m_W Results

Preliminary ALEPH results from the 189 GeV data are shown in Table 3. This example illustrates the size of calorimetric-based systematic errors (i.e. calibration uncertainties and jet corrections, shown in bold) relative to other systematic errors. One should remember that these systematic errors are evaluated with finite MC and data samples, and are therefore subject to some degree of statistical fluctuation. Combining these results with data from previous years, and with the measurement of m_W from the lepton energy spectrum at 183 GeV [2], ALEPH obtain the following preliminary result [14]:

m_W =   80.411$$\pm$$0.064$$\small (stat.)$$$$\pm$$0.037$$\small (syst.)$$$$\pm$$0.022$$\small (theory)$$$$\pm$$0.018$$\small (LEP)$$ GeV

which has a total error of $\sim$ 80 MeV. The LEP combined result for the measurement of m_W by direct reconstruction, based on preliminary results available at the time of the Spring 1999 conferences [3], was m_W = 80.368$\pm$0.065 GeV. When combined with the W mass derived from WW cross-section measurements at and above threshold, this becomes m_W = 80.370$\pm$0.063 GeV. The error is dominated by the systematic error.

Table 3: Summary of the correlated and uncorrelated systematic errors on m_W. The results are ALEPH data (preliminary) from the 189 GeV run. $\ddagger$ denotes error taken from 183 GeV studies.

	$\Delta$mW (MeV)
Error source	4q	e	$\mu$	$\tau$
Statistical	116	180	164	332
Correlated Systematics:
Fragmentation	35$\ddagger$	25$\ddagger$	25$\ddagger$	30$\ddagger$
Calorimeter calibrations	30	27	14	19
Tracking	-	7	3	3
Jet corrections	8	14	4	7
Initial state radiation	10$\ddagger$	5$\ddagger$	5$\ddagger$	5$\ddagger$
LEP energy	17	17	17	17
Uncorrelated Systematics:
Reference MC Statistics	10	16	15	23
Background contamination	10$\ddagger$	8	1	25
Colour reconnection	25$\ddagger$	-	-	-
Bose-Einstein effects	50$\ddagger$	-	-	-
Total Systematics	77	47	37	53