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Update on the pixel efficiencies in the Indium run 2003

Update on the pixel efficiencies in the Indium run 2003. Reminder: status collaboration meeting. Pixel efficiency seems to depend on the instantaneous occupancy in the analysed event (expressed by the number of VT tracks).

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Update on the pixel efficiencies in the Indium run 2003

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  1. Update on the pixel efficiencies in the Indium run 2003 NA60 Group meeting, 22 April 2005, Markus Keil

  2. Reminder: status collaboration meeting • Pixel efficiency seems to depend on the instantaneous occupancy in the analysed event (expressed by the number of VT tracks) Same behaviour for all planes, but more pronounced for the planes close to the target • Same result also using: • Matched muon tracks • Tracks with high p / low c2 NA60 Group meeting, 22 April 2005, Markus Keil

  3. Conclusion? • Decreasing efficiency not a problem of the tracks: • e = (NHits – NFakes) / (NTracks) • If NTracks is ok, problem might be in NHits – NFakes • Fake subtraction • Up to now: count number of hits in environment, subtract number of fakes in the environment NA60 Group meeting, 22 April 2005, Markus Keil

  4. At high occupancy? • Possibility of the following case: • Two tracks close to each other → merged cluster • Fake subtraction: (4 – 4) / 1 = 0 → Try to avoid counting, just check whether there is sth. NA60 Group meeting, 22 April 2005, Markus Keil

  5. Calculating efficiencies – Binomial with fakes • Consider the binomial case of success/no success: • Is there a (1,2,3…) hit in the surrounding of the track? • If the efficiency is e, in how many cases will the answer be “yes”? • A) no fakes: <NYes> = eNTracks • B) with fakes: <NYes> = eNTracks + pFake(1-e)NTracks • Instead of solving A for e, we solve B: • e = (NYes - pFakeNTracks) / (1-pFake) • This method does avoid subtraction NHits - NFakes • N.B.: Here pFake is the probability to have ANY number of fakes in the surrounding NA60 Group meeting, 22 April 2005, Markus Keil

  6. Efficiency vs. road width • Fake probability growing ~linearly with c2 • Acts only on the difference between efficiency and 100% NA60 Group meeting, 22 April 2005, Markus Keil

  7. Efficiency vs. number of VT tracks • Comparison of the two methods: • Other than in the counting method, in the yes/no method the efficiency remains stable • First two bins with compromised efficiency. Bias? (If some planes are less efficient there will be less VT tracks) • Apart from that result looks reasonable NA60 Group meeting, 22 April 2005, Markus Keil

  8. Comparison for all planes • Higher efficiency, planes much more uniform with “yes/no” efficiency NA60 Group meeting, 22 April 2005, Markus Keil

  9. Some byproducts … • Vertex distributions: a) Z distribution fit with convolution of box ⊗ gaussian: b) BS x – Vertex x: NA60 Group meeting, 22 April 2005, Markus Keil

  10. Cluster sizes • Cluster size vs. x • Minimum is not at 0 • Effect of Lorentz angle • Better variable to measure the value: • track angle • to be done… NA60 Group meeting, 22 April 2005, Markus Keil

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