1. Study of the Optimum Momentum Resolution of CMS Experiment Presented by: Timothy McDonald Faculty Mentor: Darin Acosta

2. The Compact Muon Solenoid b To be completed 2005 at CERN b At Large Hadron Collider b Collides proton bunches at 7 times Fermilab energy (7 TeV)

3. The Compact Muon Solenoid

5. Project focus Endcap Muon System

6. CMS Endcap Muon System 10 0 or 20 0 b Disk composed of 10 0 or 20 0 muon detectors b Four stations of detectors b Predominantly Only muons penetrate this much iron 4 Stations

7. Endcap Detector Station b Each Station Contains 6 cathode strip chambers b Anode wires: polar angle theta b Cathode strips: azimuthal angle phi Cathode Strip Chambers

8. More data is produced than can be easily handled b 40,000,000 collisions per second b 1 megabyte of data per collision bunch b 40 terabytes of data per second

9. Need to measure Muon Momentum b Trigger must select interesting events (Higgs, Z, W Bosons) b Heavy, interesting particles often decay into high momentum muons b Trigger must quickly measure muon momentum

10. Resolution Goals

11. Amount of Bending Proportional to Momentum b 4 tesla magnet bends escaping charged particles in azimuthal direction b high momentum muons bend less b momentum can be obtained based on bending between four detector stations

12. Parameterize momentum as a function of measurements b Can use 2,3, or 4 detector stations b Must consider change in azimuthal angle b Must consider the polar angle as well b Use simulation data to determine constants

13. Different rapidity regions b Rapidity is transformation of polar angle (eta=-ln tan  /2) b Equations must consider rapidity region b Many layers of iron and detectors means field varies

14. CMSIM simulates detectors b Mean change in angle at 15 GeV and in the eta region 1.4 to 1.5 b Data is fit to a normal curve b Provides information of how muons will behave in the experiment

15. Two station assignment b Change in muon track’s angle is inversely related to momentum b This relationship varies depending on the region of the detector

16. Uses change in angle from: *Station 1 to Station 2 *Station 2 to Station 3 The Three Station Momentum Assignment b Attempts to get a better resolution b Uses more information about muon track

17. Likelihood function b Estimate momentum from measured parameters using method of maximum likelihood b Correlation between two change in angle values must be considered b First derivative = 0 maximizes

18. Solve for momentum b Solve the likelihood function for 1/momentum b The mean and RMS spread parameterized from simulation data b results in function that depends on rapidity and change in phi angles

19. Resolution based on 3 station measurement b Resolution is about 21% for low momentum muons

20. Four Station Momentum Assignment b Attempts to bring resolution to lowest possible: 15% b Uses three change in angle values from the four stations b Not as much bending between third and fourth b Resolution same as three station assignment

21. Next Possible Step b Each station has 6 CSC chambers b They assign a direction vector b The direction can be used in the assignment