A Summary of The 18th General Meeting of the ILC Physics Subgroup
Nov. 27 (Sat) at Room 425, Building 3, KEK
0) Present:
H.Ono (NDU)
T.Saito (Tohoku)
E.Kato (Tohoku)
Y.Okada (KEK)
D.Harada (KEK)
Y.Kiyo (KEK)
R.Yonamine (Sokendai)
Y.Yamamoto (Sokendai)
P.Posch (Sokendai)
T.Yamada (Sokendai)
T.Suehara (Tokyo)
T.Tanabe (Tokyo)
S.Kawada (Hiroshima)
N. Okada (Alabama)
K.Fujii (KEK)

Via Teleconference System:
K.Kotera (Shinshu)
J.Tian (Tsinghua)

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@250 and @350GeV, Pol(e+,e-)=(+30%,-80%)
Generator: whizard
Analysis framework: ilcsoft v01-06
RDR (LOI 250GeV), SB2009 w/TF (same in the new parameter set) (350GeV)
Notice that there is more contribution from WW fusion @350GeV.
- Event selection:
Cut values have been adjusted for the 350GeV case.
--> Selection efficiencies are generally better for nunuH and qqH at 350GeV than at 250GeV. The situation is opposite for llH, where the efficiency
is better at 250GeV, which is probably because of the fusion process being rejected by the current set of cuts.
BG reduction performance seems also better at 350GeV.
- BR (cc/bb) measurements:
--> 350GeV measurements seem better than that of 250GeV, in particular for nunuH and qqH modes. --> reason under investigation.
delta BR(cc)/BR(bb): 7.75% (250GeV) -> 5.87% (350GeV) : very preliminary
10.15% (250GeV) -> 6.48% (350GeV) : very preliminary
- Recoil mass:
--> Better at 250GeV
Next Step:
- Binning dependence has been improved but there is still some problem remaining.
- Results to be presented at BAW2.
- Publication as soon as this binning dependence problem will have been solved.
Q: Is RDR 250GeV parameter set equivalent to the new beam parameter set?
A: Yes. It is even slightly better.
Q: But that is the value assuming traveling focus.
What happens if traveling focus does not work?
A: SB200 x 2 should be a sure value, since it is coming from doubling the rep. rate, which is possible at 250GeV where beam power is 1/2 of that at 500GeV.

2) ZHH Subgroup (Reported by Junping)
- Analysis modes:
ZHH (llbbbb), (nunubbbb), (qqbbbb) : full simulations @ 500GeV
nunuHH (WW fusion) : fast simulation @ 1TeV
- Sensitivities to self-coupling
delta lambda/lambda = 1.8(0.85) delta sigma/sigma for ZHH (WW fusion)
- Previous simulation results (preliminary):
- llHH: 3.6 sigma, qqHH: 2.0 sigma (full simulation)
- nunuHH: 1.3 sigma (w/o ZZH BG)
- New BG Added llbbh BG:
-> The significance dropped to 2.2 sigma (S=3.2, lobby BG=1.4 (1.1 from lobby)
w/o beam polarization.
With (-80%,+30%) polarization, 2.6 sigma (S=4.7, BG=2.3 (1.7 from lobby)).
-> 1.1 sigma (S=1.8, BG=5.1) for nunubbbb w/o beam polarization.
- Statistical independence of the different modes has been confirmed.
- New combined significance: 3 sigma (2 modes w/o qqbbbb), 3.8 sigma (3 modes)
Next Step:
- Improve nunuHH analysis. Polarization effect.
Q: Is ZZh BG included in qqbbbb analysis?
A: No, but the contribution should be small.

3) AA->HH Group
3-1) Experiment (Reported by Kawada)
- Signal and BG:
AA->HH:16ev/yr (signal), WW:15Mev/yr, ZZ:12kev/yr, 4b:960fb (w/o cuts) (BG) @sqrts=270GeV
- NN training (previous results for WW and ZZ BGs):
-> 10^-7 WW-rejection
--> 2.7 sigma
--> 5.9 sigma if cheated in jet clustering
-> 2x10^-3 ZZ-rejection
-> 1.6-sigma
--> cheated jet clustering: ZZ-rejection becomes 8.5x10^-5
--> 5.9-sigma if cheated in jet clustering
- Investigation of bbbb BG:
It turned out that the main diagram is the 2-resolved-photon process: each gamma splitting into a bar pair and forward scattering of b or bar
through gluon exchange.
Next step:
- Comparison with signal distributions.
- Decide the cut criteria.
- Convolute the luminosity distribution to the bbbb BG.
- Improve b-tagging & jet-clustering.
- Heavier Higgs.
--> Write a paper.

3-2) Theory (Reported by Harada)
- Paper submitted to PRD
- Sensitivity plot for e+e- -> Zhh and -> nunuhh
-> Assuming no BG, 100% efficiency with 1ab^-1
-> Optimal energy: 400~500GeV for Zhh
--> 400GeV might be enough for the 120GeV higgs?!
Next Step:
- HHH coupling
What happens when BG is considered?
--> S/B ratio as a function of Ecm.
--> Minimum required Ecm for the self coupling measurement after a given Higgs mass.

3) TTH Subgroup (Reported by R.Yonamine)
- Setup:
- Signal(tth): 0.45fb w/NRQCD correction (no beam pol.)
- BG: ttg(g->bb), ttZ(Z->bb), tt(reducible but large)
- NRQCD correction to ttH, ttZ
- Analysis: New BG
Added W*W->btw (94fb) and WWZ->WWbb (9fb) BGs.
(cf: tt: 484fb)
--> Got stdhep files from LOI studies.
--> Event shape cut (thrust cut) less effective for the non-resonant BG.
--> Additional BG contribution of at most about 15% of tt BG equivalent.
- Sensitivity to the Yukawa coupling (delta gt/gt) when worst case (15% more BG) assumed:
--> no pol: 11.4% -> 11.9% (4.4sigma) with 1ab^-1.
(-0.8,+0.3): 8.8% (5.7sigma)
Nest Step:
- Publish the results.
- Move on to full simulation.
- tbW BG? (KF)

[B] New physics
1) LHT: eHeH (Reported by E.Kato)
- New analysis: eHeH
Heavy lepton analysis to evaluate the sensitivity to kappa.
- Setup (MC Conditions):
Same as the previous LHT publication (f=580GeV, mH=134GeV, kappa=0.5)
- Signal mode (Today's topic):
e+e- -> eHeH followed by eH->ZH+e (eH=410GeV) with 500fb^-1
5.64fb (ZH -> AH h) 100%
- BG: tt (200fb), eeWW(1042fb), tauH tauH
- Event selection:
- isolated lepton ID: BG from electrons from H->bb and H->WW
- highs mass cut, accoplanarity, b-tag, missing Pt
--> signal significance = 20.9 sigma.
Next Step:
- Improve event selection
- Add more BGs
Q: What about nuHnuH?
A: Mh and MW are rather different so probably OK.
Q: Polarization effect?
C: Will investigate more later.

2) Quasi-stable Stau (Reported by K.Kotera on behalf of W.Yamaura)
- Setup:
Mass spectrum:
Mstau < Mser,smur < Mchi0 < Msel,Msmul
Mstau = 149GeV, Mchi0 = 200 GeV
- Strong points of ILC
Pair production in clean environment with a tunable Ecm and beam polarization.
- Analysis (stau pair):
Spin measurements with production angle.
Mass measurements with threshold scan + TOF.
-> delta M = 2GeV at around Ecm=320-300GeV with 200fb^-1.
Mass measurement with dE/dx
-> lower Ecm is better for this measurement due to blow up of dE/dx at low beta.
Lifetime measurement of stopped stau in the calorimeter.
-> beta*gamma = 0.35 (Ecm=315GeV) to stop stau in CAL (Range/M=5.1)
-> delta tau/tau = 3.7% with 200fb^-1.
- Analysis (chi0 chi0 followed by chi0 -> sat tau): 30.4fb
delta Mchi0 = 0.05GeV with 200fb^-1 with a very rough estimate with a very empirical fitting function.
Next Step:
- Continue chi0 pair simulations
  Look at production and decay angle distributions.
- Implement dE/dx to the simulator.
C: Clarify the assumed integrated luminosity for each plot.

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

Discussions on future direction and mile stones
*) BAW meeting on Jan.18-21.
*) March.19-23: ALCPG2011 Meeting
*) JPS: 3/25-28: Suehara (model ID), Kato (LHT), Ono (ZH), Yonamine (TTH), Yamaura (Stau)

Meeting Schedule:
Next general meeting (2011/01/29 10:30)

Working group web page:

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