Search for dark photons between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mn>16.96</mml:mn> <mml:mo>–</mml:mo> <mml:mn>19.52</mml:mn> <mml:mtext> </mml:mtext> <mml:mtext> </mml:mtext> <mml:mrow> <mml:m

We report dark photon results from HAYSTAC phase II using data from previously reported axion searches. Additionally, we present an analysis of an unpublished dataset covering a region between <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mn>19.46</a:mn> <a:mi>–</a:mi> <a:mn>19.52</a:mn> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi>μeV</a:mi> </a:mrow> </a:math> . This region overlaps with a recently reported dark photon signal at <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mrow> <c:mn>19.5</c:mn> <c:mtext> </c:mtext> <c:mtext> </c:mtext> <c:mi>μeV</c:mi> </c:mrow> </c:math> with a kinetic coupling strength of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mo stretchy="false">|</e:mo> <e:msub> <e:mi>χ</e:mi> <e:mrow> <e:mi>rand</e:mi> </e:mrow> </e:msub> <e:mo stretchy="false">|</e:mo> <e:mo>≃</e:mo> <e:mn>6.5</e:mn> <e:mo>×</e:mo> <e:msup> <e:mn>10</e:mn> <e:mrow> <e:mo>−</e:mo> <e:mn>15</e:mn> </e:mrow> </e:msup> </e:math> resulting from a reanalysis of previously published data from the TASEH collaboration. Given HAYSTAC’s sensitivity, if such a signal were present, it would have appeared as a large <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mn>17.1</i:mn> <i:mi>σ</i:mi> </i:math> excess above the noise. However, no such signal was observed. We thus exclude couplings <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mo stretchy="false">|</k:mo> <k:msub> <k:mi>χ</k:mi> <k:mrow> <k:mi>rand</k:mi> </k:mrow> </k:msub> <k:mo stretchy="false">|</k:mo> <k:mo>≥</k:mo> <k:mn>4.90</k:mn> <k:mo>×</k:mo> <k:msup> <k:mn>10</k:mn> <k:mrow> <k:mo>−</k:mo> <k:mn>15</k:mn> </k:mrow> </k:msup> </k:math> at the 90% confidence level over the newly reported region. In addition, using our previously reported axion data, we exclude couplings <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"> <o:mo stretchy="false">|</o:mo> <o:msub> <o:mi>χ</o:mi> <o:mrow> <o:mi>rand</o:mi> </o:mrow> </o:msub> <o:mo stretchy="false">|</o:mo> <o:mo>≥</o:mo> <o:mn>2.90</o:mn> <o:mo>×</o:mo> <o:msup> <o:mn>10</o:mn> <o:mrow> <o:mo>−</o:mo> <o:mn>15</o:mn> </o:mrow> </o:msup> </o:math> between <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:mrow> <s:mn>16.96</s:mn> <s:mi>–</s:mi> <s:mn>19.46</s:mn> <s:mtext> </s:mtext> <s:mtext> </s:mtext> <s:mi>μeV</s:mi> </s:mrow> </s:math> at the 90% confidence level.