A bstract This paper presents a study of the charmless three-body decays $$ {B}_{(s)}^0\to {K}_{\mathrm{S}}^0{h}^{+}h{\prime}^{-} $$ B s 0 → K S 0 h + h ′ − (where h ( ′ ) = π, K ), using a sample of pp collision data collected by the LHCb experiment during Runs 1 and 2 of the LHC, corresponding to an integrated luminosity of 9 fb − 1 . The decay $$ {B}_s^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-} $$ B s 0 → K S 0 K + K − is observed for the first time, and the following ratios of branching fractions are measured: $$ {\displaystyle \begin{array}{l}\frac{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.578\pm 0.007\pm 0.017,\\ {}\frac{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{K}^{\pm }{K}^{\mp}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.1363\pm 0.0035\pm 0.051,\\ {}\begin{array}{l}\frac{\mathcal{B}\left({B}_s^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.269\pm 0.011\pm 0.015\pm 0.008,\\ {}\frac{\mathcal{B}\left({B}_s^0\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=0.0303\pm 0.0041\pm 0.0025\pm 0.0009,\\ {}\frac{\mathcal{B}\left({B}_s^0\to {K}_{\mathrm{S}}^0{K}^{\pm }{\pi}^{\mp}\right)}{\mathcal{B}\left({B}^0\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-}\right)}=1.818\pm 0.021\pm 0.031\pm 0.056,\end{array}\end{array}} $$ B B 0 → K S 0 K + K − B B 0 → K S 0 π + π − = 0.578 ± 0.007 ± 0.017 , B B 0 → K S 0 K ± K ∓ B B 0 → K S 0 π + π − = 0.1363 ± 0.0035 ± 0.051 , B B s 0 → K S 0 π + π − B B 0 → K S 0 π + π − = 0.269 ± 0.011 ± 0.015 ± 0.008 , B B s 0 → K S 0 K + K − B B 0 → K S 0 π + π − = 0.0303 ± 0.0041 ± 0.0025 ± 0.0009 , B B s 0 → K S 0 K ± π ∓ B B 0 → K S 0 π + π − = 1.818 ± 0.021 ± 0.031 ± 0.056 , where the uncertainties are statistical, systematic, and due to knowledge of the ratio of hadronisation fractions of the $$ {B}_s^0 $$ B s 0 and B 0 mesons, respectively.

The first angular analysis of Λ_ b^0→ Λ(1520) μ^+μ^- decays is presented, using proton-proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb^-1. The leptonic forward-backward asymmetry, A_FB, 3/2^ℓ, and the CP-averaged angular observable, S_1cc, are determined by fitting projections of the angular distributions in four intervals of the square of the dimuon invariant mass between 0.1 and 12.5 GeV^2/c^4. The results are in good agreement with predictions based on the Standard Model of particle physics.

A search for the Cabibbo-suppressed decay Ξ_c^0 → pK^- is performed using pp collision data corresponding to an integrated luminosity of 5.4 fb^-1, collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The decay is observed for the first time and its branching fraction measured to be (4.5±0.5±0.2±0.9)×10^-5, where the uncertainties are statistical, systematic and from the branching fraction of the normalisation channel Ξ_b^- → Ξ_c^0 (→ p K^- K^- π^+) π^-. Using the decay chain Ξ_b^- → Ξ_c^0(→ pK^-)π^-, the decay asymmetry parameter of the Ξ_c^0 → pK^- decay is determined to be α_Ξ_c^0=0.32±0.15±0.01.

Branching fractions of $η$ and $η'(958)$ anomalous decays are measured using $pp$ collision data at a center-of-mass energy of $\sqrt{s}=13\,\text{TeV}$ collected by the LHCb experiment and corresponding to an integrated luminosity of $5.4\,\text{fb}^{-1}$. The measured values and upper limits are \begin{align*} \cal{B}(η\toμ^+μ^-) &= (5.30\pm0.14\pm0.18\pm0.26)\times10^{-6} , \\ \cal{B}(η'(958)\toμ^+μ^-) &<1.9\times10^{-7}\textrm{ at 90% CL} , \\ \cal{B}(η\toπ^+π^-μ^+μ^-) &<5.4\times10^{-7}\textrm{ at 90% CL}, \\ \cal{B}(η'(958)\toπ^+π^-μ^+μ^-) &= (2.73\pm0.14\pm0.13\pm0.14)\times10^{-5} , \end{align*} where the uncertainties are, respectively, statistical, systematic, and due to the external branching fraction of the $ϕ(1020)\toμ^+μ^-$ decay, which is used for normalization. This marks the first experimental search for the $η'(958)$ decay, and the most precise measurement of the branching fraction $\cal{B}(η\toμ^+μ^-)$ to date.

The production rates of (2S) and (3S) mesons relative to that of the (1S) state are measured in pp, pO, and OO collisions by the LHCb collaboration. The ratios measured in pp data are consistent with previous LHCb measurements at different center-of-mass energies. Only slight relative suppression of the (2S) and (3S) states is found in pO collisions, while in OO collisions the (2S) is suppressed by a factor of ∼2, with evidence for suppression of the (3S). The significant suppression in OO data, compared to the small effect in pO data, shows the emergence of additional suppression mechanisms in the relatively small OO collision system. Models incorporating quark-gluon plasma formation in OO collisions successfully describe the data. Implications for the interplay between cold nuclear matter effects and color screening in a deconfined quark-gluon plasma are discussed.

The first evidence for the decay B^{+}→π^{+}e^{+}e^{-} is reported using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9  fb^{-1}. A signal excess with a significance of 3.2σ is observed and the branching fraction is measured to be B(B^{+}→π^{+}e^{+}e^{-})=(2.4_{-0.8}^{+0.9} _{-0.2}^{+0.4})×10^{-8}, where the first set of uncertainties is statistical and the second is systematic. The result is consistent with the Standard Model expectation.

Abstract A measurement of the CKM angle γ using the decay channels B ± → DK ± and B ± → Dπ ± , where the D meson decays to D → K S 0 π + π − $$ D\to {K}_{\mathrm{S}}^0{\pi}^{+}{\pi}^{-} $$ or D → K S 0 K + K − $$ D\to {K}_{\mathrm{S}}^0{K}^{+}{K}^{-} $$ , is performed with a data sample corresponding to an integrated luminosity of 5.8 fb −1, collected during 2024 by the upgraded LHCb experiment. CP violation is observed through a difference in the distributions of the Dalitz plot of the D decay between the B + and B − mesons. The CKM angle γ is determined to be γ = (68.1 ± 6.7)°. Other parameters related to the examined B meson decay modes are also measured. This is the first measurement of the CKM angle γ using the upgraded LHCb detector.

The time-dependent CP asymmetry in B^0_s→ J/ψπ^+π^- decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6 fb^-1, collected with the LHCb detector at a centre-of-mass energy of 13 TeV during . The CP-violating phase, ϕ_s, the direct CP-violation parameter, |λ|, and the decay width of the heavy mass eigenstate in the B^0_s system, Γ_ H, are measured respectively to be ϕ_s = -0.077 ± 0.034 ± 0.007 rad, |λ| = 0.993 ± 0.026 ± 0.007 and Γ_ H = 0.610 ± 0.002 ± 0.004 ps^-1, where the first uncertainties are statistical and the second systematic. These results are consistent with previous measurements and the expectation based on the Standard Model. The combination with previous measurements in B^0_s→ J/ψπ^+π^- decays using 7 TeV and 8 TeV proton-proton collision data yields ϕ_s = -0.046 ± 0.031 rad, |λ| = 0.975 ± 0.024 and Γ_ H = 0.610 ± 0.004 ps^-1, while the combination including all other LHCb measurements gives ϕ_s = -0.041 ± 0.017 rad.

The first observation of the chi(c1) (3872) -> J/psi mu(+)mu(-) decay is reported using proton-proton collision data recorded with the LHCb detector corresponding to an integrated luminosity of 9 fb(-1). The decay mode is observed for the first time, with a significance of 6.5s. Its branching fraction is measured relative to the chi(c1) (3872) -> J/psi pi(+)pi(-) decay mode B(chi(c1)(3872) -> J/psi mu(+)mu(-))/B(chi(c1)(3872) -> J/psi pi(+)pi(-)) = (1.68 +/- 0.32 +/- 0.05) x 10(-3), where the first uncertainty includes both statistical contributions and systematic contributions which are uncorrelated between data-taking periods, and the second represents the systematic contributions that are correlated between data- taking periods.

A search for the rare decay B^+→Λ̅p μ^+ μ^- is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of √(s)= 13 TeV, corresponding to an integrated luminosity of 5.4 fb^-1. 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 m(Λ̅p)<2.8 GeV/c^2. The branching fraction is measured to be B_ low(B^+→Λ̅p μ^+ μ^-)=(1.70 ^+0.65_-0.56( stat) ± 0.17( syst) ± 0.14( ext)) × 10^-8, where the last uncertainty is due to external inputs on B(B^+→J/ψΛ̅p)× B(J/ψ→μ^+μ^-). With no significant signal observed in the high m(Λ̅p) region above 2.8 GeV/c^2, an upper limit is set to be B_ high(B^+→Λ̅p μ^+ μ^-)<2.8 (3.7) × 10^-9 at the 90% (95%) confidence level.

An analysis of the decay amplitudes of B^0 → K^*0(→ K^+π^-)μ^+μ^- is presented, using proton-proton collision data recorded by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 8.4 fb^-1. The amplitudes are constructed from Legendre polynomials in the μ^+μ^- invariant mass squared region 1.1<q^2<8.0 GeV^2/c^4. CP-averaged observables are obtained from the amplitudes. Some of these observables present deviations with respect to the Standard Model, which can be interpreted as shifts in the effective Wilson coefficients. This model-independent approach enables tests of theoretical predictions that can help disentangle hadronic effects from potential contributions from physics beyond the Standard Model. This allows flexibility in the choice of q^2 binning for global analyses. Depending on the binning scheme, the deviation of the Wilson coefficient C_9 from its Standard Model expectation varies from 4.3σ to 4.8σ.

Abstract A measurement of the branching fraction for the decay Λ → p μ − ν ¯ μ $$ \Lambda \to p{\mu}^{-}{\overline{\nu}}_{\mu } $$ is presented using pp collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The analysis is based on data recorded between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb −1. The result is obtained using Λ → pμ − decays as a normalisation channel. The measured branching fraction is B Λ → p μ − ν ¯ μ = 1.462 ± 0.016 ± 0.100 ± 0.011 × 10 − 4 $$ \mathcal{B}\left(\Lambda \to p{\mu}^{-}{\overline{\nu}}_{\mu}\right)=\left(1.462\pm 0.016\pm 0.100\pm 0.011\right)\times {10}^{-4} $$ , where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalisation mode branching fraction, respectively. This result improves the precision of the branching fraction measurement by a factor of two compared to the previous best measurement and sets a more stringent bound on lepton flavour universality in s → u quark transitions. It is consistent with previous measurements, and the extracted lepton flavour universality test observable, R μe = Γ Λ → p μ − ν ¯ μ Γ Λ → p e − ν ¯ e = 0.175 ± 0.012 $$ {R}^{\mu e}=\frac{\Gamma \left(\Lambda \to p{\mu}^{-}{\overline{\nu}}_{\mu}\right)}{\Gamma \left(\Lambda \to p{e}^{-}{\overline{\nu}}_e\right)}=0.175\pm 0.012 $$ , agrees with the Standard Model prediction.

Abstract A search for the charmless purely baryonic decay Λ b 0 → Λ p p ¯ $$ {\Lambda}_b^0\to \Lambda p\overline{p} $$ is performed using proton-proton collision data recorded by the LHCb experiment at a centre-of-mass energy of s = 13 $$ \sqrt{s}=13 $$ TeV and corresponding to an integrated luminosity of 6.0 fb −1. The signal decay is observed with a significance of 5.1 standard deviations. Its branching fraction is measured for the first time, relative to that of the topologically similar decay Λ b 0 → Λ K + K − $$ {\Lambda}_b^0\to \Lambda {K}^{+}{K}^{-} $$ . Contributions from intermediate charmonium resonances decaying to the p p ¯ $$ p\overline{p} $$ and K + K − final states are explicitly excluded with a requirement on the invariant mass of the companion hadron system, m h h ¯ < 2.85 $$ m\left(h\overline{h}\right)<2.85 $$ GeV, where h stands for a proton or a charged kaon. The relative branching fraction is found to be B Λ b 0 → Λ p p ¯ B Λ b 0 → Λ K + K − = 5.1 ± 1.3 stat ± 0.3 syst × 10 − 2 . $$ \frac{\mathcal{B}\left({\Lambda}_b^0\to \Lambda p\overline{p}\right)}{\mathcal{B}\left({\Lambda}_b^0\to \Lambda {K}^{+}{K}^{-}\right)}=\left(5.1\pm {1.3}_{\left(\mathrm{stat}\right)}\pm {0.3}_{\left(\mathrm{syst}\right)}\right)\times {10}^{-2}. $$

Abstract A search for long-lived heavy neutral leptons produced in B-meson decays and decaying to a μ ± π∓ final state is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 fb −1. The results are interpreted in both lepton-number-conserving and lepton-number-violating scenarios. No significant excess is observed. Constraints are placed on the squared mixing element |U μN|2 to the active muon neutrino, under the assumption that couplings to other lepton flavours are negligible, in the mass range of 1.6–5.5 GeV.

The pp → W±(→ μ±νμ)X cross-sections are measured at a proton-proton centre-of-mass energy √(s)=5.02 TeV using a dataset corresponding to an integrated luminosity of 100 pb−1 recorded by the LHCb experiment. Considering muons in the pseudorapidity range 2.2 < η < 4.4, the cross-sections are measured differentially in twelve intervals of muon transverse momentum between 28 < pT < 52 GeV. Integrated over pT, the measured cross-sections are [ σ_W^+→μ^+ν_μ=300.9± 2.4± 3.8± 6.0 pb,; σ_W^-→μ^-ν_μ=236.9± 2.1± 2.7± 4.7 pb, ] where the first uncertainties are statistical, the second are systematic, and the third are associated with the luminosity calibration. These integrated results are consistent with theoretical predictions. This analysis introduces a new method to determine the W-boson mass using the measured differential cross-sections corrected for detector effects. The measurement is performed on this statistically limited dataset as a proof of principle and yields m_W=80369± 130± 33 MeV, where the first uncertainty is experimental and the second is theoretical.

Muon-electron universality is tested in B^{0}→K^{*0}ℓ^{+}ℓ^{-} decays, in the dilepton-invariant-mass region above the ψ(2S) resonance. The analysis uses beauty mesons produced in proton-proton collisions recorded by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9  fb^{-1}. The ratio of branching fractions between the muon and electron channels R_{K^{*0}} is measured to be 1.08_{-0.12}^{+0.14}(stat)±0.07(syst) for a dilepton-invariant-mass squared above 14.0  GeV^{2}/c^{4}, consistent with the standard model prediction. This result represents the most precise measurement of R_{K^{*0}} in this region and the first such measurement performed at a hadron collider.

Abstract Measurements of the combined CP asymmetries in B ¯ 0 → D s − D + $$ {\overline{B}}^0\to {D}_s^{-}{D}^{+} $$ and B ¯ s 0 → D s − D − $$ {\overline{B}}_s^0\to {D}_s^{-}{D}^{-} $$ decays are made using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb −1. The measurements are found to be A CP B ¯ 0 → D s − D + = 0.0009 ± 0.0053 ± 0.0040 , A CP B ¯ s 0 → D s − D − = 0.103 ± 0.053 ± 0.010 , $$ {\displaystyle \begin{array}{l}{A}_{CP}\left({\overline{B}}^0\to {D}_s^{-}{D}^{+}\right)=0.0009\pm 0.0053\pm 0.0040,\\ {}{A}_{CP}\left({\overline{B}}_s^0\to {D}_s^{-}{D}^{-}\right)=0.103\pm 0.053\pm 0.010,\end{array}} $$ where the first and second uncertainties are statistical and systematic, respectively. This is the first measurement of this asymmetry in B ¯ s 0 $$ {\overline{B}}_s^0 $$ decays, and the most precise measurement to date for B ¯ 0 $$ {\overline{B}}^0 $$ decays. Both measurements are found to be consistent with CP symmetry.

A measurement of the ψ(2S)-to-J/ψ production cross-section ratio is performed in proton-argon (pAr) and proton-proton (pp) collisions in fixed-target mode at √(s_NN)=113 GeV. Data samples were collected by the LHCb experiment during argon and hydrogen gas injections in the SMOG2 storage cell, resulting in pAr and pp collisions, respectively. The ψ(2S)-to-J/ψ production cross-section ratio is measured as a function of the charmonium transverse momentum, p_T, and rapidity in the centre-of-mass system, y^*. The ψ(2S)-to-J/ψ ratio in pAr collisions over that in pp collisions is measured to be 0.90 ± 0.04 ± 0.02 for -2.3<y^*<0.0 and 0<p_T<8GeV/c, indicating the emergence of nuclear effects in the pAr system. This study acts as a baseline for the interpretation of future measurements with larger systems accessible by the LHCb experiment.

A bstract A search for the charmless purely baryonic decay $$ {\Lambda}_b^0\to \Lambda p\overline{p} $$ Λ b 0 → Λ p p ¯ is performed using proton-proton collision data recorded by the LHCb experiment at a centre-of-mass energy of $$ \sqrt{s}=13 $$ s = 13 TeV and corresponding to an integrated luminosity of 6 . 0 fb − 1 . The signal decay is observed with a significance of 5.1 standard deviations. Its branching fraction is measured for the first time, relative to that of the topologically similar decay $$ {\Lambda}_b^0\to \Lambda {K}^{+}{K}^{-} $$ Λ b 0 → Λ K + K − . Contributions from intermediate charmonium resonances decaying to the $$ p\overline{p} $$ p p ¯ and K + K − final states are explicitly excluded with a requirement on the invariant mass of the companion hadron system, $$ m\left(h\overline{h}\right)<2.85 $$ m h h ¯ < 2.85 GeV, where h stands for a proton or a charged kaon. The relative branching fraction is found to be $$ \frac{\mathcal{B}\left({\Lambda}_b^0\to \Lambda p\overline{p}\right)}{\mathcal{B}\left({\Lambda}_b^0\to \Lambda {K}^{+}{K}^{-}\right)}=\left(5.1\pm {1.3}_{\left(\mathrm{stat}\right)}\pm {0.3}_{\left(\mathrm{syst}\right)}\right)\times {10}^{-2}. $$ B Λ b 0 → Λ p p ¯ B Λ b 0 → Λ K + K − = 5.1 ± 1.3 stat ± 0.3 syst × 10 − 2 .