Muons in b-jets

30th August 2010

Erik van der Kraaij&

Przemyslaw Majewski

Events used

From Marcel Stanitzki: 500 GeV events with Z --> bb

Simulated such that at least one of the b's decays through a muon

Used 3000 events to get efficiency & purity. “Match” = the PFO is linked to a muon in the MC truth list by myMCRecoThruthLinker

Eff. = #reco mu (matched) / # true mu

Pur. = #reco mu (matched) / # reco mu

For now mostly looked at muons with E > 15 GeV.

Of the first 500 events went through the events with something going wrong with Pandora Monitoring.

23 events in the end (again, only for muons with E >15GeV)

Pandora settings

Used latest version

/afs/cern.ch/eng/clic/software/x86_64-slc5-gcc41/ILCSOFT/v01-09-02-v2/init_ilcsoft.sh

“a recent change to the TpcDigitizer, which smears the positions of the tpc hits, has caused a total failure of the FitHelix method in the MarlinUtil/ClusterShapes class. This failure badly affects the reported TrackStates at the ECal surface, to which Pandora is very sensitive. As a result, we removed all use of the ClusterShapes and MarlinUtil helix class from the MarlinPandora TrackCreator. Instead, we now use our own helix class.”

Use of the ClusterShapes information must be avoided by adding the following parameter configuration to the MarlinPandora section of your Marlin steering files:

<parameter name="UseEndTrackHelixForECalProjection" type="int">0</parameter>

For the latest versions to work, our steering files also need to change

<parameter name="CalibrMUON" type="FloatVec">10000</parameter>

to

<parameter name="CalibrMUON" type="FloatVec">90000</parameter>

Muons to be found

For now only look at muons with E > 15 GeV.

Transition region

forwardbarrel endcap

All muons in sample, with cos (Ɵ) <0.995

muon-ID by yoke hits

Identify a PFO as a muon simply by requiring that it has >2 hits in the yoke.

E> 15 GeV:

Efficiency drops slightly in transition region

Barrel & endcap have ~90% eff. and purity.

Endcap a bit better. Linking of yoke hits to cluster is easier?

muon-ID by yoke hits & HCAL

Identify a PFO as a muon by requiring that it has >2 hits in the yoke, and the mean hit distance in HCAL < 100mm.

– (particle gun study showed that 80mm was more than enough)

Extra cut removes another ~20%.

– Efficiency lower, purity hardly changes.

muon-ID by PFA

Identify a PFO as a muon internally in Pandora.

E> 15 GeV:

Efficiency does not drop in transition region

Endcap efficiency is better: 70% vs 50% in barrel

Examples of ID by yoke hits

• Sometimes the misassignment is very obvious

(used wrong Gear-file)

Cluster to which yoke hits are assigned

Track to which muon really belongs

Examples of ID by yoke hits

Cluster to which yoke hits are assigned

Track to which muon really belongs

Track to which yoke hits are assigned

Examples of ID by yoke hits

Cluster to which yoke hits SHOULD BE assigned

Examples of ID by yoke hits

• Sometimes the misassignment is more difficult to find.

GREEN and purple are two reconstructed PFOs.

Track to which muon really belongs

Towards yoke hits.

Conclusion

Most common errors:

Yoke-hits added to an HCAL cluster, which is connected to a track very nearby the muon TPCtrack

Some are by eye clearly wrong, yet for many events the density of tracks is simply very high.

Event displays with yoke-hits which really seem to be from a muon, but I don't find them in the MC truthlist.

The cut for average hit distance in HCAL < 100 is now too severe, the efficiency is low.

Talked to John about identifying yoke-hits to TPC track. This step should be done at beginning of Pandora analysis, and neglects at first the HCAL info.

– “inward” approach.

– Knowledge of muon HCAL shape (hitdistance < 80) could perhaps be used in finding then the HCAL hits which are left by the muon.

– Should also be applicable to halo muons.

Emailed Mark & John that Pandora probably needs to be tuned for tailcatcher + 2x 2 layers.