Measurement of top anti-top cross section in proton - anti-proton collider at √s = 1.96-TeV

Thesis/Dissertation · Fri Apr 01 00:00:00 EST 2005

DOI:https://doi.org/10.2172/879132· OSTI ID:879132

Mal, Prolay Kumar ^[1]

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1. Tata Inst. of Fundamental Research, Bombay (India)

Discovery of the top quark in 1995 at the Fermilab Tevatron collider concluded a long search following the 1977 discovery of bottom (b) quark [1] and represents another triumph of the Standard Model (SM) of elementary particles. Top quark is one of the fundamental fermions in the Standard Model of electroweak interactions and is the weak-isospin partner of the bottom quark. A precise measurement of top pair production cross-section would be a test of Quantum Chromodynamics (QCD) prediction. Presently, Tevatron is the world's highest energy collider where protons (p) and anti-protons ($$\bar{p}$$) collide at a centre of mass energy √s of 1.96 TeV. At Tevatron top (t) and anti-top ($$\bar{t}$$) quarks are predominantly pair produced through strong interactions--quark annihilation (≅ 85%) and gluon fusion (≅ 15%). Due to the large mass of top quark, t or $$\bar{t}$$ decays (~ 10^-25 sec) before hadronization and in SM framework, it decays to a W boson and a b quark with ~ 100% branching ratio (BR). The subsequent decay of W boson determines the major signatures of t$$\bar{t}$$ decay. If both W bosons (coming from t and $$\bar{t}$$ decays) decay into leptons (viz., ev_e, μv_μ or τc_τ) the corresponding t$$\bar{t}$$ decay is called dileptonic decay. Of all dileptonic decay modes of t$$\bar{t}$$, the t$$\bar{t}$$ → WWb$$\bar{b}$$ → ev_eμv_μb$$\bar{b}$$ (eμ channel) decay mode has the smallest background contamination from Z⁰ production or Drell-Yan process; simultaneously, it has the highest BR (~ 3.16%) [2] amongst all dileptonic decay modes of t$$\bar{t}$$. During Run I (1992-1996) of Tevatron, three eμ candidate events were detected by D0 experiment, out of 80 candidate events (inclusive of all decay modes of t$$\bar{t}$$). Due to the rarity of the t$$\bar{t}$$ events, the measured cross-section has large uncertainty in its value (viz., 5.69 ± 1.21(stat) ± 1.04(sys) pb {at} √s = 1.8 TeV measured by D0 [3]). This analysis presents a cross section measurement in eμ channel utilizing ~ 228 pb^-1 of data collected by D0 experiment during Tevatron Run II (between June 2002 and April 2004).

• Research Organization: Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-76CH03000
• OSTI ID: 879132
• Report Number(s): FERMILAB-THESIS-2005-61; TRN: US0604976
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANNIHILATION
B QUARKS
BRANCHING RATIO
CONTAMINATION
CROSS SECTIONS
DECAY
ELEMENTARY PARTICLES
FERMILAB TEVATRON
FERMIONS
FORECASTING
GLUONS
INTERMEDIATE BOSONS
LEPTONS
PAIR PRODUCTION
PROTONS
QUANTUM CHROMODYNAMICS
QUARKS
STANDARD MODEL
T QUARKS
Experiment-HEP