Measurement of W Polarisation

The polarisation of the W bosons in W-pair production was measured through the spin density matrix. It was found that (21.9 $\pm$ 3.44 $\pm$ 1.6)% of the W bosons were longitudinally polarised. This result is consistent with the Standard Model expectation and also the result measured by L3 at the same centre-of-mass energy [105], with the results presented in this thesis being more precise.

The polarisation state of the W-pairs has been measured for the first time. Of the three possible polarisation states, transverse-transverse (TT), longitudinal-longitudinal (LL), and transverse-longitudinal (TL), it was found that all were present and the fraction of each in the sample was:

$${\rm TT} = 0.768 \pm 0.090 \pm 0.032$$

$${\rm LL} = 0.206 \pm 0.072 \pm 0.018$$

$${\rm TL} = 0.026 \pm 0.147 \pm 0.038$$

These measured values are highly correlated, the correlations were found to be:

$${\rm TT}:{\rm LL} = +0.648 \pm 0.018$$

$${\rm TT}:{\rm TL} = -0.890 \pm 0.006$$

$${\rm LL}:{\rm TL} = -0.867 \pm 0.008$$

These $\chi ^{2}$ probablity of these results compared to the Standard Model expectations is 10%. Thus all results are consistent with the Standard Model expectations.