A Summary of The 31st General Meeting of the ILC Physics Subgroup
May 18, 2013 (Sat) at Room 425, Building 3, KEK

Present at KEK:
T.Tanabe (Tokyo)
T.Horiguchi (Tohoku)
C.Calancha (KEK)
H.Ono (NDU)
S.Watanuki (Tohoku)
K.Tsumura (Nagoya)
J.Tian (KEK)
S.Kawada (Hiroshima)
M.Kurata (Tokyo)
H.Yokoya (Toyama)
A.Ishikawa (Tohoku)
M.Nozoe (Saga)
K.Fujii (KEK)

0) Opening comments (K.Fujii)

1) Higgs BR Studies for DBD (H.Ono)
- New sample being prepared with new beam parameters
new mh = 125GeV
new BR : LHC Higgs XSWG
Ecm : 250,350,(500),1000
new detector model: ILD_01_v05
new software: ilcsoft v01-16
new flavor tag: LCFIPlus- #events very similar to the LoI case because of new beam parameters
in spite of the Higgs mass change to 125GeV.
- two-photon BG negligible at 250GeV -> Will not use the anti-KT jet
clustering at 250GeV
- Event selection
Basically as before with the LoI studies.
llh and vvh
Next Step:
- Compare flavor tagging performance of LCFIPlus
- Zh -> qqh
- 350GeV will start after 250GeV
- Finish the analyses in time for the Snowmass white paper.
- Investigate systematic uncertainties

2) CP mixing of Higgs and recoil mass measurement (S.Watanuki)
Measure cos(theta_Z) and extract the mixing parameter, eta.
Signal sample: eta=0 and mh=125GeV at Ecm=250 GeV with (P_e-,P_e+)=(-1,+1).
Now using the new sample with mh=125GeV!
Select Zh -> mmh using ZFinder + cuts on m_Z and m_rec
--> reconstructed cos(theta_Z)
Nonzero eta is expected to produce asymmetry in cos(theta_Z).
--> Some bias observed in <eta> for the MC sample generated with eta=0.
--> need investigation.
Recoil mass:
Checking distributions of various observables
--> modified Mdl, Mrecoil, and acop cuts.
--> clear signals.
Next Step:
- study eta pull
- BG study
- Prepare a new generator with nonzero eta and extend the analysis to
nonzero eta samples to test the sensitivity to eta.
- Try to get the results by Snowmass E-frontier meeting.

3) Higgs->AA at Ecm=250 and 500GeV (C.Calancha)
- New sample with mh=125GeV
- Expected number of signal events:
Ecm=250GeV, 250fb-1 --> 160 events
Ecm=500GeV, 500fb-1 --> 292 events
--> need to check #two-photon BG events/BC, 1.7 seems too large!
- Preselection
B/S ~ 160 for both vvh, qqh at Ecm=250GeV
~ 16 for vvh at Ecm=500GeV --> much better thanks to W-fusion vvh.
~ 119 for qqh
- Event selection
Look for the most effective cut variables by checking their distributions and
correlation matrix.
--> BG fluctuation seems to be larger than the signal size.
--> Need to increase the BG MC statistics.
vvh fusion seems very promising.
--> 5 sigma significance
Next Step:
- Upgrade lumi to 900fb-1 at 250GeV and 1100fb-1 at 500GeV.
- Increase BG statistics.
- Understand the systematic shift in mh.
- Get results by the Snowmass E-frontier meeting.

4) Self-coupling 2: HH->bbWW* (M.Kurata)
- Signature to look for
ZbbWW* --> qqbblvqq
--> bbbbqqqq
--> bbbblvqq
--> llbblvqq
--> llbbqqqq
Signal Zhh (h*->hh)
BG: Zhh (both h directly from Z*),
tt, ttQQ, ttZ, tth, and ZZh,triboson
Jet paring by chi2(m_jj) method
Soft-jet finding
gluon jets are expected to be wider than quark jets.
--> MVA to form soft-jet-likeliness
Combined results
--> 1 sigma significance so far.
Most significant is all hadronic channel with 4 tight b-tagged jets.
--> 4.3 events (including 1.61 HH->bbbb cross feed) starting from 360
with no cuts.
Next Step:
- Improve analysis
- Check overlapping with HH->bbbb analysis.
--> Probably there is no overlap after the b-tagging.
--> It us OK to treat the 1.61 events as the signal.

5) Top pair threshold (T.Horiguchi)
MC simulations with
mt=174 GeV, 11 points with 10 fb-1 each from 340 to 350 GeV in 1 GeV step.
beam polarization: (-0.8,+0.3) (Last time it was (+0.8,-0.3)
BG: WW, ZZ, qqH
efficiency: 0.4 - 0.45, almost linear function of Ecm.
Next Step:
- Evaluate sensitivity to top Yukawa
- Evaluate error on mt
Q: Why is ZZ BG so large?
A: mt cut is not yet applied.
--> Selection can be still optimized.
C: use the fact that b and W from a top are back-to-back.

6) H++ -> W+W+ (H.Yokoya)
3: Y=1
Delta = \begin{pmatrix}
\Delta^+/sqrt{2} & \Delta^{++} \cr
\Delta^0 & -\Delta^+/sqrt{2}
--> H^{\pm\pm}, H^{\pm}, H, A, h: 7 physical Higgses
H^{++} -> l^+l^+ : H^{++} has lepton number 2.
rho Parameter, neutrino mass
--> 0.1eV < v_{\Delta} < 3.5GeV
Mass spectrum (determined by \lambda_5 parameter)
--> m_A^2 \simeq m_H^2 = M_\Delta^2
m_{H^{++}}^2 \simeq M_\Delta^2 - (v^2/2) \lambda_5
m_{H^+}^2 \simeq M_\Delta^2 - (v^2/4) \lambda_5
--> equally spaced, order reversed depending on the sign of \lambda_5.
--> all degenerate if \lambda_5 = 0.
Decay modes depend on v_\Delta and m_{H^{++}}-m_{H^+}
In this talk focus on H^{++} -> W^+W^+
Current mass bound:
LEP: Z-pole --> Z boson width (Z -> H^{++} H^{--}) --> m_{H^{++}} > 43GeV
Q: what about W width constraint?
: same-sign 4-lepton search
--> no constraint due to the suppression BR^4
: possible other constraints under study
LHC: ATLAS presented a limit on same-sign dilepton events
--> m_H^{++} > 60GeV (4.7fb-1) --> expect 85GeV for 20fb-1.
Discussions (LHC):
- K factor (X-sections are evaluated at leading order).
- dileptons from H^+ are not counted.
- inclusion of jet mode may enhance the sensitivity.

7) EWkino Scan (T.Tanabe)
- Trying to inputs the results to the Snowmass process as a part of
the ILC BSM whitepaper.
- The current limits
LEP: m_{\chi^\pm} > 90GeV
ISR-tagging technique used for \Delta m ~ O(1GeV)
LHC: ATLAS 20.7fb-1 (8TeV) data
(assuming that bino LSP, \chi_1^\pm, \chi_2^0 are wino and degenerate)
- Setup
EWkinos are the only light SUSY particles.
- Outlook
M_recoil against ISR gamma (J.List) --> looks promising.
--> delta m < 1GeV
Next Step:
- Parameter scan and input the results to the Snowmass process.

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

Discussions on future direction and milestones
*) Meeting Schedule:
Next general meeting (2013/06/22 10:30) : Conf.ID: 634

*) Contributions to ECFA LCWS 2013:
- Ono: BR measurements
- Kurata: self-coupling
- Juping: self-coupling
- Horiguchi: ttbar
- Ishikawa: H -> invisible
- Kwadasa: H -> tau tau
- Tanabe: tth
- Tanabe: stau NLSP
- Tsumura: septet
- Yamada: strong but light
- Nabeshima: inflation
- ……


Working group web page:

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