Padrow 51 in the 2 and 4 A GeV data

The Problem

Padrow 51 continually causes pain to the 2D hitfinder (2dh). The following pictures, taken from a 2 A GeV event, should make clear why.

What is plotted is the ADC value (indicated by the size of the box) for each pixel (time bucket on y-axis, pad on x-axis) on the three padrows 50, 51, and 52.

Clearly, one half of padrow 51 (one stickside) has a problem.

Also clear in these pictures is a buildup of ADC counts at the bottom of the tpc (where the wires are). When these pictures were made, 2dh still did not treat these intelligently; it now does, when the "cleanup" switches are turned on (leave them at the default of h2d_sw.nbuck_cleanup=3, h2d_sw.cleanup_maxocc=0.25). These cleanup switches are implemented in version 1.14 of the 2dh. See here for details.

Our Fix

I had originally suggested that pads 1-60 on padrow 51 be declared "bad pads" for the 2 and 4 GeV data, but Heng Liu and especially Paul Chung who have done careful study of this padrow (see the Stony Brook pages about this), say that these are not always bad pads. Indeed, I also see that this wierdness comes and goes event-to-event.

The fix (implemented in version 1.14 of 2dh) is a new switch, h2d_sw.symmetrize_row51, which = 0 (off) or 1 (on). If it is on, then the threshold on the pixels for pads 1-60 in padrow 51 (these are the offending pads) is raised until the pixel occupancy (# pixels with ADC above threshold) is about equal for pads 1-60 and pads 61-120.

Here are the pixels when an affected event is processed with h2d_sw.symmetrize_row51=0 and h2d_sw.symmetrize_row51=1. The fix seems to do a good job.

Although not all files are affected, the idea is to have h2d_sw.symmetrize_row51=1 as the default for the 2 and 4 GeV data and h2d_sw.symmetrize_row51=0 for the high energy data, where the effect has not been seen.

If this "cleanup" switch is left on by mistake (i.e. when it is not needed), it should do minimal harm, which is part of its attractiveness. If this is not clear, we can talk about it.

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