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Effects of Tracking Limitations On Jet Mass Resolution

Effects of Tracking Limitations On Jet Mass Resolution. Chris Meyer UCSC ILC Simulation Reconstruction Meeting July 3, 2007. Motivation. No one has yet studied how tracking limitations effect Jet Reconstruction. Limit in P T reach Limit in cos θ reach Non prompt tracks (K S )

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Effects of Tracking Limitations On Jet Mass Resolution

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  1. Effects of Tracking Limitations On Jet Mass Resolution Chris Meyer UCSC ILC Simulation Reconstruction Meeting July 3, 2007

  2. Motivation No one has yet studied how tracking limitations effect Jet Reconstruction. • Limit in PT reach • Limit in cos θ reach • Non prompt tracks (KS) • Photon conversion in tracker material

  3. Approach • Use e+ e - q qbar at Ecm = 500 GeV (turn off ISR so that events are evenly distributed) • Find “perfect jets” from MCtruth particles that: • Originate within 1cm and terminate outside 1cm from the origin • Are FINALSTATE or INTERMEDIATE • Are not backscatter • Confirmed  Ei = 500 ± a few GeV for this selection • Using a ycut of 0.07 select events with only 2 jets • Calculate Jet/Jet invariant mass

  4. Approach cont. • Apply tracking limitation (e.g. PT > 0.5 GeV cut) • Find jets with cut applied. • If no ycut gives two jets, toss event (<1%) • Compare Jet/Jet mass with “perfect” reconstruction. • Accumulate RMS (δm) of Jet/Jet mass degradation.

  5. Goal For Maximum Degradation: 1% Need to distinguish W’s from Z’s using the Jet/Jet invariant mass from high energy Jets. Our sample has high energy Jets but a Jet/Jet mass of 500 GeV (rather than 100 GeV). Taking two jets of the same energy we find the invariant mass and associated error go as: m2 = 2 (1 – cos θ ) p2 δm2 = 2 (1 – cos θ )δp2 Error on momentum is constant wrt mass, to eliminate the mass dependence from cos θ form fractional error on mass, so that δm2 / m2 = const. wrt mass, so that δm / m = const. wrt mass also To distinguish between a Z and W 10% resolution is required, and to be outside 3 standard deviations brings it down to 3%. Finally to disregard error on tracking we require the error to be 1%. Using 500 GeV uds events, m = 500, which means δm ≤ 5 To keep from degrading W and Z seperation we need an error on invariant mass of less then 5 GeV.

  6. Cuts on charged track PT PT cut of 0.75 GeV δm= 5.62 GeV PT cut of 0.5 GeV δm= 3.49 GeV

  7. K Shorts Finding NO K Shorts δm= 43.61 GeV Finding 90% of K Shorts δm= 11.11 GeV But RMS is still dominated by tails…

  8. K Shorts Finding 90% K Shorts (cutting top 3%) δm= 2.86 GeV

  9. Gamma’s Low energy photons that convert will miss the calorimeter. How many low energy ( < 1 GeV ) photons do we need to find then? Finding NO Photons < 1 GeV δm= 3.45 GeV Finding 90% of Photons < 1 GeV δm= 0.65 GeV

  10. Gamma’s How many photons (no energy cut) do we need to find? Finding NO Photons δm= 69.28 GeV Finding 90% of Photons δm= 14.96 GeV

  11. Cuts on cos() Remove all particles with |cos()| > 0.8 Plot jet mass difference RMS vs. |cos(thrust)| RMS limit is exceeded for events with cos TA > 0.1

  12. Cuts on cos() Forward tracking: remove only charged particles with |cos | > 0.8 RMS limit is exceeded for events with cos TA > 0.1, then again for cos TA > 0.3

  13. Cuts on cos() Forward Calorimetry: Remove only neutral particles with |cos | > 0.8 RMS limit is exceeded for events with cos TA > 0.6

  14. Cuts on cos() Far forward: remove all particles below 150 mrad RMS limit is exceeded for events with 0.5 < cos TA < 0.6 and cos TA > 0.8

  15. Conclusions Looking at simple cuts on Jets we have found: • The PT range of any proposed ILC tracker looks fine. • We have to find a good percentage (90%) of the K shorts. • Low energy photons don’t play an enormous role, but when you include higher energy photons you need to find them. • Forward tracking is necessary unless we only accept Jet’s with a Thrust Axis perpendicular to the beam pipe. • The limitations of the EndCap Detector is only met when we find events with thrust axis > 0.8.

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