Top-Antitop Production at Hadron Colliders Roberto BONCIANI Laboratoire de Physique Subatomique et de Cosmologie, Universit´ e Joseph Fourier/CNRS-IN2P3/INPG, F-38026 Grenoble, France HP2.3rd GGI-Florence, September 15, 2010 – p.1/25
Plan of the Talk General Introduction Top Quark at the Tevatron LHC Perspectives Status of the Theoretical calculations The General Framework Total Cross Section at NLO Analytic Two-Loop QCD Corrections Conclusions HP2.3rd GGI-Florence, September 15, 2010 – p.2/25
Top Quark HP2.3rd GGI-Florence, September 15, 2010 – p.3/25
Top Quark With a mass of m t = 173 . 1 ± 1 . 3 GeV, the TOP quark (the up-type quark of the third generation) is the heaviest elementary particle produced so far at colliders. Because of its mass, top quark is going to play a unique role in understanding the EW symmetry breaking ⇒ Heavy-Quark physics crucial at the LHC. Pair Two production mechanisms Production q t g t p ) → t ¯ pp (¯ t · · · · · · Single Top q ¯ ¯ g ¯ t t q g t t t b W + p ) → t ¯ b, tq ′ (¯ q ′ ) , tW − pp (¯ W + · · · · · · q ′ ¯ ¯ g W − b q ′ (¯ q ′ ) q ′ (¯ q ′ ) Top quark does not hadronize, since it decays in about 5 · 10 − 25 s (one order of magnitude smaller than the hadronization time) = ⇒ opportunity to study the quark as single particle Spin properties Interaction vertices W + Top quark mass V tb t Decay products: almost exclusively t → W + b ( | V tb | ≫ | V td | , | V ts | ) b HP2.3rd GGI-Florence, September 15, 2010 – p.3/25
Top Quark With a mass of m t = 173 . 1 ± 1 . 3 GeV, the TOP quark (the up-type quark of the third generation) is the heaviest elementary particle produced so far at colliders. Because of its mass, top quark is going to play a unique role in understanding the EW symmetry breaking ⇒ Heavy-Quark physics crucial at the LHC. Pair Two production mechanisms Production q t g t p ) → t ¯ pp (¯ t · · · · · · Single Top q ¯ ¯ g ¯ t t q g t t t b W + p ) → t ¯ b, tq ′ (¯ q ′ ) , tW − pp (¯ W + · · · · · · q ′ ¯ ¯ g W − b q ′ (¯ q ′ ) q ′ (¯ q ′ ) Top quark does not hadronize, since it decays in about 5 · 10 − 25 s (one order of magnitude smaller than the hadronization time) = ⇒ opportunity to study the quark as single particle Spin properties Interaction vertices W + Top quark mass V tb t Decay products: almost exclusively t → W + b ( | V tb | ≫ | V td | , | V ts | ) b HP2.3rd GGI-Florence, September 15, 2010 – p.3/25
Top Quark With a mass of m t = 173 . 1 ± 1 . 3 GeV, the TOP quark (the up-type quark of the third generation) is the heaviest elementary particle produced so far at colliders. Because of its mass, top quark is going to play a unique role in understanding the EW symmetry breaking ⇒ Heavy-Quark physics crucial at the LHC. Pair Two production mechanisms Production q t g t p ) → t ¯ pp (¯ t · · · · · · Single Top q ¯ ¯ g ¯ t t q g t t t b W + p ) → t ¯ b, tq ′ (¯ q ′ ) , tW − pp (¯ W + · · · · · · q ′ ¯ ¯ g W − b q ′ (¯ q ′ ) q ′ (¯ q ′ ) Top quark does not hadronize, since it decays in about 5 · 10 − 25 s (one order of magnitude smaller than the hadronization time) = ⇒ opportunity to study the quark as single particle Spin properties Interaction vertices W + Top quark mass V tb t Decay products: almost exclusively t → W + b ( | V tb | ≫ | V td | , | V ts | ) b HP2.3rd GGI-Florence, September 15, 2010 – p.3/25
Top Quark Tevatron LHC To date the Top quark could be Running since end 2009 produced and studied only at the pp collisions at √ s = 7 (14) TeV Tevatron (discovery 1995) p collisions at √ s = 1 . 96 TeV LHC will be a factory for heavy quarks p ¯ ( L ∼ 10 33 − 10 34 cm − 2 s − 1 , t ¯ t at ∼ 1Hz!) L ∼ 6 . 5 fb − 1 reached in 2009 Even in the first low-luminosity phase (2 O (10 3 ) t ¯ t pairs produced so far years ∼ 1 fb − 1 @ 7 TeV) ∼ O (10 4 ) reg- istered t ¯ t pairs Only recently confirmation of single-t HP2.3rd GGI-Florence, September 15, 2010 – p.3/25
Top Quark @ Tevatron HP2.3rd GGI-Florence, September 15, 2010 – p.4/25
Top Quark @ Tevatron Events measured at Tevatron t ∼ 7 pb [ t → W + bW − ¯ b → lνlνb ¯ p → t ¯ p ¯ b Dilepton ∼ 10 % t → W + bW − ¯ q ′ b ¯ p → t ¯ σ t ¯ p ¯ b → lνq ¯ b Lep+jets ∼ 44 % t → W + bW − ¯ q ′ b ¯ p → t ¯ q ′ q ¯ p ¯ b → q ¯ b All jets ∼ 46 % HP2.3rd GGI-Florence, September 15, 2010 – p.4/25
Top Quark @ Tevatron Events measured at Tevatron t ∼ 7 pb [ t → W + bW − ¯ b → lνlνb ¯ p → t ¯ p ¯ b Dilepton ∼ 10 % t → W + bW − ¯ q ′ b ¯ p → t ¯ σ t ¯ p ¯ b → lνq ¯ b Lep+jets ∼ 44 % t → W + bW − ¯ q ′ b ¯ p → t ¯ q ′ q ¯ p ¯ b → q ¯ b All jets ∼ 46 % 2 high- p T lept, ≥ 2 jets and ME HP2.3rd GGI-Florence, September 15, 2010 – p.4/25
Top Quark @ Tevatron Events measured at Tevatron t ∼ 7 pb [ t → W + bW − ¯ b → lνlνb ¯ p → t ¯ p ¯ b Dilepton ∼ 10 % t → W + bW − ¯ q ′ b ¯ p → t ¯ σ t ¯ p ¯ b → lνq ¯ b Lep+jets ∼ 44 % t → W + bW − ¯ q ′ b ¯ p → t ¯ q ′ q ¯ p ¯ b → q ¯ b All jets ∼ 46 % 2 high- p T lept, ≥ 2 jets and ME 1 isol high- p T lept, ≥ 4 jets and ME HP2.3rd GGI-Florence, September 15, 2010 – p.4/25
Top Quark @ Tevatron Events measured at Tevatron t ∼ 7 pb [ t → W + bW − ¯ b → lνlνb ¯ p → t ¯ p ¯ b Dilepton ∼ 10 % t → W + bW − ¯ q ′ b ¯ p → t ¯ σ t ¯ p ¯ b → lνq ¯ b Lep+jets ∼ 44 % t → W + bW − ¯ q ′ b ¯ p → t ¯ q ′ q ¯ p ¯ b → q ¯ b All jets ∼ 46 % 2 high- p T lept, ≥ 2 jets and ME NO lept, ≥ 6 jets and low ME 1 isol high- p T lept, ≥ 4 jets and ME HP2.3rd GGI-Florence, September 15, 2010 – p.4/25
Top Quark @ Tevatron Events measured at Tevatron t ∼ 7 pb [ t → W + bW − ¯ b → lνlνb ¯ p → t ¯ p ¯ b Dilepton ∼ 10 % t → W + bW − ¯ q ′ b ¯ p → t ¯ σ t ¯ p ¯ b → lνq ¯ b Lep+jets ∼ 44 % t → W + bW − ¯ q ′ b ¯ p → t ¯ q ′ q ¯ p ¯ b → q ¯ b All jets ∼ 46 % 2 high- p T lept, ≥ 2 jets and ME NO lept, ≥ 6 jets and low ME 1 isol high- p T lept, ≥ 4 jets and ME Background Processes q ′ q, l − W + g g q q g q g g g Z, γ q, l + W + q g q ¯ q ¯ ¯ q ¯ W − W+jets QCD Drell-Yan Di-boson HP2.3rd GGI-Florence, September 15, 2010 – p.4/25
Top Quark @ Tevatron Events measured at Tevatron t ∼ 7 pb [ t → W + bW − ¯ b → lνlνb ¯ p → t ¯ p ¯ b Dilepton ∼ 10 % t → W + bW − ¯ q ′ b ¯ p → t ¯ σ t ¯ p ¯ b → lνq ¯ b Lep+jets ∼ 44 % t → W + bW − ¯ q ′ b ¯ p → t ¯ q ′ q ¯ p ¯ b → q ¯ b All jets ∼ 46 % 2 high- p T lept, ≥ 2 jets and ME NO lept, ≥ 6 jets and low ME 1 isol high- p T lept, ≥ 4 jets and ME Background Processes q ′ q, l − W + g g q q g q Reduction of the background: b-tagging crucial g g g Z, γ q, l + W + q g q ¯ q ¯ ¯ q ¯ W − W+jets QCD Drell-Yan Di-boson HP2.3rd GGI-Florence, September 15, 2010 – p.4/25
Top Quark @ Tevatron t = N data − N bkgr Total Cross Section σ t ¯ ǫ L Combination CDF-D0 ( m t = 175 GeV) σ t ¯ t = 7 . 0 ± 0 . 6 pb (∆ σ t ¯ t /σ t ¯ t ∼ 9%) Top-quark Mass 14 Mass of the Top Quark (*Preliminary) CDF-I di-l ± ± 167.4 10.3 4.9 Fundamental parameter of the SM. A precise D0-I di-l ± ± 168.4 12.3 3.6 measurement useful to constraint Higgs mass from * CDF-II di-l ± ± 171.2 2.7 2.9 * D0-II di-l ± ± radiative corrections ( ∆ r ) 174.7 2.9 2.4 CDF-I l+j ± ± 176.1 5.1 5.3 D0-I l+j ± ± 180.1 3.9 3.6 A possible extraction: σ t ¯ t = ⇒ need of precise theoretical * CDF-II l+j ± ± 172.1 0.9 1.3 * determination D0-II l+j ± ± 173.7 0.8 1.6 CDF-I all-j ± ± 186.0 10.0 5.7 ∆ m t ∼ 1 ∆ σ t ¯ t * CDF-II all-j ± ± 174.8 1.7 1.9 m t 5 σ t ¯ * CDF-II trk ± ± 175.3 6.2 3.0 t * Tevatron March’09 ± ± 173.1 0.6 1.1 hep-ex/0903.2503 (stat.) (syst.) ± Combination CDF-D0 χ CDF March’07 2 ± ± /dof = 6.3/10.0 (79%) 12.4 1.5 2.2 0 150 160 170 180 190 200 2 m t = 173 . 1 ± 1 . 3 GeV (0 . 75%) m (GeV/c ) top HP2.3rd GGI-Florence, September 15, 2010 – p.5/25
Top Quark @ Tevatron W helicity fractions F i = B ( t → bW + ( λ W = i )) ( i = − 1 , 0 , 1 ) measured fitting the distribution in θ ∗ (the angle between l + in the W + rest frame and W + direction in the t rest frame) 1 d cos θ ∗ = 3 d Γ 4 F 0 sin 2 θ ∗ + 3 8 F − (1 − cos θ ∗ ) 2 + 3 8 F + (1 + cos θ ∗ ) 2 Γ F 0 + F + + F − = 1 F 0 = 0 . 66 ± 0 . 16 ± 0 . 05 F + = − 0 . 03 ± 0 . 06 ± 0 . 03 Spin correlations measured fitting the double distribution ( θ 1 ( θ 2 ) is the angle between the dir of flight of l 1 ( l 2 ) in the t (¯ t ) rest frame and the t (¯ t ) direction in the t ¯ t rest frame) d 2 N 1 = 1 4 (1 + κ cos θ 1 cos θ 2 ) N d cos θ 1 d cos θ 2 − 0 . 455 < κ < 0 . 865 (68% CL ) A F B = N ( y t > 0) − N ( y t < 0) Forward-Backward Asymmetry N ( y t > 0) + N ( y t < 0) A F B = (19 . 3 ± 6 . 5( sta ) ± 2 . 4( sys ))% HP2.3rd GGI-Florence, September 15, 2010 – p.6/25
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