Higgs differential cross-sections and CP Higgs couplings results with the ATLAS experiment
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Higgs differential cross-sections and CP Higgs
couplings results with the ATLAS experiment
DIS 2022: XXIX International Workshop on Deep-Ineslastic Scattering and Related Subjects
Santiago de Compostela, Spain - 2-6 May, 2022
Sagar Vidya Addepalli (Brandeis University),
on behalf of the ATLAS Experiment
INTRODUCTION 2
The Higgs Boson!
▸ Characterised in multiple decay channels by the ATLAS and the CMS experiments.
▸ A major goal of Run 2 is to measure its properties and provide constraints on
Beyond Standard Model effects to which Higgs boson’s production and decays are
sensitive.
Time
gluon gluon fusion (ggF) Vector boson fusion (VBF) VH ttH
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
INTRODUCTION 3
Motivation
▸ Differential Cross Section Measurements -
▸ Measured in the “ ducial” region: Limited phase space de ned by the detector
acceptance. Minimal physics assumption needed for extrapolation.
▸ Minimal model dependence.
▸ Shapes of different observable sensitive to different BSM phenomena which
might not be apparent in the inclusive yield.
▸ CP (Charge Parity) Measurements -
▸ SM Predicts a CP-even Higgs boson —> CP-odd contribution out of purely BSM
effects.
▸ New source of CP violation could partly explain matter-antimatter asymmetry in
the universe.
Image Source: Sandbox Studio
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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INTRODUCTION 4
Differential XS Measurements
[1.] De ne measurement phase space and “ t” [2.] Remove detector effects: Unfolding [3.] XS Measurement
observable. Extract signal yield in each bin.
Nobs − Nbkg
σfid =
ℒ×C
Detector
Luminosity
correction
Resonant Signal
“Migration Matrix” accounts for
detector effects. In-likelihood
unfolding done for all diff XS
results shown in this talk.
N
μsi = Σj d. bins ℒ ⋅ Ai,j ⋅ Ci,j ⋅ σ d,j
+ fi ⋅ ℒ ⋅ σ d
Multivariate Approach
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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VH(bb̄) FIDUCIAL XS MEASUREMENT 5
Analysis Strategy
▸ Additional result based on resolved VH(bb̄) [Eur. Phys.
J. C 81 (2021) 178]
▸ H → bb̄ most probable decay (60%) for Higgs boson,
▸ Dif cult to isolate: very large multi-jet background,
▸ Suppressed using the associated V boson decay to
leptons for triggering (ETmiss in this case).
▸ Targets the 0-lepton channel in VH production
channel.
▸ Uses the other channels to constrain background -
▸ 2 lepton channel to constrain Z + jets,
▸ 1 lepton channel to constrain W + jets and t t̄ . Fig: Post t mbb in the 2 jets category
CRs based on ΔR b/w b-jets to constrain t t̄ and V+jets. with ETmiss ≥ 250 GeV
▸
ATLAS-CONF-2022-015
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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VH(bb̄) FIDUCIAL XS MEASUREMENT 6
Results
▸ Cross section measurements agree with the POWHEG MiNLO
standard model prediction.
▸ Hadronic jet measurement dominant
experimental uncertainty in both bins,
followed by avour tagging.
▸ tt̄ modelling dominates the background
modelling uncertainty in the rst bin, and
Z+jets in the second.
ATLAS-CONF-2022-015
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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H → γγ 7
Analysis Strategy Massive and
separated jets
▸ H → γγ decay has a very small BR (~0.002),
BSM Sensitive
▸ High photon reconstruction ef ciency in ATLAS,
▸ Sharp resonant peak above the background.
High jet multiplicity +
leptons
▸ Distinct signal signature allows a very inclusive phase
space (mostly ggF) sub-divided into more regions.
▸ Main bkg - (non resonant γ and mis-ID jets) estimated
from mγγ sidebands.
▸ Background modelled analytically with functional
parameters estimated from the t. Choice between
functions based on bias tests and goodness of ts.
arXiv:2202.00487
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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H → γγ 8
Results POWHEG Box v2
▸ 5 ducial, 20 differential, and 4 double
differential cross sections were measured,
including di-photon and di-jet masses,
momenta, angular separations, etc.
▸ Statistical uncertainty dominates followed by
background modelling and photon
reconstruction.
▸ Results consistent with SM prediction.
arXiv:2202.00487
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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H → γγ AND H → ZZ* → 4ℓ COMBINATION 9
Strategy and Results
▸ The measurement can be improved by combining multiple
channels.
▸ The combination uses similar ducial phase space
de nitions as in individual measurements.
▸ Extrapolation from ducial phase space to full phase space
done using MC (inclusive acceptance factor ~50% for both
channels).
▸ Higgs boson kinematic variables computed from the
simulated Higgs boson instead of decay products in the
total phase space.
p(NNLOPS)=78% p(NNLOPS)=92%
▸ Measurements dominated by statistical uncertainties. p(Sherpa)=2.1%
▸ Good agreement with SM.
▸ H → ZZ* → 4ℓ differential XS [arXiv:2004.03969]
▸ Yukawa couplings interpretation in Philipp Windischhofer’s
talk [link].
ATLAS-CONF-2022-002
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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INTERPRETATION 10
Interpretation - Yukawa Couplings
▸ ggF production dominated by t-quark has
negative but small interference from the b-
and c-quark loops.
H
▸ pT spectrum is sensitive to Yukawa
couplings of the Higgs boson to the b- and
c-quarks.
Bishara et al [PRL 118, 121801]
arXiv:2202.00487
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022H → γγ AND H → ZZ* → 4ℓ 11
Interpretation - Yukawa Couplings
▸ Two ts with increasing model dependency -
▸ only shape of the spectrum considered,
▸ Shape+norm along with the partial decay
width considered.
arXiv:2202.00487
▸ Direct search status -
▸ κb - 20% uncertainty at 68% CL,
▸ | κc | < 8.5 at 95% CL.
▸ See Philipp’s talk for more details.
arXiv:2004.03969
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
fiHIGGS CP MEASUREMENT 12
CP Measurements ci (6)
∑ Λ2 i
ℒEFT = ℒSM + O
i
▸ SM predicts a scalar Higgs boson, but the
presence of a pseudoscalar admixture has not yet
been excluded! Suppressed higher order terms
▸ Two main ways CP violation in the Higgs boson
sector manifests -
▸ CP-odd V to H BSM couplings: naturally
top Yukawa coupling parameter CP mixing angle (SM : α = 0∘)
suppressed by BSM scale,
▸ CP-odd fermion to H BSM Yukawa couplings:
possibly signi cant at tree level (in this talk!).
mt
v { }
ℒ=− ψ̄ t κt [ cos(α) + i sin(α)γ5 ] ψt H
2 2
σ ∼ CPeven + CPodd
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
fitop Yukawa coupling parameter CP mixing angle
tH & tt̄H (H → bb̄) 13
mt
CP Measurement ℒ=−
v { ψ̄tκt [cos(α) + i sin(α)γ5] ψt} H
▸ Analysis targets tH and t t̄H production modes.
∘ +55∘
▸ Tree level production: Less susceptible to assumptions ‣ Best t α = 11 −77∘ and κt = 0.83+0.30
−0.46.
embedded in loop-induced t-H coupling. ‣ α = 90∘ excluded at 1.2σ.
‣ Systematic uncertainties dominate.
▸ Attempts to reconstruct t and H, used to build CP
sensitive observables.
▸ Bkg dominated by t t̄ + bb̄. Shape from MC, norm from
data.
▸ tt̄ + ≥ 1b modelling uncertainty dominates with sub-
leading experimental uncertainties.
ATLAS-CONF-2022-016
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
fitop Yukawa coupling parameter CP mixing angle
tH & tt̄H (H → γγ) 14
mt
CP Measurement ℒ=−
v { ψ̄tκt [cos(α) + i sin(α)γ5] ψt} H
▸ Analysis targets tH and t t̄H production modes.
‣ Without prior constraints on κt,
▸ The CP-odd contribution introduces a second coupling | α | > 43∘(63∘expected) is excluded at 95% CL.
to the top quark, which modi es the H → γγ decay rate. ‣ α = 90∘ excluded at 3.9σ.
‣ Systematic uncertainties negligle.
“Lep” region
‣ Targets leptonic nal state
‣ >= 1 isolated lepton
“Had” region
‣ Targets hadronic nal state
‣ >= 2 additional jets and no leptons
arXiv:2004.04545
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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fiEffective Higgs gluon coupling parameter
WW*( → eνμν)jj CP mixing angle 15
gHgg
Analysis Strategy ℒ=− ( κgg cos(α)G a a,μν
μν G + κgg sin(α)G a a,μv
μν G̃ ) H
4
▸ H → WW* has a high BR (0.2) but dif cult to dσ 2 2
∼ CPeven + CPodd + CPevenCPodd
dX
isolate signal. Measurement sensitive to V-H
interaction and EWSB structure.
▸ Analysis targets ggF production mode.
▸ The CP-odd contribution to the top coupling
also affects the ggH effective coupling.
▸ Interference between CP-even and CP-odd
contributions affect the shape of the ΔΦjj
distribution.
arXiv:2109.13808
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
fiWW*( → eνμν)jj 16
Results
▸ Three different ts are performed -
▸ 1. Only tan(α) is scanned -
▸ 1A. Only shape effects are considered,
▸ 1B. Shape+normalization effects are considered,
tan(α) = 0.0 ± 0.4(stat.) ± 0.3(sys.)
▸ 2. Simultaneous t of κgg cos(α) and κgg sin(α) using
both shape and normalisation effects.
▸ Measurement of tan(α) is dominated by statistical
uncertainty in the SR followed by b-tagging and signal
modelling.
▸ Results consistent with SM prediction.
arXiv:2109.13808
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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fi17
Conclusion and Outlook
▸ Presented 6 exciting measurements done with the ATLAS Experiment using
Run 2 LHC data.
▸ Most results limited by statistical uncertainty, so Run 3 presents a promising
opportunity to improve on current limits!
▸ All results currently compatible with the standard model but scope for
improving the precision.
▸ 10 years after the Higgs boson discovery, we have made signi cant progress in
understanding its characteristics, and there’s more to come!
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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ADDITIONAL MATERIAL
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022INTRODUCTION 19
Results shown in this talk
miss
▸ Measurement of the ducial and differential cross-section of WH/ZH production for the b -jets + ET nal state in pp
collisions at s = 13 TeV with the ATLAS detector. [ATLAS-CONF-2022-015]
▸ Measurements of the Higgs boson inclusive and differential ducial cross-sections in the diphoton decay channel with pp
collisions at s = 13 TeV with the ATLAS detector. [arXiv:2202.00487 — submitted to JHEP]
▸ CP Properties of Higgs Boson Interactions with Top Quarks in the tt̄H and tH Processes using H → γγ with the ATLAS
detector. [Phys. Rev. Lett. 125, 061802 (2020)]
▸ Combined measurement of the total and differential cross sections in the H → γγ and the H → ZZ* → 4ℓ decay channels at
s = 13 TeV with the ATLAS detector. [ATLAS-CONF-2022-002]
−1
▸ Constraints on Higgs boson properties using WW*( → eνμν)jj production in 36.1 fb of s = 13 TeV pp collisions with the
ATLAS detector. [arXiv:2109.13808 — submitted to Eur. Phys. J. C]
▸ Probing the CP nature of the top-Higgs Yukawa coupling in ttH and tH events with H -> bb using the ATLAS detector at the
LHC [ATLAS-CONF-2022-016]
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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fiVH(bb̄) FIDUCIAL XS MEASUREMENT 20
Analysis Strategy
▸ Particle level categories -
▸ Ti - Pass particle selection in bin i of
miss
ET ,
miss
▸ Oi - Off ducial but in bin i of ET ,
ATLAS-CONF-2022-015
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
fiH → γγ 21
Signal and Background Modelling
▸ Signal Modelling - Double sided Crystal Ball function. Gaussian
peak with exponential tails due to photon to electron
conversions with electrons losing energy from Bremsstrahlung.
▸ Background Modelling - Main bkg are γγ, γj, and jj with jets mis-
ID as leptons. Templates estimated from CRs by inverting
isolation requirements on jets. Several functions considered -
polynomials, power law, Bernstein polynomials.
arXiv:2202.00487
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022H → γγ 22
Interpretation - SMEFT
▸ ΔΦjj observable is sensitive to CP-
odd coef cients when only
interference terms are considered.
Affect ggF
Affect VBF+VH
arXiv:2202.00487
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
fiH → ZZ* → 4ℓ 23
Introduction
▸ ZZ* decay has a very small BR (~0.03), yet 4ℓ
nal state very clean due to high S/B.
▸ Non resonant ZZ* constitutes the major bkg.
▸ Bkg normalisation estimated from m4l
sidebands for the rst time.
arXiv:2004.03969
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
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fiH → ZZ* → 4ℓ 24
Results
▸ 5 inclusive, 20 differential, and 8 double
differential cross sections measured, including
di-lepton and di-jet masses, momenta,
angular separations, etc.
▸ Statistical uncertainty dominates followed by
background modelling and lepton
measurements.
▸ Results consistent with SM prediction.
Different Z decay
Combined measurement
combinations
arXiv:2004.03969
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022top Yukawa coupling parameter CP mixing angle
tH & tt̄H (H → bb̄) 25
mt
CP Measurement ℒ=−
v { ψ̄tκt [cos(α) + i sin(α)γ5] ψt} H
( p 1⃗ × n)̂ ⋅ ( p 2⃗ × n)̂ b4 =
p1z p2z
b2 =
p 1⃗ p 2⃗ p 1⃗ p 2⃗
“Lep” region
‣ Targets leptonic nal state
‣ >= 1 isolated lepton
ATLAS-CONF-2022-016
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022
fitop Yukawa coupling parameter CP mixing angle
tH & tt̄H (H → γγ) 26
mt
CP Measurement ℒ=−
v { ψ̄tκt [cos(α) + i sin(α)γ5] ψt} H
arXiv:2004.04545
Sagar Addepalli (Brandeis University) DIS 2022 | 3 May 2022Effective Higgs gluon coupling parameter
WW*( → eνμν)jj CP mixing angle 27
gHgg
Analysis Strategy ℒ=− ( κgg cos(α)G a a,μν
μν G + κgg sin(α)G a a,μv
μν G̃ ) H
4
arXiv:2109.13808
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