Photonics/Hit-Maker Time Bug Jake Feintzeig 1 2 Contents This - PowerPoint PPT Presentation

Photonics/Hit-Maker Time Bug Jake Feintzeig 1

2 Contents  This talk covers two separate but related bugs, one in photonics and one in hit-maker  Photonics time transformation bug  Overview  Details  Time transformation plot  Example  Summary and solution  Hit-maker bug  Details  Summary and solution

3 Photonics Time Bug - Overview  Photonics bug affects: anything that uses time pdfs/cdfs with level2 tables  Simulation and reconstruction of muons  Hit-maker  Photorec  Not finiteReco, surprisingly  Not millipede (uses level 1)  The bug is a systematic timing offset that varies with track-DOM distance, but is on the order of 10 ns

4 The Details  In the level 2 tables reading routine, photonics does a time transformation to “internal residual time format” that depends on the difference between the internal table group velocity (what was simulated) and the external IceCube group velocity…yes, they’re different  In place to ensure there are no negative time residuals, since photons of different wavelengths propagate at different speeds  The result is a time shift is added or subtracted depending on whether you ask photonics for a Time or a Probability  Everything is very confusing  The bug is a math error in the time shift calculation

5 Discrepancy Varies with Distance

6 Example - Simulation -> Hit-maker asks photonics: Given a source and receiver configuration, how far after the IceCube geometric time will a photon arrive? • Let’s say t geo = 500 ns in IceCube convention IceCube t delay = ? 500 ns muon

7 Example - Simulation -> Hit-maker asks photonics: Given a source and receiver configuration, how far after the IceCube geometric time will a photon arrive? • Let’s say t geo = 500 ns in IceCube convention • Photonics table has delay times w/r/t the geometric time of the fastest photon , which has a t geo < 500 ns in Photonics IceCube Photonics t delay = ? 500 ns 488 ns muon

8 Example - Simulation -> Hit-maker asks photonics: Given a source and receiver configuration, how far after the IceCube geometric time will a photon arrive? • Let’s say t geo = 500 ns in IceCube convention • Photonics table has delay times w/r/t the geometric time of the fastest photon , which has a t geo < 500 ns in Photonics • To account for this, photonics transforms the time from the table into IceCube’s convention IceCube Photonics t delay = 38 t delay = 50 500 ns 488 ns muon

9 Summary and Solution  For much of our data (tracks ~ 100m from DOMs), the bug in the time shift is on the order of ~10 ns  The bug is easily fixed - plan is to cut a new release of photonics and update i3ports

10 Hit-maker bug  Photonics subtracts time when it returns a time delay, and shifts a pdf forward when it returns a probability (essentially adding time)  In binning mode, hit-maker uses I3PhotonicsService::GetTimeDelays() for DOMs with hits below a certain PE threshold, and GetProbabilityDensity() for DOMs above threshold  Hit-maker can miss early charge  Asks for probability starting at time=0 (IceCube), which gets transformed to time>0 in Photonics

11 Discrepancy Varies with Distance Hit-maker is off by this amount

12 Hit-maker bug solution  One possible solution: implement inverse time- transformation in hit-maker to get correct start time  Instead of asking for probability starting at t=0, hit-maker will ask for probability starting at the correct negative time  Nathan Whitehorn will do this when he rewrites hit-maker