photon as parton of electron application at muon collider: at high energy, one can consider muon as emitting photon, and that photon interact with the photon from other muon HE muon collider: EW version of HE LHC: all SM particles are partons when energy is high look at EW parton luminosities (with different polarizations) mu+mu- annihilation decreases with energy as 1/s ISR can give 10% enhancement fusion increases as ln^p(s), and at high energy takes over annihilation want to go beyond EPA; done so far: ll annihilation EPA and ISR effective W approximation (EWA), suggested by Sally Dawson in 1985 want to add: above QCD scale: QED x QCD: gluons and quark emerge above EW scale (mZ): get EW partons (W, Z...) resulting PDF for muon collider (solving DGLAP w/ more and more splittings) at 30-50GeV: see muon PDF peaking at x~1 (as expected) at 3-5TeV, stuff starts appearing with lower x (and more stuff appears: from muon/quarks/gluon alone at 30-50GeV, now have WL, WT, Z) at 3-10TeV machine, get partonic luminosity for photon-gluon and photon-quark are about 20% of photon-photon one: not small given strong QCD coupling, could get largish QCD cross sections study of jet production high-pT range (pT>(4+sqrt(s)/3TeV)GeV analysis shows dominant process at high-energy muon collider: quark/gluon initiated jet production dominates highest background is not gammagamma initiated any more two types of processes: mu+mu- annihilation vs fusion annihilation peaks at m(ij)~sqrt(s), fusion peaks near m(ij) threshold annihilation very central, fusion spread out (similar to ISR) jet pT/E distribution: see that <60GeV, QCD jet production very large, cannot see anything else only above 60GeV pT / 200GeV E can see WW production and possible new physics next step: EW FSR in future super-high-energy colliders, collinear splitting happening also in final state -> get EW jet factories need to treat: electroweak fragmentation functions (EW FF) both fragmentation and parton distributions controlled by DGLAP equations (evolutions - splittings - are in opposite direction) summary: EW PDF and EW FF: at very high energy, collinear splittings dominate ISR: EW bosons to be treated as partons FSR: EW FF work in progress; energetic final state particles also have collinear radiation: EW jet factories machine: high energy muon collider is EW version of HE LHC lots of areas to work on (SUSY, DM, Higgs, SM...) two classes of processes: annihilation and fusion main background is jet production: low-pT: non-perturbative gammagamma-initiated hadronic production dominates high-pT: q- and g-initiated jet production dominates Marc-Andre: running conventional PDFs, would be happy to be able to use PDF that give direct radiation of W.. how do you see future? when this ready for experimentalists? YM: MadGraph implementing EWA (effective W approx), people working on implementing the other, maybe not too far? Ayres: surprised to see that dijet cross section gg-initiated larger than qq-initiated, because gluons need to be irradiated by quark YM: gg to gg is large, color factor in process overpowers alpha_S Junping: was any study including these studies, e.g., Higgs measurements? Tao Han: no, our calculation is really new; will not change picture, we have cut at 60GeV (slide 11), and usually analyses have higher cut Tania Roberts: MadGraph authors concentrating on W emission Tao: comparison between fixed-order MadGraph calculation vs EWA TR: looking for test of validity of EWA for specific process YM: slide 4, see tt production: now compared with Fabio Maltoni's result, where used fixed-order ttbar, 4-leg process compared with Fabio's results, good agreement; need to be careful about EWA: to make it valid for hard process need to make sure s-hat not too small (otherwise cannot consider W ~massless; get two W that are not relativistic, EWA cannot be applied) TR: have some mumu-initiated new physics signal; expectations change dramatically if this not included properly (there is set of additional diagrams not included in EWA?)