8th General Meeting of the ILC Physics Subgroup Meeting

A Summary of The 8th General Meeting of the ILC Physics Subgroup
Jan. 21 (Thu) at Room 425, Building 3, KEK
0) Attendants:
Y.Okada (KEK)
H.Ono (NDU)
K.Itoh (Tohoku)
R.Sasaki (Tohoku)
K.Yoshida (Tohoku)
M.Asano (ICRR)
D.Harada (Sokendai)
R.Yonamine (Sokendai)
N.Maeda (Hiroshima)
K.Ikematsu (KEK)
T.Takahashi (Hiroshima)
N.Okada (KEK)
T.Suehara (ICEPP)
H.Itoh (KEK)
S.Kanemura (Toyama)
S.Matsumoto (Toyama)
H.Yamamoto (Tohoku)
Y.Takubo (Tohoku)
Y.Matumoto (KEK)
A.Sugiyama (Saga)
T.Fusayasu (NIAS)
K.Fujii (KEK)

Reports from Subgroups
1) ZHH (Reported by Y.Takubo)
HHnunu : 40 ab
HHqq : 135 ab
- Main difference from the previous report:
--> Updated simulation code to the latest.
1-1) HHnunu
- Event selection
chi2 cut
Mass cut
Missing E
lepton veto
4-b requirement
lepton veto
- Status of S/B
6.5(ZHH) + 5.4(ZZ) + 65.9(tt) +2.9(tbtb) + 0(ZH)
1-2) HHqq
- Event selection
chi2 cut
Mass cut (Mh & Mz)
Angular cut
Missing Pt
6-b requirement
- Status of S/B
3.8(ZHH) + 0(tt) +0.5(tbtb) -> observation seems possible
Q: S=3.8 is not 3-sigmas?
A: Signal is significant. will improve with optimization of cuts.
C: 6-b requirement seems too tight.
Q: Is 2ab^ commonly accepted?
A: It seems
- There is no one working on the Mh > 2xMw case.
Next Step:
- Optimize cuts for HHqq
- HHnunu will be left untouched for a while.
*) Tsinghua group started looking at WW* mode.

2) ZH subgroup
2-1) ZH (Reported by H.Ono)
- Full detector simulation, continue with Ecm=250GeV case
Analysis with
*) nunuH (2j)
sigma_Mz : PandoraPFA ~ CPFA
Kin fit
2.07 GeV (CPFA) 2.5 GeV (PandoraPFA)
*) qqH (4j)
sigma_Mz PandoraPFA >~ CPFA
Kin fit :
1.98 GeV (CPFA) 2.7 GeV (PandoraPFA)
Q: What are the free parameters of the fit?
A: Will check and report them.
Next step:
- Physics implication of various observables
- Improve fitting function (lineshape)

2-2) nunuH for ILD LoI (Reported by K.Yoshida)
- Flavor-tag study
Ecm=250 GeV, Mh=120 GeV, 250 fb^
Cross section x BR measurements
H->bb : 19.7 +/- 0.35 fb
H->cc (c-tag): 1.039+/-0.045
H->cc (bc-tag): 1.048+/-0.022
Q: What are the expected numbers for these?
A: Will check on them.
Q: What is bc-tag?
A: c-tag assuming b-BG.
C: Performance may depend on the training sample.
Next Step:
- Include all SM BG

2-2) llH for ILD LoI (Reported by K.Itoh)
- Recoil mass study
- Fully left-handed e- + fully right-handed e+
mu: 0.061 GeV
e: 0.13 GeV
Cross section
mu: 18.6+/- 1.2 fb (6.5%)
e: 16.8+/-0.82 (4.9%)
Q: What is the main remaining BG?
A: mu mu gamma.
C: Missing mass should be zero, if only a single gamma is there.
There must be a beamstrahlung photon, too.
It is interesting to see what happens if you veto hard photons.
C: With right-handed e- beam, S/B should be better.
Next Step:
- (e-, e+) = (+1, -1) combination

3) TTH (Reported by R.Yonamine)
- Currently working on the l+6j mode
- Updated the detector model and simulator with b-tag.
- ttg BG generation
The cross section now becomes consistent with Uozumi's results.
Next Step:
- Reulsts will be reported within 24h and uploaded to the meeting web page.
- Beam polarization.
--> Results l+6j mode will
- Jet clustering
- ISR/BS conditions
- 8-jet mode
- H->WW*

4) AA->HH
4-1) Theory (Reported by D.Harada)
New phys effects may appear as anomaly in the self-coupling (delta kappa)
- dim-6 effect
- non-decoupling effect
top loop ~ -10% (prop. to mt^4)
2-body -> kinematical advantage
Loop induced
Helicity selection
--> Anomaly in self-coupling appears near the threshold
--> We can tune Eee for mh
In the case of THD model
-> M^4 term appears in 1-loop correction
-> Cross section enhancement near the threshold
-> enhancement prop. to M^4
-> 3 peaks: threshold (h), tt, H+H-
C: 3rd peak is not so useful since we have H+H- pair production
Q: What about H+H- pair production at LHC?
A: Should be very difficult.
Q: What about the THD effect for a single h production?
A: Effect on the self-coupling is much more spectacular.
Nest step:
- Will extend the study to gluon gluon at the LHC.
- WW -> hh @ LHC

4-2) Exp (Reported by N.Maeda)
- Sensitivity study
1st assume 100% efficiency for S and no BG
--> E_AA~300 GeV is optimum.
2nd with BG (WW: 90 pb)
--> 10^ suppression for BG is necessary even with 100% efficiency for S
to achieve sensitivity ~ 3.
--> signal cross section x luminosity -> 16 events / year (10^7 sec)
- Simulation tools
HELAS/BASES/SPRING with Luminosity spectrum
- Analysis results
Compare chi2 for hh and chi2 for WW
-> Some signal events are better reconstructed as WW
--> probably due to H->WW*
mass cut, b-tag, ...
-> eta_b = 1.6 x 10^ (b-tag only)
-> With other cuts, WW BG will be negligible.
--> 4 events/ year with negligible BG
--> Observation seems possible!
C: Real question is if such a machine is really possible.
Next Step:
- Other BG
Q: What about tt?
A: Not open at the hh threshold!

5) Precision measurements of Higgs couplings (Reported by Y.Matsumoto)
Dim-6 operators:
HVV couplings
Used processes:
ZH, nunuH (WW fusion), eeH (double tag, no-tag, single tag)
- constraints on new combinations of dim-6 operators with similar accuracies as
with the current EW precision measurments for oblique corrections/VVV couplings.
- Beam polarization very important for precision.
- High Ecm desired for t-channel processes.
-> a factor of 2 improvement by going from Ecm=500 GeV to 1 TeV.
-> If only Ecm < 350 GeV is accessible, the precision will be one order of magnitude worse.
Q: PLC ?
Q: Next step?
A: systematic error on polarization, PLC, other operators.

6) New physics subgroup
6-1) Theory (Reported by N.Okada)
New particles with different properties
New interactions
*) Precision measurements of anomalous couplings
e+e- -> tau+tau-, ttbar
Exp: full simulation -> level of precision
Th: new physics effects on differential cross section,
initial/final state polarization, top width
--> flavor dependent Z' model (extra U(1))
Y = Y1 + Y2
LHC can find Z' -> l+ l- if MZ' ~ 1.5TeV
Q: Are flavor dependent Z' models popular.
A: There are many models. To avoid FCNC, most models are constructed so as to be
flavor-independent, but there are also many which are flavor dependent
C: There might be effect on neutrino oscillation if MZ' ~ 1.5TeV
*) Generic WIMP studies
X+/- -> W+/- X0
X+/- X0 (DM)
0 0 : Dark Higgs
0 1 : unknown
1/2 1/2 : SUSY
1 0 : unknown
1 1 : LHT
How can we distinguish them experimentally?
- Mass determination -> mass relation
- Total cross section
- Angular distributions
--> production angle distribution tells the spin
--> W polarization tells the decay vertex structure.
--> If t-channel particle is heavy, there will be no asymmetry.
--> Big asymmetry if t-channel contirubtion is significant.
--> Jet charge ID
Next step:
- W charge ID in jet mode.
- paper with simulations (SUSY+LHT+DH)

6-2) Exp-1: Tau/SUSY (Reported by T.Suehara)
Full simulation studies with ILD framework
- Cross section and A_pol
Bhabha statistics not enough yet.
-> Sensitive to MZ' up to 5TeV
Chargino/neutralino separation (chargino -> W+LSP, neutralino -> Z+LSP)
- gamma gamma -> WW BG turns out to be important
-> will investigate it with higher statistics
Cross section (arbitrary unit)
52.8+/-1.1 (2%)
7.6 +/-0.5 (6%)
- mass fit --> delta M <~ 1 (0.6) GeV for X+/- (X0) with 500 fb^
- production angle
- W/Z decay helicity angle
Jet clustering:
Modified ZVTOP (1event/1min)
--> Slow but very good performance
- Increase BG statistics where needed.
- Brush up results for LoI.
- Jet clustering: vertex finder.
-> Will be finished in 2 weeks.

6-3) Exp-2: Top (Reported by K.Ikematsu)
Full simulation studies with ILD framework
Combinatorial BG
-> b-tag turns out to be very powerful to reduce the BG.
Kinematical Fit (7C: 4C(4-momentum) +2C(mW) + 1C (mt1 = mt2)
-> mt line shape now as good as those from other studies
-> Lineshape function should be improved for mass fit.
Next Step:
- Improve fitting function (lineshape)
- Improve kinematical fitting
- Full SM BG
- Total cross section measurements
- A_FB (vertex charge)
- New physics subgruop: l+4-jet

7) A powerful tool for measuring Higgs associated LFV (S.Kanemura)
-- e-gamma collider --
Higgs mediated LFV
L_LFV prop. to (ml/v) x tan^2 beta x (kappa ....)
Present limits from LFV experiments:
e-tau < 6.4 x 10^
e-mu < 4.3 x 10^ (50/tanb)^6 (mA/350 GeV)^4
e gamma -> tau A/H : BG (WZnu?)
--> 2-3 orders of magnitude improvement
--> > 1 order of magnitude better than Super B.
--> Pol e beam useful to measure kappaL/kappaR separately
--> Better than MEG, COMET, LHCB, SKEKB?
Q: Is maximal kappa always possible THD?
A: Yes.
Q: What about effects on neutrino sector?
A: Depens on models. Possible to use seesaw and make it totally independent.
C: e-gamma: free at PLC --> cleaner luminosity spectrum
C: BG from gamma gamma
C: possible to swich off laser for a single beam.
Next Step:
- Serious simulation studies by experimentalists.

8) LHT
8-1) Theory (Reported by M.Asano)
- A paper submitted to arXiv.
--> See talks by Sasaki and this paper for details
- Major results
--> Possible to measure model parameters very accurately
--> Accuracy on DM relic abandance ~ that expected from Planck satellites
Next Step:
C: Should consider A_H decay (T-parity violation via anomaly).
- AH -> boson bson (e.g. Z gamma)
- eH- eH+ pair production
- t T+ threshold

8-2) Exp (Reported by R.Sasaki)
Goal: mass, cross section determinations
-> m(AH) and m(ZH) from E(h) min and max.
- Z_H -> A_H + h (100%) @ 500 GeV
AH=82GeV, ZH=369GeV, h=134 GeV
H decay : BR(bb)=55%, BR(WW*)=26%, BR(cc)=6.3%
- W_H W_H
m(WH) = 368 GeV, m(AH) =82 GeV
sigma_S=122 fb @ Ecm=1TeV with 500 fb^-1
W_H -> A_H + W (BR=100%)
*) Z_H A_H
- event selection
Mh cut, cos(th), Pt cuts
--> S/sqrt = 3.7
- Edge fit -> masses
--> M_AH = 83 +/- 13 GeV, M_ZH = 366 +/- 16 GeV @ 500 fb^-1
*) W_H W_H
- High statistics very clean sample available
- Edge fit -> masses
--> M_AH = 81.58+/-0.67 GeV, M_WH=368.3+/-0.63 GeV
- delta f = 580+/-0.69 GeV
- delta kappa = 0.8%

Nest Step:
- ISR+beamstrahlung
- angluar analysis: solutions
- BG study: tt, Zgamma
- Improve the fitting function.
- Draw a contour.
- Determine F from cross section.

Next step:
- Investigate past chargino studies.
- BG study.
- M_NuH from production angle and total cross section.

9) Long lived exotic particle production (M.Noiri)
Based on slides by
Jinnai (March 29, 2008)
Kitano (June 26, 2008)
Gravitino LSP: non-pointing gamma (neutralino), kink (stau)
chargino-neutralino almost degenerate
Split-SUSY (heavy squark), gravitino LSP
*) Trigger?
quasi-stable stau -> tau allows precision

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

Discussions on future direction and mile stones
Next bi-weekly meeting (2009/02/05 13:00)
Next general meeting (2009/04/04 or 11 9:30) -> Link with Detector Meeting
Proceeding deadline: the end of April 2009:
Anybody can contribute even if he or she was not present at the meeting.
Contributors are encouraged to include most updated results at the time of submission
of their proceedings papers.

Working group contact persons:
K.Ikematsu, Y.Okada, H,Ono, S.Kanemura, Y.Takubo, K.Fujii, T.Suehara

Working group web page:

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