Observation of Orbitally Excited B c + States

The observation 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 proton-proton collision data collected by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total 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 statistical significance over the background-only hypothesis exceeds seven standard deviations. The width of the observed structure is larger than the expectation from a single-peak hypothesis, and is well described by an effective minimal model consisting of two narrow peaks located at <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mn>6704.8</e:mn> <e:mo>±</e:mo> <e:mn>5.5</e:mn> <e:mo>±</e:mo> <e:mn>2.8</e:mn> <e:mo>±</e:mo> <e:mn>0.3</e:mn> <e:mtext> </e:mtext> <e:mtext> </e:mtext> <e:mrow> <e:mi>MeV</e:mi> <e:mo>/</e:mo> </e:mrow> <e:msup> <e:mi>c</e:mi> <e:mn>2</e:mn> </e:msup> </e:math> and <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mn>6752.4</g:mn> <g:mo>±</g:mo> <g:mn>9.5</g:mn> <g:mo>±</g:mo> <g:mn>3.1</g:mn> <g:mo>±</g:mo> <g:mn>0.3</g:mn> <g:mtext> </g:mtext> <g:mtext> </g:mtext> <g:mrow> <g:mi>MeV</g:mi> <g:mo>/</g:mo> </g:mrow> <g:msup> <g:mi>c</g:mi> <g:mn>2</g:mn> </g:msup> </g:math> . The uncertainty terms are statistical, systematic, and associated to the knowledge of the <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:msubsup> <i:mi>B</i:mi> <i:mi>c</i:mi> <i:mo>+</i:mo> </i:msubsup> </i:math> mass, respectively. The measured peak locations are in line with theoretical predictions for lowest excited <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mi>P</k:mi> </k:math> -wave <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:msubsup> <m:mi>B</m:mi> <m:mi>c</m:mi> <m:mo>+</m:mo> </m:msubsup> </m:math> states, marking the first observation of orbitally excited beauty-charm mesons and providing important insights into the internal dynamics of hadrons containing two heavy quarks.