Equipe ATLAS Projet Hàbb (SM and beyond) LPNHE · 1 Equipe ATLAS Projet Hàbb (SM and beyond) LPNHE Date 2016/05/10 Physique des particules et hadronique

1

Equipe ATLAS

Projet Hàbb (SM and beyond)

LPNHE

Date 2016/05/10

Physique des particules et hadronique

• We have a new particle with m~125 GeV and properties consistent with SM Higgs boson• xsection

• spin/parity• production and decay• couplings

• No evidence of beyond-SM (BSM) physics despite searches in multiple final states

• Picture (almost..) unchanged after 1st year of Run2 (3.2 fb-1 @ 13 TeV)

• Open questions:

• is it really SM(-like)? • production in VH&ttH and decays to bb not yet observed!!

• are there more Higgs bosons?2

What we know about the Higgs after Run1 (7,8 TeV)

(or m2)

• direct measurement of Yukawa coupling to b (yb)

• evidence of coupling to quarks (particularly down-type)

• largest BR (57%) @ 125 GeV

➡ significant contribution to total width

➡ large statistics in searches for rare or very rare processes (SM or BSM)

• ttH: direct measurement of coupling to top (yt~1)

• dark-matter searches in mono-Higgs signatures

• new resonances decaying to H+X (VH, HH, ..)

• VH(bb) provides information on HVV coupling complementary to H→VV and VBF

• BUT: large QCD backgrounds in main production mode (ggF: 87% of total xsec)

• search in cleaner but lower-stat modes: VH (V=W,Z; σ/σH~4%), V→ 0/1/2 leptons, ttH (σ/σH~1%)

3

Relevance of H→bb decays

[GeV]HM80 100 120 140 160 180 200

Hig

gs B

R +

Tot

al U

ncer

t

-410

-310

-210

-110

1

LHC

HIG

GS

XS W

G 2

013

bb

ττ

µµ

cc

gg

γγ γZ

WW

ZZ

The Higgs needle in the LHC haystack

Huge backgrounds:

• high-pT b-jet production:

➡ ~106 larger than H→bb ̅ production

• Drell-Yan/Z → τ+τ−:➡ 105 larger than H → τ+τ− production

0.1 1 1010

-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

108

109

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

108

109

σσσσZZ

σσσσWW

σσσσWH

σσσσVBF

MH=125 GeV

WJS2012

σσσσjet

(ET

jet > 100 GeV)

σσσσjet

(ET

jet > √√√√s/20)

σσσσggH

LHCTevatron

eve

nts

/ s

ec f

or L

= 1

03

3 c

m-2s

-1

σσσσb

σσσσtot

proton - (anti)proton cross sections

σσσσW

σσσσZ

σσσσt

σ

σ

σ

σ

(( ((nb

)) ))

√√√√s (TeV)

{

Exploit vector boson fusion and associated production:

• pp� jjV V � jjH

• pp� tt̄H

• pp�WH, pp� ZH

Gluon Fusion t t̅ H

associated production VBF

3Wednesday, 6 March 2013

(VH)

1 10 100 1000 10000

QBH (6 TeV) QBH (5 TeV)

Q* (4 Tev) Z' SSM (3 TeV)

gluino pair (1.5 TeV) stop pair (0.7 TeV)

A(0.5 TeV, ggF+bbA) ttH ttZ tt

H (VBF) H (ggF)

WH t (t-channel) t (s-channel)

ZZ Z(ll)

W(ln) Minimum bias

9000 370

56 10

46 8.4

4.0 3.9

3.6 3.3

2.4 2.3

2.0 2.5

2.2 2.0

1.7 1.6

1.2

13#TeV#/#8#TeV#inclusive#pp#cross3sec4on#ra4o#

• Integrated luminosity:

• Run1: 20.3 fb-1 ⇒ Run2: 2015: 3.2 fb-1, 2016: ~20 fb-1, end of 2018: ~80-100 fb-1

• Cross-section increase from 8 to 13 TeV depends on energy scale of process

• 125 GeV SM Higgs: ~2.3 (σH = 50.94 pb @ √s=13 TeV)

➡ 2015 statistics ~1/3 of Run1

• (much) larger increase for processes at higher energies

• Run2 sensitivity > Run1 for• first 1fb-1: strongly produced heavy states• 3-5 fb-1: most of the searches, including heavy resonances decaying to Higgs boson

• 10 fb-1 or more: ~all other analyses (some exceptions: VHbb..)➡100 fb-1: 5σ observation of H→bb and ttH?

4

Possibilities offered by Run2

• Local contact: Giovanni MARCHIORI

• Liste des chercheurs participants:

• 4 permanents

• 1 post-doctorant• Paolo FRANCAVILLA, H→bb (SM et BSM), financé par le labex ILP, 100%, Decembre 2013-

Decembre 2016

• 1 post-doc de 2 ans financé par l’ANR (projet Hbb+ttH@LHC), pas encore recruté

5

Composition de l’equipe (I) - staff & post-docs

Name Position HDRfraction du temps de recherche

Other activity @ LPNHE

Gregorio BERNARDI DR Yes 25 % directeur du labo

Giovanni CALDERINI DR Yes 40 % responsable du groupe ATLAS, R&D ATLAS upgrade

Sandro DE CECCO MdC Not yet 50 % responsable du groupe DarkSide

Giovanni MARCHIORI CR Yes 50 % ATLAS “H→γγ” et R&D ATLAS upgrade

• 5 students with diversified topics and sources of funding• good attractiveness of topic

6

Composition de l’equipe (II) - students

Name Year Subject Supervisor Funding source

Time on project Duration

Carlo PANDINI 3

SM VH et A→ZH, H→bb (0 lepton)

G. CALDERINI ED STEP-UP 100 % 10/2013 - 10/2016

Dilia PORTILLO 1

Recherche de matiere noire dans la signature mono-Higgs (H→bb + energie transverse manquante)

S. DE CECCO labex ILP 100 % 10/2015 - 10/2018

Changqiao LI 1 SM VH, H→bb

(0+1 lepton)

GM, cotutelle avec USTC - Chine (Y. LIU)

FCPPL + CSC 100 % 10/2015 - 10/2018

Louis D’ERAMO 0

H→bb (0 lepton): SM VH et nouvelles resonances

G. CALDERINI ENS 100 % 10/2016 - 10/2019

Ilaria LUISE 0 SM H→bb (VH 1 lepton + ttH)

G. BERNARDI, G. MARCHIORI ED STEP-UP 100 % 10/2016 -

10/2019

7

Students technical work for ATLAS authorship

Name Qualification task for ATLAS authorship Status of qualification

Carlo PANDINI Optimisation of bank of patterns for FTK qualified

Dilia PORTILLO Improvement of MET significance calculation started

Changqiao LI Measurement of b-tagging efficiency of calo and track jets qualified

Louis D’ERAMO Equalisation of FTK pattern performance in barrel-endcap transition started

Ilaria LUISE Electron identification optimisation/efficiency measurement will start in October

• qualification work related to improvements related to physics analysis for the thesis or on R&D activities in which the LPNHE group is strongly involved

• important fraction of time during 1st year of PhD• students qualified as ATLAS authors without delay so far

8

List of scientific activities (present & recent past)• Performance in Run2 (ongoing)

• b-tagging efficiency measurement, data/MC scale factor efficiency extraction (CL + GM)• missing ET (MET) reconstruction: MET definition and estimation of its systematic uncertainties used

in ATLAS Run2 (PF), improvement of MET significance calculation (DP + SdC)

• Physics analysis w/ Run1 data (finished) • search for SM VH(125), H(125)→bb with Run1 data (PF, CP, GC, GM + all staff) - published in JHEP

• selection/categories: leading analysis effort in 0l; x-check of 1l and 2l selection (8 TeV)• systematic uncertainties: study of uncertainties related to modelling of diboson bkg,

for 0/1/2l (8 TeV)• statistical analysis (fit): compatibility studies between different channels / flavours; study of

nuisance parameter (NP) pulls (8 TeV); combination with previous 7 TeV results; combination with other Higgs-related ATLAS results

• Physics analysis w/ Run2 data (ongoing) • preparation of software infrastructure (CxAODFramework) for analysis of new (Run2) ATLAS data

format; framework used by at least a dozen analyses (PF: coordinator; contributions from CP, GM, CL)• search for heavy VH resonances (PF) - CONF note in 2015, paper in preparation

• selection criteria definition• data/MC comparison• systematic uncertainties implementation in final fit

9

List of scientific activities (present & recent past)• Physics analysis w/ Run2 data (ongoing)

• search for pseudo scalar Higgs boson A→Zh(125), h(125)→bb (PF, CP, GC, CL + all staff) - CONF note in 2016• selection/categories (0l): optimisation of selection criteria and definition of transition region between

resolved/merged regime (2 resolved jets from h→bb or one large-R jet from boosted Higgs)• systematic uncertainties (0/1/2l): study of uncertainties related to modelling of V+jet, tt bkg• backgrounds: data-driven estimation of QCD background• statistical analysis: implementation of final fit, x-checks (pulls, correlations NP among various signal/

control regions)

• search for SM VH(125), H(125)→bb (PF, CP, GM + all staff)• prospect studies at 13 TeV with PDF reweighing of 8 TeV MC samples and Run1-like analysis• preparation of signal and diboson bkg MC samples (for all ATLAS VH analyses): validation of NLO

MC generators for qq→ZH and SM diboson• towards ICHEP:

• systematic uncertainties: study of uncertainties related to modelling of signal and VV bkg• statistical analysis: x-checks, combination of various channels, combination with Run1• constraints on BSM physics (reinterpretation in EFT context => preparation of signal MC samples)

• search for dark matter in mono-Higgs signatures, with H→bb (DP, SdC) - CONF note in 2016• started work on optimisation of categories and of discriminating variable for signal/bkg separation• started to contribute to working group activities/discussions

10

Responsibilities• Coordination of ATLAS Hbb analysis working group: PF, 10/2014-10/2015

• Coordination of software framework development: PF, 10/2014-10/2015

• Contacts between ATLAS Hbb and 3 other ATLAS physics/performance groups:• MET: PF• e/γ: GM• ATLAS Higgs combination: PF

• Editing of ATLAS papers (1), CONF notes (2), public notes (1), supporting notes (2)• main supporting note (ATL-COM-PHYS-2014-051) of SM VH Run1 paper (JHEP01(2015)069): PF• VH resonance search w/ 2015 data, CONF note for 2015 CERN EOYE (ATLAS-CONF-2015-074)

and paper (in preparation): PF• A→Zh search w/ 2015 data:

• CONF note for Moriond 2016 (ATLAS-CONF-2016-015): PF• supporting note on signal and background modelling (ATL-COM-PHYS-2015-1474): CP

• public note on MET expected performance in Run2 (ATL-PHYS-PUB-2015-023): PF• Higgs@LHC xsection working group - report 4, section on template cross sections: PF

11

Highlights: performance studies for/with Run2 data• MET systematic uncertainties before start of

2015 data taking

➡pre-recommendations on MET systematic uncertainties to all analyses of final states w/ MET

• b-tagging efficiency calibration with 2015 data

➡ data/MC b-tagging efficiency scale factors for different cone sizes and jet algorithms (calo/track-based) used in ATLAS

ATL-PHYS-PUB-2015-023

Visite de Patrice Verdier - 10/05/2016

note in preparation

ATLAS Work in progress

Track jets, R=0.2, εb=77%

12

Highlights: SM VH analysis w/ Run1 data

• Weak hint of signal despite fair sensitivity (highest single-experiment expected sensitivity to Hbb at hadron colliders):

➡ observed (expected) significance = 1.4σ (2.6σ)

➡ observed (expected) μ = 0.5±0.4 (1.0±0.4)

• On the other hand, ~1σ excess in ttH(bb) => VH+ttH: 1.7σ (2.7 σ) significance, μ=0.63 ± 0.4

JHEP01(2015)069

• Search for boosted VH resonances→ννbb̄, lνbb̄, llbb̄ (ATLAS CONF-2015-074)➡Exclude W’, Z’ with m<~1.5 TeV in heavy

vector triplet models

• Search for an additional pseudoscalar Higgs boson A, as predicted in 2HDM (ATLAS CONF-2016-015)➡σ<17fb - 4 pb for 220<mA<2200 GeV ➡Sensitivity better than Run1 at mA>800 GeV

13

Highlights: BSM Run2 searches

limits assuming pure gluon fusion production

• Search for H(125)→bb̄ in association with dark matter(→MET) (ATLAS CONF-2016-019)• limits set on benchmark models e.g: vector

mediator Z’➡exclude Z’ masses up to several hundreds of

GeV for χ relatively light

Backup

14

• We have found a Higgs boson with mass~125 GeV and properties consistent with the SM• xsection: μ=(σ*BR)/(σ*BR)SM=1.09+0.11-0.10

• spin/parity: JP=0+ favoured at >99.9% CL• production and decay: two main production

modes (gluon fusion, W/Z fusion) and decays to dibosons (γγ, ZZ*, WW*) as well as to ττ established at >5σ• production in VH&ttH and decays to bb

not yet observed!!• couplings (assuming no BSM particles in

loops and BR(inv)=0) measured to: ~10% (W,Z); 14% (t,τ); 21% (b)

• We have no evidence of beyond-SM (BSM) physics despite searches in multiple final states

• Picture (almost..) unchanged after 1st year of Run2 (3.2 fb-1 @ 13 TeV)

• Open questions: is it really SM(-like)? Are there more Higgs bosons?15

What we know about the Higgs after Run1 (7,8 TeV)

(or m2)

16

Highlights: performance studies for/with Run2 data• MET: study of systematic uncertainties on

MET before start of 2015 data taking• from comparison of MC Z→μμ samples

• different event generators• different running conditions• different detector models• full vs parametrised simulation

➡ pre-recommendations on MET uncertainties to all analyses of final states w/ MET

• b-tagging: calibration with 2015 data of the efficiency of the b-tagging algorithm• use tag & probe method on tt dilepton (eμ)

events• subtract small non-tt and non-b contamination

using MC information➡ data/MC efficiency scale factors for

different cone sizes and jet algorithms (calo/track-based) used in ATLAS

ATL-PHYS-PUB-2015-023

Visite de Patrice Verdier - 10/05/2016

note in preparation

ATLAS Work in progress

Track jets, R=0.2, εb=77%

• Search for heavy BSM particles coupled to Higgs and vector bosons• H→bb̄ reconstructed as boosted large-R calorimeter jet J (pT>250 GeV)

matched to at least one b-tagged jet of tracks in the tracker; mJ~mH

• 1l and 2l events selected with isol. leptons, pT>20 − 24 GeV, 0l with ETmiss> 80 GeV • Fit to mVH (mT,VH) in signal regions + control regions to estimate W/Z+jets and tt̄ bkg

(mJ sidebands; Nb-tag=1; ttbar: e-mu 2l CR)

17

Highlights: boosted VH resonance→ννbb̄, lνbb̄, llbb̄ATLAS CONF-2015-074

➡Exclude W’, Z’ with m<~1.5 TeV in HVT models

signal region ννbb̄

• Search for an additional pseudoscalar boson A, as predicted in 2HDM

• narrow width, mA = 220-2000 GeV, produced in gluon fusion or with bb̄

• Use jet substructure techniques for large pT(H) (i.e. large A masses) to reconstruct Higgs boson and suppress QCD background (resolved|merged analysis: pT<|>500 GeV)

• Similar strategy as previous analysis• Dominant uncertainty: stat (80%). Dominant syst: large/small-R JES, JER; mass scale; b-

tagging efficiency & mistag

18

Highlights: A→ZH(125)→ννbb, llbb (l=e,μ)ATLAS CONF-2016-015

limits assuming pure gluon fusion production

➡σ<17fb-4 pb for 220<mA<2200 GeV ➡Sensitivity better than Run1 at mA>800 GeV

Z→νν

19

Highlights: H(125) in association with dark matterATLAS CONF-2016-019

“simplified” vector model: DM (χ) +

vector mediator (Z’)

2HDM inspired: include also

pseudo scalar Higgs boson (A)

• Two benchmark models with vector mediators considered

• Search H(125) peak in di-jet (or large-R-jet) mass distribution of events with large MET and 0 e, μ

➡exclude Z’ masses up to several hundreds of GeV for χ relatively light

20

Highlights: H(125) in association with dark matter

ATLAS CONF-2016-019

• Comparison between bb and yy

ATLAS CONF-2016-011

21

ttH• 1-2σ excess wrt SM seen by ATLAS and CMS in Run1

• Preliminary 13 TeV results by CMS for ttH in all major decay channels: γγ, multi-leptons (WW/ZZ/ττ), bb

H → γγ,tt → 0 & 1 leptons

ttH → multi-leptons 2 same charge / 3 leptons

μ=3.8+4.5-3.6 μ=0.6+1.4-1.1 μ=-2.0+1.8-1.8

H → bbtt → 1 & 2 leptons

➡Naive combination: μ=0.1±0.9

22

Collaborations• ANR (Hbb+ttH@LHC) with LAL, CPPM, IRFU

• strong interaction with LAL group, mostly (so far) on VH(bb) and A—>ZH(bb), VH(bb) resonances in 0 lepton

• FCPPL project with USTC group• joint PhD program