1. 方亚泉 高能物理所 第十二届全国粒子物理学术会议 合肥科大 2016年8月21－25日
Di-photon related Higgs analyses with ATLAS detector VBF H→gg & hh→W(lν)W(qq)gg
方亚泉
高能物理所
第十二届全国粒子物理学术会议
合肥科大 2016年8月21－25日

2. Motivation
Higgs pair production has a small Xsection in SM (~33
BSM can effectively enhance Higgs pair production:
2HDM, SUSY etc..
The distribution of pt of Higgs is slightly higher than expected.
VBF is the second largest production of Higgs and has lower theoretical uncertainty (~5%) and could also probe new physics

3. Summary of RUN1 results: hh→WWgg & VBF h→gg
Phys. Lett. B 726(2013), Oct 2013, pp
Phys.Rev. D 89, (2014)
Phys.Rev. D 92, (2015)
s = 3.3
For ATLAS RUN1 VBF search, with the combination
of gg (2.5s), WW*, ZZ*, we observes 3.3 s; the combined
significance between ATLAS and CMS is 5.4s with RUN1 data.
hh->wwgg was first proposed by us at :
PLB755(2016)
hh->wwgg together with bbgg, bbtautau,bbbb are extensively
explored with RUN1 data and the results are
combined
2.5s for combined results with 1.8s from wwgg.

4. VBF H→gg

5. Event signature of VBF f h Two forward highly boosted jet.
High invariant mass of the di-jet Mjj,
No much jet activities in the
center region of the detector.
Central jet veto…
feasible to play
with Multivariate
analysis (MVA). f h
Forward jets
Higgs Decay
CERN-THESIS

6. Event display of VBF H→gg

7. VBF H->gg HGam Coupling analysis:
aim : measure the signal strength : μ=σobs/σSM in each production mode in diphoton final state
Focus on VBF
Contents
VBF signature
high-pt forward dijet
define two VBF-sensitive categories by cut-based and MVA ( BDT )
results in data
Diphoton selection
pT>25GeV, |η|<2.37,exclude crack region
two tight, isolated photon
pTγ1(γ2)/mγγ>0.35(0.25)

8. Training/optimization the MVA
[120,130] GeV window is blinded during the
process for data.
Signal : VBF 125 GeV.
Background :
ϒϒ : SHERPA Monte-Carlo normalized to
4 fb-1.
ϒjet+jets : data with at least
one photon not isolated.
The components are normalized
to the fraction from data-driven method.
Other samples such as revIso,
MC+revID, sideband were tried as well.
The performances are worse than
the first one.
For the optimization, both sideband fit
from data and MC+revIso are tested.
MC+revIso is used as the baseline
(no bias)
example
example

9. Discriminating variables used in Run2
Separation power
two forward jet → large Δηjj
high pT and large Δηjj → large mjj
central diphoton and forward dijet → large ΔRminγ,j,ηZepp
two balance high pT jet → high pTt

10. Distributions of variables
data sideband (exculde GeV ) is consistent with γγ+γj+jj background
these variables show good separation power
they are to be used in category optimization

11. correlation to mγγ
the used variables should not be correlated to mγγ

12. results in data
= 13.3 fb-1
ATLAS-CONF
the red and green show the difference between observation and SM prediction
observed signal strength is 124% larger than SM, but within 2 sigma

13. hh→WWgg →lvqqgg

14. Definition of objs and selections

15. Continuous Background estimation
A number counting analysis is used for the analysis considering low statistics.
Sideband of the di-photon is used to extract
Different control regions are used to validate.
High statistical sideband sample gg+2jets (in lepton requirement) is pragmatically used.

16. Results
The events within /-2s GeV mass window are listed in the above table.
The dominant background is still from continuum background.
From the right plot, the statistical fluctuation is still significant.

17. Systematics The most dominant resource of the systematics comes from
the statistical uncertainty of continuum background.

18. Limits
ATLAS-CONF
The selections are mass independent; the differences of the limits are mainly
due to the variations of the signal efficiencies.
No obvious new signal has been seen:
the deviations between observed limits and expected limits are around 2s.
More data will tell us the further story…

19. Summary
Conference notes about VBF H→gg and di-Higgs→w(lν)w(qq)gg are approved with ATLAS RUN2 data and shown in ICHEP:
The latter is the only channel available for di-Higgs search in ICHEP in the mass region smaller than 500 GeV.
Play a leading role in these two analyses.
Editors and contact person
5 papers, 2 conference notes, 4 editors
Global signal strength , including VBF, is consistent with SM prediction within uncertainty:
More data is needed to confirm whether there is excess with respect to SM and investigate the Higgs property

20. back up

21. VBF signature Signature : diphoton in central region
two high-pT jets in forward region
VBF pre-selection
N_jet>=2
Δηjj>2
|ηγγ-0.5*(ηj1+ ηj2)|<5