A Summary of The 35th General Meeting of the ILC Physics Subgroup
Jan. 18, 2014 (Sat) at Room 425, Building 3, KEK
0) Attendants:
Present at KEK:
A.Ishikawa (Tohoku)
Y.Shinzaki (Tohoku)
S.Watanuki (Tohoku)
A.Dubey (Tohoku)
M.Kurata (Tokyo)
T.Tanabe (Tokyo)
K.Hidaka (Gakugei)
S.Kawada (Hiroshima)
T.Tomita (Kyushu)
C.Calancha (KEK)
J.Tian (KEK)
K.Fujii (KEK)

0) Opening comments (K.Fujii)

1) ZH: Recoil mass using Z->qq (T.Tomita)
- Simulation conditions:
DBD sample at Ecm=250GeV
- Event selection
WW and ZZ rejection after forced 4-jet clustering.
+ some other cuts.
—> efficiency (Signal) = 46%
After event selection, redo the jet clustering with ycut fixed at 0.005.
- Results
eLpR: 28.3 sigmas
eRpL: 49.0 sigmas
Next Step:
- Dependence of efficiency on H decay mode
- Think about how to decide the BG and signal shape.

2) ZH: Recoil mass using Z->ll (S.Watanuki)
- Looked at decay mode dependence of selection efficiency
- Check the dependence on scaling methods for photon recovery
Next Step:
- Try Kernel function instead of GPET
- Increase the statistics for efficiency estimates
- Check the recovered photon energy fraction.

3) Higgs to tau tau (S.Kawada)
- Setup:
Ecm=500GeV, 500fb-1, mh=125GeV, 2-photon hadron: 1.7ev/bunch crossing (overestimate)
- Results:
delta (sigmaxBR)/(sigmaxBR) = 7.4% (cut-based)
delta (sigmaxBR)/(sigmaxBR) = 6.0% (TMVA)
Zh (Z->qq)
delta (sigmaxBR)/(sigmaxBR) = 5.1% (cut-based)
delta (sigmaxBR)/(sigmaxBR) = 4.6% (TMVA)
New since the last meeting:
Zh (Z->ee)
delta (sigmaxBR)/(sigmaxBR) = 20.8% (cut-based)
delta (sigmaxBR)/(sigmaxBR) = 22.7% (TMVA)
Zh (Z->mm)
delta (sigmaxBR)/(sigmaxBR) = 18.2% (cut-based)
delta (sigmaxBR)/(sigmaxBR) = 17.5% (TMVA)
- More BG
Working on aa_2f samples, checking MC statistics.
- More optimization in 500 GeV
- mh=125GeV analysis at Ecm=250GeV

4) Higgs to gamma gamma (T.Calancha)
- SM samples from DBD studies
- studying the reason for the low (<90%) preselection efficiency.
- reoptimizing final selection with TMVA.
- Results (tentative)
significance = 5.3 sigmas at 500GeV (500fb-1) -> delta (sigmaxBR)/(sigmaxBR)=18.9%
= 13.6 sigmas at 1000GeV (1000fb-1) -> 7.4%
Next step:
- Finish h->gamma gamma analsysis
- h->Z gamma
—> need to move to Whizard v2?

5) Quark Flavor Violating Bosonic Squark Decay (K.Hidaka)
- QFV decay can be large due to scharm stop mixing
- Constraints
LHC SUSY limits
LHC limits on CP odd higgs mass and tanb
b->sgamma, Delta MBs, Bs->mu mu, Bu->tau nu
vacuum stability
- benchmark scenario
mA=1.5TeV, tanb=20 —> decoupling regime
large scR-stL, stL-stR, scR-stR mxings
large stR-stL-H2, scR-stL-H2 couplings
—> all squarks are heavy ~ 2.4TeV, gluino~1.14TeV,
su1, su2 ~0.60, 0.86TeV (large scR-stR mixing)
—> large splitting: su2 —> su1 + h0 possible
su1-su2-h0 coupling can be large.
—> BR(su2->su1+h0) can be as large as ~0.5.
BR(su1->c/t chi0) can be as large as ~0.5.
- Impact on LHC squark search
signal: top + 3 charm jets + h0 + MET
sigmaxBR can be significant ~ 10fb at LHC(14TeV)
- LC search
signal: su1 su1 —> t + cbar + MET
su2 su2bar -> t + cbar + h0 + h0 + MET

6) W+H-/W-H+ (Y.Shinzaki)
Triplet H —> tree level WHZ coupling
—> e+e- -> WH possible
PRD83, 075018 (2011)
- preparing a generator.
—> Cross section values are slightly different from Kanemura-san’s paper.
-> suspecting the parameter values.
- BG analysis.
WW->2j + lepton : reconstructed as 3 jets using forced 3-jet clustering.
Next Step:
- Complete the generator.
- Generate WH sample.
- Continue WW BG analysis.

7) Discussions on Possible New Physics Studies (T.Tanabe)
- Akiya’s proposal to exhaust benchmark points by Jenny.
- Are there any other possibilities left with qualitative different features which are not covered by the benchmark points.
C: we should keep our eyes open to non-standard scenarios.
C: we should continue with our on-going studies on short-lived or quasi-stable
SUSY searches.
C: we need to communicate with the other groups in the ILD.
C: full simulation studies on benchmark points and demonstrate the precision
we could achieve with ILC on mass, coupling, … or to reconstruct BSM Lagrangian bottom-up.

8) Self-coupling measurement with Zhh -> ZbbWW* (M.Kurata)
- In search of possible analysis improvement:
Possible lepton ID improvements using
Shower profile
Lepton ID using likelihood
—> 3 times better than cut based ID
Next Step:
- More study for track properties
- Bayesian technique for jet paring?
- Bayesian technique for jet clustering?
- Jet energy correction?
- Check possible overlapping of event samples


7) HWW, ZHH, … (J.Tian)
Isolated lepton ID
- ECAL, HCAL, Yoke
- isolation criteria: small cone vs large cone
—> significant improvement seen.
Overlay removal
- kt method: works OK for h->bb but not on h->WW*
- MVA method: works OK also for h->WW*
- New idea: find a most likely overlay particle from MVA and then kt method to collect other
overlay particles around it?
Global Fit
- Sum rule for the total width (Michael Peskin’s proposal)
- Studies on systematics on F_i (theory) and on Y_i (exp)
Matrix Element Method
- HELAS based ME function is being developed.
ZHH with HH->bbbb (Claude)
- llHH done with mh=125GeV
- Weighting method
- Reoptimize selection by optimizing (I+2S)/sqrt(sigma+BGr) instead of optimizing
HWW coupling and total width

8) Discussions on detector optimization
- Recoil mass: Z->lepton pairs : Watanuki
- HWW, Gamma_h
: vvh->vvbb,vvcc, Zh->llbb, llcc : Ono, Junping, Suehara, …
: vvh->vvWW*, ZZ* : Ono, Junping, …
- PEW : evW, vvZ: ??
- Tau reconstruction: h -> tau tau : Kawada
- photon reconstruction: h -> gamma gamma : Tino
- tth, tt threshold: Horiguchi, Sudo
- crossing angle & minimum veto angle: DESY people?

Working group web page:

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