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Z  Cross Section etc

Paul Telford (and Emily Nurse) University of Manchester Manchester Group Meeting January 5 th 2005. Z  Cross Section etc. Introduction. Main body of the talk will focus on the updated Z  cross section result which I worked upon with Emily

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Z  Cross Section etc

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  1. Paul Telford (and Emily Nurse) University of Manchester Manchester Group Meeting January 5th 2005 Z Cross Section etc

  2. Introduction • Main body of the talk will focus on the updatedZcross section result which I worked upon with Emily • Will briefly discuss other work that I have been involved in • Includes Wcross section measurement, which we hope to update soon

  3. ZCross section Motivation • In combination with W cross section allows an indirect measurement of the W width • Experimentally useful as allows calibration of detector, triggers. • Use to gain understanding of effects such as Underlying event, tracker alignment in well understood process

  4. Determine using following formula • BR = Ncand.(1-fbkd)/.Luminosity • Count number of candidate events Ncand • Determine the luminosity of sample • Estimate the Background fraction of Ncand using data (cosmics, QCD) and MC (Z) • Evaluate acceptance using fast MC and efficiencies from data • Won’t talk about event selection in detail… leave this to Nasim • Backgrounds small (~1%), won’t discuss

  5. Total Efficiency • Evaluate with fast MC simulation, PMCS • Parameterise the effect of detector resolution • Tune parameters to data • Measure track, muon-ID and trigger effs in data • Introduce into PMCS as function of geometry • Co-ordinates chosen for unbiased efficiencies

  6. Result • Result = 291.3 ± 3.0 (stat) ± 6.9 (syst) ± 18.9 (lumi) pb cf theoretical prediction ≈ 250 pb • Largest systematic due to luminosity (6.5%) • Second largest due to Choice of PDF (1.7%) • Largest `experimental’ uncertainty due to modelling of the muon system efficiencies (1.0%) • Others from Uncertainty in beamspot distribution (0.6%), backgrounds in Efficiency(0.5%)…. • Statistical Uncertainty on candidates (0.9%) • Statistical Uncertainty on the Efficiency (0.6%)

  7. PDF Uncertainty • PDFs parameterise the probability to get parton of a given type with given energy • CTEQ6 comes with uncertainties on parameters • Uncertainty on observable calculated from sum of uncertainties due to those on parameters • Requires to evaluate observable 41 times…need large samples to control stat uncertainty • Wrote toy MC to model these fluctuations … need 100M events to get uncertainty to < 0.1%

  8. Muon System Uncertainty • Muon chambers divided into octants in phi • Efficiency lower in boundary between octants • No hard definition of these regions • Try to distinguish models of these regions, but limited by statistics

  9. Cross Checks • Main body of work this year has been cross checks • Use GEANT simulation to check no biases present in tag and probe • Check acceptance using HERWIG • Check trigger efficiency using independent trigger • And lots more ….

  10. W  Cross Section • Also involved with a measurement of the W cross section • Similar to Zs, but have tighter cuts due to higher backgrounds • My particular concern is the efficiencies, in particular the correlations between the W and Z analyses

  11. Other Work • Am responsible for making public the aspects of the fast MC utilised in these analyses • Have assumed responsibility for interfacing the new PDF interface with D0 software • Done `Consultancy’ work for MC aspects of equivalent measurements in Electron Channel • Given talk at DPF conference on Doubly Charged Higgs production in four muon decay channel

  12. Conclusions and Future Plans • Described an overview of the measurement of the Z cross section • Immediate future involves updatingW cross section and the ratio between W  and Z cross sections • Also continue to release (and document) the fast MC side of things for the benefit of all the collaboration

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