Latest results on the SM iggs boson in the WW decay channel using the ATLAS detector ATLAS-CONF-6- C. Bertella C. Bertella Second China LC Physics Workshop: CLCP 6 7-December 6
WW lνlν WW channel well-suited to exploring rare production modes and searching at highness Large branching ratio: % Good S/B from a clean dilepton signature iggs BR + Total Uncert - - -3 ττ cc µµ bb γγ gg Zγ WW -4 8 4 6 8 M [GeV] LC IGGS XS WG 3 ZZ /μ + /μ - iggs boson couplings measurement essential SM consistency test Search for rare production modes Provide a template for searching additional states at high mass More detail in Weimin SONG s talk on Sunday C. Bertella 7-December-6
WW lνlν @ RunI σ(pp +X) [pb] - pp (NNLO+NNLL QCD + NLO EW) pp qq (NNLO QCD + NLO EW) pp W (NNLO QCD + NLO EW) pp Z (NNLO QCD + NLO EW) pp bb (NNLO and NLO QCD) pp tt (NLO QCD) = 5 GeV MSTW8 7 8 9 3 4 s [TeV] M LC IGGS XS WG 4 Events / bin 4 ATLAS Confirmed: 5.8 σ µ ggf =. 6 Obs ± stat - Exp ± syst s =8TeV,.3fb Evidence: VBF 3. ggf σ µ VBF =.7 Top DY WW VV Misid Phys. Rev. D 9, 6 (5) iggs XS increases by factor.3 3 BDT bin number Background typically increases by factor.9 (3.3 for tt) Significance scales as S/ B.6 Sensitivity for /fb @ 3 TeV corresponds to full Run dataset Search:.5 σ µ V =3 JEP8 (5) 37 C. Bertella 7-December-6 3
WW lνlν: Signal Topology iggs boson final state: WW lνlν leptons from iggs tend to have small angular separation due to the spin ν W + W ν Final state can not be fully reconstructed due to the presence of neutrinos l + l A transverse mass m T can be calculated without the unknown longitudinal neutrino momenta VBF channel W channel Production modes investigated @ 3 TeV with 5.8 fb - : VBF and W Direct access to the iggs boson couplings to gauge bosons leptons E miss T forward jets leptons Large E miss T Low jet multiplicity C. Bertella 7-December-6 4
VBF WW lνlν VBF channel Electro-weak process with small theoretical uncertainty No color flow between the two partons, unique topology of two energetic jets with large rapidity separation Analysis Strategy: Only the different flavour channels: eµ, µe Selection criteria are applied on: m ll, m ττ, lepton and jet centrality Multivariate technique (BoostDecisionTree) is used to separate the signal from the main background processes BDT distribution used to extract the signal strength Why a MVA? Allows to combine several discriminating variables into one final discriminant > Better separation What is Decision Tree? Consecutive set of questions (nodes) Why Boosting? Misclassified events are weighted higher so that future learners concentrate on these Bonus C. Bertella 7-December-6 5
Main backgrounds: ggf estimated with MC simulation WW: estimated with MC simulation Event Selection Top and Z ττ: shape form MC simulation, NF estimated with data W+jets: data-driven from events with one lepton satisfying only loose but failing tight ID criteria; fake factors measured in a di-jet sample Cuts SR Top CR Z ττ Njets > > > b-jets mττ <66. GeV <66. GeV mττ-mz <5 GeV reject Top/select reject/select Z+jet mll - - <8 GeV jet OLV CJV MVA>-.8 lep C. Bertella 7-December-6 6
MVA Analysis The analysis uses a MVA to classify an event as signal- or background-like: Signal: VBF Events / GeV 6 5 4 ATLAS Preliminary s = 3 TeV, 5.8 fb WW eµ+µe - Data W+jets Top WW ggf VBF VBF SM (sys) Z+jets Other VV Other iggs Bkg: Top,VV, Z+jets and ggf 3 mll The training is performed after N b-jet = 3 4 5 6 7 8 9 [GeV] m ll It uses information related to the production and decay topology Events / 6-5 ATLAS Preliminary s = 3 TeV, 5.8 fb WW eµ+µe Data W+jets Top WW ggf VBF VBF SM (sys) Z+jets Other VV Other iggs Leptons: m ll, Δφ ll,m T 4 3 Δyjj Jets: m jj, Δy jj Jets/Leptons: η centrality, M lj, p T tot 3 4 5 6 7 8 9 y jj C. Bertella 7-December-6 7
BDT Modelling BDT modelling has been checked in the Top and Z ττ CRs and SR Good data/mc region in all the regions Events /. 8 6 ATLAS Preliminary s = 3 TeV, 5.8 fb WW eµ+µe VBF Top-quark CR - Data SM (sys) W+jets Z+jets Top Other VV WW Other iggs ggf VBF Important shape different between signal and background in SR 4.8.6.4...4.6.8 BDT score Events /.3 8 ATLAS Preliminary s = 3 TeV, 5.8 fb WW eµ+µe - Data W+jets Top WW ggf VBF VBF SM (sys) Z+jets Other VV Other iggs Events /.3 5 45 4 35 3 ATLAS s = 3 TeV, 5.8 fb WW eµ+µe VBF Z τ τ CR Preliminary - Data SM (sys) W+jets Z+jets Top Other VV WW Other iggs ggf VBF 6 5 4 5 5.8.6.4...4.6.8 BDT score.8.6.4...4.6.8 BDT score C. Bertella 7-December-6 8
W channel W WWW lνlνlνlν Test of the W production Direct access to the iggs boson couplings to W boson Analysis Strategy miss Final state: 3 leptons (e/µ) with charge ± and E T Origin of lepton with unique charge: iggs decay W 3l3ν SFOS + SFOS Cut-Based Analysis: SFOS Selection criteria are applied on: m ll, m lll, E T miss and ΔR signal regions: Z-dominated: at least one Z-candidate, 75% of the signal Z-depleted: no Z-candidate, 5% of the signal C. Bertella 7-December-6 Nomenclature l : lepton with unique charge l : lepton closest in R to l o l : remaining one SF: Same Flavour OS:Opposite Sign 9
Event Selection: Signal regions Category Z-dominated SR Z-depleted SR SFOS pair no SFOS pair Preselection Three isolated leptons (p T >5 GeV) total charge = ± lepton matches to the trigger Background Rejection N jet apple, N b-jet = reject Top ET miss > 5 GeV reject Z+jet reject WZ, ZZ and Z+jets m`+` m Z > 5 GeV Z/! ee veto reject WZ/Wγ m max `+` < GeV reject non prompt leptons m min `+` > GeV m min `+` > 6GeV! WW! ` ` topology R`` <. iggs Spin Main backgrounds: VV: WZ/Wγ, ZZ, Zγ VVV Top: mainly ttbar Z+jets Events / GeV 4 data Bkg (sys stat) ATLAS Preliminary VV Z +jets - s = 3 TeV, Ldt = 5.8 fb VVV Other iggs Top W 3 8 6 4 W WWW lνlνlν Z-dominated SR Z-dominated dominated by diboson with a jet faking a lepton Events / GeV 3 5 5 ATLAS Preliminary s = 3 TeV, Ldt = 5.8 fb W WWW lνlνlν Z-depleted SR - data Bkg (sys stat) VV Z +jets VVV Other iggs Top W 3 Z-depleted dominated by Top 5 5 5 5 3 [GeV] C. Bertella 7-December-6 m l l 5 5 5 3 m l l [GeV]
Event Selection: Control regions Process Reference SR Cut Top quark WZ/Wγ Z-depleted Z-dominated at least jet one b-jet one lepton without an isolation requirement SFOS pair with mll -mz <5 GeV Events / GeV 9 8 7 6 5 4 ATLAS Preliminary s = 3 TeV, Ldt = 5.8 fb W WWW lνlνlν Z-depleted top-quark CR - data Bkg (sys stat) VV Z +jets VVV Other iggs Top W Top CR Z-depleted Events / GeV 4 data Bkg (sys stat) ATLAS Preliminary VV Z +jets - s = 3 TeV, Ldt = 5.8 fb VVV Other iggs Top W 8 6 W WWW lνlνlν WZ/Wγ CR WZ/Wγ CR 3 4 5 5 5 3 4 6 8 4 6 8 m l l [GeV] m l l [GeV] Additional CRs defined for for Zγ, Z+jet used to extract Normalisation Factors C. Bertella 7-December-6
Results Category SR SR Top CR Z+jets CR VBF 9.3 ± 3.6 5. ±.8.7 ±.6. ±.4 Other iggs 8. ± 4..7 ±.4. ±.. ±. WW 3. ± 8..4 ±..4 ±.5. ±.9 Other VV 6.6 ±.6. ±.. ±..8 ±. Top quark 4. ± 7.6.9 ±.7 86 ± 7 3.6 ±.6 W +jets 4.3 ± 9.. ±.7 8.8 ± 4. 4.4 ±. Z+jets 8. ± 9.9. ±..3 ±. 7 ± Total background 5 ± 3 3.5 ±.9 99 ± 7 38.8 ± 9.8 Observed 9 4 SR with bins CRs with bin µvbf=.7 +. -.9 Events / bin 35 3 5 5 5 ATLAS Preliminary s = 3 TeV, 5.8 fb Top CR Z ττ CR - WW eµ+µe (VBF) σvbf BR=.4 +.9 -.7 pb SR -.8 < BDT <.7 Data SM (sys) W+jets Z+jets Top Other VV WW Other iggs ggf VBF Rescaled y-axis for SR 5 5 SR BDT >.7 Fit regions Category Z-dominated Z-depleted W.6 ±.. ±.8 Other iggs. ±.. ±. VV 3. ±.6.3 ±.4 VVV.5 ±..4 ±. Top quark 3.4 ±.9.8 ±.8 Z+jets. ±.6. ±. Total background 9. ±.4 5.6 ±.5 Observed 9 9 SR with bin 6 CRs with bin µw=3. +4.4-4. C. Bertella 7-December-6 Events / bin 8 7 6 5 4 3 ATLAS Preliminary CRa s = 3 TeV, 5.8 fb W WWW lνlνlν CRb CRc e-fake σw BR=.9 +.3 -. pb - CRc CRd CRe µ-fake data SM (sys) VV Z+jets VVV Top Other iggs W Rescaled y-axis for SRs 5 5 SR Z-dominated SR Z-depleted Fit regions
Systematic Uncertainties Leading sources of uncertainties on the measured signal strength, µ VBF and µ W Analyses limited by the data statistic Important impact of the MC statistic Source µ W /µ W [%] Source µ VBF /µ VBF [%] Statistical +6 / -5 Fake factor, sample composition +8 / -5 MC statistical ±5 VBF generator +4 / -5 WW generator + / -7 QCD scale for ggf signal for N jet 3 +8 / -7 Jet energy resolution +8 / -7 b-tagging +8 / -6 Pile-up +8 / -6 QCD scale for ggf signal for N jet ±6 JES flavour composition +6 / -4 WW renormalisation scale ±5 Total systematic +33 / -6 Total uncertainty +7 / -5 Statistical + / - MC statistical +6 / -7 Pile-up + / -6 Jet energy resolution + / -3 Top-quark generator +7 / - b-tagging + / - Top-quark PS/UE +7 / -8 JES flavour comp. +8 / -5 JES intercalibration +7 / -6 WZ/W generator +7 / -6 Top-quark QCD scales +6 / -7 WZ/W resum. scale ±5 Total systematic +7 / -8 Total uncertainty +4 / -3 C. Bertella 7-December-6 3
Summary VBF and W WW lνlν analyses performed using the 5.8 fb - of 5+6 data The observed (expected) signal significance at m = 5. GeV is.9σ (.σ) for VBF and.77σ (.4σ) for W The signal strengths are µ VBF =.7 +. -.9 and µ W =3. +4.4-4. Corresponding cross section times branching ratio are σ VBF BR=.4 +.9 -.7 pb > 95% CL upper limit 3. pb σ W BR=.9 +.3 -. pb > 95% CL upper limit 3.3 pb Future steps: Analyse the full 5+6 dataset ~36/fb Perform the inclusive XS measurement of gluon fusion and VBF Working on fiducial and differential measurements C. Bertella 7-December-6 4
Thanks for the attention!
MC Samples Monte Carlo generators used to model the signal and background processes with the corresponding product of cross section and the branching ratio for the iggs boson production ar 3 TeV Mode MC generator B (pb) ggf Powheg [3,4,5]+Pythia 8[9].38 +.58.77 VBF Powheg +Pythia 8.88 ±. W Powheg +Pythia 8(MiNLO[5]).93 ±.7 Z Powheg +Pythia 8(MiNLO).89 +.8.7 Background MC generator q q/g!````, ` ``, ` ` Sherpa [6] gg!````, ` ` Sherpa EW ````, ` ``, ` ` Sherpa q q/g!ww,z ( ) Z ( )!` ` Powheg +Pythia 8 t t, tw Powheg +Pythia 6[38] t tw/z, tz MadGraph 5[7] W, Z Sherpa Z+jets MadGraph 5 VBF q q!(z! )q q Sherpa WWW, WWZ, ZZW, ZZZ Sherpa C. Bertella 7-December-6 6
Main backgrounds: Event Selection ggf estimated with MC simulation WW: estimated with MC simulation Top and Z ττ: shape form MC simulation, NF estimated with data W+jets: data-driven from events with one lepton satisfying only loose but failing tight ID criteria; fake factors measured in a di-jet sample Preselection Signal region Z! CR Top-quark CR Two isolated leptons (` = e, µ) with opposite charge p lead T > 5GeV (plead T > GeV for muons in 5), psublead T > 5GeV m`` > GeV, N jet N b-jet = N b-jet = N b-jet = A BDT is trained at this level. Eight discriminant variables are used: ``, m``, m T, y jj, m jj, p tot T, P`,j m`j, and centrality ` Selection m < 66.GeV m m Z < 5GeV m`` < 8GeV OLV applied, CJV applied, BDT >.8 SR:.8 < BDT apple.7 SR:.7 < BDT apple lep jet C. Bertella 7-December-6 7
MVA Analysis The analysis uses a BDT to classify an event as signal- or background-like: Events / GeV 6 5 4 3 ATLAS Preliminary s = 3 TeV, 5.8 fb WW eµ+µe - Data W+jets Top WW ggf VBF VBF SM (sys) Z+jets Other VV Other iggs Signal: VBF Bkg: Top,VV, Z+jets and ggf 3 4 5 6 7 8 9 [GeV] m ll The training is performed after N b-jet = It uses information related to the production and decay topology Leptons: m ll, Δφ ll,m T Jets: m jj, Δy jj Jets/Leptons: η centrality, M lj, p T tot C. Bertella 7-December-6 8
MVA Analysis The analysis uses a BDT to classify an event as signal- or background-like: Signal: VBF Bkg: Top,VV, Z+jets and ggf The training is performed after N b-jet = It uses information related to the production and decay topology Events / 6-5 ATLAS Preliminary s = 3 TeV, 5.8 fb WW eµ+µe Data W+jets Top WW ggf VBF VBF SM (sys) Z+jets Other VV Other iggs 4 Leptons: m ll, Δφ ll,m T 3 Jets: m jj, Δy jj Jets/Leptons: η centrality, M lj, p T tot 3 4 5 6 7 8 9 y jj C. Bertella 7-December-6 9
MVA Analysis The analysis uses a BDT to classify an event as signal- or background-like: Signal: VBF Bkg: Top,VV, Z+jets and ggf The training is performed after N b-jet = It uses information related to the production and decay topology Leptons: m ll, Δφ ll,m T Jets: m jj, Δy jj Jets/Leptons: η centrality, M lj, p T tot C. Bertella 7-December-6
BDT Modelling mt m ATLAS Preliminary mjj Yjj Ô s = 3 TeV, 5.8 fb ptot T m 5 5 8 3 mt 5 5 5 5 4 6 4 6 mjj Yjj 5.5.5.5 3 5 4 6 4 4 3 3 4 3 3 5 5 3 5.5.5.5.5 5 5 5.5 6 3 4 6 4 6 3 4 5 6.6 3 3...9.8.7.8 5 5 7.6 7 4 6 3 4 5 6...9.8.7 4 6 3 4 5 6 8 8 4 4 4 4 4 q 5...4.4.6.6.6.8.8.8 5 5 3.5.5.5.5.5.5.5.5.5.5 8 6 4 4 6 8.5 4 6 5 4 4 3 3 3 3 4.5.5 4 6.4.6.8 3 4 5 6 5.5.5.5.5.5 5 5 5 5.5 5.8.8.6.6 3 4 5 7 3.4.5.5.5 3 6 4 4 3 4.4.5.5..4.6.8.6.8 3 4.5..4.6.6.8 8 5 4.5 6 5.5...7.5.5 5.5.5 6. 7-December-6 5..8.6.4. 6. 4 6 4 3.5.8 7 6.4 3 4 8 6..5 4 6 8 8.9.6.5.5.5 3 5 3 5.5.8 5 4.5 5.5. 6 5 5.5.5.5 3 6 8 4.8 5 3 5 5.5 6 4 5..5 5 5..5 5.5 5.5 5 5.5.5.5.5 3 5 6 3 4 5 5 5 3.5 5 3 4 3.5.5 3 BDT 4 3.5.5.5 3 3.5 3.5 5 4 4 3.5 5 3.5 3 4 m,j 8 6 4 5 6.5 ptot T 5 3 4 5 centrality 6 m,j 6.5.5.5 3 3 4 5 6 6 q 5 8 8 4 BDT 3 4 5 6 8 5 3.5 C. Bertella 5 For variable vx and vy in row x and column y, the distributions of < vx > versus <vy >, and vice versa, are shown for each pair of training variable in the BDT as well as the correlation of each training variable with BDT 5 6 8 6 4 3 Correlation plots of BDT classification variables in the signal region of BDT 4 8 6 5 centrality.8.5.5 5
Event Selection: Control regions CR Process Reference SR Changes w.r.t. reference SR CRa W Z/W Z-dominated SFOS pair with m`` m Z < 5 GeV CRb Z Z-dominated no Z-mass veto m``` m Z < 5 GeV ET miss < 5 GeV only eee, µµe CRc Z+jets Z-dominated SFOS pair with m`` m Z < 5 GeV ET miss < 5 GeV m``` m Z > 5 GeV one lepton without an isolation requirement (NFs are derived for e-fake sample and µ-fake sample separately) CRd Top quark Z-dominated no m max `+` and R`` cuts at least jet one b-jet one lepton without an isolation requirement CRe Top quark Z-depleted no m max `+` and R`` cuts at least jet one b-jet one lepton without an isolation requirement Events / GeV Events / GeV 9 8 7 6 5 4 3 4 data Bkg (sys stat) ATLAS Preliminary VV Z +jets - s = 3 TeV, Ldt = 5.8 fb VVV Other iggs Top W 5 5 5 3 8 6 4 ATLAS Preliminary s = 3 TeV, Ldt = 5.8 fb W WWW lνlνlν Z-depleted top-quark CR W WWW lνlνlν WZ/Wγ CR - data Bkg (sys stat) VV Z +jets VVV Other iggs Top W Top CR Z-depleted m l l WZ/Wγ CR [GeV] 4 6 8 4 6 8 m l l [GeV] C. Bertella 7-December-6
Results Category SR SR Top CR Z+jets CR VBF 9.3 ± 3.6 5. ±.8.7 ±.6. ±.4 Other iggs 8. ± 4..7 ±.4. ±.. ±. WW 3. ± 8..4 ±..4 ±.5. ±.9 Other VV 6.6 ±.6. ±.. ±..8 ±. Top quark 4. ± 7.6.9 ±.7 86 ± 7 3.6 ±.6 W +jets 4.3 ± 9.. ±.7 8.8 ± 4. 4.4 ±. Z+jets 8. ± 9.9. ±..3 ±. 7 ± Total background 5 ± 3 3.5 ±.9 99 ± 7 38.8 ± 9.8 Observed 9 4 SR with bins CRs with bin Events / bin 35 3 5 5 5 ATLAS Preliminary s = 3 TeV, 5.8 fb Top CR Z ττ CR - WW eµ+µe (VBF) SR -.8 < BDT <.7 Data SM (sys) W+jets Z+jets Top Other VV WW Other iggs ggf VBF Rescaled y-axis for SR 5 5 SR BDT >.7 Fit regions Category CRa CRb CRc CRc CRd CRe e-fake µ-fake W. ±.4.3 ±..4 ±..5 ±.. ±.. ±. Other iggs.8 ±.. ±..4 ±..4 ±.. ±.. ±. VV 7 ± 5 63 ± 53 56 ± 3 63 ± 4 4.4 ±.8. ±.5 VVV.9 ±.. ±.. ±.. ±.. ±.. ±. Top quark 3.7 ±.6.4 ±. 7.3 ±.9 9. ±. 34 ± 9 94 ± 9 Z+jets.5 ±.. ±. 3 ± 83 ± 73 ±.7. ±. Total background 5 ± 5 63 ± 5 394 ± 8 385 ± 7 4 ± 95 ± 9 Observed 7 63 393 387 4 95 SR with bin 6 CRs with bin C. Bertella 7-December-6 Events / bin 8 7 6 5 4 3 ATLAS Preliminary CRa s = 3 TeV, 5.8 fb W WWW lνlνlν CRb CRc e-fake - CRc CRd CRe µ-fake data SM (sys) VV Z+jets VVV Top Other iggs W Rescaled y-axis for SRs 5 5 SR Z-dominated SR Z-depleted Fit regions 3