Higgs properties measurement through H ZZ* 4l with the ATLAS Detector

Transcription

1 Higgs properties measurement through H ZZ* 4l with the ATLAS Detector Haijun Yang (SJTU) The 2 nd China LHC Physics Workshop Peking University, December 17-19, 2016

2 Higgs Productions and Decays ggh, tth, bbh Yukawa coupling VBF, VH Gauge coupling H. Yang - Higgs->ZZ*->4l Properties Measurement 2

3 Higgs ZZ* 4l Analysis Extreme y c ea Gold-plated channel o Fu y reco structed fi a states o Good mass reso utio (~ GeV) o High S/B ratio (~ ) o Lo decay bra chi g fractio (2.67%) Properties measureme t o Higgs mass, idth, spi, parity o Tota a d differe tia cross sectio o Coup i gs 3

4 Higgs ZZ* 4l Selections Trigger match ith si g e a d/or di- epto trigger Four sub-cha e s: 4e, 2e2m, 2m2e, 4m 4

5 Estimated Backgrounds in Control Regions Main background is ZZ: estimated from MC simulation, scaled to theoretical xsection Reducible backgrounds: Zbb, Z+light jets, ttbar, using data-driven method Zbb ttbar Z+jets Estimates agree with data in control regions where isolated & d0 requirements are removed for subleading pairs. Estimated background using data-driven methods by extrapolating to signal region using extrapolation factors. 5

6 H ZZ* 4l Eve ts Observed 10s Expected 8.6s 6

7 Analysis Strategy ATLAS-CONF

8 Higgs ZZ* 4l BDT Outputs 8

9 Higgs ZZ* 4l Cross Sectio Total and fiducial cross section measurement. 9

10 Higgs Fiducia a d Tota Cross Sectio Tota a d fiducia cross sectio measureme t at 13 TeV. 10

11 Higgs ZZ* 4l Couplings The u iversa coup i g stre gth sca e factors - K F for a fermio s - K V for a vector boso s. The H ZZ* 4 cha e is ot se sitive to the K F a d re ative sig of the t o coup i gs, o y a quadra t is sho i K V -K F p a e. Assume SM Higgs ith mass of 125GeV, the fitted coup i g sca e factors are compatib e ith the SM predictio s. 11

12 Higgs ZZ* 4l Production Modes Compatibility between measured cross section and SM prediction is: - 1.1s for ggf+bbh+tth - 1.4s for VBF+VH 12

13 Higgs Production Cross Sections Combining gg and ZZ final states The compatibility between measurement and SM prediction corresponds to a p-value of 21%. ATLAS-CONF

14 Higgs Cross Sections x Br The compatibility between the measurement and SM prediction corresponds to a p-value of 11%. 14

15 Higgs Production Cross Sections The compatibility between measurement and SM prediction corresponds to a p-value of 43%. The global signal strength is measured to be: The local significance of Higgs boson is 10s (exp: 8.6s) 15

16 Search for BSM Higgs Limits o the BSM parameters K HVV, K AVV si are derived ith a fit of yie ds i differe t categories. K SM hich sca es SM i teractio s is fixed to u ity. ggf productio is fixed to SM va ue, but Br(H ZZ*) a d BSM coup i gs are free parameters. 16

17 Search for Heavy Higgs 17

18 Search for Heavy Higgs BSM: t o Higgs doub et mode (2HDM); E ectro eak si g et mode (EWS) The maximum deviatio from SM bkgd is fou d at a mass ~705 GeV ith NWA the g oba p-va ue is ~1.9s. No sig ifica t excess has bee observed. 18

19 A a ysis usi g fu datasets is sti o goi g, p ease stay tu ed! Tha k you! 19

20 Combined Higgs Mass ATLAS + CMS: PRL114 (2015) Higgs mass precision is better than 0.2%. PRL Editor Suggestion H. Yang - Higgs->ZZ*->4l Properties Measurement 20

21 Higgs Properties Measurement Higgs Strength m = 1.09 ± 0.14 Spin/Parity: 0 + Couplings: agree with SM predictions H. Yang - Higgs->ZZ*->4l Properties Measurement 21

22 Higgs Properties Measurement Coupling scale factors 2-parameter benchmark model: k V = k W =k Z k F = k t =k b =k c =k t =k g (Gluon coupling are related to top, b, and their interference in tree level loop diagrams) Assume no BSM contributions to loops: gg H and no BSM decays (no invisible decays) k F = 0 is excluded (>5s) 22

23 Fermionic & Bosonic production Can also fit μ Vf vs μ Ff per decay: μ Vf =μ f VBF+VH μ Ff =μ f ggf+tth μ V/ μ f can be measured in the different decay channels and combined: μ V/ μ f = in agree with SM H. Yang - Higgs->ZZ*->4l Properties Measurement 23

24 Analysis of Single Resonance Z 4l The Z 4l production was first observed at the LHC by ATLAS and CMS. It serves as a standard candle for 4l decay channel along the Higgs discovery. Cross section and BR measurement of the Z 4l production provides A SM test for a rare decay process, measurements of σ(4l) and BR(Z 4l) A complementary test of the detector response for H 4l detection BR(meas.)=3.20±0.25± BR(SM NLO)=3.33± Phys. Rev. Lett. 112, (2014) 24

25 Z/ZZ 4l Productions arxiv: Very rich physics: resonant Z 4l, H ZZ* 4l, SM ZZ 4l Differential cross section measurements in m 4l and P T for inclusive 4l (80<m 4l <1000 GeV) First try to constraint gg 4l contribution from data Theoretical predictions available at different level of corrections Theoretical Predictions: qq ZZ: Powheg (NLO) on-shell H: Powheg (NLO) gg ZZ : MCFM (LO) H 4l & on-shell qq ZZ: NNLO QCD + NLO EWK H. Yang - Higgs->ZZ*->4l Properties Measurement 25