Production of hidden-heavy and double-heavy hadronic molecules at the Z factory of CEPC

With a clean environment and high collision energy, the Circular Electron Positron Collider (CEPC) would be an excellent facility for heavy flavor physics. Using the Monte Carlo event generator ythia, we simulate the production of the charmed (bottom) hadron pairs in the electron-positron collisions at the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>Z</a:mi></a:math> factory of CEPC, and the inclusive production rates for typical candidates of the hidden/double-charm and hidden/double-bottom <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>S</c:mi></c:math>-wave hadronic molecules are estimated at an order-of-magnitude level with the final state interactions after the hadron pair production. The predicted cross sections for the hidden-charm meson-meson molecules <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>X</e:mi><e:mo stretchy="false">(</e:mo><e:mn>3872</e:mn><e:mo stretchy="false">)</e:mo></e:math> and <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi>Z</i:mi><i:mi>c</i:mi></i:msub><i:mo stretchy="false">(</i:mo><i:mn>3900</i:mn><i:mo stretchy="false">)</i:mo></i:math> are at pb level, which are about two to three orders of magnitude larger than the production cross sections for the double-charm meson-meson molecules <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:msub><m:mi>T</m:mi><m:mrow><m:mi>c</m:mi><m:mi>c</m:mi></m:mrow></m:msub></m:math> and <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:msubsup><o:mi>T</o:mi><o:mrow><o:mi>c</o:mi><o:mi>c</o:mi></o:mrow><o:mo>*</o:mo></o:msubsup></o:math>, as the double-charmed ones require the production of two pairs of <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mi>c</q:mi><q:mover accent="true"><q:mi>c</q:mi><q:mo stretchy="false">¯</q:mo></q:mover></q:math> from the <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:mi>Z</u:mi></u:math> boson decay. The production cross sections for the hidden-charm pentaquark states <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:msub><w:mi>P</w:mi><w:mi>c</w:mi></w:msub></w:math> and <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:msub><y:mi>P</y:mi><y:mrow><y:mi>c</y:mi><y:mi>s</y:mi></y:mrow></y:msub></y:math> as meson-baryon molecules are a few to tens of fb, which are about one magnitude larger than those of the possible hidden-charm baryon-antibaryon and double-charm meson-baryon molecules. In the bottom sector, the production cross sections for the <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:msub><ab:mi>Z</ab:mi><ab:mi>b</ab:mi></ab:msub></ab:math> states as <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"><cb:msup><cb:mi>B</cb:mi><cb:mrow><cb:mo stretchy="false">(</cb:mo><cb:mo>*</cb:mo><cb:mo stretchy="false">)</cb:mo></cb:mrow></cb:msup><cb:msup><cb:mover accent="true"><cb:mi>B</cb:mi><cb:mo stretchy="false">¯</cb:mo></cb:mover><cb:mo>*</cb:mo></cb:msup></cb:math> molecules are about tens to hundreds of fb, indicating <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"><ib:msup><ib:mn>10</ib:mn><ib:mn>6</ib:mn></ib:msup><ib:mi>–</ib:mi><ib:msup><ib:mn>10</ib:mn><ib:mn>7</ib:mn></ib:msup></ib:math> events from a two-year operation of CEPC, and the expected events from the double-bottom molecules are about 2–5 orders of magnitude smaller than the <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML" display="inline"><kb:msub><kb:mi>Z</kb:mi><kb:mi>b</kb:mi></kb:msub></kb:math> states. Our results shows great prospects of probing heavy exotic hadrons at CEPC.