The measurement of the W cross section in DELPHI

This page describes preliminary results of the DELPHI collaboration. If you like to show them please ask for confirmation!


161 GeV results:

The W pair production cross section at a cms energy of 161.31 +/- 0.05 GeV has been measured to be

3.67 +0.97 -0.85(stat) +/- 0.19(syst) pb.
Assuming the standard model this converts into a measurement of the the W mass of
m_W = 80.40 +/- 0.44(stat) +/- 0.09(syst) +/- 0.03(LEP) GeV.

The plot shows the SM prediction of the cross section as a function of the W mass together with the DELPHI measurement.

The interpretation of the cross section in terms of W couplings is shown elsewhere.

The analysis is published in Phys. Lett. B397 (1997) 158. You can also get fig.1 , fig.2 , fig.3 of the publication.


183 and172 GeV results:

These are the DELPHI measurements of the W pair production cross section at the different LEP2 operation energies:

LEP c.m.s. Energy (GeV) Measured WW cross-section
171.2 11.58 +1.44 -1.35 (stat) +/- 0.32 (syst) pb
182.7 16.01 +/- 0.71 (stat) +/- 0.43 (syst) pb

The plot shows the DELPHI measurements at the three centre of mass energies together with the standard model prediction using m_W = 80.35 GeV



In addition we have measured the W branching ratios:

Without lepton universality:
Br(W -> e nu) 0.099 +/- 0.011(stat) +/- 0.005 (syst)
Br(W -> mu nu) 0.114 +/- 0.011(stat) +/- 0.005 (syst)
Br(W -> tau nu) 0.112 +/- 0.011(stat) +/- 0.005 (syst)
With lepton universality:
Br(W -> l nu) 0.108 +/- 0.005 (stat) +/- 0.003 (syst)
Br(W -> hadr.) 0.675 +/- 0.015 (stat) +/- 0.009 (syst)


The 172 GeV analyses are published in Eur. Phys. J C 2 (1998) 581 and you can get all the figures .

The preliminary183 GeV results can be found in DELPHI 98-80 CONF 148.