Study of B c ( 1 P ) + states in the B c + γ mass spectrum

The study of a wide peaking structure in the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msubsup> <a:mi>B</a:mi> <a:mi>c</a:mi> <a:mo>+</a:mo> </a:msubsup> <a:mi>γ</a:mi> </a:math> mass spectrum is reported using a data sample of proton-proton collisions collected by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mn>9</c:mn> <c:mtext> </c:mtext> <c:mtext> </c:mtext> <c:msup> <c:mi>fb</c:mi> <c:mrow> <c:mo>−</c:mo> <c:mn>1</c:mn> </c:mrow> </c:msup> </c:math> . The observed structure is consistent with the lowest excited <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mi>P</e:mi> </e:math> -wave <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:msubsup> <g:mi>B</g:mi> <g:mi>c</g:mi> <g:mo>+</g:mo> </g:msubsup> </g:math> states and exhibits a statistical significance exceeding 7 standard deviations relative to the background-only hypothesis. A two-peak model serves as an effective description of the data, with various theory-constrained models further explored to provide physical interpretation. Based on the predictions for the <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:msub> <i:mi>B</i:mi> <i:mi>c</i:mi> </i:msub> <i:mo stretchy="false">(</i:mo> <i:mn>1</i:mn> <i:mi>P</i:mi> <i:msup> <i:mo stretchy="false">)</i:mo> <i:mo>+</i:mo> </i:msup> </i:math> spectrum, the relative production cross section of the overall <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:msub> <m:mi>B</m:mi> <m:mi>c</m:mi> </m:msub> <m:mo stretchy="false">(</m:mo> <m:mn>1</m:mn> <m:mi>P</m:mi> <m:msup> <m:mo stretchy="false">)</m:mo> <m:mo>+</m:mo> </m:msup> </m:math> states with respect to the <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"> <q:msubsup> <q:mi>B</q:mi> <q:mi>c</q:mi> <q:mo>+</q:mo> </q:msubsup> </q:math> ground state with the transverse momentum <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:msub> <s:mi>p</s:mi> <s:mi mathvariant="normal">T</s:mi> </s:msub> </s:math> and rapidity <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"> <v:mi>y</v:mi> </v:math> of <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"> <x:msubsup> <x:mi>B</x:mi> <x:mi>c</x:mi> <x:mo>+</x:mo> </x:msubsup> </x:math> mesons in the regions <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"> <z:msub> <z:mi>p</z:mi> <z:mi mathvariant="normal">T</z:mi> </z:msub> <z:mo><</z:mo> <z:mn>20</z:mn> <z:mtext> </z:mtext> <z:mtext> </z:mtext> <z:mi>GeV</z:mi> <z:mo>/</z:mo> <z:mi>c</z:mi> </z:math> and <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"> <cb:mn>2.0</cb:mn> <cb:mo><</cb:mo> <cb:mi>y</cb:mi> <cb:mo><</cb:mo> <cb:mn>4.5</cb:mn> </cb:math> at <eb:math xmlns:eb="http://www.w3.org/1998/Math/MathML" display="inline"> <eb:msqrt> <eb:mi>s</eb:mi> </eb:msqrt> <eb:mo>=</eb:mo> <eb:mn>13</eb:mn> <eb:mtext> </eb:mtext> <eb:mtext> </eb:mtext> <eb:mi>TeV</eb:mi> </eb:math> is measured to be <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"> <gb:mn>0.20</gb:mn> <gb:mo>±</gb:mo> <gb:mn>0.03</gb:mn> <gb:mo>±</gb:mo> <gb:mn>0.02</gb:mn> <gb:mo>±</gb:mo> <gb:mn>0.03</gb:mn> </gb:math> , where the uncertainty terms represent statistical, systematic, and uncertainties related to the choice of theoretical models, respectively. The results provide a test of theoretical models and deepen our understanding of quantum chromodynamics.