A Summary of The 34th General Meeting of the ILC Physics Subgroup
Nov. 6, 2013 (Sat) at Room 425, Building 3, KEK
0) Attendants:
Present at KEK:
T.Horiguchi (Tohoku)
A.Ishikawa (Tohoku)
Y.Shinzaki (Tohoku)
S.Watanuki (Tohoku)
M.Kurata (Tokyo)
T.Mori (Tokyo)
T.Tanabe (Tokyo)
H.Yokoyama (Tokyo)
S.Kawada (Hiroshima)
T.Suehara (Kyushu)
R.Settles (MPI)
C.Duerig (DESY)
C.Calancha (KEK)
J.Tian (KEK)
A.Miyamoto (KEK)
K.Fujii (KEK)
Via remote connection:
H.Ono (NDU)

0) Opening comments (K.Fujii)

1) Higgs BR measurements (H.Ono)
- Condition changes from LoI analysis:
mh=120 -> 125GeV
- BR updated (LHC) + new analysis tools
- Results for 250GeV, 250fb-1
full simulation results are consistent with the extrapolated values for vvh and mmh but they differ for h->cc/gg with qqh and eeh (worse).
Next step:
- Understand the difference for qqh and eeh.
- 350GeV analysis

2) Higgs to tau tau (S.Kawada)
- Setup:
Ecm=500GeV, 500fb-1, mh=125GeV, 2-photon hadron: 1.7ev/bunch crossing (overestimate)
- Results:
13.6 sigma --> delta (sigmaxBR)/(sigmaxBR) = 7.4% (cut-based)
16.6 sigma --> delta (sigmaxBR)/(sigmaxBR) = 6.0% (TMVA)
Zh (Z->qq)
19.9 sigma --> delta (sigmaxBR)/(sigmaxBR) = 5.0% (cut-based)
22.2 sigma --> delta (sigmaxBR)/(sigmaxBR) = 4.5% (TMVA)
--> The results are very consistent with the extrapolation
Next step:
- More optimization
- llh at 500GeV
- mh=125GeV analysis at Ecm=250GeV

3) Higgs to tau tau (H.Yokoyama)
- Today: CP=+/- separation
- Setup:
250fb-1 at 250GeV
- Method:
Use impact parameter vectors to decide the angle between two decay planes.
- Event selection
Use tau tau ->(piv)(piv), (piv)(e2v), (piv)(m2v), (e2v)(piv), (m2v)(piv)
which is 8.8% of all the tau tau decays.
--> 98% CL rejection of pure CP-odd hypothesis for a pure CP-even h.
Next step:
- estimate the sensitivity to CP mixing angle.
- optimization of tau decay classification.
- use rho, 3-prong

4) Higgs to gamma gamma (T.Calancha)
MC signal samples ready for 500, 1000GeV.
high statistics qq gamma gamma and vv gamma gamma BG ready.
- Results
vvh at 500GeV (500fb-1)
--> significance: 5.2 sigma (BDT)
vvh at 1000GeV (1000fb-1)
--> significance: 10.2 sigma (cut-based)
Next step:
- BDT for 1000GeV analysis
- qqh mode

5) Recoil mass study (S.Watanuki)
- Setup:
mh=125GeV, 250fb-1 at Ecm=250GeV, P(e-,e+)=(-0.8,+0.3)
with DBD simulation tools
- Event selection
bremsstrahlung photon recovery
mmh: S: 2574 (no cut) --> 1564 (final sample)
- Results:
Model-independent analysis
Gaussian Peak with Exponential Tail (GPET)
- mmh: delta sigma / sigma = 3.6% delta mh/mh = 37MeV
eeh: delta sigma / sigma = 5.2% delta mh/mh = 147MeV combined --> 3.0% 36MeV
Semi-model-independent analysis (exclude invisible decays)
- mmh: delta sigma / sigma = 3.0%
eeh: delta sigma / sigma = 4.6% combined --> 2.5% 36MeV
Next step:
- Understand why eeh spectrum so much wider than the LoI analysis.
- Make sure that the result is not sensitive to the choice of fitting function.

6) Recoil mass @ 500GeV (T.Suehara)
- Motivation
Combine higher energy data (Ecm=500GeV)
recoil mass in jetty mode (Ecm=350GeV, 500GeV)
- Results:
delta sigma / sigma = 6.5% with 500 fb^-1 (-80,+30)
delta sigma / sigma = 7.1%
--> 4.8% (combined)
delta sigma / sigma = 3.6% with 300 fb-1 at Ecm=350GeV
delta sigma / sigma = 3.9% with 500 fb-1 at Ecm=500GeV
Ecm=250GeV on going
Next step:
- Check WW/ZZ events before LCWS.
- Improve analysis.
- qqh at Ecm=250GeV
- Increase BG statistics.
- Check Z purity with MC truth.

7) vvh followed by h->WW* and Higgs width @ 500GeV (J.Tian)
Today's topic: vvh
delta (sigmaxBR(bb))/(sigmaxBR(bb)) = 0.667%
delta ghWW / ghWW = 4.8% (250GeV), 1.2% (500GeV)
delta (sigmaxBR(WW*))/(sigmaxBR(WW*)) = 2.8%
delta (sigmaxBR(WW*))/(sigmaxBR(WW*)) = 4.4%
delta Gamma_h / Gamma_h = 11% (250GeV), 5.0% (500GeV)
Next step:
- Study effect recoil mass measurements at 500GeV
Q: What about 350GeV?
A: If we naively optimize integrated luminosity at each energy of 3-stage running for coupling and total width, the optimal integrated luminosity at 350GeV would be zero.

8) ttbar threshold (T.Horiguchi)
- Setup:
mt=174GeV, 341-350GeV (10-point scan with 1GeV step, 5fb-1 each)
- Results:
cross section measurements
delta sigma / sigma (6J) = 2.9% (-0.8,+0.3)
delta sigma / sigma (6J) = 4.1% (+0.8,-0.3)
delta sigma / sigma (4J) = 3.3% (-0.8,+0.3)
delta sigma / sigma (4J) = 4.6% (+0.8,-0.3)
--> delta y_t / y_t = 4.4%
mass-width measurements
delta mt / mt (MSbar) = 17 GeV (stat. only)
Q: Why efficiency is almost completely flat in Ecm?
Cuts are now optimized at each energy.
Next step:

9) Self-coupling measurement with Zhh -> Zbbbb (C.Duerig)
- Setup:
Ecm=500GeV, mh=125GeV
Zhh : sensitivity factor = 1.74 (as compared to 1.8 for mh=120GeV)
Previous result (Junping):
delta sigma / sigma = 27% (>3.5 sigma) for mh=120GeV with 2ab-1
- Analysis
New lepton selection (MVA based):
--> better efficiency and much better BG rejection.
2-photon BG removal (<N>=1.7: overestimate)
--> kt ExclusiveNJets4 with R=1.3
--> mh distribution very close to Durham w/o 2-photon BG!
Next step:
- Finish llhh analysis with new lepton selection and 2-photon BG.
- Fix <N(2-photon BG)>=1.7, which is an overestimate.
- Weighting.
- jet-finding, jet-clustering.
- vvhh at 1TeV.

10) Self-coupling measurement with Zhh -> ZbbWW* (M.Kurata)
- Setup:
mh=125GeV, full simulation at 500GeV (-0.8,+0.3)
fast simulation at 1000GeV (-0.8,+0.2)
- Analysis:
Soft (gluon) jet finding to reject BG with fewer number of quark jets.
m(jjjj), m(lvjj) are the most powerful variables in MVA
Fox-Wolfram moments
- Results:
--> combined significance ~1.9 sigma
- 1TeV analysis is ongoing for Zhh and vvhh with (hh->bbWW*)
Next step:
- Optimize b-tagging
- Improve basic analysis tools: lepton ID, b-tagging, jet energy correction, jet clustering.
C: full simulation sample is available for 1TeV analysis.
C: Need to separate Zhh and vvhh since the lambda dependence is opposite.
C: Zhh at 1TeV has less sensitivity to lambda since the relative contribution from the self-coupling diagram is much less there.

11) Stau NLSP (T.Mori)
- Setup:
stable stau mass > 360GeV (LHC limit)
stau mass > 90GeV (LEP limit)
--> stay mass: 120-240GeV, life time 10um-10mm
GMSB with Gravitino LSP
m_3/2 ~ O(10)eV
stay -> tau + axino, tau v (RPV) have the same signature: tau pair + MET
- Results:
>6 sigma discovery for all the benchmark points
delta ctau / ctau = 5% (200GeV, 100um)
delta mass / mass = 1.2% (240GeV, 100um)
Next step:
- Optimize cuts for kinematical mass resolution.
- 3-prong decays.

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

Discussions on future direction and milestones
*) Meeting Schedule:
Next general meeting (2014/01/18 10:30) : Conf.ID: 134

Working group web page:

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