Monitoring/Measuring $\rm\bf T_{max}$

1.

Second-Derivative method.

• Find the `cusp' in the X-T correlation.

• Fails miserably; uncertainties are too large.

2.

Set a threshold on the X-T correlation.

• Find the drift time when the X-T correlation reaches X_max.

• Works reasonably well.

3.

Set a threshold on the integrated drift time spectrum.

• The integrated drift time spectrum is proportional to X(T).

• Find the fraction of the integrated sum that returns an accurate T_max

• Works better than 2 (smaller uncertainty).

Results of using a threshold set on the integrated drift time spectrum to measure T_max (run 8774).

	Region	Method 2 Tmax (ns)	Method 3 Tmax (ns)	Qin, et al Tmax (ns)
	1	$198\pm 11$	$216\pm 1$	195
	2	$591\pm 76$	$463\pm 2$	526
	3	$1144\pm 71$	$1144\pm 4$	1150

Comparison of T_max measured with different methods.

Results of measurements of T_max for several runs using a threshold set on the integrated drift time spectrum.

Monitoring/Measuring $\rm\bf T_0$

1.

Fit the small X drift time spectrum.

• Use functional form from study of discrete ionization.

• Fit parameters are ambiguous.

2.

Set a threshold on the small X drift time spectrum.

• Find reasonable lower limit.

• It works.

Results of measuring T₀ using a threshold applied to the small-X drift time spectrum for each region.

Results of measurements of T₀ for several runs using a threshold set on the small-X drift time spectrum.