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

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Presentation on theme: "Effects of Tracking Limitations On Jet Mass Resolution Chris Meyer UCSC ILC Simulation Reconstruction Meeting July 3, 2007."— Presentation transcript:

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 P T reach Limit in cos θ reach Non prompt tracks (K S ) Photon conversion in tracker material

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

4 Approach cont. Apply tracking limitation (e.g. P T > 0.5 GeV cut) Find jets with cut applied. If no y cut 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: m 2 = 2 (1 – cos θ ) p 2 δm 2 = 2 (1 – cos θ ) δp 2 Error on momentum is constant wrt mass, to eliminate the mass dependence from cos θ form fractional error on mass, so that δm 2 / m 2 = 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 P T P T cut of 0.75 GeV δm = 5.62 GeV P T 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 Finding NO Photons < 1 GeV δm = 3.45 GeV Finding 90% of Photons < 1 GeV δm = 0.65 GeV Low energy photons that convert will miss the calorimeter. How many low energy ( < 1 GeV ) photons do we need to find then?

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

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 P T 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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