Observation of double J/ψ meson production in pPb collisions at sNN=8.16 TeV

Abstract

The first observation of the concurrent production of two <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mi>J</a:mi><a:mo>/</a:mo><a:mi>ψ</a:mi></a:mrow></a:math> mesons in proton-nucleus collisions is presented. The analysis is based on a proton-lead (<c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>p</c:mi><c:mi>Pb</c:mi></c:math>) data sample recorded at a nucleon-nucleon center-of-mass energy of 8.16 TeV by the CMS experiment at the CERN LHC and corresponding to an integrated luminosity of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mn>174.6</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:msup><e:mi>nb</e:mi><e:mrow><e:mo>−</e:mo><e:mn>1</e:mn></e:mrow></e:msup></e:math>. The two <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>J</g:mi><g:mo>/</g:mo><g:mi>ψ</g:mi></g:math> mesons are reconstructed in their <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mrow><i:msup><i:mrow><i:mi>μ</i:mi></i:mrow><i:mrow><i:mo>+</i:mo></i:mrow></i:msup><i:msup><i:mrow><i:mi>μ</i:mi></i:mrow><i:mrow><i:mo>−</i:mo></i:mrow></i:msup></i:mrow></i:math> decay channels with transverse momenta <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:msub><k:mi>p</k:mi><k:mi mathvariant="normal">T</k:mi></k:msub><k:mo>&gt;</k:mo><k:mn>6.5</k:mn><k:mtext> </k:mtext><k:mtext> </k:mtext><k:mi>GeV</k:mi></k:math> and rapidity <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:mrow><n:mo stretchy="false">|</n:mo><n:mi>y</n:mi><n:mo stretchy="false">|</n:mo></n:mrow><n:mo>&lt;</n:mo><n:mn>2.4</n:mn></n:math>. Events where one of the <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:mi>J</r:mi><r:mo>/</r:mo><r:mi>ψ</r:mi></r:math> mesons is reconstructed in the dielectron channel are also considered in the search. The <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:mi>p</t:mi><t:mi>Pb</t:mi><t:mo stretchy="false">→</t:mo><t:mrow><t:mrow><t:mi>J</t:mi><t:mo>/</t:mo><t:mi>ψ</t:mi></t:mrow><t:mrow><t:mi>J</t:mi><t:mo>/</t:mo><t:mi>ψ</t:mi></t:mrow><t:mo>+</t:mo><t:mrow><t:mi>X</t:mi></t:mrow></t:mrow></t:math> process is observed with a significance of 5.3 standard deviations. The measured inclusive fiducial cross section, using the four-muon channel alone, is <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:mi>σ</w:mi><w:mo stretchy="false">(</w:mo><w:mi>p</w:mi><w:mi>Pb</w:mi><w:mo stretchy="false">→</w:mo><w:mrow><w:mi>J</w:mi><w:mo>/</w:mo><w:mi>ψ</w:mi></w:mrow><w:mrow><w:mi>J</w:mi><w:mo>/</w:mo><w:mi>ψ</w:mi></w:mrow><w:mo>+</w:mo><w:mrow><w:mi>X</w:mi></w:mrow><w:mo stretchy="false">)</w:mo><w:mo>=</w:mo><w:mspace linebreak="goodbreak"/><w:mn>22.0</w:mn><w:mo>±</w:mo><w:mn>8.9</w:mn><w:mo stretchy="false">(</w:mo><w:mi>stat</w:mi><w:mo stretchy="false">)</w:mo><w:mo>±</w:mo><w:mn>1.5</w:mn><w:mo stretchy="false">(</w:mo><w:mi>syst</w:mi><w:mo stretchy="false">)</w:mo><w:mtext> </w:mtext><w:mtext> </w:mtext><w:mi>nb</w:mi></w:math>. A fit of the data to the expected rapidity separation for pairs of <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"><gb:mi>J</gb:mi><gb:mo>/</gb:mo><gb:mi>ψ</gb:mi></gb:math> mesons produced in single (SPS) and double (DPS) parton scatterings yields <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"><ib:mrow><ib:msubsup><ib:mrow><ib:mi>σ</ib:mi></ib:mrow><ib:mrow><ib:mi>SPS</ib:mi></ib:mrow><ib:mrow><ib:mi>p</ib:mi><ib:mi>Pb</ib:mi><ib:mo stretchy="false">→</ib:mo><ib:mrow><ib:mi>J</ib:mi><ib:mo>/</ib:mo><ib:mi>ψ</ib:mi></ib:mrow><ib:mrow><ib:mi>J</ib:mi><ib:mo>/</ib:mo><ib:mi>ψ</ib:mi></ib:mrow><ib:mo>+</ib:mo><ib:mrow><ib:mi>X</ib:mi></ib:mrow></ib:mrow></ib:msubsup><ib:mo>=</ib:mo><ib:mn>16.5</ib:mn><ib:mo>±</ib:mo><ib:mn>10.8</ib:mn><ib:mo stretchy="false">(</ib:mo><ib:mi>stat</ib:mi><ib:mo stretchy="false">)</ib:mo><ib:mo>±</ib:mo><ib:mn>0.1</ib:mn><ib:mo stretchy="false">(</ib:mo><ib:mi>syst</ib:mi><ib:mo stretchy="false">)</ib:mo><ib:mtext> </ib:mtext><ib:mtext> </ib:mtext><ib:mi>nb</ib:mi></ib:mrow></ib:math> and <pb:math xmlns:pb="http://www.w3.org/1998/Math/MathML" display="inline"><pb:msubsup><pb:mi>σ</pb:mi><pb:mi>DPS</pb:mi><pb:mrow><pb:mi>p</pb:mi><pb:mi>Pb</pb:mi><pb:mo stretchy="false">→</pb:mo><pb:mrow><pb:mi>J</pb:mi><pb:mo>/</pb:mo><pb:mi>ψ</pb:mi></pb:mrow><pb:mrow><pb:mi>J</pb:mi><pb:mo>/</pb:mo><pb:mi>ψ</pb:mi></pb:mrow><pb:mo>+</pb:mo><pb:mrow><pb:mi>X</pb:mi></pb:mrow></pb:mrow></pb:msubsup><pb:mo>=</pb:mo><pb:mn>5.4</pb:mn><pb:mo>±</pb:mo><pb:mn>6.2</pb:mn><pb:mo stretchy="false">(</pb:mo><pb:mi>stat</pb:mi><pb:mo stretchy="false">)</pb:mo><pb:mo>±</pb:mo><pb:mn>0.4</pb:mn><pb:mo stretchy="false">(</pb:mo><pb:mi>syst</pb:mi><pb:mo stretchy="false">)</pb:mo><pb:mtext> </pb:mtext><pb:mtext> </pb:mtext><pb:mi>nb</pb:mi></pb:math>, respectively. This latter result can be transformed into a lower bound on the effective DPS cross section, closely related to the squared average interparton transverse separation in the collision, of <wb:math xmlns:wb="http://www.w3.org/1998/Math/MathML" display="inline"><wb:msub><wb:mi>σ</wb:mi><wb:mi>eff</wb:mi></wb:msub><wb:mo>&gt;</wb:mo><wb:mn>1.0</wb:mn><wb:mtext> </wb:mtext><wb:mtext> </wb:mtext><wb:mi>mb</wb:mi></wb:math> at 95% confidence level. © 2024 CERN, for the CMS Collaboration 2024 CERN