<p>A precise determination of the CKM angle <i>γ</i> from <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13130_2025_26528_Article_IEq2.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="21" /> </InlineMediaObject> <EquationSource Format="MATHML"><math display="inline"> <msubsup> <mi>B</mi> <mi>s</mi> <mn>0</mn> </msubsup> </math></EquationSource> <EquationSource Format="TEX">\( {B}_s^0 \)</EquationSource> </InlineEquation> oscillations in <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13130_2025_26528_Article_IEq1.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="99" /> </InlineMediaObject> <EquationSource Format="MATHML"><math display="inline"> <msubsup> <mi>B</mi> <mi>s</mi> <mn>0</mn> </msubsup> <mo>→</mo> <msubsup> <mi>D</mi> <mi>s</mi> <mo>∓</mo> </msubsup> <msup> <mi>K</mi> <mo>±</mo> </msup> </math></EquationSource> <EquationSource Format="TEX">\( {B}_s^0\to {D}_s^{\mp }{K}^{\pm } \)</EquationSource> </InlineEquation> decays offers a critical test of the Standard Model and probes for new physics. We present a comprehensive study on the prospects of measuring <i>γ</i> at a future Tera-<i>Z</i> factory, utilizing the baseline detector concept of the Circular Electron Positron Collider (CEPC). A two-dimensional simultaneous fit framework, incorporating flavor tagging, decay time resolution modeling, and acceptance corrections, is developed using full Monte Carlo simulations of <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13130_2025_26528_Article_IEq4.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="210" /> </InlineMediaObject> <EquationSource Format="MATHML"><math display="inline"> <msubsup> <mi>B</mi> <mi>s</mi> <mn>0</mn> </msubsup> <mo>→</mo> <msubsup> <mi>D</mi> <mi>s</mi> <mo>∓</mo> </msubsup> <mfenced close=")" open="("> <mrow> <mo>→</mo> <msup> <mi>K</mi> <mo>∓</mo> </msup> <msup> <mi>K</mi> <mo>±</mo> </msup> <msup> <mi>π</mi> <mo>∓</mo> </msup> </mrow> </mfenced> <msup> <mi>K</mi> <mo>±</mo> </msup> </math></EquationSource> <EquationSource Format="TEX">\( {B}_s^0\to {D}_s^{\mp}\left(\to {K}^{\mp }{K}^{\pm }{\pi}^{\mp}\right){K}^{\pm } \)</EquationSource> </InlineEquation> decays and inclusive background processes. The effective flavor tagging power reaches 23.6%, while the decay time resolution is determined to be 26 fs. Projecting to full statistics of signal events across three dominant <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13130_2025_26528_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="27" /> </InlineMediaObject> <EquationSource Format="MATHML"><math display="inline"> <msubsup> <mi>D</mi> <mi>s</mi> <mo>−</mo> </msubsup> </math></EquationSource> <EquationSource Format="TEX">\( {D}_s^{-} \)</EquationSource> </InlineEquation> decay channels, we estimate a statistical precision of <i>σ</i>(<i>γ</i>) = 0<i>.</i>69<sup><i>°</i></sup>, which corresponds to 4.1 Tera-<i>Z</i> boson equivalent data. This study has established the feasibility of sub-degree level <i>γ</i> measurements at a <i>Z</i> factory, highlighting its unique advantages in time-dependent <i>CP</i> violation studies through ultra-precise vertexing and background suppression capabilities.</p>

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Prospect for measurement of CP-violating observables in \( {B}_s^0\to {D}_s^{\mp }{K}^{\pm } \) decays at a future Z factory

  • Ji Peng,
  • Mingrui Zhao,
  • Xiaolin Wang,
  • Manqi Ruan,
  • Hengne Li,
  • Shanzhen Chen

摘要

A precise determination of the CKM angle γ from B s 0 \( {B}_s^0 \) oscillations in B s 0 D s K ± \( {B}_s^0\to {D}_s^{\mp }{K}^{\pm } \) decays offers a critical test of the Standard Model and probes for new physics. We present a comprehensive study on the prospects of measuring γ at a future Tera-Z factory, utilizing the baseline detector concept of the Circular Electron Positron Collider (CEPC). A two-dimensional simultaneous fit framework, incorporating flavor tagging, decay time resolution modeling, and acceptance corrections, is developed using full Monte Carlo simulations of B s 0 D s K K ± π K ± \( {B}_s^0\to {D}_s^{\mp}\left(\to {K}^{\mp }{K}^{\pm }{\pi}^{\mp}\right){K}^{\pm } \) decays and inclusive background processes. The effective flavor tagging power reaches 23.6%, while the decay time resolution is determined to be 26 fs. Projecting to full statistics of signal events across three dominant D s \( {D}_s^{-} \) decay channels, we estimate a statistical precision of σ(γ) = 0.69°, which corresponds to 4.1 Tera-Z boson equivalent data. This study has established the feasibility of sub-degree level γ measurements at a Z factory, highlighting its unique advantages in time-dependent CP violation studies through ultra-precise vertexing and background suppression capabilities.