TOF/T0 Update

	Issues to be discussed:
		Time stability of the system.
		Saturation effect of the T0 system.
		T0 efficiency for d + Au.
		Commissioning the T0 system.

T0/TOF Update Time Stability

	The stability of the timing system has been studied by running the time calibrator overnight:
		Start: 11/18/2002 18:34:49
		Stop:  11/19/2002 08:26:58
	We observe slow variations of the time delay as function of time, but with a higher-frequency (15 - 25 minutes) fine structure (± 250 ps) superimposed on it.

T0/TOF Update Time Stability

	The technique used to monitor the stability is sensitive to both the variations in cable delay and the variations in trigger timing (for example, variations in the electronics used to generate the FASTBUS gates).
	The temperature variations in the tunnel are too slow to change the electronics in the tunnel over a period of 15 - 25 minutes.
	The variations of the temperature in the electronics room are rapid and could produce the fine structure observed.

T0/TOF Update Time Stability

	The variations in timing due to changes in the CH electronics should cancel when physics results are derived since time difference between different channels.
	The overall monitoring scheme is unchanged as a result of the high frequency component, although it will require that the delay corrections need to be calculated more frequently than anticipated.

T0/TOF Update T0 Saturation Effect

	The T0 counters exhibit a saturation effect when many MIPS are detected simultaneously.
	This saturation effect shifts the time to longer times, and thus does not effect the T0 OR as long as not all PMTs saturate.
	We have determined that this is a discriminator problem and not a PMT problem.

T0/TOF Update T0 Saturation Effect

	To study this effect we create huge signals by replacing the radiator with a scintillator.
	The signals is split and used to START and STOP a TAC.  The STOP is attenuated to ensure that the amplitude is below the clamping amplitude.
	The time jump is observed during PR01 shows up when we use the 4413 CAMAC discriminator.
	No time jump is observed when use the 623B NIM discriminator.

T0 Efficiency

	Based on HIJING for d + Au we estimate the number of charged particles detected in the T0 counters:
		P side: <NP> = 1.2
		N side: <NN> = 2.1

T0 Efficiency

	Based on the number of charged particles detected we can estimate our efficiency for d + Au:
		P side: P(NP = 0) = 0.30
		N side: P(NN = 0) = 0.12
		Vertex efficiency = P(NP > 0) x P(NN > 0) = 0.62
		Collision time efficiency = 1 - P(NP = 0) x P(NN = 0) = 0.96
	Note: the numbers quoted here are the number of primary particles.  The number of secondaries is a factor of 2 - 3 larger than the number of primaries.
	Saturation certainly will not be a problem for d + Au.

Commissioning T0 Counters

	The main task is to align the T0 counters in time using the time equalizer.
	Procedure:
		Disable all but 1 T0 counter on either side.
		Measure the time of the OR for either side:
			Need collisions.
			Need to correct for the vertex dependence (vertex position influences timing of START and STOP).
			The width of the timing peak will be determined by jitter in START.
			We need 500 - 1000 collisions to be able to determine the centroid with an accuracy of better than 100 ps.
		Repeat the same measurement for all 10 T0 counters on either side.
		Determine appropriate delays for each channel and verify that correct delays are assigned by repeating this sequence of measurements.
	This procedure requires a silicon vertex.