Standard Model Physics Results at CMS - Andrew Levin (Peking University) 28 March 2021 Moriond QCD 2021
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Standard Model Physics Results at CMS Andrew Levin (Peking University) 28 March 2021 Moriond QCD 2021 28 March 2021 Andrew Levin 1
Introduction • “Standard Model Physics” = Standard Model Physics – Higgs Physics – Top Physics • Physics processes we measure (boson = W, Z, γ) • Multijet production • Double parton scattering (DPS) • Single boson production • Boson+jets production • Multiboson production • Vector boson scattering (VBS) • Observables that we measure • Inclusive cross sections over X orders of magnitude • Differential, double-differential, even triple- differential cross sections • Searches for rare processes • Limits on anomalous couplings • Precise measurements of Standard Model parameters • Polarization fractions • In principle, observables depend on SM parameters. In practice, observables depend on SM parameters + generator tools. 28 March 2021 Andrew Levin 2
SMP-20-009 Preliminary result DPS with Z + jets final state • Jets are expected to balance each other in the DPS case but not in the SPS case • Study variables sensitive to the pT balance Ԧ (A)+ Ԧ (B) • ∆rel A, B = Ԧ (A) + Ԧ (B) • Δφ(Z,j) SPS DPS 28 March 2021 Andrew Levin 3
SMP-20-007 DPS with four jet final state Preliminary result • = (n = 2 if A = B and 1 otherwise) 2 • σeff extracted using distribution of −1 Ԧ ,1 + Ԧ ,2 ∙ Ԧ ,3 + Ԧ ,4 ∆ = cos Ԧ ,1 + Ԧ ,2 Ԧ ,3 + Ԧ ,4 • σeff is heavily model-dependent SPS DPS 28 March 2021 Andrew Levin 4
SMP-20-008 → Submitted to PLB Search for W± π± γ • A decay to all visible decay products: would provide a precise way to measure the W mass • Exclusion limit (95% confidence): B(W± → π±γ) < 1.50 × 10-5 • Trigger on additional electrons or muons (separated from the pion) • Train BDT to separate signal vs. background , input variables include kinematics and pion isolation • Signal extracted through fit to mπγ after BDT cut • Signal modeled with double crystal ball + Gaussian, background modeled with Chebyshev polynomial 28 March 2021 Andrew Levin 5
SMP-18-011 W branching fractions (I) Preliminary result • Important test of lepton universality • Use events with 2 Ws, mainly tt,ҧ but also tW and WW • Events categorized based on lepton flavor (muon, electron, or hadronic τ), jet multiplicity, and b-tagged jet multiplicity • Simultaneous fit of all categories and the distribution of a single kinematic variable within each category 28 March 2021 Andrew Levin 6
SMP-18-011 W branching fractions (II) Preliminary result • Both leptonic and hadronic branching fractions measured • Hadronic branching fractions reported with and without assuming lepton universality • Constrain the CKM matrix parameters and the strong coupling constant: 2 ( ) = 0.094 ± 0.033 • Uncertainties are comparable to or smaller than LEP σ 2 = 1.989 ± 0.021 |Vcs| = 0.969 ± 0.011 28 March 2021 Andrew Levin 7
SMP-18-003 Z→νν differential cross section Submitted to JHEP • Important background to new physics searches (e.g. dark matter) miss distribution plus two control regions • Signal is extracted from fits to T • Fiducial cross section measured for Z pT > 200 GeV • Measured: 3000+180 −170 fb • Predicted using MadGraph5_aMC@NLO: 2700 ± 440 fb • Differential measurement in 5 Z pT bins • Combination with charged lepton channels 28 March 2021 Andrew Levin 8
SMP-19-011 Z+c differential cross sections Accepted by JHEP • Probe the charm content of the proton • Extract Z+c component by fitting to: MSV = invariant mass of all tracks associated with a secondary vertex • Integrated cross section: • Measured: 405.4 ±5.6 (stat) ± 24.3 (exp) ± 3.7 (theo) pb • Prediction from MadGraph5_aMC@NLO at NLO: 524.9 ±11.7(theo) pb • Is charm content overestimated? 28 March 2021 Andrew Levin 9
SMP-20-012 Diboson cross section measurements Preliminary result at 5.02 TeV • Based on 304 pb-1 collected in November 2017 during a “pp reference” run for heavy ion physics • Reduces the gap between Tevatron and LHC measurements • All calibration/scale/correction factors need to remeasured for different conditions • Some systematic uncertainties are reduced due to lower pileup, but overall uncertainty dominated by statistical component 28 March 2021 Andrew Levin 10
SMP-20-014 WZ cross section, polarization, and gauge Preliminary result coupling measurements (I) • Inclusive cross section • Observed: σ = 50.6 ± 0.8 (stat) ± 1.5 (syst) ± 1.1 (lumi) ± 0.5 (theo) pb • MATRIX NNLO QCD × NLO EWK: σ = 50.7+1.1 −1.0 (scale) pb • POWHEG NLO QCD: σ = 42.5+1.6 −1.4 (scale) ± 0.6 (PDF) pb • First observation of longitudinally polarized W bosons in WZ production • Charge asymmetry ratio = σfid(W+Z)/σfid(W-Z) • Measured: 1.41 ± 0.04 (stat) ± 0.01 (syst) ± 0.01 (lumi) • MATRIX NNLO QCD × NLO EWK: 1.427+0.002 −0.002 (scale) +0.06 • POWHEG NLO QCD: 1.42−0.05 (scale+PDF) 28 March 2021 Andrew Levin 11
SMP-20-014 WZ cross section, polarization, and gauge Preliminary result coupling measurements (II) • Many flavors of triple gauge coupling measurements extracted from MWZ distribution • 1D and 2D • 68, 95, 99% confidence • Interference-only and interference+pure BSM • Likelihood scans • With and without cutoff scale • Differential cross sections for several variables 28 March 2021 Andrew Levin 12
SMP-19-002 Wγ cross section and effective field Submitted to PRL theory constraints • Wγ fiducial cross section measurement based on fit to mlγ distribution: • σ = 15.44 ± 0.05 (stat) ± 0.84 (exp) ± 0.12 (theory) pb • Theoretical cross sections: • MadGraph5_aMC@NLO 0+1 jets at NLO: 15.44 ± 1.24 pb • POWHEG with “NLO competition” scheme: 22.45 ± 3.21 pb • Limits on dimension 6 EFT operators based on photon pT distribution 28 March 2021 Andrew Levin 13
SMP-20-005 Wγ differential cross section and Preliminary result effective field theory constraints • Technique called interference resurrection used to enhance anomalous coupling sensitivity • Phenomenon called radiation amplitude zero: a 0 in the LO cross section at Δη(l,γ) = 0 28 March 2021 Andrew Levin 14
SMP-19-013 Wγγ and Zγγ production Preliminary result • Significances, cross section, and anomalous couplings limits extracted from fit to diphoton mass distribution • Observed 3.1 σ Wγγ signal and 4.8 σ Zγγ signal, expected 4.5 σ and 5.8 σ, respectively • Measured cross sections: • σWγγ = 13.63+1.93 +4.04 −1.89 (stat)−4.02 (syst) ± 0.08 (PDF+scale) fb Quartic gauge coupling • σZγγ = 5.41+0.58 +0.64 −0.54 (stat)−0.70 (syst) ± 0.06 (PDF+scale) fb 28 March 2021 Andrew Levin Triple gauge coupling 15
Wγ scattering SMP-19-008 Published in PLB • Probe triple and quartic gauge coupling diagrams • VBS signature: two jets with large η separation and large dijet mass • SM signal extracted through 2D mjj vs. mlγ fit Quartic gauge coupling Triple gauge coupling • Observed (expected) significance for new 13 TeV analysis: 4.9 (4.6) • Observed (expected) significance for new 13 TeV + older 8 TeV analyses: 5.3 (4.8) • Anomalous coupling limits set using mWγ distribution 28 March 2021 Andrew Levin 16
SMP-20-001 Published in PLB ZZ scattering • Matrix element discriminant (KD) to separate signal from QCD ZZ+jets, inputs include both lepton and jet kinematics • Signal strength extracted through fit KD to distribution • 4.0 σ signal observed, while 3.5 σ expected • Limits on dimension 8 anomalous couplings calculated based on m4l distribution • Measured cross section for EW pp → ZZjj → 4ljj is smallest cross section measured by CMS: = 0.33+0.11 −0.10 (stat) +0.04 −0.03 (syst) fb 28 March 2021 Andrew Levin 17
Zγ scattering SMP-20-016 Preliminary result • Observed significance much greater than 5 σ • Fiducial cross section measured based on 2D mjj vs Δηjj distribution: 5.43 ± 0.65 (stat) ± 0.71 (syst) fb • Differential cross section in 4 observables • Anomalous coupling limits set based Quartic gauge coupling on mZγ distribution Triple gauge coupling 28 March 2021 Andrew Levin 18
SMP-20-006 Longitudinally-polarized W±W± scattering Published in PLB • The Higgs boson is expected to restore unitarity to the WLWL scattering amplitude → WLWL scattering is a good place to search for non-SM Higgs couplings • First attempt at measuring EW WLWLjj, building on our unpolarized EW WWjj result • Fit 2D BDT distribution • BDT1 separates VBS from non-VBS • BDT2 separates polarization states within VBS • Observed (expected) significance for LL: 0.88 (1.17) • Observed (expected) significance for LT+LL: 2.3 (3.1) 28 March 2021 BDT2 score Andrew Levin BDT2 score 19
More CMS SM results to be shown later this week • Henning’s talk “Standard Model QCD with jet and photons at CMS and ATLAS” • Angular distances and momentum ratios in Z+2 jet and 3 jet events (SMP-17-008) • Z+jets and γ+jets differential cross section (SMP-19-010) • Davide’s talk “Standard Model soft QCD at ATLAS and CMS” SMP-17-008 • Hard color-singlet exchange in dijet events (SMP-19-006) Submitted to EPJC SMP-19-010 SMP-19-006 Submitted to JHEP Submitted to PRD 28 March 2021 Andrew Levin 20
Conclusions • The CMS Standard Model group continues to dig deeper into the Run 2 data • Always exploring new machine learning tools, anomalous coupling frameworks, generator tools, limit setting tools, data formats • Also promoting more consistent use of Rivet and HepData to share results with outside community • Stepping back to look at the progress we have made: LEP Tevatron Cross section 15 years 15 years ? W Z Wγ Zγ WW WZ ZZ 28 March 2021 Andrew Levin 21
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