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Veto strategy for S2 burst analysis

Veto strategy for S2 burst analysis. (detection oriented). Detection hypothesis. At the end of the S2 analysis we could find ourselves facing the possibility of remaining with few burst candidate triggers , which emerge from the pipeline and survive all possible cuts.

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Veto strategy for S2 burst analysis

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  1. Veto strategy for S2 burst analysis (detection oriented) A. Di Credico Syracuse University

  2. Detection hypothesis • At the end of the S2 analysis we could find ourselves facing the possibility of remaining with few burst candidate triggers, which emerge from the pipeline and survive all possible cuts. • We need to tailor a detection strategy for the veto analysis before this happens (open the box), using our knowledge of the auxiliary channels and the playground veto analysis A. Di Credico Syracuse University

  3. Auxiliary channels • We should be able to answer a few questions on the nature of the auxiliary channels: • Justified: is it possible to find a good reason for thinking that a glitch in the instrument or in the environmental variables (not gw related) is reflected in any manner on both the gw channel and the auxiliary channel ? • Safe: how can we assess the safety of the auxiliary channel ? • Not all auxiliary channels are equally suitable for ‘vetoing’ a burst candidate event trigger A. Di Credico Syracuse University

  4. Auxiliary channels – 2 • Given a set of justified and safe auxiliary channels for each IFO, we need to: • Assess their overall efficiency in vetoing ETG triggers (coincidence analysis/lag plot): • Efficiency = (# of ETGs vetoed)/ (tot # of ETGs) • DeadTime = (tot duration of aux chan glitches)/(tot duration of data sample) • F.o.M. = (Efficiency/DeadTime) - 1 …not the only way • Characterize them through a glitch monitor (glitchMon, WaveMon) • Plots of Deadtime vs Sigma (significance of glitch) A. Di Credico Syracuse University

  5. Figure of Merit These quantities are computed using WB GC>1.3 triple coinc A. Di Credico Syracuse University

  6. Strategy • Associate to each auxiliary channel a minimum sigma value (sigma_thr) which corresponds to a maximum deadtime produced in the data by applying this channel as an 'a priori' veto. • The deadtime takes the role of probability of random coincidence between the auxiliary channel glitch and the ETG event. Higher the deadtime (lower the sigma) higher the chance that an auxiliary channel X glitch of that significance (sigma) is in random coincidence with the ETG event. • Since we put ourselves in detection mode, in order to state that a candidate event is successfully vetoed, we would like it to be in coincidence with a LOW probability auxiliary channel glitch => high sigma value. • First approximation: all auxiliary channels are treated in the same way, independently from their FOM value. A. Di Credico Syracuse University

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  8. Other examples - L1 A. Di Credico Syracuse University

  9. Other examples – H1 A. Di Credico Syracuse University

  10. Sigma_thr • We select for each channel a sigma_thr so that the probability for the single channel to be in random coincidence with the candidate GW event, is 10^-3. • The value of sigma_thr can be inferred by the plot deadtime vs sigma, assuming that the deadtime associated with the event well represents this probability. A. Di Credico Syracuse University

  11. Case study • WB (GC>1.3) 4 interesting events • We have already computed the FoM based on these events (in order to choose efficient channels) A. Di Credico Syracuse University

  12. Coincidence check • Run chosen glitch monitor on selected auxiliary channels, with selected sigma_thr • Run the time coincidence code between the (4) burst event triggers and the auxiliary channel triggers • Determine how many coincidences occur: IN OUR CASE STUDY THERE WAS NO COINCIDENCE FOUND WITH CHANNEL GLITCHES ABOVE THE SIGMA_THR VALUE But , in general, we expect to observe N (number of channels selected = 10) times P (10^-3) = 10^-2 coincidences. We plan to check this using a large set of random events (times) as burst event triggers and run them against the selected auxiliary channels A. Di Credico Syracuse University

  13. Summary • A strategy has been proposed to attack the problem of ‘vetoing’ a posteriori burst candidate events, based on the auxiliary channel efficiency/deadtime • This strategy has been tested on the 4 WB interesting events, which have not been successfully vetoed • More tests are needed and suggestions on how to improve it are very welcome A. Di Credico Syracuse University

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