A Summary of The 20th General Meeting of the ILC Physics Subgroup
May 14(Sat) at Room 425, Building 3, KEK
0) Present:
S.Shirai (Sokendai)
Y.Okada (KEK)
T.Tanabe (Tokyo)
Y.Yamamoto (Sokendai)
S.Kikuta (Sokendai)
T.Yamada (Sokendai)
K.Harigaya (IPMU)
K.Yagyu (Toyama)
S.Kanemura (Toyama)
A.Ishikawa (Tohoku)
M.Asano (Tokyo)
E.Kato (Tohoku)
S.Kawada (Hiroshima)
S.Matsumoto (IPMU)
H.Ono (NDU)
R.Yonamine (Sokendai)
F.Uchiyama (KEK)
T.Suehara (Tokyo)
R.Katayama (Tokyo)
P.Posch (Sokendai)
D.Harada (KEK)
K.Fujii (KEK)

Opening Comments

New Topics
[*] CDF Dijet Mass Anomaly (Reported by Satoshi Shirai)
- A di-jet peak at around 150GeV: 3.2-sigma
-> O(1)pb
-> naive SM Higgs: inconsistent: x-section too small
-> no resonance production: Phi -> phi + W
- Z', gz'jj=O(0.1), gz'll~0 -> severe cancellation in rho-parameter
- SM: kinematical reflection from single top production
-> a few 10% discrepancy accountable by ambiguity in acceptance?
R-parity conserving -> no peak -> scalar top version of the SM single top case above.
R-parity violating
large -> resonance peak
small -> scalar tau LSP
-> stau -> lnu & qqbar due to R-parity violation
Small R-parity violation scenario:
- wino ~ stau ~ 140GeV
-> wino pair production -> (lnu nu) (qqbar nu)
- Tests
-> High Elepton, same sign lepton, ...
-> easy to test.

[*] Very light gravitino (Reported by Shigeki Matsumoto)
m_gravitino = <F>/Mpl/3^{1/2} with 1/<F> ~ 1/(Mplm_{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.
Next step:
- More realistic simulations

Reports from Subgroups
[A] New physics
1) HW subgroup
1-1) Theory (Reported by K.Yagyu)
- HWZ vertex: very exotic
In general from loop:
- Signal at ILC: e+e- -> H-W+
W -> 2jets -> recoil mass measurement
H -> lnu
- Results
- |F|^2>10^{-3} can be excluded a 95%CL
Next step
- model dependent analysis
triplet H (type II seesaw)

2) LHT subgroup
2-1) Theory (Reported by K.Harigaya)
- General characteristics
existence of top partner
existence of gauge boson partner
* definite relation between parameters
- How to test the relation
3 parameters: mT, sin\thetaL, Br(T->th)/Br(T->bW)
--> can be determined at LHC by measuring mT, Br(th), Br(bW)
lambda' = lambda'_cr x a: a=1 <-> LHT relation holds
Usable processes: tTh, TTh, tT threshold, TT threshold
Expected deviations for a=3, -1 from a=1
- tTh associate production: 10% ~ 0.1fb
- TTh: 1fb
- tT threshold: 10% ~ 6fb
- TT threshold: 30% ~ a few 100fb

2-2) Experiment (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)
- eHeH:
e+e- -> eHeH followed by eH->ZH+e (eH=410GeV) with 500fb^-1
- Mass from Endpoints:
--> eH mass = 412.8+/-1.7GeV, ZH mass=371.2+/-1.5GeV
- Parameter fit
--> f=579.6+/-3.0GeV, kappa=0.5+/-4x10^-4
- nuHnuH: new
e+e- -> nuHnuH followed by nuH -> WH+e (nuH=400GeV)
- Mass from Endpoints:
--> nuH mass = 400.8+/-0.4GeV, WH mass: 369.6+/-0.4GeV
- Parameter fit
--> f=582.0+/-0.6GeV, kappa=0.5+/-1x10^-4
- Summary:
- masses can be determined to 1% or better.
-> high precision determination of model parameters possible.
Next Step:
- Polarization dependent cross section measurements
-> extraction of couplings.

[B] 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:
delta BR(cc)/BR(bb): 9.3% (250GeV) -> 6.4% (350GeV)
--> Almost final values.
--> 350GeV measurements are better than that of 250GeV.
Next Step:
- Summarize the results for publication
- DBD analysis: nunuH@1TeV

2) TTH Subgroup (Reported by T.Tanabe)
- Setup:
- Signal(tth): 0.45fb w/NRQCD correction (no beam pol.)
- BG: ttg(g->bb), ttZ(Z->bb), tt(reducible but large)
- NRQCD correction to ttH, ttZ
- QuickSim
- Analysis:
Solved problem with numerical integration for the btw generator
Optimized selection cuts
Final results:
--> With 1ab^-1
ttH(l+6j): significance 3.7
ttH(8j): significance 3.7
for (-0.8,+0.3) polarization.
--> combined significance 5.2 -> delta gt/gt = 9.6%
--> combined significance 4.0 -> delta gt/gt = 12% for no beam polarization
--> submitted to P.R.D. (arXiv:hep-ph:1104.5132)
Nest Step:
- Move on to full simulation.
- tth @ 1TeV as part of the DBD benchmark studies.

3) AA->HH Group
3-1) Experiment (Reported by Kawada)
- bbbb 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)
- Trying to find effective cut variables:
--> Mcut (bbbar:gamma*), costh_q, E_bbar, costh_bbar, …
--> Looking at the distributions of these variables
--> bbbar pair mass peaks at the threshold and very forward peaked
--> For instance if we require, at the BASES levee,
LowINV (lowest bb inv. mass) < 90GeV or LowP (remaining pair) > 150GeV
|costheta|<0.99 then 4bBG cross section becomes 5.8ab.
Next step:
- detector simulation and optimization of cuts.
- Heavier Higgs.
--> Write a paper.
- Improve b-tagging & jet-clustering.

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

Discussions on future direction and mile stones
*) DBD Studies
Physics chapter will include precision Higgs physics:
- If mh>140GeV, the LHC will see it soon. In that case we should redo the
analysis. If mh<140GeV, there will be no qualitative difference from the mh=120GeV
case. We only need to regenerate the signal sample for the measured mh; we can
use the same BG samples generated at Ecm=500GeV, since the sensitivity for the
self-coupling, for instance, does not depend on mh so much.
Detector concept chapters will include the new benchmarks.
Ono san will be responsible for nnH, Yonamine san and Tanabe
san will be responsible for ttH.
*) Possible new projects
- Flavor violating SUSY: s-charm stop mixing, slepton…
s-charm pair -> charm+LSP + top+LSP
- Light gravitinos
*) ILC acc/phys Joint Summer Camp: Aug.8~11 (tentative schedule)
*) LCWS2011 Meeting: September 26-30, Granada

Meeting Schedule:
Next general meeting (2011/07/16 10:30)

Working group web page:

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