BESIIIBESIIITrack Extrapolation & MatchingTrack Extrapolation & Matching

Wang LiangliangWang Liangliang

EPC IHEPEPC IHEP

OutlineOutline

• Track ExtrapolationTrack Extrapolation• Track Information MatchingTrack Information Matching

(Event assembly)(Event assembly)• Analysis of MC sampleAnalysis of MC sample• SummarySummary

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Track Extrapolation (1)Track Extrapolation (1)

• Introduction:Introduction:

MDC Tracking

Track Parameter& error matrix

TOF(2 layers) EMC MUC

ExtrapolationExtrapolation

Expected position, momentum,Corresponding Error matrix,

projected error on certain directions

Track Extrapolation (2)Track Extrapolation (2)

• Method:Method:

Part1:Extrapolation of track parameters (Part1:Extrapolation of track parameters (xx, , pp))

Based on some Geant4 codes, we construct the Based on some Geant4 codes, we construct the same detectors and magnetic field as simulation, same detectors and magnetic field as simulation, and perform the track extrapolation in small steps, and perform the track extrapolation in small steps, which considered the charged track deflection in which considered the charged track deflection in the magnetic field, the ionization energy loss in the the magnetic field, the ionization energy loss in the material of detectors.material of detectors.

Track Extrapolation (3)Track Extrapolation (3)

• Method:Method:Part2:Transformation of Error Matrix for small stepsPart2:Transformation of Error Matrix for small steps

After each step, the infinitesimal propagation of the error matAfter each step, the infinitesimal propagation of the error matrix is calculated byrix is calculated by

EE′′=J=J∙E ∙J∙E ∙JTT+E+Emm

EE′ ′ is the error matrix at the end point of the current stepis the error matrix at the end point of the current stepEE is the error matrix at the end point of the last step is the error matrix at the end point of the last stepJ J is the Jacobian for the transformationis the Jacobian for the transformation

EEmm is the multiple scattering effect term of the current stepis the multiple scattering effect term of the current step

Track Extrapolation (4)Track Extrapolation (4)• Flow diagramFlow diagram

(in a event loop):(in a event loop):Get next MDC trackGet next MDC track

Transform the helix parameters Transform the helix parameters and matrix to (x,p) form and matrix to (x,p) form

Perform extroplation and Perform extroplation and propogate matrix in a small steppropogate matrix in a small step

Particle is out of BESIII worldParticle is out of BESIII worldor it’s energy equals 0or it’s energy equals 0

If the track reached a certain sensitive If the track reached a certain sensitive detector’ surface for the first time, detector’ surface for the first time,

its parameters and matrix is recorded.its parameters and matrix is recorded.

nono

yesyes

successfulsuccessful

End a eventEnd a event

failurefailure

Start a eventStart a event

Register results to TDSRegister results to TDS

Track Extrapolation (5)Track Extrapolation (5)• Some results of an example:Some results of an example:

Track Information MatchingTrack Information Matching(Event assembly)(Event assembly)

• Event model:Event model:

DstTrackList

trackIDDstMdcTrackDstMdcKalTrackDstDedxDstExtTrackDstTofTrackDstEmcTrackDstMucTrack

DstTrackListCol: (DstTrackListCol: (collectioncollection of of tracks belong to a event)tracks belong to a event)

EventList : (Global event information)EventList : (Global event information) totalTrkstotalTrksnChrnChrnNeunNeunVEEs(Ks, Lambda, gamma conversion )nVEEs(Ks, Lambda, gamma conversion )nPi0nPi0

Track Information Matching (2)Track Information Matching (2)

Mdc TrackMdc Track dEdxdEdx

Kalman TrackKalman Track

Ext TrackExt Track

TofTof

Muc TrackMuc Track

Track IDTrack ID

• Method:Method:

Emc Information Matching:Emc Information Matching:We just simply match one We just simply match one showershower to each charged track here. First, we find to each charged track here. First, we find the smallest angle between the the smallest angle between the Ext Track’Ext Track’s position vector and the showers’ s position vector and the showers’ position vectors; if the corresponding shower’s position locates in our matchposition vectors; if the corresponding shower’s position locates in our matching window, this shower will be matched to the charged track. These unmating window, this shower will be matched to the charged track. These unmatched showers will be treated as neutral tracks.ched showers will be treated as neutral tracks.

Track Information Matching (3)Track Information Matching (3)

• Emc Information Matching WindoEmc Information Matching Window:w:

using sampleusing sample

Theta: -10Theta: -10º~10ºº~10ºPhi: -15º~15ºPhi: -15º~15º

)(2/ J

Track Information Matching (4)Track Information Matching (4)

• Emc matching efficiency:Emc matching efficiency:

Using Using psi→psi→anything anything MC sample (50000 events)MC sample (50000 events)

Analysis of MC sampleAnalysis of MC sample(The first example of MC sample analysis in BOSS beta release)(The first example of MC sample analysis in BOSS beta release)

pi0pi0 Rho0Rho0

RhoPlusRhoPlus RhoMinusRhoMinus

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SummarySummary

• Track extrapolation is a necessary part of Track extrapolation is a necessary part of reconstruction and a base work before Event reconstruction and a base work before Event assembly. And this package works well in the BOSS assembly. And this package works well in the BOSS beta release. beta release.

• Event assembly is also accomplished. And it is the Event assembly is also accomplished. And it is the base of physics data analysis, and the start of the base of physics data analysis, and the start of the more advanced more advanced AnalysisAnalysis Event Data ModelEvent Data Model which which will be used in data analysis in future. will be used in data analysis in future.

Thank you!Thank you!