T0 Update Analysis Meeting March 13, 2003

	Topics to be discussed:
		T0 electronics
		New results of T0 studies:
			Intrinsic resolution
			Adjusting individual T0 delays
			Run dependence
		Comparing T0 signals with Ckv signals.
		Are we any closer to a solution?

T0 Electronics

	The T0 electronics is very simple.
	We know that for beam-gas events, the T0 signals are highly correlated, suggesting that the electronics functions properly for those events.
	The electronics for T0P is completely separate from the electronics for T0N, except for the TDC.

T0 Studies Run 10920: #T0N=1 and #T0P=1

T0 Studies Run 10920: #T0N=1 and #T0P=1

	What do we learn from this analysis?
		If we require a multiplicity of 1 in either array, we rule out contributions from cross talk.
		The vertex resolution for all combinations of detectors is between 2.5 and 3.5 cm.
		The different detectors are clearly not aligned in time (a 1 ns shift is required to move the vertex by 15 cm).
		The centroids of the vertex difference distributions can be used to realign the individual T0 counters on either side.

T0 Studies Run 10920: #T0N=1 and #T0P=1

	After correcting the delays of the T0 channels for the relative time delays obtained by from the previous analysis, all vertex difference distributions (calculated with respect to sensor T0N2 and T0P2) are aligned.
	The width of the vertex difference distribution is 3.2 cm (1s).  This corresponds to a T0 time resolution of 150 ps (without slewing corrections).

T0 Studies Run 10920: #T0N=1 and #T0P=1

T0 Studies Run 10920: #T0N=1 and #T0P=1

	Conclusions:
		Fine tuning T0 delays works for one particular combination of counters.
		However, the same T0 delays do not line up the T0 counters if we take a different counter as our reference.
		Since there is only one T0 counters hit in these event, cross talk is not considered to be an issue in this effect.

T0 Studies  Run 10920: Use T0N2/T0P2 as references

	The response is influenced by the event selection (difference between single T0N/T0P hits and multiple T0N/T0P hits).
	Changes in both centroid and width.

T0 Studies Run 11420: #T0N=1 and #T0P=1

	In order to consider the effect of the changes in the environment at PHOBOS, I have looked at the data collected last weekend.
	Run 11420 was analyzed in the same manner as run 10920.
	The basic observations made are the same for both runs.

T0 Studies  Run 10920: T0 - Ckv Correlations

	To investigate the origin of the observed correlation we have looked at correlations between T0 and Ckv counters.
	In this analysis we have looked at the same events (T0N = 1 and T0P = 1).
	The vertex is calculated on the basis of the time difference between the T0 and the Ckv counters (T0P/CkvN and T0N/CkvP) and compared to OctDeVertex.

T0 Studies MC results

	MC studies of the time of primaries and secondaries show a significant probability of a prompt primary in coincidence with a delayed secondary.
	The simulations do not show the observed correlations.

T0 studies Summary

	As of yet, the source of the correlations has not been identified.
	This is what we know:
		No problems for Au + Au
		No problems for beam-gas events
		Correlations for d Au collisions
		Correlations are not present in the MC data
	What do these observations have in common?
		Events with a large number of primaries look OK
		Events for which there is significant probability of seeing no primaries show correlations.
	What are we going to do?
		In parallel to continuing studies of the data collected, a number of experts are looking at the hardware.
		I plan to switching to TOF integration next week, using the collision time of the ORs to correct for the START jitter.