Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel

Transcription

1 Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel DPG-Frühjahrstagung, Mainz, March 24th - 28th, 24 J. Berger, R. Caspart, F. Frensch, R. Friese, Thomas Müller, G. Quast, R. Wolf March 24th, 24 INSTITUTE OF EXPERIMENTAL NUCLEAR PHYSICS (IEKP, KIT) KIT University of the State of Baden-Wuerttemberg and National Laboratory of the Helmholtz Association

2 Outline Ideas for the parity measurement in the H τ τ Channel Example of 3-prong decays 2 Identification of hadronically decaying τ leptons in CMS Reconstruction of τ leptons Study of improvements of the τ identification Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 2/

3 SM H(25 GeV) ττ Data - background Bkg. uncertainty Motivation Evidence: H ττ Local p-value Events CMS H ττ, 4.9 fb - CMS, 4.9 fb - at 7 TeV, 9.7 fb at 8 TeV Observed p-value Expected for SM H(m ) H 2 4 m H [GeV] SM H(25 GeV) ττ Observed -jet -jet VBF tag - at 7 TeV, 9.7 fb l+lτ h ll+ll' log(s/(s+b)) log(s/(s+b)) at 8 TeV CMS-HIG-3-4, arxiv:4.54 Talk by Joram Berger (T 6.2) σ 2σ 3σ 4σ 5σ Expect significant number of H ττ events in the next data taking period Measure properties of Higgs boson in τ τ channel Possible CP scenarios Scalar J PC = ++ : H (SM), h and H (2HDM) Pseudoscalar J PC = + : A (2HDM) Mixed CP state: h Single Higgs boson with pure or mixed CP state? Degenerate mass states with superpositions of (pure) CP states? Decay in τ leptons best suited for CP measurement High branching ratio, good signal over background ratio Fermionic couplings allow to access both CP even and odd components of Higgs bosons at born level; not possible in bosonic final states Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 3/

4 Spin and Parity in the Scope of H τ τ General model for Yukawa Lagrangian: L Y (cos Φ CP ττ + sin Φ CP τ iγ 5 τ) H CP mixing angle (Φ CP), scalar (ττ) and pseudoscalar (τ iγ 5 τ ) couplings CP properties are important measure for dynamics of the Higgs boson Scalar: J PC = ++ Pseudoscalar: J PC = + τ spins parallel (S = ), angular momentum L = τ spins anti-parallel (S = ), no angular momentum (L = ) P(ττ) = ( ) L+ = + P(ττ) = ( ) L+ = τ τ spin correlation (s τ s τ ) separates between CP = ± states Decay via Scalar Meson s ν s τ s π= ν τ τ - π - Decay via Vector Meson s a a - s τ τ - s ν ν τ Correlation between τ spins and flight directions of decay products due to CP violation of weak interaction Infer from flight directions of visible decay products in τ rest frames on CP properties of the Higgs boson Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 4/

5 Parity and 3-Prong Tau Decays () τ decays into three charged particles (prongs): τ a ντ π π + π ν τ Fit reconstructed tracks to τ decay vertex (secondary vertex, SV) Full reconstruction of τ rest frame possible Talk by Bastian Kargoll (T 3.6) Scalar Pseudoscalar ν a + τ s sν a Visible decay products τ + sτ sτ s a τ - s ν in τ ± rest frames a - ν τ preferably anti-parallel a a + - sa sa Visible decay products τ + sτ sτ s ν τ - s ν rest frames ν ν τ τ preferably parallel in τ ± Angle ϕ ( a, ) a+, definded in τ ± rest frames, separates between CP = ± Slope is a measure for the CP mixing angle Φ CP, but experimentally difficult to measure pp φ ττ _ a L a L.4.3 A, no smearing A, with smearing.2 H, no smearing. H, with smearing arxiv:8.2297v Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 5/

6 Parity and 3-Prong Tau Decays (2) Separation between single Higgs boson and superpositions of Higgs bosons degenerated in mass via observable [ ] ] O CP p(τ ) p(τ + ) [p(a ) p(a+ )] pp φ ττ _ a L L a.4.3 A+H, no smearing A+H, with smearing.2 CPmix, no smearing. CPmix, with smearing Pure CP states yield O CP =, because decay products are preferably (anti-) parallel Mixed CP states yield asymmetry arxiv:8.2297v Experimental challenges Impact of detector resolution? Exp. uncertainties on τ SV? Background shapes? Which integrated luminosity is needed to reach a certain precision? Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 6/

7 Tau Reconstruction in CMS Particle Flow (PF) algorithm Reconstruct all stable particles in the event (e, µ, γ, ch. and neutr. hadrons) Decouple further reconstruction from detector pecularities Events Single Hadron CMS, 9.7 fb Hadron+Strips at 8 TeV µ Observed τ h Bkg. uncertainty Z ττ Z ττ Z ττ Z µµ ± 3 π ± π ± π Electroweak Three Hadrons + photons no photons τ h tt QCD m vis [GeV] CMS-PAS-HIG-3-4 Hadron Plus Strips (HPS) algorithm Four hypotheses build for every combination of particles in PF jet ch. hardon +, or 2 strips (π ) 3 charged hadrons Track quality and mass window cuts Retain τ h candidate with highest p T Decay Mode Resonance BR [ % ] τ e ν e ντ 7.8 τ µ νµ ντ 7.4 τ π ντ π(4).6 τ π π ντ ρ(77) 26. τ π π π ντ a (26).8 τ π π + π ντ a (26) 9.8 τ π π + π π ντ 4.8 Other hadronic modes.7 All hadronic modes 64.8 PDG Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 7/

8 Tau Isolation Expect low hadronic activity in cone ( R =.5) arround colorless τ leptons Isolation requirements are main handle to suppress jet fake-rate Cut-based isolation Fake-rate I τ = P charged T (d Z <.2 cm) + max ( P γ T β, ) with β =.4576 P charged T (d Z >.2 cm) Cuts on I τ define loose, medium and tight working points -2 CMS Preliminary 22 MVA2 Isolation HPS MVA2 Loose HPS MVA2 Medium HPS MVA2 Tight HPS Loose Comb dβ HPS Medium Comb dβ HPS Tight Comb dβ Tau POG MVA-based isolation τ h candidate kinematics (p T and η) and decay mode Individual contributions to formula for isolation I r Charged and neutral isolation, β correction Efficiency Displacement of τ decay vertex (lifetime variables) Impact parameter of leading track Distance between primary and secondary vertex (in cases it gets reconstructed) Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 8/

9 Studies Improving the Tau ID MVA performance Comparison BDT vs. NeuroBayes Study training in different categories (e.g. in p T(τ) or decay mode) Study impact of number of training events Preparation for LHC Run II Higher energy ( s = 3 GeV) and more Pile-up interactions Neutral particle isolation is expected to be affected most by the higher pile-up Study robustnes of discriminators Fake Rate Private Work BDT (inclusive) NeuroBayes (inclusive) NeuroBayes (/3 prongs) Cut-based Signal Efficiency Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 9/

10 Outlook CP Measurement Tau Identification H ττ channel perfectly suited for the CP measurement of the Higgs boson Various ideas for CP observables are proposed by theorists Example for 3-prong τ decay presented Next step: study of experimental feasibility Good τ ID performance in LHC Run I Initial studies of improvements for the MVA presented Main goal: robustnes of MVAs in high pile-up environment in LHC Run II Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 /

11 Additional Material Thomas Müller Preparations for the Spin and Parity Measurement of the Higgs Boson in the H ττ Channel March 24th, 24 /

12 τ ID MVA Trainings Current Status Studied impact of separate trainings for and 3 prong events Compared BDT with NeuroBayes trainings BDT Trainings Methods Comparison BDT (inclusive) NeuroBayes (inclusive) NeuroBayes (/3 prongs) BDT (inclusive) BDT (/3 prongs) BDT ( prongs) BDT (3 prongs) - Cut-based Private Work Fake Rate - NeuroBayes Trainings Private Work Fake Rate Fake Rate Private Work Signal Efficiency BDT better than first tests with NeuroBayes NeuroBayes provides efficient tools for variable rankings Thomas Mu ller NeuroBayes (/3 prongs) NeuroBayes ( prongs) NeuroBayes (inclusive).8 Signal Efficiency -4 NeuroBayes (3 prongs) Signal Efficiency /3 prongs categorisation improves NeuroBayes trainings but does not change the performance of the BDT Plots do not take into account the different reconstruction probabilities for and 3 prong taus in the signal and background samples Preparations for the Spin and Parity Measurement of the Higgs Boson in the H τ τ Channel March 24th, 24 2/