Z→ μμ in the CSC: Efficiency and momentum resolution

1. Z→μμ in the CSC:Efficiency and momentum resolution CSC reconstruction and commissioning David Adams Brookhaven National Laboratory October 21, 2010 Updated 21Oct 13:00 EDT

2. Introduction • I look at dimuon events to study CSC performance • Require two muons • Muons must be combined but momenta are taken from the MS track • Both pT > 20 GeV • Opposite sign • One in muon barrel: |η| < 1.05 • One in CSC region: |η| > 2.05 • Following plots are generated • # CSC eta hits • 80 < m < 100 GeV • Dimuon mass • # CSC hits > 2 • For three samples • Pythia Z→μμ • Run periods A-F (before CSC alignment) • Run periods G-H1 (after CSC alignment) D. Adams Overview CSC reconstruction

3. Performance metrics • I extract the following performance metrics • CSC efficiency • Fraction of events (in Z-mass peak) with more than 2 CSC hits • This is efficiency to find CSC hits on a track • At yesterday’s MCP meeting, the T&P efficiency to find a track in CSC region was about 1% below the MC value of 95% • CSC overlap fraction • Fraction of events in Z-peak with more than 6 CSC hits • Momentum scale and resolution • Mass spectrum is fit to Breit-Wigner convoluted with Gaussian • BW Γ = 2.5 GeV • Gaussian mean and sigma reported D. Adams Overview CSC reconstruction

4. Mass spectra • Plots show mass for all CSC • Before alignment, resolution is very bad • After, resolution is similar to that of Monte Carlo D. Adams Overview CSC reconstruction

5. CSC hit multiplicities • Plots show CSC hit multiplicities • Efficiency in data is 98% • Data overlap is only 4% compared to 14% in MC • Previously reported • Due to misalignment? D. Adams Overview CSC reconstruction

6. CSC hit multiplicities (good CSC) • More CSC hit multiplicities • Same as previous page except G6 runs with bad CSC sectors are excluded • Efficiency increases D. Adams Overview CSC reconstruction

7. CSC hit multiplicities by side (MC and data) D. Adams Overview CSC reconstruction

8. CSC hiot multiplicities by side (good CSC data) D. Adams Overview CSC reconstruction

9. Mass by side (MC and data) D. Adams Overview CSC reconstruction

10. Mass by side and charge (data) Splitting due to misalignment? More likely statistics. D. Adams Overview CSC reconstruction

11. Conclusions • Z analysis shows • Efficiency to find CSC hits on track is high • But efficiency to find two chambers in overlap is small • Previously attributed to misalignment • Resolution averaged over all CSC is consistent with MC • Statistics limited D. Adams Overview CSC reconstruction

12. Appendix Muon system layout CSC hit multiplicity CSC acceptance Z→μμ event display D. Adams Overview CSC reconstruction

13. Muon detector D. Adams Overview CSC reconstruction

14. CSC hit multiplicity Plot was shown at the last ATLAS weekly • Plot shows the multiplicity of CSC eta hits on muons with |eta| > 2.0 • Muid combined • Both collision data and Monte Carlo • Observations • Beam data shows very few 8-hit clusters: misalignment? • Three hits due to single plane inefficiency? • Should investigate • AOD or MCP tree • Volunteer? D. Adams Overview CSC reconstruction

15. CSC acceptance • I checked an MC08 Zmumu sample • Plot eta-phi of muons with • 0 CSC hits • More than 1 CSC hits • CSC has full acceptance for |eta| > 2.04 • Small chambers down to 2.00 W candidate No CSC hits 2 or more CSC hits D. Adams Overview CSC reconstruction

16. Z with muon in CSC: OK for public viewing D. Adams Overview CSC reconstruction