Velo to T Alignment - Reminder General Strategy  Perform relative VELO-to-IT/OT alignment using  X,  Y at the center of magnet and  X,  Y (each vs X, Y).   X,  Y,  X,  Y must all peak at 0 (vs X, Y, as well) for proper alignment  With magnet OFF data the 7 relative misalignments can be determined – 3 translations, rotation around Z axis, Shearing along X, Y, & Z scaling  X,  X ~ 4 meter track projection

One bothersome Issue Alignment first done with field OFF. 3 translations and 3 rotations determined. Once magnet is turned ON and T & VELO realigned. How do we know that we did not induce a small kink, or rotation angle between the two systems? Simple check: –The effective center of the magnet should be the same for both positive & negative charge

VELO The geometry Can easily calculate the shift Where: Z int = intersection point of VELO and T-Station track zMagnet = 5294 = nominal center of curvature zTstation = center of T station system = 8634 tan  T,V are X slopes in T-Stations and VELO Simulate a 1 mrad rotation min bias events

Separation by charge Clear separation Peak at 1 mrad, as expected Error on mean for this 1K events ~ 50  rad (rough, not fit yet) Clearly will scale with Ntracks.. Recall single track angular resolution ~0.3 mrad Need to check a couple of things, but seems simple enough…