ALICE 3 FORWARD DETECTOR

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ALICE 3 Tracker Barrel

This is top page for the TRK detector documentation.

Specific detector setup

Configurables for various sub-detectors are presented in the following Table:

Subsystem	Available options	Comments
`TRKBase.layoutVD`	`kIRIS4` (default), `kIRISFullCyl`, `kIRIS5`, `kIRIS4a`	link to definitions
`TRKBase.layoutMLOT`	`kCylindrical`, `kSegmented` (default)	`kSegmented` produces a Turbo layout for ML and a Staggered layout for OT
`TRKBase.layoutSRV`	`kPeacockv1` (default), `kLOISymm`	`kLOISymm` produces radially symmetric service volumes, as used in the LoI
`TRKBase.disableFT3`	`false` (default), `true`	toggle to disable the forward disks
`TRKBase.layoutFT3`	`kSegmentedStave` (default), `kSegmentedFT3`, `kTrapezoidal`	disk geometry settings `kSegmentedFT3` refers to an outdated segmentation
`TRKBase.nTrapezoidalSegments`	integer; default: 32	number of trapezoidal segments in the disks for kTrapezoidal layout

For example, a geometry with fully cylindrical tracker barrel (for all layers in VD, ML and OT) can be obtained by

o2-sim-serial-run5 -n 1 -g pythia8hi -m A3IP TRK TF3 \

--configKeyValues "TRKBase.layoutVD=kIRISFullCyl;TRKBase.layoutMLOT=kCylindrical"

Custom Geometry Configuration

The geometry of the ML and OT layers can be overridden by providing a custom plain-text configuration file via TRKBase.configFile=filename.txt. The parser interprets the file differently depending on the active TRKBase.layoutMLOT setting (kCylindrical or kSegmented).

General Syntax Rules

Separators: All columns must be separated by a single TAB (\t). Using spaces will result in a parsing error.
Comments: Any line starting with a forward slash (/) is treated as a comment and ignored.
Layer Count: The parser reads valid lines sequentially. The first valid line corresponds to Layer 0, the second to Layer 1, and so on.
Material Budget Mode: All layer definitions accept an optional matBudgetMode parameter at the end of the line (e.g., 0 = Thickness, 1 = X2X0). If omitted, it defaults to Thickness.

1. Cylindrical Layout (`kCylindrical`)

When TRKBase.layoutMLOT=kCylindrical is used, each layer requires a minimum of 3 parameters to define the TRKCylindricalLayer.

Format: rInn \t length \t thick \t [optional_mode]
*(Note: rInn, length, and thick map directly to the constructor arguments for the cylindrical layer, typically corresponding to Radius, Length, and Thickness).*

Example for kCylindrical:

/ Configuration for kCylindrical layout - ALICE3 TRK
/ rInn  length  thick [optional_mode]
0 127.985 0.1
0 127.985 0.1
0  127.985 0.1
0  127.985 0.1
0  127.985 0.1
0  255.9 0.1
0  255.9 0.1
0  255.9 0.1

2. Segmented Layout (`kSegmented`)

When TRKBase.layoutMLOT=kSegmented is used, each layer requires a minimum of 5 base parameters to define the geometry. The parser distinguishes between Middle Layers (ML) and Outer Layers (OT) based on the sequential layer index.

*(Note: The 5 base parameters map directly to: Inner Radius (rInn), Thickness (thick), Tilt Angle (tiltAngle), Number of Staves (nStaves), and Number of Modules per stave (nMods)).*

Middle Layers (ML) - Indices 0 to 4 The first 5 valid lines are parsed as TRKMLLayer objects. These layers require a 6th parameter for the staggering offset (stagOffset).

Format: rInn \t thick \t tiltAngle \t nStaves \t nMods \t stagOffset \t [optional_mode]

Outer Layers (OT) - Indices 5 and above From the 6th valid line onwards, lines are parsed as TRKOTLayer objects. These layers do not have a staggering offset. The optional mode parameter shifts to the 6th column.

Format: rInn \t thick \t tiltAngle \t nStaves \t nMods \t [optional_mode]

Example for kSegmented:

/ Configuration for kSegmented layout - ALICE3 TRK
/ --- ML LAYERS (Indices 0 to 4) ---
/ rInn  thick tilt  nStaves nMods stagOffset  [optional_mode]
7.0 0.01  11.2  10  11  0.0 1
9.0 0.01  11.9  14  11  0.0 1
12.0  0.01  11.4  18  11  0.0 1
20.0  0.01  0.0 26  11  1.17  1
30.0  0.01  0.0 38  11  0.89  1
/
/ --- OT LAYERS (Indices 5 to 7) ---
/ Outer layers do NOT have stagOffset.
/ rInn  thick tilt  nStaves nMods [optional_mode]
45.0  0.01  0.0 32  22  1
60.0  0.01  0.0 42  22  1
80.0  0.01  0.0 56  22  1

Additional options for forward disks

Furthermore, there are more options in the case of stave segmentation – for only OT or both. The user can set to cut the staves exactly on the nominal inner radii (true by default), and outer radii (false by default) of the disks. This exists since (planned) placements of sensors & staves often protrude out of the nominal radii to be more able to cover the nominal disk area. In addition, it is possible to draw reference circles (TRKBase.drawReferenceCircles) in root for the stave segmented layouts for both the inner (red) and outer (blue) radii. This is off by default, yet can be toggled if the user wants to see how tight the tiling is to the nominal radii – for visualisation purposes only.