15th General Meeting of the ILC Physics Subgroup Meeting
May 15 (Sat) at Room 425, Building 3, KEK
0) Attendants:
Y.Takubo (Tohoku)
H.Ono (NDU)
Y.Kikuta (Sokendai/KEK)
Y.Yamamoto (Sokendai/KEK)
T.Takahashi (Hiroshima)
T.Saito (Tohoku)
Posch (Sokendai/KEK)
S.Kawada (Hiroshima)
J.Tian (Tsinghua)
M.Asano (Tohoku)
E.Kato (Tohoku)
Y.Kiyo (KEK)
T.Suehara (Tokyo)
T.Tanabe (ICEPP)
Y.Okada (KEK)
D.Harada (KEK)
Y.Okada (KEK)
K.Fujii (KEK)

Via video
K.Ikematsu (Siegen)
H.Yamamoto (Tohoku)
Kamai (Tohoku)

Opening Comments
Reports from Subgroups
[A] Symmetry breaking & mass generation
1) ZH subgroup
1-1) xxH analysis (Reported by H.Ono)
- Setup: mh=120GeV, 250fb^-1@250GeV, Pol(e+,e-)=(+30%,-80%)
- qqH:
efficiency = 53% (cc), 56% (bb), 44% (Higgs BG), 5% (SM BG)
- nunuH:
efficiency = 45% (cc), 45% (bb), 35% (nunuH), 0.04% (SM BG)
- C.L. Template fitting
Introduced C.L. templates to reduce the binning dependence.
Next Step:
- Binning dependence has been improved significantly but there is
still some problem remaining -> to be investigated.
- Publication as soon as this binning dependence problem will have been solved
- New benchmark processes.
Q: What is your prospect for H -> glue glue
A: We will try the C.L. template method, but the template shapes for H -> WW* and gg
are similar.
C: H -> WW* can be positively identified.

1-2) ZH -> nunuH followed by H->WW* (Reported by Y.Takubo)
N.Hodgkinson, N.Okada, K.Ikematsu, and K.Fujii
- Looking for anomaly in the HWW vertex:
a/Lambda : HWW
b/Lambda : HW_{\mu\nu}W^{\mu\nu}
b~/Lambda : HW_{\mu\nu}~W^{\mu\nu}
- MC conditions
mh=120GeV, 250fb^-1@Ecm=250GeV -> Br(H->WW*)=15%
Polarization: use (Pol_e-,Pol_e+)= (+80%, -30%) to suppress WW BG.
- Event selection
mh, mm, cos_h, y-value, Etk<30GeV, Nb<=1 -> likelihood cut
-> 7.4 sigma signal --> delta sigma_ZH * Br(H->WW*) = 15%
Jet angle in W rest frame.
- Looked at phi between two decay planes by IDing charm quarks (eff_c=0.8 purity_c=0.2)
--> Reconstructed phi distribution by fitting mh distributions for different phi bins.
--> Asymmetry seen as expected.
- Prepared a physsim generator with anomalous couplings and generated MC events with anomalous
- Looked at the phi distributions for the generated events and investigated if the deviation
from the SM case is detectable.
Next Step:
- Draw a contour plot to show the sensitivity to a, b, and btilde.

2) ZHH
2-1) ZHH (Z->ll) full simulation status (Reported by Junping)
- Event selection for full simulation MC sample
lepton ID: E_cone(charged) turned out to be a better quantity than E_cone(all)
-> Optimized the cone angle and the cut in the (E_l, E_cone) plane.
-> Efficiency ~ 98% for leptons
< O(2%) for hadrons
- M_ll distribution: similar for both electrons and muons
Next Step:
- About 10% efficiency improvement with about 1% purity drop.
- ll4b, nunu4b, qq4b, and qqWW*
- New BG: ZZH (WWH will not be a problem but ZZH could be).
- WW fusion at 1TeV.

3) Top Yukawa in TT
3-1) Theory (Reported by Y.Kiyo)
- Can we measure the effect of H exchange?
SM: 9(4) % for mh=120(200)GeV
1-loop: +6(3)%
h+QCD: +3(1)%
SUSY: (~2HDM) 5% effect (-5% compared to the SM case,
which is due to the highs mixing angles, alpha and beta)
--> 4% or better theoretical accuracy desired to see the effect
- Big scale variation even after including 3-loop (NNLO'/NNLL') corrections
- RG improvement to the static QCD potential stabilizes the variation significantly
--> Though we need to improve NNNLO'/NNLL', we can hope that top Yukawa can be measurable.
Next Step:
- Improve NNNLO'/NNLL'.
C: Check the top Yukawa effect for H->gg.
Q: Time scale?
A: ~ 1 month.

3) TTH
3-1) TTH (Reported by T.Tanabe)
- We have looked at the validity of the signal MC, the QCD correction, in particular.
--> The correct function from a theorist, Yokoya-san, has been compared with the
currently used heuristic one. The difference turned out to be small.
Nest Step:
- We are going to weight the results.
- Then publish the results.


4) AA->HH Group
4-1) Experiment (Reported by Kawada)
- Updated the previous results by increasing statistics of ZZ BG to 1M events
- NN analysis
1st step: HH vs WW
2nd step: HH vs ZZ+WW (after filter 1)
--> significance 1.16 sigma
- Kawada (M1) took over Maeda's work.
Next step:
- Other BG like AA->bbbb.
- Verify the current scheme of AA->ZZ generation assuming on-shell Z's in the helicity eigen-states.
C: The current scheme is probably OK.
C: We will look into the program together with Posch-san.
- Investigation of statistical independence of training and analysis samples.
Q: Should we try a Higgs mass other than Mh=120GeV?
C: It is meaningful to try Mh=130, 140 GeV.
C: We had better publish our result now, since if we change Mh, we will need to generate new WW BG
sample at the new optimized energy.
4-2) Theory
Status and Plan:
- Writing a paper.

[B] New physics
1) Right-handed Neutrino (Reported by T.Saito)
Seasaw: Mnu = v^2 y^2 / 2 M_N
--> XD can make y small
--> M_N = (2n-1)/2R in TeV scale XD model --> can be as light as O(100GeV)
- Setup
Seasaw: Mnu = v^2 y^2 / 2 M_N
--> XD can make y small
--> M_N = (2n-1)/2R in TeV scale XD model
--> M_N = O(100GeV) and y = 0.1 possible
--> M_N = 150GeV to avoid the LEP constraint.
- M_NR measurements
*) e nu qq (1st KK: 150 GeV, 2nd KK: 450 GeV, 3rd KK: 750 GeV)
Degenerate case:
1st KK: 0.42%
1st KK: 0.7%, 2nd KK: 3.0%, 3rd KK: 12.0%
Inverted case has similar precisions
In the normal case, only 1st KK can be observed.
*) tau nu qq
forced 3-jet clustering, tau jet ID, W reconstruction,
then likelihood analysis -> significance 4.0
-> No peak -> Difficult to observed the tau mode.
Next Step:
C: Use the measured M_NR in the electron mode analysis and estimate the tau
energy as E_tau = E_NR - E_W, then we can calculate M_NR much more accurately.
Q: Is the LFV constraint imposed?
A: Yes. That's why we hat to use electrons instead of muons.

2) LHT: ZHZH (Reported by E.Kato)
- MC Conditions
Same as the previous LHT publication
- Study the effect of the energy resolution
- Study the shifting of the energy edges.
--> The shift is significant: delta E = 26 GeV (all), 15.1GeV(bb), 33.6GeV(WW)
estimated by e+e- -> ZH @ Ecm=250GeV
--> average shift turned out to be delta E = 21.8GeV
C: Leptonic W decays should be removed for the mass measurement.
--> Problem: 2 peaks in M_ZH distribution.
Next Step:
- Understand the 2 peaks.
- Update the event selection criteria.

3) Model Discrimination
3-1) @ 500 GeV (I) (Reported by T.Suehara)
3 generic cases to be discriminated:
a) J=0: Inert H-like model
b) J=1/2: SUSY-like case
c) J=1: LHT-like case
- Event selection study using full simulation (signal and BG) samples
--> Performance good enough for the E_W end-point study.
- Mass determination
delta E_W = O(0.1(0.5)GeV) for 200(40)fb^-1
delta M_X = O(0.1(0.5)GeV) for 200(40)fb^-1
delta M_DM = O(0.5(2)GeV) for 200(40)fb^-1
- Angular distribution
200fb^-1 -> Separation possible
40fb^-1 -> Some separation
Next Step:
- 25 mass points (5 M_X and 5_DM) to investigate the effect of mass errors.
--> Use Reco/MC ratio? -> several days
- Threshold scan (Toy MC?) -> 1 day
- Write a paper -> 1 dedicated week?

3-2) @ 1 TeV (II) (Reported by T.Saito)
- E_W endpoints
-> delta M_DM ~ 1% if X-section = 200 fb with 500fb^-1.
- Production angle distributions
--> |cos th1| vs |cos th2|
--> Template fitting
--> Possible to discriminate different models.
--> Effect of the mass error.
- Threshold scan
Fit region; 740~800 GeV assuming the same X-section @ 1 TeV
--> model discrimination seems possible with 200 fb.
Next Step:
- Analysis completed.
- Prepare for the publication.
Q: Why 40fb and 200fb?
A: IH: 3fb, SUSY: 110fb, LHT: 300fb

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

Discussions on future direction and mile stones
*) Physics-Accelerator joint meeting
August 9-12 at Kama-saki onsen

*) Oct.18-22: ECFA/CLIC Meeting

Meeting Schedule:
Next general meeting (2010/07/17 10:00)

Working group web page:

Slides are available from http://ilcphys.kek.jp/meeting/physics/