Here, we study PDC position with respect to BLC, for which the position is precisely known with respect to VDCtop by the preceding study. It should be noted that the reaction product(s) is not very strongly forward-boosted, so that there exist many events with moderate inclination to PDC sensitive planes. The distribution of the PDCdetected directrion vector y, and z are shown below. On the distribution for dirvec z, strange peak structure exists at around dirvec z =0. At this moment, the reason of the appearance is not investigated. Since this does not clearly appear on same distributions for the next runs(see, those for run293), this is considered to be caused by trigger-wise.
PDC tracking is fairly reliable for run 292. The resulting residual distribution is shown below.
Vertex x VS vertex y obtained with BLC and PDC-L.
Vertex x VS vertex z obtained with BLC and PDC-L.
Vertex y VS vertex z obtained with BLC and PDC-L.
Vertex z obtained with BLC and PDC-L.
DCA with BLC-PDC-L(top) and BLC-PDC-R(bottom). Because PDC L and R have similar resolution, this indicates the presence of serious rotation or position offset for R. Even this moment, DCA half width is about 2.5 mm for L.
Vca with BLC-PDC-L(1st) and BLC-PDC-R(2nd). Relatively large y offset exists for PDC-R, by which the DCA distribution previously shown has been broadened.
Vertex_z (horizontal) - VS - VCA_y (vertical), by which rotation around x axis is studied. PDC L is found to be rotating with respect to E549 global coordinate system by several mrad.
Vertex_x (horizontal) - VS - VCA_y (vertical), by which rotation around z axis is studied. PDC L is found to be rotating with respect to E549 global coordinate system by several mrad.
PDCby (horizontal) - VS - VCA_y (vertical), by which x offset is studied.
Z shift and rotation around y axis are not clearly detected with BLC and PDC tracks, but easily detected with those from VDC and PDC. Vca distribution for run 292 between VDCtop and PDC are shown below. Z offset is clearly detected.
PDC rotation around y axis is easily seen in the correlation between vertex_x VS vca_z between VDCtop-PDC.
All PDC position offset and rotation had been successfully eliminated. The result is tabulatted below.
| L arm | R arm | |
|---|---|---|
| x offset | -1.5 mm | 1.65 mm |
| y offset | 0.6 mm | 2.0 mm |
| z offset | -7.1 mm | -3.5 mm |
| phi (around x) | 6.5 mrad | 1.6 mrad |
| theta (around y) | 7.2 mrad | 16.7 mrad |
| psi (around z) | -5.4 mrad | 3.1 mrad |
Variation of DCA distribution with respect to rotation and shift correction - black:nominal position, red:after shift correction, blue:after shift correction and inverse-rotation. Resulting DCA half width is 2.25~2.5 mm for pion scattered run.
