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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