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| CMS-BPH-23-005 ; CERN-EP-2024-120 | ||
| Search for CP violation in $ \mathrm{D^0}\to\mathrm{K^0_S}\mathrm{K^0_S} $ decays in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 19 May 2024 | ||
| Submitted to Eur. Phys. J. C | ||
| Abstract: A search is reported for charge-parity CP violation in $ \mathrm{D^0}\to\mathrm{K^0_S}\mathrm{K^0_S} $ decays, using data collected in proton-proton collisions at $ \sqrt{s} = $ 13 TeV recorded by the CMS experiment in 2018. The analysis uses a dedicated data set that corresponds to an integrated luminosity of 41.6 fb$ ^{-1} $, which consists of about 10 billion events containing a pair of b hadrons, nearly all of which decay to charm hadrons. The flavor of the neutral $ \mathrm{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_S}\mathrm{K^0_S} $ is measured to be $ A_{CP}(\mathrm{K^0_S}\mathrm{K^0_S}) = $ (6.2 $ \pm $ 3.0 $ \pm $ 0.2 $ \pm $ 0.8)%, where the three uncertainties represent the statistical uncertainty, the systematic uncertainty, and the uncertainty in the measurement of the CP asymmetry in the $ \mathrm{D^0}\to\mathrm{K^0_S}\pi^{+}\pi^{-} $ decay. This is the first CP asymmetry measurement by CMS in the charm sector as well as the first to utilize a fully hadronic final state. | ||
| Links: e-print arXiv:2405.11606 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The decay of neutral charm meson to two neutral kaons: exchange (left) and penguin annihilation (right) diagrams. |
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Figure 1-a:
The decay of neutral charm meson to two neutral kaons: exchange (left) and penguin annihilation (right) diagrams. |
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Figure 1-b:
The decay of neutral charm meson to two neutral kaons: exchange (left) and penguin annihilation (right) diagrams. |
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Figure 2:
The $ \mathrm{D^0}\pi^{+} $ (left) and $ \overline{\mathrm{D}}^{0}\pi^{-} $ (right) invariant mass distributions for the $ \mathrm{K^0_S}\pi^{+}\pi^{-} $ channel, with the result of the fit to both distributions. |
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Figure 2-a:
The $ \mathrm{D^0}\pi^{+} $ (left) and $ \overline{\mathrm{D}}^{0}\pi^{-} $ (right) invariant mass distributions for the $ \mathrm{K^0_S}\pi^{+}\pi^{-} $ channel, with the result of the fit to both distributions. |
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Figure 2-b:
The $ \mathrm{D^0}\pi^{+} $ (left) and $ \overline{\mathrm{D}}^{0}\pi^{-} $ (right) invariant mass distributions for the $ \mathrm{K^0_S}\pi^{+}\pi^{-} $ channel, with the result of the fit to both distributions. |
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Figure 3:
The invariant mass distributions for $ \mathrm{D}^{*+} $ candidates (left) and $ \mathrm{D}^{*-} $ candidates (right), with the $ m(\mathrm{D}\pi^{\pm}) $ distributions in the upper row and the $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distributions in the lower row. Projections of the simultaneous 2D fit are also shown. |
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Figure 3-a:
The invariant mass distributions for $ \mathrm{D}^{*+} $ candidates (left) and $ \mathrm{D}^{*-} $ candidates (right), with the $ m(\mathrm{D}\pi^{\pm}) $ distributions in the upper row and the $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distributions in the lower row. Projections of the simultaneous 2D fit are also shown. |
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Figure 3-b:
The invariant mass distributions for $ \mathrm{D}^{*+} $ candidates (left) and $ \mathrm{D}^{*-} $ candidates (right), with the $ m(\mathrm{D}\pi^{\pm}) $ distributions in the upper row and the $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distributions in the lower row. Projections of the simultaneous 2D fit are also shown. |
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Figure 3-c:
The invariant mass distributions for $ \mathrm{D}^{*+} $ candidates (left) and $ \mathrm{D}^{*-} $ candidates (right), with the $ m(\mathrm{D}\pi^{\pm}) $ distributions in the upper row and the $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distributions in the lower row. Projections of the simultaneous 2D fit are also shown. |
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Figure 3-d:
The invariant mass distributions for $ \mathrm{D}^{*+} $ candidates (left) and $ \mathrm{D}^{*-} $ candidates (right), with the $ m(\mathrm{D}\pi^{\pm}) $ distributions in the upper row and the $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ distributions in the lower row. Projections of the simultaneous 2D fit are also shown. |
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Figure 4:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*+} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\mathrm{D^0}\pi^{+}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\mathrm{D^0}\pi^{+}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). |
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Figure 4-a:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*+} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\mathrm{D^0}\pi^{+}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\mathrm{D^0}\pi^{+}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). |
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Figure 4-b:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*+} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\mathrm{D^0}\pi^{+}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\mathrm{D^0}\pi^{+}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). |
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Figure 4-c:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*+} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\mathrm{D^0}\pi^{+}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\mathrm{D^0}\pi^{+}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). |
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Figure 4-d:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*+} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\mathrm{D^0}\pi^{+}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\mathrm{D^0}\pi^{+}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). |
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Figure 4-e:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*+} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\mathrm{D^0}\pi^{+}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\mathrm{D^0}\pi^{+}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). |
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Figure 4-f:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*+} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\mathrm{D^0}\pi^{+}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\mathrm{D^0}\pi^{+}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). |
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Figure 4-g:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*+} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\mathrm{D^0}\pi^{+}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\mathrm{D^0}\pi^{+}) $: left sideband (left), signal region of $ \mathrm{D^0}\pi^{+} $ (center), and right sideband (right). |
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Figure 5:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*-} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). |
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Figure 5-a:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*-} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). |
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Figure 5-b:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*-} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). |
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Figure 5-c:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*-} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). |
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Figure 5-d:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*-} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). |
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Figure 5-e:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*-} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). |
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Figure 5-f:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*-} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). |
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Figure 5-g:
Results of the 2D fit to the $ m(\mathrm{D}\pi^{\pm}) \times m(\mathrm{K^0_S}\mathrm{K^0_S}) $ for the signal channel, $ \mathrm{D}^{*-} $ candidates. Upper and middle rows show 1D projections of the 2D fit on $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $ in ranges of $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $: left sideband (upper left), region of $ \mathrm{D}_{s}^{\pm}\to\mathrm{K^0_S}\mathrm{K^0_S}\pi^{\pm} $ contamination (upper right), signal region of $ \mathrm{K^0_S}\mathrm{K^0_S} $ (middle left), and right sideband (middle right). Lower row shows 1D projections of the 2D fit on $ m(\mathrm{K^0_S}\mathrm{K^0_S}) $ in ranges of $ m(\overline{\mathrm{D}}^{0}\pi^{-}) $: left sideband (left), signal region of $ \overline{\mathrm{D}}^{0}\pi^{-} $ (center), and right sideband (right). |
| Tables | |
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Table 1:
Optimized selection criteria in the signal channel $ \mathrm{K^0_S}\mathrm{K^0_S} $. The requirements on the $ \mathrm{K^0_S} $ candidates in the third and fourth lines are given first for the $ \mathrm{K^0_S} $ with larger $ p_{\mathrm{T}} $, then for the $ \mathrm{K^0_S} $ with lower $ p_{\mathrm{T}} $. |
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Table 2:
Results of the 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. |
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Table 3:
Results of the 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 $ {\mathrm{D}^{\ast}(2010)^{\pm}} $ signal yields $ N $ given in the second column 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. |
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Table 4:
Absolute systematic uncertainties in the measurement of $ \Delta A_{CP} $. |
| Summary |
| A measurement of CP violation in $ \mathrm{D^0} $ decays is reported, using proton-proton collision data collected at $ \sqrt{s} = $ 13 TeV with a novel high-rate data stream (B parking). These data correspond to an integrated luminosity of 41.6 fb$ ^{-1} $ and include about 10 billion events containing beauty hadron decays. The difference in the CP asymmetries between $ \mathrm{D^0}\to\mathrm{K^0_S}\mathrm{K^0_S} $ and $ \mathrm{D^0}\to\mathrm{K^0_S}\pi^{+}\pi^{-} $ is measured to be: $ \Delta A_{CP} \equiv A_{CP}(\mathrm{K^0_S}\mathrm{K^0_S})-A_{CP}(\mathrm{K^0_S}\pi^{+}\pi^{-}) = $ (6.3 $\pm$ 3.0 (stat) $\pm$ 0.2 (syst) )%. Using the world-average value of $ A_{CP}(\mathrm{K^0_S}\pi^{+}\pi^{-}) = (- $ 0.1 $ \pm $ 0.8 $)% $ [18,35,4], we report the measurement, $ A_{CP}(\mathrm{K^0_S}\mathrm{K^0_S}) = $(6.2 $\pm$ 3.0 $\pm$ 0.2 $\pm$ 0.8)%, where the three uncertainties represent the statistical uncertainty, the systematic uncertainty, and the uncertainty in the measurement of the CP asymmetry in the $ \mathrm{D^0}\to\mathrm{K^0_S}\pi^{+}\pi^{-} $ decay. The measured value is consistent with no CP violation within 2.0 standard deviations. Likewise, it is consistent with the LHCb [16] and the Belle measurements [17] at the level of 2.7 and 1.8 standard deviations, respectively. Tabulated results are provided in the HEPData record for this analysis [36]. This is the first CMS search for CP violation in the charm sector, paving the way for future measurements with more data, using new techniques, and in other channels. |
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Compact Muon Solenoid LHC, CERN |
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