Evidence for the Rare Decay <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> </mml:msup> <mml:mo stretchy="false">→</mml:mo> <mml:mover accent="true"> <mml:mrow> <mml:mi mathvariant="normal">Λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="false">¯</mml:mo> </mml:mrow> </mml:mover> <mml:mi>p</mml:mi> <mml:msup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math>

2026/01/31 by LHCb collaboration, R. Aaij, Carlos Abellán Beteta +1212
Physics and Astronomy · #Neutrino Physics Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #hep-ex

paper · pdf · doi:10.1103/pl88-4435

published as Phys. Rev. Lett. 137 (2026) 051801 · All figures and tables, along with any supplementary material and additional information, are available at https://lhcb-glance.cern.ch/alcm/public/analysis/full-details/5370

openalex publication_date 2026/03/24 · openalex created_date 2026/03/25 · arxiv created 2026/07/29 · arxiv updated 2026/07/30 · openalex updated_date 2026/07/30

Abstract

A search for the rare decay <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:msup> <a:mrow> <a:mi>B</a:mi> </a:mrow> <a:mrow> <a:mo>+</a:mo> </a:mrow> </a:msup> <a:mo stretchy="false">→</a:mo> <a:mrow> <a:mover accent="true"> <a:mrow> <a:mi mathvariant="normal">Λ</a:mi> </a:mrow> <a:mrow> <a:mo stretchy="false">¯</a:mo> </a:mrow> </a:mover> <a:mi>p</a:mi> <a:msup> <a:mrow> <a:mi>μ</a:mi> </a:mrow> <a:mrow> <a:mo>+</a:mo> </a:mrow> </a:msup> <a:msup> <a:mrow> <a:mi>μ</a:mi> </a:mrow> <a:mrow> <a:mo>−</a:mo> </a:mrow> </a:msup> </a:mrow> </a:mrow> </a:math> is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mrow> <g:msqrt> <g:mrow> <g:mi>s</g:mi> </g:mrow> </g:msqrt> <g:mo>=</g:mo> <g:mn>13</g:mn> <g:mtext> </g:mtext> <g:mtext> </g:mtext> <g:mi>TeV</g:mi> </g:mrow> </g:math> , corresponding to an integrated luminosity of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mn>5.4</i:mn> <i:mtext> </i:mtext> <i:mtext> </i:mtext> <i:msup> <i:mi>fb</i:mi> <i:mrow> <i:mo>−</i:mo> <i:mn>1</i:mn> </i:mrow> </i:msup> </i:math> . An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mrow> <k:mi>m</k:mi> <k:mo stretchy="false">(</k:mo> <k:mover accent="true"> <k:mrow> <k:mi mathvariant="normal">Λ</k:mi> </k:mrow> <k:mrow> <k:mo stretchy="false">¯</k:mo> </k:mrow> </k:mover> <k:mi>p</k:mi> <k:mo stretchy="false">)</k:mo> <k:mo>&lt;</k:mo> <k:mn>2.8</k:mn> <k:mtext> </k:mtext> <k:mtext> </k:mtext> <k:mrow> <k:mi>GeV</k:mi> <k:mo>/</k:mo> <k:msup> <k:mrow> <k:mi>c</k:mi> </k:mrow> <k:mrow> <k:mn>2</k:mn> </k:mrow> </k:msup> </k:mrow> </k:mrow> </k:math> . The branching fraction is measured to be <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"> <r:mrow> <r:msub> <r:mrow> <r:mi mathvariant="script">B</r:mi> </r:mrow> <r:mrow> <r:mi>low</r:mi> </r:mrow> </r:msub> <r:mo stretchy="false">(</r:mo> <r:msup> <r:mrow> <r:mi>B</r:mi> </r:mrow> <r:mrow> <r:mo>+</r:mo> </r:mrow> </r:msup> <r:mo stretchy="false">→</r:mo> <r:mrow> <r:mover accent="true"> <r:mrow> <r:mi mathvariant="normal">Λ</r:mi> </r:mrow> <r:mrow> <r:mo stretchy="false">¯</r:mo> </r:mrow> </r:mover> <r:mi>p</r:mi> <r:msup> <r:mrow> <r:mi>μ</r:mi> </r:mrow> <r:mrow> <r:mo>+</r:mo> </r:mrow> </r:msup> <r:msup> <r:mrow> <r:mi>μ</r:mi> </r:mrow> <r:mrow> <r:mo>−</r:mo> </r:mrow> </r:msup> </r:mrow> <r:mo stretchy="false">)</r:mo> <r:mo>=</r:mo> <r:mrow> <r:mo minsize="1ex" stretchy="true">(</r:mo> <r:mn>1.7</r:mn> <r:msubsup> <r:mrow> <r:mn>0</r:mn> </r:mrow> <r:mrow> <r:mo>−</r:mo> <r:mn>0.56</r:mn> </r:mrow> <r:mrow> <r:mo>+</r:mo> <r:mn>0.65</r:mn> </r:mrow> </r:msubsup> <r:mo stretchy="false">(</r:mo> <r:mrow> <r:mi>stat</r:mi> </r:mrow> <r:mo stretchy="false">)</r:mo> <r:mo>±</r:mo> <r:mn>0.17</r:mn> <r:mo stretchy="false">(</r:mo> <r:mrow> <r:mi>syst</r:mi> </r:mrow> <r:mo stretchy="false">)</r:mo> <r:mo>±</r:mo> <r:mspace linebreak="goodbreak"/> <r:mn>0.14</r:mn> <r:mo stretchy="false">(</r:mo> <r:mi>ext</r:mi> <r:mo stretchy="false">)</r:mo> <r:mo minsize="1ex" stretchy="true">)</r:mo> </r:mrow> <r:mo>×</r:mo> <r:msup> <r:mrow> <r:mn>10</r:mn> </r:mrow> <r:mrow> <r:mo>−</r:mo> <r:mn>8</r:mn> </r:mrow> </r:msup> </r:mrow> </r:math> , where the last uncertainty is due to external inputs on <lb:math xmlns:lb="http://www.w3.org/1998/Math/MathML" display="inline"> <lb:mrow> <lb:mi mathvariant="script">B</lb:mi> <lb:mo stretchy="false">(</lb:mo> <lb:msup> <lb:mrow> <lb:mi>B</lb:mi> </lb:mrow> <lb:mrow> <lb:mo>+</lb:mo> </lb:mrow> </lb:msup> <lb:mo stretchy="false">→</lb:mo> <lb:mrow> <lb:mrow> <lb:mi>J</lb:mi> <lb:mo>/</lb:mo> <lb:mi>ψ</lb:mi> </lb:mrow> <lb:mover accent="true"> <lb:mrow> <lb:mi mathvariant="normal">Λ</lb:mi> </lb:mrow> <lb:mrow> <lb:mo stretchy="false">¯</lb:mo> </lb:mrow> </lb:mover>

Citations

• A Decision-Theoretic Generalization of On-Line Learning and an Application to Boosting
• The Large-Sample Distribution of the Likelihood Ratio for Testing Composite Hypotheses
• Review of Particle Physics
• The LHCb Stripping Project: Sustainable Legacy Data Processing for High-Energy Physics
• Minimal Flavor Violation
• Geant4 developments and applications
• Sensitivity of searches for new signals and its optimization
• Presentation of search results: the CL s technique
• A complete analysis of FCNC and CP constraints in general SUSY extensions of the standard model

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• Search for B_(s)^*0→μ⁺μ^- in B_c⁺→π⁺μ⁺μ^- decays
• An analysis of Λ_b⁰ → Λμ⁺μ^- decays at the LHCb experiment