Constraining the top Yukawa coupling from tt differential - PowerPoint PPT Presentation

CMS-PAS-TOP-17-004 Constraining the top Yukawa coupling from tt differential distributions in lepton+jets at 13 TeV Yi-Ting Duh (Brown University & University of Rochester) on behalf of the CMS Collaboration Young Scientist Forum 54th Rencontres de Moriond La Thuile, Italy, 16-23 March 2019

Yukawa coupling in tt differential Example diagrams of tt production and the virtual Higgs exchange Corrections due to electroweak boson exchange, including the Higgs boson, • between the final state top quarks Have a very small effect on the total cross section; Not implemented in the MC • event generators However, they have a sizable impact on differential distributions and sensitive • to the top quark Yukawa coupling through weak force mediated corrections, especially near the energy of production threshold [Ref]. In this analysis: explore a complementary approach to measure top quark Yukawa • coupling by utilizing precise measurements of tt differential distributions Ref: Phys. Rev. D 91 (2015) 014020 Yi-Ting Duh 2

Yukawa coupling in tt differential Y t : the ratio of the top quark Yukawa coupling to its SM predicted value • Calculate weak correction factors for different value of Y t in a given (M tt , Δ y tt ) • Apply the correction factors at the parton level to existing tt simulated samples. • Obtain distributions at detector level that can be directly compared to data. 0.5 0.08 ) ) t t t t CMS CMS /dM y Y = 0 Δ Y = 0 t Simulation Simulation /d t 0.06 LO 0.4 Y = 1 Preliminary Preliminary LO Y = 1 t t σ σ Y = 2 )/(d (HATHOR inputs) (HATHOR inputs) )/(d Y = 2 0.04 t t 0.3 Y = 4 t Y = 4 t t /dM t t t y Δ 0.02 top mass uncert top mass uncert /d EW 0.2 EW σ 0 σ δ (d δ (d 0.1 -0.02 0 -0.04 -0.1 -0.06 400 600 800 1000 1200 1400 1600 1800 2000 -3 -2 -1 0 1 2 3 y Δ M [GeV] t t t t The most Invariant mass of top pairs Rapidity difference between top and antitop sensitive region Yi-Ting Duh 3

Analysis overview e l e c t r o n / m u o n e t a g g e d j b - t Vector+jets p Tmiss (Simulation) Multi-jets (Data sideband) jet Single top (Simulation) b-tagged jet j e t • Reconstruct tt events separately with two • Lepton+jets event signature: algorithms: – At least 4 jets – One lepton (electron or muon) – Four or more jets and two are b-tagged – 3 jets (if one of the jets is below p T or η event – Missing transverse momentum selection); developed for threshold regions -1 -1 -1 3 35.8 fb (13 TeV) 3 35.8 fb (13 TeV) 35.8 fb (13 TeV) × 10 × 10 140 Events / 20 Events / 20 Events / 20 Data Data Data 45000 CMS e/ µ +jets, 3 jets CMS e/ µ +jets, 4 jets CMS e/ µ +jets, ≥ 5 jets 100 t wrong reco t right reco t wrong reco t right reco t wrong reco t right reco Preliminary Preliminary Preliminary 120 40000 t t t t t t t bck t not reco t bck t not reco t bck t not reco 35000 80 t t t t t t 100 single top single top single top 30000 V+jets V+jets V+jets 80 60 QCD QCD QCD 25000 Total unc. Total unc. Total unc. 60 20000 40 15000 40 10000 20 20 5000 0 0 0 Pred. Pred. Pred. 1.4 1.4 1.4 Data Data Data 1.2 1.2 1.2 1 1 1 0.8 0.8 0.8 0.6 0.6 0.6 0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500 p (t t ) p (t t ) p (t t ) t t t Yi-Ting Duh 4

Extracting Yukawa coupling -1 35.8 fb (13 TeV) Events Data t t single top V+jets QCD CMS e/ +jets, 3 jets µ ≥ Preliminary 30000 After the likelihood fit 3 jets 4 jets ≥ 5 jets 0-0.6 0.6-1.2 0-0.6 0.6-1.2 0-0.6 0.6-1.2 >1.2 >1.2 >1.2 20000 • Likelihood fit in (M tt , Δ y tt ) to constrain Y t 10000 Data/Pred. 1.02 1 0.98 500-2000 520-2000 660-2000 540-2000 580-2000 700-2000 540-2000 580-2000 700-2000 0-300 300-320 320-340 340-360 360-400 400-440 440-500 0-340 340-380 380-420 420-460 460-520 0-400 400-440 440-480 480-520 520-580 580-660 0-360 360-400 400-440 440-480 480-540 0-400 400-440 440-480 480-520 520-580 0-500 500-560 560-620 620-700 0-360 360-400 400-440 440-480 480-540 0-400 400-440 440-480 480-520 520-580 0-500 500-560 560-620 620-700 2 m [GeV/c ] t t y-axis: 1.3 1.3 yields)/(Powheg yields) 1.3 yields)/(Powheg yields) yields)/(Powheg yields) CMS CMS CMS 1.25 Simulation 1.25 Simulation 1.25 3 jets Simulation 3 jets 3 jets Preliminary Preliminary Strength of the Preliminary 1.2 1.2 1.2 bin 1 bin 2 EW correction bin 3 1.15 1.15 1.15 1.1 Uncorrected MC yields 1.1 1.1 1.05 1.05 1.05 (At detector level) 1 1 1 t t t 0.95 Y 0.95 0.95 Y Y ( ( ( 0.9 0.9 0.9 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 Y Y Y t t t Example bins, more for each bin Yi-Ting Duh 5

Results -1 35.8 fb (13 TeV) 6 ln L e/ +jets, 3 jets µ CMS Preliminary Δ Expected 5 -2 Observed 4 95% CL • Combined fit extract to an upper limit on the top 3 quark Yukawa coupling of 1.67 (1.62 expected) 2 at 95% confidence level 1 68% CL 0 0 0.5 1 1.5 2 2.5 3 Y t • Promising sensitivities compare to Z Z -1 -1 35.8 fb (13 TeV) 35.8 fb (13 TeV) 6 6 ln L ln L e/ +jets, 4 jets e/ +jets, 5 jets µ µ ≥ CMS CMS other measurements Preliminary Preliminary Δ Δ Expected Expected 5 5 -2 -2 Observed Observed 4 4 95% CL 95% CL tttt production constraints the 3 3 Yukawa coupling indirectly <2.1 2 2 with the same dataset 1 1 68% CL 68% CL 0 0 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 Y Y t t Z Z Z Z -1 35.8 fb (13 TeV) 6 ln L e/ +jets, all jets combined µ CMS Preliminary Δ Expected 5 -2 Observed 4 95% CL 3 ≧ 2 1 68% CL 0 0 0.5 1 1.5 2 2.5 3 Y t Z Z Yi-Ting Duh 6

Backup

Control Plots, 3 jets 8

Control Plots, 4 jets 9

Control Plots, ≧ 5 jets 10

Uncertainties: experimental • All POG recommendations: ID/trigger, tagging, JEC/JER, pileup, lumi, MET variation is negligible • JEC split into 19 independent sources → the dominant experimental uncertainty • Corresponding normalization uncertainties for backgrounds • QCD shape uncertainty derived by b-tagging inversion → larger and higher impact uncertainties for 3 jets channel 11

Uncertainties: modelling • Renormalization & Factorization scale uncertainties are evaluated by varying each scale independently by a factor of 2. • Top mass systematic derived by ±1GeV MC samples • Parton shower (prescribed by TOP PAG): 6 nuisances, UE tuning variation is negligible • Uncertainty due to weak correction estimated by bin-by-bin (scale variation)x(weak correction) → tiny systematic variation and low impact 12

Background Estimation • Backgrounds of tt production decays into lepton+jets including: • Single top Simulation Simulation • V+jets: W+jets and Drell Yan+jets • QCD Multijets Data-driven QCD shape is obtained from data sideband defined by the maximum CSVv2 discriminator <0.6 QCD normalization is estimated by the ratio of the yields between data and MC in signal region and in sideband region subtract contribution from V+jets, t, ttbar 13

QCD Systematic Uncertainty signal QCD shape iso region templates Ⅱ Ⅰ invert iso derive shape sys (remove trigger, Ⅲ Ⅳ p T ( μ )>50 GeV) CSV<0.6 medium CSV • Evaluate the shape systematics by considering the difference in shape between regions III and IV • Normalization systematics 30% is assigned 14

Reconstruct tt events : 3 jets • At the threshold of tt production, quarks from tt decay are likely to have p T or η outside of the selection thresholds (mostly happens in the softer p T jet from W decays) Assuming that the two jets with the highest value of b-tagging discriminator are associated with b-quarks, the ambiguity is the assignment of the b jets Construct a likelihood discriminant to identify the best jet-to-parton assignment Hypothesized Solution distance m (b h +W h jets) 80% correctly identify [Nucl. Instrum. Meth. A 736 (2014) 169] Intersect an ellipse in 3D momentum space Select p 𝑤 as the point on the ellipse for which the distance bwt p Tmiss is minimal Yi-Ting Duh 15