HH prospects for HL(HE)-LHC, Yellow Report results

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02/23/12 1 HH prospects for HL(HE)-LHC, Yellow Report results Elisabeth Petit (LPSC/CPPM) on behalf of the ATLAS, CMS and theory communities HL/HE-LHC Physics Workshop: final jamboree 1 st of March 2019

Transcript of HH prospects for HL(HE)-LHC, Yellow Report results

Page 1: HH prospects for HL(HE)-LHC, Yellow Report results

02/23/12 1

HH prospects for HL(HE)-LHC, Yellow Report results

Elisabeth Petit (LPSC/CPPM)

on behalf of the ATLAS, CMS and theory communities

HL/HE-LHC Physics Workshop: final jamboree

1st of March 2019

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HH production and decay

yt

yt

yt

λHHH

Non-resonant production: rare process of the SM– destructive interference– σ(gg→HH) ≈ 0.1%*σ(gg→H)

– BSM contributions can modify the Higgs boson coupling parameters and modify the HH cross section:define

NB: search for Resonant production not addressed here– HH→bbbb searches by ATLAS and CMS

All plots and results from the YR document (1902.00134)

κλ=chhh=λHHH /λHHHSM

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HH production cross-section (1)

SM calculation– ggF: state of the art NNLO

calculation with finite mt effects at NLO

● -8% wrt YR4, used in previous projections

– other production modes: NLO with full m

t-dependence

Higgs self-coupling variations with full m

t-dependence at NLO

– LO to NLO K-factors vary from 1.6 to 2.2!– m

HH differential cross-sections

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HH production cross-section (2)

BSM model: Non-linear EFT Cross-sections and m

HH at NLO QCD for

some selected benchmark points

Available data files to reconstruct the full NLO resultfor any values of the 5 modifying parameters

κt

κt

κt

κλ

κλ

ctt

cggh

cgghh

LO

κt

κt

cggh

κt

NLO

Benchmark 8a

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Experimental perspective, introduction

Either extrapolations from Run-2 analyses, or dedicated studies with smeared/parametric detector response, corresponding to pile-up of 200

– summary of channels/methods:

Systematic uncertainties: common agreement between ATLAS and CMS– performance uncertainties scaled by 0.5 to 1– theoretical uncertainties divided by 2– MC stat uncertainties neglected

ATLAS CMS

extrapolation parametric

extrapolation parametric

smearing parametric

parametric

parametric

bbbbLargest BR ☺

Large multijet and tt bkg ☹

bbττSizeable BR ☺

Relatively small bkg ☺

bbγγSmall BR ☹

Good diphoton resolution ☺Relatively small bkg ☺

bbVV(→lνlν)lνlν))

Large BR ☺Large bkg ☹

bbZZ(→4l)

Very small BR ☹Very small bkg ☺

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Experimental perspective, methods

General analysis strategy: – candidate mass consistent with SM Higgs boson– multivariate methods to reject background– use m

HH when possible

A few examples:

NB: some inputs or systematics with large unknowns– multijet bkg modelling for HH→bbbb– τ fake-rate– …

⇒ room for improvement

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Experimental perspective, results

Expected significance (SM) with and without systematics at HL-LHC

– 4σ expected with ATLAS+CMS!

Measurement of μ (SM signal injected):– ~25% (30%) without (with) systematics– μ = 0 (no SM HH signal) excluded

at 95% CL

Measurement of κλ:

– 68% CI of 50%– 2nd minimum excluded at 99.4% CL

thanks to the mHH

shape information

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signal background

HL-LHC, ‘alternative’ methods

HH→bbWW(→lνlν):lνlν):):Introduce two new variables

– Topness (T): degree of consistency with di-lepton tt production

– Higgsness (H): compatibility with Higgs and W masses

Could enhance the significance from 0.6 to 1.4-3.0σ

– effect of pile-up on those variables?

HH→bbγγ:Bayesian optimisation and BDT compared to cut-based

No pile-up included, but shows the potential of sophisticated techniques: could achieve up to 4σ

– illustrated in the YR with ATLAS and CMS using MVA techniques

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HE-LHC extrapolation of direct measurements

Extrapolation of ATLAS HL-LHC results to HE-LHC– only scale cross-section to 27 TeV (*4) and luminosity to 15 ab-1 (*5),

no systematic uncertainties

– bbττ channel: significance: 10.7σ, precision on κλ: 20%

– bbγγ channel: significance: 7.1σ, precision on κλ: 40%

● pessimistic because analysis not optimised for measurement of κλ

Phenomenology study: 15% precision on κλ

● realistic detector performance● no pile-up considered (μ=800-1000)● interesting categorisation of b-jets

κλ could be measured with a 68% CI

of 10 to 20 %– without uncertainties– effect of pile-up?– contribution of ggF+jets?

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κt κ

λκλ

κt

κt

κt

Indirect probes via single-Higgs (1)

Single-Higgs production: Higgs self-interaction only via one-loop corrections (ie two loop-level for ggF)

κλ-dependent corrections to the tree-level cross-sections, depends on:

– production mode → mainly ttH, tH, VH– kinematics properties of the event

Method applied to ttH(→γγ) differential cross-section measurement:

68% CI: -1.9 < κλ < 5.3 if only κ

λ varied

First test with experimental “data”, more channels to be added

68% CI: -1.9 < κλ < 5.3

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Indirect probes via single-Higgs (2)

Global fits of single-Higgs inclusive couplings and ttH differential measurements

– for HL-LHC and HE-LHC

Different BSM scenarios– only κ

λ can be varied (dotted line)

– EFT framework (solid line) Different scenarios for systematics (bands)

Biggest impact from diff. cross-section Improvement of di-Higgs direct

measurements for variations of κλ only

HL-LHC: 68% CI (optimistic systematics): – -0.1 < κ

λ < 2.3 if only κ

λ varied

– -2 < κλ < 3.9 for global fit

NB: More on Global analyses with EFT in F. Riva’s talk

68% CI: -1.9 < κλ < 5.3

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h=

cos(β−α)

tan(β)+sin (β−α)

cos(β-α) = -0.45) = -0.45

κfh=3

κfh=4

κfh=5

Implications

Flavour physics: 2HDM model where flavor symmetry broken at the electroweak scale

– κfh = enhancement of Higgs

Yukawa couplings to fermions

Enhancement of the di-Higgs production + change of m

HH shape

with interference

EWK phase transition: – 1st order possible with additional

bosons interacting with the Higgs ● discovery possible at HL-LHC for

m < 500 GeV

– modification of κλ visible at

HL-LHC or HE-LHC

=κλ

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Conclusions

State-of-the-art computations of the cross-sections and mHH

available

State-of-the art experimental studies on direct measurements– coherent results by ATLAS and CMS– went from ~2σ last year to a combined significance of 4σ!

● first real measurements possible, eg precision on κλ: 50%

– much room for improvement

Nice developments on indirect constrains

– single-Higgs differential cross-sections, global fits

Estimates of sensitivity at HE-LHC– experimental and phenomenology

YR on arxiv: 1902.00134

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Back-up

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Higgs potential

Higgs potential:

Approximation around the v.e.v:

λ known from v.e.v and Higgs mass:

BSM effect could change λ define ⇒

V (Φ)≈λ v2h+λ v h3+

14

λ h4

mass term self-coupling terms

V (Φ)=12μ

2+

14

λΦ4

λ=mH

2

2⋅v2≈0.13

κλ=chhh=λHHH

λHHHSM

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TDAQ TDR

HH→bbbb (ATLAS)

Extrapolation from Run-2 analysis– fit of m

4j distribution

– pT

jet > 40 GeV, different thresholds tested

Systematics– dominated by multijet data-driven model– conservative assumption:

Run-2 systematics used

Significance: 1.4/0.61σ without/with syst

Run-2

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HH→bbbb (CMS)

SM sigmal + BSM benchmark points Resolved and boosted b-jets

– boosted topologies more sensitive to BSM scenarios where high m

HH is enhanced

Resolved: – p

T > 45 GeV, different thresholds tested

– BDT against multijet bkg + tt and single-Higgs Small uncertainty considered for multijet background

Significance:1.2σ wo/syst0.95σ w/ syst

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HH→bbττ (ATLAS)

Extrapolation from Run-2 analysis Three signal regions:

– τlep

τhad

(Single Lepton Trigger)

– τlep

τhad

(Lepton Tau Trigger)

– τhad

τhad

(Single Tau Trigger and Di-Tau Trigger)

BDT output used as final discriminant– binning adapted to higher statistics

Limit on κλ: LTT category not included and

dedicated BDT trained on κλ = 20

Different assumptions for systematics

Significance: 2.5/2.1σ without/with syst

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HH→bbττ (CMS)

3 categories: μτh, eτ

h, τ

h

Use of a neural network– 27 basic + 21 reconstructed + 4 global features– deep learning techniques, with optimal data preprocessing, study of the

activation functions, and data augmentation

Simultaneous fit of the NN output for the 3 decay channels– discriminant binned per decay channel via adaptive binning

Significance: 1.6/1.4σ without/with syst

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HH→bbγγ (ATLAS)

Dedicated analysis with smearing functions: upgraded detector geometry and performance functions

– mγγ

resolution ~ 1.6 GeV

Dedicated BDT trained to remove continuum background and main single-Higgs background (ttH)

Limit on κλ: use of the m

bbγγ distribution for

events with 123 < mγγ

< 127 GeV

Systematics: very small impact in general

Significance: 2.1/2.0σ without/with syst

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250-350 GeV

350-480 GeV

> 480 GeV

Dedicated BDT to reject ttH– 75% reduction for 90% signal efficiency

Classification of events based on MX = m

jjγγ - m

γγ - m

jj + 250 GeV into low

and high mass categories MVA event categorisation BDT to separate background and HH signal into

medium (MP) and high (HP) purity

Fit of mγγ

x mjj

Significance: 1.8/1.8σ without/with syst– difference with ATLAS partly due to m

γγ resolution

HH→bbγγ (CMS)

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HH→bbVV(lνlν)lνlν)), CMS only

Optimised on WW, but ZZ signal included for the results Large irreducible backgrounds: tt, DY Neural Network discriminant

– 9 input angular and mass variables– signal extracted from the NN ouput (3 categories ee, μμ, eμ)

Results: 0.6σ significance

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HH→bbZZ(4l), CMS only

Very rare but clean final state, yet unexplored at the LHC Powerful H→4ℓ signature ⇒ single Higgs dominant background

Select events with m4ℓ compatible with mH

Counting experiment with events around mH

~1 signal event after selection– S/B ~0.1

Results: 0.4σ significance

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Combined results (ATLAS+CMS)

Comparison of negative log-likelihood ratios:

Difference on 2nd minimum mainly from the bbγγ channel: 3 categories of m

HH (especially a low-m

HH one) to remove the degeneracy around κ

λ=6

(while this low-mHH

category has no effect around 1)

CMS slightly better below 1: bbbb + other smaller channels

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Combined results (ATLAS+CMS)

68% CI, channel by channel Dashed line = no ATLAS analysis, using value from CMS (as for Higgs

couplings)

κλ measured with a precision of 50%