The following deficit of the CVS version of PPV have been corrected for in December of 2008

1.  PPV requires at least 2 matched tracks for a valid primary vertex saved in muDst with positive rank. 

   Problem: For W-events there may be less then 2 tracks in the eta range [-1,+1.4] to satisfy the above requirement. Although recent change in PPV causes additional 5 sub-prime vertices are saved with negative rank, it does not guarantee the vertex containing just a single 20+ GeV track will beat other minBias vertices from the pileup and make to this top 5.

   Remedy: Extend criteria for valid primary vertex and save also those which contain at least one track with pT>15 GeV matched to BTOW or ETOW tower with ADC>=MIP. I do not want to impose ADC>1000 cut, because reco high pT electron track may miss the hit-tower and point to the neighbor one. There will be very few events with such high pT tracks so on average # of vertices per event will not change.

    

   Implementation:  PPV 'natural ranking' for pp events has dynamic range of [0+eps ... 10,000].

   • for events with 2 or more matched tracks PPV rank will be increased by 1000,000 (so vertex will be on the top of the vertex list)
   • for events with  only one high pt track(for W reco)  live the  PPV rank as is (will be in the middle of vertex list)
   • for (the first five) sub-prime vertices (for Akio's study) subtract 1000,000 from 'natural' PPV rank, it will be a negative number

    

   Consequences: The 1-track vertex will be listed after any 2+ track vertex. However, in none 2-track vertex is found the 1-track vertex will be firts on the list with positive rank. I maintain people should not use the top rank PPV vertex blindly but QA prime vertices according to their needs.  
   

---

Modified PPV produces vertices with the following rank distribution:

Fig 1. Example of PPV vertex rank distribution for 200 W-events generated by Pythia. Top plot show vertex rank, X-axis range [-1.2e6, +1.2e6]. The 3 groups of vertices are those with 2 or more matched tracks (most right), 1-track vertices (12 events in the middle), sub-rime vertices (negative rank). Bottom plots shows the same events but Log10(rank) is used on the X-axis to make this 3 categories better visible.


---

Fig 2. Example of PPV vertex rank distribution for 200 st_physics 2008 pp events. 


2. Plot below shows ADC of BTOW for towers pointed by TPC MIP track, for a subset of ~200 towers, from fmsslow pp 2008 events. The red band is pedestal, the green band is MIP peak position. The maximum of MIP distribution as at ADC~17.

   No change needed: PPV is tagging BTOW tower as fired if ADC>8. This item is here because I misremembered sth about PPV code, the plot is correct and nice so I live it for the record.
   

Fig 3.