A study of positron-electron going to positive muon muon and positron-electron going to positive tau lepton tau lepton reactions at TRISTAN

Barry Lee Howell, Purdue University

Abstract

The electroweak process $e\sp{+}e\sp{-} \to \mu\sp{+}\mu\sp-$ and $e\sp{+}e\sp{-} \to \tau\sp{+}\tau\sp-$ are studied in the energy range $\sqrt{s}$ = 52.0 $\sim$ 61.4 GeV, using the TOPAZ detector at the TRISTAN $e\sp{+}e\sp-$ collider. From an integrated luminosity of L = 74 pb$\sp{-1}$, the lowest order cross sections and forward-backward asymmetries measured for these reactions are $\langle\sigma\sb{\mu\mu}\rangle$ = 25.4 $\pm$ 0.9 $\pm$ 1.2 pb, $\langle A\sb{\mu\mu}\rangle = -32.2 \pm 3.1$ $\pm$ 1.1%, $\langle\sigma\sb{\tau\tau}\rangle$ = 27.1 $\pm$ 1.1 $\pm$ 1.2 pb, $\langle A\sb{\tau\tau}\rangle$ = $-$33.9 $\pm$ 4.9 $\pm$ 1.0%, at an average energy of $\langle\sqrt{s}\rangle$ = 57.87 GeV. At $\sim$10 standard deviations from QED, this represents the most significant measurement of the asymmetry for lepton pairs to the present date. Weak axial vector couplings of $a\sb{e}a\sb\mu$ = 0.96 $\pm$ 0.09 $\pm$ 0.01, and $a\sb{e}a\sb\tau$ = 1.01 $\pm$ 0.14 $\pm$ 0.01 are determined from the asymmetry. These results agree with the electroweak standard model prediction for $\gamma$-$Z\sp0$ interference below the $Z\sp0$ pole. Lepton compositeness is also tested. Lower limits in the range 2 $\sim$ 5 TeV at the 95% confidence level are placed on the compositeness scale parameters for $\mu$ and $\tau$. No evidence for compositeness is observed.

Degree

Ph.D.

Advisors

Koltick, Purdue University.

Subject Area

Particle physics

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