Physics

Observation of the $Ξ_{c}^{0} \to p K^{-}$ decay and measurement of its decay asymmetry

LHCb collaboration: R. Aaij, et al.

Featured September 6, 2026

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Simply

Scientists at a giant particle collider saw a new, rare way a tiny particle breaks apart, then measured how often it happens and how its pieces fly off, helping them understand the universe's fundamental rules.

In depth

The paper reports the first observation of a rare particle decay,

Ξ_{c}^{0} \to p K^{-}

, which is crucial for understanding fundamental particle interactions. The authors achieved this by meticulously analyzing high-energy collision data and employing a multivariate classifier to distinguish the tiny signal from overwhelming background. Beyond just observing it, they precisely measured its branching fraction (how often it occurs) and, for the first time, its decay asymmetry parameter, which reveals insights into the underlying parity-violating and strong-interaction dynamics that cannot be obtained from decay rates alone.

Key Takeaways

1
The LHCb collaboration reports the first observation of the singly Cabibbo-suppressed (SCS) decay $Ξ_{c}^{0} \to p K^{-}$ , a purely W-exchange process previously unobserved.
2
The study provides the first measurement of the $Ξ_{c}^{0} \to p K^{-}$ branching fraction ( $B = (4.5 \pm 0.5 \pm 0.2 \pm 0.9) \times 1 0^{- 5}$ ) and its decay asymmetry parameter ( $α_{Ξ^{0, c}} = 0.32 \pm 0.15 \pm 0.01$ ).
3
The measured values show sizeable differences from most theoretical predictions, offering critical experimental input to improve models of charm-baryon decay dynamics and nonperturbative QCD effects.

Conceptual Flow

HIGH LEVEL

Methodology: Uncovering Rare Decays

Scientists collected many particle crashes, then carefully sorted through them to find tiny clues of a new particle breaking apart.

Particle Collisions

Filter & Analyze

Rare Particle Decays

Results: First Observation and Key Measurements

They found the new particle decay for the first time and measured its properties, which were different from what was expected.

Old Predictions

New Measurements

Updated Understanding

First Observation

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Observation of the Ξc0​→pK− decay and measurement of its decay asymmetry

Key Takeaways

Conceptual Flow

Observation of the $Ξ_{c}^{0} \to p K^{-}$ decay and measurement of its decay asymmetry