1. Samir Guragain, Marcus Hohlmann Florida Institute of Technology, Melbourne, FL Z′ Mass Reach MC Analysis USCMS meeting Brown University May 6 – 8, 2010 Providence, RI Effect of muon misalignments on the muon p T resolution and on the search for Z′→ μ + μ - in pp collisions at 7 TeV Mass and p T Resolutions with 3 Misalignment Scenarios Muon Endcap Alignment Systematics Muon Endcap Alignment Systematics Muon Endcaps Yokes ME+1 ME+2 ME+3 ME+4 +z Muon Endcap stations: ME - Ideal (MC_31X_V5) Startup STARTUP31X_V4 50 pb -1 (50PBMU31X_V1) LHC STARTUP (now) Up to muon p T = 200 GeV/c, no significant change due to bias but changes at higher p T Muon alignment becomes prominent at higher p T in all scenarios Demonstrates tracker-only does not change with or without bias on endcap stations Abstract: Using simulated proton-proton (pp) collisions at √s = 7 TeV, we study the expected effect of muon misalignments on the transverse muon momentum (p T ) 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 p T resolutions for muons from Z′ decays at different masses and center-of-mass energies using different muon misalignments. The simulation results show that the p T 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 p T resolution is also studied and quantified. Using the MC samples, the discovery potential for M Z′ 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. Startup alignment and normalized to 200 pb -1 M Z′ =1.2 TeV Muons from 2 TeV Z′ at  s = 7 TeV Significance Estimator: Shape-based – likelihood ratio of signal + background and background-only fits to data 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 p T > 20 GeV/c - Isolation Σ track p T (ΔR < 0.3 cm) < 10 GeV/c Collision data Transverse momentum Pseudorapidity Comparisons: 7 TeV Data vs. MC MC: /MinBias/Spring10-START3X_v26A_356ReReco-v1/GEN-SIM-RECO Data: /MinimumBias/Commissioning10-GOODCOLL-v8/RAW-RECO Ideal alignment Tracker + Muon Ideal alignment + 2mm shift of muon endcap Tracker + Muon Muon p T resolution vs. η Muon p T resolution vs. p T Acknowledgments : Jordan Tucker, Jim Pivarski, Piotr Traczyk, Martijn Mulders, the CMS Collaboration, and the US Department of Energy Method: Muon Endcap was misaligned with respect to ideal or startup muon geometry. Then, a signal sample (M Z′ =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(X CMS, Y CMS, Z CMS ) up to 2 mm or a bias on rotation (φ Z CMS ) up to 0.5 mrad of muon endcap stations together or individual ME stations. Method: Muon Endcap was misaligned with respect to ideal or startup muon geometry. Then, a signal sample (M Z′ =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(X CMS, Y CMS, Z CMS ) up to 2 mm or a bias on rotation (φ Z CMS ) 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 ∆φ Z CMS ] µ+µ+ µ−µ− Resolution table Run 133928 Event 2538823 Date: April 25, 2010 cm Z′ + DY DY Dimuon mass [GeV/c 2 ] 50 pb -1 alignment and normalized to 50 pb -1 Dimuon Mass spectra and fitting: : Dimuon Mass spectra and fitting: : Z′ + DY DY Significance in 1000 pseudo-experiments STARTUP alignment scenario 1.2 TeV Z′ 50 pb -1 alignment scenario L int = 200 pb -1 Discovery  L int fit For 1.2 TeV Z′ Better alignment equals doubling the data set Better alignment puts us over 5  discovery threshold This result matches well with scaling results from 14 TeV to 7 TeV => 5  discovery possible with 200 pb -1 of data with the estimated 50 pb -1 alignment or better Global muons Data MC Dimuon mass [GeV/c 2 ] 1.2 TeV Z′ + DY Generated dimuon mass Events Signal Significance S L An Event Display Dimuon Analysis Ideal alignment Ideal alignment + 2mm shift of muon endcap A simulated Z′→ µ + µ − Event L int = 200 pb -1 Data: GOODCOLL-v7-9 J/ψ Global muons