BeamCal

BeamCal is an electromagnetic sandwich calorimeter that uses Tungsten as absorber. It serves three major purposes:

Improving the hermeticity of the ILC detector by providing electron and photon identification down to polar angles of a few mrad. This is a specially challenging task due to the vast amount of deposited energy from the electron-positron pairs originating from beamstrahlung.
Reducing the backscattering from pairs into the inner ILC detector part and protecting the final magnet of the beam delivery system.
Assisting beam diagnostics. A fast luminosity signal will be provided by BeamCal. The detailed analysis of the shape of the energy deposition from pairs hitting the BeamCal grants access to parameters of the colliding beams.

The sensors of the BeamCal must be very radiation hard. The technologies under investigation are:

- polycrystalline CVD diamond (Chemical Vapor Deposition),
- single crystal CVD diamond,
- GaAs,
- radiation hard silicon.

Geometries:

Table 1: BeamCal geometries for different beam settings.
^* We assume an Anti-Detector Integrated Dipole field: the magnetic field is parallel to the outgoing beams. Optimized for low backgrounds.
^**Crossing angles of 14 or 20mrad require an additional hole in each BeamCal for the incoming beams.
		Unit	14 mrad
Graphite shield thickness		mm	100
Absorber layer	1 X₀	mm	3.5
Sensor layer		mm	0.3
Readout plane /air gap		mm	0.2
total X₀		int	30
x/y/z position		mm	+24.2/0/±3595
R_inner (sensitive area)		mm	20
R_outer^* (sensitive area)		mm	150
R_{beam_in}^**		mm	15
θ_inner		mrad	5.6
θ_outer		mrad	41.7
Tilt		mrad	7
~ Weight of absorber and sensor (sensitive area)		kg	144.4

Segmentation:

Table 2: BeamCal segmentation.
		Unit	14 mrad
0.8 R_M cell size	Rings	int	16
	ΔR	mm	8.125
	Sectors	int	8 of 45 degree
	Cells per sector	int	160
	Cells/layer	int	1280
	Blind area	degree	±22.5 around incoming beam, rings with R>63.4 are complete (n > 6)