Track reconstruction and hyperon simulations

Track reconstruction and hyperon Track reconstruction and hyperon simulationssimulations

Evgeny Kryshen (PNPI, SPbSPU)

28 Feb 2005 CBM Collaboration meeting 2

OutlineOutline

• Analysis strategy and simulation of STS detector inefficiencies

• Impact of STS detector inefficiencies on tracking

• Tracking performance for 8 station setup

• Impact of STS detector inefficiencies for 8 station setup

• Tracking performance for 9 station setup

• Replacing hybrid stations with strips

• Studies of the half-length strip configuration

• Conclusions and outlook


Analysis strategyAnalysis strategy

• No pile-up in MAPS stations is assumed• “Realistic” station thickness and strip pitch• 1 level of the the CA track finder (primary search)• Statistics: 100 central 25 GeV UrQMD events• Active shielding field map• Performance criteria:

Tracking performance - all tracksTracking performance - primariesTracking performance – lambda (2 level – all search)Momentum resolutionTime consumption


““Realistic” geometry vs CVSRealistic” geometry vs CVS

“Realistic” geometry (sts-2maps-1pix-4strips.geo + sts_digi_50.par):

Type: Z Position: Thickness: Resolution:

Maps 5,10 cm 150 μm sigma = 5 μm

Hybrid 20 cm 700 μm pixel size = 50 μm

Strips 40,60,80,100 cm 400 μm pitch = 50 μm

“Realistic” geometry (sts-2maps-1pix-4strips.geo + sts_digi_50.par):





CVS geometry (sts-3maps-4strips.geo + sts_digi.par):





CVS geometry (sts-3maps-4strips.geo + sts_digi.par):






Efficiency simulationEfficiency simulation

• Hit efficiency is already implemented in MAPS hit producer (flag = -1 in the case of lost hits)

• Hybrid pixel hit efficiency was added into Hybrid pixel hit producer

• Strip efficiency is added for each side of the strip station

• In the present analysis equal efficiency rate is set for all detector types


Tracking vs STS efficiencyTracking vs STS efficiency

CA track finder performance is almost the same:

AllSet: 0.89 -> 0.87,RefSet: 0.97-> 0.94


8 station geometry8 station geometry

Type: Z Position: Thickness:

Maps 5,10 cm 150 μm

Hybrid 20,30 cm 700 μm

Strips 40,60,80,100 cm 400

μm




Strips 40,60,80,100 cm 400

μm

Geometry: sts-2maps-2pix-4strips.geo Strips: sts_digi_50_5-8.par



Track reconstruction with 8 STS stationsTrack reconstruction with 8 STS stations

Parameter 7 stations 8 stationsRefPrim /event 363 397AllSet /event 503 573Ghosts/event 26.2 13.2Clones/event 1.4 6.7RECO Lambda / event 2.5 4.0CPU sec. / event 141 134Momentum resolution 1.00% 1.18%

At 99% STS hit efficiency

Advantages of the 8 station:• significant increase (12%) in the number of reconstructed tracks• less calculation time• 60% increase in the number of reconstructed Lambda decays• More stable to STS hit inefficiencies• 2 times lower ghost rate

Advantages of the 8 station:• significant increase (12%) in the number of reconstructed tracks• less calculation time• 60% increase in the number of reconstructed Lambda decays• More stable to STS hit inefficiencies• 2 times lower ghost rate

Statistics: 100 events

Disadvantages of the 8 station:• increase in clones rate (1.4 6.7)• decrease in momentum resolution (1.00% 1.18%)

Disadvantages of the 8 station:• increase in clones rate (1.4 6.7)• decrease in momentum resolution (1.00% 1.18%)


Tracking vs STS efficiency (7 or 8 stations)Tracking vs STS efficiency (7 or 8 stations)

8 stations – better resistance to the STS hit inefficiency


Momentum resolution vs STS hit efficiencyMomentum resolution vs STS hit efficiency

Worse momentum resolution:

8 stations – 1.14 %7 stations – 0.97 %

Possible solution: use strip stations


Ghosts and clones (8 stations)Ghosts and clones (8 stations)

Advantages of the 8 station:• Lower ghost rate• Better resistance to the STS

inefficiency

Advantages of the 8 station:• Lower ghost rate• Better resistance to the STS

inefficiency


9 STS stations9 STS stations

Problem: what could we gain from the additional 9th station?




Strips 40,55,70,85,100 cm 400

μm




Strips 40,55,70,85,100 cm 400

μm



Additional strip station inserted. 5 equidistant strip stations are parameterized with the usual sector geometry applying simple sector scaling


Track reconstruction with 9 STS stationsTrack reconstruction with 9 STS stations

Parameter 7 stations 8 stations 9 stationsRefPrim /event 363 397 401AllSet /event 503 573 583Ghosts/event 26.2 13.2 15.6Clones/event 1.4 6.7 11.4RECO Lambda / event 2.5 4.0 5.7CPU sec. / event 141 134 82Momentum resolution 1.00% 1.18% 1.32%

At 99% STS hit efficiency

Advantages of the 9 station:• slight increase (2%) in the number of reconstructed tracks• 40% increase in calculation time performance• 40% increase in the number of reconstructed Lambda decays• More stable to STS hit inefficiencies

Advantages of the 9 station:• slight increase (2%) in the number of reconstructed tracks• 40% increase in calculation time performance• 40% increase in the number of reconstructed Lambda decays• More stable to STS hit inefficiencies

Statistics: 100 events

Disadvantages of the 9 station:• increase in ghost rate (13.2 15.6)• increase in clones rate (6.7 11.4)• decrease in momentum resolution (1.18% 1.32%)

Disadvantages of the 9 station:• increase in ghost rate (13.2 15.6)• increase in clones rate (6.7 11.4)• decrease in momentum resolution (1.18% 1.32%)


Strips vs hybrids (7 station setup)Strips vs hybrids (7 station setup)

Do we need the third technology (hybrid pixels)? What we get when replacing hybrids with strips?

Parameter 3 station - hybrid

3 station – strips

RefPrim /event 363 351

AllSet /event 503 472

Ghosts/event 26.2 54.0

Clones/event 1.4 0.8

RECO Lambda / event 2.5 2.4

CPU sec. / event 141 176

Momentum resolution 1.00% 0.96%

• 6% decrease in the number of rec. tracks• Small gain in momentum resolution• 2 times higher ghost rate

• 6% decrease in the number of rec. tracks• Small gain in momentum resolution• 2 times higher ghost rate

• 3rd hybrid station (700 μm) replaced with strip station (400 μm).

• Simple scaling of strip sector geometry (minimum strip length – 1 cm)



Can we achieve better momentum resolution by replacing hybrids (700 μm) with strips (400μm)?

Parameter 3,4 station - hybrid

3,4 station –

strips





RECO Lambda / event 4.0 ?



• 10% decrease in the number of rec. tracks• 0.08% gain in momentum resolution• 4 times higher ghost rate

• 10% decrease in the number of rec. tracks• 0.08% gain in momentum resolution• 4 times higher ghost rate

• 3 and 4 hybrid stations (700 μm) replaced with strip stations (400 μm).




Can we achieve better momentum resolution by replacing hybrids (700 μm) with strips (400μm)?

Parameter 3,4 station - hybrid

3,4 station –

strips





RECO Lambda / event 5.7 4.7



• 8% decrease in the number of rec. tracks• 0.08% gain in momentum resolution• 3.5 times higher ghost rate

• 8% decrease in the number of rec. tracks• 0.08% gain in momentum resolution• 3.5 times higher ghost rate

• 3 and 4 hybrid stations (700 μm) replaced with strip stations (400 μm).



Half-length strip parametrizationHalf-length strip parametrization

Parameter Full-length, 7 stations

Half-length, 7 stations




RECO Lambda / event

35 43


Momentum resolution

0.974% 0.977%


Conclusions and outlookConclusions and outlook

• 7 station setup is quite sensitive to the STS inefficiencies

• 8 station setup allows to improve track reconstruction performance significantly,

the only drawback – lower momentum resolution

• 9 station setup – slight improvement in track reconstruction performance, further

increase of reconstructed lambda

• Hybrid stations are desirable in respect to the track finding

• CPU consumption is very sensitive to the number and type of STS stations

• Reduction of strip length does not provide a significant gain in track reconstruction

• New “realistic” sector geometry (J. Heuser) to be tested

Documents

Track reconstruction and hyperon simulations