Abstract

Measurements of the differential cross sections of Z + jets and γ + jets production, and their ratio, are presented as a function of the boson transverse momentum. Measurements are also presented of the angular distribution between the Z boson and the closest jet. The analysis is based on pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb−1 recorded by the CMS experiment at the LHC. The results, corrected for detector effects, are compared with various theoretical predictions. In general, the predictions at higher orders in perturbation theory show better agreement with the measurements. This work provides the first measurement of the ratio of the differential cross sections of Z + jets and γ + jets production at 13 TeV, as well as the first direct measurement of Z bosons emitted collinearly with a jet.

Highlights

  • Background estimation5.1 The Z + jets channelThe selection of Z + jets events produces a relatively pure sample of Z bosons decaying to muons

  • This paper presents measurements of standard model processes that probe regions of phase space characterized by the production of Z + jets and γ + jets at large boson transverse momentum, and of a Z boson in association with at least one very high pT jet. √

  • The measurements utilize data recorded with the CMS detector in pp collisions at s = 13 TeV at the LHC that correspond to an integrated luminosity of 35.9 fb−1

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Summary

The CMS detector

The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections. The ECAL provides coverage in pseudorapidity |η| < 1.48 in the barrel region (EB), and 1.48 < |η| < 3.0 in two endcap regions (EE). Forward calorimeters extend the pseudorapidity coverage provided by the barrel and endcap detectors. Events of interest are selected using a two-tiered trigger system [27]. The first level, composed of custom hardware processors, uses information from the calorimeters and muon detectors to select events at a rate of around 100 kHz within a fixed latency period of less than 4 μs. A more detailed description of the CMS detector, together with a definition of the coordinate system used and the relevant kinematic variables, is reported in ref. [28]

Event simulation
Event reconstruction and selection
Background estimation
Corrections for detector effects
Systematic uncertainties
Results
Summary
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