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Z boson production in p+Pb collisions at s NN =5.02 TeV measured with the ATLAS detector

Physical Review C - Nuclear Physics (2015) 92(4)
DOI: 10.1103/PhysRevC.92.044915
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Abstract

The ATLAS Collaboration measures the inclusive production of Z bosons via their decays into electron and muon pairs in p+Pb collisions at sNN=5.02TeV at the Large Hadron Collider. The measurements are made using data corresponding to integrated luminosities of 29.4 and 28.1 nb-1 for Z→ee and Z→μμ, respectively. The results from the two channels are consistent and combined to obtain a cross section times the Z→ℓℓ branching ratio, integrated over the rapidity region |yZ∗|<3.5, of 139.8±4.8(statistical)±6.2(systematic)±3.8 (luminosity) nb. Differential cross sections are presented as functions of the Z boson rapidity and transverse momentum and compared with models based on parton distributions both with and without nuclear corrections. The centrality dependence of Z boson production in p+Pb collisions is measured and analyzed within the framework of a standard Glauber model and the model's extension for fluctuations of the underlying nucleon-nucleon scattering cross section.

Figures

  • FIG. 1. (Color online) Centrality bias correction factors and their uncertainties (bars), fromRef. [30], for the Glauber and GGCFmodel configurations, and bias correction factors derived from data (points) as explained in the text. The reciprocals of the correction factors are applied as multiplicative factors to the centrality-dependent Z boson yields.
  • FIG. 2. (Color online) Dilepton invariant mass distributions in data and MC simulation. (a) Z → ee candidates with both electrons at midrapidity (|η| < 2.47); (b) candidates in which the nontriggering electron is a forward electron (2.5 < |η| < 4.9); (c) Z → μμ candidates. The midrapidity Z → ee and Z → μμ distributions are overlaid with the mass distributions of like-sign lepton pairs. For candidates in which the nontriggering electron is a forward electron (2.5 < |η| < 4.9) the background, estimated based on a decomposition of the invariant mass distribution (see text), is shown. In all plots the vertical lines indicate the mass window within which candidates are defined, and the MC simulation is normalized to the data inside this region.
  • TABLE I. Relative systematic uncertainties (in percent) associated with the measurement of Z → ee. The uncertainties typically increase at the more forward rapidities. Background includes charge misreconstruction, and electron reconstruction includes resolution. The last two rows refer only to pairs where one of the electrons was reconstructed in the range 3.1 < |η| < 4.9.
  • FIG. 3. (Color online) (a) Differential Z boson production cross section, dσ/dy∗Z , as a function of Z boson rapidity in the centerof-mass frame y∗Z , for Z → ee and Z → μμ. (b) Their ratio. Bars indicate statistical uncertainty; shaded boxes, systematic uncertainty.
  • TABLE II. Relative systematic uncertainties (in percent) associated with the measurement of Z → μμ.
  • TABLE III. The measured integrated cross section (in nb) for several rapidity ranges, for Z → μμ, Z → ee, and the combined Z → . The first uncertainty listed is statistical, and the second systematic. There is an additional 2.7% luminosity uncertainty for each cross section. Cross sections predicted by the models (see text) are also listed. Uncertainties listed with the model calculations are the PDF and scale uncertainties added in quadrature.
  • FIG. 4. (Color online) (a) The dσ/dy∗Z distribution from Z → , shown along with several model calculations in the upper panel. Bars indicate statistical uncertainty, and shaded boxes systematic uncertainty, of the data; uncertainties of model calculations are not shown. (b)–(d) Ratios of the data to the models. Uncertainties of the model calculations (scale and PDF uncertainties added in quadrature) are shown as bands around unity in each panel. An additional 2.7% luminosity uncertainty of the cross section is not shown.
  • FIG. 5. (Color online) (a) The differential cross section of Z boson production multiplied by the Bjorken x of the parton in the lead nucleus, xPbdσ/dxPb, as a function of xPb using Z → events shown along with several model calculations. Bars indicate statistical uncertainty, and shaded boxes systematic uncertainty, of the data; uncertainties of the model calculations are not shown.(b)–(d) Ratios of the data to the models. Uncertainties of the model calculations are shown as bands around unity in each panel. There is an additional 2.7% luminosity uncertainty of the cross section.

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APA

Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Aben, R., Abolins, M., … Zwalinski, L. (2015). Z boson production in p+Pb collisions at s NN =5.02 TeV measured with the ATLAS detector. Physical Review C - Nuclear Physics, 92(4). https://doi.org/10.1103/PhysRevC.92.044915

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