5th General Meeting of the ILC Physics Subgroup Meeting

A Summary of The 5th General Meeting of the ILC Physics Subgroup
May 31 (Sat) at Room 425, Building 3, KEK
0) Attendants:
at KEK

T.Kusano (Tohoku)
R.Sasaki (Tohoku)
M.Asano (ICRR)
K.Ikematsu (KEK)
H.Itoh (KEK)
N.Okada (KEK)
Y.Okada (KEK)
D.Harada (Sokendai)
K.Fujii (KEK)
R.Yonamine (Sokendai)
Y.Kamiya (Tokyo)
Y.Yasui (Tokyo keiei)
T.Yoshioka (Tokyo)
H. Ono (NDU)
S.Matsumoto (Toyama)

through video conference system
H.Yamamoto (Tohoku)
N.Maeda (Hiroshima)

Reports from Subgroups
1) LHT
1-1) Theory (S.Matsumoto)
- Little hierarchy: global SU(5) -> SO(5) : H as pseudo NG boson
--> T odd LH partners + T+
- DM: T parity ensures stability of the lightest T odd particle: AH as DM
- Mass spectrum -> prop. to f (VEV of SU(5)->SO(5) breaking), m_T+/- = lambda2 x f
EWPM, WMAP --> f > 570 GeV, lambda2 >~ 1
fine-tuning -> lighter spectrum favored?
C: should compare 0.1%, 1%, and 10% fine-tuning
Q: is there any pssibility that the LHC fails to detect any of the LHT signals?
A: No. T+/- should be seen.
- MadGraph model files --> completed
- eH- eH+ pair production
Q: Other lpeton flavors?
A: Yes. No universality.
Q: T parity violation problem.
A: there exits an existence proof (elementary scalar instead of fermion composites)
- t T+ threshold
C: t->T+ transition through h exchange should be suppresed.
C: We can use T+ -> t h decay.
1-2) ZH AH Experiment (T.Kusano)
- p(h) dependent angular distribution.
-> still correlation is insufficient for spin analysis.
- Mass determination
-> m(AH) from missing mass
-> m(AH) and m(ZH) from E(h) min and max.
- BG study
ZZ --> probably OK with b-tag.
ZH --> Next step.
1-3) WH WH (R.Sasaki)
Generaltor level studies:
- m(WH) = 368 GeV, m(AH) =82 GeV, 1TeV
C: t-channel nu_eH exchange --> negative interference --> kappa_l determination.
Q: LHC signature?
C: there exits a paper saying that it is difficult at the LHC.
- angular analysis.
- mass determination.
Next step:
- Start detector simulations.

2) AA -> HH
2-1) Theory (Harada)
- Non-decoupling effects to hhh
e.g.) top loop in SM (10% effect to hhh coupling)
THDM --> 100% effect from heavy higgs contributions
- THDM also contributes through box diagrams
--> needs ZH to separate self coupling and box contributions.
- If laser wave length is fixed to 1micron, the sensitiviy will degrade by a few %.
Next step:
- Separtion of effects of box and self-coupling
- Full BG simulatilons.
2-2) Experiment (Ikematsu)
- Kickoff meeting.
- N.Maeda, R.Yonamine joined the group.
- Beam spectrum generation tried by N.Maeda
- QCD BG (qqg) by T.Takahashi
Next step:
- Signal amplitudes by Kanemura and Harada.
- Contact Kurihara for BG generators.
- LCWS2008 (Nov.)

3) ZHH (Y.Takubo, D.Jeans, TY. Reported by T.Yoshioka)
3-1) HH nunu (120GeV)
Status after TILC08
--> Added tt BG, improved cuts
--> 1.4 sigma -> 2.0 sigma (S: 12.1 ev, B: 23.5 ev) with 2 ab^
--> Comparable to Djamel's result
Next step:
- tbtb BG
- Further optimization of selection cuts (neural net??)
- ZHH (120 GeV) Z--> ll, qq by Y.Kamiya
3-2) Mh = 170 GeV, Ecm=750 GeV
- Huge BG, analysis is quite challenging.
- Event selection stragegy:
topology dependent jet clustering
--> With neural network, fighting the huge ZWW BG
--> Selection seems very difficult.
C: Inclusion of beam polarization. Pol e+ might be necessary to suppress ZWW BG.
Next step:
- Try e-, and e+ if neccessary, beam polarization.

4) ZH subgroup (H.Ono)
- Full detector simulation
- 250 GeV data now available --> new development.
- Ejet very different from Ecm=350 GeV case.
- 2-jet mode
Mjj resolution slightly worse than Ecm=350GeV case, probably because of lower Ejet.
- 4-jet mode
Mh distribution is much broader than Ecm=350GeV case.
--> If jet clustering is cheated using generator info, the mass distribution becomes reasonable.
--> The problem is coming from the jet clustering.
Q: Why Mh at Ecm=350 GeV is lower than that at Ecm=250GeV.
Next step:
- Cut optimization for 4-jet mode.
- Investigate the 4-jet mode problem.
- Kinematical fitting
- Realistic PFA.
C: Important to measure decay angular distribution of Z to separate T/L.

5) New physics subgroup
Theory (reported by N.Okada)
- Hidden sector --> a paper submitted to PRD
- New activity started on e+e- -> tau+ tau-, t tbar
(NO, T.Suehara, K.Ikematsu, T.Yoshioka, H.Itoh, R.Yonamine, K.Fujii)
- Theory side investigating possible models.
- Flavor dependent Z' models: Y = Y1 +Y2 --> coupling to Z' is flavor-dependent in general.
--> Possible to make 3rd generation very different from the 1st and the 2nd.
- Bulk SM in RS: v(EW) = M(pl) x e^{- pi k r_c}
--> y_i = O(1) x e^{- pi C_i k r_c}
--> fermion mass hierarchy can be induced through configurations:
light l, q localized near Planck brane, 3rd generation near TeV brane.
while all the KK modes are localized near TeV brane due to eq. of motion.
--> KK Vector will strongly couple only to the 3rd generation.
--> 10% shift for KK mass around a few TeV.
- LH: heavy top (T) effects
--> tL -> TR -> TL -> TR -> tL --> delta g_L(Ztt) = lambda_T^2 v^2 g_A~Z / m_T^2
--> Anomaly appears only in tL
--> Anomaly in top width
- Use beam pol., decompose differential cross sections to helicitie states.
- Study sensitivities with full simulations.
Exp (reported by T.Yoshioka)
- tau+ tau- studies
pi nu, rho nu analysis. --> ready to do polarization measurements.
Currently there seems to be some problem with the input MC data (no tau polarization???)
- ttbar
signal data avaialble.started event reconstruction.
- Full simulations with higher stat. and polarization.

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

Discussions on future direction and mile stones
The next bi-weekly on June 19, 13:00 as usual.
The next (6th) general meeting on Aug. 30 13:30, focusing on results to be presented at
the Oxford meeting.

Working group contact persons:
K.Ikematsu, 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/