6th General Meeting of the ILC Physics Subgroup Meeting

Summary of The 6th General Meeting of the ILC Physics Subgroup
Sep. 6 (Sat) at Room 425, Building 3, KEK
0) Attendants:

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

Reports from Subgroups
1) ZHH
1-1) HH nunu: 120GeV (Reported by Y.Takubo)
- sigma_S = 40 ab
- Event selection
Mass cut
Missing Pt
4-b requirement
vertex mass > 1 GeV
- Status of S/B
7.3(ZHH) + 1.8(ZZ) + 420(tt) +20.8(tbtb) + 0(ZH)
4.6 (ZHH) + 1.8(ZZ) + 70(tt) + 10.6 (tbtb) + 0(ZH)
Next Step:
- Increase tt BG statistics
- Try isolated lepton veto
- Look at remaining BG events with event display
- Other decay

1-2) HH qq with Mh=120 GeV
- sigma_S = 140 ab
sigma_B = ZWW(40fb), hWW(6fb), ZZZ(1fb), hZZ(0.6)
- Event selection (6-jet mode)
-20 < E_miss < 90 GeV
m_jj3 < 120 GeV
b-tag -> btag(3,3)
S/B = 32.5/99.6 = 0.33
-> 3-sigma
-Tried Neural Net
nbtag, btag(jet3), cos(thj1) cos(thj2)
-> 4.5-sigma
Next Step:
- b-tag is essential. --> better to improve
- check jet-pairing
- reject Z -> ll, Z -> nunu beforehand
- use b-tag information for jet pairing
- tune up preselection
- Try cheated jet finder
- Look at tt and ttbb BG
- Z decay at generator level to take into account helicity correlation.

1-3) Mh = 170 GeV, Ecm=750 GeV
- Tried 100% right-handed polarization
--> seems promising
- Daniel san will leave the group.
C: There is no heavy Higgs study in the past.
It is very important to continue and finish the study.
Next step:
- Find a successor of Daniel san.

2) ZH subgroup (H.Ono)
- Full detector simulation, continue with Ecm=250GeV case
- 2-jet mode
Gamma= 6.6 GeV @ 250 GeV (cf 6.42 GeV @ 350 GeV)
C: There is no point of using BW for the signal.
-> HWHM = Gamma/2
- 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.
--> Tried minimum opening angle cut to avoid mis-clustering.
--> significant improvement.
Compared JadeE and Darham -> Darham seems better.
Gamma=8.8 GeV @ 250 GeV (cf 6.0 GeV @ 350 GeV)
Next step:
- Kinematical fitting.
- BG rejection.
- Realistic PFA.
C: Important to measure decay angular distribution of Z to separate T/L.

3) TTH (Reported by R.Yonamine)
l+6-jet mode
- Study with cheated jet finder
--> This sets the ultimate goal of event selection
- Event selection
isolated lepton
mass cut
Next Step:
- Study further the ttZ BG
- Realistic jet finder
- tt and ttg BG

4) AA->HH
4-1) Theory (Reported by D.Harada)
- non-decoupling loop effect know for top ~ mt^4
- consider this in 2HDM
mphi^2 = lambda v^2 + M^2
--> M=0 (non-decoupling limit) --> mphi all comes from vev.
--> submitted to arXiv yesterday.
Q: heavy fermion effect --> -ve contirbution to self-coupling
as compared to +ve contirbution from heavy higgs.
Next Step:
- How to uncover higgs sector when only the llightest is accessible?

4-2) Exp (Reported by N.Maeda)
- Sensitivity study
1st assume 100% efficiency for S and no BG
--> E_AA~300 GeV is optimum.
2nd with BG (WW: 90 pb)
--> 10^{-6} suppression for BG is necessary even with 100% efficiency for S
to achieve sensitivity ~ 3.
- Signal study
mass cut, b-tag, ...
- BG study (WW: 90 pb)
generated BG with Grace thanks to Kurihara-san.
- Look at luminosity spectrum.
Next Step:
- BG study:
cross section, detector simulation, analysis
- Take into account luminosity distirbution with CAIN (so far delta fun).
Q: Why chose Grace instead of Madgraph?
A: There is an expert at KEK.
C: We compared Madgraph and Grace and found them consistent.
C: At this moment, it is easier to extract MC truth from Grace than from Madgraph.

5) LHT
5-1) Exp: e+e- -> Z_H A_H (Reported by T.Kusano)
Goal: mass, cross section determinations
-> m(AH) from missing mass
-> m(AH) and m(ZH) from E(h) min and max.
- Z_H -> A_H + h (100%) @ 500 GeV
AH=82GeV, ZH=369GeV, h=134 GeV
- ZZ -> bbnunu BG study
bbnunu ~ 100fb
cf) beam pol no use since both S and B couple to eL.
- event selection
Mh cut, cos(th) cut, beta_h cut
cf) b-tag is not effective! (BR(h->bb)=55%)
--> S/sqrt{B} = 9
--> S/sqrt{B} = 5.5 w/o beta_h cut
C: F can already be detemined.
Q: Other BG?
cc nunu, tt, ZZ-> nunu jj
C: tt should be accompanied with isolated leptons.
C: b-tag should be useful for ZZ-> nunu + qq (q=light quark)
- p(h) dependent angular distribution.
-> still correlation is insufficient for spin analysis.
Nest Step:
- BG study.
- Determine F from cross section.
- Remove h to WW followed by W->l nu mis-identified as h -> 2jets.
- Try BG subtraction for mass determination.

5-2) Exp: e+e- -> W_H W_H (Reported by R.Sasaki)
Mass, spin, cross section determinations
- m(WH) = 368 GeV, m(AH) =82 GeV, 1TeV
sigma_S=122 fb
- Wiht detector simulation studying event selection to fight WW BG.
mW chi2 cut, missing PT --> S/B = 7
Next step:
- Investigate past chargino studies.
- BG study.

5-3) Theory (Reported by S.Matsumoto)
- Little hierarchy: global SU(5) -> SO(5) : H as pseudo NG boson
--> T odd LH partners + T+ + Triplet Higgs
--> T+/T- should be relatively light to cancel radiative correction to Mh
and detectable at LHC.
T+ -> W+b 51%, Zt 21%, ht 16%, T- AH 12%
--> delta MT = 10~20 GeV
mixing 5~10%
- DM abandance prediction possible but f has to be determined reasonably well.
Next Step:
C: Should consider A_H decay (T-parity violation via anomaly).
- AH -> boson bson (e.g. Z gamma)
- eH- eH+ pair production
- t T+ threshold

6) New physics subgroup
6-1) Theory (Reported by H.Itoh)
LOI benchmark analysis (top & tau) -> Physics
- 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.
See Chen & Okada: arXiv: 0808.0331for details.
- Use beam pol., decompose differential cross sections to helicitie states.
--> Seems easy to see the Z' effect @ Ecm=500 GeV for MZ'=1.5TeV.
C: Consider two cases (i) signal seen at LHC (ii) no signal at LHC (tau or MZ' too heavy)
- Dark Higgs doublet (Z2 parity odd)
--> loop level seesaw.
--> DM candidate (eta_I)
--> H -> eta_I eta_I possible in some region. --> H becomes invisible.
J=1/2: chi^{+/-}, J=1: WH^{+/-}, J=0: eta^{+/-}
--> eta+ eta- pair production, eta_I eta_R production.
--> J=0,1/2,1 discrimination through angular analysis
C: Yukawa forbidden by Z2 parity.
--> eta couples only to gauge bosons.
Next Step:
- Generator preparation.

6-2) Exp (Reported by T.Suehara)
chargino/neutralino separation (chargino -> W+LSP, neutralino -> Z+LSP)
--> mass fit --> delta M < 1 GeV with 500 fb^{-1}
smuon pair
--> no problem.
- tau+tau- @ Ecm=500 GeV (sigma=2.3pb)
sigma, dsigma/dcos(th), A_FB, A_pol
tau -> l nu nu, pi nu, rho nu for polarization measurements.
--> delta A_FB < 0.2% with 500 fb^{-1}
--> delta A_pol < 0.8% (from tau -> pi nu)
- Translate experimental precision to parameter errors.

6-3) Exp (Reported by K.Ikematsu)
e+e- -> ttbar full simulator study
- Tool (M@rs) development for full MC analysis
- ttbar analysis with M@rs + LCFIvertex
--> b-tagging needs to be retuned for multi-jet final states.
--> top mass reconstruction seems promising.
Next Step:
- still in the tool develepment phase.
- l+4-jet mode.

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 Sep. 18 (Thu), 13:00 as usual.

The next (7th) general meeting on Nov. 8 (Sat) 10:30, focusing on results to be presented at
the Chicago meeting.
People planning to attend the meeting include:
D.Harada, S.Matsumoto, N.Okada, Y.Okada, Y.Takubo, T.Suehara, K.Ikematsu, K.Fujii

Working group contact persons:
K.Ikematsu, S.Uozumi, Y.Okada, H,Ono, S.Kanemura, Y.Takubo, K.Fujii, T.Suehara

Working group web page:

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