The 44th General Meeting of ILC Physics Subgroup

Keisuke Fujii (IPNS, KEK)

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:

A Summary of The 44th General Meeting of the ILC Physics Subgroup
October 24, 2015 (Sat) at Room 425, Building 3, KEK
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)
 Improvements since the last meeting:
    More understanding of remnant tiny mode-dependence.
 Cross section measurements (combined with invisible cross section)
    (-0.8,+0.3)    2.65%     35MeV
    (+0.8,-0.3)    2.92%     40MeV
    (-0.8,+0.3)    3.30%     95MeV
    (+0.8,-0.3)    3.59%    110MeV
    (-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)
 Anomalous HWW couplings:
    SM-like, FF, FFtilde
   e+e- -> Zh -> vvh followed by h->WW*.
    - 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)
 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)
 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)
       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)
 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)
   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)
 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
   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.

The slides shown at the meeting is available from
see them for details.

*) Meeting Schedule:
 Next general meeting (2016/1/16 10:30) : Conf.ID: 146

Working group web page:

There are minutes attached to this event. Show them.
    • 10:30 11:00
      Opening Remarks 30m
      Speaker: Keisuke Fujii (IPNS, KEK)
    • 11:00 11:20
      recoil mass study using Z-->ll at 250, 350 and 500 GeV ILC 20m
      Speaker: Dr Jacqueline Yan (KEK)
    • 11:20 11:40
      study of anomalous HVV coupling measurement at ILC 20m
      Speaker: Tomohisa Ogawa (Shinshu University)







                                   this will be updated by Dec.

    • 11:40 12:00
      Top-Yukawa coupling study at 500 GeV 20m
      Speaker: Yuji SUDO (Kyushu University)
    • 12:00 13:30
      Lunch 1h 30m
    • 13:30 13:50
      study Higgs self-coupling 20m
      Speaker: Mr Masakazu Kurata (The university of Tokyo)
    • 13:50 14:10
      control systematics using Z control sample 20m
      Speaker: Koya Tsuchimoto (Shinshu University)
    • 14:10 14:30
      Study in top pair creation threshold range 20m
      Speaker: Mr Kiyoaki Ozawa (Tohoku University)
    • 14:30 14:50
      study of jet clustering algorithms 20m
      Speaker: Dr Junping Tian (KEK)
    • 14:50 15:50
      Discussion: next plans, missing studies, etc.