Samir Guragain , Marcus Hohlmann Florida Institute of Technology, Melbourne, FL

1. Effect of muon misalignments on the muon pT resolution and on the search for Z′→ μ+ μ-in pp collisions at 7 TeV ME- Muon Endcap stations: ME+2 ME+3 ME+1 ME+4 +z Muon Endcaps Yokes Tracker + Muon 50 pb -1 (50PBMU31X_V1) Ideal alignment Better alignment puts us over 5 discovery threshold Lint fit • Up to muon pT = 200 GeV/c, no significant change due to bias but changes at higher pT • Muon alignment becomes prominent at higher pT in all scenarios • Demonstrates tracker-only does not change with or without bias on endcap stations Discovery Tracker + Muon Better alignment equals doubling the data set Ideal (MC_31X_V5) USCMS meeting Brown University May 6 – 8, 2010 Providence, RI Samir Guragain, Marcus HohlmannFlorida Institute of Technology, Melbourne, FL Startup STARTUP31X_V4 For 1.2 TeV Z′ LHC STARTUP (now) Ideal alignment + 2mm shift of muon endcap Abstract: Using simulated proton-proton (pp) collisions at √s = 7 TeV, we study the expected effect of muon misalignments on the transverse muon momentum (pT) resolution and on the search for high-mass resonances decaying to dimuons, in particular Z′→ µ+ µ− and Drell-Yan events, for the CMS experiment. We present the pT resolutions for muons from Z′ decays at different masses and center-of-mass energies using different muon misalignments. The simulation results show that the pT resolutions in the endcap are about 15% (5%) with the startup (ideal) muon misalignment scenario. The impact of systematic biases in the muon endcap positions and rotations on the pT resolution is also studied and quantified. Using the MC samples, the discovery potential for MZ′SSM= 1.2 TeV with different muon misalignments and integrated luminosities is evaluated. We find that a better aligned detector requires significantly less data, i.e. ~200 pb-1 of integrated luminosity, to discover a Z′ signal with 5σ significance than the CMS detector with current startup muon alignment. A preliminary analysis of dimuon data from first collisions at √s = 7 TeV is also presented. Mass and pTResolutions with 3 Misalignment Scenarios • Misalignment scenarios • Ideal Alignment (MC_31X_V5): Corresponding to ideal geometry of the detector • Startup Alignment (STARTUP31X_V4): Based on CRAFT 2008 and 2009 data analysis and produced by randomly misaligning chambers with an RMS consistent with cross-checks in CRAFT 2008 & 2009 • 50 pb-1 (50PBMU31X_V1) : Assuming alignment with tracks using 50 pb-1 data. Estimated with the Reference-Target algorithm [aligns a Target set of chambers using global muon tracks from a fixed Reference (tracker)] on appropriate MC samples • MC production at 7 TeV (at Fl. Tech.): Signal (Z′SSM) and background (Drell-Yan) samples with 3 standard misalignments using CMSSW_3_1_X • Ran Z′→ μ+ μ- analysis code in 3_X_Y • Event selection: • - Two opposite sign muons with pT > 20 GeV/c • - Isolation Σ track pT (ΔR < 0.3 cm) < 10 GeV/c Generated dimuon mass 1.2 TeV Z′ + DY Resolution table Dimuon mass [GeV/c2] Dimuon mass [GeV/c2] Dimuon mass [GeV/c2] Dimuon mass [GeV/c2] Muon Endcap Alignment Systematics Method: Muon Endcap was misaligned with respect to ideal or startup muon geometry. Then, a signal sample (MZ′=1.2TeV or 2.0TeV) was reconstructed and analyzed repeatedly with each studied misalignment. The sample was reconstructed with a customized global tag by inputting a modified SQLite file, with a bias for the position(XCMS, YCMS, ZCMS) up to 2 mm or a bias on rotation (φZCMS) up to 0.5 mrad of muon endcap stations together or individual ME stations. [For comparison: Current startup ME disk misalignments are 0.5 mm in (∆x, ∆y, ∆z) & 0.1 mrad in ∆φZCMS] Muon pTresolution vs. pT Muon pTresolution vs. η Ideal alignment Muons from 2 TeV Z′ at s = 7 TeV Muon pTresolution vs. pT Ideal alignment + 2mm shift of muon endcap Z′ Mass Reach MC Analysis Collision data Comparisons: 7 TeV Data vs. MC MC: /MinBias/Spring10-START3X_v26A_356ReReco-v1/GEN-SIM-RECO Data: /MinimumBias/Commissioning10-GOODCOLL-v8/RAW-RECO • Dimuon Mass spectra and fitting: : • Significance Estimator: • Shape-based – likelihood ratio of signal + background • and background-only fits to data Events Events Transverse momentum 50 pb-1 alignment and normalized to 50 pb-1 Pseudorapidity Startup alignment and normalized to 200 pb-1 DY Global muons DY Z′ + DY MZ′ =1.2 TeV Z′ + DY Data MC Global muons Dimuon mass [GeV/c2] An Event Display Dimuon Analysis Dimuon mass [GeV/c2] J/ψ Significance in 1000 pseudo-experiments => 5 discovery possible with 200 pb-1 of data with the estimated 50 pb-1alignment or better Data: GOODCOLL-v7-9 A simulated Z′→ µ+ µ− Event µ+ Lint = 200 pb-1 Run 133928 Event 2538823 Date: April 25, 2010 µ− Lint = 200 pb-1 1.2 TeV Z′ STARTUP alignment scenario 50 pb-1 alignment scenario This result matches well with scaling results from 14 TeV to 7 TeV cm Signal Significance SL Signal Significance SL Acknowledgments : Jordan Tucker, Jim Pivarski, PiotrTraczyk, MartijnMulders, the CMS Collaboration, and the US Department of Energy