Observation of Structures in the Mass Spectrum with the ATLAS Detector

Abstract

A search for resonant structures in the <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:mo>+</a:mo> <a:mi>ψ</a:mi> <a:mo stretchy="false">(</a:mo> <a:mn>2</a:mn> <a:mi mathvariant="normal">S</a:mi> <a:mo stretchy="false">)</a:mo> </a:mrow> </a:math> mass spectrum is performed using proton-proton collision data at <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:msqrt> <f:mi>s</f:mi> </f:msqrt> <f:mo>=</f:mo> <f:mn>13</f:mn> <f:mtext> </f:mtext> <f:mtext> </f:mtext> <f:mi>TeV</f:mi> </f:math> , corresponding to an integrated luminosity of <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mn>140</h:mn> <h:mtext> </h:mtext> <h:mtext> </h:mtext> <h:msup> <h:mi>fb</h:mi> <h:mrow> <h:mo>−</h:mo> <h:mn>1</h:mn> </h:mrow> </h:msup> </h:math> , recorded by the ATLAS experiment at the LHC. The decay channels of <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mi>J</j:mi> <j:mo>/</j:mo> <j:mi>ψ</j:mi> <j:mo>+</j:mo> <j:mi>ψ</j:mi> <j:mrow> <j:mo stretchy="false">(</j:mo> <j:mn>2</j:mn> <j:mi mathvariant="normal">S</j:mi> <j:mo stretchy="false">)</j:mo> </j:mrow> <j:mo stretchy="false">→</j:mo> <j:mn>4</j:mn> <j:mi>μ</j:mi> </j:math> and <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"> <p:mi>J</p:mi> <p:mo>/</p:mo> <p:mi>ψ</p:mi> <p:mo>+</p:mo> <p:mi>ψ</p:mi> <p:mrow> <p:mo stretchy="false">(</p:mo> <p:mn>2</p:mn> <p:mi mathvariant="normal">S</p:mi> <p:mo stretchy="false">)</p:mo> </p:mrow> <p:mo stretchy="false">→</p:mo> <p:mn>4</p:mn> <p:mi>μ</p:mi> <p:mo>+</p:mo> <p:mn>2</p:mn> <p:mi>π</p:mi> </p:math> are analyzed. An excess near 6.9 GeV is observed in both channels with a combined significance of <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"> <v:mrow> <v:mn>8.9</v:mn> <v:mi>σ</v:mi> </v:mrow> </v:math> . No significant signal is observed near 7.2 GeV, and an upper limit on its yield relative to <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"> <x:mi>X</x:mi> <x:mo stretchy="false">(</x:mo> <x:mn>6900</x:mn> <x:mo stretchy="false">)</x:mo> </x:math> is provided. A simultaneous fit with the di- <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML" display="inline"> <bb:mi>J</bb:mi> <bb:mo>/</bb:mo> <bb:mi>ψ</bb:mi> </bb:math> channel is carried out under assumptions regarding the resonance interferences, yielding a ratio of the partial decay widths between the <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"> <db:mi>J</db:mi> <db:mo>/</db:mo> <db:mi>ψ</db:mi> <db:mo>+</db:mo> <db:mi>ψ</db:mi> <db:mrow> <db:mo stretchy="false">(</db:mo> <db:mn>2</db:mn> <db:mi mathvariant="normal">S</db:mi> <db:mo stretchy="false">)</db:mo> </db:mrow> </db:math> and di- <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"> <ib:mi>J</ib:mi> <ib:mo>/</ib:mo> <ib:mi>ψ</ib:mi> </ib:math> channels of <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML" display="inline"> <kb:mn>1.08</kb:mn> <kb:mo>±</kb:mo> <kb:mn>0.2</kb:mn> <kb:msubsup> <kb:mn>0</kb:mn> <kb:mrow> <kb:mo>−</kb:mo> <kb:mn>0.17</kb:mn> </kb:mrow> <kb:mrow> <kb:mo>+</kb:mo> <kb:mn>0.40</kb:mn> </kb:mrow> </kb:msubsup> </kb:math> for the resonance near 6.9 GeV.