DØ Angular Distribution of Electrons in W -> e nu Decays

We have made a measurement of the electron angular distribution parameter alpha_2 in W -> e \nu events using data from Run 1b (1994-95). At leading order (O(alpha_s)) the V-A angular distribution (1 +- cos theta*)^2 is modified by initial state radiation and when next-to-leading order QCD effects are taken into account, the angular distribution has the form 1 + alpha_1 cos theta* + alpha_2 cos^2 theta*, Here theta* is the angle between the charged lepton and the antiproton in the Collins-Soper frame and the parameters alpha_1 and alpha_2 are functions of q_T, the W boson transverse momentum. This is the first measurement of alpha_2 as a function of q_T, and it provides an important test of next-to-leading order QCD corrections to W boson production.

The NLO calculation of the angular distribution has been carried out by Erwin Mirkes, see
E. Mirkes, "Angular Decay Distribution of Leptons from W bosons at NLO in Hadronic Collisions", Nucl. Phys. B387:3-85, 1992.

Plots
The following plots summarize the results of this analysis.
(Click on the plot to get the postscript file).

The results have been submitted for publication:
Measurement of the Angular Distribution of Electrons from W->e(nu) Decays Observed in pbarp Collisions at sqrt(s)=1.8 TeV
submitted to Phys. Rev. D {xx} pppp (2000)
FERMILAB-Pub-00/228-E, hep-ex/0009034. PS

Monte Carlo cos theta* distributions for different values of alpha_2, with a PT(W) < 10 GeV cut applied.

Monte Carlo cos theta* distributions for different values of alpha_2, for events with 20 < PT(W) < 35 GeV.

Since the z-component of the neutrino momentum is not measured, the W rest frame cannot be reconstructed. Therefore, a Bayesian approach expoliting the correlation between the W transverse masss and cos theta* is used to infer the cos theta* distribution. This plot shows the W transverse masss vs. cos theta* for PT(W) < 10 GeV. A fast Monte Carlo is used to simulate the repsonse of the D0 detector.

The measured values of alpha_2 vs. pT(W) (points with error bars) compared with the NLO calculation of Mirkes (Nucl. Phys. B387:3-85, 1992). The combined statistical+systematic errors are shown as vertical bars, while the statistical errors alone are marked by horizontal ticks.

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Last modified: Tue Oct 17 13:57:53 PDT 2000

	Monte Carlo cos theta* distributions for different values of alpha_2, with a PT(W) < 10 GeV cut applied.
	Monte Carlo cos theta* distributions for different values of alpha_2, for events with 20 < PT(W) < 35 GeV.
	Since the z-component of the neutrino momentum is not measured, the W rest frame cannot be reconstructed. Therefore, a Bayesian approach expoliting the correlation between the W transverse masss and cos theta* is used to infer the cos theta* distribution. This plot shows the W transverse masss vs. cos theta* for PT(W) < 10 GeV. A fast Monte Carlo is used to simulate the repsonse of the D0 detector.
	The measured values of alpha_2 vs. pT(W) (points with error bars) compared with the NLO calculation of Mirkes (Nucl. Phys. B387:3-85, 1992). The combined statistical+systematic errors are shown as vertical bars, while the statistical errors alone are marked by horizontal ticks.