FirstYearReport

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Published on October 31, 2007

Author: Chyou

Source: authorstream.com

Investigating Drell-Yan Z0 production at ATLAS:  Investigating Drell-Yan Z0 production at ATLAS ATLAS and Drell-Yan Z0 production Lepton selection Results First look at Rome data Michael Flowerdew, Department of Physics University of Liverpool ATLAS and the LHC:  ATLAS and the LHC p-p collisions √s = 14 TeV 40 MHz rate L = 1034 cm-2s-1 Almost 4π steradian coverage |η| < 2.5 precision coverage Forward physics to |η| < 4.9 Why study the Z0?:  Why study the Z0? High statistics Drell-Yan production σ (14 TeV) ≈ 50 nb Intrinsic interest Cross-section measurements (σ, dσ/dpT, dσ/dη, …) Information on parton density functions Electroweak measurements Decay patterns, asymmetries, sin2 θW Discovering ATLAS… Energy scale calibration (from MZ) Lepton trigger & analysis efficiencies The samples:  The samples Drell-Yan Z0 → e+e- / Z0 → μ+μ- events 5400 of each Equivalent to ~ 3.5 pb-1 No filters, so shows full detector efficiency, including acceptance Pythia 6.2, linked to full ATLAS simulation Data converted to ROOT NTuple for analysis Unfortunately, no truth information Electron selection:  Electron selection Good calorimeter cluster Narrow, 1 maximum, < 5GeV hadronic leakage Good track Matches cluster, precision hits, impact parameter TRT selection neglected Require pT > 15 GeV Imitates trigger threshold Kinematic edge visible in pT Detector acceptance seen in η E/p peaks at 1 Muon selection:  Muon selection Tracks in Inner Detector and Muon Spectrometer |η| < 2.5 (ID range) Pixel hit required pT > 10 GeV required This seems to be sufficient Clear pT edge again Gap for services at η = 0 Other cuts to investigate Isolation Impact parameter Track χ2 Aside: Like-charge pairs:  Aside: Like-charge pairs Combine l+l+/l-l- Judge effectiveness of cuts without backgrounds Data near Z0 mass Misassigned sign? Data near Mll = 0 Duplicated lepton? High-pT, low-pT partners? Z0 mass spectra:  Z0 mass spectra Combine l+l- pairs Gaussian fit On third-order pedestal Assumes ATLAS resolution dominates width Mass cut to define Z0 candidate 84 < MZ < 97 GeV Cut just as tails start to dominate Z0 candidates:  Z0 candidates Graphs from electron and muon samples combined Maximises statistics Many highly forward Z0s pz ~ 10pT typically Peaks at |η| ~ 3 (θ = 6˚) Efficiency < 25% Lepton pair distributions I:  Lepton pair distributions I Naively expect back-to-back leptons (neglecting pT of Z0) Large peak at |Δφ| = 180˚ (E ± pz)/2Ebeam indicative of x1, x2 of partons in collision Satisfy x1x2 = (0.0065)2 based on Z0 mass Good sensitivity down to x ~ 0.0015 Lepton pair distributions II:  Lepton pair distributions II Energy scale of leptons important for calibration Several leptons with E ~ 200 GeV in End Cap with 3.5 pb-1 of data Lower energy range in Barrel Should improve with luminosity First look at Rome samples:  First look at Rome samples Wide-ranging set of physics samples, including Drell-Yan Z0 production Filtered events pT > 15 GeV for all decay leptons |η| < 3.3 for electrons, |η| < 2.7 for muons ~ 94,000 Z0 → ee and ~ 95,000 Z0 → μμ Equivalent to about 0.1 fb-1 Analysis and selections identical to previous study Z0 properties in Rome samples:  Z0 properties in Rome samples New results seem consistent with previous sample, but Less of a tail on Z0 mass plot Z0 is asymmetric in φ! Higher efficiencies Caused by filtering Quantitative comparison in progress Rome Z0/lepton pair distributions:  Rome Z0/lepton pair distributions Future directions:  Future directions Analyse and weight background data from Rome samples Dijets, top, W+jets especially Re-evaluate lepton selection criteria Compare reconstruction with truth True efficiencies and purity CSC samples out soon Trigger decision and misalignments Extension to Z' ATLAS cross-sections:  ATLAS cross-sections ATLAS triggering:  ATLAS triggering Particle issues:  Particle issues Template:  Template First level Second level Third level New First level Another one

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