Date/Time: 10:30~17:30 JST, October 24, 2015
Place: Room 425, Building No.3, KEK
Official Language: English
Video Conference ID: 667 (KEK MCU2)
Fuze connection: http://fuze.me/30957058
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A Summary of The 44th General Meeting of the ILC Physics Subgroup
October 24, 2015 (Sat) at Room 425, Building 3, KEK
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0) Attendants:
Present at KEK:
K.Ozawa (Tohoku)
K.Fujii (KEK)
J.Tian (KEK)
J.Yan (KEK)
T.Ogawa (Sokendai)
M.Kurata (Tokyo)
K.Hidaka (Tokyo gakugei)
Remote connection:
K.Tsuchimono (Shinshu)
K.Ikematsu (Saga)
Y.Sudo (Kyushu)
T.Suehara (Kyushu)
A. Ishikawa (Tohuko)
0) Opening comments (K.Fujii)
1) Leptonic recoil mass analysis (Jacqulline Yan)
Status:
Improvements since the last meeting:
More understanding of remnant tiny mode-dependence.
Cross section measurements (combined with invisible cross section)
Ecm=250GeV
(-0.8,+0.3) 2.65% 35MeV
(+0.8,-0.3) 2.92% 40MeV
Ecm=350GeV
(-0.8,+0.3) 3.30% 95MeV
(+0.8,-0.3) 3.59% 110MeV
Ecm=500GeV
(-0.8,+0.3) 5.20% 481MeV
(+0.8,-0.3) 4.91% 573MeV
Investigation of mode dependence
-> Pt sum > 10GeV too tight, now loosened to Pt sum > 6 GeV.
-> The bias is now very small:
~0.1% for Zmm, ~0.5% for Zee
even with the very pessimistic assumption that there is 10% “unknown mode”
having a selection efficiency that differs from the SM average by the same
amount as the maximum deviation from the average seen among the SM modes.
1st look at hadronic recoil
-> mode dependence seems rather small, promising.
Next Step:
- Finalize results for LCWS2015.
- Mass measurement requiring h->bb.
- Remove Ptdl from TMVA.
- Test necessity of costhetaZ.
- Publication.
- Continue with hadronic recoil.
2) Anomalous HWW couplings (Tomohisa Ogawa)
Status:
Anomalous HWW couplings:
SM-like, FF, FFtilde
e+e- -> Zh -> vvh followed by h->WW*.
Observables:
- pW
- helicity angles of on-shell W: theta
- phi (angle btw two decay planes of W and W*)
Update since the last meeting:
phi calculation.
Use pW, theta, phi simultaneously.
Separate shape and normalization contributions in chi2 definition.
Sensitivity is O(1).
C: If c-tagging is not used, the useful phi range should be 0 to pi/2.
Next Step:
- Fix the phi-range.
- Other energy and other processes.
- Do other channels and add them to the chi2.
3) Top Yukawa coupling study at 500 GeV (Yuji Sudo)
Status:
500GeV (500fb-1), (-0.8,+0.3)
New from the last meeting
High statistics 6f_ttbar MC sample
Correct sigma_tth = 0.408 fb @ 500GeV
Jet paring based on maximum likelihood
Optimization of selection cuts.
Results: (significance) for 500fb-1
(-0.8,+0.3) 2.98
(+0.8,-0.3) 1.54 -> 3.35 combined
-> |delta gt/gt| = 7.6% for H20
C: Treat all tth as signal.
Next step:
- Recalculate the significance including all the tth events as signal.
\x{2014} TMVA, expecting 10% improvement.
4) Higgs self-coupling (Masakazu Kurata)
Status:
Possible lines of attack:
Lepton ID, b-tagging, jet pairing, E,p measurements, jet clustering, MVA+kin-fit
This talk: kin-fit+MVA
Kin-fit in the case of fully hadronic final states:
Is it useful for BG rejection?
bbbbWW* -> (bb)(bb)(jjjj)
Results
8jets : 1.94 sigma (H20) : 4 b-tag
l+6jets: 0.68 sigma (H20) : 3 b-tag (0.60 sigma for 4 b-tag)
Q: Why 3 b-tag better than 4 b-tag?
C: Lepton ID improvement seemed to have increased ttbar BG.
Need some tweaking.
Next Step:
- Include ISR effect in Kin-fit.
- Improve basic analysis tools.
- Improve jet clustering.
- Combine everything to get the best result.
5) Controlling systematic Errors (Koya Tsuchimoto)
Status:
Z control samples
ZZ, gammaZ, vvZ, eeZ
Estimated the available statistics for these control Z samples.
-> 22M control sample events after H20.
-> delta m_W ~ 1.4MeV (sys) seems possible.
Next Step:
- More study on systematics including hadronization.
- m_W resolution vs cal. technology?
- Estimate systematic error on b-tagging efficiency, etc. (Z->bb)?
- Estimate systematic error on lepton momentum calibration.
6) ttbar at threshold (Kiyoaki Ozawa)
Status:
Objective:
top momentum measurement
Now looking at momentum distributions at the generator level.
C: Switch off ISR and beamstrahlung.
Next Step:
- Further studies at the generator level (w/ ISR & beamstrahlung off)
- Study parameter dependence.
7) Jet Clustering (Junping Tian)
Status:
Updates from the last meeting:
a new implementation of jet clustering.
more study on traditional jet clustering.
possible algorithm for color-singlet clustering.
New implementation:
2 new classes: JJet and Jets
F_mis:
new measure for mis-clustering.
-> mis-clustering happens at around log_10 y_cut ~ -3.
-> y_T ~ 1GeV is the transition point.
y_T ~ 10GeV is the boundary between hard gluon and soft gluon.
-> Use fixed y_cut!
-> 6 jets seem already reasonably good.
Bug if we do the paring with mass, BG also comes into the signal region.
-> We should not use the mass to do the pairing.
-> Use b-tagging first,
then parton shower probability and color correlation.
-> One interesting variable is “jet pull”.
Next Step:
- Try “jet pull”.
- Use MC truth to check the pull angle distribution.
- Parton shower probability.
8) Discussions: all
Prepare for LCWS2015.
Reorganization of BSM efforts.
Publication plan.
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The slides shown at the meeting is available from
https://agenda.linearcollider.org/event/6793/
see them for details.
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*) Meeting Schedule:
Next general meeting (2016/1/16 10:30) : Conf.ID: 146
Working group web page:
http://www-jlc.kek.jp/jlc/en/subg/physics