A Summary of The 36th General Meeting of the ILC Physics Subgroup
April 19, 2014 (Sat) at Room 425, Building 3, KEK
0) Attendants:
Present at KEK:
A.Ishikawa (Tohoku)
J.Strube (Tohoku)
S.Watanuki (Tohoku)
C.Calancha (KEK)
Y.Okada (KEK)
J.Tian (KEK)
K.Fujii (KEK)
A.Dubey (Tohoku)
M.Kurata (Tokyo)
K.Hidaka (Gakugei)
H.Ono (NDU)
H.Yokoya (Toyama)
S.Kawada (Hiroshima)
Y.Sudo (Kyushu)

Remote connection:
J.Yan (Tokyo)
T.Tomita (Kyushu)
S.Kanemura (Toyama)

0) Opening comments (K.Fujii)

1) ZH: Recoil mass using Z->ll (Shun Watanuki)
- Effects of the binning for different line shape models
—> found some bias in pull distributions
—> moved to unbinned likelihood method
—> the bias disappeared
- Trying to estimate the BG line shape with side bands
—> Question is how to eliminate the signal to estimate
the BG line shape.
Next Step:
- BG line shape
- eeX

2) ZH: Recoil mass study at 350 GeV (Jacqueline Yan)
simulation conditions:
- 333fb-1 at Ecm=350GeV with (-0.8,+0.3)
- BG at 350GeV includes ttbar.
- mh=125GeV
- line shape model
GPET for signal and 3rd order polynomial for BG
- Results:
delta sigma/sigma = 4.5% (114-140 GeV)
- Did 250 GeV analysis too for comparison
- Muon track angles
—> more FB-peaked at 250GeV than at 350GeV.
Nest Step:
- Improve event selection
- Improve fitting method
C: Use toy MC for the estimation of stat. errors on mh and sigma(Zh).
Comparison of different line shape models is useful to estimate systematic
errors due to imperfect modeling of the actual line shape.
C: Show cut table for different polarizations.

3) ZH: Recoil mass using Z->qq at 250GeV (Tatsuhiko Tomita)
- Simulation conditions and event selection:
DBD sample at Ecm=250GeV
2 jets + a system categorized using its features
—> semi-model-independent recoil mass analysis taking advantage of the higher Z->qq branching ratios.
- Mode dependence of selection efficiencies
—> Is it possible to categorize H decays in a model independent manner?
Next Step:
- Study how to categorize events.

4) Higgs branching ratios for H->bb, cc, gg (Hiroaki 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).
- Results for 350GeV are more consistent with the extrapolations.
- Found some difference in flavor tagging using LCFIPlus for the DBD samples from the old LOI samples
- Fixed a bug in the h->cc template, which slightly degraded the precision.
- Understand the difference for qqh and eeh.
C: There is no reason to believe the extrapolation, if the full sim. has no apparent problems.
- Finish up the update to mh=125GeV.
- 350GeV vvh will be shared with DESY.


5) Direct searches of additional Higgs bosons in the 2HDM at the LHC and the ILC (Hiroshi Yokoya)
- Setup
SM-limit: sin(beta-alpha) —> 1
—> no finger printing possible.
—> phi-V-V coupling vanishes, while Yukawa couplings remain.
Type I, II, X, and Y 2HDMs
- LHC search
(bb+)H/ —> tau+ tau-
bb+H/A —> bbbb
gb —> tH-; H- —> tb
qq —> HA —> 4tau
- ILC search
e+e- —> HA, H+H-
e+e- —> ffH/A, ff’H+/-
- There is a certain complementarity between LHC and ILC.
Next Step:
- Study the case with sin(beta-alpha)<1
- Do realistic simulations.

6) Top pair production near threshold (Tomohiro Horiguchi)
- Setup:
mt=174GeV, 341-350GeV (10-point scan with 1GeV step, 5fb-1 each)
Fixed a problem with the BG overlay (1TeV overlay was used by mistake)
Added a new BG: wworzz
- Results: 100fb-1 (50 L and 50 R)
m_t(PS)=172+/-0.018 GeV
Gamma_t=1.4+/-0.024 GeV
y_t=1+/-0.037 (as compared to old value delta y_t / y_t = 4.4%
C: Why did you loosen the b-tag?
wworzz should be eliminated if two b jets are required.
Next step:
- Understand the reason why BG increased for the new sample.

7) Top Yukawa coupling study at 500 GeV (Yuji Sudo)
- Setup:
mh=125 GeV, 1ab-1 at Ecm=500GeV,
beam polarization=(-0.8,+0.3)
- Results:
8-jet : S=26.0 BG=41.74 —> delta y_t / y_t = 15.8%
L+6-jet: S=27.7 BG=35.64 —> delta y_t / y_t = 14.5%
—> delta y_t / y_t = 10.6% (combined)
—> comparable with the extrapolation even before MVA.
—> maybe because of the better separation between mZ and mh.
Nest Step:
- Increase MC statistics
- Confirm tbW shape
- Systematics including those from b-tag, Ejet, …

8) Higgs to tau tau (Shin-ichi Kawada)
- Setup:
Ecm=500GeV, 500fb-1, mh=125GeV, 2-photon hadron: 1.7ev/bunch crossing (overestimate)
new from the last meeting: aa_2f BG added.
- Results:
Zh (Z->qq)
delta (sigmaxBR)/(sigmaxBR) = 4.9% (cut-based)
delta (sigmaxBR)/(sigmaxBR) = 4.7% (TMVA)
delta (sigmaxBR)/(sigmaxBR) = 8.5% (cut-based)
delta (sigmaxBR)/(sigmaxBR) = 7.4% (TMVA)
Zh (Z->ee)
delta (sigmaxBR)/(sigmaxBR) = 31.3% (cut-based)
delta (sigmaxBR)/(sigmaxBR) = 31.2% (TMVA)
Zh (Z->mm)
delta (sigmaxBR)/(sigmaxBR) = 20.0% (cut-based)
delta (sigmaxBR)/(sigmaxBR) = 17.6% (TMVA)
- More optimization in 500 GeV
- Separte Zh and WW-fusion in vvh
- mh=125GeV analysis at Ecm=250GeV
C: Use MC truth to see the composition (Zh vs fusion) of the remaining vvh events.

9) Self-coupling measurement with Zhh -> ZbbWW* (Masakazu Kurata)
- In search of possible analysis improvement:
Possible lepton ID improvements using
mu type
Shower profile
e type
mu type
mu fake
- Track properties for mu ID
- transverse absorption length
—> momentum dependent (curvature effect) —> corrected.
- xl20
- Results:
Cut based Likelihood (old) (new)
signal (%) 98.4 98.1 98.2
bbcssc (%) 7.9 3.1 2.6
Next Step:
- More study for track properties
- Tracks from 2ndary vertices
- dE/dx

10) Matrix element method and its application to eeH (Junping Tian)
- ME tools development
C++ version of HELAS (HELLib)
LCME (linear collider matrix element libs)
- Test
Verified the flat ness of the MC distributions weighted by 1/ME_weight.
- Test with eeH at the generator level
Nest Step:
- detector transfer function.

11) Discussions
11-1) To do in Higgs analyses
We have gone through the table of Higgs related analyses to see how the necessary channels are covered by on-going efforts.
11-2) Task Force for new physics
@ We have discussed our strategy to enforce the BSM studies.

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

Discussions on future direction and milestones
*) Meeting Schedule:
Next general meeting (2014/06/21 10:30) : Conf.ID: 291

This is the minutes of today’s discussion of new physics at ILC.

What kind of role ILC could play in terns of different new physics yields at LHC 14 TeV run?
(A) new particle / new physics discovered
(B) no new physics, but see deviations from SM in the Higgs properties, etc.
(C) no new physics, no deviation

Comments from Y. Okada:
a.) strategy: elaborate promising new physics models;
for each model, cases A, B and C can be discussed.
Pay special attention to SUSY, i.e. loopholes or heavy SUSY;
possible discovery in top physics should also be included.
b.) first step is to define good benchmark models, for which brainstorming
by theorists is needed. In particular, it is important to review existing
studies on expected physics outputs from various stages of LHC.
We will then be able to discuss what ILC can add.
We will contact theorists who might be interested in this kind of studies.
c.) possible time line: the coming Toyama meeting can be a good opportunity
to start planning the brainstorming meeting (kick-off meeting).
We will decide the date for the kick-off meeting of this task force (in 1~2 months);
after the kick-off meeting, some study framework should be figured out,
either with more theoretical or experimental studies;
We need to formulate an effective way to demonstrate various opportunities
provided by the future stages of LHC and ILC.
For instance, we may layout physics opportunities in a matrix consisting
of observables/measurements in rows and physics objectives in columns.
Assigning existing studies to this matrix for both LHC and ILC would identify
missing studies if any.
Our primary goal is to get some output at LCWS14;
whole study should be more or less completed in about 1 year.

Comments from K.Fujii and J.Strube:
Snowmass report of New Particle Working Group would be a good starting point;
Kind of discoveries stories would also be useful.

Working group web page:

Slides are available from http://agenda.linearcollider.org/categoryDisplay.py?categId=131