Start and Vertex DetectorW. Boeglin, A.Klein

Current Design:

• 3300 scintillating fibers 1mm diameter• 3 double layers (1 axial, 2 stereo)• cylindrical geometry• spherical cap for forward coverage• estimated position resolution < 1mm

QuickTimeª and aTIFF (LZW) decompressor

are needed to see this picture.

Photon beam

Helical stereo layers

Target chamber

Scintillator array

• fast timing using scintillators/PMT (0.3cm thick)• fibers for position only

First design idea:

• fiber coverage of cone section virtually impossible• increased multiple scattering• no position information in conical section

Pro:

Con:

Current design

Helical double layers Support structure

Target volume

Forward detector, with hole for -beam

• fibers provide position and timing information• forward detector coverage• multiple scattering can be minimized• forward detector feasible (at least so far)

Vertex Detector Dimensions

Views of detector I

Double layer in front detector

Down stream iso view

Rate Studies: Geant Simulation (thanks to Richard Jones)

Target: • 30 cm liquid Hydrogen• diameter 3cm• target cell : Al 0.5 mm• vacuum vessel: Be 0.5 mm

Beam:• 3 A electron beam • coherent bremsstrahlung

Detectors:• cylindrical detector surrounding the target cylinder• flat detector with a 1.4 cm hole for the photon beam

hits on fiberse+/e- rate 3.3 MHz

forward detectore+/e- rate 18 Mhzp >1 MeV

rate per fiber: 10 kHz

Forward detector rates

p>1 MeV

all

bin width: 1mm

700kHz

200 kHz

• cylinder section has no problem with rate per fiber• forward section: large rate

needs large segmentation possible radiation damage (to be studied) creates readout problem (signal lines, to be studied)

• position resolution < 1mm (‘FWHM’,to be studied)• timing resolution : extrapolated: = 0.6ns

conceptual design of vertex detector exists using proven technology

What do we need and how to we get the answer?

What is the function of the START counter ? Start signal for what : TOF, beam pulse identification ? Vertex reconstruction: connect tracks to FDC’s , resolution (0.5 mm) ? Part of the hardware trigger? Part of the “software” trigger? All of the above? Readout/frontend electronics ADC/TDC logic

Justification of requirements: physics driven• minimal position resolution requirements as a function z and direction• minimal timing resolution requirement • efficiency, redundancy, uniqueness• multiple scattering tolerance • alignment requirements, fiber location• phase space considerations, shadow regions (minimize impact of shadow regions)• kinematic reconstruction, over determination of tracks, redundancy

Trigger Integration

• any signals used in trigger• if yes at what level, what information