Search for non-standard model right-handed weak interaction (or V+A)

For Physicists

Abstract of CDF analysis

Plain English (Or at least a bit more understandable):

The top quark is predicted by the Standard Model to decay into a bottom quark and a W boson by the electroweak interaction. The spin-one W boson can have 3 different "helicities" or orientations of its spin relative to its direction of motion. These are called "left-handed", "right-handed", and "longitudinal". Because of the heavy top quark mass relative to the W boson mass, the top decays most of the time to a longitudinal W boson (70%). However, because the weak interaction violates parity maximally, the remaining time it decays to left-handed W bosons (30%). Nature appears to have made a random choice of this left-handed (called "V minus A") interaction instead of a right-handed interaction (called "V plus A").

The purpose of this analysis is to test whether the "V minus A" rule holds true for the top quark, the heaviest particle known to exist in nature. By taking advantage of a relationship between the helicity of the W boson, and the invariant mass of the charged lepton from the W decay and the b quark from the top decay, we are able to distinguish between left-handed and right-handed W bosons using the data from Run I at the Tevatron. This allows us to test the electroweak interaction itself to determine if it is a "minus" theory or a "plus" theory in top quark decays. We combine our measurement with a previous measurement from Run I for improved sensitivity. The results of the measurement can be interpreted in two ways:

  • A limit can be assigned based on the largest fraction of top decays which decay with a V plus A interaction. This number (f_V+A) can vary between 0 (no V plus A) and 1 (all V plus A), and is found to be less than 0.61 at 95% confidence. This is equivalent to the statement that f_+ is less than 18% (out of 30%) at 95 % confidence.
  • The limit can be turned around to state with how much confidence a V plus A interaction can be ruled out entirely. The result is that with 99.67 % certainty, the top does not decay entirely with a V plus A interaction.

    • The measured helicity fraction is consistent with the Standard Model.

    Even plainer english ...

  • Plain"-er" English Summary of analysis

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    More information

  • Copy of PhD Thesis Dissertation pdf (3 MB)
  • First reporting of final result shown at CIPANP 2003 ppt
  • Reference to CIPANP 2003 Conference proceedings Link to Full text
  • CDF preliminary plots for V+A fraction using invariant mass technique Approved plots
  • A paper is almost ready for journal submission.

    Last updated 9 September 2004

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