recotracks revisited

UCSD meeting November 2, 2007 R. Kelley

RecoTracks Revisited

UCSD meeting November 2, 2007 R. Kelley2

RecoTracks Revisited

• A quick word on association by hits• Clear up a question on the low pt cut-off RS

vs CTF• Charge of recoTracks• The resolutions plots revisited• CMSSW 1_6_X

– Ran over ~5k events from TTbar release validation sample(/RelValTTbar/CMSSW_1_6_0-RelVal-1189470628/GEN-SIM-DIGI-RECO )


Association by Hits

• Definition of association by hits: A matched recoTrack is a recoTrack that has 50% or more of its tracker hits overlap the simulated hits from a simTrack.


Fraction of Shared Hits

Note: Most of the associated recoTracks share 100% of their hits with their corresponding simTrack.


RS vs CTF

Last time there was some confusion on why it seemed that RS reconstructed many less tracks than CTF


A Quick and Dirty on RS Tracks(Kevin Burkett)


RS vs CTF

• This shows clearly that the RS algorithm has a higher minimum seed pT value (≈1.5GeV).

• The ‘bleed off’ is due to misestimate of pT from only a few [seed] hits.

• So in order to be fair to RS, we should make a minimum pT cut.


Efficiency (pT > 3.0 GeV)


Charge Asymmetry

• There seems to be less negatively charged recoTracks than positive. Why?

+ charge

- charge


Charge Asymmetry

• One possible explanation is that π+ reacts differently than π- at lower energies.

• some of the charged tracks are never reconstructed after they react with the material.

• Since σπ-p > σπ+p, more negatively charged tracks are lost in the material.

1 GeV

≈ 60 mb

≈ 20 mb


Resolution Revisited• Resolution = RecoTrack – SimTrack (denoted by δ)• All these plots were made with CTF tracks and associated by Hits.• There seems to be a similar trend in variables defined in the r-z plane.

– An initial improvement in resolution followed by a steady decrease.


Steady Rise• Touch light affect: as you move in |η|, the distance from the first

measurement point to the point of closest approach increases.• This causes this point to be reconstructed with less precision which

is responsible for the steady rise in the resolution plots for variables defined in the r-z plane.

• The r-z plane reco variables to be less precise as |η| increases.


Small |η| improvement (Charge Sharing)

• The improvement for small |η| can be seen from considering charge sharing.


More Resolution Plots

• Consider the plots in the r-φ plane.• They suffer from a similar rise in resolution for

increasing |η|.• They do not have the improvement at low |η|.


Tracker Geometry

• This can be explained by looking at the geometry of the tracker.


R-Z plane vs R-Phi Plane

z

2

720

0.3 4x TT

T

pp

p BL N

L2

L1


What About pT?

• There is an additional affect for the pt measurement to multiple scattering.


Accounting for the Effects

Total Affect


Pull Distributions

• Pull = resolution / error

• Since the pull distribution depends also on error, it is a bit more complicated since the error determination may not be fully accurate.

• We’ll get back to you on these.


Pull in r-z Plane


Pull in r-φ Plane


Back up


CombinatorialTrackFinder (CTF)(Kevin Burkett)


RoadSearch Tracking(Kevin Burkett)


A Quick and Dirty on RS Tracks(Kevin Burkett)


RoadSearch Tracking(Kevin Burkett)

• Above pT~5GeV, efficiencies about equal.• The overall inefficiency dominated below 2 GeV.


Efficiency (pT > 3.0 GeV)


design of the tracking system (Boris)

Some formulae stolen from books. The L.Rolandi’s one on your shelf contains them

(“Particle Detection with Drift Chambers” by Blum and Rolandi)


design of the tracking system (Boris)

recotracks revisited

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