Measurement of associated Z + charm production in proton-proton collisions at $\sqrt{s} =$ 8 TeV

The collaboration
Eur.Phys.J.C 78 (2018) 287, 2018.

Abstract (data abstract)
A study of the associated production of a Z boson and a charm quark jet (Z+c), and a comparison to production with a b quark jet (Z+b), in pp collisions at a centre-of-mass energy of 8 TeV are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb$^{-1}$, collected with the CMS detector at the CERN LHC. The Z boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of c or b flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with $p_T^l > 20$ GeV, $|\eta_l| < 2.1$, $71 < m_{\ell\ell} < 111$ GeV, and heavy flavour jets with $p_T^{\text{jet}} > 25$ GeV and $|\eta_\text{jet}| < 2.5$. The Z+c production cross section is measured to $\sigma(pp \to Z + c + X) \mathcal{B}(Z \to \ell^+\ell^-) = 8.8 \pm 0.5$ (stat) $\pm 0.6$ (syst) pb. The ratio of the Z+c and Z+b production cross sections is measured to be $\sigma(pp \to Z + c + X)/\sigma(pp \to Z + b + X) = 2.0 \pm 0.2$ (stat) $\pm 0.2$ (syst). The Z+c production cross section and the cross section ratio are also measured as a function of the transverse momentum of the Z boson and of the heavy flavour jet. The measurements are compared with theoretical predictions.

• #### Table 1

Data from Table 1

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Signal yields N(Z+c) and N(Z+b), efficiency*acceptance correction factors C(Z+c) and C(Z+b), cross section sigma(Z+c)B and cross section ratios sigma(Z+c)/sigma(Z+b) in...

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Data from Table 2

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Z+c and Z+b signal yields, differential cross section dsigma(Z+c)/dpTZ times branching ratio and differential cross sections ratio dsigma(Z+c)/dpTZ / dsigma(Z+b)/dpTZ...

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Data from Table 3

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Z+c and Z+b signal yields, differential cross section dsigma(Z+c)/dpTZ times branching ratio and differential cross sections ratio dsigma(Z+c)/dpTZ / dsigma(Z+b)/dpTZ...

• #### Table 4 upper

Data from Table 4 upper

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Differential cross section dsigma(Z+c)/dpTZ times branching ratio and differential cross sections ratio dsigma(Z+c)/dpTZ / dsigma(Z+b)/dpTZ for three ranges of the...

• #### Table 4 lower

Data from Table 4 lower

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Differential cross section dsigma(Z+c)/dpTjet times branching ratio and differential cross sections ratio dsigma(Z+c)/dpTZ / dsigma(Z+b)/dpTjet for three ranges of the...

• #### Figure 1 a

Figure 1 a

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Transverse momentum distribution of the selected muon-inside-a-jet for events with an identified muon among the jet constituents in the dielectron...

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Figure 1 b

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Transverse momentum distribution of the selected muon-inside-a-jet for events with an identified muon among the jet constituents in the dimuon...

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Figure 2 a

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The invariant mass distribution of three-prong secondary vertices for events selected in the D± mode, in the dielectron channel

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Figure 2 b

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The invariant mass distribution of three-prong secondary vertices for events selected in the D ± mode, in the dimuon channel

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Figure 3 a

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The invariant mass distribution of the three-track system composed of a two-prong secondary vertex and a primary particle for events...

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Figure 3 b

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The invariant mass distribution of the three-track system composed of a two-prong secondary vertex and a primary particle for events...

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Figure 4 a

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Transverse momentum distribution of the c-tagged jet normalized to unity, in simulated W+c and Z+c samples and in W+c data...

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Figure 4 b

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Number of reconstructed secondary vertices normalized to unity, in simulated W+c and Z+c samples and in W+c data events.

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Figure 5 a

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Distribution of the corrected secondary-vertex mass normalized to unity, in simulated W + c and Z + c samples, and...

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Figure 5 b

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Distribution of the JP discriminant for the D± mode normalized to unity, in simulated W + c and Z +...

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Figure 5 c

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Distribution of the JP discriminant for the D∗(2010) ± mode normalized to unity, in simulated W + c and Z...

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Figure 6

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Distribution of the corrected secondary-vertex mass normalized to unity from simulated Z + b and eμ-tt data events

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Figure 7 a

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Corrected secondary-vertex mass distributions, after background subtraction in the dielectron channel for events selected in the semileptonic mode.

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Figure 7 b

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Corrected secondary-vertex mass distributions, after background subtraction in the dimuon channel for events selected in the semileptonic mode.

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Figure 8a

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Background-subtracted distributions of the JP discriminant in the dielectron channel for Z + jets events with a D± → K∓...

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Figure 8 b

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Background-subtracted distributions of the JP discriminant in the dimuon channel for Z + jets events with a D± → K∓...

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Figure 9 a

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Background-subtracted distributions of the JP discriminant in the dielectron channel for Z +jets events with a D∗(2010)± → D0 π±...

• #### Figure 9 b

Figure 9 b

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Background-subtracted distributions of the JP discriminant in the dimuon channel for Z +jets events with a D∗(2010)± → D0 π±...

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Figure 10

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ontributions to the systematic uncertainty in the measured Z+c cross section and in the (Z+c)/(Z+b) cross section ratio.

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Figure 11 a

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Differential Z + c cross section as a function of the transverse momentum of the Z boson

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Figure 11 b

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(Z +c)/(Z +b) cross section ratio as a function of the transverse momentum of teh Z boson

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Figure 11 c

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Differential Z + c cross section as a function of the transverse momentum of the jet

• #### Figure 11 d

Figure 11 d

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(Z +c)/(Z +b) cross section ratio as a function of the transverse momentum of the jet.