Top quark properties within the Standard Model LHC

Top quark properties within the Standard Model LHC possibilities after one year and more Bernardo Resende on behalf of the ATLAS collaboration TOP 2006 Workshop, Coimbra B. Resende - TOP 2006 - Top SM properties

Introduction High top statistics at LHC (8 M tt + 3 M EW top/year at 1033 cm-2 s-1) – Top quark properties checked precisely ( verify SM ? ) • Quantum numbers ; branching ratios (Vtb) ; Higgs coupling • Similar reconstruction for all studies (based on crosssection) Window into new physics : • Mtop close to EWSB scale • New particles and couplings • Background for Higgs, . . . B. Resende - TOP 2006 - Top SM properties Top quark physics at the frontier 17/09/2020 2

Some top studies Charge : lept + b 10 fb-1 Top polarization 10 -1 fb Top spin correlations 10 fb-1 W polarization 10 fb-1 Vtb 30 fb-1 Ø Charge : tt 10+ fb-1 Ø Yukawa coupling : tt. H 30+ fb-1 17/09/2020 B. Resende - TOP 2006 - Top SM properties 3

Selection and reconstruction ref : hep-ex/0508061 Event selection in semileptonic channel : 1 isolated lepton PT>20 Ge. V, |η|<2. 5 > 2 b-jets PT>30 Ge. V, |η|<2. 5 > 2 light jets PT>30 Ge. V, |η|<2. 5 Event reconstruction : > 20 Ge. V missing PT – Hadronic W : pair with Mjj closest to MW – Leptonic W : lepton + missing PT • Pzn constrained by MW – Hadronic top : match W-b with MWb closest to Mtop – Leptonic top : b closest to lepton 17/09/2020 B. Resende - TOP 2006 - Top SM properties 4

Spin and polarization studies Top decay faster than hadronization timescales – Spin information transmitted to Wb jjb / lnb Test SM couplings with clean probe – Polarization from angular distributions of spin θ daughters : i Particl e daughter i αi : spin analyzing power of daughter particle i (-1 to 1) 17/09/2020 B. Resende - TOP 2006 - Top SM properties 5

W polarization in top decay Top decay : major source of longitudinal W’s – Polarization depends only on Mt and MW (LO) Longitudinal W+ (F 0) Standard Model (Mtop=175 Ge. V) 0. 703 NLO Left-handed W+ (FL) Right-handed W+ (FR) 0. 297 0. 695 0. 000 0. 304 Sensitive to EWSB 0. 001 Test of V-A structure 1/N d. N/dcos All 3 components in angular distribution of lepton in W rest frame : n b t W+ l+ 17/09/2020 Angle between: • lepton in W rest frame and • W in top rest frame B. Resende - TOP 2006 - Top SM properties cos 6

Measurement methodref : hep-ex/0508061 Ratio reco / theory (MC) correct bias of detector/trigger effects, analysis cuts… Correction function : cos 1/N d. N/dcos Reconstruction and cuts parton level 1/weight 1/N d. N/dcos – Use two independent samples (in simulation) cos apply weights event by cos 17/09/2020 event Apply this method for W polarization and spin correlation B. Resende - TOP 2006 - Top SM properties 7

W helicity results ref : hep-ex/0508061, L. Sonnenschein, Ph. D th. Results for 10 fb-1, fast simulation : SM values CMS ± Stat semileptonic F 0 FR 0. 703 0. 000 ± ± 0. 023 0. 015 ATLAS 10 fb 1 semileptonic (corrected) ATLAS semi + ± ± dilep 0. 004 0. 003 CMS 10 fb-1 CMS Precision ± driven±by semileptonic 0. 022 0. 053 ± semileptonic (not corrected Syst ATLAS semi + ± ± ) Precisiondilep between 0. 016 1% and 7% dominated by 0. 012 systematics 17/09/2020 B. Resende - TOP 2006 - Top SM properties 8

Sensitivity to new physics ref : hep-ex/0508061 From W polarization, deduce sensitivity to t. Wb anomalous couplings model independent approach, i. e. effective Lagrangian F 0 and 4 couplings (in SM LO ± 1 s Anomalous coupling 17/09/2020 ) 2σ limit (stat syst) on = 0. 04 3 times better than indirect limits (B-factories, LEP) Less sensitive to and already severely constrained by B-factories B. Resende - TOP 2006 - Top SM properties 9

Spin studies with detailed simulation Full detector simulation more realistic predictions – Better understanding of systematics Spin correlation and W helicity studies currently being done – First comparisons : reasonable agreement with previous results – Very CPU-consuming global collaboration efforts F 0=0. 699 ± 0. 005 FL=0. 299 ± 0. 003 FR=0. 002 ± 0. 003 F 0=0. 677 ± 0. 015 FL=0. 309 ± 0. 009 FR=0. 014 ± 0. 009 Latest simulations (ATLAS) : Fast simulation 10 fb-1 17/09/2020 Full simulation (preliminary) 1. 5 fb-1 B. Resende - TOP 2006 - Top SM properties 10

Top spin with single tops ref : ATL-PHYS-2000017 Polarization > 90% along d-type quark direction u, d, s, c – Spectator basis used (if b missed, ~ helicity basis) Theory : mostlyand left- lepton in – θ angle between top direction handed top decay parton level reco + cuts 17/09/2020 low PT : often missed Deformation corrected through a χ² Minimize a set of fth(cos θ, P) – fdata(cos θ) selecte S/ polarization statistical Extract P with uncertainties d B (%) precision events 3500 2. 6 parton reco 2 pb-1 10 fb-1 94. 6 95. 8 4% 1. 6 %11 B. Resende - TOP 2006 - Top SM properties

tt spin correlation Tops not polarized in pairs, but correlations between spins – Like-spin pairs more abundant in LHC A=0. 33 SM ; or top spin ≠ 1/2, anomalous coupling, t H+b AD=-0. 24 Measure angular distributions of daughters in top rest frames Angle between t(t) and spin analysers Angle between spin analysers 17/09/2020 B. Resende - TOP 2006 - Top SM properties 12

Background and systematics ref : hep-ex/0508061 Nb of selected events (10 fb-1) Q-scale tt semilep 85000 ISR/FSR tt t + X 6200 S/B= 12 W+4 jets [400, 1000] Single top 350 of Nb selected 290 events (10 fb-1) Other S/B=6 (sum) tt dileptonic 21000 PDFs b-frag. Hadronization b-tag. (± 5%) b-miscalib. (± 3%) light-miscalib. (± 1%) Top mass (± 2 Ge. V) S/B (± 10%) Pile-up (2. 3) t + lbackground 3700 : tt Main Dominant contributions (semilep) taus Other <350 B. Resende - TOP 2006 - Top SM properties 17/09/2020 13 (sum)

ref : hep-ex/0508061, Spin correlation results L. Sonnenschein, Ph. D th. Results with fast simulation of detector : A 0. 33 AD A 1 AD 1 1(Mtt<550 Ge. V) SM enhance 0. 42 -0. 29 correlation values 0. 24 ΔA/A ΔAD/A relative errors D CMS, 30 fb-1, dileptonic 11% Statistical ATLAS, 10 fb-1, semi + 3% 3% dileptonic Systemati cs CMS, 30 fb-1, dileptonic 9% precision 3% driven by ATLAS, 10 fb-1, semi +A, AD 5% dileptonic (ATLAS) Precision dominated by systematics dileptonic – CMS does not include semileptonic channel 17/09/2020 B. Resende - TOP 2006 - Top SM properties 14

Top charge Motivation : confirm Qtop = 2/3 t t – Exotic Qtop = -4/3 could be hidden in tt pair W b + Two methods for direct measurement : – Study of radiative top processes • Production of in tt event depends on Qtop • Low statistics, high background – Charge of decay products (lepton and b) • Good measurement of Qlep with LHC detectors • Qb-jet more challenging 17/09/2020 B. Resende - TOP 2006 - Top SM properties 15

Top charge through decay products ref : ATL-PHYS-2003035 Charge of decay products : t Wb lnb ; Qtop = Qb + Correctly assign Qfrom l+b lepton to b-jet : Mlb < Mtop Semilep : 1 good matching, others wrong Dilep : only one lepton may match both b’s Results : lepton+je ts eff (%) S/ B nb of evts 0. 7 65 1200 same top Mtop Estimate b-jet charge : wrong associatio ns b-jet -0. 109 ± 0. 007 b-jet 0. 112 ± 0. 007 dilepton Results could arrive rapidly (5σ separation between b and b 5. 4 10 1200 with 24 pb-1) Systematics to be. B. done 17/09/2020 Resende - TOP 2006 - Top SM properties 16

Vtb (1) SM prediction : Vtb ~ 1 – Confirm three-generation structure – Look for exotic top decays tt pairs : SM-dependent measurement (3 generations) – Estimate of Electroweak single top : direct measurement – Cross-sections proportional to |Vtb|² • Uncertainty on Vtb ~ ½ uncertainty on σ – Wg fusion and s-channel studied 17/09/2020 B. Resende - TOP 2006 - Top SM properties 17

ref : SN-ATLAS-2000017 SN-ATLAS-2001 -007 Vtb (2) Backgrounds : tt, W+jets, Wbb (+ other single top channels) – Cross-section at LHC not well-known for W+jets and Wbb – Selection constrained by need of background suppression Chann Select S/B Uncertainties ΔVtb/V tb el for 30 edfb-1 3 years on σat low luminosity Results : events statistics theory W* 900 0. 5 5. 6% 5 7. 5% 4. 7% Limited by theoretical uncertainties μ scale, Wg 49000 2. 3 0. 54% 11%(pdf, 5. 5% ΔMtop) Systematics to be estimated 17/09/2020 B. Resende - TOP 2006 - Top SM properties 18

Top Yukawa couplingref : ATL-PHYS-2003 -030 gt 2 = 2 Mt 2 / v 2 ~ 1 : a coincidence ? Measurement from tt. H ( bb, WW) + other channels – Without total H width, ratio of couplings or gt under hypotheses Relative precisions : ATLAS 30 fb-1 300 fb -1 ratio g²t / g²W : 15 to 30 % @ 300 fb-1 17/09/2020 ATLAS 300 fb-1 gt : 20 to 30 % @ 300 fb-1 B. Resende - TOP 2006 - Top SM properties 19

Conclusions LHC will be a top factory – Precision physics possible Results available already after first year – Strict (common) cuts good rejection of background – Percent-level precision expected for many studies – Various channels combined for better results Still work to be done – Update with detailed, realistic (as-built) detector simulation 17/09/2020 B. Resende - TOP 2006 - Top SM properties 20

Spare slides B. Resende - TOP 2006 - Top SM properties

Selection criteria for top spin studies Selection for single top : Wg s-channel 1 isolated lepton, PT > 20 Ge. V, |η| < 2. 5 1 b-tagged jet, PT > 50 Ge. V, |η| < 2. 5 Selection for tt pairs : CMS semilep 1 forward light jet, PT > 50 Ge. V, 2. 5 < |η| < 5 ATLAS semilep 1 other jet (light or b), PT > 30 Ge. V, |η| < 2. 5 CMS dilep 2 opp. charge : PT>20 Ge. V, |η|<2. 4 ATLAS dilep 2 opp. charge : PT>20 Ge. V, |η|<2. 5 isolated lepton 1 : PT>20 Ge. V, |η|<2. 4 1 : PT>20 Ge. V, η|<2. 5 b-jets 2 : PT>30 Ge. V, |η|<2. 5 >2 : PT>30 Ge. V, |η|<2. 5 2 : PT>20 Ge. V, |η|<2. 5 light jets >2 : PT>20 Ge. V, |η|<2. 5 >2 : PT>30 Ge. V, |η|<2. 5 any number missing PT 17/09/2020 > 20 Ge. V B. Resende - TOP 2006 - Top SM properties > 40 Ge. V 22

Measurement method (Top polarization) Ratio reconstructed / theory (MC) correct bias – Use two independent samples (in simulation) parton level 1/weight Correction function : Reconstruction and cuts 9*cosθ 1*cosθ 2 apply weights event by event 17/09/2020 Apply this method for spin correlation and W polarization B. Resende - TOP 2006 - Top SM properties 23

Background and systematics (W polarization) Nb of selected events (10 fb-1) Q-scale tt semilep 85000 ISR/FSR tt t + X 6200 b-frag. W+4 jets [400, 1000] Hadronization Single top 350 of Nb selected 290 events (10 fb-1) S/B= 12 Other S/B=6 (sum) tt dileptonic ref : hep-ex/0508061 PDFs b-tag. (± 5%) 21000 b-miscalib. (± 3%) Top mass (± 2 Ge. V) S/B (± 10%) Pile-up (2. 3) t + lbackground 3700 : tt Main Dominant contributions (semilep) taus Other <350 B. Resende - TOP 2006 - Top SM properties 17/09/2020 24 (sum)

Top charge in radiative processes ref : ATL-PHYS-2003035 Radiative production : pp tt σ proportional to |Qtop|² Radiative decay : pp tt Wb. Wb interferences σ higher for Qtop =Select 2/3 and count events in each case pp tt Qtop = 2/3 Qtop = -4/3 nb of evts S/ B nb of evts 80 ± 9 1. 1 250 ± 16 S/ B 3. 6 Qtop = 2/3 10 ± 3 0. 4± 2 0. tt Wb. Wb More statistics probably needed 7 2 Systematics to be done 17/09/2020 ATLAS 10 fb-1 Qtop = -4/3 B. Resende - TOP 2006 - Top SM properties pp tt 25