Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS 27th May 2020 1 / 19
Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Introduction ◮ The Top pair cross-section at the LHC is large! - ∼ 830 pb at 13 TeV ◮ In Run II over 100 Million top–anti-top pair will have been produced in ATLAS. ◮ This gives us a large dataset to study the different properties of the top, the production mechanisms and its decay. ◮ We study the properties of all the different parts of top production, the top quark, the top decay, and the properties of the decay products... ◮ ATLAS has produced a large number of results so I will focus on a few here; LINK TO ALL RESULTS Properties Related to Production - Cross-section and Kinematics of the top and top+anti-top system -> see talk by P. Jacka - Spin correlations - Charge asymmetry - Top quark polarization - FCNCs - Many more . . . 2 / 19
Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Introduction ◮ The Top pair cross-section at the LHC is large! - ∼ 830 pb at 13 TeV ◮ In Run II over 100 Million top–anti-top pair will have been produced in ATLAS. ◮ This gives us a large dataset to study the different properties of the top, the production mechanisms and its decay. ◮ We study the properties of all the different parts of top production, the top quark, the top decay, and the properties of the decay products... ◮ ATLAS has produced a large number of results so I will focus on a few here; LINK TO ALL RESULTS Properties Fundamental Related to Properties of Production the top quark - Cross-section and Kinematics - Mass of the top and top+anti-top -> see talk by M. Negrini system - Width -> see talk by P. Jacka -> see talk by M. Negrini - Spin correlations - Charge - Charge asymmetry - Spin (indirectly) - Top quark polarization - FCNCs - Many more . . . 3 / 19
Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Introduction ◮ The Top pair cross-section at the LHC is large! - ∼ 830 pb at 13 TeV ◮ In Run II over 100 Million top–anti-top pair will have been produced in ATLAS. ◮ This gives us a large dataset to study the different properties of the top, the production mechanisms and its decay. ◮ We study the properties of all the different parts of top production, the top quark, the top decay, and the properties of the decay products... ◮ ATLAS has produced a large number of results so I will focus on a few here; LINK TO ALL RESULTS Properties Fundamental Properties Related to Properties of Related to Production the top quark Decay - Cross-section and Kinematics - Mass - W-helicity measurements of the top and top+anti-top -> see talk by M. Negrini - CLFV: t->ll'q system - Width - FCNC: eg. t->hu, t->hc, -> see talk by P. Jacka -> see talk by M. Negrini t->Zu, t->Zc, - Spin correlations - Charge t-> γ u, t-> γ c - Charge asymmetry - Spin (indirectly) -> see talk by K. Skovpen - Top quark polarization - Jet shapes and colour flow - FCNCs - Anomalous couplings - Many more . . . - Many more . . . 4 / 19
Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Introduction ◮ The Top pair cross-section at the LHC is large! - ∼ 830 pb at 13 TeV ◮ In Run II over 100 Million top–anti-top pair will have been produced in ATLAS. ◮ This gives us a large dataset to study the different properties of the top, the production mechanisms and its decay. ◮ We study the properties of all the different parts of top production, the top quark, the top decay, and the properties of the decay products... ◮ ATLAS has produced a large number of results so I will focus on a few here; LINK TO ALL RESULTS Properties Fundamental Properties Properties Related to Properties of Related to of W-boson Production the top quark Decay from tt events - Cross-section and Kinematics - Mass - W-helicity measurements - Measurement of universality of the top and top+anti-top -> see talk by M. Negrini - CLFV: t->ll'q lepton c ♦ ns ♦ � ✁ ✂ ✄☎ ✆ ✝ ✞♦ ✟ ✠ ✡ ♦ ✝ system - Width - FCNC: eg. t->hu, t->hc, through: N -> see talk by P. Jacka -> see talk by M. Negrini t->Zu, t->Zc, ❊ ❲ - Spin correlations - Charge t-> γ u, t-> γ c ✦ - Charge asymmetry - Spin (indirectly) -> see talk by K. Skovpen - Top quark polarization - Jet shapes and colour flow - FCNCs - Anomalous couplings - Many more . . . - Many more . . . 5 / 19
Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Introduction ◮ The Top pair cross-section at the LHC is large! - ∼ 830 pb at 13 TeV Too many results to cover! ◮ In Run II over 100 Million top–anti-top pair will have been produced in ATLAS. ◮ This gives us a large dataset to study the different properties of the top, the Today I focus on 3 results... production mechanisms and its decay. - Charge as ymmetry A N LAS ❚ Comparison ✭ ◮ We study the properties of all the different parts of top production, the top quark, ✮ CMS - Spin Correlations bet ween t ✣✤ i-top ✴ the top decay, and the properties of the decay products... ✚ ✛ ✜ ✢ - Measurement of the universality of the lepton ◮ ATLAS has produced a large number of results so I will focus on a few here; N couplings t ✪ ✚ ✥ ✧ ★ ✚ ✩ ✚ ✣ ✫ LINK TO ALL RESULTS ✬ Properties Fundamental Properties Properties Related to Properties of Related to of W-boson Production the top quark Decay from tt events - Cross-section and Kinematics - Mass - W-helicity measurements - Measurement of universality of the top and top+anti-top -> see talk by M. Negrini - CLFV: t->ll'q lepton c ☛ ns ☛ ☞ ✌ ✍ ✎✏ ✑ ✒ ✓☛ ✔ ✕ ✖ ☛ ✒ system - Width - FCNC: eg. t->hu, t->hc, through: N -> see talk by P. Jacka -> see talk by M. Negrini t->Zu, t->Zc, ✗ ✘ - Spin correlations - Charge t-> γ u, t-> γ c ✙ - Charge asymmetry - Spin (indirectly) -> see talk by K. Skovpen - Top quark polarization - Jet shapes and colour flow - FCNCs - Anomalous couplings - Many more . . . - Many more . . . 6 / 19
Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Charge Asymmetry ATLAS-CONF-2019-026 ◮ At leading order t ¯ t production is charge symmetric. ◮ However, at higher orders inferference in qg and q ¯ q , and EW contributions lead to asymmetries. Also BSM physics can lead to enhancements! ◮ The gg initiated process remains charge symmetric to all orders and as this is the dominant production mechanism this dilutes the asymmetry significantly. A C = N (∆ | y | > 0) − N (∆ | y | < 0) . ∆ | y | = | y t | − | y ¯ t | N (∆ | y | > 0)+ N (∆ | y | < 0) ◮ This expresses the asymmetry between the top or the anti-top being more forward; positive values indicate the top is more forward than the anti-top. q t Not t anti-top ✯ ✰ ✱ ✲ ✳✵ ✶ q t q t top q t 7 / 19
Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Charge Asymmetry - Selection and t ¯ t Reco. ATLAS-CONF-2019-026 ◮ In the resolved analysis (boosted events removed); ◮ A BDT is used to assign the different jets to the top systems, including KLFitter, mass of the hadronic top and W, and various angular variables. ◮ The best combination is used and only events with good reconstruction according to the BDT output are retained. ◮ Boosted reconstruction to access highest kinematic regions; ◮ At high p T the hadronic top can be reconstructed as a single large-R jet with p T > 350 GeV, and the mass and τ 32 is used to “tag” hadronic tops. ◮ The leptonic side is reconstructed from the E miss , lepton and a R = 0 . 4 jet. T 8 / 19
Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Charge Asymmetry - Results ATLAS-CONF-2019-026 ◮ Results are presented for the inclusive value of A C ; A C = 0 . 0060 ± 0 . 0015[ ± 0 . 0011( stat. ) ± 0 . 0009( syst. ) ± 0 . 0005( MC stat. ) ± 0 . 0001( bias. )] ◮ 4 σ from 0! - first evidence of non-zero charge asymmetry in t ¯ t ! ◮ This is in good agreement of the NNLO calculation of 0 . 0064 ± 0 . 0006 ◮ Additionally A C is also unfolded in bins of the mass of the t ¯ t system and also in the absolute longitudinal boost of the t ¯ t system in the z -direction, β t ¯ t , z . ◮ In both variables good agreement is seen with the SM. ◮ Limits are set in an EFT based on the inclusive and m t ¯ t results. 9 / 19
Top Properties from ATLAS Chris Young (CERN), on behalf of ATLAS Charge Asymmetry - Results ATLAS-CONF-2019-026 ◮ Results are presented for the inclusive value of A C ; A C = 0 . 0060 ± 0 . 0015[ ± 0 . 0011( stat. ) ± 0 . 0009( syst. ) ± 0 . 0005( MC stat. ) ± 0 . 0001( bias. )] ◮ 4 σ from 0! - first evidence of non-zero charge asymmetry in t ¯ t ! ◮ This is in good agreement of the NNLO calculation of 0 . 0064 ± 0 . 0006 ◮ Additionally A C is also unfolded in bins of the mass of the t ¯ t system and also in the absolute longitudinal boost of the t ¯ t system in the z -direction, β t ¯ t , z . ◮ In both variables good agreement is seen with the SM. ◮ Limits are set in an EFT based on the inclusive and m t ¯ t results. 10 / 19
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