We studied a number of different geometrical configurations of the TOF system. The specific restrictions on the possible geometries are as follows.

• We have to leave free a few meters downstream of the analyzer for the DDC mount.
• The MUFFINs plastic is already being cut for the smaller disk size. This more or less freezes the position of the MUFFINs in the beam-line relative to the analyzer. Salvo has agreed that any possible future changes in the MUFFINs positioning will be done only after consultation with the TOF Group.
• There are potential obstructions in the beam area, e.g. the mechanical structure of EVA.
• The path of the Au beam must be kept in mind. During the actual experiment, we will have to remove any slats that are struck at high rates by uninteracting Au beams. Otherwise, the high rate Au ions in the beam-line produce copious secondaries in the the experiment. Also, the scintillators that are struck would soon be damaged.
• The resources of the E896 trigger and DAQ are not infinite, so the total channel count must be limited to values that can reasonably be handled by these systems. Also, we intend to borrow as many of the components for the TOF system as possible, which will also limit the total channel count.

We compared the performance of three different configurations called Options A, B, and C. These configurations are sketched in the following figure.

To make a long story short, the basic problems with Options A, B, and C are as follows. At the previous collaboration meetings, we showed that the product of the geometrical efficiency and the TOF efficiency is relatively flat versus the length of the flight path for particular parents. This makes the product of these efficiencies for the Options A, B, and C rather similar. However, Option A has a noticably poorer geometrical efficiency for the low momentum daughters (the pi- from measurable H0's, the pi- from measurable Lambdas, and the pi+ from measurable Antilambdas), and a poor TOF efficiency in general. The DSW in Option A would have to be very granular (well exceeding any realistic number of read-out channels) because of the multiple-hit probabilities. The DSW in Option C is rather large, which has several unattractive implications. Furthermore, and most importantly for Options B and C, the DSW in these two options gets pounded by secondaries produced in the MUFFINs.

Our simulations implied that a fourth configuration, called A', would easily outperform the A, B, and C configurations. For the remainder of this write-up, we will concentrate on variety of results on the performance of the A' wall. The A' wall looks like this:

Figures

Figure 1 In the upper frames, the probabilities for two or more hits per slat versus the local-X distribution. Complete central Au+Au events were used, and all secondaries produced in interactions downstream of the target are included. Note the bin widths in the upper two frames are the slat size. In the lower two frames, the local-X distributions as shown for the daughters of all four interesting parents. Note the bin widths are not the slat size. The thick vertical lines in the lower frames indicates the local-X position of the uninteracting Au beam (see the following figure)
Figure 2 The local-X distributions of 197-Au ions on the E896-TOF wall, including the beam-spot size, the angular divergance of the beam, and beam momentum smearing. Note that the bin-width is not the slat size.
Figure 3 The local-X distributions on the E896 TOF wall for various primaries and secondaries in b=0 Hijet events.
Figure 4 The 1/velocity versus momentum distributions for negatively charged particle hits on the E896 TOF wall. The various frames show the results for different values of the momentum and TOF resolution.
Figure 5 The 1/velocity versus momentum distributions for positively charged particle hits on the E896 TOF wall. The various frames show the results for different values of the momentum and TOF resolution.
Figure 6 The total path length (target to TOF wall) for all interesting daughters.
Figure 7 The momentum distributions at the E896 TOF wall for the daughters of interesting parents in the MC events. The distributions for Cuts 2, 3, and 4 are shown, as is the cut-off momentum for PID via TOF obtained using a DDC momentum resolution of dp/p=1% and an 80 ps TOF resolution.
Figure 8 The momentum distributions at the E896 TOF wall for the daughters of interesting Fiducial parents. The distributions for cuts 2, 3, and 4 are shown, as is the cut-off momentum for PID via TOF obtained using a DDC momentum resolution of dp/p=1% and an 80 ps TOF resolution.
Figure 9 The local-X distributions on the E896 TOF wall for daughters passing Cuts 2, 3, and 4 in the MC events. These distributions have been normalized to give the probabilities as numbers/event that pass each level of cuts. Note that the bin-width is not the slat size.
Figure 10 The local-X distributions on the E896 TOF wall for daughters passing Cuts 2, 3, and 4 for Fiducial parents. These distributions have been normalized to give probabilities as numbers/event that pass each level of cuts. Note that the bin-width is not the slat size.
Figure 11 The parent rapidity versus the daughter local-X position on the E896 TOF wall for Fiducial events and for those daughters passing Cut 1.
Figure 12 The parent rapidity versus the daughter local-X position on the E896 TOF wall for Fiducial parents and for those daughters passing Cut 2.
Figure 13 The parent rapidity versus the daughter local-X position on the E896 TOF wall for Fiducial parents and for those daughters passing Cut 3.
Figure 14 The parent rapidity versus the daughter local-X position on the E896 TOF wall for Fiducial events and for those daughters passing Cut 4.
Figure 15 The parent (y,Pt) distributions from Fiducial parents for daughters that pass Cut 1 on the E896 TOF wall information.
Figure 16 The parent (y,Pt) distributions from Fiducial parents for daughters that pass Cut 2 on the E896 TOF wall information.
Figure 17 The parent (y,Pt) distributions from Fiducial parents for daughters that pass Cut 3 on the E896 TOF wall information.
Figure 18 The parent (y,Pt) distributions from Fiducial parents for daughters that pass Cut 4 on the E896 TOF wall information.
Figure 19 The parent rapidity distributions for Fiducial parents and for those daughters passing Cuts 2, 3, and 4 as labelled.
Figure 20 The parent rapidity distributions for MC events and for those daughters passing Cuts 2, 3, and 4 as labelled.
Figure 21 The parent (y,Pt) distributions from MC events for daughters that pass Cut 1 on the E896 TOF wall information.
Figure 22 The parent (y,Pt) distributions from MC events for daughters that pass Cut 2 on the E896 TOF wall information.
Figure 23 The parent (y,Pt) distributions from MC events for daughters that pass Cut 3 on the E896 TOF wall information.
Figure 24 The parent (y,Pt) distributions from MC events for daughters that pass Cut 4 on the E896 TOF wall information.
Figure 25 The parent rapidity versus the daughter local-X position on the E896 TOF wall for MC events and for those daughters passing Cut 1.
Figure 26 The parent rapidity versus the daughter local-X position on the E896 TOF wall for MC events and for those daughters passing Cut 2.
Figure 27 The parent rapidity versus the daughter local-X position on the E896 TOF wall for MC events and for those daughters passing Cut 3.
Figure 28 The parent rapidity versus the daughter local-X position on the E896 TOF wall for MC events and for those daughters passing Cut 4.
Figure 29 The parent transverse momenta for Fiducial parents and for those daughters passing Cuts 1, 2, 3, and 4. These distributions are not corrected for the various measurement efficiencies. The acceptance extends to Pt=0 for all parents and all levels of the cuts.
Figure 30 The parent transverse momenta for MC events for those daughters passing Cuts 1, 2, 3, and 4. These distributions are not corrected for the various measurement efficiencies. The acceptance extends to Pt=0 for all parents and all levels of the cuts.
Figure 31 The comparison of the numbers of parents that pass the full cuts from the MC events (black), and the numbers that pass the full cuts from the Fiducial events (red). The scale factors relating the Fiducial parent generation to the equivalent number of complete or MC events were obtained as described in the Introduction. The differences in the relative heights of the two histograms for each parent are related primarily to the different proper lifetimes. Of these, the K-short has the smallest lifetime, hence the largest difference in the rates between the MC events (decay vertex not required to be in the DDC) and the Fiducial events (decay vertex inside the DDC). MC events were not generated for the H0.

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Rates Table

Notes

• These rates are the numbers/event that pass the Cut level listed. For a description of these cuts, see the Introduction above.
• The Lambda-bar rates are calculated assuming the same multiplicity/event and pt-y spectra as lambdas. One should mentally include factors on the order of a few times 10^-3 for the actual production rate of Lambda-bars as compared to Lambdas.
• The H0 rates are calculated assuming 0.1 H0 per central event.
• The rates per week are calculated assuming 250 central events per second are written to tape, and that there are 100 hours of beam per week.