BFEM Telemetry data vs. Rescued data (2) -- TKR data size distribution --

1. BFEM Telemetry data vs. Rescued data (2)-- TKR data size distribution -- November 27, 2002 Tsunefumi Mizuno mizuno@SLAC.Stanford.EDU • What is studied here? (p.2) • TKR data size distribution (pp.3-5) • Effect on the track length (p.6) • Summary (p.7): modified after the discussion with JJ. Note: Please read the previous memo (BfemTelemetry_vs_Rescued_2002-11-14.ppt) for better understanding of this one.

2. What is studied in this memo? • In the previous report, we found that BFEM telemetry data differs (slightly) from that stored in the disk, indicating that telemetry sampling is somewhat biased and prefers events of short track. Tune proposed that this could be due to the data size: telemetry might prefer data of smaller size. With the help of Tony, I compared the data size between telemetry and rescued data. • BFEM data format is designed by Dave Lauben and called “IVTE format”. Detector data consists of 6 parts, DAQ, LTC (live time counter), ACD, CAL, L1T and TKR. Among them, 5 except TKR has fixed length, and the total data size of them is 1500 byte. The size of TKR data varies from ~150byte to up to ~2000 byte. Hereafter, TKR data size are compared between telemetry and rescued data.

3. TKR data size distribution (1) Figure1: L1T count rate of Run54 (during ascent). This consists of 16 small runs, and run#0, #2, #3, #5 and #6 are recovered from the disk (i.e., rescued data). #5 #3 #6 #2 #0 telemetry data rescued data Figure2: TKR data size distribution of rescued data #0. Left panel shows an overview and right one shows an expanded distribution. No significant difference is observed between telemetry and rescued data.

4. TKR data size distribution (2) telemetry data rescued data Figure3: TKR data size distribution of rescued data #2 (upper figures) and #3 (lower figures). Left panel shows an overview and right one shows an expanded distribution. Clear difference is seen between telemetry and rescued data. Telemetry prefers data of smaller size.

5. TKR data size distribution (3) telemetry data rescued data Figure4: TKR data size distribution of rescued data #5 (upper figures) and #6 (lower figures). Left panel shows an overview and right one shows an expanded distribution. Clear difference is seen between telemetry and rescued data. Telemetry prefers data of smaller size.

6. Does the preference for small data affects the track length? • As we saw, BFEM telemetry tended to pick up events of smaller size when the trigger rate was high. Does this explain why BFEM telemetry prefers short track events? Below, events are sorted based on the TKR data size and the number of layers with hit is histogrammed. • Figure5: The number of layers with hit distribution of rescued data of #2. Here, events are divided into 5 based on the TKR data size. Events of smaller data size show smaller number of layers with hit, or, in other words, has shorter track. BFEM telemetry prefers events of shorter track (events of smaller data size). 0-200 byte 200-400 byte 400-600 byte 600-800 byte >=800 byte # of layers with hit

7. Summary and issues to be examined • TKR data size were compared between telemetry data and rescued data. (p.2) • BFEM telemetry were likely to collect data of smaller size when the trigger rate was high. (pp.3-5) • This could, at least partially, explain why BFEM telemetry prefers events of shorter track. (p.6) • Will this happen to DAQ of GLAST satellite? -> Yes, but less prominent. GLAST DAQ ask data size before acquisition and throw away if the size is large. There will be no (or, little) effect for events whose size is not large. For more detail, contact JJ. • Is there any way to extract unbiased events from the telemetry data? -> Probably no. It is impossible to compensate the lost data. Instead, it could be possible to apply telemetry sampling algorithm to rescued data and simulation data.