Evidence for production of single top quarks

Journal Article · Tue Jul 01 00:00:00 EDT 2008 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.78.012005· OSTI ID:21250193

Abazov, V M; Alexeev, G D; Kalinin, A M; Kharzheev, Y M; Malyshev, V L; Tokmenin, V V; Vertogradov, L S; Yatsunenko, Y A ^[1]; Abbott, B; Gutierrez, P; Hossain, S; Jain, S; Rominsky, M; Severini, H; Skubic, P; Strauss, M ^[2]; Abolins, M; Benitez, J A; Brock, R; Dyer, J ^[3]

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1. Joint Institute for Nuclear Research, Dubna (Russian Federation)
2. University of Oklahoma, Norman, Oklahoma 73019 (United States)
3. Michigan State University, East Lansing, Michigan 48824 (United States)

We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron pp collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top-quark partner that is always produced from strong-coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top-quark production has been searched for in ever larger data sets. In this analysis, we select events from a 0.9 fb{sup -1} data set that have an electron or muon and missing transverse energy from the decay of a W boson from the top-quark decay, and two, three, or four jets, with one or two of the jets identified as originating from a b hadron decay. The selected events are mostly backgrounds such as W+jets and tt events, which we separate from the expected signals using three multivariate analysis techniques: boosted decision trees, Bayesian neural networks, and matrix-element calculations. A binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single top-quark production of {sigma}(pp{yields}tb+X,tqb+X)=4.7{+-}1.3 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.014%, corresponding to a 3.6 standard deviation significance. The measured cross section value is compatible at the 10% level with the standard model prediction for electroweak top-quark production. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa quark mixing matrix element that describes the Wtb coupling and find |V{sub tb}f{sub 1}{sup L}|=1.31{sub -0.21}{sup +0.25}, where f{sub 1}{sup L} is a generic vector coupling. This model-independent measurement translates into 0.68<|V{sub tb}|{<=}1 at the 95% C.L. in the standard model.

• OSTI ID: 21250193
• Journal Information: Physical Review. D, Particles Fields, Vol. 78, Issue 1; Other Information: DOI: 10.1103/PhysRevD.78.012005; (c) 2008 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANTIPARTICLES
COUPLING
CROSS SECTIONS
D QUARKS
DECISION TREE ANALYSIS
ELECTRONS
FERMILAB TEVATRON
FORECASTING
HADRONS
MATRIX ELEMENTS
MIXING
MULTIVARIATE ANALYSIS
MUONS
NEURAL NETWORKS
PAIR PRODUCTION
PARTICLE DECAY
PROBABILITY
PROTON-PROTON INTERACTIONS
SIMULATION
STANDARD MODEL
STRONG-COUPLING MODEL
T QUARKS
TRANSVERSE ENERGY
U QUARKS
W MINUS BOSONS
W PLUS BOSONS
WEINBERG-SALAM GAUGE MODEL