CMS-PAS-EXO-16-032 | ||

Search for narrow resonances decaying to dijets in pp collisions at $\sqrt{s}=$ 13 TeV using 12.9 fb$^{-1}$ | ||

CMS Collaboration | ||

August 2016 | ||

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Abstract:
A search is presented for narrow resonances decaying to dijet final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV from an integrated luminosity of 12.9 fb$^{-1}$. Results are presented for two searches. A low-mass search, for a resonance mass between 0.6 TeV and 1.6 TeV, is performed using dijets that are reconstructed from calorimeter information in the high-level trigger. A high-mass search, for resonances with mass above 1.6 TeV, is performed using dijets reconstructed with the particle flow algorithm from the normal reconstruction chain. The pseudorapidity separation of the two jets is required to satisfy $|\Delta\eta_{\text{jj}}|< $ 1.3 with each jet inside the region $|\eta| < $ 2.5. The spectra are well described by a smooth parameterization and no significant evidence for new particle production is observed. Upper limits at 95% confidence level are reported on the production cross section times branching ratio to dijets times acceptance of the $|\Delta\eta_{\text{jj}}|$ and $|\eta|$ cuts for narrow resonances from quark-quark, quark-gluon and gluon-gluon final states. When interpreted in the context of specific models, the limits exclude string resonances with masses below 7.4 TeV, scalar diquarks below 6.9 TeV, axigluons and colorons below 5.5 TeV, excited quarks below 5.4 TeV, color-octet scalars below 3.0TeV, W' bosons below 2.7 TeV, Z' bosons below 2.1 TeV and between 2.3 to 2.6 TeV, and RS gravitons below 1.9 TeV, extending previously published limits in the dijet channel.
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PLB 769 (2017) 520.The superseded preliminary plots can be found here. |

Figures & Tables | Summary | Additional Figures & Tables | References | CMS Publications |
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Figures | |

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Figure 1-a:
Dijet mass spectrum (points) compared to a fitted parameterization of the background (solid curve) for the low-mass search (a) and the high-mass search (b). The lower panel in each plot shows the difference between the data and the fitted parametrization, divided by the statistical uncertainty of the data. Predicted signals from narrow gluon-gluon, quark-gluon, and quark-quark resonances are shown with cross section equal to the observed upper limit at 95% CL. |

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Figure 1-b:
Dijet mass spectrum (points) compared to a fitted parameterization of the background (solid curve) for the low-mass search (a) and the high-mass search (b). The lower panel in each plot shows the difference between the data and the fitted parametrization, divided by the statistical uncertainty of the data. Predicted signals from narrow gluon-gluon, quark-gluon, and quark-quark resonances are shown with cross section equal to the observed upper limit at 95% CL. |

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Figure 2-a:
The event with the highest dijet invariant mass: three dimensional view (a), 2D view in the $\rho $-$\phi $ plane (b). The ${p_{\mathrm {T}}} $, $\eta $, and $\phi $ values of the two wide jets are indicated. The invariant mass of the two wide jets is 7.7 TeV . |

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Figure 2-b:
The event with the highest dijet invariant mass: three dimensional view (a), 2D view in the $\rho $-$\phi $ plane (b). The ${p_{\mathrm {T}}} $, $\eta $, and $\phi $ values of the two wide jets are indicated. The invariant mass of the two wide jets is 7.7 TeV . |

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Figure 3-a:
The reconstructed resonance mass spectrum predicted by the PYTHIA-8 MC event generator including simulation of the detector. Resonances from quark-quark processes modeled by $ {\mathrm {q}} {\overline {\mathrm {q}}} \to {\mathrm {G}} \to {\mathrm {q}} {\overline {\mathrm {q}}} $ (blue), quark-gluon processes modeled by $ {\mathrm {q}} {\mathrm {g}} \to { {\mathrm {q}} ^*} \to {\mathrm {q}} {\mathrm {g}} $ (red), and gluon-gluon processes modeled by $ {\mathrm {g}} {\mathrm {g}} \to {\mathrm {G}} \to {\mathrm {g}} {\mathrm {g}} $ (black), where ${\mathrm {G}}$ is an RS graviton and ${ {\mathrm {q}} ^*}$ is an excited quark. (a) Resonances generated with a mass of 750 GeV are shown for wide jets from PF-jet reconstruction (solid) and calo-jet reconstruction (dashed). Also shown is a hypothetical Gaussian shape (dotted green) with a mean mass of 750 GeV and an RMS width equal to 10% of the mean mass. (b) Resonances generated with a mass of 1, 3, 5 and 7 TeV are shown for wide jets from PF-jet reconstruction. |

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Figure 3-b:
The reconstructed resonance mass spectrum predicted by the PYTHIA-8 MC event generator including simulation of the detector. Resonances from quark-quark processes modeled by $ {\mathrm {q}} {\overline {\mathrm {q}}} \to {\mathrm {G}} \to {\mathrm {q}} {\overline {\mathrm {q}}} $ (blue), quark-gluon processes modeled by $ {\mathrm {q}} {\mathrm {g}} \to { {\mathrm {q}} ^*} \to {\mathrm {q}} {\mathrm {g}} $ (red), and gluon-gluon processes modeled by $ {\mathrm {g}} {\mathrm {g}} \to {\mathrm {G}} \to {\mathrm {g}} {\mathrm {g}} $ (black), where ${\mathrm {G}}$ is an RS graviton and ${ {\mathrm {q}} ^*}$ is an excited quark. (a) Resonances generated with a mass of 750 GeV are shown for wide jets from PF-jet reconstruction (solid) and calo-jet reconstruction (dashed). Also shown is a hypothetical Gaussian shape (dotted green) with a mean mass of 750 GeV and an RMS width equal to 10% of the mean mass. (b) Resonances generated with a mass of 1, 3, 5 and 7 TeV are shown for wide jets from PF-jet reconstruction. |

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Figure 4-a:
Limits from the low-mass search. The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for quark-quark (a), quark-gluon (b), and gluon-gluon (c) type dijet resonances. The corresponding expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are also shown. (bottom right) The observed limits (solid) are summarized for fully simulated shapes from all three physical types of resonances along with the limit for a hypothetical Gaussian shape with RMS width equal to 10% of the mean mass. Limits are compared to the predicted cross sections of excited quarks [24,25], axigluons [21], colorons [23], scalar diquarks [20], RS gravitons [28], and new gauge bosons W' and Z' [27]. |

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Figure 4-b:
Limits from the low-mass search. The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for quark-quark (a), quark-gluon (b), and gluon-gluon (c) type dijet resonances. The corresponding expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are also shown. (bottom right) The observed limits (solid) are summarized for fully simulated shapes from all three physical types of resonances along with the limit for a hypothetical Gaussian shape with RMS width equal to 10% of the mean mass. Limits are compared to the predicted cross sections of excited quarks [24,25], axigluons [21], colorons [23], scalar diquarks [20], RS gravitons [28], and new gauge bosons W' and Z' [27]. |

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Figure 4-c:
Limits from the low-mass search. The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for quark-quark (a), quark-gluon (b), and gluon-gluon (c) type dijet resonances. The corresponding expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are also shown. (bottom right) The observed limits (solid) are summarized for fully simulated shapes from all three physical types of resonances along with the limit for a hypothetical Gaussian shape with RMS width equal to 10% of the mean mass. Limits are compared to the predicted cross sections of excited quarks [24,25], axigluons [21], colorons [23], scalar diquarks [20], RS gravitons [28], and new gauge bosons W' and Z' [27]. |

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Figure 4-d:
Limits from the low-mass search. The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for quark-quark (a), quark-gluon (b), and gluon-gluon (c) type dijet resonances. The corresponding expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are also shown. (bottom right) The observed limits (solid) are summarized for fully simulated shapes from all three physical types of resonances along with the limit for a hypothetical Gaussian shape with RMS width equal to 10% of the mean mass. Limits are compared to the predicted cross sections of excited quarks [24,25], axigluons [21], colorons [23], scalar diquarks [20], RS gravitons [28], and new gauge bosons W' and Z' [27]. |

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Figure 5-a:
Limits from the high-mass search. The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for quark-quark (a), quark-gluon (b), and gluon-gluon (c) type dijet resonances. The corresponding expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are also shown. (d) The observed limits (solid) are summarized. Limits are compared to the predicted cross sections of string resonances [18,19], excited quarks [24,25], axigluons [21], colorons [23], scalar diquarks [20], color-octet scalars [26], new gauge bosons W' and Z' [27], and RS gravitons [28]. |

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Figure 5-b:
Limits from the high-mass search. The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for quark-quark (a), quark-gluon (b), and gluon-gluon (c) type dijet resonances. The corresponding expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are also shown. (d) The observed limits (solid) are summarized. Limits are compared to the predicted cross sections of string resonances [18,19], excited quarks [24,25], axigluons [21], colorons [23], scalar diquarks [20], color-octet scalars [26], new gauge bosons W' and Z' [27], and RS gravitons [28]. |

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Figure 5-c:
Limits from the high-mass search. The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for quark-quark (a), quark-gluon (b), and gluon-gluon (c) type dijet resonances. The corresponding expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are also shown. (d) The observed limits (solid) are summarized. Limits are compared to the predicted cross sections of string resonances [18,19], excited quarks [24,25], axigluons [21], colorons [23], scalar diquarks [20], color-octet scalars [26], new gauge bosons W' and Z' [27], and RS gravitons [28]. |

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Figure 5-d:
Limits from the high-mass search. The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for quark-quark (a), quark-gluon (b), and gluon-gluon (c) type dijet resonances. The corresponding expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are also shown. (d) The observed limits (solid) are summarized. Limits are compared to the predicted cross sections of string resonances [18,19], excited quarks [24,25], axigluons [21], colorons [23], scalar diquarks [20], color-octet scalars [26], new gauge bosons W' and Z' [27], and RS gravitons [28]. |

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Figure 6:
Limits from both the low-mass and high-mass search. The observed 95% CL upper limits on the product of the cross section, branching fraction, and acceptance for quark-quark, quark-gluon, and gluon-gluon type dijet resonances. The observed limits (solid) are presented from the low mass search, for resonance masses between 0.6 TeV and 1.6 TeV , and from the high mass search for resonance masses greater than or equal to 1.6 TeV . Limits are compared to the predicted cross sections of string resonances [18,19], excited quarks [24,25], axigluons [21], colorons [23], scalar diquarks [20], color-octet scalars [26], new gauge bosons W' and Z' [27], and RS gravitons [28]. |

Tables | |

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Table 1:
Observed and expected mass limits at 95% CL from this analysis with 12.9 fb$^{-1}$ at $\sqrt {s}=$ 13 TeV compared to previously published limits on narrow resonances from CMS with 2.4 fb$^{-1}$ at $\sqrt {s}=$ 13 TeV [3] and with 20 fb$^{-1}$ at $\sqrt {s}=$ 8 TeV [9]. The listed models are excluded between 0.6 TeV and the indicated mass limit by this analysis. For the Z' model, in addition to the observed mass limit listed below, this analysis also excludes the mass interval between 2.3 and 2.6 TeV . |

Summary |

In summary, two searches for narrow resonances decaying into a pair of jets have been performed using pp collisions at $\sqrt{s}=$ 13 TeV corresponding to an integrated luminosity of 12.9 fb$^{-1}$. A low-mass search using data scouting from the HLT trigger with calorimeter jets and a high-mass search using particle flow jets. The dijet mass spectra have been measured to be smoothly falling distributions. In the analyzed data samples, there is no evidence for resonant particle production. We present generic upper limits on the product $\sigma\, B\, A$ for narrow quark-quark, quark-gluon and gluon-gluon resonances that are applicable to any model of narrow dijet resonance production. We set mass limits at 95% CL on models of string resonances, scalar diquarks, excited quarks, axigluons, colorons, color octet scalars, W' bosons, Z' bosons, and RS gravitons, which extend previously published limits in the dijet channel. |

Additional Figures | |

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Additional Figure 1:
The dijet mass of the two wide jets after all selection criteria are applied, for data from the low-mass search (points) and {{pythia} 8} MC with detector simulation (histogram) normalized to the data. |

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Additional Figure 2:
The azimuthal angle of the two wide jets after all selection criteria are applied, for data from the low-mass search (points) and {{pythia} 8} MC with detector simulation (histogram) normalized to the data. |

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Additional Figure 3:
The azimuthal angular separation between the two wide-jets after all selection criteria are applied, for data from the low-mass search (points) and {{pythia} 8} MC with detector simulation (histogram) normalized to the data. |

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Additional Figure 4:
The absolute difference in pseudorapidity between the two wide-jets after all selection criteria are applied, for data from the low-mass search (points) and {{pythia} 8} MC with detector simulation (histogram) normalized to the data. |

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Additional Figure 5:
The dijet mass of the two wide jets after all selection criteria are applied, for data from the high-mass search (points) and {{pythia} 8} MC with detector simulation (histogram) normalized to the data. |

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Additional Figure 6:
The azimuthal angle of the two wide jets after all selection criteria are applied, for data from the high-mass search (points) and {{pythia} 8} MC with detector simulation (histogram) normalized to the data. |

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Additional Figure 7:
The azimuthal angular separation between the two wide-jets after all selection criteria are applied, for data from the high-mass search (points) and {{pythia} 8} MC with detector simulation (histogram) normalized to the data. |

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Additional Figure 8:
The absolute difference in pseudorapidity between the two wide-jets after all selection criteria are applied, for data from the high-mass search (points) and {{pythia} 8} MC with detector simulation (histogram) normalized to the data. |

Additional Tables | |

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Additional Table 1:
Limits from the low-mass search. Observed and expected upper limits at 95% CL on $\sigma \times B \times A$ for a $\mathrm{g} \mathrm{g} $ resonance, a $\mathrm{ q } \mathrm{g} $ resonance, a $\mathrm{ q } \mathrm{ q } $ resonance, and a 10% Gaussian lineshape as a function of the resonance mass. |

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Additional Table 2:
Limits from the high-mass search. Observed and expected upper limits at 95% CL on $\sigma \times B \times A$ for a $\mathrm{g} \mathrm{g} $ resonance, a $\mathrm{ q } \mathrm{g} $ resonance, and a $\mathrm{ q } \mathrm{ q } $ resonance as a function of the resonance mass. |

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