A Summary of The 23rd General Meeting of the ILC Physics Subgroup
Nov.5, 2011 (Sat) at Room 425, Building 3, KEK
0) Attendants:
R.Settles (MPI)
A.Ishikawa (Tohoku)

A.Yamamoto (Tohoku)
T.Tanabe (Tokyo)
T.Suehara (Tokyo)
R.Katayama (Tokyo)
H.Ono (NDU)

S.Kawada (Hiroshima)
Y.Okada (KEK)
J.Tian (KEK)
T.Yamada (Sokendai)
R.Yonamine (Sokendai)
P.Posh (Sokendai)
D.Harada (KEK)
K.Fujii (KEK)

Opening Comments

[A] Symmetry breaking & mass generation

1) ZH subgroup
1-1) ZH analysis (Reported by H.Ono)
- Setup: mh=120GeV,
250fb^-1@250 and @350GeV, Pol(e+,e-)=(+30%,-80%)
- BR(H->bb,cc,gg) -> preparing 1st draft for publication.
delta BR(bb)/BR(bb) = 2.7% (250GeV)
delta BR(cc)/BR(cc) = 8.1% (250GeV)
delta BR(gg)/BR(gg) = 9.0% (250GeV)
- Updated recoil mass plots @250GeV for mh=120, 130, 140GeV.
--> seems much nicer than the old GLD plot.
- New projects: include other decay modes such as H->WW*, …,
taking into account LHC results, focus on 115 < mh < 140 GeV
(Takubo: delta BR(WW*)/BR(WW*) = 15.7% (250GeV): 4J only)
- nnH @ 1TeV strategy
Next Step:
- Publication.
- Full simulation for different decay modes, masses
- nnH @ 1TeV
--> WL, ZL, H as new particles to be probed by high virtuality probe.
C: we need BR(H->tau+tau-, ZZ*, ZA, AA).

2) ZHH subgroup (Reported by J.Tian)
2-1) ZHH @ 500GeV
- Previous analysis
mH=120GeV, 2ab^-1
--> excess significance: 3.9 sigma
--> delta sigma_ZHH = 0.22+/-0.07fb (32%)
--> delta lambda/lambda = 57% (= 1.8 x delta sigma/sigma)
--> Not enough
- Temporary goal: a factor of 2 improvement!
- Possible places for the future improvements
jet clustering, b-tagging, jet paring, lepton ID
--> In order to estimate the limit we can achieve, develop cheaters
- Findings:
There are a significant number of photons associated with isolated leptons (FSR).
With cheated jet clustering, the mass separation became very good.
--> ZZZ, ZZH BG could be more cleanly separated.
--> llbbbb significance could be improved from 2.1sigma to 3.9sigma by cheating!!
Next Step:
- Continue cheating for other modes.
- Publication of the current results
- nnHH @ 1TeV
- different mH

2) AA->HH Group
2-1) Experiment (Reported by Kawada)
- Increased the BG statistics and use different samples for NN training.
--> Signal significance dropped from 1.17 to 0.7 for 5 yeas running (TESLA optimistic).
--> With cheated jet clustering, the significance is 4.7.
Next step:
- Write a paper.
- Improve b-tagging & jet-clustering.
C: Higher Ecm might be more advantageous in terms of S/B ratio.
C: Check what happens to sensitivity plot if eta_BG is nonzero and eta_S is less than 1.

3) TTH Subgroup (Reported by R.Yonamine)
- Moved on to full simulation for Ecm=500GeV, mh=120GeV, mt=175GeV
- ttH, ttg* MC samples: produced. ttZ: not yet.
- Now investigating lepton ID.
Next Step:
- ttZ data production.
- parameter optimization for lepton ID.
- cheated jet clustering.
- 1TeV
- mH=140GeV using H->WW*

[B] New physics
1) Higgs Portal (Reported by A.Yamamoto)
By definition, Higgs portal DM only interacts with Higgs.
Signal: e+e- -> ZH -> ffbar (DM DM): 15fb @ 250GeV.
BGs: ZZ, nnZ, WW, enW, eeZ, ZH
- Event Selection
isolated lepton cut: effective to reprove WW BG.
forward e+/- cut to reject enW, eeZ BG.
Z mass cut
- Preliminary results
-->There is some inconsistency between the present analysis and that of Honda.
BGs are still high. --> Need to improve event selection.
Next Step:
- Optimize event selection.
- Try right-handed polarization.
- Do the same at 500GeV.
- t-channel H production at 1TeV.
C: Check the cross sections with other tools such as Madgraph.
C: Check the h-DM-DM Lagrangian.

2) Very light gravitino (Reported by R.Katayama)
m_\tilde{G} = <F>/Mpl/3^{1/2} with 1/<F> ~ 1/(Mpl m_{3/2})
-> directly connected to the SUSY breaking scale.
m_\tilde{G} = O(1)-O(10)eV
-> interesting allowed region
ILC signal:
ctau ~ 100 microns (m_LSP=6.5eV, m_NLSP=120GeV)
(tau ~ 48pi M_pl^2 m_\tilde{G}^2 / m_stau^5)
Want to measure ctau, from which m_gravitino is extractable
given the stau mass is measured beforehand by E_tau, etc.
Simulation & Analysis:
Measure the deviation of the impact parameters for the tau decay products
from the SM prediction.
- A signal generator prepared.
- BG: tau+tau-, W+W-, Z0Z0, two-photon tau+tau-.
- Event selection using full sim. samples
--> Look at impact parameter distributions for tau+tau- & mu+mu- BG.
--> Cuts on Evis, Pt, acoplanarity, angle/Evis: essential to suppress AA->tau+tau-
--> AA->tau+tau- :suppressed from O(10^9) to 0.
- Stau mass reconstruction from end point.
--> delta m /m = 1.1 x 10^-2
--> Effect of non-Gaussian Ebeam spread?
- Life time fit
--> delta tau /tau = 1.4 x 10^-2
- Gravitino mass from tau and m measurements:
--> delta m_\tilde{G}/m_\tilde{G} = 3 x 10^-2
Next Step:
- More statistics for two-photon and Bhabha BGs.
- Study the mass extraction from threshold scan.
- Different stau mass and life time.
C: First make sure it is stau then make sure it decays into non-standard LSP.
Q: What is the range of life time to which this analysis method can be applied?

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

Discussions on future direction and mile stones
*) Higgs WG
1st meeting: Nov.11 (fri) 16:00 : Conf. ID: 633.
Meeting Schedule:
*) ACFA2012 Meeting: April 23-26, Degu.
*) LCWS2012 Meeting: Oct 22-26, Arlington, Texas.
Next general meeting (2012/01/28 10:30) : Conf.ID: 863

Working group web page:

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