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N 2 Ring Reconstruction Studies

N 2 Ring Reconstruction Studies. Starting Point – q C Too Small Methodology to Resolve This Current Situation Next Steps. Andrew Powell RICH Testbeam Meeting - Monday, 30 th July 2007. Status with N 2 Reco. Within Gaudi Software Environment. Gaudi.

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N 2 Ring Reconstruction Studies

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  1. N2 Ring Reconstruction Studies • Starting Point – qC Too Small • Methodology to Resolve This • Current Situation • Next Steps Andrew Powell RICH Testbeam Meeting - Monday, 30th July 2007

  2. Status with N2 Reco. Within Gaudi Software Environment Gaudi Jeremy D. Stand Alone There is a discrepancy between the two reconstruction packages Where does this discrepancy originate from?

  3. Aim: Make direct comparisons between Jeremy’s and the Gaudi frameworks reconstruction at each stage of the calculation on a event-by-event basis and determine at which stage the discrepancy occurs. Method: In order to make such comparisons, we need to transform the results from the TB analysis code using the default coordinate system into the coordinate system used by Jeremy in the 2004 TB analysis. The coordinate system he used was that defined by Gianluca: http://lhcb-rich-project-beamtests.web.cern.ch/lhcb-rich-project-beamtests/

  4. 264 116 282 265 117 283 222 88 36 Global (Default) Coordinate System in DB y = 0 (Mirror & Entrance Window Centre) 21.7 89.5 mm HPD Panel A: y’=0 B: HPD222 Centre

  5. Coordinate Transformation from Jeremy’s System to Default TB System (x,y,z): Gianluca System (x’,y’,z’): TB System Axis Along HPD Centre To Mirror y y’ f x’ f z = z’ x (Beam Axis) A: y’=0 B: HPD222 Centre O (SSB Entrance Window Centre)

  6. Simple Rotation about z-Axis: (x,y,z) (x’,y’,z’) (x’,y’,z’) (x,y,z) xGL = xTBcos(f) + yTBsin(f) yGL = -xTBsin(f) + yTBcos(f) xTB = xGLcos(f) – yGLsin(f) yTB = xGLsin(f) + yGLcos(f) If we were to ‘transform’ the database description of the SSB from the default coordinate system to Gianluca’s, we could then make direct comparisons between Jeremy’s 2004 code and the TB Gaudi software at each stage of the reconstruction on an event-by-event basis and isolate where the discrepancy in the angle measurement comes from…

  7. For simplicity we cheat (a little): we move HPD264 (HPD with N2 ring data) to the HPD222 position in both Jeremy’s and our approaches. Remember, we’re only looking to see where the discrepancy in cherenkov angle determination arises from the two approaches NOT to correctly reconstruct the ring. Hence, this procedure is justifiable. Essentially, this means moving the HPD panel down by: 264 116 282 2 x (HPD Pitch) – 21.7mm 265 117 283 and applying the relevant rotation around an axis parallel to the z-axis but incident through the point B (i.e. the centre of the HPD quartz window) 222 88 36

  8. Comparison of Run003, Event 1 (In Global Coordinate System) Result after moving HPD264 down in Xml DB: It is clear that there is a p radian rotation about the y-axis between the two schemes

  9. Comparison of Run003, Event 1 (In Global Coordinate System) Correcting for the rotation: Now it is evident that there is also an additional translation needed

  10. Comparison of Run003, Event 1 (In Global Coordinate System) Now aligning ring centres: It’s now evident that the rotation about the axis defined on slide 5 is needed as well.

  11. What does this all mean? • Since the HPD quartz window is known to be in the correct position in the XML DB, it is evident that the z-axis of the HPD needs realigning against the global z(beam)-axis. The ring centres should then coincide. • The (small) rotation along the axis defined on slide 5 is still necessary. How to include such a rotation within the XML DB? • Hopefully, then, the raw pixel hits as determined by Jeremy’s code and the Gaudi software will have the same coordinates.

  12. Next Step • Hopefully Antonis can help me correct the alignment of the HPD panel and perform the necessary rotation within the XML DB • Once we have agreement at the pixel level between the two reconstruction packages, we should then be able to uniquely identify at which stage of the reconstruction the results differ. Thanks to Antonis and Ulrich for all their help with this study so far.

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