NLO+PS off-shell effects in precise determinations of the mass and width of the top-quark at the LHC Eps-Hep 2023 Aug 22nd, 2023 Simone Amoroso, D. Britzger, S. Kluth, L. Scyboz 1 Top quark mass at hadron colliders Most accurate top quark mass determinations through direct measurements, from the reconstruction of the top decay products (lepton, jets, b-jets) Fits to data using templates obtained from exclusive Monte Carlo predictions ATLAS+CMS Preliminary LHCtop WG World comb. (Mar 2014) [2] stat total uncertainty LHC comb. (Sep 2013) World comb. (Mar 2014) LHCtop WG ATLAS, l+jets ATLAS, dilepton ATLAS, all jets ATLAS, single top ATLAS, dilepton ATLAS, all jets ATLAS, l+jets Oct 2022 total stat mtop ± total (stat ± syst) 173.29 ± 0.95 (0.35 ± 0.88) 173.34 ± 0.76 (0.36 ± 0.67) 172.33 ± 1.27 (0.75 ± 1.02) s Ref. 7 TeV [1] 1.96-7 TeV [2] 7 TeV [3] 173.79 ± 1.41 (0.54 ± 1.30) 175.1± 1.8 (1.4 ± 1.2) 7 TeV [3] 172.2 ± 2.1 (0.7 ± 2.0) 172.99 ± 0.85 (0.41± 0.74) 173.72 ± 1.15 (0.55 ± 1.01) 172.08 ± 0.91 (0.39 ± 0.82) 172.69 ± 0.48 (0.25 ± 0.41) 8 TeV [5] ATLAS, leptonic invariant mass ATLAS, dilepton (*) CMS, l+jets CMS, dilepton CMS, all jets CMS, l+jets CMS, dilepton CMS, all jets CMS, single top 174.41± 0.81 (0.39 ± 0.66 ± 0.25) 172.63 ± 0.79 (0.20 ± 0.67 ± 0.37) 173.49 ± 1.06 (0.43 ± 0.97) 172.50 ± 1.52 (0.43 ± 1.46) 13 TeV [9] 173.49 ± 1.41 (0.69 ± 1.23) 172.35 ± 0.51 (0.16 ± 0.48) 172.82 ± 1.23 (0.19 ± 1.22) 7 TeV [13] 172.32 ± 0.64 (0.25 ± 0.59) 172.95 ± 1.22 (0.77 ± 0.95) 8 TeV [14] CMS comb. (Sep 2015) 172.44 ± 0.48 (0.13 ± 0.47) 172.25 ± 0.63 (0.08 ± 0.62) 7+8 TeV [14] 172.33 ± 172.34 ± 172.13 ± 171.77 ± 172.76 ± 13 TeV [17] ATLAS comb. (Oct 2018) CMS, l+jets CMS, dilepton CMS, all jets CMS, single top CMS, l+jets (*) CMS, boosted (*) 165 0.70 (0.14 ± 0.73 (0.20 ± 0.77 (0.32 ± 0.38 0.81 (0.22 ± [1] ATLAS-CONF-2013-102 [2] arXiv:1403.4427 [3] EPJC 75 (2015) 330 [4] EPJC 75 (2015) 158 [5] ATLAS-CONF-2014-055 [6] PLB 761 (2016) 350 [7] JHEP 09 (2017) 118 * Preliminary ATLAS-CONF-2022-058 mtop summary, s = 7-13 TeV 170 175 mtop [GeV] 0.69) 0.70) 0.70) 8 TeV [6] 8 TeV [7] 8 TeV [8] 7+8 TeV [8] 13 TeV [10] 7 TeV [11] 7 TeV [12] 8 TeV [14] 8 TeV [14] 8 TeV [15] 13 TeV [16] 13 TeV [18] 13 TeV [19] 13 TeV [20] 0.78) [8] EPJC 79 (2019) 290 [9] arXiv:2209.00583 [10] ATLAS-CONF-2022-058 [11] JHEP 12 (2012) 105 [12] EPJC 72 (2012) 2202 [13] EPJC 74 (2014) 2758 [14] PRD 93 (2016) 072004 180 7 TeV [4] 13 TeV [21] [15] EPJC 77 (2017) 354 [16] EPJC 78 (2018) 891 [17] EPJC 79 (2019) 368 [18] EPJC 79 (2019) 313 [19] arXiv:2108.10407 [20] CMS-PAS-TOP-20-008 [21] CMS-PAS-TOP-21-012 185 TOPLHCWG 2 The Powheg bb4l event generator All recent direct measurements of mtop use NLO+PS Monte Carlo samples • NLO in production, LO spin correlations and NLO decay through shower ME corrections S. Frixione, P. Nason, G. Ridolfi JHEP 0709 (2007) 126 double-resonant single-resonant non-resonant State of the art since a few years the bb4l code in Powheg-Box-RES • NLO computation of the full 6-fermion process • non-resonant, off-shell , interference & spin-correlation effects at exact NLO QCD T. Jezo, P. Nason, JHEP 12 (2015) 065 • Unified treatment of ttbar and Wt single-top T. Jezo et al, Eur.Phys.J.C 76 (2016) 12, 691 T. Jezo, J.M. Lindert, S. Pozzorini, [2307.15653] [hep-ph] 3 Off-shell effects in top production Compare bb4l with hvq including NLO decays of the tops in the NWA Distortions in the mWb lineshape at particle level Do they impact direct determinations of mtop? T. Jezo, J.M. Lindert, S. Pozzorini, [2307.15653] [hep-ph] 4 Off-shell effects in top production Particle-level study including smearing to emulate detector effects Finds effects of the order of O(200 MeV) on the peak position of the reconstructed top mass Some dependence on the specific observable and parton shower code Can we learn anything using existing measurements? S. Ferrario Ravasio, T. Jezo, P. Nason, C.Oleari Eur.Phys.J.C 78 (2018) 6 5 ATLAS measurement of mlbminimax ATLAS √s = 13TeV measurement • 36.1 fb-1 of Run-II data • Dileptonic channel (ee, eµ, µµ) • Combine one lepton and one b-jet using mlbminimax variable Kinematic endpoint at 2 mtop − 2 mW sensitive to the top quark mass Above endpoint sensitive to tt/Wt interference and top-quark width effects ATLAS Collaboration, Phys.Rev.Lett. 121 (2018) 15 6 ATLAS measurement of mlbminimax ATLAS √s = 13TeV measurement • 36.1 fb-1 of Run-II data • Dileptonic channel (ee, eµ, µµ) • Combine one lepton and one b-jet using mlbminimax variable C. Herwig, T. Jezo, B. Nachman, Phys.Rev.Lett. 122 (2019) 23 Kinematic endpoint at 2 mtop − 2 mW sensitive to the top quark mass Above endpoint sensitive to tt/Wt interference and top-quark width effects ATLAS measurement used for a competitive direct extraction of Γtop Can we use it to also learn something on mtop? 7 2 ⋅107 bb4l LHE events generated mtop = 172.5 GeV, Γtop = 1.33 GeV hdamp = mtop NNPDF31_nnlo_hessian PDF !" 10−2 ATLAS Data, 36.1 fb−1 nominal bb4l Γtop ± 0.66 GeV mtop ± 2.5 GeV !"! !" !!" !" 10−3 "!! Same-flavor lepton decays included by relabeling LHE events (see L. Jeppe poster) Interfaced to Pythia8.307 using dedicated bb4l UserHook Templates generated for • mtop = 170.0, 171.5, 173.5, 175.0 GeV • Γtop = 0.66, 1.00, 1.66, 2.00 GeV ! !" "! ! !" ! !" 10−4 ! !" ! ! !" !" "!! ! ! !" !" 10−5 MC/Data • • • • 1 dσ [1/GeV] minimax σ dmbℓ bb4l predictions 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 ! ! !" ! !" !"! !" !" ! !" ! ! ! !" !" 0 !" ! ! ! !" !" ! Δmtop 100 150 200 ΔΓtop !" 250 ! !" !" 50 ! 300 350 mminimax bℓ !" 400 [GeV] 8 The “linear template fit” Goodness of fit for binned distributions with gaussian uncertainties T −1 2 χ (α) = (d − λ(α)) V (d − λ(α)) λ: theory-prediction α parameter(s) of interest, (top mass and/or width) d the measurement, V covariance matrix (W=V-1) D. Britzger, Eur.Phys.J.C 82 (2022) 8, 731 The Linear Template Fit The parameter dependence λ(α) approximated linearly from 'templates' → Valid approximation when templates are close to the best estimator The fit result ('best estimator') is directly obtained in closed analytic form: T −1 T α̂ = [(YM̃) WYM̃] [(YM̃) W(d − Ym)] Y: matrix of the templates M, m: quantities computed from the reference values of the templates 9 Sensitivity Templates generated for • mtop {170, 171.5, 172.5, 173.5, 175} GeV • Γtop {0.66, 1.0, 1.33, 1.66, 2.0 } GeV Good linearity observed in all bins • No difference between linear and quadratic interpolation Low mlb mostly sensitive to mtop High mlb mostly sensitive to Γtop 10 Systematic uncertainties Experimental uncertainties all encoded in data covariance matrix Dominated by uncertainties in the theoretical modeling of tt+Wt and in the description of additional b-tagged jets Could be significantly reduced in the future by directly using bb4l predictions in the measurement 11 Systematic uncertainties • 7-point scale variations and NNPDF31 eigenvector variations obtained through bb4l reweighting dσ 1 [1/GeV] minimax σ dmbℓ For the interpretation, need to consider theoretical uncertainties on bb4l prediction: • 3-point hdamp variations (0.5, 2.0 mtop) !" 10−2 nominal bb4l 7-point µ R , µ F PDF variations 3-point hdamp 3-point shower ATLAS Data, 36.1 fb−1 !"! !" "!! !" 10−3 "!! !" ! !" 10−4 ! !" ! !" !" • 3-point shower scales and • NB: Work ongoing to evaluate ! ! !" ! "!! ! ! 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 !" !" 10−5 MC/Data non-singular terms variations in the splitting kernels through Pythia8 reweighting !" ! ! !" !" ! !"! !" !" ! !" ! ! ! !" !" 0 !" ! ! ! !" !" ! 100 150 200 uncertainties on the matching to Pythia (negligible) and possible bias due to wrong shower recoils (few ~100 MeV on mtop) !" 250 ! !" !" 50 ! 300 350 mminimax bℓ !" 400 [GeV] 12 GoF dependence on the fit range χ²/ndf for different mbl fit ranges before and after the fit Very good agreement of the post-fit predictions with data in the entire mbl range 13 Fit performed between 40 < mlb < 380 GeV Results 1 dσ [1/GeV] σ dmminimax bℓ Simultaneous determination of mass and width #$!" 10−2 nominal bb4l post-fit bb4l ATLAS Data, 36.1 fb−1 #$!"! #$!" !#$!" #$!" 10−3 !" #$ ! !#$!" !#$" !#$ !" !#$ !" 10−4 ! #$ !" ! !#$ !" !"#$ #$! !" #$! $#! Weak correlation (-30%) between mtop and Γtop Extracted width consistent with previous determination MC/Data Excellent agreement of data and bb4l post-fit 10−5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 !" !" ! ! #$!" ! #$!" #$!"! !"#$ #$!" #$ ! !" ! !" ! #$! !" #$!" 0 #$ #$ ! #$ #$! ! !" #$ !" ! !" !" 50 100 150 200 !" 250 300 #$! ! #$ 350 mminimax bℓ !" 400 [GeV] Theoretical uncertainty dominated by hdamp and shower variations 14 Simultaneous determination of mass and width Fit performed between 40 < mlb < 380 GeV Results Excellent agreement of data and bb4l post-fit Weak correlation (-30%) between mtop and Γtop Extracted width consistent with previous determination Theoretical uncertainty dominated by hdamp and shower variations 15 Top quark mass determination mtop determination including the top-mass dependence in Γtop LO Γtop relation Result Moderate reduction of exp. uncertainties (limited precision of data at large mlb) Reduced theoretical uncertainties Competitive with dedicated measurements 16 Summary Simultaneous determination of mtop and Γtop from a single measurement • First mtop with full NLO treatment of non-resonant and interference effects exploiting the bb4l Monte Carlo event generator • • Multivariate Linear Template Fit to study sensitivity to mtop and Γtop Using ATLAS measurement of mlbminimax at √s=13 TeV Already competitive uncertainties to dedicated measurements Results consistent with world average and previous determinations Top-quark mass effects in Γtop provides small additional sensitivity to mtop with dominant model uncertainties found to be reduced Promising avenue for future LHC measurements 17 Backup 18