Based on <math><mo>(</mo><mn>10</mn><mn>087</mn><mo>±</mo><mn>44</mn><mo>)</mo><mo>×</mo><msup><mn>10</mn><mn>6</mn></msup><mtext> </mtext><mtext> </mtext><mi>J</mi><mo>/</mo><mi>ψ</mi></math> events collected with the BESIII detector, the process <math><mi>J</mi><mo>/</mo><mi>ψ</mi><mo>→</mo><mi>γ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><msup><mi>η</mi><mo>′</mo></msup></math> is studied using two largest decay channels of the <math><msup><mi>η</mi><mo>′</mo></msup></math> meson, <math><msup><mi>η</mi><mo>′</mo></msup><mo>→</mo><mi>γ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> and <math><mrow><msup><mrow><mi>η</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>→</mo><mi>η</mi><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math>, <math><mrow><mi>η</mi><mo>→</mo><mi>γ</mi><mi>γ</mi></mrow></math>. A new resonance, which we denote as the <math><mi>X</mi><mo>(</mo><mn>2600</mn><mo>)</mo></math>, is observed with a statistical significance larger than <math><mrow><mn>20</mn><mi>σ</mi></mrow></math> in the <math><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><msup><mi>η</mi><mo>′</mo></msup></math> invariant mass spectrum, and it has a connection to a structure around <math><mrow><msup><mrow><mn>1.5</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><mrow><mi>c</mi></mrow></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> in the <math><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> invariant mass spectrum. A simultaneous fit on the <math><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><msup><mi>η</mi><mo>′</mo></msup></math> and <math><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> invariant mass spectra with the two <math><msup><mi>η</mi><mo>′</mo></msup></math> decay modes indicates that the mass and width of the <math><mi>X</mi><mo>(</mo><mn>2600</mn><mo>)</mo></math> state are <math><mrow><mn>2618.3</mn><mo>±</mo><mn>2.</mn><msubsup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>1.4</mn></mrow><mrow><mo>+</mo><mn>16.3</mn></mrow></msubsup><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> and <math><mn>195</mn><mo>±</mo><msubsup><mn>5</mn><mrow><mo>−</mo><mn>17</mn></mrow><mrow><mo>+</mo><mn>26</mn></mrow></msubsup><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>, where the first uncertainties are statistical, and the second systematic.

China

Russia

Sweden

Germany

Italy

JINR

Poland

Mongolia

United States

Türkiye

United Kingdom

Observation of a State <math><mi>X</mi><mo>(</mo><mn>2600</mn><mo>)</mo></math> in the <math><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mi>η</mi><mo>′</mo></math> System in the Process <math><mi>J</mi><mo>/</mo><mi>ψ</mi><mo>→</mo><mi>γ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mi>η</mi><mo>′</mo></math>