Millepede package

Spiros found the Millepede program for Linear Least Squares Fits with a Large Number of Parameters. The Millepede's idea is to define two sets of parameters:

and fit local parameters for each event with fixed global ones, substruct result from resudials and then fit global parameters. The procedure is iterative because it supposes to refit local parameters with the corrected global ones and tigher cuts.

The test case provided with the package contains alignment of 10 planes with one measurement calibrated with straught tracks.

Plane test

To check performance of MIllepede for our case

I create a plane test example. The events contain 5 tracks coming from the same vertex with pT exponentially distributed from 0.2 GeV/c Notation: (u,v,w) are (x,y,z) is the plane local coordinated system, (α,β,γ) are rotation along (u,v,w). Histogram is simulated misalignment, points are reconstructed ones.

Layer alignment

Yuri Fisyak
Last modified: Wed Feb 1 14:49:09 EST 2006