Measurement of the Z boson differential production cross section using its invisible decay mode (Z$\nu\bar{\nu}$) in proton-proton collisions at $\sqrt{s}=$ 13 TeV

Albert M. Sirunyan, Armen Tumasyan, Wolfgang Adam, Thomas Bergauer, Marko Dragicevic, Alberto Escalante Del Valle, Rudolf Fruehwirth, Manfred Jeitler, Natascha Krammer, Lukas Lechner, Dietrich Liko, Ivan Mikulec (+2313 others)
Measurements of the total and differential fiducial cross sections for the Z boson decaying into two neutrinos are presented at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were collected by the CMS detector in 2016 and correspond to an integrated luminosity of 35.9 fb −1 . In these measurements, events are selected containing an imbalance in transverse momentum and one or more energetic jets. The fiducial differential cross section is measured as a
more » ... of the Z boson transverse momentum. The results are combined with a previous measurement of charged-lepton decays of the Z boson. The measured total fiducial cross section for events with Z boson transverse momentum greater than 200 GeV is 3000 +180 −170 fb. Open Access, Copyright CERN, for the benefit of the CMS Collaboration. Article funded by SCOAP 3 . JHEP05(2021)205 muons, which leads to a smaller statistical uncertainty. This can only be fully exploited at large transverse momenta of the Z boson (p Z T ), above ≈500 GeV, where the measurement of the missing transverse momentum (p miss T ) is sufficiently accurate. This measurement therefore complements those using the charged lepton final states and improves their precision at a higher energy scale. A significant deviation, in particular at large p Z T , could reveal signs of physics beyond the SM [20][21][22]. This paper presents the first inclusive, differential, and normalized fiducial cross section measurements as functions of p Z T , where the Z boson is identified via its decay to a pair of neutrinos. The neutrinos are not detected by the CMS detector, but are reconstructed indirectly through the transverse momentum imbalance in the event. We use events with energetic jets and large p miss T , where the jets mainly arise from the fragmentation and hadronization of quarks or gluons that are produced in the hard scattering process as initial-state radiation. The analysis is based on a data sample of proton-proton (pp) collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 ± 0.9 fb −1 collected with the CMS detector at the LHC in 2016. This paper is organized as follows. A brief overview of the CMS detector is given in section 2. Information about the definition of objects used in the analysis and the event selection is summarized in section 3. Event simulations with various Monte Carlo (MC) generators are discussed in section 4. Section 5 explains the signal-extraction strategy and section 6 discusses the total, differential, and normalized fiducial cross section measurements. A combined analysis of the current measurements with those from charged leptons is presented in section 7. Finally, we summarize our results in section 8. Tabulated results are available in the HepData database [23]. The CMS detector and event reconstruction The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. 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 end sections reside within the solenoid volume. Forward calorimeters extend the pseudorapidity (η) coverage provided by the barrel and end-section detectors. Muons are detected in gas-ionization chambers embedded in the steel flux-return yoke outside the solenoid. A more detailed description of the CMS detector, together with a definition of the coordinate system and kinematic variables, can be found in ref. [24]. Events of interest are selected using a two-tiered trigger system [25]. The first level, composed of custom hardware processors, uses information from the calorimeters and muon detectors at an output rate of ≈100 kHz within a fixed latency of about 4 µs. The second level, known as the high-level trigger, consists of a farm of processors running a version of the full event reconstruction software optimized for fast processing, that reduces the event rate to ≈1 kHz before data storage. Additional pp interactions to the studied collision that take place in the same or nearby bunch crossings are referred to as pileup. -2 -
doi:10.18154/rwth-2021-06285 fatcat:lcr2ua35gbafhkalkjxuopb6hq