A Summary of The 21st General Meeting of the ILC Physics Subgroup
July 16, 2011 (Sat) at Room 425, Building 3, KEK
0) Attendants:
A.Ishikawa (Tohoku)
E.Kato (Tohoku)
A.Yamamoto (Tohoku)
T.Tanabe (Tokyo)
T.Suehara (Tokyo)
R.Katayama (Tokyo)
H.Ono (NDU)
S.Kawada (Hiroshima)
F.Uchiyama (KEK)
Y.Okada (KEK)
S.Kikuta (Sokendai)
T.Yamada (Sokendai)
K.Fujii (KEK)

Via video conf. system:
Y.Kiyo (Tohoku)

Opening Comments
Reports from Subgroups
[A] Symmetry breaking & mass generation
1) ZH subgroup
1-1) xxH analysis: BR measurements (Reported by H.Ono)
- Setup: mh=120GeV,
250fb^-1@250 and @350GeV, Pol(e+,e-)=(+30%,-80%)
- Results of BR (cc/bb) measurements with improved statistics
Combined results of nnH, qqH, and llH (revised):
delta BR(cc)/BR(bb): 9.2% (250GeV) -> 6.8% (350GeV)
--> Almost final values.
--> 350GeV measurements are better than that of 250GeV.
- Started drafting a journal paper.
- Started thinking about DBD analysis strategy.
Next Step:
- Summarize the results for publication (in this month)
- DBD analysis: nunuH@1TeV
Q: What about H -> tau+tau-?
A: Very important in the light of non-standard Higgs sector possibilities.
C: H -> mu+mu- is also important to confirm mass-coupling relation in the lepton sector.

2) AA->HH Group
2-1) Experiment (Reported by Kawada)
- 4b BG study:
It turned out that the main diagram is the 2-resolved-photon process:
each gamma splitting into a bbar pair and forward scattering of b or bar
through gluon exchange.
960fb @ 270GeV, 109fb with luminosity function (cf. signal: 13ab)
- Preselection:
chi2_H < 150 & chi2_A > 100, 190GeV < Evis < 320GeV
|Pl| < 70 GeV, |csjmax| < 0.95, sphericity > 0.1
- NN: thrust, sphericity, aplanarity, Y-value,
--> significance: 1.81 (1.47) for optimistic (pessimistic) 4b
Next step:
- Investigate other observables:
cos(theta) of jets
- Use jet-pairing hypothesis-dependently:
Pair jets regarding an event as signal (4b BG) and calculate observable.
- Heavier Higgs.
--> Write a paper.
- Improve b-tagging & jet-clustering.

3) ZHH Subgroup (Reported by T.Suehara)
- Observation:
b-tagging essential to BG reduction
current b-tagging scheme, which does b-tagging after jet clustering,
often mis-assign particles from a single b-hadron to different jets.
-> We should do the vertex finding before jet clustering.
- Developed new jet clustering along this line.
- Preparatory study with this new jet clustering
--> 30% improvement in ttbar BG reduction
Next step:
- Optimization of flavor tagging for multi-jets
- Realistic ZHH analysis with new algorithms


[B] New physics
1) LHT subgroup (Reported by E.Kato)
- So far AHZH, WHWH, ZHZH, and eHeH have been studied.
- Setup (MC Conditions):
Same as the previous LHT publication (f=580GeV, mH=134GeV, kappa=0.5)
- Coupling studies
eZheH coupling
ZHZH production:
--> delta M_ZH/M_ZH = 0.56%
--> g_R < O(10^-2), delta g_L/g_L = O(10^-3)
eHeH production:
e+e- -> eHeH followed by eH->ZH+e (eH=410GeV) with 500fb^-1
--> delta M_eH/M_eH =
--> delta sigma/sigma =
nHnH production:
e+e- -> nuHnuH followed by nuH -> WH+e (nuH=400GeV)
--> delta M_nH/M_nH = 0.1%
--> delta sigma/sigma <~ 1%
--> delta g_R < 0.07, delta g_L/g_L = O(10^-4)
- Summary
L/R couplings for eZHeH, eWHnH, WHZWH
Next Step:
- AHZH @ 1TeV -> eAHZH
- nu_muH nu_muH couplings
- LHT gauge couplings
Q: What about flavor mixing in T-odd sector?
C: Degenerate but with no mixing or 1 relatively light generation + 2 heavy.
C: Is LSP really stable? Maybe not like pi0 -> 2gammas in QCD, AH might decay
into boson pairs through anomaly. In that case, DM constraint disappears.

2) Very light gravitino (Reported by R.Katayama)
m_gravitino = <F>/Mpl/3^{1/2} with 1/<F> ~ 1/(Mpl m_{3/2})
-> directly connected to the SUSY breaking scale.
m_gravitino = O(1)-O(10)eV
-> interesting allowed region
ILC signal:
ctau ~ 100 microns
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.
- BG: tau+tau-, W+W-, Z0Z0, two-photon tau+tau-
- Look at impact parameter distributions for tau+tau- & mu+mu- BG.
Next step:
- Generate signal events
- More BG.
- Optimize event selection.
- Decide graviton mass precision.
C: Investigate the impact parameter tail for mu+mu- BG.

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

Discussions on future direction and mile stones
*) Prioritization
Higgs (ZH, ZHH, ttH) + Top (tt) -> consensus
BSM? -> strongly interacting light Higgs?
-> schedule review by Kikuta san for the next meeting.
*) 1 TeV analysis should wait until the MC data become available.
ttH -> Start with 500 GeV making good use of LOI BG sample.
ZHH -> Start with 500 GeV.
*) Minimum cost detector?
*) Ishikawa san (Tohoku) will serve as a co-convener of this WG.

Meeting Schedule:
*) ILC acc/phys Joint Summer Camp: Aug.8~11
*) LCWS2011 Meeting: September 26-30, Granada
Next general meeting (2011/09/03 10:30)

Working group web page:

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