4th General Meeting of the ILC Physics Subgroup Meeting
February 16 (Sat) at Room 425, Building 3, KEK
0) Attendants:
at KEK
K.Fujii (KEK)
R.Yonamine (Sokendai)
H.Itoh (KEK)
T.Yoshioka (Tokyo)
T.Kusano (Tohoku)
Y.Takubo (Tohoku)
K.Itho (Tohoku)
E.Asakawa (Meijigakuin)
K.Ikematsu (KEK)
M.Asano (Sokendai)
S.Matsumoto (Tohoku)
T.Kubo (Sokendai)
D.Harada (Sokendai)
H. Ono (NDU)
Y.Okada (KEK)
through video conference system
D.Jeans (Kobe)
S.Uozumi (Kobe)

1) Reports from subgroups
1-1) ZHH subgroup I (Y.Takubo)
- Started quick simulator studies for ZHH followed by Z->nu nu with Mh=120 GeV.
- S/N = 10^{-4} with no selection cuts with sigma(HH nu nu)~0.04 fb.
- With the current set of selection cuts S/N ~ 10^{-2}.
--> Another factor of 100 reduction of the ZZ BG is necessary.
--> Will try b-tagging and cuts on angular distributions, etc.
C: Try looking at the ycut at which the number of jets becomes 4.
C: Investigate previous works.
Next step:
- Study the nature of the remaining ZZ BG events and work out some way to eliminate them.
- Try the 6-jet mode.
1-1') ZHH subgroup II (D.Jeans)
- Studying the ZHH events and possible BGs for Mh = 170 GeV and developing selection cuts for 10f final states.
--> Although the BG cross sections are huge compared with the signal cross section, the combination of various event shape cuts, chi^2 cuts on masses, and b-tagging seems to be able to reduce the BGs to a managable level. --> Encouraging.
Q: Does the event generation include beamstrahlung and ISR?
A: No.
C: If you switch on the beamstrahlung and ISR, the reconstruction of the1 neutrino missing case will be more difficult, though you can still try the reconstruction assuming that the radiated photon has no Pt.
Next step:
- Develop more chi^2 variables
- Quick simulations.
1-2) TTH subgroup (S.Uozumi)
- Developed an event generator with the QCD threshold enhancement and beam polarization.
--> about 100 tth (Mh=120GeV) events expected at Ecm=500 GeV for 1ab^{-1}.
- Investigated BG processes and found that ttbb (mostly from ttg) dominates.
- BG generators are ready.
- Considering the signal cross section, the TTH for a high mass Higgs is difficult to measure at 500 GeV.
C: It is probably better to say that we can measure the top Yukawa coupling up to such and such Mh if the beam energy is such and such than to say that we cannot measure the top Yukawa for Mh heavier than such and such.
Next step:
- Start analysis with quick simulator.
1-3) Hidden sector subgroup (H.Itho)
- Parameter choice that is consistent with Tevatron constraints.
- Decided to finish up the studies for the gluophobic case by TILC08 and postpone the more general case including X->Z gamma decays as the next project.
Next step:
- Finish analysis and summarize the results on Feb.25.
- Move on to include the Zgamma decay.
1-4) ZH subgroup (H.Ono)
- The GLD full simulation study for the e+e- -> ZH process with Cheated and Real Particle Flow Algorithm for Mh = 120 and and 160 GeV.
- Real PFA seems OK for the 2-jet final states though the Mh resolution is still worse than the Cheated PFA case.
- For the 4-jet final states, the RPFA performance is poor.
C: Judging from the energy and mass shift for the 4-jet case, there must be some over-deleting of energies. The degradation does not seem like coming only from the jet clustering.
Nest step:
- Investigate the reason for the mass and energy shifts for the 4-jet mode.
- Include the tt BG at 350 GeV.
C: For the Higgs study, you had better go to a lower energy avoiding the tt BG.
1-5) LHT Subgroup (T.Kusano)
- Event generation started for a sample point: AH (80.3GeV), ZH(371GeV), h(134GeV), eH(430GeV). The signal cross section for e+e- -> AH+ZH followed by ZH->h + AH is 2.2fb at Ecm=500GeV.
- Looking at Eh, cos(ZH), cos(theta_h), etc.
--> Forward-Backward asymmetry due to the t-channel eH (left-handed) exchange.
C: Eh measurement will be affected significantly by neutrinos from b-decays.
Q: Is AH still a dark matter candidate? T-parity seems to be violated by anomaly and the detail could depend on the underlying dynamics at higher scale.
A: We can assume an effective theory at 10TeV scale where the T-parity is not violated. It might be violated at even higher scale though. It will still solve the little hierarchy problem though it won't solve the big hierarchy problem.
Q: Can you increase the H mass, say above 2xM_AH?
C: The invisible width for H->AH AH is less than 7% to be consistent with the WMAP results.
C: We should be able to measure the invisible branching fraction by the recoil mass measurements.
Next step:
- Start simulation studies with the quick simulator.
- Feasibility studies for mass and production angle measurements.
1-6) Gamma Gamma -> HH (Y.Okada)
- Fixed a few bugs. Kanemura-san will report on the results at TILC08.
- Complete check of the SM 1-loop on going.
- New physics effects that would affect the production vertex (1-loop) as well as the self-coupling.
- The best sensitivity is at the threshold but there seems to be subtle cancellation and sensitivity curves can be quite asymmetric about delta-kappa=0.
Q: How do you calculate the sensitivity?
A: From the crossection and luminosity assuming a100% acceptance.
Next step:
- Finish checking out the SM 1-loop.
- Simulation studies after TILC08 with experimentalists.
The slides shown at the meeting is available from
see them for details.

2 ) Discussions on future direction and mile stones
C: We have an ACFA meeting (TILC08) on March 3-6 in Sendai. We have altogether 8 talks proposed, one of which (Ono-san's) has been moved to the simulation session. In addition. we will have 2 talks on ZHH by Takubo-san and Daniel-san, 1 talk on TTH by Uozumi-san, and 1 talk on LHT by Kusano-san. We have now 11 talks, which means 20min x 11 = 3hr40min. Maybe we need to ask Dr.Zhinqing Zhang planning to talk on recoil mass measurements if we could move his talk to the simulation session, too.
C: After TILC08, the next target will be Warsaw conference in June.
C: We may have one general meeting on some Saturday in April, say 12th or 19th in conjunction with the April detector meeting on Friday. One more just before the Warsaw meeting.

Working group contact persons:
S.Uozumi, Y.Okada, H,Ono, S.Kanemura, Y.Takubo, K.Fujii, T.Yoshioka
Working group web page:
Slides are available from http://ilcphys.kek.jp/meeting/physics/