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| CMS-PAS-HIN-24-007 | ||
| Exploring small-angle emissions in prompt D$ ^0 $ jets in proton-proton collisions at $ \sqrt{s} = $ 5.02 TeV | ||
| CMS Collaboration | ||
| 6 August 2024 | ||
| Abstract: This note presents a measurement of the angular structure of jets containing a prompt D$ ^0 $ meson and of inclusive jets in proton-proton (pp) collisions at the LHC at a center-of-mass energy of 5.02 TeV. The measurement uses collision data collected by the CMS experiment in 2017, corresponding to an integrated luminosity of 301 pb$ ^{-1} $. Two jet grooming algorithms, late-$ k_\mathrm{T} $ and soft drop, are used to study the intrajet radiation pattern of these jets using the iterative Cambridge-Aachen declustering. The late-$ k_\mathrm{T} $ algorithm selects hard collinear emissions, such that the sensitivity to the charm quark mass is enhanced with strong resilience to soft- and wide-angle radiation and to gluon splitting to charm quark-antiquark pairs. In contrast to the late-$ k_\mathrm{T} $ algorithm, the soft-drop grooming algorithm tends to select emissions at larger angles, with reduced sensitivity to the charm quark mass and enhanced contributions from gluon splitting to charm quark-antiquark pairs. The splitting angle distributions obtained with these two algorithms show that there is a shift of the distribution of prompt D$ ^0 $ jets with respect to inclusive jets for jet transverse momentum of 100 $ < p_\mathrm{T}^\text{jet} < $ 120 GeV. The shift observed in late-$ k_\mathrm{T} $ is consistent with the dead cone effect, whereas the shift for splittings selected with soft drop appears to be dominated by gluon splitting to charm quark-antiquark effects. The measured distributions are corrected to the particle level and set constraints on the substructure of high-$ p_\mathrm{T} $ charm quark jets. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Left: Schematic diagram of two subjets, with their splitting angle $ \theta $ and the relative transverse momentum $ k_{\mathrm{T}} $ of the softer subjet with respect to the harder subjet. Right: Different Lund jet plane regions for charm quark jet showers. The vertical axis is the logarithm of the relative momentum $ k_{\mathrm{T}} $ of the emission and $ \theta $ the angle between the emission and the emitter. Gluon splitting to charm quark-antiquark pairs contribute primarily at large angles $ \theta $, hadronization effects contribute primarily to low $ k_{\mathrm{T}} < $ 1 GeV and the dead cone effect located at small angles. |
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Figure 1-a:
Left: Schematic diagram of two subjets, with their splitting angle $ \theta $ and the relative transverse momentum $ k_{\mathrm{T}} $ of the softer subjet with respect to the harder subjet. Right: Different Lund jet plane regions for charm quark jet showers. The vertical axis is the logarithm of the relative momentum $ k_{\mathrm{T}} $ of the emission and $ \theta $ the angle between the emission and the emitter. Gluon splitting to charm quark-antiquark pairs contribute primarily at large angles $ \theta $, hadronization effects contribute primarily to low $ k_{\mathrm{T}} < $ 1 GeV and the dead cone effect located at small angles. |
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Figure 1-b:
Left: Schematic diagram of two subjets, with their splitting angle $ \theta $ and the relative transverse momentum $ k_{\mathrm{T}} $ of the softer subjet with respect to the harder subjet. Right: Different Lund jet plane regions for charm quark jet showers. The vertical axis is the logarithm of the relative momentum $ k_{\mathrm{T}} $ of the emission and $ \theta $ the angle between the emission and the emitter. Gluon splitting to charm quark-antiquark pairs contribute primarily at large angles $ \theta $, hadronization effects contribute primarily to low $ k_{\mathrm{T}} < $ 1 GeV and the dead cone effect located at small angles. |
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Figure 2:
Comparison of the ln(1/$ \theta_{l} $) distributions for different windows of the invariant mass of the track pairs and the inclusive jets selection. The black rectangles represent the selection for $ \mathrm{D^0} $ meson candidates in the resonance region (dominated by signal $ \mathrm{D^0} $ meson candidates), the red circles represent $ \mathrm{D^0} $ meson candidates from the mass sideband region (dominated by combinatorial background), and green triangles represent the inclusive jet. In the lower pannel, a ratio to nominal signal is shown. The error bands represent the statistical uncertainties. |
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Figure 3:
Left: Detector-level DCA significance distribution in data fitted with PYTHIA8 CP5 templates for prompt and nonprompt $ \mathrm{D^0} $ mesons contained in jets. In the lower panel, the ratio between the data and the fit values is presented. Right: Measured $ \mathrm{D^0} $ meson yields (black circles) and nonprompt $ \mathrm{D^0} $ meson contribution (filled histogram) as function of the late $ k_{\mathrm{T}} $ splitting angle $ \theta_l $. |
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Figure 3-a:
Left: Detector-level DCA significance distribution in data fitted with PYTHIA8 CP5 templates for prompt and nonprompt $ \mathrm{D^0} $ mesons contained in jets. In the lower panel, the ratio between the data and the fit values is presented. Right: Measured $ \mathrm{D^0} $ meson yields (black circles) and nonprompt $ \mathrm{D^0} $ meson contribution (filled histogram) as function of the late $ k_{\mathrm{T}} $ splitting angle $ \theta_l $. |
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Figure 3-b:
Left: Detector-level DCA significance distribution in data fitted with PYTHIA8 CP5 templates for prompt and nonprompt $ \mathrm{D^0} $ mesons contained in jets. In the lower panel, the ratio between the data and the fit values is presented. Right: Measured $ \mathrm{D^0} $ meson yields (black circles) and nonprompt $ \mathrm{D^0} $ meson contribution (filled histogram) as function of the late $ k_{\mathrm{T}} $ splitting angle $ \theta_l $. |
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Figure 4:
The unfolded late-$ k_{\mathrm{T}} $ angular distribution for prompt $ \mathrm{D^0} $ jets (left) and inclusive jets (right) compared with predictions from PYTHIA8 CP5 and HERWIG 7 CH3. The error bands in the upper panel represent the total systematical uncertainty, whereas the vertical bars represent the statistical uncertainties. In the lower panel, the error band in the ratio plot represents the total experimental uncertainty from the measurement. |
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Figure 4-a:
The unfolded late-$ k_{\mathrm{T}} $ angular distribution for prompt $ \mathrm{D^0} $ jets (left) and inclusive jets (right) compared with predictions from PYTHIA8 CP5 and HERWIG 7 CH3. The error bands in the upper panel represent the total systematical uncertainty, whereas the vertical bars represent the statistical uncertainties. In the lower panel, the error band in the ratio plot represents the total experimental uncertainty from the measurement. |
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Figure 4-b:
The unfolded late-$ k_{\mathrm{T}} $ angular distribution for prompt $ \mathrm{D^0} $ jets (left) and inclusive jets (right) compared with predictions from PYTHIA8 CP5 and HERWIG 7 CH3. The error bands in the upper panel represent the total systematical uncertainty, whereas the vertical bars represent the statistical uncertainties. In the lower panel, the error band in the ratio plot represents the total experimental uncertainty from the measurement. |
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Figure 5:
The unfolded soft-drop angular distribution for prompt $ \mathrm{D^0} $ jets (left) and inclusive jets (right) compared with predictions from PYTHIA8 CP5 and HERWIG 7 CH3. The error bands in the upper panel represent the total systematical uncertainty, whereas the vertical bars represent the statistical uncertainties. In the lower panel, the error band in the ratio plot represents the total experimental uncertainty from the measurement. |
png pdf |
Figure 5-a:
The unfolded soft-drop angular distribution for prompt $ \mathrm{D^0} $ jets (left) and inclusive jets (right) compared with predictions from PYTHIA8 CP5 and HERWIG 7 CH3. The error bands in the upper panel represent the total systematical uncertainty, whereas the vertical bars represent the statistical uncertainties. In the lower panel, the error band in the ratio plot represents the total experimental uncertainty from the measurement. |
png pdf |
Figure 5-b:
The unfolded soft-drop angular distribution for prompt $ \mathrm{D^0} $ jets (left) and inclusive jets (right) compared with predictions from PYTHIA8 CP5 and HERWIG 7 CH3. The error bands in the upper panel represent the total systematical uncertainty, whereas the vertical bars represent the statistical uncertainties. In the lower panel, the error band in the ratio plot represents the total experimental uncertainty from the measurement. |
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Figure 6:
The late-$ k_{\mathrm{T}} $ (upper plot) and modified soft-drop (lower plot) angular distribution for prompt $ \mathrm{D^0} $ jets and inclusive jets. It the lower panels, the ratio to the inclusive jets is shown. The error band represents the total systematic uncertainty, whereas the vertical bars represent the statistical uncertainties. |
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Figure 6-a:
The late-$ k_{\mathrm{T}} $ (upper plot) and modified soft-drop (lower plot) angular distribution for prompt $ \mathrm{D^0} $ jets and inclusive jets. It the lower panels, the ratio to the inclusive jets is shown. The error band represents the total systematic uncertainty, whereas the vertical bars represent the statistical uncertainties. |
png pdf |
Figure 6-b:
The late-$ k_{\mathrm{T}} $ (upper plot) and modified soft-drop (lower plot) angular distribution for prompt $ \mathrm{D^0} $ jets and inclusive jets. It the lower panels, the ratio to the inclusive jets is shown. The error band represents the total systematic uncertainty, whereas the vertical bars represent the statistical uncertainties. |
png pdf |
Figure 7:
The ratio of the late-$ k_{\mathrm{T}} $ angle distributions (left panel) and SD angle (right panel) for prompt $ \mathrm{D^0} $ jets to inclusive jets, the data are compared with PYTHIA8 CP5 and HERWIG 7 CH3 with and without gluon splitting to charm quark-antiquark pairs. |
png pdf |
Figure 7-a:
The ratio of the late-$ k_{\mathrm{T}} $ angle distributions (left panel) and SD angle (right panel) for prompt $ \mathrm{D^0} $ jets to inclusive jets, the data are compared with PYTHIA8 CP5 and HERWIG 7 CH3 with and without gluon splitting to charm quark-antiquark pairs. |
png pdf |
Figure 7-b:
The ratio of the late-$ k_{\mathrm{T}} $ angle distributions (left panel) and SD angle (right panel) for prompt $ \mathrm{D^0} $ jets to inclusive jets, the data are compared with PYTHIA8 CP5 and HERWIG 7 CH3 with and without gluon splitting to charm quark-antiquark pairs. |
| Tables | |
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Table 1:
Summary of percentual relative uncertainties. |
| Summary |
| This note has presented a measurement of the substructure of jets containing prompt $ \mathrm{D^0} $ mesons and of inclusive jets in proton-proton (pp) collisions at a collision energy of $ \sqrt{s} = $ 5.02 TeV, corresponding to an integrated luminosity of 301 pb$^{-1}$, collected in 2017 with the CMS experiment. The analysis focuses on the substructure of jets initially clustered with the anti-$ k_{\mathrm{T}} $ algorithm and a distance parameter of $ R = $ 0.2 with transverse momentum 100 $ < p_{\mathrm{T}}^\text{jet} < $ 120 GeV and pseudorapidity $ |\eta| < $ 1.6. Both neutral and charged particles are used for the substructure of these jets. The $ \mathrm{D^0} $ meson is identified via its two-pronged decay into a kaon and pion pair. The analysis focuses on the opening angle between the subjet pair found with two different grooming algorithms that are based on Cambridge-Aachen (CA) reclustering. The angular separation between the two hard subjets found with the soft-drop grooming algorithm is studied, using the parameters $ z_\text{cut} = $ 0.1 and $ \beta = $ 0, with the additional requirement that the emission has a minimum relative transverse momentum of $ k_{\mathrm{T}} > $ 1 GeV. The splitting angle distribution, in this case, is sensitive to contributions from $ \mathrm{g} \to \mathrm{c} \bar{\mathrm{c}} $ splitting at large angles and has sensitivity to the dead cone effect for small-angle emissions. The late-$ k_{\mathrm{T}} $ grooming algorithm, distinct from the soft-drop grooming case, gives access to hard, collinear emissions in an algorithmic way. The late-$ k_{\mathrm{T}} $ algorithm consists of selecting the last splitting with a $ k_{\mathrm{T}} > $ 1 GeV in the CA tree. The resulting angular distribution is more resilient to $ \mathrm{g} \to \mathrm{c} \bar{\mathrm{c}} $ splittings and to soft- and wide-angle radiation, and is more sensitive to the dead cone effect. A stronger suppression with respect to the inclusive jet baseline is observed, as expected from the dead cone effect. This is the first measurement of charm quark jet substructure that probes the hard and collinear region of the jet shower, in a way such that the contribution from hadronization effects is reduced and the connection with the expected parton-level shower is more direct. The jet $ p_{\mathrm{T}} > $ 100 GeV selection, used for the first time for charm quark jet substructure, increases the phase space available for an interpretation of the jet substructure in terms of perturbation theory calculations. Although the jet $ p_{\mathrm{T}} $ is much larger than the charm quark mass, it is possible to isolate hard collinear emissions and observe the suppression due to the charm quark mass in the hard and collinear region. |
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