[Paper Review] Conclusions of the MITP Workshop on T Violation and CPT Tests in Neutral-Meson Systems

K. R. Schubert, L. Li Gioi+2 more|arXiv (Cornell University)|Jan 27, 2014

Nuclear Materials and Properties3 citations

TL;DR

This paper summarizes key conclusions from the MITP workshop on T violation and CPT tests in neutral-meson systems, focusing on T-symmetry violation in B⁰–B̄⁰ transitions via time-dependent decay rates in B⁰→J/ψK_S decays. It demonstrates that Imλ ≠ 0 in the sin(Δmt) term confirms T-symmetry violation, while CPT tests in the K⁰–K̄⁰ system via ratios of decay rates at a φ-factory can probe CPT violation independently of CP violation, with KLOE-2 experiment expected to achieve high significance in the 0–300τ_S region.

ABSTRACT

The conclusions summarize the main, but not all, aspects of a two-days workshop held at MITP Mainz. The four covered aspects are T violation in decays of neutral B mesons, T and CPT studies in B0B0bar transitions with Belle, future measurements of T violation in B and D decays, and direct tests of T and CPT symmetries in the entangled neutral Kaon system at a ?Phi factory.

Motivation & Objective

• To clarify the distinction between T-symmetry violation (fundamental time-reversal symmetry breaking) and motion-reversal violation (asymmetric transition rates in time-reversed processes) in B⁰–B̄⁰ systems.
• To evaluate the sensitivity of time-ordered decay rate ratios to T and CPT violation in neutral kaons at a φ-factory, particularly in the context of KLOE-2 experiment.
• To assess the robustness of CPT tests in the K⁰–K̄⁰ system against uncertainties in CP violation and invisible decay modes.
• To demonstrate that CPT violation can be probed independently of CP violation in the K⁰–K̄⁰ system, especially in the Δt > 0 region where T-violation effects vanish in the ΔΓ → 0 limit.

Proposed method

• Uses time-ordered decay rate ratios R₂^exp(Δt) and R₄^exp(Δt) to test T violation in the K⁰–K̄⁰ system, defined as the ratio of probabilities for K⁰(0)→K₊(Δt) and K₊(0)→K̄⁰(Δt) decays.
• Defines CPT-violating ratios R₂,CPT^exp(Δt) and R₄,CPT^exp(Δt), where deviations from unity signal CPT violation, with normalization D_CPT independent of CPT violation in semileptonic decays.
• Applies the Bell-Steinberger unitarity approach to test CPT symmetry via the overlap ⟨K_L|K_S⟩, with sensitivity reaching |m(K̄⁰)−m(K⁰)| < 4×10⁻¹⁹ GeV at 95% C.L. in 2012.
• Analyzes the dependence of T and CPT tests on ΔΓ (width difference), showing T violation vanishes as ΔΓ→0, while CPT violation remains detectable.
• Uses the KLOE-2 experiment at DAΦNE with ∼10 fb⁻¹ luminosity to measure these ratios in the Δt ∈ [0, 300τ_S] region, where the ratios are expected to be constant and sensitive to Reε and Reδ.

Experimental results

Research questions

• RQ1 Can time-ordered decay rate ratios in the K⁰–K̄⁰ system provide a direct test of T-symmetry violation independent of CP violation?
• RQ2 How does the presence of invisible decay modes affect the unitarity test of CPT symmetry in the K⁰–K̄⁰ system?
• RQ3 Why is the CPT test in the K⁰–K̄⁰ system more robust than the T test in the Δt > 0 region, especially in the limit ΔΓ → 0?
• RQ4 To what extent can the normalization constant D_CPT be determined without assuming CPT invariance in semileptonic decays?

Key findings

• Imλ ≠ 0 in B⁰→J/ψK_S decays, confirmed by BABAR in 2012, provides direct evidence for T-symmetry violation via the sin(Δmt) term in the time-dependent decay rate.
• The KLOE-2 experiment at DAΦNE is expected to achieve a statistically significant test of T violation by measuring R₂^exp(Δt) and R₄^exp(Δt) in the 0–300τ_S region, where these ratios are constant and proportional to Reε.
• CPT violation can be probed via R₂,CPT^exp(Δt) and R₄,CPT^exp(Δt), with deviations from unity indicating CPT violation, and the normalization D_CPT independent of CPT violation in semileptonic decays.
• Unlike T violation, CPT violation remains detectable in the ΔΓ → 0 limit, as it depends on Reδ, which does not vanish even when ΔΓ → 0.
• The impact of direct CP violation on the orthogonality condition is negligible in the 0–300τ_S region, making the CPT test robust and highly significant.
• The unitarity test of CPT symmetry in the K⁰–K̄⁰ system has reached a sensitivity of |m(K̄⁰)−m(K⁰)| < 4×10⁻¹⁹ GeV at 95% C.L. as of 2012, but the role of invisible decays remains an open question.