20080906-e

Dear colleagues,

Since the 24th meeting on Jan. 28, 2012, the working group
had made significant progress, thanks to your contributions,
and we could successfully hold our 25th general meeting.

Thank you very much for those who participated in the meetings.
The following is a short summary of the 25th meeting.

if you find any mistakes or accidental omissions, please let us know.

The next general meeting will be on June 9, 2012.
--
Sincerely yours,

Working group contact persons
A.Ishikawa, Y.Okada, H,Ono, S.Kanemura, K.Fujii, T.Suehara
T.Tanabe, J.Tian, and R.Yonamine

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A Summary of The 25th General Meeting of the ILC Physics Subgroup
Apr. 14, 2012 (Sat) at Room 425, Building 3, KEK
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0) Attendants:
Present at KEK:
T.Tanabe (Tokyo)
T.Suehara (Tokyo)
R.Katayama (Tokyo)
H.Ono (NDU)
J.Tian (KEK)
C.Calancha (KEK)
R.Yonamine (Sokendai)
K.Fujii (KEK)
A.Ishikawa (Tohoku)
A.Yamamoto (Tohoku)
T.Tai (Osaka City)
S.Matsumoto (IPMU)
K.Tsumura (Nagoya)
Y.Kikuta (KEK)
T.Shindo (Kogakuin)
S.Kanemura (Toyama)
T.Nabeshima (Toyama)
Y.Okada (KEK)
M.Nojiri (KEK)
K.Uchida (KEK)
T.Yamada (Tokyo)
Y.Yamamoto (Tokyo)

Via video conf.
K.Kotera (Shinshu)

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Opening Comments
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[A] Higgs Related Topics
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1) ZH analysis: main decay modes (H.Ono)
Status:
- LHC
some hint of a light Higgs at Mh ~ 125GeV
- DBD physics chapter
- A list of topics to cover shown.
H -> bb, cc, gg: done --> publication by the end of Apr.
We need someone to work on H->tau+tau-.
- 1st attempt at H->WW* study (with one W*->lnu)
Requiring W*->lnu is a powerful cut to reduce BGs, but still
a lot of BGs. We may use R-handed e- beam to suppress WW, etc.
- 1st attempt at ZH->nnH followed by H->ZZ* (Z->4j)
Next Step:
- Publication of H->bb,cc,gg: soon
- Full simulation for different decay modes.
- nnH @ 1TeV

2) Theory: Strongly Interacting N Higgs Doublets (Y.Kikuta)
L_SILH = L_dim4(SM-like) + L_dim6(H/f, D_mu/Lambda)
NL Sigma Model
A general construction method developed for SU(2)xU(1) invariant dim6 Lagrangian
N=1 fundamental Re: 3, Im: 1
composite Re: 2, Im:0
N=N fundamental Re: (3/2)N^2(N^2+1), Im: (1/2)N^2(3N^2-1)
composite Re: (1/2)N^2(N^2+3), Im: (1/2)N^2(N^2-1)
Collider Study:
Feature:
sigma(VLVL->HH:N=2) ~ s/f^4
Discrimination of 2HDM from SILH with alpha-beta is possible.

3) VVH measurements (Junping Tian)
Status:
[I] nnH followed by H->bb
- Full simulation study using the LOI framework:
Signal: nnH (160fb @ 500GeV) --> very large!
BG: nnZ, ZH, WW, eeZ
- Event selection:
Evis, Pt, b-tag,
--> 175-sigma significance!!
- Expected measurement accuracy
delta (sigma*BR(H->bb)) / (sigma*BR(H->bb)) = 0.57%
--> delta sigma / sigma = 2.8% --> delta g_WWH / g_WWH = 1.4%
--> delta Gamma_H / Gamma_H = 5%
Adding all the data at 250fb^-1@250GeV and 500fb^-1@500GeV, corresponding to
a factor of 2.5 gain in statistics, we can achieve
--> delta g_ZZH / g_ZZH = 0.80% and delta g_WWH / g_WWH = 0.85%
[II] nnH followed by H->WW*
- Dominant BG: nnH followed by H->other modes
delta sigma(nnH)*BR(H->WW*) / (sigma(nnH)*BR(H->WW*)) ~ 3.0%
--> WTWT: 14.7%, WTWL: 57.0%, WLWL: 28.3%
Next Step:
- Response to change of potential shape (dim4+dim6 incl. derivative couplings)
--> Needs inputs from theorists.

4) Decoupling Properties of SUSY Higgs Sector (T.Shindo)
- Is it the SM Higgs or a SM-like Higgs in some extended Higgs sector?
mH=125GeV -> large mA and large tanb if SUSY
--> We need to know the decoupling properties of the heavy sector of the model.
If F-term contribution dominates, we can expect significant non-decoupling effects.
Even in the case w/o F-term, quasi non-decoupling effects on the MSSM sector may be
visible.
--> Investigate the effects of extra 2HD on the MSSM Higgs sector in 4HDSSM.
--> 20% effect on mH+, mh-mA relation.

5) ZH analysis: rare modes, H->AA, AZ (C.Calancha)
Status:
- Z->H->gamma gamma @ Ecm=250GeV
sigma*BR(H->AA) = 332fb * 0.3% = 0.9fb --> 249 ev
BR(Z->ee/mm) = 0.14% --> 116 ev
- Full simulation study (w/ LOI samples)
--> Now looking at leptons for lepton selection.
Next step:
- Concentrate on H->AA to produce some results for ACFA meeting.
- After ACFA, move on to H->ZA.

6) Multi-tau signature of leptophilic 2HDM (K.Tsumura)
- Motivation:
tiny nu mass, anomalous a_mu, e+ excess@PAMERA/FERMI
--> suggesting a scalar.
--> FCNC --> needs Z2 symmetry to forbid it.
- Model:
SM-like limit: sin(beta-alpha)=1
--> Type X model to realize leptophilic 2HDM.
--> enhancement of H->tau tau in the high tanb region.
--> no constraint from B-decay (suppression by 1/tanb)
--> Production of ZA --> tau+ tau- tau+ tau-
--> We can extract the H and A masses from higher end point of M_jj distribution
at LHC.
--> At ILC we can apply collinear approx. Then we can solve for tau momenta and
precisely (much better than at LHC) determine the masses.

7) TTH Subgroup (R.Yonamine)
Status:
- Moved on to full simulation for Ecm=500GeV, mh=120GeV, mt=175GeV
new feature: more realistic lepton ID, b-tagging.
- Preliminary results show no significant difference from the fast simulation results.
- Current problem:
There seems to be some inconsistency in the ttZ cross section estimates between the
fast simulation and the full simulation.
Next Step:
- Investigate the ttZ cross section problem.
- Currently we are using a simple cut-based analysis. We will try more sophisticated
likelihood analysis.

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[B] Other New Physics
------------------------------------
1) Seesaw model with a loop-induced Dirac mass term and DM from U(1)B-L
gauge symmetry breaking
- Motivation:
U(1)B-L gauge symmetry:
common origin to tiny neutrino masses, DM mass, and stability of DM.
- Physical states
h, H, S1, S2, eta+/-
- Signals:
LHC: Z'(1-10TeV)
ILC: l+missing
C: Comment on the recent theta_13 measurements should be made in one of the slides.

2) Very light gravitino with stay NLSP (R.Katayama)
Status:
- Stau mass reconstruction from end point.
--> delta m /m = 1.3 x 10^-2
(0.3 x 10^-2 from threshold scan)
- Life time fit
--> delta tau /tau = 2.1 x 10^-2 (revised)
- Gravitino mass from tau and m measurements:
--> delta m_\tilde{G}/m_\tilde{G} = 3 x 10^-2 (E_track fit)
--> delta m_\tilde{G}/m_\tilde{G} = 1 x 10^-2 (threshold scan)
Next Step:
- Include 3-prong decays of taus.
C: Refer to Shirai and Moroi for the plot on page 3.
Q: What are the spikes in the impact parameter plot?
A: Two-photon BG with weight > 1.
C: Either increase the statistics or address its effect on the fit result.

3) Search for Higgs Portal DM (A.Yamamoto)
Status:
- Signal and BG
Signal: e+e- --> ZH followed by H->DM DM
BG: ZZ, nnZ, WW, enW, eeZ
- Simulation conditions:
mH=120GeV, mDM=50GeV, J(DM)=1/2, CF=6.86, A=1000GeV
--> Signal cross section is about 15fb at Ecm=250GeV.
- Event selection:
isolated lepton cut, forward e+/- veto, mZ cut, cos(Z), cos(qq), cos(q_in Z rest frame)
Next Step:
- Derive upper limit on the signal cross section.
- Scan model parameter space.
- Study at Ecm=500GeV
Q: Have you check the implication of the 125GeV Higgs candidate at the LHC?
The observation should put the upper limit on the invisible width of H.
C: Fermion DM with (B-L)gauge charge may be interesting since it naturally explains its
stability.
C: Use HH\bar{\chi}\gamma_5\chi (which vanishes at beta=0) instead of HH\bar{\chi}\chi,
which is severely constrained by direct searches.

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The slides shown at the meeting is available from
http://ilcphys.kek.jp/meeting/physics/
see them for details.
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Discussions on future direction and mile stones
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*) Higgs Physics at the ILC
Introduction by T.Tanabe
C: mA-RWW/tautau plot should be updated.
--> Depends on other measurements like Bs->mu+mu-.
--> One needs to use the most updated formulas available in the market.
Plan:
- Prepare 1st draft of DBD physics chapter by June 15, 2012 so as to feed back the results
to European strategy making.

Meeting Schedule:
*) ACFA2012 Meeting: April 23-26, Degu.
*) LCWS2012 Meeting: Oct 22-26, Arlington, Texas.
Next general meeting (2012/06/09 10:30) : Conf.ID: 551

Working group web page:
http://www-jlc.kek.jp/subg/physics/ilcphys/

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