First Evidence of the Decay B + → π + e + e −

The first evidence for the decay <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:msup> <a:mrow> <a:mi>B</a:mi> </a:mrow> <a:mrow> <a:mo>+</a:mo> </a:mrow> </a:msup> <a:mo stretchy="false">→</a:mo> <a:msup> <a:mrow> <a:mi>π</a:mi> </a:mrow> <a:mrow> <a:mo>+</a:mo> </a:mrow> </a:msup> <a:msup> <a:mrow> <a:mi>e</a:mi> </a:mrow> <a:mrow> <a:mo>+</a:mo> </a:mrow> </a:msup> <a:msup> <a:mrow> <a:mi>e</a:mi> </a:mrow> <a:mrow> <a:mo>−</a:mo> </a:mrow> </a:msup> </a:mrow> </a:math> is reported using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:mn>9</d:mn> <d:mtext> </d:mtext> <d:mtext> </d:mtext> <d:msup> <d:mi>fb</d:mi> <d:mrow> <d:mo>−</d:mo> <d:mn>1</d:mn> </d:mrow> </d:msup> </d:math> . A signal excess with a significance of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:mrow> <f:mn>3.2</f:mn> <f:mi>σ</f:mi> </f:mrow> </f:math> is observed and the branching fraction is measured to be <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mrow> <h:mi mathvariant="script">B</h:mi> <h:mo stretchy="false">(</h:mo> <h:msup> <h:mrow> <h:mi>B</h:mi> </h:mrow> <h:mrow> <h:mo>+</h:mo> </h:mrow> </h:msup> <h:mo stretchy="false">→</h:mo> <h:msup> <h:mrow> <h:mi>π</h:mi> </h:mrow> <h:mrow> <h:mo>+</h:mo> </h:mrow> </h:msup> <h:msup> <h:mrow> <h:mi>e</h:mi> </h:mrow> <h:mrow> <h:mo>+</h:mo> </h:mrow> </h:msup> <h:msup> <h:mrow> <h:mi>e</h:mi> </h:mrow> <h:mrow> <h:mo>−</h:mo> </h:mrow> </h:msup> <h:mo stretchy="false">)</h:mo> <h:mo>=</h:mo> <h:mo stretchy="false">(</h:mo> <h:msubsup> <h:mrow> <h:mn>2.4</h:mn> </h:mrow> <h:mrow> <h:mo>−</h:mo> <h:mn>0.8</h:mn> </h:mrow> <h:mrow> <h:mo>+</h:mo> <h:mn>0.9</h:mn> </h:mrow> </h:msubsup> <h:msubsup> <h:mrow> <h:mtext> </h:mtext> </h:mrow> <h:mrow> <h:mo>−</h:mo> <h:mn>0.2</h:mn> </h:mrow> <h:mrow> <h:mo>+</h:mo> <h:mn>0.4</h:mn> </h:mrow> </h:msubsup> <h:mo stretchy="false">)</h:mo> <h:mo>×</h:mo> <h:msup> <h:mrow> <h:mn>10</h:mn> </h:mrow> <h:mrow> <h:mo>−</h:mo> <h:mn>8</h:mn> </h:mrow> </h:msup> </h:mrow> </h:math> , where the first set of uncertainties is statistical and the second is systematic. The result is consistent with the Standard Model expectation.