Chapter 5. Projections

Table of Contents

5.1 Y/X Projection
5.1.1 Muon Detector Endcaps in Y/X Projection
5.1.2 LAr and HEC Endcaps in Y/X Projection
5.2 φ/η Projection
5.3 φ/λ Projection
5.4 ρ/Z Projection
5.5 φ/ρ Projection
5.6 φ/Z Projection
5.7 X'/Z Projection
5.8 Y'/Z Projection
5.9 3D Projection
5.10 3DBox Projection
5.11 Lego Plot

Available Projections

The projections that are available in Atlantis are data oriented, that is, they are adapted to the cylindrical structure of helices and of the ATLAS detector. The following projections are available:

Selection of Projections

A projection is selected via the Parameter Control (3.1.4 Parameter Control) of the Control Window or via the projection pop-up menu (3.3.2 Projection Menus).

Projections and Data

In the program a distinction is made for data in 3D space between space points (e.g. silicon hits) and space lines (e.g. straws from the TRT).

All projections may be used for both types of data. However, space lines are best viewed in the following projections:

Table 5.1. Display of space lines

ProjectionSpace line
Y/X (5.1 Y/X Projection)TRT, LAr and TILE barrels, RPC φ-strips, vertex region (intuitive view)
φ/ρ (5.5 φ/ρ Projection)TRT, LAr and TILE barrels, RPC φ-strips, tracks are straight lines
ρ/Z (5.4 ρ/Z Projection)Barrel and endcap calorimeters; approximate extrapolation to all MDT, RPC z-strips and TGC ρ-strips superimposed
X'/Z (5.7 X'/Z Projection)MDT, RPC z-strips and TGC ρ-strips, vertex region (intuitive view)
Y'/Z (5.8 Y'/Z Projection)Vertex region, orthogonal view with respect to X'/Z projection
φ/Z (5.6 φ/Z Projection)TRT endcaps, calorimeter endcaps and TGC φ-strips
φ/η (5.2 φ/η Projection)Calorimeters, and their association to tracks and S3D hits
3DBox (5.10 3DBox Projection)Shows tracks near the primary vertex to investigate secondary vertices


Projections and Magnetic Field

Depending on the projection and the type of magnetic field, tracks of charged particles will be more or less straight. The following table gives an overview:

Table 5.2. Shape of trajectories in magnetic fields

 Y/Xφ/ρφ/Zρ/Z
Solenoidalcurvedcurvedcurvedstraight
Toroidalstraightstraightstraightcurved


Checking the Tracking

In the Y/X (5.1 Y/X Projection), φ/ρ (5.5 φ/ρ Projection) and φ/Z (5.6 φ/Z Projection) projections tracks are seen from the side of maximum curvature. In the ρ/Z (5.4 ρ/Z Projection) projection they are seen from the "orthogonal" side, i.e. the side of minimum curvature. Therefore ρ/Z is said to be orthogonal to Y/X, φ/ρ and φ/Z.

In order to check in space if a track passes through a set of 3D hits or if it points to a set of calorimeter hits the hits and the track must be displayed in at least two 2-dimensional projections which are orthogonal to each other i.e. in ρ/Z and in one of the projections Y/X, φ/ρ or φ/Z.

Instead of using a pair of projections the 3-dimensional V-plot (5.4 ρ/Z Projection) is sufficient to check pattern recognition and track extrapolation.

5.1 Y/X Projection

The Y/X projection presents an intuitively understandable picture of data with a precise Y/X measurement. This projection may be used to view 3D tracks and hits and to associate them to data in the TRT, LAr and TILE barrels, and to the RPC φ-strips. All other data would appear as lines. In this projection the momentum of tracks may be estimated form the curvature. This projection also provides an intuitively understandable view of the region around the primary vertex.

In the standard view of the Y/X projection, data from the calorimeter and muon detector endcaps are not displayed (in order not to complicate the picture) as they would fall on top of data from the tracking chambers or data from the calorimeter barrel.

Alternatively, the view parameter may be used to select a single layer of the muon detector endcaps (3.1.4 Parameter Control). In this case, the TGC Gas Gap parameter may be used to further select data from only a given sublayer of the detector.

The Y/X projection is special in that it allows both the particle's charge and P t to be estimated from the track curvature.

Even with fisheye (4.5 Fisheye) the inner layers of the pixel detector fall on rather small circles, which do not take into account the high resolution of the pixel detector. The pixel data are better visualised in the φ/ρ projection (5.5 φ/ρ Projection).

The orthogonal projection to Y/X is the ρ/Z projection (5.4 ρ/Z Projection).

The Y/X Projection Menu (see 3.3.2 Projection Menus)

  • Aspect Ratio 1 - Sets the aspect ratio (width/height) of the picture to 1. The operation ensures that the original picture which was in the window does not go outside the window.

Parameters

  • View

    Select the data type, choice between:

    • Standard (default)

    • TGC Inner 1

    • TGC Middle 1

    • TGC Middle 2

    • TGC Middle 3

    • MDT/CSC Inner

    • MDT Extension

    • MDT Middle

    • FCAL EM

    • FCAL HAD 1

    • FCAL HAD 2

    • LAr Endcap Presampler

    • LAr Endcap 1 (outer wheel 1)

    • LAr Endcap 2 (outer wheel 2, inner wheel 1)

    • LAr Endcap 3 (outer wheel 3, inner wheel 2)

    • HEC 1

    • HEC 2

    • HEC 3

    • HEC 4

    • LAr Summed

    • HEC Summed

    • MBTS

  • Summed LAr binning

    Select the data type, choice between:

    • 0.1x0.1 (default)

    • 0.2x0.2

    • split

  • Summed HEC binning

    Select the data type, choice between:

    • 0.1x0.1

    • 0.2x0.2 (default)

    • split

  • Eta of split binning

  • Draw FCAL inside HEC

  • CSC Gas Gap

    Select value, choice between:

    • 1 (default)

    • 2

    • 3

    • 4

  • TGC Gas Gap

    Select value, choice between:

    • 1 (default)

    • 2

    • 3

5.1.1 Muon Detector Endcaps in Y/X Projection

In order to display the muon detector endcaps and the respective hits (drawn as points or lines) single stations must be selected:

  • TGC - Inner 1, Middle 1, Middle 2 and Middle 3. The TGC data may belong to different sublayers selected by the TGC Gas Gap parameter.

  • MDT - Inner 1, Extension, Middle and Outer.

These pictures show best the structure of the layers. Their position can be seen best from ρ/Z (5.4 ρ/Z Projection). The name of a specific module may be obtained by picking (4.3 Pick).

In the standard Y/X view (5.1 Y/X Projection) the inner detector and the calorimeter and muon barrel are displayed.

5.1.2 LAr and HEC Endcaps in Y/X Projection

In order to display the LAr and HEC endcaps there are several options:

  • Individual layers - Shows the hits in both endcaps unless a cut on η is applied.

  • Summed layers - Takes the sum of all the layers in the endcap, as with the individual layers this takes the hits in both endcaps unless a cut on η is applied.

  • Multiple layers - These projections can also be used by using the rectangle selection on the rubberband menu (4.2.1 Rubberband in YX Projection).

In the standard Y/X view (5.1 Y/X Projection) the LAr and HEC Endcaps are not displayed.