3rd General Meeting of the ILC Physics Subgroup Meeting
Time: Nov. 10(Sat), 2007
Place: KEK (Room 425, Building 3)
Number of participants: 20

0) Attendants:
at KEK
K.Fujii (KEK)
T.Yoshioka (Tokyo)
A.Ishikawa (Saga)
H.Itho (KEK)
Y.Okada (KEK)
K.Itoh (Tohoku)
Y.Kurihara (KEK)
Y.Takubo (Tohoku)
E.Asakawa (Meijigakuin/KEK)
S.Kanemura (Toyama)
M.Asano (Sokendai)
N.Okada (KEK)
D.Harada (Sokendai)
T.Kusano (Tohoku)
H.Ono (NDU)
Y.Shimizu (KEK)
R.Belusevic (KEK)

through video conference system
K.Kodera (Osaka)
D.Jeans (Kobe)
T.Takahashi (Hirosima)

1) Reports from subgroups
1-1) ZHH subgroup I (Y.Takubo)
- The contribution from the BG diagrams in the ZWWWW gnerator was previously reported as unexpectedly large (~40%). This turned out to be due to a mis-interpretation of the MadGraph outputs on the contributions from individual diagrams.
The cross sections now seem consistent with the ZHH results. --> OK!
- Prepared a generator for the signal process: e+ e- -> f fbar + H H with MadGraph.
The jet jet HH cross section seems in consistent with the sigma(ZHH) x Br (Z -> q qbar).
C: For comparison tree level branching fractions should be used.
C: You should check the ratios of different modes with those expected from the coupling difference.
- Start preparing an analysis program. There seems to be a strange peak above the Ecm in the total CAL energy deposit distribution, which is prominent when the number of jets is small.
C: There seems to be some kind of energy double counting.
Next step:
- Check on the inconsistency between jet jet HH and ZHH followed by Z to q qbar.
- Investigate and fix the origin of the strange CAL energy peak above Ecm.
1-1') ZHH subgroup II (D.Jeans)
- Studied the effects of anomalous HHH coupling using ZHH for Mh = 170 GeV.
--> The comparison of ZHH with ZWWWW tells us that the BG diagram contribution is negligible from the threshold 430 GeV up to 600 GeV.
--> Anomalous coupling changes the total cross section significantly at all energies.
--> Anomalous coupling changes the kinematics significantly in particular at high energies, since the virtual Higgs propagator in the signal diagram tends to pull the invariant mass of the HH system.
This is reflected in the kinematics of the Z recoiled against the HH system.
C: This tells us that we don't have to reconstruct individual Higgs bosons in the final state.
We should just reconstruct the Z boson correctly.
C: Very interesting. This shows the importance of the Z boson ID.
C: Investigate the kinematics at Mh = 120 GeV.
C: Optimal energy depends on Mh. One should do the measurement at the optimal energy.
Next step:
- Produce larger samples of ZWWWW at 750, 1000 GeV with anomalous coupling.
- Think about BGs.
- Apply quick simulation.

1-2) TTH subgroup (A.Ishikawa)
- Prepared a ttH genertor with threshold correction, where H decays in PYTHIA hadronizer.
Q: Why is the top mass 170 GeV?
A: That's the current world average.
- Uozumi is investigating BG processes. ttg seems be dominant with non-negligible contributions from ttZ, tt, and WW. Calculated cross sections for BG processes.
- Investigated the effects of polarization. The polarization enhances the cross section significantly.
Q: Is e+ polarization realistic?
C: We have polarized e+ at ATF.
C: Given a polarized e+ beam with an intensity comparable to that of unpolarized beam, we do benefit from the polarization.
- At 1st stage ILC, Mh > 170 GeV seems difficult.
Q: What is the highest Mh that can be studied at the 1st stage?
A: Mh < 140 GeV.
C: The cross section is rapidly rising near the threshold. One can adjust the maximum energy of the 1st stage if necessary.
Next step:
- Calculate BG cross sections at energies other than 500 GeV.
- BG and signal generation.
- Start analysis.

1-3) 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, 140, and 160 GeV.
- At Mh = 120 GeV, both Evis and Mh distributions seem consistent between CPFA and RPFA on the higher side, but the RPFA is significantly wider on the lower side of the peak.
CPFA gives sigma_Mh = 3.5 GeV, while RPFA gives 6.2 GeV.
Q: What is the higgs mass resolution?
A: sigma_Mh / sqrt(N_events).
C: If the mass shift is 1 GeV, it is meaningless.
C: It depends on how much we can trust MC. If MC is perfect, we can use any observable that depends on the mass. By fitting the observale distribution moving the input mass value, we can in principle determine the mass. The mass distribution is one of many such observables.
- At Mh = 160 GeV, E_lepton cut effectively selects W -> jet jet and gives sigma_Mh = 4.3 GeV with CPFA.
For RPFA, however, the E_lepton cut does not remove W -> l nu perfectly.
- At Mh = 140 GeV, CPFA gives sigma_Mh = 3.75 GeV.
Nest step:
- Investigate the mass shift in RPFA.
- study 4-jet, 6-jet final states from Zh -> qq h at Mh = 120, 160 GeV.
- BG studies.

1-4) Hidden sector subgroup (N.Okada)
- Reconciled the purpose of the study in such a way that it could cover a wider range of models.
--> Review of generic theoretical situations
- Parameter choice that is consistent with Tevatron constraints.
Q: What about X -> f fbar?
A: X->ffbar is suppressed by m_f/Lambda.
Q: Is there any reason to choose Mx = 120 GeV.
A: It is because of ILC. It could be anything.
Q: What is the role of ILC after LHC?
A: Xgg coupling is a free parameter of the model. It can be small.
There are three independent parameters corresponding to SU(3)xSU(2)xU(1).
X -> gamma gamma, X -> ZZ, and X -> gamma Z are thus related.
There will be both h and X in this scenario. The ILC is going to separate them.
C: "Does this belong to the Higgs sector or not?" This is the question.
C: As long as X -> gg is sizable, LHC is going to see X -> VV. It is interesting to make a Map in the parameter space to tell the LHC and ILC coverage.
Q: Is there any theoretical constraints such as unitarity bound?
A: It depends on models.
Q: What about X-h mixing?
A: The mixining is not considered in the current study but may be there.
The higgs properties could be significantly modified by the mixing if there.
C: The ILC is going to disentangle the mixing.
Next step:
- Finish analysis and summarize the results.
1-5) Little Higgs with T-Parity, Non-Universal Higgs scenario in MSSM (M.Asano/S.Matusmoto)
- Theoretical studies by S.Matsumoto, M.Asano, and E.Asakawa.
Simulations studies will be done by Y.Takubo, T.Kusano, and an under graduate student.
- LHT: sample points already selected, model files is in preparation, will be avaiable soon.
- NUHM contains many regions which are absent in CMSSM.
--> Long lived stop scenario or light higgs scenario (Mh < 100 GeV).
- NUHM-1(Long lived stop):
The stop will form an R-hadron which could be accumulated.
Q: What is the LSP?
A: Gravitino.
Q: What is its mass?
A: Could be anything. 100 GeV, 50 GeV,....
Reheating temperature could be estimated by gravitino relic abandance.
C: It could be accumulated in the calorimeter. It decays inside the detector eventually.
The trigger may be difficult. We need to tune the energy so that it would stop in the calorimeter.
- NUHM-2 (Light higgs scenario):
All SUSY particles may be light and Dircet DM search should be possible.
Q: Are there light SUSY particles that could be prodeced at the ILC?
A: There are many. tilde{e}_R, stau, charginos, higgses, ...
Q: What about the constraints from the precision EW measurements?
A: SUSY effects quickly decouple in general.
Next step:
- Model file preparation for LHT.
- Study R-hadron properties for NUHM-1.
- Sample point selection for NUHM-2.

1-6) Gamma Gamma -> HH (S.Kanemura)
- HHH measurement hopeless at LHC unless H decays to VV.
--> Self-coupling measurement at ILC.
- Numerically reproduced previous results fro SM with self-coupling anomaly (delta_lambda).
- Complete check of the SM 1-loop on going.
Q: What gauge are you using?
A: Non-linear gauge.
Next step:
- Finish checking out the SM 1-loop.
- Sensitivity studies to produce similar plots as with e+e- -> ZHH, nu nu HH.
- New physics effects.
--> dim 6 model. 2HD, ....
C: delta_lambda should affect the loop, too. New physics affects both the loop and the self coupling.
C: Need both e+e- (tree-dominated) and gamma gamma (loop-induced) processes to disentangle the new physics effects.
- Theoretical feasibility studies by the Dec. meeting, to be followed by simulation

2) Announcement of WS on Laser-Electron Interaction toward the ILC (LEI2007) (T.Takahashi)
- Dec. 12-14, 2007 in Hiroshima.
- A tentative agenda shown. Contributions from the gamma gamma subgroup requested.

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

3) Discussions on future direction and mile stones
C: We have some mile stones, an anual meeting of ILC physics and detctor working group in Japan on Dec.4-6 at KEK, an ACFA meeting on March 3-6 in Sendai.
C: We can show our physics subgroup activities in the physics session of the Dec. meeting. For the ZHH/TTH/ZH/HS studies we can show some simulation results there.
For LHT and other new physics, and gamma gamma -> HH, we may have a short talk on each topic.
C: The physics session has only 1 hour in the tentative schedule.
C: It is too short, we need to have at least 1.5 hours to cover our activities:
30min(Exp: Higgs) + 15min (Exp/Th: HS) + 15minx3 (Th: LHT, other new phys, gamma gamma -> HH)
C: KF will contact the conference organizer about the scheduling.
C: We will have lectures by M.Peskin attached to the meeting.
4) Next Meeting
Q: When will we have the next subgroup meeting?
A: It should be about one month before the Sendai meeting.
We may decide the exact date after looking at the outcome of the anual meeting on Dec.4-6.

Working group contact persons:
A.Ishikawa, 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/