A Summary of The 28th General Meeting of the ILC Physics Subgroup
Oct. 13, 2012 (Sat) at Room 425, Building 3, KEK
0) Attendants:
Present at KEK:
T.Horiguchi (Tohoku)
A.Ishikawa (Tohoku)
A.Yamamoto (Tohoku)
A.Dubey (Tohoku)
J.Tian (KEK)
C.Calancha (KEK)
R.Yonamine (Sokendai)
M.Nojiri (KEK)
K.Fujii (KEK)
T.Tanabe (Tokyo)
T.Suehara (Tokyo)
T.Yamada (Tokyo)
S.Kanemura (Toyama)
H.Sugiyama (Toyama)
K.Tsumura (Nagoya)
S.Kawada (Hiroshima)
D.Harada (IIS)

Via video conf.
H.Ono (NDU)

Opening Comments
1) nnHH (Junping Tian)
Status: (Analysis using SGV sample)
- New BG: nnZH and ttH
Created a new nnZH generator with ISR from Whizard and DBD beamshtrahlung.
Used the ttH generator for DBD by Miyamoto-san.
- Results
--> S=35.6, BG=27.6 (nnZH dominates)
--> delta sigma / sigma = 22% --> delta lambda / lambda = 19% (w/o weighting)
or 17%? (w/ weighting) with 2ab^-1 @ 1TeV
- Full simulation sample generation for ZHH @ 500 GeV:
--> ~10M done, ~15M more to generate.
--> reconstruction on going.
--> use ILC-DIRAC to boost the generation (thanks to S.Poss).
Next Step:
- Produce preliminary results by LCWS12.
- Update Higgs mass: mh=120 -> 125GeV
- Full simulation of ZHH and nnHH.

2) ZH analysis: H->tau+tau- (S.Kawada)
- Z->H->tau+tau- @ Ecm=250GeV 250fb^-1, P(e+,e-)=(+0.3,-0.8) (mh=120GeV)
- Full simulation study (w/ LOI samples)
1st step: (Z->ll)
lepton ID: Eecal/Etotal, E/p
Separation of leptons from Z and leptons from H: impact parameters, Elepton
FSR/bremsstrahlung recovery
2nd step: (H->tau tau)
tau mass
--> rerusts:
delta (sigma x BR) / (sigma x BR) = 8.85% (w/o requiring isolation for leptons)
Next step:
- Include full SM BG. (currently 4 leptons only) --> expected to be negligible.
- Include Z->qq --> probably a factor of 2 improvement?
- Results by LCWS12
C: What about using collinear approximation for taus from H and reconstructing H mass?

3) Radiative Type-I Seesaw Model with DM (H.Sugiyama)
- The Model
Majorana mass
1/2 m e^{-i phi) \bar(\nu_L^C} \ + .c
Vector-like mass for \nu_R
m_\nu \simeq y^2 <\phi^0>^2/M_R ~ 0.1eV = 10^-10 GeV
--> y small or M_R large
but we want coupling reasonably large and M_R small to make nu_R relevant to
collider physics.
--> M_R ~ 10^3 GeV with y generated radiatively so that y small ~ 10^-6.
--> Introduce U(1)_{B-L}
Fermion (i=1,2): nu_Ri, Psi_Li, Psi_Ri
Boson: eta, s^0 (w/o vev), sigma^0 (w/ vev)
with fractional (half integers) U(1)_{B-L} charges to Psi_Li, Psi_Ri, eta, and s^0
integer or 1/3 to SM particles.
--> Unbroken global U(1)_{DM} due to fractional charges:
U(1)_{B-L} (gauged) x U(1)_{DM}
--> The lightest becomes DM.
--> h0, H0 as physical higgs
--> <sigma> ~ 10TeV, Psi1 (DM) ~ mh/2
- Phenomenology
LHC: Z' (2TeV) : 70fb @ 14TeV
-> nu_R \bar{nu_R} : BF(Z' -> nu_R \bar{nu_R}) ?
followed by nu_R -> W^\pm l^\mp --> O(1) fb
Q: What about nu_R -> Z nu_L or h nu_L?
ILC: e^+e^- --> Psi2 \bar{Psi1}(DM) followed by Psi2 --> nu_R S1^0
and nu_R -> W^\pm l^\mp and S1^0 -> nu_L Psi1 (DM)
-> ~ 0.1fb
e^+e^- --> e^+ mu^- DM DM
-> ~ 1fb
Q: What about mu -> e gamma?

4) nnH @ 1TeV analysis (H.Ono)
- ZH: BR studies (bb, cc, gg)
- arXiv:1207.0300v1 --> submitted to EPJ
- Input to DBD physics chapter:
- Update mh to 125GeV.
- Use LHC HDECAY-based BRs instead of Pythia-based ones.
- Extrapolation from 120GeV to 125GeV: (250fb^-1@250GeV)
delta (sigmaxBR)/(sigmaxBR)
1.0% -> 1.1 (bb)
7.6% -> 8.5 (cc)
6.7% -> 7.2 (gg)
8.4% -> 7.2 (WW)
- nnH @ 1TeV
- mh=125GeV
BR bb: 57.8
cc: 2.7
gg: 8.6
WW*: 21.6
mm: 0.02
- Pol=(+/-0.8,-+0.2)
- two-photon hadron BG
--> mh distribution significantly affected by the BG.
--> Used kt instead of Durham for jet clustering.
--> R=1.0~1.3 looks suitable.
--> mh distribution improved but needs more tuning.
- Reconstruction finalized. Mass reconstruction process on going.
Next Step:
- 1TeV analysis for LCWS12 (priority).
C: Try 6jet clustering and then remove forward going two.
- Publication of H->bb,cc,gg: very soon.

5) Measurements of tan(beta) in 2HDMs (K.Tsumura)
- Introduction:
Softly Z2 broken 2HDM --> 5 degrees of freedom left
* m^2_H,A,H+/- ~ M^2 + lambda v^2/2
* sin(beta-alpha) <-> VVH
* tan(beta) = v2/v1
- LHC data suggests sin(beta-alpha) ~ 1?
- FCNC -> 4 types if extra Z2 parity is imposed.
- Type-II
- LHC's H search
production: bbH followed by H->tau tau
-> small mA large tan(beta) region has been excluded.
Gamma_H,A propto tan^2(beta) -> not useful considering LHC limit
--> Not very much room left for ILC.
sigma(HA) propto tan^2(beta) -> not useful considering LHC limit
BR(H/A->bb) loses sensitivity to tan(beta) if tan(beta)>>1 since (H->bb becomes almost 100%)
- BR(h->bb): there is some region where we can determine tan(beta) rather precisely.
C: sing(beta-alpha) measurement and BR measurement are not statistically independent.
Q: What about a very light mH?
A: Maybe possible.


6) Higgs Portal (A.Yamamoto)
- Setup:
DM couples only to Higgs.
Signal: e^+e^- -> ZH -> q qbar DM DM
BG: eeZ, enW, nnZ, WW, ZZ
1^-1ab @ 250GeV, pol=(0.8,-0.3)
- Event Selection:
- Forward veto to eliminate eeZ, enW.
- Z mass cut
- Likelihood analysis: Zmass, cos(thetaZ), cos(theta_qq)
- Results
95% CL upper limit on BR(invisible)=3.4x10^{-3}
Next Step:
- Try analysis with H->ZZ*->4nu.
- Update the Higgs mass: mh=120 -> 125GeV
- Try different DM mass.
- e^+e^- -> ZH* -> Z DM DM -> q qbar DM DM (2 m_DM > mH)
with gamma_5 insertion to the DM DM HH vertex.

7) Strongly Coupled Higgs Sector in SUSY Models (T.Yamada)
- Introduction
mh=126GeV --> Naively this suggests the Higgs sector being weakly interacting.
Is there still room for strong coupling possibility?
- mu-term from strong dynamics. --> can explain why mu is not O(Mpl).
- strong 1st order EW phase transition possible.
- Landau pole at around 10TeV.
- UV completion: SUSY SU(2) gauge theory.
- UV Theory
SUSY SU(2)_H gauge theory with 6 doublets = 3 pairs of doublets w/ a new Z_2 parity
g_H (QCD-like) blows up at Lambda_H --> Below Lambda_H --> pion theory like
--> Can estimate lambda(Mz) which is about 2.
--> Hu, Hd, Phi_u, Phi_d: SU(2) doublet
N, N_Phi, N_Omega: SU(2) single
zeta, eta : SU(2) singlet
Omega^+/- : SU(2) singlet (2 charged singlets)
- Phenomenology
Under studies.
--> BR(h->gamma gamma), BR(h->gamma Z)
--> hhh coupling should significantly deviate from the SM value.
--> only way to see the effect of SU(2)_H
--> can modify BR(h->gamma gamma), m_H+^2 - m_A^2.
--> strongly 1st order EW phase transition possible.

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

Discussions on future direction and mile stones
*) Meeting Schedule:
LCWS2012 Meeting: Oct 22-26, Arlington, Texas.
HPNP213: Feb 13-16, Toyama.
Next general meeting (2013/01/12 10:30) : Conf.ID: 971
*) Talks to be submitted to LCWS2012
Higgs BR (main mode, …): Ono
Higgs BR (rare mode: AA, mumu): Tino
Higgs BR (tau tau): Kawada
Self-coupling: Junping
TTH: Tony
K.Tsumura: tan(beta)
T.Nabeshima: Higgs inflation and ILC
K.Yagyu: Triplet Higgs and ILC
M.Kakisaki: ILC and GUT with Hosotani mech.
M.Aoki: ILC and Majorana nu in radiative seesaw
T.Shindou: Extended SUSY, EW-baryogenesis, and ILC
T.Yamada: Strongly coupled SUSY and ILC
H.Sugiyama: Radiative seesaw with spontaneous breaking of (B-L)-gauge symmetry and ILC
Y.Kikuta: Composite Higgs and ILC?

Working group web page:

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