Study of violation of CP invariance in VBF H γγ with the ATLAS detector using Optimal Observables. Florian Kiss

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1 Study of violation of CP invariance in VBF H γγ with the ATLAS detector using Optimal Observables Florian Kiss GK Seminar: Physik an Hadron-Beschleunigern,

2 ) Motivation: Higgs boson properties Experimental results Coupling parameters Spin CP Observed boson behaves SM like Normalised to unity.5 ATLAS Data H ZZ* 4l P + 1 J = s = 7 TeV. Ldt = 4.6 fb P 1 s = 8 TeV Ldt =.7 fb J = ATLAS Prelim. m H = 15.5 GeV H γγ µ +.33 = H ZZ* 4l +.4 µ = H WW* lνlν +.3 µ = Combined H γγ, ZZ*, WW* +.1 µ = W,Z H bb µ H ττ Combined H bb, ττ µ +.7 =. -.6 (8 TeV data only) µ +.5 = = Combined +.18 µ = s = 7 TeV Ldt = fb -1 s = 8 TeV Ldt =.3 fb ±.5 ±.4 <.1 σ(stat.) sys inc. σ( theory ) σ(theory) Total uncertainty ± 1σ on µ Signal strength (µ) P ( J CL s alt ATLAS H γγ -1 s = 8 TeV Ldt =.7 fb H ZZ* 4l -1 s = 7 TeV Ldt = 4.6 fb -1 s = 8 TeV Ldt =.7 fb H WW* eνµν/µνeν -1 s = 8 TeV Ldt =.7 fb -6 1 P - J = P + J = 1 Data CL s expected P assuming J = ± 1 σ P - P + J = 1 J = m + 1σ σ 3σ 4σ q Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar /

3 Motivation: Photons, VBF Di-photon channel Highest sensitivity in Higgs discovery with ATLAS Promising also for properties measurements No CP information from decay q 3 q 1 V V q 4 H q γ γ VBF topology Use vector boson fusion (VBF) to explore HVV vertex Pure CP odd HVV coupling already experimentally excluded This study: anomalous CP odd admixture to standard model couplings Test of CP invariance in the process: VBF H γγ Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 3 /

4 Outline Theoretical background Parametrizations Methodology Test of CP invariance, CP odd observables Optimal Observables Gauge curves Limit setting, statistics Analysis Selection cuts Reweighting Background estimation Expected sensitivity Towards optimization Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 4 /

5 Theoretical background General HVV vertex T µν (p 1, p ) = a 1 (p 1, p ) g µν (SM: CP even) + a (p 1, p ) [p 1 p g µν p µ pν 1 ] (CP even) q 3 q 1 V V q 4 H q γ γ + a 3 (p 1, p ) ε µνρσ p 1ρ p σ (CP odd) Parametrization Standard model (SM) a 1 = m V v, a =, a 3 = Anomalous couplings a 1 = m V v, a =, a 3 a3 HZZ e = d cos θ W sin θ W M W a3 HWW e = d sin θ W M W d: anomalous contribution of CP odd scalar Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 5 /

6 Methodology Example: φ jj Test of CP invariance Define CP odd observable X Mean X : model independent test of CP invariance X = violation of CP invariance CP odd observables φ jj = φ + φ : Signed azimuthal angle between jets (Klämke, Zeppenfeld: arxiv:hep-ph/73) Optimal Observable a.u Ch. Englert et al. [arxiv:11.843v1/hep-ph]. SM VBF H.18 ATLAS simulation CP mixed work in progress CP odd φ jj Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 6 /

7 Optimal Observables Definition and properties Definition: O := dσ nonsm R(M SM M CPodd ) dσ SM M SM Optimal to investigate deviations in ME: M nonsm = M SM + d M CPodd M nonsm = M SM (CP even) + d R(M SM M CPodd ) (CP odd) + d M CPodd (CP even) Computed from events kinematics, using information from full phase space First used Magnetic Moment and Electric Dipole Moment Form Factors of the Top Quarks via e + e t t, D. Atwood and A. Soni, Phys.Rev. D45(199) a.u ATLAS simulation work in progress SM VBF H CP mixed CP odd Previous applications Measurement of tau polarization (LEP) Weak dipole moment of tau (LEP) Triple gauge boson couplings (LEP) Sensitivity study of CP violation in ZH process (ILC) O Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 7 /

8 Optimal Observables: details Goal dσ( Φ) = dσ + η dσ 1 + η dσ Find best estimator for η Φ = (Φ 1,..., Φ n) : phase space variables Problem n-dim maximum likelihood fit most efficient estimator: N data L = dσ i i=1 VBF topology: phase space 1 dimensional High amount of simulated events needed N data log L = log (dσ + η dσ 1 + η dσ ) d log L dη Definition i=1 N data = = i=1 dσ 1 + η σ dσ + η dσ 1 + η dσ O 1 = dσ1 dσ, O = dσ dσ N data O 1 + η O = i=1 1 + η O 1 + η O Fit in O 1, O equivalent to n-dim fit in phase space Consider only O 1 = O in the following Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 8 /

9 Optimal Observable and mean values Optimal Observable Consider mean value O instead of full distribution No loss in sensitivity Proven by toy MC studies <Ο> 1 Gauge curve Translation: Mean of observable O into coupling parameter d Neyman construction of confidence intervals d Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 9 /

10 Optimal Observable and mean values <Ο> 1 Neyman construction Translation: Uncertainty on observable mean into uncertainty on coupling parameter Error band Distribution of O by toy MC simulation Confidence belt from quantiles of O distribution 68% quantiles are shown no. of pseudo experiments d <Ο> Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 1 /

11 Selection, Physics processes Signal Cut based selection tight, isolated photons p T (γ) > 4, 3 GeV jets, anti-k T, dr =.4 m jj > 5 GeV, η jj >.8 φ γγ,jj >.6, R min,γj >. η γγ.5 (η j1 + η j ) >.4 VBF H with anomalous couplings (VBFNLO reweighted to several d models) Background QCD γγ (Sherpa), (γj, jj data driven) ggf H (Powheg) VH H (Pythia) tth H (Pythia) Used for analysis of 1 ATLAS dataset Optimized for highest significance Maybe not optimal for current study Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 11 /

12 Signal event generation Reweighting Generate prediction for different models by reweighting For every value of d: compute weight w from matrix elements w = w ( d) = M d M SM a.u..16 SM.14 ATLAS simulation SM reweighted work in progress CP odd.1 VBFNLO φ jj Technicalities ME for Optimal Observable and reweighting extracted from HAWK. (Ciccolini, Denner, Dittmaier: arxiv: [hep-ph]) Direct generation of d : VBFNLO (Arnold et al.: arxiv: [hep-ph]) a.u ATLAS simulation work in progress SM SM reweighted CP odd VBFNLO Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 1 O/

13 Background: data in sidebands Theory No CP violation in SM background processes O = expected Verification in data sidebands CP properties of detector components Sideband regions 15 GeV < m γγ < 1 GeV 13 GeV < m γγ < 16 GeV Signal region 1 GeV < m γγ < 13 GeV Mean values in data Lower sideband O =.6 ±.19 Upper sideband O =.1 ±.1 Events ATLAS work in progress SM H ggf SM H VBF SM γγ SM γj, jj Data 1 sidebands Events from both sideband regions O Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 13 /

14 Background: MC simulation QCD γγ background Region O σ( O ) σ(o) Lower sideband Signal region Upper sideband a.u ATLAS simulation work in progress Lower sideband Signal region Upper sideband O =, independent of m γγ Width σ(o) depends on m γγ Important if background is estimated from sidebands O Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 14 /

15 Expected sensitivity on anomalous couplings Performance on ATLAS dataset of 1 s = 8 TeV,.7 fb 1 Expected number of events: QCD γγ, γ jet, jet jet: ggf H: 1.7 VH H:.1 tth H:.5 anomalous VBF H: 5 Same number for all values of d No cross section prediction for anomalous coupling models used Gauge curve of O to extract confidence intervall on d Only statistical uncertainties included First result: No limit on anomalous coupling parameter <Ο> signal signal + background s=8 TeV 1 L dt=.7fb d Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 15 /

16 Comparison of O and φ jj Performance of Observables Only VBF signal, no backgrounds considered Gauge curve to estimate confidence intervall on d Expected result for d = : a.u SM d =. > jj <O>,< φ 3 Conf. intervall O φ jj on d (68%) without BG [.8,.8] [.1,.1] Optimal Observable φ jj a.u φ SM d = d Ο [Plots by Michaela Oettle] Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 16 /

17 Cut optimization Optimization of cut based selection η jj >.8 4. m jj > 5 GeV 6 GeV φ γγ,jj >.6.8 R min,γj >. 1.5 η γγ.5 (η j1 + η j ) >.4.5 Result: Higher s s+b, s.5.33 b Benefit for CP mixing study Lower signal yield s, tiny gain in sensitivity on d [Study by Michaela Oettle] s+b s/ <Ο> η jj m jj significance significance default Φ γγjj R min,γj η γγ.5*(η +η ) j1 j VBF tight cuts Optimized cuts d Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 17 /

18 nd order Optimal Observable: Recap Goal dσ( Φ) = dσ + η dσ 1 + η dσ Find best estimator for η Φ = (Φ 1,..., Φ n) : phase space variables Problem n-dim maximum likelihood fit most efficient estimator: N data L = dσ i i=1 VBF topology: phase space 1 dimensional High amount of simulated events needed N data log L = log (dσ + η dσ 1 + η dσ ) d log L dη Definition i=1 N data = = i=1 dσ 1 + η σ dσ + η dσ 1 + η dσ O 1 = dσ1 dσ, O = dσ dσ N data O 1 + η O = i=1 1 + η O 1 + η O Also consider O now Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 18 /

19 nd order Optimal Observable: Gauge curves 1st order Optimal Observable O 1 Higher d: O 1 loses sensitivity Model becomes pure CP odd O 1 for d nd order Optimal Observable O O := M CPodd M SM Recover sensitivity for higher d by combining O 1 and O <O 1 > <O > d d Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 19 /

20 nd order Optimal Observable Combination of O 1 and O ( d ) χ = i,j=1, ( ) O i E[O i ]( d) Cov 1 [O i, O j ] ( ) O j E[O j ]( d) χ O 1 +O +Correlations O 1 O φ 1 O 1, O : expected mean values for SM, later actual measurement E[O 1 ], E[O ]: from gauge curves Cov(O 1, O 1 ), Cov(O, O ): expected uncertainties (variances) on mean values Cov(O 1, O ): expected correlation d Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar /

21 nd order Optimal Observable: Confidence intervalls χ.5 O 1 +O +Correlations Expected sensitivity with ATLAS 1 dataset 68% confidence intervalls from χ < 1 points Only statistical uncertainties included Assuming d = d <. using O 1 and O O 1 O φ d χ 3 Next steps Recover pure CP odd model (flat χ ) Confidence levels 9% could be feasible Systematic uncertainties not yet ready, but probably statistically limited measurement d Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 1 /

22 Summary and outlook Summary First look at CP properties in VBF H γγ Method of Optimal Observables used Expected sensitivity on anomalous, CP odd coupling parameter estimated Outlook Cut optimization: use confidence intervall on d as figure of merit Include cross section prediction for anomalous couplings Background estimation: Optimal Observables from sidebands Assessment of systematic uncertainties Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar /

23 Backup Florian Kiss (Univ. Freiburg) CP in VBF H γγ GK Seminar 3 /