# Linked List Segment Reconstruction

### Monday, July 16, 2001

## Introduction

This paper gives a short overview of the performance of the Linked List
algorithm from Monday, July 16 on. The plots in this paper are made with
the package version v00-00-22, which first appears in t01.53.00. All
plots in this document are based on the file:

/prj_root/779/alg_7/mudata/d0sim_mu_mb1.1_t01.24

which holds 5000 events.

## Reconstruction efficiency

![](media/image1.wmf){width="5.992361111111111in"
height="4.061805555555556in"}

Figure 1: Reconstruction efficiency

The overall reconstruction efficiency is 96.4%. This efficiency is
without the geometrical acceptance, but does have the hit reconstruction
efficiency folded in.

## Reconstruction resolution

![](media/image2.wmf){width="5.992361111111111in"
height="4.061805555555556in"}

Figure 2: Resolution in the central region with a vertex constraint on
the A-layer segment

Figure 2 shows the resolution in the central region. For the A-layer, a
vertex constraint is put on the direction of the segment: it is required
to point to the origin. For high p~T~ tracks, this might be a sensible
thing to do (the file analyzed contains tracks between 0 and 100 GeV
with a uniform distribution, so most are 'high' p~T~ tracks). However,
for low p~T~ tracks I am not too sure if a vertex constraint is
applicable, due to the multiple scattering in the calorimeter. Figure 3
shows the resolution without this vertex constraint.

The use of this vertex constraint is governed by a RCP switch in
MuoSegmentLLReco.rcp, called 'useVertexA' so that it can be turned on
and off at will.

Note, that the combinatorial algorithm uses this vertex constraint by
default.

![](media/image3.wmf){width="5.992361111111111in"
height="4.061805555555556in"}

Figure 3: Reconstruction resolution in the central region without a
vertex constraint on the A-layer segment

![](media/image4.wmf){width="5.992361111111111in"
height="4.061805555555556in"}

Figure 4: Reconstruction resolution in the forward region with a vertex
constraint on the A-layer segment

Figure 4 shows the reconstruction resolution in the forward region,
using the vertex constraint on the A-layer segment. Figure 5 shows the
same resolution, without that constraint.

![](media/image5.wmf){width="5.992361111111111in"
height="4.061805555555556in"}

Figure 5: Reconstruction resolution in the forward region without a
vertex constraint on the A-layer vertex

## Pull distributions

![](media/image6.wmf){width="5.992361111111111in"
height="4.061805555555556in"}

Figure 6: Pull distributions for the angle in the drift plane

![](media/image7.wmf){width="5.992361111111111in"
height="4.061805555555556in"}

Figure 7: Pull distributions for the position in the wire plane,
perpendicular to the wires

![](media/image8.wmf){width="5.992361111111111in"
height="4.061805555555556in"}

**Figure 8: Pull distributions for the position in the wire plane, along
the wires**

From the pull plots, it is clear that not all errors are assigned
correctly. However, whether this is due to an bug in the error
assignment in the segment reconstruction or due to incorrect errors on
the reconstructed hits can only be seen when the pull distribution for
the hits are found to be correct.

## Timing

For L3, we need to have a reasonable timing. In this version of the
software, the segment reconstruction takes 26 ms. per event (i.e. per
single muon), in the unoptimized build on d0mino. In the optimized
build, the segment reconstruction takes 12 ms. per event.