Defiducialization: providing experimental measurements for accurate fixed-order predictions
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Regular Article - Theoretical Physics
Defiducialization: providing experimental measurements for accurate fixed-order predictions A. Glazova Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
Received: 25 January 2020 / Accepted: 6 September 2020 © The Author(s) 2020
Abstract An experimental procedure is proposed to perform measurements of differential cross sections for vector boson production which can be compared to fixed-order QCD predictions with improved accuracy. The procedure relies on applying theoretical acceptance corrections computed as a function of the transverse momentum of the W/Z boson, pT , to the experimental measurement, rather than comparing data directly against fiducial fixed-order predictions. It is demonstrated that, contrary to standard fiducial computations, these acceptance factors vary little at low pT , so they can be reliably computed using fixed-order perturbation theory. An example analysis is performed using the ATLAS measurement of the Z -boson production cross section at center-of-mass energy of 8 TeV. The resulting full phase space measurement of the cross section differential in the boson rapidity is compared to theoretical predictions computed with next-to-nextto leading-order accuracy in QCD. Further extensions of the approach which include different types of measurements and improved theoretical predictions are discussed.
1 Introduction Accurate knowledge of parton distribution functions of the proton (PDFs) is essential for the physics program at the LHC. PDF uncertainties are the leading source of systematics for precision measurements of the W -boson mass and effective weak mixing angle, sin2 θW [1,2]. Reduction of the PDF uncertainties is important in particular for the interpretation of high statistics measurements for the future LHC data. PDFs can be constrained using W - and Z -boson production in the charged and neutral current Drell–Yan processes. These processes can be measured with sub-percent experimental accuracy and thus provide a valuable input for the PDF determination. An example of an accurate measurement a e-mail:
is the ATLAS result on γ ∗ /Z - and W -boson production at √ the center-of-mass energy of s = 7 TeV [3]. For the Z boson, the measurement is performed in bins of the invariant mass of the lepton pair, m , and of the lepton pair rapidity, y . For the W boson, the results are reported as a function of the lepton pseudorapidity, η . Excluding the global normalisation uncertainty, the measurement reaches better than 0.5% experimental uncertainty. The cross sections differential in y , m and η are known at next-to-next-to leading-order (NNLO) accuracy in perturbative QCD [4–8]. For these observables, the corresponding computations are inclusive in the boson transverse momentum pT and thus insensitive to ln pT /m divergences, providing a robust input for determination of collinear PDFs. However the ATLAS measurement is performed in a fiducial volume with experimental cuts on the lepton transverse momentum and lepton pseudorapid
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