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| CMS-PAS-BPH-23-005 | ||
| Search for $ CP $ violation in $ \mathrm{D}^0\to\mathrm{K}^0_{\mathrm{S}}\mathrm{K}^0_{\mathrm{S}} $ decay from proton-proton collisions at 13 TeV | ||
| CMS Collaboration | ||
| 26 March 2024 | ||
| Abstract: A search is reported for $ CP $ violation in the $ \mathrm{D}^0\to\mathrm{K}^0_{\mathrm{S}}\mathrm{K}^0_{\mathrm{S}} $ decay, using data collected from proton-proton collisions at $ \sqrt{s} = $ 13 TeV recorded by the CMS experiment in 2018. A dedicated data set of about 10 billion events containing a pair of b hadrons, nearly all of which decay to charm hadrons, is used. The flavor of the neutral D meson is determined by the pion charge in the reconstructed decays $ \mathrm{D}^{*+}\to\mathrm{D}^0\pi^+ $ and $ \mathrm{D}^{*-}\to\overline{\mathrm{D}}^0\pi^- $. The $ CP $ asymmetry in $ \mathrm{D}^0\to\mathrm{K}^0_{\mathrm{S}}\mathrm{K}^0_{\mathrm{S}} $ is measured to be $ A_{CP}(\mathrm{K}^0_{\mathrm{S}}\mathrm{K}^0_{\mathrm{S}}) = $ 6.2 $ \pm $ 3.0 (stat) $\pm$ 0.2 (syst) $\pm$ 0.8 $(A_{CP}(\mathrm{K}^0_{\mathrm{S}}\pi^+\pi^-))$ %, where the last uncertainty is the $ CP $ asymmetry in the $ \mathrm{D}^0\to\mathrm{K}^0_{\mathrm{S}}\pi^+\pi^- $ decay. This result is consistent with no $ CP $ violation within 2 standard deviations. This is the first measurement of $ CP $ violation in the charm sector by the CMS experiment, and the first measurement of $ CP $ asymmetry in the fully hadronic final state performed by CMS at the nominal LHC luminosity, using the new data parking technique. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The decay of neutral charm meson $ \mathrm{D^0} $ (top) or $ \overline{\mathrm{D}}^{0} $ (bottom) to two neutral kaons: exchange diagram (left) and penguin annihilation diagram (right). |
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Figure 1-a:
The decay of neutral charm meson $ \mathrm{D^0} $ (top) or $ \overline{\mathrm{D}}^{0} $ (bottom) to two neutral kaons: exchange diagram (left) and penguin annihilation diagram (right). |
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Figure 1-b:
The decay of neutral charm meson $ \mathrm{D^0} $ (top) or $ \overline{\mathrm{D}}^{0} $ (bottom) to two neutral kaons: exchange diagram (left) and penguin annihilation diagram (right). |
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Figure 1-c:
The decay of neutral charm meson $ \mathrm{D^0} $ (top) or $ \overline{\mathrm{D}}^{0} $ (bottom) to two neutral kaons: exchange diagram (left) and penguin annihilation diagram (right). |
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Figure 1-d:
The decay of neutral charm meson $ \mathrm{D^0} $ (top) or $ \overline{\mathrm{D}}^{0} $ (bottom) to two neutral kaons: exchange diagram (left) and penguin annihilation diagram (right). |
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Figure 2:
Simultaneous fit of the $ \mathrm{D}^{*+} $ (left) and $ \mathrm{D}^{*-} $ (right) candidate invariant mass distributions in the $ \mathrm{K^0_S}\pi^{+}\pi^{-} $ channel. |
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Figure 2-a:
Simultaneous fit of the $ \mathrm{D}^{*+} $ (left) and $ \mathrm{D}^{*-} $ (right) candidate invariant mass distributions in the $ \mathrm{K^0_S}\pi^{+}\pi^{-} $ channel. |
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Figure 2-b:
Simultaneous fit of the $ \mathrm{D}^{*+} $ (left) and $ \mathrm{D}^{*-} $ (right) candidate invariant mass distributions in the $ \mathrm{K^0_S}\pi^{+}\pi^{-} $ channel. |
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Figure 3:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}) \times\ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distribution for the signal channel, for $ \mathrm{D}^{*+} $ (left) and $ \mathrm{D}^{*-} $ (right) candidates: projections of the 2D fit on the $ m(\mathrm{D}\pi^{\pm}) $ (top) and $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ (bottom) axes. |
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Figure 3-a:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}) \times\ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distribution for the signal channel, for $ \mathrm{D}^{*+} $ (left) and $ \mathrm{D}^{*-} $ (right) candidates: projections of the 2D fit on the $ m(\mathrm{D}\pi^{\pm}) $ (top) and $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ (bottom) axes. |
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Figure 3-b:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}) \times\ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distribution for the signal channel, for $ \mathrm{D}^{*+} $ (left) and $ \mathrm{D}^{*-} $ (right) candidates: projections of the 2D fit on the $ m(\mathrm{D}\pi^{\pm}) $ (top) and $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ (bottom) axes. |
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Figure 3-c:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}) \times\ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distribution for the signal channel, for $ \mathrm{D}^{*+} $ (left) and $ \mathrm{D}^{*-} $ (right) candidates: projections of the 2D fit on the $ m(\mathrm{D}\pi^{\pm}) $ (top) and $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ (bottom) axes. |
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Figure 3-d:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}) \times\ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distribution for the signal channel, for $ \mathrm{D}^{*+} $ (left) and $ \mathrm{D}^{*-} $ (right) candidates: projections of the 2D fit on the $ m(\mathrm{D}\pi^{\pm}) $ (top) and $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ (bottom) axes. |
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Figure 4:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*+} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \mathrm{D^0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 4-a:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*+} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \mathrm{D^0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 4-b:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*+} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \mathrm{D^0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 4-c:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*+} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \mathrm{D^0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 4-d:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*+} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \mathrm{D^0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 4-e:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*+} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \mathrm{D^0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 4-f:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*+} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \mathrm{D^0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 4-g:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*+} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \mathrm{D^0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 5:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*-} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \overline{\mathrm{D}}^{0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 5-a:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*-} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \overline{\mathrm{D}}^{0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 5-b:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*-} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \overline{\mathrm{D}}^{0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 5-c:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*-} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \overline{\mathrm{D}}^{0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 5-d:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*-} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \overline{\mathrm{D}}^{0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 5-e:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*-} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \overline{\mathrm{D}}^{0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 5-f:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*-} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \overline{\mathrm{D}}^{0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
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Figure 5-g:
Results of the 2D fit to $ m(\mathrm{D}\pi^{\pm}):m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel in measured data, $ \mathrm{D}^{*-} $ candidates. Top row: the projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (left) and signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (right). Middle row: projections of the 2D fit on $ m(\mathrm{D}\pi^{\pm}) $ in the ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (left) and right sideband (right). Bottom row: projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in the ranges of $ m(\mathrm{D}\pi^{\pm}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). The green line corresponds to the signal component, the blue short-dashed line shows the combinatorial background, the purple long-dashed line shows the combinations of $ \overline{\mathrm{D}}^{0} $ with background pions, and the magenta dash-dotted line illustrates the contamination of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ decay. |
| Tables | |
png pdf |
Table 1:
Optimized selection criteria in the signal channel $ \mathrm{D^0}\to\mathrm{K^0_S}\mathrm{K^0_S} $. |
png pdf |
Table 2:
Results of the simultaneous fit to the selected $ \mathrm{D}^{*+}\to\mathrm{D^0}\pi^{+} $ and $ \mathrm{D}^{*-}\to\overline{\mathrm{D}}^{0}\pi^{-} $ candidates, where $ \mathrm{D^0}\,(\overline{\mathrm{D}}^{0}) \to\mathrm{K^0_S}\pi^{+}\pi^{-} $. The $ {\mathrm{D}^{\ast}(2010)^{\pm}} $ signal yields $ N $ given in the second column are used in the evaluation of $ A_{CP}^{\text{raw}} $. The uncertainties are statistical only. |
png pdf |
Table 3:
Results of the simultaneous 2D fit to the selected $ \mathrm{D}^{*+}\to\mathrm{D^0}\pi^{+} $ and $ \mathrm{D}^{*-}\to\overline{\mathrm{D}}^{0}\pi^{-} $ candidates, where $ \mathrm{D^0}\,(\overline{\mathrm{D}}^{0}) \to\mathrm{K^0_S}\mathrm{K^0_S} $. The yields $ N $ given in the second column correspond to the $ \mathrm{D^0} \,\times\,{\mathrm{D}^{\ast}(2010)^{\pm}} $ component in the 2D fit and are used in the evaluation of $ A_{CP}^{\text{raw}} $. The $ \chi^2 $ corresponds to the fit projection with 100 bins in the $ x=m(\mathrm{D}\pi^{\pm}) $ axis and 90 bins in the $ y=m(\mathrm{K^0_S}\mathrm{K^0_S}) $ axis, as shown in Fig 3. The uncertainties are statistical only. |
png pdf |
Table 4:
Absolute systematic uncertainties in the measurement of $ \Delta A_{CP} $. |
| Summary |
| This is the first CMS measurement of $ CP $ violation in the charm sector, paving the way for future measurements with more data, using refined techniques, and in different channels. |
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