Summary of Muon Combined Performance

1. Summary of Muon Combined Performance Peter Kluit (NIKHEF) On behalf of the MCP group and convenors Ed Moyse and Massimo Corradi

2. Topics that will be discussed • Efficiencies and scale factors • Momentum resolution and smearing • Low pT: Jpsi efficiencies • Understanding the Jpsi mass in the endcaps • Backgrounds and their impact on physics • High Pile up • Cavern background • Overlay studies • New Small Wheel studies • Third Chain and Physics • LS1 activities • Notes, papers and conclusions

3. Z Efficiencies and scale factors • Efficiencies and scale factors for the Z • Closer look at systematic errors for the background • Effect of background negligible in most bins: covered by statistical uncertainties • Other systematic errors such as the dependence on isolation are under study https://indico.cern.ch/conferenceDisplay.py?confId=254509

4. Z Efficiencies and scale factors at high eta • Efficiencies and scale factors for the Z • In the η region where no ID is present at lηl > 2.5 only StandAlone (SA) muons can be reconstructed. https://indico.cern.ch/conferenceDisplay.py?confId=254509

5. Momentum smearing • MCP muon momentum resolution and scale correction is: • p`T =pT Scale (1+∆p1G1+∆p2pT G2) • - pT the MC transverse momentum • - Scale, ∆p1and∆p2are fitted to Z including constraints • G1 and G2 are random gaussian numbers The yellow band gives the total systematic error https://indico.cern.ch/conferenceDisplay.py?confId=258263

6. Low pT: Jpsi efficiencies • Tag and Probe efficiencies for 2012 Chain 3 The hatched blue area gives the total systematic error https://indico.cern.ch/conferenceDisplay.py?confId=251141

7. Understanding the Jpsi mass in the endcaps • Puzzle that was also discussed in the Higgs mass studies • Data-MC mismatch up to 0.6% for all reconstruction algorithms • The origin lies in the SA track that has a more precise momentum measurement than the ID at high eta (right plot shows the SA momentum). • It is more pronounced at low pT (not present in the Z). • Our current best guess is that it comes from a bad description of the dead material Eloss and B field in particular in the endcaps • https://indico.cern.ch/conferenceDisplay.py?confId=258263

8. Understanding of backgrounds and the modeling in the simulation • Comparisons have been made for data and MC for high pile up runs, cavern background and for standard high luminosity running. See workshop data MC: https://indico.cern.ch/conferenceDisplay.py?confId=250975 • In all cases there is substantial mismodeling for the background in the Muon detector at the hit level with scale factors ranging from 0.5 to 10. • There is better agreement for higher level objects such as segments. • For physics what mostly matters is the modeling of the reconstructed muons in the pile up and cavern background. • In the next slides I will show the reconstructed muons data-MC for high pile up data and cavern background

9. Muons in High pile Up data Data to MC ratio Combined CB muons 1.03 ± 0.04 Tagged muons 1.09 ± 0.07 Standalone SA muons 0.84 ± 0.14 The High Pile Up MC does an excellent modeling of the reconstructed muons. The pile up simulation is used in all the ATLAS MC productions. The CB and Tagged muons have to pass the MCP ID track selection. The SA muons are required to have hits in the Inner MDT orCSC station.

10. Cavern background hits The bunch trains studies from Harvard indicated that there is a long lived background with a typical lifetime of 50 micro sec. Ratio of cavern bkg / total = 1.75/2.75. More details can be found in: https://indico.cern.ch/getFile.py/access?contribId=9&resId=7&materialId=slides&confId=247906

11. Cavern background Muons No muons found in the empty bunches • No muons were reconstructed in the Empty bunches of the bunch • trains. In total 21k events in Empty bunches were analyzed. • (Note that there are abundant MDT hits and clusters found). • NB One only would expect SA muons as no ID track will be made • It is expected that the Muon reconstruction strongly suppresses out of • time cavern background.

12. Muon Overlay studies • With the current detector background overlays can be made and extrapolations to very high backgrounds can be made. See talk in Simulation SG: https://indico.cern.ch/getFile.py/access?contribId=2&resId=0&materialId=slides&confId=224606 Example of a 10 times overlayed event at 3 1034/cm2/s

13. New Small Wheel studies The NSW TDR is now available https://cds.cern.ch/record/1552351/ Many of us have contributed to the performance chapters. Background simulations allowed to e.g. the segment finding efficiency with the new detector:

14. Third Chain and Physics • A nice overview of the third chain has been given in the Physics and Performance week https://indico.cern.ch/conferenceDisplay.py?confId=248907 • In close collaboration with the Standard Model and MET • group some problems are now addressed and solved: • - MET tails were due to an inconsistent use of the MET • - propose with the MET group a consistent MET calculation • that can be redone on the D3PD: • - the code for this is under validation • - Unexpected large fake rate observed in the WZ analysis • was traced down to a (known) bug in the MC • - We plan to develop with SM a slightly tighter working point • than the current Chain 3 "medium” selection: • - first version of "medium+" is under study

15. LS1 activities • Full list of acticities and plans: https://twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/MuonPerformanceTasks2013 • In particular relevant: • Common D3PD validation framework for Z, Jpsi Tag and • Probe, momentum resolution and precision studies • Very high precision tuning of the Energy loss aim 20 MeV in • the Muon System and the Calorimeter. For this we need a • volume Base Tracking Geometry for the Calorimeter - like • we have already for the Muon Spectrometer – that will give • for each track the volumes crossed and an estimate of the • MOP value for the Eloss and its error (spread).

16. Notes and papers & conclusions • The 2010 Performance paper is now circulating • https://cds.cern.ch/record/1517074 • For 2012 a Performance note is in preparation that will be turned into a run 1 Muon Performance paper • A summary of results and current understanding have been given for the topics of: • Muon efficiencies and momentum scales • Jpsi studies show a need for an improved Eloss tune in particular in the endcaps • Muon pile up background – at the level of reconstructed muons – is well modeled. Cavern background can be neglected. • Plans and activities for the third chain and in the LS1 have been presented.