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A Summary of The 38th General Meeting of the ILC Physics Subgroup
Aug. 30, 2014 (Sat) at Room 425, Building 3, KEK
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0) Attendants:
Present at KEK:
A.Ishikawa (Tohoku)
J.Strube (Tohoku)
A.Dubey (Tohoku)
S.Watanuki (Tohoku)
Y.Okada (KEK)
C.Calancha (KEK)
K.Fujii (KEK)
J.Tian (KEK)
Shaofeng Ge(KEK)
T.Ogawa (Sokendai)
E.Asakawa
T.Tanabe (Tokyo)
M.Kurata (Tokyo)
K.Hidaka (Gakugei)
Y.Kiyo (Juntendo)
H.Ono (NDU)
H.Yokoya (Toyama)
Remote connection:
S.Kanemura (Toyama)
Y.Sudo (Kyushu)
T.Tomita (Kyushu)
T.Suehara (Kyushu)
K.Ikematsu (Saga)
M.Nozoe (Saga)
0) Opening comments (K.Fujii)
1) ZH: Recoil mass using Z->qq (Tatsuhiko Tomita)
Status:
ZH->qqH @250GeV
New cuts: sphericity and minor thrust
-> left pol: delta sigma / sigma = 4.8%
right pol: = 3.2%
Next Step:
- 4-fermion BG remains
- Use a tau finder
- Optimize cuts.
- MVA to reduce 4-f BG.
Q: jet selection: Durham for all particles?
What about two-photon hadron BG?
A: As long as the BG tracks are not included in qq jets, it’s OK
C: They could be included.
Q: What is the source of the BG in your ISR tagging? 80% purity seems too low.
A: Maybe from evW…
C: Check possible bias due to the sphericity cut.
2) H->bb,cc,gg (Hiroaki Ono)
Status:
250fb-1@250GeV, 330fb-1@350GeV
Small difference from extrapolation from 120GeV.
Maybe this is due to low BG statistics for qqH.
Comparison of LCFIPlus and LCFIVTX
New X-likeness definition
Next Step:
- Try different X-likeliness.
- Check selection code for eeh channel and cut optimization.
- Different polarizations.
3) Top Yukawa coupling study at 500 GeV (Yuji Sudo)
Status:
new: overlay low Pt beam background
- Setup:
mh=125 GeV, 500fb-1 at Ecm=500GeV,
beam polarization=(-0.8,+0.3)
- Results:
At AWLC14: (w/o kT clustering)
8-jet : S/sqrt(S+B)=2.04
L+6-jet: S/sqrt(S+B)=2.42
—> delta y_t / y_t = 15.7%
Use kT clustering.
Found t->bW->btauv is non-existent!
-> now S/sqrt(S+B)=2.35 for 8-jet
=2.04 for l+6-jet
Studies of systematic errors
-> then S/sqrt(S+B)=2.31 for 8-jet
=1.92 for l+6-jet
Q: How did you estimate the systematic errors?
A: Guesstimates.
Nest Step:
- Further studies on systematic errors.
- MVA.
- Analysis at higher Ecm, say at 520 or 550GeV.
4) ZH: Recoil mass using Z->ll (Shun Watanuki)
Status:
- tried mass template method
-> x=125.084+/-0.013GeV (Z -> mu+mu- alone!)
C: Need to smooth templates (both S and BG)
- improve bias for cos(theta_missing)
-> cos(amiss) < 0.99 or |cosZ| < 0.9 -> bias improved at the cost of BG increase.
- CP mixture
Next:
- Solve the strange behavior of chi2: Fix BG fluctuation
- Estimate precisions with new cuts.
- cos(theta) distribution by fitting m_recoil in each cos(theta) bin.
- Do the same for the signal sample with anomalous couplings.
5) Higgs self-coupling (Junping Tian)
Status:
- Update mh to 125GeV.
-> extrapolation confirmed with full simulations.
- Study effects of 2-photon hadron BG
-> Optimization of R and Njets
Njets=6 is better than Njets=4.
53%->58% with 2ab-1 at 500GeV (hh -> bbbb only)
On-going and/or future improvements:
isolated lepton tag:
2-cone algorithm (significant improvement) -> multi-cone algorithm (future)?
—> significant improvement
shower profile (cf. Kurata)
kinematic fitting
-> nicer peak but BG might have a similar peak. need to check.
optima cuts for coupling precision
ME method
-> tested for eeH (ZZ fusion)
color-singlet jet clustering
-> Comparison of perfect jet clustering and realistic jet clustering
shows that there is a significant room (~40%) for improvement.
mini-jet clustering:
Up to 20 mini-jets, mis-clustering is not significant.
Needs likelihood function at the parton-shower level.
Next Step:
- Try to improve 500GeV precision.
- Use ME method.
- Kinematic fitting also for BG.
- jet-clustering, …
- Publish results.
6) 2HDM searches at the ILC in the 4 top quarks process (Hiroshi Yokoya)
Setup:
sin(beta-alpha)=1 case: alignment limit:
-> Direct search
Searches for H/A —> ttbar (low tan beta)
e+e- —> HA —> tttt : O(1)fb for mH/A=450GeV (SM BG: 4ab @ 1TeV)
Next Step:
- Discovery reach.
- Determination of mass and tan beta.
Q: Where did you get b-tagging efficiency 60%?
It seems a little bit low.
A: It is a number taken from some study. It does not take into account E-dependence, etc.
Q: What about the MSSM case?
A: It is similar.
Q: Does the decay mode depend on the choice of M?
A: The dependence is weak as long as the alignment limit is imposed.
Q: How big the mass difference can be?
A: delta m^2 ~ (80GeV)^2 (constrained by triviality, unitarity, vacuum stability)
7) The Georgi Algorithms of Jet Clustering (Shaofeng Ge)
- Jet function: J_beta increasing with clustering
-> global clustering (not pairing algorithm)
C: It is very nice if we can apply this to color singlet clustering.
8) Heavy Higgs search at ILC (Abhinav Dubey)
Status:
e+e- -> HA -> bbbb
mA=mH=400GeV, tanb=10, 2.7fb @ 1TeV
H->bb (77%) A->bb (65%)
Generated a signal MC sample, looking at mH, mA, (mH+mA)/2, etc.
Next:
- Understand reconstruction
- Understand beam BG
- Include SM BG.
9) Attaching pi0 to vertices (Masakazu Kurata)
Status:
- pi0 vertex finder using qqHH@500GeV sample
MVA <- vertex mass
-> Clear D meson peak for 2 tracks (K+pi) with a tertiary vertex !!!
Next Step:
- vertex mass breaks the generality of MVA.
-> requires classifier for each vertex pattern?? -> maybe hopeless.
-> need better and more general classifier.
Now using gradient BDT (NN didn’t work well).
- Kaon ID in the case of 0 vtx:
-> ~30% from D meson and ~70% from primary.
-> need to separate the 30% from the rest.
10) Si vs Sci for H->invisible (Tomohisa Ogawa)
Status:
Sample: 250fb-1@250GeV, 350fb-1@350GeV with beam polarization: (-0.8,+0.3)
invisible BR(10%)
Si ECAL: sigma_mZ ~ 10.2% @ 250GeV (10.0% @ 350GeV)
Sci ECAL: ~ 10.4% @ 250GeV (10.7% @ 350GeV)
Next Step:
- Understand the mass resolution.
- Optimize cuts.
- Investigate the reason for mass shift.
11) Impact of photon energy resolution on H->gamma gamma measurement (Constantino Calancha)
Status:
vvh followed by h->aa @ 500GeV
Artificially make sigma_E worse and look at single photon and m(aa) resolutions.
Next:
- Study the effect of energy resolution degradation.
12) Physics case for the ILC: Post LHC8 (Tomohiko Tanabe)
Tomohiko showed the slides prepared primarily for the ILC review by the MEXT
Physics WG.
C(p08): Use the same L everywhere.
Importance of c-coupling should be mentioned somewhere maybe on a separate page.
C(p29): This is very impressive.
However, the expression “XX-like” is misleading here.
It just shows the ordering and does not exclude the cases with large mixings.
What about naturalness and DM constraints?
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The slides shown at the meeting is available from
http://agenda.linearcollider.org/conferenceDisplay.py?confId=6422
see them for details.
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*) Meeting Schedule:
Next general meeting (2014/11/01 10:30) : Conf.ID: 834
Working group web page:
http://www-jlc.kek.jp/jlc/en/subg/physics
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