New high-statistics measurement of the π 0 → e + e − γ Dalitz decay at the Mainz Microtron

The Dalitz decay <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msup> <a:mi>π</a:mi> <a:mn>0</a:mn> </a:msup> <a:mo>→</a:mo> <a:msup> <a:mi>e</a:mi> <a:mo>+</a:mo> </a:msup> <a:msup> <a:mi>e</a:mi> <a:mo>−</a:mo> </a:msup> <a:mi>γ</a:mi> </a:mrow> </a:math> has been measured with the highest statistical accuracy obtained so far in the <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mi>γ</b:mi> <b:mi>p</b:mi> <b:mo>→</b:mo> <b:msup> <b:mi>π</b:mi> <b:mn>0</b:mn> </b:msup> <b:mi>p</b:mi> </b:mrow> </b:math> reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value of the slope parameter for the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msup> <c:mi>π</c:mi> <c:mn>0</c:mn> </c:msup> </c:math> electromagnetic transition form factor, <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:msub> <d:mi>a</d:mi> <d:mi>π</d:mi> </d:msub> <d:mo>=</d:mo> <d:mn>0.0315</d:mn> <d:mo>±</d:mo> <d:mn>0</d:mn> <d:mo>.</d:mo> <d:msub> <d:mn>0026</d:mn> <d:mi>stat</d:mi> </d:msub> <d:mo>±</d:mo> <d:mn>0</d:mn> <d:mo>.</d:mo> <d:msub> <d:mn>0010</d:mn> <d:mi>syst</d:mi> </d:msub> </d:mrow> </d:math> , is obtained from the analysis of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mn>2.4</e:mn> <e:mo>×</e:mo> <e:msup> <e:mn>10</e:mn> <e:mn>6</e:mn> </e:msup> </e:mrow> </e:math> <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mrow> <f:msup> <f:mi>π</f:mi> <f:mn>0</f:mn> </f:msup> <f:mo>→</f:mo> <f:msup> <f:mi>e</f:mi> <f:mo>+</f:mo> </f:msup> <f:msup> <f:mi>e</f:mi> <f:mo>−</f:mo> </f:msup> <f:mi>γ</f:mi> </f:mrow> </f:math> observed decays. Within experimental uncertainties, it is in agreement with existing measurements and theoretical calculations, with its own uncertainty being smaller than previous results based on the analysis of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:mrow> <g:msup> <g:mi>π</g:mi> <g:mn>0</g:mn> </g:msup> <g:mo>→</g:mo> <g:msup> <g:mi>e</g:mi> <g:mo>+</g:mo> </g:msup> <g:msup> <g:mi>e</g:mi> <g:mo>−</g:mo> </g:msup> <g:mi>γ</g:mi> </g:mrow> </g:math> decays.