Radius Dependency of the Vertex Detector

The dependency of the performance of the vertex_detecor on its radius is studied by using the ILC framework modified for BELLE. Therefore several single muon events were generated with Mokka, using a detector model (DetectorModels) which consists of a beampipe, a Central Drift Chamber and a 6 layer Vertex-detector (two pixel (thickness 0.05mm) and 4 strip(0.3mm; radius[mm] 45, 70, 100, 138) in ladder structure, which distinguish only in their geometrical features) while the radius of the pixel detector (the first two inner layers) was varied. The first radius runs from 12mm to 26mm in 1mm steps, the second is always three mm larger. Other parameters which are varied are: Energy(0.2 GeV - 2 GeV) and shooting angle (theta: 20degree - 80degree; in 20 degree steps; phi:0 - 2pi homogeneous smeared).

The digitization, reconstruction and analysis is done with Marlin using the following processors:

We take a look at the resolution of the track-parameter d0 (the point of closest approach in the R-phi plane, ImpactParameterResolution) of reconstructed tracks as measurement of the performance.All plots show the rms (from the histogramm, (with a 90% cut)) and/or the sigma (from tha gaussian fit) of d0.

The result is an improvement of the resolution with a decreasing radius of the vertex detector (and also with a decreasing radius of the beampipe, see mu+diffBPradi.ps). Although the tendency is clear, the statistical error is not yet fully understood as the plot in mu+statERROR.ps indicates.

• mu+d0Radius.ps: Radius Dependency of d0 resolution: d0 is plotted against the radius of the inner layer of the VTX-Detector for different energies and thetas (beampipe radius is 10mm)

• mu+Radi_example.ps: example of the d0 distribution of the reconstructed track with a Gaussian fit (1. plain; 2. with a 90% cut; 3 simulated)

• mu+Energy.ps: energy dependency of the d0-resolution for different radii with fit, different thetas are merged into one plot (page 2: only the fit functions)

• mu+statERROR.ps: Error uncertainty (here a 30000 event file was splitted into three parts to compare the d0-parameter of the different parts, the two plots show the same)

• mu+diffBPradi.ps: the same as mu+d0Radius.ps but with different beampipe radii

-- PitVanhoefer - 18 Mar 2009