Messung des differentiellen Wirkungsquerschnitts der Z-Boson Produktion im Elektron-Zerfallskanal mit dem CMS-Detektor bei s=8 TeV.

Transcription

1 Messung des differentiellen Wirkungsquerschnitts der Z-Boson Produktion im Elektron-Zerfallskanal mit dem CMS-Detektor bei s=8 TeV. DPG Frühjahrstagung 2015 Dominik Haitz, Klaus Rabbertz, Günter Quast INSTITUT FÜR EXPERIMENTELLE KERNPHYSIK (EKP) FAKULTÄT FÜR PHYSIK KIT Universität des Landes Baden Württemberg und nationales Forschungszentrum in der Helmholtz Gemeinschaft

2 Introduction Z boson production Standard candle process at the LHC Decay in two leptons high precision reconstruction LHC: high luminosity, high s Z bosons in abundance private work Goals of this analysis Test of Standard Model predictions Constrain parameters of gluon PDF Sensitivity at lower x especially at high Z rapidity Electrons can be reconstructed at higher rapidities compared to muons 2

3 Electron Reconstruction with the CMS Detector Involved detector subsystems: Silicon Tracker Covers η <2.4 Reconstruct electron tracks with Gaussian sum filter ECAL Covers η <3.0 Build Supercluster from energy deposits Tracks and superclusters are matched reconstructed electron arxiv: : Performance of electron reconstruction and selection with the CMS detector in proton proton collisions at (s)=8 TeV 3

4 Electron Trigger and Identification Trigger efficiency from MC Tag and Probe study in progress Trigger efficiency vs pt and η Several methods to for electron identification Robust cutbased ID (loose, medium, tight) Sophisticated multivariate ID (used here) ID efficiency vs pt ID purity vs. efficiency High efficiency and purity achieved 4

5 Electron Momentum Corrections Multivariate corrections to electron momentum Using information from tracks and superclusters Electron pt reco/gen vs. eta Reconstructed Z boson mass in data Reconstructed momentum less dependent on η region 5

6 Z Boson Reconstruction 6 Data vs. Madgraph (LO) and Powheg (NLO) Rapidity spectrum: Comparison of Z ee and Z μμ pt spectrum well described Electrons: higher reach in y

7 Background Estimation Background samples: Diboson, t and W processes Small total background: ~1.4%, thereof 1% WZ, ZZ Data driven background estimation with the e μ method in progress 7

8 Unfolded Distribution Unfolding of pt distribution in bins of Z y (0., 0.4, ) RooUnfold: iterative Bayesian unfolding in 4 steps Comparison of MC reco/gen/unfolded Unfolded Data & MC Unfolding works, unfolded data well described by simulation 8

9 First Look at Systematic Uncertainties Background uncertainty: effect of +50% on background cross sections Unfolding: effect of +1σ on response matrix entries Other errors (trigger efficiency, ) yet to be determined These preliminary results show small uncertainties of few percent 9

10 PDF Fits from Z ee data Sensitivity to gluon PDF at lower x at high y Theory calculation with Sherpa and fastnlo (work in progress) Sherpa: General purpose MC Generator fastnlo: Tool to compute NLO predictions for e.g. different PDFs Goal: Complement fit results of Z μμ channel K. Rabbertz, Parton Distributions for the LHC, Benasque

11 Conclusion Measurement of differential Z boson cross section progressing well First (private) results are available PDF fits in the making Refine 8 TeV results, study 13 TeV data when available 11

12 Backup Slides 12