latest results on the standard model higgs in atlas€¦ · mar 3rd, 2011 open discussion meeting...

Latest Results on the Standard Model Higgs in ATLAS

Koji Nakamura (KEK) on behalf of ATLAS collaboration

20th Nov, 2013 1 KEK Seminar

Geneve

Jura

We had fruitful discussions in Japan

20th Nov, 2013 KEK Seminar 2

Hadron Collider Physics Symposium 2012

Kyoto, Japan

HC2012 - Higgs Coupling 2012 Tokyo in Japan

http://www.icepp.s.u-tokyo.ac.jp/hc2012/

http://www.icepp.s.u-tokyo.ac.jp/hcp2012/

LHC and ATLAS experiment

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ATLAS

• 7TeV collisions are Started in March 2010. • Upgraded CM energy to 8TeV in 2012. • Extremely successful operation for these

2.5 years.

Historical observation

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Phys.Lett. B716 (2012) 1-29

“These results provide conclusive evidence for the discovery of a new particle with mass 126.0±0.4 (stat)±0.4 (sys) GeV. ”

But what’s the new particle?

Post Observation

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ICHEP/Observation

HCP

5.8fb-1

13fb-1

Post Observation

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12th July, 2012 KEK seminar

Today’s topic How coupling measurements are started? What are Hττ and bb going on?

We had progress on this.

Post ICHEP results

• Coupling measurements in Sep 2012 :

• Updated searches for each channels in Nov 2012 :

– (HWW)

– H ττ

– H bb

– (combination)

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ATLAS-CONF-2012-127

4.6fb-1(7TeV)+13fb-1(8TeV)

Will be updated to : https://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults

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Coupling measurement

Higgs production and decay @ LHC

Mar 3rd, 2011 Open discussion meeting 9

Gluon Fusion(ggF) Vector Boson Fusion W/Z Associated

Production Decay

All of bb, WW, ττ, γγ, ZZ can be observed!!

tt/bb Associated

Channels included in the measurement

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Signal strength for each channel

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Signal strength for each channel

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Coupling measurement : Notation

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All measurements assume mH=126GeV

Production process dependent μ

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Gw/z

Yt

Gw/z

= =

= μVBF+VH

= μggF+ttH

VVH coupling in production

qqH coupling in production

We can measure the ratio of Boson and Fermion coupling using different production processes with the same decay mode.

Yt =

Production process dependent μ

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Hγγ

HWW

Take a ratio to avoid BR effect :

Hγγ , HWW and combination.

Coupling with Gauge boson

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Gw Gz λWZ = κW / κZ =

We saw clear excess on the both WW and ZZ decay channels so meaningful HVV measurement could be presented

Observed :

Coupling with Fermion

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May be this is too early to discuss since not yet observed bb and ττ

Up type v.s. down type Lepton v.s. quark

More global view

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New results for each channel

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HW(lν)W(lν) channel in ATLAS

• One of the highest sensitivity channel.

• Contributed to the observation a lot.

• May probe production mechanism dependence – VBF HqqWW

– VHVWW

– ttHttWW

• Analysis is assuming/using spin 0, this means that it’s quite sensitive to the spin measurement.

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For HCP, only different flavor leptons channels with 0/1jet are updated.

Event selection & background estimation • two leptons + Missing ET

• ggF : 0,1 jet

Mar 3rd, 2011 Open discussion meeting 21

Sign

al

regi

on

WW control region W+jets/Wγ* : Fake lepton background. Prepare Loose lepton CR And multiplied by Fake rate.

WW: Normalized by WW control region.

Top : Apply b-tagging to enhance ttbar background.

Z+jets : MET vs mll Mainly for met correction.

HWW results.

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0jet 1jet

Close to 3σ !

Hbb searches in ATLAS

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0 lepton 1 lepton 2 lepton

Show the results with 4.6fb-1(7TeV) and 13fb-1 (8TeV) data

Background and estimation

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0 lepton 1 lepton 2 lepton

Shapes are obtained by MC and normalized to data by Control region. Multi-jet background was determined by data-driven way. WZ/ZZ(Zbb) resonant backgrounds fully rely on the MC.

High sensitivity categories

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0 lepton 1 lepton 2 lepton

After background subtraction

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Results : combined limit and p0

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• Calculated limit and significance using MMC distribution as the discriminant. • To extract signal, Profile likelihood was used.

Expected:1.9xSM Observed:1.8xSM Expected:15% Observed:64% (μ=0) (μ=1)

Best fit value of Signal Strength (μ) is -0.4±0.7±0.8

Hττ searches in ATLAS

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• Three Higgs production processes are considered in this analysis.

•

• Separate analysis for three different ττ decay mode.

– lep-lep = ll4ν : (ee)+eμ+μμ – lep-had = lτhad3ν : eτhad+ μτhad – had-had = τhadτhadνν : (τhadτhad)

• Combined all three channels to search for Hττ signature. Show the results with 4.6fb-1(7TeV) and 13fb-1 (8TeV) data

Di-tau Mass reconstruction

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• Solve τ, ETmiss in Δφ(τvis,ν)

parameter space using Δθ3D(τvis,ν) template from simulation as PDF.

Missing Mass Calculator(MMC)

Need… Event by Event estimator of true di-τ mass likelihood. Full reconstruction of event kinematics.

Di-tau invariant mass should be a important discriminating variable from backgrounds. But having 2-4ν in a events.

Background and estimation

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• Opposite sign tau decay products are required.

• High Missing ET and low MT cuts are added.

QCD and W+Jets – Estimated from Same Sign events(lephad) -- Template fit by loose selection (lep-lep,hadhad)

Zee/μμ + jets, Top, di-boson Estimated by MC with correction.

Zττ estimated by embedding+MC -- used Zμμ data and replace μ by full simulated τ, so that all the objects except tau decay product are obtained by real data. -- Used high statistics MC for VBF channel with correction by data.

Z(ττ)+jets modeling validation

13th Nov, 2012 HCP 2012 31

Higgs Signal is on the right hand side tail of Z. Need carful varidation of the Zττ shape.

Non-VBF channel : Embedding Checked with MC sample Assigned systematics by varying condition. VBF channel : High statistics MC Jet kinematics are validated by Zee/μμ data. Reweighted kinematics for MC mismodeling.

MMC distribution embedding vs MC

MET distribution. estimation vs data

Results: discriminant distributions

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leplep lephad hadhad

2xSM signal 1xSM signal 5xSM signal

ggF

sen

siti

ve c

han

nel

s V

BF

sen

siti

ve c

han

ne

ls

Results : combined limit and p0 • Calculated limit and significance using MMC distribution as the discriminant. • To extract signal, Profile likelihood was used.

13th Nov, 2012 HCP 2012 33

Expected:1.2xSM Observed:1.9xSM Expected:1.7σ Observed:1.1σ (μ=0) (μ=1)

Best fit value of Signal Strength (μ) is 0.7 ±0.7

Summary of production dependence

• H ττ result.

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Summary of production dependence

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What we achieved post-observation

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Observation paper HCP preliminary

We observed something in July

• Indeed the observation was clear! (6σ)

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• Indeed the observation was clear! (6σ)

• But still not sure what it is.

We observed something in July

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With full data in 2012

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LHC after 2yr shutdown

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Open question : next generation exp.

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How easy to see who is sitting on the plane ? Do we have enough motivation for the cost?

backup

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Other measurement

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Loop coupling : photon and gluon Higgs decaying to invisible particles.

Systematic Uncertainties. • Systematic uncertainties for Zττ background and Signal. • Dominant systematics are Embedding, Tau Energy Scale

and Jet Energy Scale. Both Shape and Normalization variation are taken into account.

13th Nov, 2012 HCP 2012 45