Phase-2 Muon Simulations

1. Phase-2 Muon Simulations Alexei Safonov Texas A&M University

2. Background Assumptions • GE-1/1 will save the day for muon trigger between LS-2 and LS-3 • GE-1/1 covers the region 1.6<|h|<2.2 planned to be installed in LS2 as part of “early” Phase-2 upgrades • Post-LS-2 is the worst time ever: no track trigger yet • Critical post LS-3 concerns • Avert loss of triggering in 2.2<|h|<2.5 (region beyond GE-1/1) • Take advantage of a terrific opportunity to expand physics reach by extending offline muon coverage to 2.4<|h|<4.0

3. Bending Angle View from the top of the CMS down • An increased lever arm of the combined CSC+GEM system allows accurate measurement of the bending angle • Excellent discrimination power to distinguish soft muons from hard • Larger lever arm for “far” chambers provides even better separation

4. Trigger Rate • Illustration of the achievable trigger rate reduction in the region covered by GEM station GE-1/1 using bending angle measured using GEM and CSC stations • Each Level-1 muon track of a given moment is required to have its measured bending angle be less than the working point Df cut value defined for the momentum range, to which the track in question belongs • In this simplified scenario, the tracks are required to satisfy a requirement of having hits in at least two stations (out of four possible) • Results are compared with that for the standard CMS configuration used in 2012 (red line in the rate vspT curve)

5. GE-1/1: Bending Angle Cut • Illustration of the achievable trigger rate reduction in the region covered by GEM station GE-1/1 using bending angle measured using GEM and CSC stations • Each Level-1 muon track of a given moment is required to have its measured bending angle be less than the working point Df cut value defined for the momentum range, to which the track in question belongs • In this simplified scenario, the tracks are required to satisfy a requirement of having hits in three or more stations (out of four possible) • Results are compared with that for the standard CMS configuration used in 2012 (red line in the rate vspT curve)

6. MUON Trigger: POST LS-3

7. Trigger Concerns Past LS-3 • Muon Level-1 Trigger will rely on tracking trigger and Muon matching • The “double problem” region is 2.15<|h|< 2.5 • Either large efficiency losses or high fake rate in L1 Track Trigger • The exact same region where muon trigger rates shoot up • Solvable if we can suppress muon trigger rate by about ~x5 Reco’ed stubs pT>2 Stubs from true particles w/ pT>2 Tracker Muon gun pT>5 GeV Efficiency includes track finding only. No muon system inefficiencies incorporated. Muon System

8. Post-LS3 Trigger Scenarios • Motivation: prevent collapse of CMS muon trigger coverage from the current |h|<2.4 down to |h|< 2.1 or less • Strategy: build “Maximum Scenario” and see what works best • Maximum configuration: • Near tagger ME-0 at the back of present HE with trigger capabilities in 2.1<|h|<2.4 (can be long or short) • GEM stations: • “Old ”GE-1/1 • Already there in LS2 • “New” GE-2/1 • iRPCstations: • “New” GE-3/1 and 4/1 • Goal: seek a factor of ~x5 in trigger rate reduction • Evaluate impact of each new component on the trigger

9. Bending Angle and Distance to IP • Apply the same technique in Station 2: • It works, but not as well as in station 1 • Muon bending reduces due to radial B-field turning muons back • Multiple scattering smearing reduces discrimination • Reducing trigger rate in 2.1<|h|~2.4 requires measuring bending angle in close to IP stations

10. Trigger Rate Reduction: Preliminary GE-1/1: 1.6<|h|<2.1 • The “all of the above solution” provides a strong rate reduction • Phase-2 muon trigger design: define “lose track trigger tracks” to match with standalone L1 muons, use combined tracking and muon information to control the rate • Simulation used pitch of 1.9 mrad (~2 mm @ R=1m) • Precision important for bending angle, not for redundancy • * A combined effect of new redundancy in all 4 stations exclusive of bending angle reductions is x1.5

11. Precision Timing in YE-3 and 4 • New physics with B-mesons (Bs/d) • Trigger: two soft forward muons (on the same side) • High precision timing (100 ps range?) can be used to confirm that both muons come from the same vertex • Need to measure t1-t2, many systematics effect can potentially cancel • Need simulation to evaluate if it can help or not • Reduce neutron hits by utilizing timing windows • Lower background can potentially benefit the single muon trigger (more reliable points means better momentum measurement and thus lower trigger rate) • It appears that windows can’t be less than a few nsec • That gives the required level of precision for the detectors

12. Offline Muon reconstruction: Extension to eta=4.0

13. Forward Region: Physics • The hard part is the region of 2.1 <|h|>2.4: • Highest background rates yet least redundancy, most vulnerable at high luminosity • Challenging B-field topology • Radial field turning muons back • Awkwardly, if there is one place to make large physics acceptance gains, it is in the forward region • Also improve MET by tagging muons in the forward region HZZ4m : ~50% acceptance increase if hmax=2.44.0

14. Phase-2 Near Tagger ME-0 Scenario • Near tagger ME-0 at the back of present HE • Coverage: 2.1<|h|<4.0 • Upper portion of 2.1<|h|<2.5 has trigger capabilities • Lower portion is only used in the offline • Muon reconstruction based on matching tracks reconstructed in forward muon extension with hits in the muon system

15. High h offline extension • General strategy for performance estimates (same strategy will be used to provide extrapolation tools) • In absence of GEANT simulation of the extended muondetector use Fastsim with forward pixel geometry • muon detector emulated as a flat surface at |z| = 560 cm, covering |η| = 2.4-4.0 → only 2D hits for now • material effects can be studied using parametrization in SteppingHelixPropagator • Propagate the generated-track initial state and covariance matrix (null at IP) to a surface at z = 560 cm, using the SteppingHelixPropagator • after the propagation, the covariance matrix will include the uncertainty from material effects only (multiple scattering, energy-loss fluctuations, bremsstrahlung, etc.) • Use position error on the muon detector surface to smear the propagated position and “emulate” a sim-hit longitudinal view transversal view y r = (x2 + y2)½ “sim-hit” “sim-hit” r · Δφ gen track Δr rec-hit rec-hit reco pixel track IP IP x 560 cm z

16. Example: performance of ME0 as a tagger • Contributions to the total muon resolution after propagation to ME0, from • detector effects (multiple scattering):from RMS b/w “GEN” and “SIM” hits • pixel detector resolution:from RMS b/w “RECO” and “GEN” hits • Total resolution can be used to determine “matching windows” for muon tagging in ME0 • e.g. at pT = 5 GeV/c, we can chooseΔη × Δφ = 0.002 ⇒ 2 RMS = 95% matching prob. • With this window, and the average expected pile-up in phase-2 (N ~ 0.25 tracks/pp inter.or 50 tracks/BX) we can estimate the mis-tag rates for topologies with • known vertex (e.g. H → 4μ): < 0.004 • unknown vertex (e.g. VH → γγμ): < 0.8 • *** Performance studies are on hold and will be redone with new pixel geometries rφ coordinate RMS Muon gun with pT = 5 and 20 GeV/c

17. Thinking of Simulations Strategy For TP

18. Simulation Strategy Options for TP • Need reliable results on a short time scale - “emulated” simulation? • Trigger: Use simHit or digis information for CSC and extrapolators to make fake “hits” in detectors being simulated • Faithful representation of magnetic field and material budget important for multiple scattering • Smear to fake resolution effects • Combine with track trigger simulation in FullSim, develop algorithms • Use extrapolations for the new ME-0 • Muon hits: use gen level particles, extrapolate to muon chambers using realist extrapolators to create muon “hits” • Will wrap the machinery in producers making CMSSW objects usable in full sim or fast sim studies • Inner tracks: Use whatever available for tracking (currently using fastSim but waiting for a new layout, can switch to FullSim easily – whatever tracking people do, we will do the same)

19. Trigger: “Emulated Simulation” • Use the same emulator as used for making estimates for ME0 for eta>2.1 and for GE2/1. • As a reference, below is the comparison of the full-sim GE1/1 bending angle and the emulated-simversion • The emulated-simperformance is reproduced well GE1/1 FullSim GE1/1 FastSim

20. Extended Offline Coverage: Options • Emulated simulation (slides 14-15) is working well • However, given that calorimeter simulation goes into CMSSW, we can also add sensitive volumes behind it to emulate ME-0 • SimHits created by GEANT, use simple smearing to emulate detector granularity, wrap things up to make CMSSW objects • Will work in fullSim or fasSim • Doable on the time scales of the TP

21. Trigger Simulation: Options • Can do the same trick and add sensitive volumes for exploring trigger scenarios: • Add detectors: • GE-1/1 is already there in all detail • GE-2/1 (almost done and will be in CMSSW in ~0.5 week) • RE-3/1 and RE-4/1 (already available)

22. Caveat: Non-Prompt Backgrounds • Neutron backgrounds are a potential concern • Details in the next talk • Need flux estimations: • Close to where we can modify FLUKA geometries and calculate rates where we need them, including in the space behind the new calorimeter • Currently can already use dual-readout calorimeter geometry (thanks to them for their help!) • Relies on FLUKA and is decoupled from CMSSW developments • Can go on a parallel track

23. Strategy: Options • Seems like we can factorize simulation work: • In-CMSSW: performance studies of the “detector package” using a combination of true GEANT simulation and reliable extrapolation techniques • But assume neutron backgrounds will be taken care of (they are not in simulation) • Outside-CMSSW: Optimization of what’s inside the “detector package” • Fluka for background rates and working out shielding issues • Optimize the inner structure of the “detector package” • How many layers? Do we need material between detector sensitive layers for background rejection (where and how much)?