TOF/T0 Status Biweekly Meeting - April 24, 2003

	Topics to be covered:
		Changes for pp
		What have we learned up to now?
			T0 performance and issues:
				T0 OR
				Rates
				Energy distributions
			TOF performance and issues:
				Rates
				Energy distributions

Changes for pp

	To increase the T0 efficiency, the T0N array was moved from its position behind ring # 3 to a position behind ring # 1.
	The center of each radiator is located at z = -121.8 cm.
	This T0 array covers a pseudorapidity region between 2.93 and 3.42.

T0 OR Correlations

	The first pp data revealed an strong correlation between the T0 OR from T0P and the T0 OR from T0N.
	The correlations between the Ors leads to a significant structure in the T0 vertex distributions, obtained from the OR signals.
	Andrei determined that the correlation in the OR signals is most likely due to cross talk in the twisted pair cable that is used to delay the twinax signals (a 180 ns delay is required).

T0 OR Correlations (Summary of AndreiÕs studies)

	The T0 OR data are digitized with FB TDCs and VME TDCs.
	The FB and VME T0 OR information comes from the same source in the CH, but the delays are different (VME requires a shorter delay).
	The correlations in the T0 OR do not show up in the VME data.
	The signal that is effected is the FB OR of T0P.  This signal arrives about 4 ns after T0N.
	This is cross talk in the cable ÒcoilÓ if the timing is just right.

T0 OR Correlations Changes implemented

	The correlations in the OR signals has no effect on the on-line vertex.
	Based on the observed correlations, which are most likely caused by the twisted pair delay cables, we must also suspect the VME Ors.
	Due to the importance of the OR we decided to delay the FB OR signals using BNC delay cables and use TDC 17 to digitize the time information.

T0 OR Vertex

	T0 OR vertex is correlated with the Octagon vertex.
	Current resolution is about 7 cm, which is primarily limited by the accuracy with which the T0 counters are aligned in time (especially T0N which is now in a new location).
	Data collected on Tuesday will be used to determine the new TEQ settings for pp today.

Occupancy T0 Counters

	The occupancy of the T0 counters, especially T0N, depends very much on the trigger conditions.
	Expectations based on UA5 data:
		T0N: <N> = 0.56 (P(N=0) = 57%)
		T0P: <N> = 0.41 (P(N=0) = 66%)
	The data show that the occupancy for T0P is higher than the occupancy of T0N.  Is this due to a much higher background in T0P?

Occupancy T0 Counters

T0 Energy

	The energy spectra of each T0 counters is dominated by the 1 MIP peak.
	The sum energy spectra have a clear 2 MIP peak, dominated by T0 coincidences.

T0 Energy and Magnetic Field

	We have examined the influence of the magnetic field on the performance of T0N (due to its proximity to the magnet).
	We made the following observations (using the same calibration data):
		Run 12037 (B+): 1 MIP peak centered at 1.00.
		Run 12054 (B-): 1 MIP peak centered at 1.04.
		Run 12067 (B off): 1 MIP peak centered at 0.95 (but with a different trigger).

T0 Timing Correlations

	The time signals of the individual T0 counters on an array are highly correlated in time.
	The observed correlation is MUCH better than the correlations we observed for dAu.
	The width of the time difference distributions implies a time resolution of 140 - 160 ps for the T0 counters, which would improve to 70 - 80 ps with slew corrections.

TOF Studies

	We have studied the TOF performance for pp by looking at the data collected on Monday and Tuesday with different triggers.
	Some issues with the time calibrator data needs to be resolved (16 missing channels in the calibrated data, which show up in the raw data).
	The occupancy of the TOF is very low that the on-line monitoring of the TOF is ÒslowÓ and  will trigger on occasion the TOF on-line alarm.

Occupancy T0F Counters

TOF Event Distribution

TOF Energy

	The data collected in run 12045 were used to examine the TOF energy distributions.
	Run 12045:
		Field on (B-)
		Trigger: dAPaddleNarrow
	The TOF shows a clear MIP peak at an energy of around 1.4 MeV.

Summary

	Major changes were made to the T0 OR signals.
	The T0 and TOF counters are fully operational.
	The background in T0P appears to be much higher than the background in T0N.
	New TEQ delays will be determined today and loaded into the TEQ before we collect collisions tonight.
	Minor issues with the recent time calibrator data and the on-line event display will need to be resolved.