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

Updated 20-March-2000 for Phat5 by
A.Olszewski

Global Coordinate System, Detector elements, Naming Conventions, Sensor Numbering Conventions, Pixel Numbering Conventions
Spectrometer, Vertex, Multiplicity, TOF, Trigger, ZDC

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.
Module: A set of sensors connected to a common electronics board (see a list of predefined modules in TPhSensorModule class).
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 (see a list of predefined planes in TPhSensorPlane class).
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. (see a list of predefined layers in TPhSensorLayer class).
Subdetector: "RingsP", "RingsN" Ring Positive Z and Negative Z Multiplicity detectors, "Octagon" Octagon Multiplicity detector, "VtxT", "VtxB" Vertex top and bottom detectors, "SpecP" Positive X Spectrometer arm, "SpecN" Negative X Spectrometer arm, "TOFP" Positive X Time of flight detector, "TOFN" Negative X Time of flight detector, "Paddle" Paddle detectors, "Cerenkov" Cerenkov detectors, "ZDC" Zero Degree Calorimeter detectors.

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. These numbers are coded in the sensor names.

The layer, plane, module nr stored in data, member fLayer, fPlane, fModule of TPhSensor and TPhLayer are counted through the subdetector.

Pixel numbering conventions:

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

Naming conventions:

1st (sometimes also 2nd and 3rd) letter specifies the subdetector:
- P, N - Spectrometer
  - P - positive (X) spectrometer arm
  - N - negative (X) spectrometer arm
- M - Multiplicity
  - MO - multiplicity barrel (octagonal prism)
  - MP - positive (Z) multiplicity rings
  - MN - negative (Z) multiplicity rings
- V - Vertex
  - VT - top (Y) vertex detector
  - VB - bottom (Y) vertex detector
- X, T - Time Of Flight
  - X - positive (X) TOF counters
  - T - negative (X) TOF counters
- G - Trigger
  - GPA, GNA - Paddle counters
  - GPB, GNB - Cerenkov counters
- Z - ZDC calorimeters
The sensor names are constructed 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.

Spectrometer:

1st letter specifies one of the two spectrometer subdetectors
- P for positive X
- N for negative X

2nd letter specifies the layer

A is closest to the beamline or nominal vertex.
The spectrometer arms contain 16 nominaly layers A-P

3rd character (a number) specifies the plane within a given layer.

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))

4th character specifies the sensor in a plane.

Vertex:

1st letter:
- Vertex detector is divided into two subdetectors each of them starting with V as a first letter.
2nd letter specifies one of the multiplicity subdetectors
- VT - top vertex layers (positive Y)
- VB - bottom vertex layers (negative Y)
3rd letter
- 3rd letter indicate layer within a subdetector part. There is only one plane in each of the layers. A is closest to the beamline/nominal interaction point. Both subdetectors contain an inner (A), and an outer (B) layers
4th character is a hex coded number, specifying sensor within a plane.

Multiplicity subdetectors:

1st letter M is the same for all multiplicity detectors
2nd letter specifies one of the multiplicity subdetectors
- MO - multiplicity barrel (octagonal prism)
- MP - positive (Z) multiplicity rings
- MN - negative (Z) multiplicity rings
3rd letter
- In octagon 3rd letter specifies a plane, since consists only of one layer of sensors. Each plane has a fixed phi and runs along the z axis and contains up to 13 sensors.
- In rings 3rd letter specifies a layer, with A ring being the closest to the vertex.
4th character is a hexadecimal coded number, specifying sensor within a plane.

TOF:

This detector is divided into two parts, each starting with a different letter:
- X - positive (X) TOF counters
- T - negative (X) TOF counters
2nd letter specifies layer which in TOF case means one of the walls of scintillators, layer A being the closest to the vertex
3rd and
4th character in hexadecimal code number scintillators within each of the walls, starting from 00 at the locations closest to the nominal vertex position.

Trigger:

1st letter, G, specifies a group of detectors with the aim to form a trigger.

2nd letter indicates position of detectors in Z direction
- P for the positive Z side
- N for the negative Z side

3rd letter specifies subdetectors, which in the trigger group case are of different types

Paddle detectors (A)
Cerenkov detector (B)

4th character specifies an individual detector element

ZDC:

1st letter, Z.

2nd letter indicates position of detectors in Z direction

P for the positive Z side
N for the negative Z side

3rd letter, always A, stands for a single layer of detectors on each Z side

4th character specifies an individual detector element

see RowCol.htm for these conventions.