Physicists map exotic particle decays with new precision measurements
Researchers have completed the most detailed analysis yet of how certain B mesons decay into pairs of K* particles, measuring both the decay rates and quantum properties with unprecedented accuracy. The findings refine our understanding of fundamental particle interactions and could help identify physics beyond current theory.
Originaltitel: Measurement of the branching fractions and longitudinal polarizations of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msubsup> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>s</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo stretchy="false">→</mml:mo> <mml:msup> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> decays
A time- and flavor-integrated amplitude analysis of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msup> <a:mi>B</a:mi> <a:mn>0</a:mn> </a:msup> </a:math> and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msubsup> <c:mi>B</c:mi> <c:mi>s</c:mi> <c:mn>0</c:mn> </c:msubsup> </c:math> decays to the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mo stretchy="false">(</e:mo> <e:msup> <e:mi>K</e:mi> <e:mo>+</e:mo> </e:msup> <e:msup> <e:mi>π</e:mi> <e:mo>−</e:mo> </e:msup> <e:mo stretchy="false">)</e:mo> <e:mo stretchy="false">(</e:mo> <e:msup> <e:mi>K</e:mi> <e:mo>−</e:mo> </e:msup> <e:msup> <e:mi>π</e:mi> <e:mo>+</e:mo> </e:msup> <e:mo stretchy="false">)</e:mo> </e:math> final state in the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:msup> <k:mi>K</k:mi> <k:mo>*</k:mo> </k:msup> <k:mo stretchy="false">(</k:mo> <k:mn>892</k:mn> <k:msup> <k:mo stretchy="false">)</k:mo> <k:mn>0</k:mn> </k:msup> <k:msup> <k:mover accent="true"> <k:mi>K</k:mi> <k:mo stretchy="false">¯</k:mo> </k:mover> <k:mo>*</k:mo> </k:msup> <k:mo stretchy="false">(</k:mo> <k:mn>892</k:mn> <k:msup> <k:mo stretchy="false">)</k:mo> <k:mn>0</k:mn> </k:msup> </k:math> region is presented, using <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:mi>p</s:mi> <s:mi>p</s:mi> </s:math> collision data recorded with the LHCb detector in 2011–2018, corresponding to an integrated luminosity of <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"> <u:mn>9</u:mn> <u:mtext> </u:mtext> <u:mtext> </u:mtext> <u:msup> <u:mi>fb</u:mi> <u:mrow> <u:mo>−</u:mo> <u:mn>1</u:mn> </u:mrow> </u:msup> </u:math> . The branching fractions of the <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"> <w:msup> <w:mi>B</w:mi> <w:mn>0</w:mn> </w:msup> </w:math> and <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"> <y:msubsup> <y:mi>B</y:mi> <y:mi>s</y:mi> <y:mn>0</y:mn> </y:msubsup> </y:math> decays are measured relative to the <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"> <ab:msup> <ab:mi>B</ab:mi> <ab:mn>0</ab:mn> </ab:msup> <ab:mo stretchy="false">→</ab:mo> <ab:msup> <ab:mi>D</ab:mi> <ab:mo>−</ab:mo> </ab:msup> <ab:msup> <ab:mi>π</ab:mi> <ab:mo>+</ab:mo> </ab:msup> </ab:math> and <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"> <db:msubsup> <db:mi>B</db:mi> <db:mi>s</db:mi> <db:mn>0</db:mn> </db:msubsup> <db:mo stretchy="false">→</db:mo> <db:msubsup> <db:mi>D</db:mi> <db:mi>s</db:mi> <db:mo>−</db:mo> </db:msubsup> <db:msup> <db:mi>π</db:mi> <db:mo>+</db:mo> </db:msup> </db:math> modes, respectively. The corresponding longitudinal polarization fractions are found to be <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"> <gb:msubsup> <gb:mi>f</gb:mi> <gb:mi>L</gb:mi> <gb:mi>d</gb:mi> </gb:msubsup> <gb:mo>=</gb:mo> <gb:mn>0.600</gb:mn> <gb:mo>±</gb:mo> <gb:mn>0.022</gb:mn> <gb:mo>±</gb:mo> <gb:mn>0.017</gb:mn> </gb:math> and <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"> <ib:msubsup> <ib:mi>f</ib:mi> <ib:mi>L</ib:mi> <ib:mi>s</ib:mi> </ib:msubsup> <ib:mo>=</ib:mo> <ib:mn>0.159</ib:mn> <ib:mo>±</ib:mo> <ib:mn>0.010</ib:mn> <ib:mo>±</ib:mo> <ib:mn>0.007</ib:mn> </ib:math> , where the uncertainties are statistical and systematic, respectively. The theory-motivated ratio of the squared <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML" display="inline"> <kb:msubsup> <kb:mi>B</kb:mi> <kb:mi>s</kb:mi> <kb:mn>0</kb:mn> </kb:msubsup> </kb:math> to <mb:math xmlns:mb="http://www.w3.org/1998/Math/MathML" display="inline"> <mb:msup> <mb:mi>B</mb:mi> <mb:mn>0</mb:mn> </mb:msup> </mb:math> longitudinally polarized decay amplitudes is found to be <ob:math xmlns:ob="http://www.w3.org/1998/Math/MathML" display="inline"> <ob:msub> <ob:mi>L</ob:mi> <ob:mrow> <ob:msup> <ob:mi>K</ob:mi> <ob:mrow> <ob:mo>*</ob:mo> <ob:mn>0</ob:mn> </ob:mrow> </ob:msup> <ob:msup> <ob:mover accent="true"> <ob:mi>K</ob:mi> <ob:mo stretchy="false">¯</ob:mo> </ob:mover> <ob:mrow> <ob:mo>*</ob:mo> <ob:mn>0</ob:mn> </ob:mrow> </ob:msup> </ob:mrow> </ob:msub> <ob:mo>=</ob:mo> <ob:mn>4.92</ob:mn> <ob:mo>±</ob:mo> <ob:mn>0.55</ob:mn> <ob:mo>±</ob:mo> <ob:mn>0.48</ob:mn> <ob:mo>±</ob:mo> <ob:mn>0.02</ob:mn> <ob:mo>±</ob:mo> <ob:mn>0.10</ob:mn> </ob:math> , where the uncertainties are statistical, systematic, due to uncertainty of external mass and lifetime measurements, and due to knowledge of the fragmentation fraction ratio, respectively. This confirms the previously reported tension between experimental determinations and theoretical predictions of longitudinal polarization in <sb:math xmlns:sb="http://www.w3.org/1998/Math/MathML" display="inline"> <sb:mi>B</sb:mi> <sb:mo stretchy="false">→</sb:mo> <sb:mi>V</sb:mi> <sb:mi>V</sb:mi> </sb:math> decays at the level of 4.4 standard deviations.