CFT Material Geometry

Introduction

This document describes how the DØ CFT material geometry was implemented for the Sept. 98 milestone. Other detectors may use this approach when implementing their material geometries.

The CFT Detector

The CFT detector is composed of 8 barrels, with each barrel consisting of an axial and a stereo fiber doublet. To construct the detector, the fiber doublets are glued to carbon-fiber support cylinders. In the representation of the CFT material described here, appropriate effective material is associated with each doublet layer. For example, the inner (axial) doublet's material corresponds to the cylinder + glue + fibers. The outer (stereo) doublet's material corresponds to glue + fibers. The parameters describing this effective material have been calculated by hand, and are supplied to the material geometry via an RCP. Specifically, in the current implementation the following fractions of a radiation length are assumed:

• Support cylinder: 0.22%
• Fiber doublet: 0.28%
• Glue (for one doublet): 0.14%

(These numbers were supplied by Norman Graf.)

We thus associate 0.64% of a radiation length (0.22% + 0.28% + 0.14%) with the inner fiber doublet, and 0.42% of a radiation length (0.28% + 0.14%) with the outer doublet. We currently assume this material is carbon.

CFT Material Geometry Implementation

To represent material, a new class Material was created, which resides in the CVS package material. Since we are representing effective material, we've calculated the amount of carbon which corresponds to the above fractions of radiation lengths, and use the Material constructor with the form

Material(name, symbol, zeff, aeff, rho, x0)

where all parameters are supplied "by hand".

The geometrical properties of the material are represented by the new class CylindricalShell, which resides in the CVS package thinshells. A CylindricalShell is created by supplying a Handle to a CylindricalSurface, a Material (see above) and a thickness. (CylindricalSurface and Handle are classes which reside in the CVS package geometry_system.) Properties of the cylindrical surface supplied to create the shell (size, position, orientation) are obtained from the CftBaseGeometry. The use of a Handle allows any changes in the CftBaseGeometry to be automatically propagated to the material geometry (for example, when new alignment constants are needed).

The singleton class CftMaterialGeometer provides the following functionality:

• Build the material geometry.
• Keep the material geometry "in sync" with the base geometry.
• Supply the user access to the CylindricalShell's associated with each doublet.

This class has been designed to be used in conjunction with the framework package geometry_management, which builds the complete DØ geometry (d0_geometry). To initialize the detector geometries, a build request is sent from the geometry_management package to the d0_geometry, which in turn sends build requests to each of the detector geometries (base, channel and material). To include the new CFT material geometry into the DØ geometry, a new MaterialGeometry class was included in d0_geometry.

In addition to building the geometries, the geometry_management package must keep these geometries valid (i.e. to account for run dependences). When a new BaseGeometry is detected, the geometry_management package sends a refresh message to each of the detector geometries. To avoid physical couplings, each detector geometry has been required to create a "Geometer Decoupler". The refresh messages actually go to the decouplers, which pass the message on to the detector geometries. In order to keep the material geometry in sync with any new base geometries, the CftGeometerDecoupler was modified to also call the refresh method of the CftMaterialGeometer. The material geometer then updates all existing Handle's to the material geometry.

Steps To Follow To Implement Material Geometry For Other Detectors

The following steps should allow other detectors to implement material geometries in a similar way as described above:

• Determine effective materials needed to describe detector.
• Implement any required new thinshells (see CylindricalShell as an example).
• Create a material component in the detector geometry (see cft_geometry/material as an example).
• Update xxxGeometerDecoupler to refresh material geometry (see CftGeometerDecoupler).
• "Register" new material geometry with d0_geometry (i.e. tell Harry or John).

This page maintained by Harry Melanson
Last modified: Oct. 27, 1998