Download - Bs->mumu update In depth FTKSIM performance analysishep.uchicago.edu/cdf/shochet/ftk_03_07/Francesco.pdf · Bs->mumu update In depth FTKSIM performance analysis F. Crescioli, M. Dell'Orso,

Bs->mumu updateIn depth FTKSIM performance

analysis

F. Crescioli, M. Dell'Orso, P. Giannetti, G. Punzi, G. Volpi

13/3/2007 Francesco Crescioli 2

Bs->mumu status update● Produced background sample (generic bb with

one muon with Pt > 6 GeV)● Produced signal sample with both muons in the

barrel● Re-run reconstruction with 7 layers ftksim● Not analyzed yet:

Stopped to work on important FTKSIM issues


FTKSIM tracking debugging● Monica highlighted some problems with WHuu/bb sample

– FTK worse than iPat on uu/bb separation– FTK IP distribution much different from iPat for high

Pt tracks● In our analysis for fake tracks, unmatched tracks with

some bad reconstructed parameter never really disappeared– Are them responsible for the behaviour observed by

Monica?


Debugging sample● Produced special debug events

– ATHENA v12.0.31 (exactly the same version as training)– 10 tracks per event

● Fixed zero impact parameter● Other parameters with the same distributions as training sample● Vertex spread on

– Low noise digitization– Muon and pion samples– FTKSIM with 7 layers configuration


Debug sample (muons) IP resolution

Looking at unmatched IP distribution (resolution because truth is zero IP) we observe a significant difference in IP resolution vs Pt

The difference correspond to 30um smearing on resolution

There's also an offset in the mean of the reconstructed IP

FTKiPat


Looking at the matched (with truth, for both FTK and iPat) resolution shows some significant change in the sigma at low Pt

Mean offset is still there

Matched iPat tracks seems to have much less tail than unmatched. Smaller effect for FTK matched tracks.

Debug sample (muons) IP resolution - matched

FTKiPat


Unmatched tracksVariance difference is almost constant for Pt > 3 GeV and increase for low Pt tracks

Debug sample (muons) IP resolution – variance difference

Matched tracks

Matching tracks grately reduce the increase of variance difference for low Pt tracks leaving the costant part almost the same


Unmatched integrated tails shows that FTK and iPat have similar behaviour until tracks with Pt > 6 GeV are selected.Note that at Pt > 3 GeV, IP > 0.2 mm tail fraction is very similiar.

FTKiPat

Debug sample (muons) IP distribution integrated tails


Matched tracks shows some improvement for FTK and big change for iPat tracks.Tails are almost gone for iPat, at every Pt cut.

FTKiPat

Debug sample (muons) IP distribution integrated tails - matched


Debug sample (pions) IP resolution

Unmatched IP resolution shows no significant change in both mean and sigma from the muon case

FTKiPat


Debug sample (pions) IP resolution - matched

For matched tracks mean don't change.Sigma is reduced for low Pt. There's some effect on the tails, but not as significant as in the muon case.

FTKiPat


Unmatched tracksVariance difference is almost constant for Pt > 3 GeV and increase for low Pt tracks.Less difference than with muons.

Debug sample (pions) IP resolution – variance difference

Matched tracks

Matching further reduces difference.


Debug sample (pions) IP tails

Tails seems better with FTK than with iPat, but there's some visible improvement of iPat with Pt which there isn't in FTK.

FTKiPat


Debug sample (pions) IP tails - matched

As expected from scatterplot, matched tails are sligthly better but there isn't the big improvement for iPat as in the muon case.

Again at Pt > 3 GeV, IP > 0.2 mm our performance is quite similar to iPat.

FTKiPat


Debug sample ~ Conclusions● Resolutions shows the same Pt dependence with FTK and

iPat due to multiple scattering at low Pt– At high Pt iPat goes asymptotically to a better

resolution than FTK (~20μm vs ~40μm)● FTK IP mean shows an offset of ~5μm● Integrated tail is reduced by Pt cuts for iPat, on both

muons and pions, much less for FTK● Performances at Pt > 3 GeV with 200μm IP cut should be

similar


A real case: WHuu/bb● Reconstructed Monica's WHuu/bb sample with 7 layer

configuration


WHuu/bb – IP distributionsAs predicted by debug sample we have slightly better performance with no Pt cut.

At Pt > 1.5 GeV iPat start to perform better.

We have a strange asymmetry.

No P

t C

ut

Pt

> 1

. 5 G

eV

FTK iPatWHuu

WHbb


WHuu/bb – IP distributionsAs Pt cut increase iPat performances increase faster than ours.

Our strange asymetric second peak is more visible.

Pt

> 3

GeV

Pt

> 6

GeV

FTK iPatWHuu

WHbb


WHuu – IP distributionsiPat tends to perform better increasing Pt cut, and the asymmetric second peak in FTK is more visible.

Is the peak an artifact from nonmatched tracks?


WHuu/bb – 7 layers vs 6 layers

WHuu

WHbb

FTK 7 layers iPatFTK 6 layers


WHuu/bb● As expected from debug our performance is similar to

iPat and greatly improved since 6 layer configuration– iPat improves more than FTK applying Pt cuts

● There is a strange second peak in the IP distribution of FTK– Not evident in 6 layer configuration– Under investigation


Conclusions● 7 layer configuration give better resolution performance

than 6 layer● FTK is still slightly worse than iPat but tails are not

much different for low Pt (important for B-tagging)– There's some problem that generate the asymmetric

second peak– Next step: study and fix it


WHuu – IP distributions (matched)With matched tracks iPat performs much better.

FTK doesn't improve much and the second peak is still there.

Under investigation.