2nd General Meeting of the ILC Physics Subgroup
Time: Sep. 8(Sat), 2007
Place: KEK (Room 425, Building 3)
Number of participants: 22
through video conference system
1) Introduction (Y.Okada+K.Fujii)
- Working group charge
- Discussions and decisions made at the last meeting
--> subgroup formation and subgroup activities
- adgenda of this meeting
- subgroup reports
- discussions on future direction and mile stones
2) Reports from subgroups
2-1) ZHH subgroup (Y.Takubo)
Generator preparations for the signal process: e+ e- -> Z WW WW.
- Yoshioka prepared an event generator besed on Grace with Yasui's help. Combined with Pythia,
10 jet final states have successfully been generated.
Q: What do you mean by "angular distribution of W from H is not taken into accout"?
A: W->ffbar distribution is not properly taken into account when decayed by Pythia.
In that sense, we had better stop at ZHH and let Pythia decay H to WW.
- Takubo is working on cross section calculation with Madgraph. the Madgraph result seems much
too large, two-orders of magnitude off the expectation from the calculation for e+e- -> ZHH.
C: Beign 5-body final-sates, the off-resonant diagram cannot explain the difference.
The cross section should be O(0.1) fb.
C: There seems to be some problem with the scale/unit or branching fraction.
C: It might be due to a wrong Higgs width value used in the propagator denominator.
- Daniel is investigating literatures about the past studies on the top Yukawa measurements and
other existing generators in the market such as Wizard which used internally Comphep and/or
- Takubo/Yoshioka/Daniel will check on the Higgs width used in the propagator and make sure
that the crosection for ZWWWW is consistent with that expected from ZHH with various
generators (Grase-based/Madgraph/Wizard/...) in the market.
- An e+e- -> ZHH generator with H decay handled by Pythia.
2-2) TTH subgroup (A.Ishikawa)
- Investigations on BG processes and analysis methods are on going.
--> Since cross section is expected to be low at around 500 GeV, we had better use some
inclusive analysis method.
- Ishikawa has been working on signal generator, implemented QCD threshhold correcton to the
ttbar subsystem with Sumino's theoretical assistance. It turned out that to the lowest order
it just suffices to import the S-wave Green function with QCD threshold correction from
the the e+e- -> ttbar generator.
The resultant cross section and Eh spectral shape differ from hep-ph/0512246.
Q: Is the QCD correction used in the reference the same as ours?
A: It should be essentailly the same. The Born results should agree anyway.
Q: Are the ISR and beamstrahlung included in their results?
A: Yes. But for the Eh figure I don't know.
Q: what kind of top mass is used for the calculation?
A: 180 GeV. In the 1S-scheme.
C: Then it should be something like 190 GeV in the pole-mass scheme.
C: If you look at the shoulder position of the Eh distribution, their result falls off at lower Eh,
which is consistent with the higher mt.
C: The peak in their Eh distribution seems much too sharp. It looks like they didn't include
the ISR and beamstrahlung in the calculation. Try switching off ISR and beamstrahlung
and see what happens.
Q: Is it necessary to consider threshold QCD correction to the e+e- -> ttZ BG?
A: It depends on the size of the Born cross section. If it is negligible we don't have to.
C: It is merginal.
C: The correction differs diagram by diagram. It also depends on whether it is
vector or axial vector couplings.
- Uozumi is working on BG generators.
- Change the top mass, switch off the ISR/beamstrahlung effect, and compare the result
again with hep-ph/0512246.
--> Later in the meeting Ishikawa confirmed that with mt=185 GeV and without the ISR
and beamstrahlung, the result became consistent wth the reference.
- BG estimation and preparation for relevant BG processes.
- Sumino will check on how to implement the threshold QCD correction to ttZ.
- Start preparation of analysis code.
2-3) ZH subgroup (H.Ono)
- The GLD full simulation study for the e+e- -> ZH process with Cheated and Real Particle
Flow Algorithm. The higgs mass resolution in the mH=120 GeV case is about 3.3 GeV
with CPFA and 5.1 GeV in RPFA. The Higgs mass distribution has a lower tail due to
neutrinos from b decays.
- Started analysis for mH=160GeV with CPFA. With the neutrinos from W decay artificially
added to the final states using breakpoints (=MC truth), we can see a clear H mass peak.
- Further analysis using breakpoints.
- RPFA for mH=160 GeV.
- BG studies for the higher mass Higgs.
2-4) Hidden sector subgroup (H.Itoh)
- Analyses for e+e- -> Z X or gamma X followed by X -> gamma gamma or glue glue
Q: S(ZX)/B(ZH) ratio doesn't seem to improve with the cuts. Why do you apply the cuts?
A: The ZH is not a BG. It is also a signal. If the hidden sector scenario is correct we would
have both H and X with probably different masses. To separete them from other standard
model BG like e+e- -> Z gamma + (gamma), we need to apply cuts anyway.
The purpose of the analysis is to study, when we see some scalar-like particle that decays
into 2 photons, how can we tell what it is. In the case of X, the associated Z is transverse
and the production angle distribution differs from the ZH case which is dominated by
longitudinal Z. Whether Z is transverse or longitudinal can also be studied by observing
the Z decay angle distribution in the Z helicity frame.
Q: What is H-> AA?
A: Higgs decays into very light pseudo scaler Higgses that subsequently decay into two
photons. When the detector resolution is not enough these two photons would be misidentified
as a single photon.
Q: What about productions at hadron colliders?
A: X can be produced through couplings to glue glue.
C: In the beginning we have overlooked the hadron collider constraint. We need to reduce
the coupling to glue glue to avoid the Tevatron bound but there is still some parameter
space left. Anyway we are now trying to reformulate the analysis so as to be more generic.
We want to show a strategy to model-independently study a generic scalar particle to tell
what it is. The hidden sector scenario is one example. We can use the production angle of
the scalar, the decay angle of the associated Z, the branching fraction.
If we see an X mass peak for the gamma gamma or jet jet subsystem in the e+e- -> 3 gammas
or gamma + 2 jets, we can definitely say that it is not Higgs.
C: It is important to study generic situation. One can measure absolute cross section for
the recoil mass against the gamma. We had better consider generic situation with effective
- More on generic strategy.
- Reanalysis with the hadron collider constraints.
2-5) Little Higgs with T-Parity (S.Matsumoto)
- Theoretical studies by S.Matsumoto, M.Asano, and E.Asakawa.
- General introduction to the model. A note by S.Matsumoto and M.Asano is available.
- Selection of sample points in the parameter space (mh, f, lambda_2) being consistent with
the WMAP and the LEP constraints.
- Selection of processes of interest at the ILC (Ecm < 1 TeV):
e+e- -> W_H W_H, A_H Z_H, Z_H Z_H, t T_+bar
--> only A_H Z_H is availabe at 500 GeV.
anomalous coupling studies would be interesting.
Q: What about FCNC constraints?
A: Good point. The T-odd sector has a different mixing matrix. But it is OK as long as we impose
T-parity, since then FCNC appears only through 1-loop.
Q: What about FCNC in the top sector?
C: htt anomaly is very large!
C: It is interesting since it is essential for the canncellation at the heart of the model.
C: Anomalies in Wtb and Ztt is also interesting. They might be experimentally accessible.
C: The deviation is coming mostly from the mixing and it becoms smaller for higher
lambda_2. In the case of htt, there is the coupling enhancement that compensates
the decrease of the mixing.
- Trying to write a model file for Madgraph.
- Studies on some other models like gravitino LSP scenarios are also on going.
- Model file preparation for Madgraph/Grace
- Formation of a subgroup including experimentalists to carry out MC simulations.
--> Senior people should try to recruit younger people.
2-6) Comment on Linear Polarization at the gamma gamma collider
- Luminosity spectrum, analyzing power as a function of laser/e-beam energies.
--> For higher analyzing power, we need lower x, necessitating higher e-beam
energy to get one's desired gamma energy.
--> can be used to study CP properties of H through its s-channel production.
- There is a meeting (LEI2007) on Dec.12-14 in Hiroshima.
The slides shown at the meeting is available from
see them for details.
3) Discussions on future direction and mile stones
C: We should set some mile stones. We have an ACFA meeting in March in Sendai.
C: We have a annual meeting on Dec.4-6 at KEK. There will be a physics session.
The ZHH/TTH/ZH/HS subgroups should show some simulation results there.
We will have lectures by M.Peskin attached to the meeting.
C: If you need a new event generator, please contact Minamitateya group.
C: We need to start a new subgroup for LHT studies. Senior people should try to recruit
younger people. Of course anybody in this room can volunteer.
C: We want to hear report from the gamma gamma -> HH subgroup next time.
4) Next Meeting
13:30, November 10 (Sat) at KEK, Conference ID (31425)Working group contact persons:
A.Ishikawa, S.Uozumi, Y.Okada, H,Ono, S.Kanemura, Y.Takubo, K.Fujii, T.Yoshioka
Working group web page:
Slides are available from http://ilcphys.kek.jp/meeting/physics/