Status of the T0/TOF studies


	Frank Wolfs
	Department of Physics and Astronomy
	University of Rochester, Rochester, NY 14627

Status of the T0/TOF studies
Issues to be discussed


	Progress since last bi-weekly meeting

	T0 performance studies:

		Beam-gas interactions

		Vertex studies

	Particle identification:

		PR01 studies

		Outlook for PR03

	Summary

Status of the T0/TOF studies


	Since the last bi-weekly meeting we have completed the following tasks:
		Studied drifts in TDC gains and determined that this is a small effect. The changes in gain can not be responsible for the excess drifts we have observed.
		Implemented a new calibration procedures that corrects for drifts associated with for example the crossing clock. This procedures looks at the average time of prompt peak of T0N and the T0P counters and calculates a common shift required to align the centroids of the T0N and the T0P counters with the expected position of the prompt peak. The same procedure will also work for the TOF since it does not require high statistic in each individual channel.
		Determined first order slewing parameters for the T0N sensors using beam-gas interactions. Work on the T0P sensors is in progress.
		Continued DST production required for TOF studies.

Beam-gas Studies


	Beam-gas events are the only events in which we observe a strong time correlation between the T0 counters in each array.
	The beam-gas data are being used to optimize the slewing parameters for the T0 counters.
	We have obtained a first set of slewing parameters for T0N and are working now on T0P. Slewing corrections have brought the T0 resolution to around 100 ps (1s).
	We need more beam-gas events to study T0 alignment (0.25 M).

T0 Vertex Studies


	The collision time, obtained from the T0 array, is equal to

		t_col = (t_T0N + t_T0P)/2

	The resolution of the collision time is equal to

		s_Tcol = s_T0/Ã2

	The vertex position, obtained from the T0 array, is equal to

		z_vertex = c (t_T0N - t_T0P)/2

	The resolution of the collision vertex is equal to

		s_vertex = c s_T0/Ã2 = c s_col

	We use s_vertex to determine s_Tcol.

T0 Vertex Studies:
Comparing Spec Vertex with T0 OR Vertex


	The T0 OR Vertex is obtained from the OR information obtained using TDC 8:

		T0 OR Vertex = 29.979*((tExtra[19] - 311.87) - (tExtra[20] - 302.65))/2.0

	The vertex resolution is 4.8 cm (1s).
	This implies a resolution of the T0 ORs of 225 ps (1s). This resolution is most likely dominated by the alignment accuracy.

T0 Vertex Studies:
Comparing Spec Vertex with T0 Fast Vertex


	If all T0 counters are properly aligned in time, we expect that by using the time of the first T0 to fire we should be able to exceed the performance of the T0 OR vertex.

	The results obtained with these first T0 signals are very poor, clearly showing that the T0 counters are not properly aligned in time.

T0 Vertex Studies:
Comparing Spec Vertex with T0 Fast Vertex


	Using the Fast vertex requires that the prompt signals of all T0 counters are aligned in time.
	The current alignment procedures align the centroid of the wide T0 time distributions with an accuracy of 100 ps or better.
	A more accurate alignment can be made by comparing the vertex distributions obtained with individual T0 counters.
	Small differences in alignment will result in displacement of the vertex difference distributions (z_T0 - z_Si) from 0.

T0 Vertex Studies:
T0N0 - T0P0 Vertex vs Spec Vertex


	The vertex resolution based on T0N0 and T0P0 is 7.0 cm (1 s).
	This vertex resolution would imply a T0 resolution of 330 ps (1 s). This resolution must be dominated by secondaries.

T0 Vertex Studies
Check relative timing of T0N detectors.


	In order to verify the alignment of the T0 counters, we look at all possible combinations between T0N and T0P0.

	We expect that in each case the vertex resolution is the same, but the centroid of the vertex difference distribution moves as a result of errors in the alignment of the T0 counters.

T0 Vertex Studies:
T0N5 - T0P0 Vertex vs Spec Vertex


	That is not what we see!
	The vertex resolution based on T0N5 and T0P0 is 15.1 cm (1 s).
	This vertex resolution would imply a T0 resolution of 710 ps (1 s). This resolution must be dominated by secondaries.

T0 Vertex Studies:
T0N5 - T0P5 Vertex vs Spec Vertex


	The vertex resolution based on T0N0 and T0P0 is 7.4 cm (1 s).
	This vertex resolution would imply a T0 resolution of 350 ps (1 s). This resolution must be dominated by secondaries.

T0 Vertex Studies:
T0N0 - T0P5 Vertex vs Spec Vertex


	The vertex resolution based on T0N5 and T0P0 is 19.2 cm (1 s).
	This vertex resolution would imply a T0 resolution of 910 ps (1 s). This resolution must be dominated by secondaries.

T0 Vertex Studies:
T0N5/T0P5 Vertex vs Spec Vertex

T0 Vertex Studies:
T0N2/T0P2 Vertex vs Spec Vertex

T0 Vertex Studies






	The strong correlation between T0 counters at the same location (T0Nx and T0Px) is not present in the simulated data.

"The ratio of primaries to..."


	The ratio of primaries to secondaries that loose energy in the T0 counters is about 1 to 10.

	Taking into consideration that the T0 are Cerenkov counters, only 1 out of every 3 secondaries will produce a T0 signal.

	The expected ration of primary to secondary T0 signals is about 1 to 3.

T0 Vertex Studies


	What can cause this asymmetry?
		It is not the calculated time delay (this effect the position of the vertex distribution for a specific counter combination, not the width).
		Bug in software when T0 event is created? Not likely, since asymmetry is clearly visible in the raw FB data.
		Effect of magnetic field? No; runs with no magnetic field show the same effect.
		Secondaries? Most likely, but the asymmetry does not show up in the Monte-Carlo simulations.
	Conclusion: this is a real effect but not understood yet.

TOF Particle Identification


	In parallel to our studies of PR03 data, we are continuing our studies of PR01 data.
	All techniques and tools that we need for the PR03 data are used by Erik for his analysis of PR01 data, and will be used to analyze the PR03 data once the T0 studies have been completed.
	Major improvements have been made in back ground reduction (e.g. using the TOF energy information) and PID spectra are very clean.

T0 Vertex Studies
Summary


	Our alignment procedure for the T0 counters clearly does not work.
	It appears that our T0 time distributions are dominated by secondaries, and that the actual secondaries effect different counters in different ways.
	In principle we can obtain the collision time from the T0 OR. However, this will limit the collision time resolution to about 160 ps.
	We have developed and fine-tuned most procedures to obtain PID with the TOF. The PID spectra obtained from PR01 are clean, and we are now optimizing the slewing corrections using the tracked particles.