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Meeting ID: 955 4136 9778
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Intro
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shall have CLIC talk at next meeting, continuation on today's theme
Zhijun L: MC: must people use a special production?
Ayres: any MC works; in fact, if collaboration has samples that they are willing to share, that would be ideal
Zhijun Liang - EWPO at CepC
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summary of machine: 100km machine; 1.5e12 Z; 2e7 WW, 2e6 H
key observable contributed to EWK fit: mZ, mW, mixing angle, mH
can improve using ZH run, Z run, and WW threshold scan
first estimation of precision that can be achieved is in CDR
estimated extrapolating from LEP experiments
gain about one order of magnitude on each parameter: Z mass and width, mW, Z
branching ratios, forward-backward asymmetry in b, c, e, mu, tau cases, number of
neutrinos
would like to do realistic systematic studies
e.g., Rb: SUSY models predict corrections to Z->bb vertex, CepC aims at improving by factor 20 the LEP measurement
complementary to direct searches
hemisphere correlations: subtle systematic
angular effects (inefficient regions in detector), QCD effects (g->bb)
LEP did study, showed correlations depend on efficiency (when efficiency high,
correlations reduced - no correlation if efficiency is 100%)
e.g. mW
small tension among measurements and EWK fit (about 2 sigma)
LEP has WW threshold measurement (measure cross section vs. WW system), expected CEPC sensitivity with
statistical uncertainty 0.5MeV, and leading systematic (0.5MeV) beam energy and a total uncertainty of 1MeV
trade-off with lumonosity
EFT fits
expect improvement by 1-2 orders of magnitude on EFT operators
plan for Snowmass EF04
- want to do detailed study on 2-3 EWK observables: weak mixing angle; more realistic simulation; experimental and theory systematics
- higher-order EWK calculation: interest of a theorist (NNLO EWK)
- EFT fits from EWPO
- aTGC and aQGC in WW events; interested to present more details in future meetings
Sven: mentioning Rb and SUSY: surprised to see sensitivity to inaccessible scales;
what can be done with Rb, and otherwise?
A: paper linked from theorist arXiv:1601.07758v2
Ayres: kind of SUSY one can have access here is third-generation
Graham: Rb study: there is a group by Roman Poeschl et al working on it, and finding that correlations at
SLD were smaller (smaller beam spot)
Michael Peskin: Rb interesting for composite Higgs, this is strongest constraint, good for those models; analysis of hemisphere correlations is still at '90 levels: we learned a lot since then, and can go further than a factor of 20 with the huge statistics of CepC: need to work on this with QCD expert!
Ayres: request first! Interested theorist on NNLO EWK corrections; could you put them in contact with me?
A: Zhao Li (at meeting)
Ayres: is there full simulation for Rb, and what is level of work to get realistic systematics?
A: full simulation is available, trying to generate large samples to nail down the correlations
Graham Wilson - EWPO at ILC
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information in arXiv:1908.11299
motivation: before direct discoveries, we see effects in precision measurements
ultra-precise measurements compelling: probe much higher energy scales, and associated new physics
polarized beams give essential insight
linear collider only practical way to go significantly above ttbar threshold with e+e-
recently, focus on getting 250GeV as quickly as possible, keeping energy
extensibility to 500-1000GeV
now also achievable running at Z pole w/ polarized beams
ILC foreseen in northern Japan (Tohoku)
ILC detectors: ILD (quite big) and SiD
PF for jets, TPC / all-Si tracking
ILC parameters: arXiv:1903.01629
three recent publications (linked) on physics
running below 250GeV?
now have design that can give 4.2e33/cm^2/s at 91GeV: broader program of EW measurements
question is how one can control systematics
slide with details on how one can use Z(mumu) to estimate sqrt(s)
suggestion is to use _all_ di-muons (full energy, intermediate energy, radiative return), and use momentum measured in tracker (use J/psi to calibrate tracker)
center-of-mass energy critical input for mt, mW, mH, mZ
targeting 1e-5 precision in sqrt(s) for mW; 1e-4 (for mt) straightforward
mZ: better than 1e-5 helps
longitudinally polarized beams: expect 80% e-, 30% e+
4 methods to measure mW, using runs at 161GeV and >250GeV (need more studies)
polarized threshold scans; need 10ppm error on sqrt(s) to get 2MeV uncertainty on mW
table w/ systematics (based on a 19-parameter fit including polarizations that can
be effectively determined using Z-like events for ++ / +- / -+ / - - runs assuming polarizations can be perfectly flipped.
work in progress on mW from >250GeV runs
idea is to use hadronic mass or leptonic observables (shape)
hadronic mass: limited by JES; statistical sensitivity ~ 2.4MeV
leptonic observables: expect small experimental uncertainties; stat ~ 4.4MeV
forward-backward asymmetry: using polarized beams, one measures left-right
asymmetry, and ends up with uncertainty of order 1e-5 on ALR
c.o.m. calibration at Z pole
with tracker momentum resolution ~ 0.15%, one can measure average sqrt(s) to 0.18ppm with 100/fb in same data, use J/psi to measure tracker momentum scale: easy to saturate systematic from J/psi mass
uncertainty of order 2.5ppm on mZ are thinkable
higher energy: WWG and WWZ
key observation are 4f processes, in addition to WW: e+e- -> W e nu; useful to disentangle beam polarization
Robert Karl worked on this, ongoing by Jakob Beyer
global TGC fit
question: can polarization isolate and eliminate systematic effects?
2f and 4f contact interactions
current ILC projections extend limit from O(10TeV) to 151-478TeV (depending on model)
conventionally limits done in 4-parameter space
polarization here is really helpful: LEP uses AFB, ILC adds ALR, AFBLR
slides on detector calibration and hadronization systematics
momentum scale: one really needs to understand tracker, table shows why J/psi is great
summary:
polarized electron and positron are unique asset
Sven: surprised by high precision in Z mass, factor 4 better than last year (1MeV)
A: what changed w.r.t. in 2015 is publication of new J/psi mass (factor of 2 improvement), and more aggressive design of accelerator
Alain Blondel - EWPO at FCC-ee
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hot news: 2020 update to ESG: want to have Higgs factory, followed by hadron collider
Higgs and electroweak factory are possible first stage for high-priority future initiatives
FCC-ee: 4 runs, Z, WW, HZ, tt
5e12 Z: 10^5 more than LEP, statistical uncertainties go down by factor 500
1e8 WW
focus of talk is Z factory part, and experimental errors
goal is TFDR around 2025
2 to 4 detectors, not all of them need to do everything
motivation is that precision measurements contain sensitivity to new phenomena
are there more weakly coupled particles? At LEP, top effects were 10 sigma effects: there are no more t-b pairs
any SU(2)-violating effect will appear strongly, regardless of scale (oblique parameter T is affected)
is there mixing (active sterile neutrino mixing)?
high-mass SM coupled SU(2)-respecting? Z', degenerate SUSY? see with EFT
EWPO sensitive to heavy neutrinos: GF (decay of muon) sensitivity at 1e-5 level
plot of mixing vs mass: mixing is independent of mass, as long as you run below mass of heavy neutrino
complementarity with hh and eh collider
CDR table with achievable precision on EWPO measurements
statistical precision is of order keV or ppm, very low!
systematics are preliminary: estimation based on LEP, but we shall do better
systematic uncertainties
common mistake is underestimation of creativity of 100% dedicated team of physicists: gross overestimation of systematics (factor of 10)
issue is that based on that number suggested in 1988 yellow report that equipment to get polarized beams was needed (but it was not)
bottom line is that conservative behavior can have consequences on detector design and running plan
should use statistical uncertainty only to asses the performance of a facility, and make only sure that there are no showstoppers
Z line shape and W threshold measurement
could use AFB to measure alpha_QED from slope; Z width; number of neutrinos...
arXiv:1909.12245
conclusion: most important is reduction of uncertainty on energy calibration
(shall have no non-linearity; progress on this achieved, and more to come)
next: want to re-start the systematic evaluation
start from statistical uncertainty, _not_ from LEP/SLD
identify limiting factors in detector design
list of Z line shape measurements: assumed systematics about 50 times larger than statistical uncertainty, based on lepton measurements: shall study this
tau: lifetime should be measured at level of 1e-6
need to be able to fix radial alignment of detector to 1e-6; seems crazy, but it is indeed aligned at level of 1e-5, only one order of magnitude to gain
much to gain from highly segmented ECAL and vertex detector, to be quantified
now FCC-ee starting the Technical and Financial Design
plan is to bring systematic uncertainties at level of statistical uncertainty, or identify stumbling blocks and work on them
LOI for Snowmass being prepared: draft of table of contents
Graham: using fully-hadronic channel to measure W mass is appropriate?
A: best measurement should be from WW threshold scan (due to luminosity); Ph.D. student used higher energy data; problem here is ZG interpretation. mW in fully hadronic channel sensitive to color reconnection; could be interesting to use leptonic channel, compare to hadronic, and learn about color reconnection
systematic in leptonic channel should be dominated by beam energy uncertainty
have 500keV precision on scan, without caring about color reconnection
there is uncertainty from background
Graham: there are channels in which it is worth pursuing multiple directions
(different systematics?)
A: should go to Novosibirsk and do J/psi measurement