CMSFSQ13010 ; CERNEP2016191  
Studies of inclusive fourjet production with two btagged jets in protonproton collisions at 7 TeV  
CMS Collaboration  
12 September 2016  
Phys. Rev. D 94 (2016) 112005  
Abstract: Measurements are presented of the cross section for the production of at least four jets, of which at least two originate from b quarks, in protonproton collisions. Data collected with the CMS detector at the LHC at a centerofmass energy of 7 TeV are used, corresponding to an integrated luminosity of 3 pb$^{1}$. The cross section is measured as a function of the jet transverse momentum for $p_{\mathrm{T}} > $ 20 GeV, and of the jet pseudorapidity for $  {\eta}  < $ 2.4 (b jets), 4.7 (untagged jets). The correlations in azimuthal angle and $p_{\mathrm{T}}$ between the jets are also studied. The inclusive cross section is measured to be $\sigma(\mathrm{ p }\mathrm{ p }\to 2 \mathrm{ b } + 2 \mathrm{j} + \mathrm{X}) =$ 69 $\pm$ 3 (stat) $\pm$ 24 (syst) nb. The $\eta$ and $ p_{\mathrm{T}}$ distributions of the four jets and the correlations between them are well reproduced by event generators that combine perturbative QCD calculations at nexttoleadingorder accuracy with contributions from parton showers and multiparton interactions.  
Links: eprint arXiv:1609.03489 [hepex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; 
Figures  
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Figure 1:
Uncorrected transverse momentum (left) and pseudorapidity (right) distributions of data and simulations (PYTHIA 6 and HERWIG++) for the leading btagged (top) and leading untagged (bottom) jets. Only statistical uncertainties are shown. 
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Figure 1a:
Uncorrected transverse momentum distribution of data and simulations (PYTHIA 6 and HERWIG++) for the leading btagged jet. Only statistical uncertainties are shown. 
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Figure 1b:
Uncorrected pseudorapidity distribution of data and simulations (PYTHIA 6 and HERWIG++) for the leading btagged jet. Only statistical uncertainties are shown. 
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Figure 1c:
Uncorrected transverse momentum distribution of data and simulations (PYTHIA 6 and HERWIG++) for the leading untagged jet. Only statistical uncertainties are shown. 
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Figure 1d:
Uncorrected pseudorapidity distribution of data and simulations (PYTHIA 6 and HERWIG++) for the leading untagged jet. Only statistical uncertainties are shown. 
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Figure 2:
Response matrices obtained with the PYTHIA 6 tune Z2* simulation for the transverse momentum (left) and pseudorapidity (right) of the leading btagged (top) and leading untagged (bottom) jets. 
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Figure 2a:
Response matrices obtained with the PYTHIA 6 tune Z2* simulation for the transverse momentum of the leading btagged jet. 
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Figure 2b:
Response matrices obtained with the PYTHIA 6 tune Z2* simulation for the pseudorapidity of the leading btagged jet. 
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Figure 2c:
Response matrices obtained with the PYTHIA 6 tune Z2* simulation for the transverse momentum of the leading untagged jet. 
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Figure 2d:
Response matrices obtained with the PYTHIA 6 tune Z2* simulation for the pseudorapidity of the leading untagged jet. 
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Figure 3:
Differential cross sections unfolded to the particle level as a function of the jet transverse momenta $ {p_{\mathrm {T}}} $ (left) and pseudorapidity $\eta $ (right) compared to predictions of POWHEG+PYTHIA 8 tune CUETS1. Scale factors of $10^8$, $10^6$, and $10^2$ are applied (for clarity) to the measurement of the leading, subleading, and third jet, respectively. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. The band represents the theoretical uncertainty due to the choice of the scales and PDFs. 
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Figure 3a:
Differential cross sections unfolded to the particle level as a function of the jet transverse momenta $ {p_{\mathrm {T}}} $ compared to predictions of POWHEG+PYTHIA 8 tune CUETS1. Scale factors of $10^8$, $10^6$, and $10^2$ are applied (for clarity) to the measurement of the leading, subleading, and third jet, respectively. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. The band represents the theoretical uncertainty due to the choice of the scales and PDFs. 
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Figure 3b:
Differential cross sections unfolded to the particle level as a function of the jet pseudorapidity $\eta $ compared to predictions of POWHEG+PYTHIA 8 tune CUETS1. Scale factors of $10^8$, $10^6$, and $10^2$ are applied (for clarity) to the measurement of the leading, subleading, and third jet, respectively. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. The band represents the theoretical uncertainty due to the choice of the scales and PDFs. 
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Figure 4:
Ratios of the absolute cross section predictions of POWHEG, MadGraph, PYTHIA 6 (P6), PYTHIA 8 (P8), and HERWIG++ over data (unfolded to the particle level) as a function of the jet transverse momenta $ {p_{\mathrm {T}}} $ for each jet. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG ratio for clarity, but affecting all predictions in the same way). 
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Figure 5:
Ratios of the absolute cross section predictions of POWHEG, MadGraph, PYTHIA 6 (P6), PYTHIA 8 (P8), and HERWIG++ over data (unfolded to the particle level) as a function of the jet pseudorapidity $\eta $ for each jet. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG ratio for clarity, but affecting all predictions in the same way). 
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Figure 6:
Normalized cross sections unfolded to the particle level as a function of $\Delta \phi ^{\text {light}}$, compared to predictions of POWHEG, MadGraph, PYTHIA 8 (P8), and HERWIG++ (left), and of the POWHEG+PYTHIA 8 tune CUETS1 without MPI (right). The lower panels show the ratios of the MC predictions over the data. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG line for clarity, but affecting all predictions in the same way). 
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Figure 6a:
Normalized cross sections unfolded to the particle level as a function of $\Delta \phi ^{\text {light}}$, compared to predictions of POWHEG, MadGraph, PYTHIA 8 (P8), and HERWIG++. The lower panels show the ratios of the MC predictions over the data. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG line for clarity, but affecting all predictions in the same way). 
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Figure 6b:
Normalized cross sections unfolded to the particle level as a function of $\Delta \phi ^{\text {light}}$, compared to predictions of the POWHEG+PYTHIA 8 tune CUETS1 without MPI. The lower panels show the ratios of the MC predictions over the data. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG line for clarity, but affecting all predictions in the same way). 
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Figure 7:
Normalized cross sections unfolded to the particle level as a function of $\Delta ^{\text {rel}}_{\text {light}} {p_{\mathrm {T}}} $, compared to predictions of POWHEG, MadGraph, PYTHIA 8 (P8), and HERWIG++ (left), and of the POWHEG+PYTHIA 8 tune CUETS1 without MPI (right). The lower panels show the ratios of the MC predictions over the data. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG line for clarity, but affecting all predictions in the same way). 
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Figure 7a:
Normalized cross sections unfolded to the particle level as a function of $\Delta ^{\text {rel}}_{\text {light}} {p_{\mathrm {T}}} $, compared to predictions of POWHEG, MadGraph, PYTHIA 8 (P8), and HERWIG++. The lower panels show the ratios of the MC predictions over the data. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG line for clarity, but affecting all predictions in the same way). 
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Figure 7b:
Normalized cross sections unfolded to the particle level as a function of $\Delta ^{\text {rel}}_{\text {light}} {p_{\mathrm {T}}} $, compared to predictions of the POWHEG+PYTHIA 8 tune CUETS1 without MPI. The lower panels show the ratios of the MC predictions over the data. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG line for clarity, but affecting all predictions in the same way). 
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Figure 8:
Normalized cross sections unfolded to the particle level as a function of $\Delta $S, compared to predictions of POWHEG, MadGraph, PYTHIA 8 (P8), and HERWIG++ (left), and of the POWHEG+PYTHIA 8 tune CUETS1 without MPI (right). The lower panels show the ratios of the MC predictions over the data. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG line for clarity, but affecting all predictions in the same way). 
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Figure 8a:
Normalized cross sections unfolded to the particle level as a function of $\Delta $S, compared to predictions of POWHEG, MadGraph, PYTHIA 8 (P8), and HERWIG++. The lower panels show the ratios of the MC predictions over the data. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG line for clarity, but affecting all predictions in the same way). 
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Figure 8b:
Normalized cross sections unfolded to the particle level as a function of $\Delta $S, compared to predictions of the POWHEG+PYTHIA 8 tune CUETS1 without MPI. The lower panels show the ratios of the MC predictions over the data. The error bars on the data represent the total uncertainties, i.e., statistical and systematic added quadratically. Data are shown with markers at unity. The band represents the theoretical uncertainty due to the choice of the scales and PDFs (shown only around the POWHEG line for clarity, but affecting all predictions in the same way). 
Tables  
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Table 1:
Phase space for the cross section measurement. 
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Table 2:
Systematic and statistical uncertainties affecting the absolute and the normalized cross sections for each measured observable: each source of uncertainty is specified and the value is the average over all the bins of the observable. The 4% uncertainty from the integrated luminosity is included in the total uncertainty affecting the absolute cross sections. The total uncertainty is obtained by summing the individual experimental uncertainties quadratically. The theoretical uncertainties, listed in the last two columns, affect all the predictions. The systematic uncertainties in the normalized cross sections are smaller than those for the absolute cross sections, since, among others, they are not affected by the migration effects from outside the selected phase space. 
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Table 3:
Inclusive cross section for $\mathrm{ p } \mathrm{ p } \to 2 \mathrm{ b } + 2 {\mathrm {j}} + \mathrm{X} $ for jet $ {p_{\mathrm {T}}} > $ 20 GeV, with b jets within $ { \eta  }< $ 2.4, and the other jets within $ { \eta  }< $ 4.7. The measurements are compared to the MC predictions. 
Summary 
A study of events with at least four jets, at least two of which are b jets, in protonproton collisions at 7 TeV is presented. The data, corresponding to an integrated luminosity of 3 pb$^{1}$, were collected with the CMS experiment in 2010. The two b jets must be within pseudorapidity $  {\eta}  < $ 2.4, and the two other jets must be within $  {\eta}  < $ 4.7. The transverse momenta of all the jets are required to be greater than 20 GeV. The cross section is measured to be $\sigma(\mathrm{ p }\mathrm{ p } \to 2 \mathrm{ b } + 2 \mathrm{j} + \mathrm{X}) = $ 69 $\pm$ 3 (stat) $\pm$ 24 (syst) nb. The differential cross sections as a function of the $ p_{\mathrm{T}} $ and $\eta$ of each of the four jets are presented, along with the cross sections as a function of kinematic jet correlation variables. The results are compared to several theoretical predictions with and without contributions from double parton scattering. The models based on leading order or nexttoleadingorder dijet matrix element calculations, matched to parton shower and including multiparton interaction (MPI) contributions, describe well the differential cross sections as a function of $ p_{\mathrm{T}} $ and $\eta$ in the whole measured region. The differential cross sections as a function of the jet correlation variables are poorly reproduced by models that do not include contributions from MPI. Specifically, the predictions of POWHEG interfaced with PYTHIA 8 without the simulation of multiple parton interactions underestimate the cross sections as a function of $\Delta \mathrm{S} $ and $\Delta^{\text{rel}}_{\text{light}}p_{\mathrm{T}}$ in the regions of the phase space where a double parton scattering (DPS) signal is expected. These results demonstrate, for the first time, the sensitivity of kinematic jet correlation variables, such as $\Delta \mathrm{S} $ and $\Delta^{\text{rel}}_{\text{light}}p_{\mathrm{T}}$, to DPS processes in multijet final states with heavyquarks. 
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