Evaluation of alignment Hidemitsu Asano 1 Evaluation method

Evaluation of alignment Hidemitsu Asano 1

Evaluation method of alignment -Use multi track events (# of segment > 5) -Reconstructed Vertex position of each track in one collision should be same point. -Deviation of vertex position can be used of evaluation of alignment. Beam center (xoffset, yoffset) -vertex position (x, y) is projected position on the (y=yoffset plane, x=xoffset plane) Definition of deviation: R. M. S. of (DCA)i of <vtx(x, y)>k (i= 1, 2, ……nsegment(of kth event)) : mean of vertex position of kth event 2

Deviation of DCA (simulation) - Hijing 20 k event (generated by Sasha. /direct/phenix+subsys+vtx/hijing) - Beam size 130 um (gauss. Distribution) - Zerofield - Ideal geometry No quality cut RMS = 155 um quality cut (>98% ) RMS = 118 um 3

Analysis of zero fieldrun - No magnetic bending. Momentum can not be calculated, but vertex position can be reconstructed using by only pixel ladders. Setup of analysis -run 346977 (Jun, 2 nd) -bbccharge <600 -|bbcz| <8 cm -zerofield flag : on (Svx. Tracker) -quality Cut parameter in standalonereco = -5. (default) -beam offset west : (x, y) =(0. 232, 0. 074) cm east : (x, y) = (0. 082, 0. 046) cm -Track finding is done by Svx. Standalonereco -use associated clusters on pixel layer for calculation of vertex position. Vertex position can be calculated using by straight track in zero magnetic field. 4

Analysis To reduce ghost track… - Multiplicity cut (=# of cluster/event on layer 0) <250 - 5 < # of segment /event <40 - DCA 0 (2 D-DCA calculated by pixel layer ) cut<0. 1 cm I decided these cut parameter by looking S/N. of dca 0 distribution 5

Real data ? ? ? 6

backup 7

Multiplicity vs # of segment (Real data) 8

Multiplicity vs # of segment (sim. ) 9

Z_vtx (sim. ) 10