Track segment finding with CGEM-IT and

matching to tracks in outer-MDC

X.H Sun, L.L Wang, L.H Wu, L.Y Dong

Institute of High Energy Physics

Mar 12, 2016

BESIII Physics and Software Workshop

OUTLINE

• Motivation

• Track segment finding with CGEM-IT

• Track segment matching to track in outer-MDC

• Summary and outlook

MOTIVATION

• MDC (Inner Tracker) ages:• Hit efficiency

• Relative gain

Rel

ativ

e ga

in c

han

ge

MDC-IT needs to be update

• CGEM-IT is a candidate• Good spatial resolution• Significant radiation

tolerance• High rate capability• Limited radiation length

CGEM-IT and track segment

• CGEM-IT contains three cylindrical CGEM• Each CGEM consists of:

• Anode (include XV strips)

• Three GEM foils (multiplied electron)

• Drift area (include gas for ionization)

• Cathode

• Track segment• One cluster in one CGEM

• Each track segment consists of three clusters

clusters

One charged track

CGEM

Track segment

dj and dZ pattern

• Two dimensional readout: 𝜑 =

𝑋

𝑟𝑙𝑎𝑦𝑒𝑟

𝑍 = (𝑉 − 𝑋 𝑐𝑜𝑠𝑎)/𝑠𝑖𝑛𝑎

• The relative differences in 𝜑 and 𝑍 are used to study the relation between the three clusters from each track:

IP

x

y

O

vs𝛿𝜑21= 𝜑1 −𝜑2

𝛿𝜑23=𝜑3 − 𝜑2

IP

vs 𝛿𝑍23= Z3 −Z2

𝛿𝑍21= Z1 −Z2

dj pattern

dj pattern

dZ pattern

dZ pattern

Efficiency

Track segment fitting method

• Track model: Helix (5 parameters)• 𝑑𝜌• 𝜑0

• 𝜅

• 𝑡𝑎𝑛𝜆

• 𝑑𝑧

• Fit with the Least Square Method

𝜒2 =

𝑗

𝑖

(𝑋𝑖(𝐻) − 𝑋𝑖,𝑚𝑒𝑎𝑠𝑢𝑟𝑒)

𝜎𝑖2

2

H means helix parameters, X means cluster position, i =1~2 for𝜑and Z, s is resolution, and j=1~3 for 3 clusters

Track segment fitting for high pt• The success rate of fitting drops for high pt ( red

points)

• As the high pt track is quite straight in the detector, only three clusters close-by can not well determine k.

• Fixing k can improve the success rate of fitting (blue points)

Residuals of the track parameters from the track segments fitting

dHi = Hi,rec - Hi,truth• H is helix parameter• rec: fitting result• truth: MC truth at generation

Single m MC sample pt=0.8GeV/c

Track finding with outer-MDC

• Tracks are reconstructed by PAT/TSF with the outer-MDC

• Track parameters are obtained by Helix fitting

• Efficiency for track finding with outer-MDC as a function of pt:

Matching to tracks (segments) between CGEM-IT and outer MDC

• Introduced a new variable 𝜒2 for the combine:

𝜒2 =𝐻𝐶𝐺𝐸𝑀 − 𝐻𝑀𝐷𝐶

2

𝜎𝐶𝐺𝐸𝑀2 + 𝜎𝑀𝐷𝐶

2

• H is one of the helix parameters, and s is the resolution of each helix

• Each helix parameter tried to find out the window of 𝜒2 independently

MC sample in the plots is:Single mpt=0.8GeV/c

• The window of 𝜒2, which showed purple arrow in plots, is sign of 99% efficiency, when chosen 𝜒2 is smaller than this value

Matching to tracks (segments) between CGEM-IT and outer MDC

• Introduced a new variable 𝜒2 for the match:

𝜒2 =𝐻𝐶𝐺𝐸𝑀 − 𝐻𝑀𝐷𝐶

2

𝜎𝐶𝐺𝐸𝑀2 + 𝜎𝑀𝐷𝐶

2

• H is one of the helix parameters, and s is the resolution of each helix

• Each helix parameter tried to find out the window of 𝜒2 independently

MC sample in the plots is:Single mpt=0.8GeV/c

• The window of 𝜒2 varys with pt

Efficiency

After all selection

SUMMARY AND OUTLOOK

• Segment finding

• Fitting

• Match

• plan

Thank you