Conventions

CONVENTIONS FOR PHOBOS PAD COORDINATES AND SENSOR NAMES

Baker, Verdier 28-Aug-1997
update by Katzy (with comments of Baker,Wozniak) 11-Dec-1998
web-ized by manly on 12/15/98

Global Coordinate System:

The origin of the PHOBOS global coordinate system is the nominal vertex position. The Z axis is the beam axis, with positive Z in the direction of the PHOBOS spectrometer which is clockwise when the RHIC ring is viewed from above. The Y axis is vertical with the positive Y direction being up. The X-axis completes a right-handed coordinate system. This means that the "left arm" is the positive arm P*** when the spectrometer is viewed from the vertex. The "right arm" is the negative arm N***.

Detector Elements:

Pad: A pad is a single pixel
Sensor: A sensor is a contiguous array of Silicon pads from one wafer.
Plane: A plane is a collection of sensors of the same hardware type which are nearly coplanar. Typically they are slightly offset from each other and overlapping.
Layer: A layer is a group of planes which will only be traversed once by a normal particle trajectory. These planes are on one side of a given frame (front or back). For instance the horseshoe layers in the spectrometer comprise 3 or 4 planes each, while the spectrometer layers closest to the beampipe have only one plane each. The octagon is one layer as a whole.
Subdetector: "RingMult" Ring Multiplicity detectors, "Octagon" Octagon Multiplicity detector, "Vertex" Vertex detector, "SpectP" Positive Spectrometer arm, "SpectN" Negative Spectrometer arm, "TOFP" Positive Time of flight detector, "TOFN" Positive Time of flight detector, "Trigger" Trigger detectors

Naming conventions:

1st letter specifies the subdetector:
- exception: MP (MN) - positive (negative) (Z) multiplicity ring

for the spectrometer and multiplicity octagon-

2nd letter specifies the layer

A is closest to the beamline.
The spectrometer arms contain 16 layers A-P
The octagon contains only one layer: 'O'. That's why all actagon sensors start with 'MO'.

3rd character (a number) specifies the plane within a given layer.
- Plane numbers start at 0.
- In the spectrometer, plane 0 is the plane in a given layer closest to theta=0 and the plane #s increase with increasing |theta|.
- Sensors in one plane should be from the same hardware type. (E.g. that's the difference between PO00-PO02 (type 1) and PO10-PO13 (type 2))
- In the multiplicity octagon one plane has a fixed phi and runs along the z axis and contains up to 13 sensors.
- The planes are numbered as if the frames were fully loaded even though there are places where we don't currently plan to have Silicon, e.g., there is no MOC5, but the name is reserved in case Silicon is later placed.
- In the rings one layer contains only one plane.

4th specifies the sensor in a plane.

for the rest (Vertex, Trigger,Tof, MultiplicityRings)-

2nd letter is subdetector part:
- Multiplicity: O (octagon), P (positive rings), N (negative rings)

3rd letter indicate layer within a subdetector part. A is closest to the beamline/nominal interaction point. that means a layer is for:
- Trigger: paddle (A), ring (B)
- TOF : wall A,B,C
- Rings : sensors at same z position (A,B,C)
- Vertex : inner (A), outer (B)

Note: since there is no TPhSubDetectorPart, the layer nr stored in data, member fLayer of TPhSensor and TPhLayer are counted through the subdetector.

4th specifies the sensor in a layer.

Sensor numbering conventions:

Within a plane, the sensor closest to the beampipe in theta is sensor 0 and the sensor numbers increase away from the beampipe.

Pixel numbering conventions:

Each pad in a given sensor is identified by 2 integer indices i,j which start from 0.

see RowCol.htm for these conventions.