# Top Quark Mass Measurements and Decay Properties CDF

- Slides: 22

Top Quark Mass Measurements and Decay Properties CDF and DØ collaborations Robert Zitoun Stony Brook and LAPP Outline : 3 new (preliminary) measurements • Mass CDF Run II • Improved mass DØ Run I • W helicity CDF Run I R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Motivation • • Discovered ~ 8 years ago. Still little known (~100 events + background) Mass Mt is a basic standard model parameter • Affects observables (LEP/SLD, n. N) through radiative corrections • 2 Ge. V on Mt is worth 10 Me. V on MW • Mt ~ <f > = v√ 2 =175 Ge. V EW symmetry breaking understanding might benefit from study of its decay properties R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Top Mass: Published Results DØ CDF dilepton 168. 4 ± 12. 3 ± 3. 6 Ge. V lepton + jets combined 172. 1 ± 5. 2 ± 4. 9 Ge. V 172. 1 ± 7. 1 Ge. V dilepton + jets all hadronic combined 167. 4 ± 10. 3 ± 4. 8 Ge. V 176. 1 ± 5. 3 Ge. V 186. 0 ± 10. 0 ± 5. 7 Ge. V 176. 1 ± 6. 6 Ge. V Tevatron • 174. 3 ± 5. 1 Ge. V statistics background • 2ℓ + 2 jets 5% Z, instrumental • 1ℓ(e/ ) + 4 jets 30% W + 4 jets • 6 jets 45% QCD combinatorics jet energy scale b-tagging reduces background and combinatorics R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Mt measurement Case of 1ℓ + 4 jets event • 2 -constraint kinematical fit → Mt • pn unknown – 3 • Impose p. T balance +2 • M(q 1 q 2) = MW +1 • M(ℓn) = MW +1 • M(W+b) = M(W–b) +1 • 4 jets: 12 combinations per event (× 2 depending on kinematics ambiguities) → keep best c 2 • Fit Mt distribution with modeled production and background q 1 q 2 b q W t q R. Zitoun, Stony Brook and LAPP t n W b ℓ CDF Run 1 Moriond 2003, QCD session

CDF Run II Data Mass Measurement ℓ + 4 jets channel R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Data • Integrated luminosity 72 pb-1 • Event selection (similar to Run I) • • One isolated high p. T central e or 4 jets ET>15 Ge. V & | |<2. 0 ET>20 Ge. V Z veto Jet 1 Jet 2 Jet 4 µ • muon • electron • photon 33 candidates • Jet 3 Background (~13 events) • • W + 4 jets fake leptons, diboson, Drell-Yan, single top R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Result CDF preliminary • • • was 4. 4 Ge. V in Run I should improve quickly with improved detector understanding Systematics break down R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Using b-tagging • Reduce background with b-tagging (56 pb-1 only) • • event tagging efficiency = 45 ± 1 ± 5 % (from data + MC) Relax 4 th jet > 8 Ge. V 11 candidates (background ~ 1 event) • Not yet fitted, but looks like a mass peak R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

DØ Run I Data Mass Reanalysis ℓ + 4 jets channel R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

• Outline of the method Kondo’s method (uses full set of event observables) • Define a signal event probability • Define a background probability i-th event final state • Build an event probability parameters (Mt, c 1, c 2) • Build a likelihood • Minimize to get Mt (c 1 and c 2) R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Signal and Background • Signal probability • Background probability • Only W + 4 jets background considered MC signal MC bkg • 80% of total • found adequate to represent multijet background • Calculated with VECBOS • Keep events with Pbkg<10– 11 R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

• Result DØ Run. I statistics (125 pb– 1) [PRD 58 (1998), 052001] • events: 91 → 77 with exactly 4 jets → 22 after prob cut -log(likelihood) vs Mt • likelihood vs Mt Preliminary result: Mt = 179. 9 3. 6 6. 0 Ge. V was 5. 6 Ge. V eq. × 2. 4 increase in stat R. Zitoun, Stony Brook and LAPP next slide Moriond 2003, QCD session

• • • Systematic Uncertainty Main contribution from jet energy scale Signal model 1. 5 Ge. V Jet Energy Scale 5. 6 Ge. V Background model 1. 0 Ge. V Parton Distribution Function 0. 2 Ge. V Noise and multiple interactions PRD 58 52001, (1998) 1. 3 Ge. V Acceptance Correction 0. 5 Ge. V Improvement in systematics coming soon Further improvement by controlling the W→jj mass -log(likelihood) vs MW R. Zitoun, Stony Brook and LAPP likelihood vs MW Moriond 2003, QCD session

CDF Run I Data W helicity in top decay R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Top quark Decay • In V–A theory, top produces no h = +1 W; only • h = 0: 70% t • h = – 1: 30% b n W+ yℓ * ℓ+ • Angle accessible through associated mass M 2ℓb = ½ (M 2 t – M 2 W)(1 + cosy*ℓ) R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

New CDF W helicity study (Run I) • Use dilepton and lepton+jets events with 1 and 2 SVX b-tagged jets) • Preliminary (f = 0 in SM; f = 1 if all V+A) y ar in lim f. V+A= – 0. 21+0. 42– 0. 25 ± 0. 21 • F CD n Ru I e Pr Expect ± 0. 1 stat± 0. 1 syst with 2 fb-1 R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

• Run II Outlook • • Run II with 2 fb– 1 (~2005) • 14000 top events produced per expt • O(500) ℓ + jets with b-tagging. Improvements to Mt • Increased statistics × 20 • New method (× 2. 5) • Improved b-tagging (CDF increased acceptance, DØ lifetime tag) • Better understanding of jet energy scale (W→jj helps) • Better knowledge of ISR/FSR • DMt ~ 2 -3 Ge. V / expt Rare decays cg , cg, c. Z, H+b |Vtb| (single top x-section) • Is top playing a special role in the breaking of electroweak symmetry? • R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Summary • • • Mass from Run II (CDF) 171. 2 ± 13. 4 ± 9. 9 Ge. V SV m- Improved mass from Run I (DØ) 179. 9 ± 3. 6 ± 6. 0 Ge. V IP Jet 2 W helicity from Run I (CDF) f. V+A= – 0. 21+0. 42– 0. 25 ± 0. 21 Jet 1 IP SV R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

• Top production and decay ~5 pb cross section (7 pb @ 1. 96 Te. V) q 6 jets 45% e/ + 4 jets 15% each 2ℓ + 2 jets ~1% each ~35% with t • 2 b jets b q W p t t p b n W l R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

Fermilab Tevatron • • Main Injector (150 Ge. V) has replaced Main Ring pbar recycler? ? √s = 1. 8→ 1. 96 Te. V • increases 35% Run IIa • goal 8. 6× 1031 cm-2 s-1 (× 5) • 2 fb-1 by 2004 -05 (× 20) 160 pb– 1 4 pb– 1 week– 1 3× 1031 cm– 2 s– 1 Jan 2002 ↓ ↑ Jan 2003 DØ Booster p Tevatron p CDF source R. Zitoun, Stony Brook and LAPP Main Injector & Recycler Moriond 2003, QCD session

• • DØ Run I Mass Reanalysis (ℓ + jets) New method Use of full set of event observables through likelihood allows unnormalized P parameters (Mt, . . . ) • i-th event final state • integration over n + incident parton momenta (5 dim) Real life issues: • Acceptance • Final state parton momenta not really observed x = e– and jets x = e– and partons transfer function from partons to jets R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

• • • Technicalities For each event, probability is an integral over 5 variables • 20 variables (2 in + 6× 3 final) • 4 constraints (E, p conservation) • 11 measures (3 pe + 8 partons) • optimized choice : Mt, Mtbar, m. W–, m. W+, E 1(1 jet) 12 undistiguishable parton configurations: sum 12 probabilities W(x, y) probability of measuring x when y was produced in the collision • Monte Carlo used to compute Wjet (different for q and b’s) • Parametrized as the sum of 2 gaussians (E-dependent parameters) x = e– and jets x = e– and partons transfer function from partons to jets R. Zitoun, Stony Brook and LAPP Moriond 2003, QCD session

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