1. David Silvermyr Lund University for the PHENIX Collaboration Early global event results using the PHENIX Pad Chambers at RHIC

2. PHENIX Year 1 Configuration The Pad Chambers (PC) are MWPCs that provide 3D position information. - essential for pattern recognition in central arm track reconstruction - readout scheme insures noise immunity - 99 % efficiency in active area For detailed performance info, see K. El Chenawi, DC 11 This analysis also use the Zero-Degree Calorimeter (ZDC) and Beam Beam Counter (BBC) for triggering and vertex reconstruction comparisons. See H. Ohnishi, DC 9 (BBC) and S. White, JC 8 (ZDC) ZDC

3. PCMON: A Central Event in PC3 East

4. Hit Matching Procedure The analysis presented here was performed with field off runs only and using PC1 and PC3 in the East arm. The background contribution is determined by a mixed event technique of exchanging each PC1 sector with its neighbour.

5. Vertex Reconstruction The vertex position is determined by 1) Combining all PC1 and PC3 hits to a line 2) Project the lines to the plane and save all within an appropriate X and Y window. 3) Calculate the peak position of the Z distribution. The vertices found by PC and BBC agree nicely. By repeating the procedure with a tighter cut placed around the found vertex, one can estimate the number of tracks in the collision.

6. Raw Multiplicity Distributions The number of hits in PC1 W, PC1 E and PC3 E are very similar. Differences from the expected are due to less geometrical active area coverage in PC3. The number of background tracks dependence on the total number of tracks agree with expectations from first principles.

7. Vertex Distribution Plot shows contributions from different sources to the distance from vertex distribution. By knowing these contributions, we can estimate the effects of our applied R-cut. Tracks/(event*cm) comparison between the PHENIX Integrated Simulation Application (PISA) and data are in reasonable agreement. PISA does not include any detector response or detector resolution.

8. Correction Factors & Trigger Information Number of triggers Acceptance The acceptance of the Pad Chambers in the east tracking arm is about 90 degrees in  and ± 0.35 in . Correction factors within that acceptance are due to small gaps between the active areas of the chambers, misbehaving electronics and the effect of applied cuts. EfficiencyCuts

9. Multiplicity distribution PHENIX PRELIMINARY Distribution has been scaled by the known correction factors, to correspond to a coverage of ± 0.5 in  and 2  in . Width of high N ch roll-off is a function of finite aperture.