Phase space matching and finite lifetime effects for top-pair production close to threshold

Journal Article · Thu Jul 01 00:00:00 EDT 2010 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.82.014005· OSTI ID:21410027

Hoang, Andre H; Reisser, Christoph J; Ruiz-Femenia, Pedro ^[1]

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1. Max-Planck-Institut fuer Physik (Werner-Heisenberg-Institut), Foehringer Ring 6, D-80805 Muenchen (Germany)

The top-pair tt production cross section close to threshold in e{sup +}e{sup -} collisions is strongly affected by the small lifetime of the top quark. Since the cross section is defined through final states containing the top decay products, a consistent definition of the cross section depends on prescriptions of how these final states are accounted for the cross section. Experimentally, these prescriptions are implemented, for example, through cuts on kinematic quantities such as the reconstructed top quark invariant masses. As long as these cuts do not reject final states that can arise from the decay of a top and an antitop quark with a small off-shellness compatible with the nonrelativistic power counting, they can be implemented through imaginary phase space matching conditions in nonrelativistic QCD. The prescription-dependent cross section can then be determined from the optical theorem using the e{sup +}e{sup -} forward scattering amplitude. We compute the phase space matching conditions associated to cuts on the top and antitop invariant masses at next-to-next-to-leading logarithmic order and partially at next-to-next-to-next-to-leading logarithmic order in the nonrelativistic expansion accounting also for higher order QCD effects. Together with finite lifetime and electroweak effects known from previous work, we analyze their numerical impact on the tt cross section. We show that the phase space matching contributions are essential to make reliable nonrelativistic QCD predictions, particularly for energies below the peak region, where the cross section is small. We find that irreducible background contributions associated to final states that do not come from top decays are strongly suppressed and can be neglected for the theoretical predictions.

• OSTI ID: 21410027
• Journal Information: Physical Review. D, Particles Fields, Vol. 82, Issue 1; Other Information: DOI: 10.1103/PhysRevD.82.014005; (c) 2010 The American Physical Society; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CROSS SECTIONS
DAUGHTER PRODUCTS
ELECTRON-POSITRON COLLISIONS
FORECASTING
LIFETIME
MASS
OPTICAL THEOREM
PAIR PRODUCTION
PARTICLE DECAY
PHASE SPACE
QUANTUM CHROMODYNAMICS
SCATTERING AMPLITUDES
T QUARKS
AMPLITUDES
COLLISIONS
DECAY
ELECTRON COLLISIONS
ELEMENTARY PARTICLES
FERMIONS
FIELD THEORIES
INTERACTIONS
ISOTOPES
MATHEMATICAL SPACE
PARTICLE PRODUCTION
POSITRON COLLISIONS
POSTULATED PARTICLES
QUANTUM FIELD THEORY
QUARKS
SPACE
TOP PARTICLES