Diffraction at the LHCb Experiment
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
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The LANL Participation in the LHCb Experiment at CERN
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Atomic, Nuclear and Particle Physics↗
Search for the rare hadronic decay $B^0_s → p\overline{p}$
A search for the rare hadronic decay B s 0 → p p ¯ is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb - 1 . No evidence of the decay is found and an upper limit on its branching fraction is set at B ( B s 0 → p p ¯ ) < 4.4 ( 5.1 ) × 10 - 9 at 90% (95%) confidence level; this is currently the world’s best upper limit. The decay mode B 0 → p p ¯ is measured with very large significance, confirming the first observation by the LHCb experiment in 2017. The branching fraction is determined to be B ( B 0 → p p ¯ ) = ( 1.27 ± 0.15 ± 0.05 ± 0.04 ) × 10 - 8 , where the first uncertainty is statistical, the second is systematic and the third is due to the external branching fraction of the normalization channel B 0 → K + π - . The combination of the two LHCb measurements of the B 0 → p p ¯ branching fraction yields B ( B 0 → p p ¯ ) = ( 1.27 ± 0.13 ± 0.05 ± 0.03 ) × 10 - 8 .
Bottom mesons↗
Heavy-ion physics at the LHC
Heavy-ion collisions have been part of the programme of the LHC since its conception. The main nucleus–nucleus system is 208 82 + Pb + 208 82 + Pb . During the Runs 1 and 2, the LHC provided Pb+Pb collisions with centre-of-mass energy per nucleon pair √ s NN = 2.76 and 5.02 TeV, Xe+Xe with √ s NN = 5.44 TeV, and p+Pb with √ s NN = 5.02 and 8.16 TeV. The LHC performance with heavy-ion beams is described in Ref. 1. The ALICE detector was conceived to be dedicated to the study of heavy-ion collisions. The ATLAS and CMS experiments participated in the programme since the very beginning, and the LHCb experiment participated since the end of Run 1. Figure 1 shows event displays of Pb+Pb collisions from the four experiments.
Audurier, Benjamin↗
Enhanced Production of Λ b 0 Baryons in High-Multiplicity p p Collisions at s = 13 TeV
The production rate of Λ b 0 baryons relative to B 0 mesons in p p collisions at a center-of-mass energy s = 13 TeV is measured by the LHCb experiment. The ratio of Λ b 0 to B 0 production cross sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in e + e − collisions, and increases by a factor of ∼ 2 with increasing multiplicity. At relatively low transverse momentum, the ratio of Λ b 0 to B 0 cross sections is higher than what is measured in e + e − collisions, but converges with the e + e − ratio as the momentum increases. These results imply that the evolution of heavy b quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with several models and implications for the mechanisms enforcing quark confinement are discussed. © 2024 CERN, for the LHCb Collaboration 2024 CERN
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Unleashing the full power of LHCb to probe stealth new physics
In this paper, we describe the potential of the LHCb experiment to detect stealth physics. This refers to dynamics beyond the standard model that would elude searches that focus on energetic objects or precision measurements of known processes. Stealth signatures include long-lived particles and light resonances that are produced very rarely or together with overwhelming backgrounds. We will discuss why LHCb is equipped to discover this kind of physics at the Large Hadron Collider and provide examples of well-motivated theoretical models that can be probed with great detail at the experiment.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Software Citation in HEP: Current State and Recommendations for the Future
In November 2022, the HEP Software Foundation and the Institute for Research and Innovation for Software in High-Energy Physics organized a workshop on the topic of Software Citation and Recognition in HEP. The goal of the workshop was to bring together different types of stakeholders whose roles relate to software citation, and the associated credit it provides, in order to engage the community in a discussion on: the ways HEP experiments handle citation of software, recognition for software efforts that enable physics results disseminated to the public, and how the scholarly publishing ecosystem supports these activities. Reports were given from the publication board leadership of the ATLAS, CMS, and LHCb experiments and HEP open source software community organizations (ROOT, Scikit-HEP, MCnet), and perspectives were given from publishers (Elsevier, JOSS) and related tool providers (INSPIRE, Zenodo). This paper summarizes key findings and recommendations from the workshop as presented at the 26th International Conference on Computing in High Energy and Nuclear Physics (CHEP 2023).
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of antiproton production from antihyperon decays in ${p} \textrm{He}$ collisions at $\sqrt{s_{\scriptscriptstyle \mathrm NN}} =110$ GeV
The interpretation of cosmic antiproton flux measurements from space-borne experiments is currently limited by the knowledge of the antiproton production cross-section in collisions between primary cosmic rays and the interstellar medium. Using collisions of protons with an energy of 6.5 TeV incident on helium nuclei at rest in the proximity of the interaction region of the LHCb experiment, the ratio of antiprotons originating from antihyperon decays to prompt production is measured for antiproton momenta between 12 and 110 GeV/c. The dominant antihyperon contribution, namely ${\overline{\varLambda }} \rightarrow {\overline{{p}}} {{\pi } ^+}$ decays from promptly produced $\overline{\varLambda }$ particles, is also exclusively measured. The results complement the measurement of prompt antiproton production obtained from the same data sample. At the energy scale of this measurement, the antihyperon contributions to antiproton production are observed to be significantly larger than predictions of commonly used hadronic production models.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
A study of $CP$ violation in the decays $B^±$ → [$K^+ K^-π^+π^-$]$_Dh^±$ ($h$ = $K, π$) and $B^±$ → [$π^+π^-π^+π^-$]$_Dh^±$
The first study of CP violation in the decay mode $B^±$ → [$K^+ K^-π^+π^-$]$_Dh^±$, with $h$ = $K, π$, is presented, exploiting a data sample of proton–proton collisions collected by the LHCb experiment that corresponds to an integrated luminosity of 9 fb -1 . The analysis is performed in bins of phase space, which are optimised for sensitivity to local CP asymmetries. CP-violating observables that are sensitive to the angle γ of the Unitarity Triangle are determined. The analysis requires external information on charm-decay parameters, which are currently taken from an amplitude analysis of LHCb data, but can be updated in the future when direct measurements become available. Measurements are also performed of phase-space integrated observables for $B^±$ → [$K^+ K^-π^+π^-$]$_Dh^±$ and $B^±$ → [$π^+π^-π^+π^-$]$_Dh^±$ decays.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Study of the B - → Λ c + Λ ¯ c - K - decay
The decay B - → $Λ^+_c \overline{Λ}^-_c K^-$ is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV using data corresponding to an integrated luminosity of 5 fb -1 collected by the LHCb experiment. In the $Λ^+_c K^-$ system, the Ξ c (2930) 0 state observed at the BABAR and Belle experiments is resolved into two narrower states, Ξ c (2923) 0 and Ξ c (2939) 0 , whose masses and widths are measured to be m(Ξ c (2923) 0 ) = 2924.5 ± 0.4 ± 1.1 MeV, m(Ξ c (2939) 0 ) = 2938.5 ± 0.9 ± 2.3 MeV, Γ(Ξ c (2923) 0 ) = 4.8 ± 0.9 ± 1.5 MeV, Γ(Ξ c (2939) 0 ) = 11.0 ± 1.9 ± 7.5 MeV, where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt $Λ^+_c K^-$ sample. Evidence of a new Ξ c (2880) 0 state is found with a local significance of 3.8σ, whose mass and width are measured to be 2881.8 ± 3.1 ± 8.5 MeV and 12.4 ± 5.3 ± 5.8 MeV, respectively. In addition, evidence of a new decay mode Ξ c (2790) 0 → $Λ^+_c K^-$ is found with a significance of 3.7σ. The relative branching fraction of B - → $Λ^+_c \overline{Λ}^-_c K^-$ with respect to the B - → D + D - K - decay is measured to be 2.36 ± 0.11 0.22 ± 0.25, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.
79 ASTRONOMY AND ASTROPHYSICS↗
Test of Lepton Flavor Universality with B s 0 → ϕ ℓ + ℓ − Decays
Lepton flavor universality in rare b → s transitions is tested for the first time using B s 0 meson decays. The measurements are performed using p p collision data collected by the LHCb experiment between 2011 and 2018, corresponding to a total integrated luminosity of 9 fb − 1 . Branching fraction ratios between the B s 0 → ϕ e + e − and B s 0 → ϕ μ + μ − decays are measured in three regions of dilepton mass squared, q 2 , with 0.1 < q 2 < 1.1 , 1.1 < q 2 < 6.0 , and 15 < q 2 < 19 GeV 2 / c 4 . The results agree with the standard model expectation of lepton flavor universality. © 2025 CERN, for the LHCb Collaboration 2025 CERN
Aaij, R. (ORCID:0000000305331952)↗
Measurement of CP observables in B ± → D (*) K ± and B ± → D (*) π ± decays using two-body D final states
Measurements of CP observables in B ± → D (*) K ± and B ± → D (*) π ± decays are presented, where D (∗) indicates a neutral D or D ∗ meson that is an admixture of meson and anti-meson states. Decays of the D (∗) meson to the Dπ 0 and Dγ final states are partially reconstructed without inclusion of the neutral pion or photon. Decays of the D meson are reconstructed in the K ± π ∓ , K + K - , and π + π - final states. The analysis uses a sample of charged B mesons produced in proton-proton collisions and collected with the LHCb experiment, corresponding to integrated luminosities of 2.0, 1.0, and 5.7 fb -1 taken at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The measurements of partially reconstructed B ± → D (*) K ± and B ± → D (∗) π ± with D → K ∓ π ± decays are the first of their kind, and a first observation of the B ± → (Dπ 0 ) D ∗ π ± decay is made with a significance of 6.1 standard deviations. All CP observables are measured with world-best precision, and in combination with other LHCb results will provide strong constraints on the CKM angle γ.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Measurement of the Branching Fraction Ratios R ( D + ) and R ( D * + ) Using Muonic τ Decays
The branching fraction ratios of B ¯ 0 → D + τ − ν ¯ τ and B ¯ 0 → D * + τ − ν ¯ τ decays are measured with respect to their muonic counterparts, using a data sample corresponding to an integrated luminosity of 2.0 fb − 1 collected by the LHCb experiment in proton-proton collisions at s = 13 TeV . The reconstructed final states are formed by combining D + mesons with τ − → μ − ν ¯ μ ν τ candidates, where the D + is reconstructed via the D + → K − π + π + decay. The results are R ( D + ) = 0.249 ± 0.043 ± 0.047 , R ( D * + ) = 0.402 ± 0.081 ± 0.085 , where the first uncertainties are statistical and the second systematic. The two measurements have a correlation coefficient of − 0.39 and are compatible with the standard model. © 2025 CERN, for the LHCb Collaboration 2025 CERN
Aaij, R. (ORCID:0000000305331952)↗
Search for the rare decay of charmed baryon Λ c + into the p μ + μ − final state
A search for the nonresonant Λ c + → p μ + μ − decay is performed using proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the LHCb experiment, corresponding to an integrated luminosity of 5.4 fb − 1 . No evidence for the decay is found in the dimuon invariant-mass regions where the expected contributions of resonances is subdominant. The upper limit on the branching fraction of the Λ c + → p μ + μ − decay is determined to be 2.9 ( 3.2 ) × 10 − 8 at 90 % ( 95 % ) confidence level. The branching fractions in the dimuon invariant-mass regions dominated by the η , ρ and ω resonances are also determined. © 2024 CERN, for the LHCb Collaboration 2024 CERN
Aaij, R. (ORCID:0000000305331952)↗
New Structures in the J / ψ J / ψ Mass Spectrum in Proton-Proton Collisions at s = 13 TeV
A search is reported for near-threshold structures in the J / ψ J / ψ invariant mass spectrum produced in proton-proton collisions at s = 13 TeV from data collected by the CMS experiment, corresponding to an integrated luminosity of 135 fb − 1 . Three structures are found, and a model with quantum interference among these structures provides a good description of the data. A new structure is observed with a local significance above 5 standard deviations at a mass of 6638 − 38 + 43 ( stat ) − 31 + 16 ( syst ) MeV . Another structure with even higher significance is found at a mass of 6847 − 28 + 44 ( stat ) − 20 + 48 ( syst ) MeV , which is consistent with the X ( 6900 ) resonance reported by the LHCb experiment and confirmed by the ATLAS experiment. Evidence for another new structure, with a local significance of 4.7 standard deviations, is found at a mass of 7134 − 25 + 48 ( stat ) − 15 + 41 ( syst ) MeV . Results are also reported for a model without interference, which does not fit the data as well and shows mass shifts up to 150 MeV relative to the model with interference. © 2024 CERN, for the CMS Collaboration 2024 CERN
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for resonance-enhanced C P and angular asymmetries in the Λ c + → p μ + μ − decay at LHCb
The first measurement of the C P asymmetry of the decay rate ( A C P ) and the C P average ( Σ A FB ) and C P asymmetry ( Δ A FB ) of the forward-backward asymmetry in the muon system of Λ c + → p μ + μ − decays is reported. The measurement is performed using a data sample of proton-proton collisions, recorded by the LHCb experiment from 2016 to 2018 at a center-of-mass energy of 13 TeV, which corresponds to an integrated luminosity of 5.4 fb − 1 . The asymmetries are measured in two regions of dimuon mass near the ϕ -meson mass peak. The dimuon-mass integrated results are A C P = ( − 1.1 ± 4.0 ± 0.5 ) % , Σ A FB = ( 3.9 ± 4.0 ± 0.6 ) % , Δ A FB = ( 3.1 ± 4.0 ± 0.4 ) % , where the first uncertainty is statistical and the second systematic. The results are consistent with the conservation of C P symmetry and the Standard Model expectations. © 2025 CERN, for the LHCb Collaboration 2025 CERN
Aaij, R. (ORCID:0000000305331952)↗
Measurement of Λ b 0 , Λ c + , and Λ Decay Parameters Using Λ b 0 → Λ c + h − Decays
A comprehensive study of the angular distributions in the bottom-baryon decays Λ b 0 → Λ c + h − ( h = π , K ) , followed by Λ c + → Λ h + with Λ → p π − or Λ c + → p K S 0 decays, is performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 9 fb − 1 collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The decay parameters and the associated charge-parity ( C P ) asymmetries are measured, with no significant C P violation observed. For the first time, the Λ b 0 → Λ c + h − decay parameters are measured. The most precise measurements of the decay parameters α , β , and γ are obtained for Λ c + decays and an independent measurement of the decay parameters for the strange-baryon Λ decay is provided. The results deepen our understanding of weak decay dynamics in baryon decays. © 2024 CERN, for the LHCb Collaboration 2024 CERN
Aaij, R. (ORCID:0000000305331952)↗
Branching fraction measurement of the decay B + → ψ ( 2 S ) ϕ ( 1020 ) K +
The branching fraction of the decay B + → ψ ( 2 S ) ϕ ( 1020 ) K + , relative to the topologically similar decay B + → J / ψ ϕ ( 1020 ) K + , is measured using proton-proton collision data collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb − 1 . The ratio is found to be 0.061 ± 0.004 ± 0.009 , where the first uncertainty is statistical and the second systematic. Using the world-average branching fraction for B + → J / ψ ϕ ( 1020 ) K + , the branching fraction for the decay B + → ψ ( 2 S ) ϕ ( 1020 ) K + is found to be ( 3.0 ± 0.2 ± 0.5 ± 0.2 ) × 10 − 6 , where the first uncertainty is statistical, the second systematic, and the third is due to the branching fraction of the normalization channel. © 2025 CERN, for the LHCb Collaboration 2025 CERN
Aaij, R. (ORCID:0000000305331952)↗