The frames:

The so-called "June '99" background frames are our current guess as to what the running conditions may be at the experiment start-up. The expected PEP-II performance was discussed in detail at the January Background Remediation workshop (see the executive summary for more detail). A description of PEP-II parameters for the frames is available here (Witold Kozanecki's note).

At the moment, 235 such frames are available. We've looked at generic B Bbar events mixed with these frames.

Occupancies:

These plots shows per-module occupancies in the SVT with the new frames (made by using Al Eisner's kumac file). Note that they were made assuming a 500 ns trigger jitter window, not 1 microsecond which has been used previouly. It's interesting to compare them with the occupancies obtained with the TDR x10 background frames, as given here. If one takes into account the difference in the trigger jitter window, one can see that the occupancies with the new background frames are about twice as large, with the maximum phi occupancy of ~6% and the maximum z occupancy of ~12%.

Tracking efficiencies:

• SvtTrackFinder

Even though 235 events isn't much, we can still do some tracking studies. This plot shows the track finding efficiency for the SVT track finder (stand-alone) as a function of transverse momentum (plot a) and cos(Theta) (plot b). Again, the performance is compatible with what we saw for TDR x10 frames (see, for example, these plots), with about 93% track finding efficiencies.




• AddSvtHits

These plots show "hit adding efficiencies" for the new frames. The efficiency is defined as the number of "good" DCH tracks with layer 5 hit added correctly divided by the number of "good" DCH tracks ("good" means likely to go through the 1st layer of the SVT). Similarly, these plots are for TDR x 10 frames. The efficiencies are about the same, ~93%.

Tracking parameter resolutions:

The d₀ and z₀ track parameter resolutions for the new frames are given here. Without backgrounds, we see delta(d₀) of 86 microns for no background and 94 microns with TDR x10. For delta(z₀) it's 74 microns and 82 microns, respectivelly. So to first approximation the resolution remains about the same.

Preliminary conclusions:

As far as we can judge with such rather limited statistics, the performance of the SVT reconstruction software with the June'99 backgrounds is similar to what we saw with the TDR x10 frames, and remains acceptable.