20080906-e

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A Summary of The 19th General Meeting of the ILC Physics Subgroup
Jan. 29 (Sat) at Room 425, Building 3, KEK
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0) Present:
M.Asano (Tohoku)
E.Kato (Tohoku)
S.Kawada (Hiroshima)
H.Ono (NDU)
S.Matsumoto (ITMU)
T.Honda (Tohoku)
S.Kikuta (Sokendai)
J.Tian (Tsingha)
R.Yonamine (Sokendai)
F.Uchiyama (KEK)
T.Tanabe (Tokyo)
Y.Okada (KEK)
T.Suehara (Tokyo)
D.Harada (KEK)
P.Posch (Sokendai)
K.Fujii (KEK)

Via Teleconference System:
K.Kotera (Shinshu)

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Opening Comments
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Reports from Subgroups
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[A] Symmetry breaking & mass generation
1) ZH subgroup
1-1) xxH analysis (Reported by H.Ono)
Status:
- SB2009 caused a significant drop (< 1/3) of the luminosity at 250GeV, which motivated the Higgs measurements at 350GeV, where the luminosity is much higher.
-> With the new parameter set presented at BAW2 this problem is largely ameliorated.
- Setup: mh=120GeV, 250fb^-1@250 and @350GeV, Pol(e+,e-)=(+30%,-80%)
- Analysis: this time, eliminated 0-entry bins, which caused a performance drop.
--> need higher statistics for template samples
BR (cc/bb) measurements:
--> 350GeV measurements seem better than that of 250GeV.
delta BR(cc)/BR(bb): 13.7% (250GeV) -> 10.0% (350GeV)
--> should be improved by increasing statistics for template sample.
Recoil mass: --> Better at 250GeV
Next Step:
- Apply kinematical fitting to improve higgs mass resolution.
- Increase template statistics.
- Compare results with SiD.
- Publication as soon as this binning dependence problem will have been solved.

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2) ZHH Subgroup (Reported by Junping)
Status:
- 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)
- Increased BG statistics and trying to improve selection cuts:
- New analysis results
-> Finite number of llbb BG (from bbZ) survived all the cuts
   llHH: S/B=4.24/3.74 for (Pe-,Pe+)=(0,0), S/B=6.39/6.51 for (-0.8,0.3)
   nnHH: S/B=7.81/3.16 for (0,0), S/B=4.96/5.99 for (-0.8,0.3)
   qqHH: S/B=6.52/6.83 (tight), S/B=11.5/86.2 (loose) for (-0.8,0.3)
   --> New combined significance: 4.6 sigma (excess), 4.1 sigma (measrement)
   --> delta sigma / sigma ~ 25% -> delta lambda / lambda ~ 45% with 2ab^-1.
Next Step:
- Increase BG statistics.
- Optimize qqHH selection.
- Try kinematical fitting.
- Study the expected effects of b-tagging and jet clustering improvements using MC truth.

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3) TTH Subgroup (Reported by T.Tanabe)
Status:
- 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.
Optimized selection cuts
--> With 1ab^-1
ttH(8j): significance 3.43 for (0,0) polarization.
Nest Step:
- Check the BG consistency and increase statistics.
- Publish the results.
- Move on to full simulation.

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4) AA->HH Group
4-1) Experiment (Reported by Kawada)
Status:
- bbbb BG study:
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.
960fb @ 270GeV, 109fb with luminosity function.
- Trying to find effective cut variables:
--> Mcut (bbbar:gamma*), costh_q, E_bbar, costh_bbar, …
--> Looking at the distributions of these variables
--> bbbar pair mass peaks at the threshold and very forward peaked
Next step:
- Try more cuts in the generator level.
- Prepare the bbbb generator.
- Improve b-tagging & jet-clustering.
- Heavier Higgs.
--> Write a paper.

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[B] New physics
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1) LHT: eHeH (Reported by E.Kato)
Status:
- 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%
- Added more BG:
--> BGs now include tt (200fb), eeWW(1042fb), tauH tauH, ttZ, ttH, enWZ, eeZZ, WWZ, ZZZ
- Event selection:
- isolated lepton ID: BG from electrons from H->bb and H->WW
- highs mass cut, accoplanarity, b-tag, missing Pt
--> signal significance = 24.7 sigma.
- Mass from Endpoints:
--> eH mass = 411.9+/-1.9GeV, ZH mass=370.5+/-1.8GeV
- Parameter fit
--> f=583.7+/-2.3GeV, kappa=0.5+/-3.3x10^-4
cf) f=580+/-0.98GeV from WHWH
Next Step:
- Improve fitting of electron energies
- Simultanes fitting

2) Higgs Portal (Reported by T.Honda)
Status:
- Signal & BGs
Signal: e+e- -> ZH(*) -> Z DM DM
BGs considered: nnZ, ZZ, WW, enW, eeZ
- Setup:
mh=120GeV, mDM=10,20,…,100GeV
2ab^-1 @ Ecm=300GeV
(Pe-,Pe+)=(+0.8,-0.3)
- Selection Cuts:
No isolated lepton, FB veto, Z-prod/decay angles, mZ,
- Upper limit on the signal cross section as a fun. of mDM.
Next Step:
- Add more points in the upper limit plot.

3) Model Discrimination (Reported by T.Suehara)
3 generic cases to be discriminated:
a) J=0: Inert H-like model
b) J=1/2: SUSY-like case
c) J=1: LHT-like case
Status:
- The paper draft is almost ready.
- Mass determination
--> <5% accuracy achievable with 40fb^-1.
- Angular distribution
SUSY and LHT are difficult to separate, though IH can be separated.
- Threshold scan
SUSY can be separated from the other two, LHT, IH.
--> With 200fb^-1, all the three models can be separated. IH-like model can be separated from the other two even with 40fb^-1.
Next Step:
- 1TeV analysis update.
- Finish up and submit the paper.

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The slides shown at the meeting is available from
http://ilcphys.kek.jp/meeting/physics/
see them for details.
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Discussions on future direction and mile stones
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*) Reviewed the expected LHC's sensitivity to the SM Higgs boson and discussed the strategy for the DBD studies. Main points can be summarized as follows:
- If mh>140GeV, the LHC will see it in one year. In that case we should redo the analysis. If mh<140GeV, there will be no qualitative difference from the mh=120GeV case. We only need to regenerate the signal sample for the measured mh; we can use the same BG samples generated at Ecm=500GeV, since the sensitivity for the self-coupling, for instance, does not depend on mh so much.
- We discussed who is going to do what for the new benchmarks. Ono san will be responsible for nnH, Yonamine san and Tanabe san will be responsible for ttH.
--> To be discussed at the ild-opt meeting.
- There will be a separate physics volume.
--> To be discussed at the next physics panel meeting scheduled at the beginning of Feb.
*) Annual Meeting: March 9-11 (will be a physics session)
*) ALCPG2011 Meeting: March 19-23
*) JPS: 3/25-28: Suehara (model ID), Kato (LHT), Ono (ZH), Yonamine (TTH), Yamaura (Stau)
Tanabe (Tools)

Meeting Schedule:
Next general meeting (2011/05/14 10:30)

Working group web page:
http://www-jlc.kek.jp/subg/physics/ilcphys/

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