Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Observation and properties of a Higgs boson andsearch for additional Higgs bosons in theTwo-Photon Decay Channel with CMS

Benoit Courbon

IPN Lyon/Universite Claude Bernard Lyon 1, on behalf of the CMS collaboration

Higgs Hunting, 30/07/2015

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Overview of the Standard Model H → γγ analysis

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Diphoton channel : Small branching fraction(∼ 2.10−3 at mH = 125 GeV) but cleansignature : 2 high-pT isolated photons

Analysis strategy : Search for a narrow peak on asmoothly decreasing background in the diphotonmass spectra

Large diphoton background : Reducible (jet-jetor γ-jet with jet faking photon) and irreducible(γ-γ)

Mass resolution is crucial (energy correctionsand vertex identification)

Categorization of diphoton events to gain insensitivity and to tag production modes

We use the full run 1 dataset : 5.1 fb−1 (2011, 7 TeV) + 19.6 fb−1 (2012, 8TeV)

Trigger : pT ,γ > 26(18) or pT ,γ > 36(22) on the leading (trailing) photon +loose isolation, shower shape criteria and mass cut → 99.5 % efficiency

Challenging Pile-Up conditions : <PU>=21, up to 40

Eur. Phys. J. C 74(2014) 3076 ;Hgg Public TWiki

Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Mass resolution

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mγγ =√

2E1E2 cosα1,2

Energy measurment :

ECAL performance (crystal intercalibration,response changes correction...)

High-level correction : Photon energyregression method. Multivariate approachaiming to take in account showering,gap/crack effects, PU ...

Final energy scale extraction from Z → eeevents (cross-check with Z → µµγ)

Vertex identification :

The angular term is negligible if δz < 1 cm

CMS has no intrisic pointing capability

We use Boosted Decision Trees to identify the primary vertex, based on thekinematics of the recoiling tracks + the tracks of identified conversions

More than 80% average vertexing efficiency

Energy resolution vs η

arXiv :1502.02702

Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Selection and categorization

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We apply a first BDT classifier (photon ID)to discrimate prompt photons from fakes(neutral hadrons), based on shower shape andisolation

Then we categorize diphoton events :We build exclusive classes (1% of theevents) in order to tag specificproduction modes, by requiringadditional objects (forward jets,leptons, MET...) in the event.We apply another classifier (diphotonBDT) to categorize the remainingdiphoton events (99%) based on theirmass resolution, their kinematics andthe photon ID.5 (4) untagged categories + 9 (7)exclusive categories for 2012 (2011)dataset

Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Signal and background modelling

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Signal model :We fit MC signal samples with a sumof gaussians, with granularity of 5GeV, for each processThen the signal model is interpolatedbetween these points.

Background model :It is data driven : We choose thefunctional form with the best fit todata, among a class of differentfunctions (exponentials, power laws,polynomials...).The choice of the bkg model istreated as a discrete nuisanceparameter.We make sure that the potential biason the signal strength is negligible.

Signal model at mH = 125 GeV

Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Results

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Local significance of 5.7 σ

mH = 124.70± 0.34[±0.31(stat)± 0.15(syst)] GeV

µ(mH = 124.7GeV ) = 1.14+0.26−0.23

[±0.21(stat)+0.09−0.05(syst)+0.13

−0.09(theo)]

Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Low-mass search

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CMS-HIG-14-037

Light scalar searches in the diphoton channel areperformed in the range [80,110] GeVMotivations of this search : NMSSM, 2HDM ...

The Z peak contamination, with 2 electronsmisidentified as photons, needs to be added to thediphoton continuum background

4 categories (using the diphoton classifier fromstandard H→ γγ analysis)

No evidence for new particle production has beenobserved

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8TeV Observed

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High-mass search

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arXiv :1506.02301

Heavy scalar searches in the diphoton channel are performed in the range[150,850] GeVThese searches are motivated by several BSM scenarios, such as 2HDM

Not only mass scan but also width scan (from 0.1 GeV to 10% of the scalar mass)

4 categories (barrel/endcap, converted/unconverted)

No evidence for new particle production has been observed

Γ = 0.1GeV Γ = 10%mX

Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Conclusion

H→ γγ is one of the most sensitive channels and allows precise measurementof the Higgs sector :

Observation with 5.7σ significance (single-channel discovery)mH = 124.7± 0.34 GeVµ = 1.14± 0.24

All the measured properties are compatible with the SM Higgs bosonAdditional Higgs bosons searches, motivated by BSM scenarios, have beenperformed at low and high mass, showing no evidence of a new scalar

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

BACK-UP

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

H → γγ vertexing efficiency

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

H → γγ categories

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

H → γγ significance plot

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

H → γγ mass measurment

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

H → γγ reduced couplings

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

H → γγ width

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

H → γγ spin

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Low-mass Data/MC comparison

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Low-mass exclusion limits (ggh+tth)

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Low-mass significance plot (ggh+tth)

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Low-mass exclusion limits (vbf+vh)

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

Low-mass significance plot (vbf+vh)

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

High-mass Data/MC comparison

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Introduction Analysis strategy Results Additional Higgs bosons ? Conclusion

High-mass exclusion limits in spin 2 interpretation

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