Physicists spot unexpected spin behavior in exotic particle decay
Scientists using China's BESIII collider detected an unusual sideways spin in a rare particle interaction, a finding that challenges existing theoretical models. The 4.4-sigma result, based on nearly 3 billion collision events, opens questions about how fundamental forces shape particle behavior and could inform next-generation detector design.
Originaltitel: Evidence of transverse polarization of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msup> <mml:mi mathvariant="normal">Ξ</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:math> hyperon in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>ψ</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3686</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mo stretchy="false">→</mml:mo> <mml:msup> <mml:mi mathvariant="normal">Ξ</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:msup> <mml:mover accent="true"> <mml:mi mathvariant="normal">Ξ</mml:mi> <mml:mo stretchy="false">¯</mml:mo> </mml:mover> <mml:mn>0</mml:mn> </mml:msup> </mml:math>
Using <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mo stretchy="false">(</a:mo> <a:mn>2.712</a:mn> <a:mo>±</a:mo> <a:mn>0.014</a:mn> <a:mo stretchy="false">)</a:mo> <a:mo>×</a:mo> <a:msup> <a:mn>10</a:mn> <a:mn>9</a:mn> </a:msup> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi>ψ</a:mi> <a:mo stretchy="false">(</a:mo> <a:mn>3686</a:mn> <a:mo stretchy="false">)</a:mo> </a:math> events collected with the BESIII detector at the BEPCII collider, we report an evidence of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:msup> <g:mi mathvariant="normal">Ξ</g:mi> <g:mn>0</g:mn> </g:msup> </g:math> transverse polarization with a significance of <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mrow> <j:mn>4.4</j:mn> <j:mi>σ</j:mi> </j:mrow> </j:math> , a precise measurement of the branching fraction and the ratios between the <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"> <l:mi>S</l:mi> </l:math> -wave and <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"> <n:mi>D</n:mi> </n:math> -wave contributions of <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"> <p:mi>ψ</p:mi> <p:mo stretchy="false">(</p:mo> <p:mn>3686</p:mn> <p:mo stretchy="false">)</p:mo> <p:mo stretchy="false">→</p:mo> <p:msup> <p:mi mathvariant="normal">Ξ</p:mi> <p:mn>0</p:mn> </p:msup> <p:msup> <p:mover accent="true"> <p:mi mathvariant="normal">Ξ</p:mi> <p:mo stretchy="false">¯</p:mo> </p:mover> <p:mn>0</p:mn> </p:msup> </p:math> . The weak decay parameters ( <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"> <y:msub> <y:mi>ϕ</y:mi> <y:mrow> <y:msup> <y:mi mathvariant="normal">Ξ</y:mi> <y:mn>0</y:mn> </y:msup> <y:mo>/</y:mo> <y:msup> <y:mover accent="true"> <y:mi mathvariant="normal">Ξ</y:mi> <y:mo stretchy="false">¯</y:mo> </y:mover> <y:mn>0</y:mn> </y:msup> </y:mrow> </y:msub> </y:math> , <eb:math xmlns:eb="http://www.w3.org/1998/Math/MathML" display="inline"> <eb:msub> <eb:mi>α</eb:mi> <eb:mrow> <eb:msup> <eb:mi mathvariant="normal">Ξ</eb:mi> <eb:mn>0</eb:mn> </eb:msup> <eb:mo>/</eb:mo> <eb:msup> <eb:mover accent="true"> <eb:mi mathvariant="normal">Ξ</eb:mi> <eb:mo stretchy="false">¯</eb:mo> </eb:mover> <eb:mn>0</eb:mn> </eb:msup> </eb:mrow> </eb:msub> </eb:math> ) and the angular distribution ( <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML" display="inline"> <kb:msub> <kb:mi>α</kb:mi> <kb:mi>ψ</kb:mi> </kb:msub> </kb:math> ) are also measured with higher precision compared to the previous measurements. Furthermore, two the <mb:math xmlns:mb="http://www.w3.org/1998/Math/MathML" display="inline"> <mb:mi>C</mb:mi> <mb:mi>P</mb:mi> </mb:math> observables are also determined to be <ob:math xmlns:ob="http://www.w3.org/1998/Math/MathML" display="inline"> <ob:msubsup> <ob:mi>A</ob:mi> <ob:mrow> <ob:mi>C</ob:mi> <ob:mi>P</ob:mi> </ob:mrow> <ob:msup> <ob:mi mathvariant="normal">Ξ</ob:mi> <ob:mn>0</ob:mn> </ob:msup> </ob:msubsup> <ob:mo>=</ob:mo> <ob:mo>−</ob:mo> <ob:mn>0.014</ob:mn> <ob:mo>±</ob:mo> <ob:mn>0.030</ob:mn> <ob:mo>±</ob:mo> <ob:mn>0.010</ob:mn> </ob:math> and <rb:math xmlns:rb="http://www.w3.org/1998/Math/MathML" display="inline"> <rb:mi mathvariant="normal">Δ</rb:mi> <rb:msubsup> <rb:mi>ϕ</rb:mi> <rb:mrow> <rb:mi>C</rb:mi> <rb:mi>P</rb:mi> </rb:mrow> <rb:msup> <rb:mi mathvariant="normal">Ξ</rb:mi> <rb:mn>0</rb:mn> </rb:msup> </rb:msubsup> <rb:mo>=</rb:mo> <rb:mn>0.000</rb:mn> <rb:mo>±</rb:mo> <rb:mn>0.028</rb:mn> <rb:mo>±</rb:mo> <rb:mn>0.003</rb:mn> <rb:mtext> </rb:mtext> <rb:mtext> </rb:mtext> <rb:mi>rad</rb:mi> </rb:math> , which are still consistent with <vb:math xmlns:vb="http://www.w3.org/1998/Math/MathML" display="inline"> <vb:mi>C</vb:mi> <vb:mi>P</vb:mi> </vb:math> conservation at <xb:math xmlns:xb="http://www.w3.org/1998/Math/MathML" display="inline"> <xb:mrow> <xb:mn>1</xb:mn> <xb:mi>σ</xb:mi> </xb:mrow> </xb:math> level under the current statistics.