A Summary of The 24th General Meeting of the ILC Physics Subgroup
Jan. 28, 2012 (Sat) at Room 425, Building 3, KEK
0) Attendants:
T.Tanabe (Tokyo)
T.Suehara (Tokyo)
R.Katayama (Tokyo)
H.Ono (NDU)
S.Kawada (Hiroshima)
J.Tian (KEK)
C.Calancha (KEK)
R.Yonamine (Sokendai)
K.Fujii (KEK)
A.Ishikawa (Tohoku)
T.Tai (Kinki)

Opening Comments
[A] Symmetry breaking & mass generation

1) ZH subgroup
1-1) ZH and nnH analyses (Reported by H.Ono)
  ATLAS: 115.5 < Mh < 131 GeV
  CMS: 115 < Mh < 127 GeV
some hint of a light Higgs at Mh ~ 125GeV
- DBD benchmark process:
- nnH BR studies at 1TeV
- 1TeV beam parameters have just been fixed and event generation will start soon. Some test samples available already for checking out.
- Software setup will also be fixed soon.
- sigma*BR for H->mumu, bb, cc, WW*, gg
- New activities:
- H->AA, ZA by Constantino.
- H->WW*, ZZ* (currently nn+4j only)
- Current status of H->WW* studies @ Ecm=250GeV
- signal significance = 7.7(15.6) for Mh=120(130)GeV
- Current status of expected relative BR accuracies:
   H->bb 3.8%
    ->cc 8.3%
    ->gg 10.6%
    ->WW* 13.4% (nnH and 4j only)
    ->ZZ* just started
Next Step:
- Publication: 1st draft
- Full simulation for different decay modes, masses
- nnH @ 1TeV
- Include W(*)->lnu
Q: Who is going to do H->mu mu and tau tau?
A: H->mu mu by Constantino, H->tau tau ?
C: We need to find someone to do H->tau tau.

1-2) e+e- -> ZH followed by H->AA analysis (Reported by C.Calancha)
- Z->l+l-, H->gamma gamma @ Ecm=250GeV
  sigma*BR(H->AA) = 354.3fb * 0.2% = 0.7fb
- Looking at generator level distributions.
Next step:
- full simulation data
- Get used to Whizard tools
C: Maybe you should investigate the possibility of using decay modes other than Z -> l+l-.

2) ZHH subgroup (Reported by J.Tian)
2-1) ZHH @ 500GeV
- Possible places for the future improvements
  jet clustering, b-tagging, jet paring, lepton ID
- Studies using cheated jet clustering
  --> In order to estimate the limit we can achieve, developed cheaters
    --> delta sigma/sigma = 20% (32%)
       delta lambda/lambda = 36% (57%)
  where the numbers in () are for real jet clustering.
- Started investigating the mini-jet clustering idea:
What we really need is not a good jet clustering but a good color-singlet clustering.
- Mjj resolution degrades rapidly when the number of mini-jets becomes less than 15 or so.
- How to re-cluster mini-jets?
- discriminant: chi2 = sum pt^2
- suppression factor: e^{-(Nb-1)(Nb-2)}
Next Step:
- Possible improvements:
- isolated lepton ID. -> lepton jets (including radiation)
- flavor tagging: LCFI+
- mini-jet clustering
- leptons inside jets -> recovering missing neutrinos?
C: Look at the chi2 for wrong combinations and compare the results.
A: OK. There are two problems. One is to how to find the correct planes and the second is whether we can correctly do color-singlet clustering once the correct planes are found. We are now investigating the 2nd question.

3) TTH Subgroup (Reported by R.Yonamine)
- Moved on to full simulation for Ecm=500GeV, mh=120GeV, mt=175GeV
- ttH, ttg* MC samples: produced.
  ttZ: not yet because of a geant4 problem (maybe inconsistent geometry?)
   -> being investigated.
- Preparation of analysis code: almost finished, now looking at various distributions to optimize the event selection.
C: Compare the invariant mass resolutions with those of the fast simulations.
Next Step:
- ttZ data production.
- Further improvements of event selection.
- Try cheated jet clustering.
- Comparison with the fast simulation results.
- 1TeV analysis.

[B] New physics
1) Very light gravitino (Reported by R.Katayama)
- Motivation:
- Gauge hierarchy.
- B-L conserving shereron process + lepton number generation heavy nu_R decay --> thermal leptogenesis
  --> High reheating temperature required.
  Q: What about dark matter? Gravitino mass seems too light for it.
  C: We need some other particles outside the GMSB framework.
  m_\tilde{G} = <F>/Mpl/3^{1/2} with 1/<F> ~ 1/(Mpl m_{3/2})
     -> directly connected to the SUSY breaking scale.
  m_\tilde{G} = O(1)-O(10)eV
     -> interesting allowed region   (hep-ph/9503210)
ILC signal:
  ctau ~ 100 microns (m_LSP=6.5eV, m_NLSP=120GeV)
         (tau ~ 48pi M_pl^2 m_\tilde{G}^2 / m_stau^5)
  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, Bhabha, two-photon tau+tau-, mu+mu-, e+e-.
- Event selection using full sim. samples
  --> Look at impact parameter distributions for tau+tau- & mu+mu- BG.
  --> Cuts on 2-prong, Evis, Pt, acoplanarity, angle/Evis: essential to suppress AA->tau+tau-, d0/sigma(d0), lepton veto.
  --> AA->tau+tau- :suppressed from O(10^9) to 0.
- Stau mass reconstruction from end point.
  --> delta m /m = 1.1 x 10^-2
Q: Effect of non-Gaussian Ebeam spread?
- Life time fit
  --> delta tau /tau = 2.1 x 10^-2 (revised)
- Investigated the possibility of using neutral clusters to improve statistics near the end point. Found a higher tail possibly coming from mis-clustering in PFA.
  --> Confirmed that there is indeed mis-clustering. --> Future improvement.
- Gravitino mass from tau and m measurements:
  --> delta m_\tilde{G}/m_\tilde{G} = 3 x 10^-2
Next Step:
- Further investigation of the possibility of using neutral clusters.
C: Use e+/e- veto to suppress two-photon BGs.

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

Discussions on future direction and mile stones
*) Higgs Physics at the ILC
Introduction by T.Tanabe
C: mA-RWW/tautau plot should be updated. The asymptotic value seems to be consistent with the mH=120GeV SM case.
- Create 10-page slides, which can be used to explain the ILC physics case to scientists.

*) Junping Tian joined the group of physics WG conveners.

Meeting Schedule:
*) ACFA2012 Meeting: April 23-26, Degu.
*) LCWS2012 Meeting: Oct 22-26, Arlington, Texas.
Next general meeting (2012/04/14 10:30) : Conf.ID: 628

Working group web page:

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