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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Measurements of differential cross-sections in four-lepton events in 13 TeV proton-proton collisions with the ATLAS detector. J. High Energy Phys., 07(7), 005–67pp.
Abstract: Measurements of four-lepton differential and integrated fiducial cross-sections in events with two same-flavour, opposite-charge electron or muon pairs are presented. The data correspond to 139 fb(-1) of root s = 13 TeV proton-proton collisions, collected by the ATLAS detector during Run 2 of the Large Hadron Collider (2015-2018). The final state has contributions from a number of interesting Standard Model processes that dominate in different four-lepton invariant mass regions, including single Z boson production, Higgs boson production and on-shell ZZ production, with a complex mix of interference terms, and possible contributions from physics beyond the Standard Model. The differential cross-sections include the four-lepton invariant mass inclusively, in slices of other kinematic variables, and in different lepton flavour categories. Also measured are dilepton invariant masses, transverse momenta, and angular correlation variables, in four regions of four-lepton invariant mass, each dominated by different processes. The measurements are corrected for detector effects and are compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. The Z -> 4l branching fraction is extracted, giving a value of (4.41 +/- 0.30) x 10(-6). Constraints on effective field theory parameters and a model based on a spontaneously broken B – L gauge symmetry are also evaluated. Further reinterpretations can be performed with the provided information.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Improved measurement of η/η′ mixing in B0(s) → J/ψ(η′) decays. J. High Energy Phys., 10(10), 113–32pp.
Abstract: Branching fraction ratios between the decays B-(s)(0) -> J/psi eta(()'()) are measured using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13TeV, corresponding to an integrated luminosity of 9 fb(-1). The measured ratios of these branching fractions are B(B-0 -> J/psi eta')/B(B-0 -> J/psi eta) = 0.48 +/- 0.06 +/- 0.02 +/- 0.01, B(B-s(0) -> J/psi eta')/B(B-s(0) -> J/psi eta) = 0.80 +/- 0.02 +/- 0.02 +/- 0.01, where the uncertainties are statistical, systematic and related to the precision of the eta(()'()) branching fractions, respectively. They are used to constrain the eta/eta' mixing angle, phi(P), and to probe the presence of a possible glueball component in the eta' meson, described by the gluonic mixing angle phi(G). The obtained results are phi(P) = (41.6(-1.2)(+1.0))degrees, phi(G) = (28.1(-4.0)(+3.9))degrees, where the uncertainties are statistically dominated. While the value of phi(P) is compatible with existing experimental determinations and theoretical calculations, the angle phi(G) differs from zero by more than four standard deviations, which points to a substantial glueball component in the eta' meson and/or unexpectedly large contributions from gluon-mediated processes in these decays. The absolute branching fractions are also measured relative to that of the well-established B-s(0) -> J/psi phi decay, which serves as the normalisation channel. These results supersede the previous LHCb measurements and are the most precise to date.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2026). Branching fraction measurement of the Λ → pμ- (v)over-barμ decay. J. High Energy Phys., 04(4), 096–27pp.
Abstract: A measurement of the branching fraction for the decay Lambda -> p mu(-) (v) over bar (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 Lambda -> p mu(-) decays as a normalisation channel. The measured branching fraction is B(Lambda -> p mu(-) (v) over bar (mu)) = (1.462 +/- 0.016 +/- 0.100 +/- 0.011) x 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-mu e = Gamma(Lambda -> p mu(-)(v) over bar (mu))/Gamma(Lambda -> pe(-)(v) over bar (e)) = 0.175 +/- 0.012, agrees with the Standard Model prediction.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2026). Measurement of the branching fraction of the Λb0 → J/ψΛ decay and isospin asymmetry of B → J/ψK decays. J. High Energy Phys., 01(1), 159–28pp.
Abstract: This paper describes a measurement of the Lambda(0)(b) -> J/psi Lambda branching fraction using data collected with the LHCb experiment in proton-proton collisions from 2016 to 2018. The dataset corresponds to an integrated luminosity of 5.4 fb(-1). The branching fraction is determined relative to that of B-0 -> J/psi K-S(0) decays, B(Lambda(0)(b) -> J/psi Lambda)/(B-0 -> J/psi K-S(0)) = 0.750 +/- 0.005 +/- 0.022 +/- 0.005 +/- 0.062, yielding B(Lambda(0)(b) -> J/psi Lambda) = (3.34 +/- 0.02 +/- 0.10 +/- 0.08 +/- 0.28) x 10(-4), where the first uncertainty is statistical, the second systematic, the third due to external inputs on branching fractions and the fourth due to the ratio of Lambda(0)(b) baryon and B-0 meson hadronisation fractions. In addition, the isospin asymmetry between the rates of B-0 -> J/psi K-S(0) and B+ -> J/psi K+ decays is measured to be A(I) = -0.0135 +/- 0.0004 +/- 0.0133, where the first uncertainty is statistical and the second systematic.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Measurement of branching fractions and CP asymmetries in Λb0 (Ξb0) → pKS0h- decays. J. High Energy Phys., 10(10), 169–28pp.
Abstract: A study of Lambda(0)(b) and Xi(0)(b) baryon decays to the final states pK(S)(0)pi(-) and pK(S)(0)K(-) is performed using pp collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). The decays Lambda(0)(b)-> pK(S)(0)K(-) and Xi(0)(b)-> pK(S)(0)K(-) are observed for the first time, with significances reaching eight standard deviations. The branching fractions and integrated CP asymmetries are measured for the Lambda(0)(b)-> pK(S)(0)pi(-), Lambda(0)(b)-> pK(S)(0)K(-), and Xi(0)(b)-> pK(S)(0)K(-) decays. For the decay Lambda(0)(b)-> pK(S)(0)pi(-), the CP asymmetries are measured in different regions of the Dalitz plot. No evidence of CP violation is observed.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2025). Observation of the decay B0s → K0p(p)over-bar and measurement of the B0(s) → K0p(p)over-bar branching fractions. J. High Energy Phys., 07(7), 121–25pp.
Abstract: A study of the charmless baryonic decays B-(s)(0) -> K(0)p (p) over bar is presented, where B-(s)(0) denotes either a B-0 or a B-s(0) meson. The analysis is based on proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). The decay B-s(0) -> K(0)p (p) over bar is observed for the first time, with a measured branching fraction of (9.14 +/- 1.69 +/- 0.90 +/- 0.33 +/- 0.20) x 10(-7) and a significance of 5.6 sigma. The uncertainties respectively account for statistical and systematic contributions, the precision of the branching fraction of the normalisation channel B-0 -> K-0 pi(+)pi(-) and the fragmentation fraction ratio f(s)/f(d). The branching fraction determined for B-0 -> K(0)p (p) over bar is (2.82 +/- 0.08 +/- 0.12 +/- 0.10) x 10(-6), which is the most precise measurement to date.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2024). Study of b-hadron decays to Λc+h-h′- final states. J. High Energy Phys., 08(8), 132–32pp.
Abstract: Decays of Xi(-)(b) and Omega(-)(b) baryons to Lambda(+)(c)h(-)h(-) final states, with h(-)h '(-) being pi(-)pi(-), K-pi(-) and K-K- meson pairs, are searched for using data collected with the LHCb detector. The data sample studied corresponds to an integrated luminosity of 8.7 fb(-1) of pp collisions collected at centre-of-mass energies root s = 7, 8 and 13 TeV. The products of the relative branching fractions and fragmentation fractions for each signal mode, relative to the B- -> Lambda(+)(c)(p) over bar pi(-) mode, are measured, with Xi(-)(b) -> Lambda K-+(c)-pi(-), Xi(-)(b) -> Lambda+cK-K- and Omega(-)(b) -> Lambda+cK-K- decays being observed at over 5 sigma significance. The Xi(-)(b) -> Lambda K-+(c)-pi(-) mode is also used to measure the Xi(-)(b) production asymmetry, which is found to be consistent with zero. In addition, the B- -> Lambda(+)(c)(p) over barK(-) decay is observed for the first time, and its branching fraction is measured relative to that of the B- -> Lambda(+)(c)(p) over bar pi(-) mode.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2025). Observation of the doubly-charmed-baryon decay Ξcc++ → Ξc0 π+ π+. J. High Energy Phys., 10(10), 136–23pp.
Abstract: A search for the doubly-charmed-baryon decay Xi(++)(cc) -> Xi(0)(c)pi pi(+) pi(+) is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13TeV and corresponding to an integrated luminosity of 5.4 fb(-1). A significant structure consistent with the Xi(++)(cc) cc baryon is observed in the Xi(0)(c) pi(+)pi(+) invariant-mass spectrum. Using the Xi(++)(cc) ->Lambda(+)(c) K- pi(+pi+) decay as the normalisation channel, the branching fraction ratio, B(Xi(++)(cc) -> 0c p+p+)/ B(Xi(++)(cc) -> Lambda K-+(c)- pi(+)pi(+)), is measured to be 1.37 +/- 0.18 (stat) +/- 0.09 (syst) +/- 0.35 (ext). This measurement provides critical input for testing QCD factorisation methods in the weak decays of doubly-heavy baryons, particularly in quantifying nonperturbative effects such as final-state interactions and resonance contributions to the hadronisation process.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., et al. (2025). Search for the Bc+→ χc1(3872)π+ decay. J. High Energy Phys., 06(6), 013–28pp.
Abstract: A search for the decay B-c(+)-> chi(c1)(3872)pi(+) is reported using proton-proton collision data collected with the LHCb detector between 2011 and 2018 at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb(-1). No significant signal is observed. Using the decay B-c(+)-> psi(2S)pi(+) as a normalisation channel, an upper limit for the ratio of branching fractions R psi(chi c1(3872))((2s)) = BBc+-> chi c1(3872)pi+/BBc+-> psi(2S)pi+ x B chi c1(3872)-> J/psi pi(+)pi(-)/BB psi(2S)-> J/psi pi+pi- <0.05(0.06), is set at the 90 (95)% confidence level.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). A search for Xi(++)(cc) -> D(+)pK(-)pi(+) decays. J. High Energy Phys., 10(10), 124–21pp.
Abstract: A search for the Xi(++)(cc) baryon through the Xi(++)(cc) -> D(+)pK(-)pi(+) decay is performed with a data sample corresponding to an integrated luminosity of 1.7 fb(-1) recorded by the LHCb experiment in pp collisions at a centre-of-mass energy of 13 TeV. No significant signal is observed in the mass range from the kinematic threshold of the decay to 3800 MeV/c(2). An upper limit is set on the ratio of branching fractions R = B(Xi(++)(cc) -> D(+)pK(-)pi(+))/B(Xi(++)(cc) -> A(c)(+) K- pi(+)pi(+)) with R < 1.7 (2.1) x 10(-2) at the 90% (95%) confidence level at the known mass of the Xi(++)(cc) state.
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