LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2021). Observation of Multiplicity Dependent Prompt chi(c1) (3872) and psi (2S) Production in pp Collisions. Phys. Rev. Lett., 126(9), 092001–11pp.
Abstract: The production of chi(c1)(3872) and psi(2S) hadrons is studied as a function of charged particle multiplicity in pp collisions at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2 fb(-1). For both states, the fraction that is produced promptly at the collision vertex is found to decrease as charged particle multiplicity increases. The ratio of chi(c1) (3872) to psi(2S) cross sections for promptly produced particles is also found to decrease with multiplicity, while no significant dependence on multiplicity is observed for the equivalent ratio of particles produced away from the collision vertex in b-hadron decays. This behavior is consistent with a calculation that models the chi(c1) (3872) structure as a compact tetraquark. Comparisons with model calculations and implications for the binding energy of the chi(c1)(3872) state are discussed.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2025). Measurement of D0 – (D)over-bar0 mixing and search for CP violation with D0 →K+ π- decays. Phys. Rev. D, 111(1), 012001–25pp.
Abstract: A measurement of the time-dependent ratio of the D-0 -> K+ to (D) over bar (0) pi(-) decay rates is reported. The analysis uses a sample of proton-proton collisions corresponding to an integrated luminosity of 6 fb- 1 recorded by the LHCb experiment from 2015 through 2018 at a center-of-mass energy of 13 TeV. The D-0 meson is required to originate from a D*(2010)(+) -> D-0 pi(+) decay, such that its flavor at production is inferred from the charge of the accompanying pion. The measurement is performed simultaneously for the K+ pi(-) and K- pi(+) final states, allowing both mixing and CP-violation parameters to be determined. The value of the ratio of the decay rates at production is determined to be R-K pi = (343.1 +/- 2.0) x 10(-5). The mixing parameters are measured to be c(K pi) = (51.4 +/- 3.5) x 10(-4) and c(K pi)(0) = (13 +/- 4) x 10(-6), where root R(K pi)c(K pi) is the linear coefficient of the expansion of the ratio as a function of decay time in units of the D-0 lifetime, and c(K pi)(0) is the quadratic coefficient, both averaged between the K+ pi(-) and K- pi(+) final states. The precision is improved relative to the previous best measurement by approximately 60%. No evidence for CP violation is found.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Study of charmonium production via the decay to p pbar at √s=13 TeV. Eur. Phys. J. C, 84(12), 1274–19pp.
Abstract: Charmonium production cross-section in protonpvroton collisions is measured at the centre-of-mass energy root s = 13 TeV using decays to pp final state. The study is performed using a data sample corresponding to an integrated luminosity of 2.2 fb(-1) collected in 2018 with the LHCb detector. The production cross-section of the h(c) meson is measured in a rapidity range of 2.0 < y < 4.0 and in a transverse momentum range of 5.0 < p(T) < 20.0GeV/c, which is extended compared with previous LHCb analyses. The differential cross-section is measured in bins of pT and, for the first time, of y. Upper limits, at 90% and 95% confidence levels, on the h(c)(2S) and h(c)(1P) prompt production cross-sections are determined for the first time.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Amplitude analysis of the radiative decay Bs0 → K+K-γ. J. High Energy Phys., 08(8), 093–39pp.
Abstract: A search for radiative decay of B-s(0) mesons to orbitally excited K+K- states is performed using proton proton collisions recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). The dikaon spectrum in the mass range m(KK) < 2400 MeV/c(2) is dominated by the phi(1020) resonance that accounts for almost 70% of the decay rate. Considering the possible contributions of f(2)(1270), f(2)'(1525) and f(2)(2010) meson states, the overall tensor contribution to the amplitude is measured to be F-{f2} = 16.8 +/- 0.5 (stat.) +/- 0.7 (syst.)%, mostly dominated by the f2 '(1525) state. Several statistically equivalent solutions are obtained for the detailed resonant structure depending on whether the smaller amplitudes interfere destructively or constructively with the dominant amplitude. The preferred solution that corresponds to the lowest values of the fit fractions along with constructive interference leads to the relative branching ratio measurement B(B-s(0) -> f(2)'gamma)/B(B-s(0) -> phi gamma) = 19.4(-0.8)(+0.9)(stat.)(-0.5)(+1.4) (syst.) +/- 0.5(B)%, where the last uncertainty is due to the ratio of measured branching fractions to the K+K- final state. This result represents the first observation of the radiative B-s(0) -> f(2)'(1525)gamma decay, which is the second radiative transition observed in the B-s(0) sector.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). First observation of the Λb0→ D+D-Λ decay. J. High Energy Phys., 07(7), 140–22pp.
Abstract: The Lambda(0)(b) -> D+D-Lambda decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.3 fb(-1). Using the B-0 -> (D+D-KS0) decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be R = sigma(Lambda b0)/sigma(B0) x B(Lambda(0)(b) -> D+D-Lambda)/B(B-0 -> (D+D-KS0))=0.179 +/- 0.022 +/- 0.014, where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, B(B-0 -> (D+D-KS0)), and the cross-section ratio, sigma Lambda(b0)/sigma(B0), previously measured by LHCb are used to derive the branching fraction of the Lambda(0)(b)-> D+D-Lambda decay B(Lambda(0)(b) -> D+D-Lambda) = (1.24 +/- 0.15 +/- 0.10 +/- 0.28 +/- 0.11)x10(-4), where the third and fourth contributions are due to uncertainties of B(B-0 -> (D+D-KS0)) and sigma(Lambda b0)/sigma(B0), respectively. Inspection of the D+Lambda and D+D- invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Lambda(0)(b) -> D*+D-Lambda decay is also observed for the first time as a partially reconstructed component in the D+D-Lambda invariant mass spectrum.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Search for the Bs0 → μ+ μ-γ decay. J. High Energy Phys., 07(7), 101–27pp.
Abstract: A search for the fully reconstructed B-s(0)-> mu(+)mu(-)gamma decay is performed at the LHCb experiment using proton-proton collisions at root s = 13 TeV corresponding to an integrated luminosity of 5.4 fb(-1). No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are set B(B-s(0)-> mu(+)mu(-)gamma) < 4.2 x 10(-8), m(mu(+)mu(-)) is an element of[2m(mu),1.70] GeV/c(2), B(B-s(0) -> mu(+)mu(-)gamma) < 7.7 x 10(-8), m(mu(+)mu(-)) is an element of [1.70, 2.88] GeV/c(2), B(B-s(0) -> mu(+)mu(-)gamma) < 4.2 x 10(-8), m(mu(+)mu(-) ) is an element of[3.92, m(Bs0)]GeV/c(2), at 95% confidence level. Additionally, upper limits are set on the branching fraction in the [2m(mu), 1.70] GeV/c(2) dimuon mass region excluding the contribution from the intermediate phi(1020) meson, and in the region combining all dimuon-mass intervals.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). First observation of Λb0 → Σc(*)+ + D(*) – K- decays. Phys. Rev. D, 110(3), L031104–13pp.
Abstract: The four decays, Λ0b→Σ(∗)++cD(∗)−K−, are observed for the first time using proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 6fb−1. By considering the Λ0b→Λ+cD⎯⎯⎯⎯0K− decay as reference channel, the following branching fraction ratios are measured to be
(Λ0b→Σ++cD−K−)(Λ0b→Λ+cD⎯⎯⎯⎯0K−)=0.282±0.016±0.016±0.005,(Λ0b→Σ∗++cD−K−)(Λ0b→Σ++cD−K−)=0.460±0.052±0.028,(Λ0b→Σ++cD∗−K−)(Λ0b→Σ++cD−K−)=2.261±0.202±0.129±0.046,(Λ0b→Σ∗++cD∗−K−)(Λ0b→Σ++cD−K−)=0.896±0.137±0.066±0.018,
where the first uncertainties are statistical, the second are systematic, and the third are due to uncertainties in the branching fractions of intermediate particle decays. These initial observations mark the beginning of pentaquark searches in these modes, with more data set to become available following the LHCb upgrade.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Search for the rare decay of charmed baryon Λc+ into the pμ+ μ- final state. Phys. Rev. D, 110(5), 052007–13pp.
Abstract: A search for the nonresonant Lambda(+)(c) -> p mu(+) mu(-) 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 Lambda(+)(c) -> p mu(+) mu(-) decay is determined to be 2.9(3.2) x 10(-8) at 90%(95%) confidence level. The branching fractions in the dimuon invariant-mass regions dominated by the eta, rho and omega resonances are also determined.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Precision measurement of the Ξb- baryon lifetime. Phys. Rev. D, 110(7), 072002–16pp.
Abstract: A sample of pp collision data, corresponding to an integrated luminosity of 5.5 fb(-1) and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the Xi(-)(b) baryon to that of the A(b)(0) baryon, r(tau) equivalent to tau(Xi b-)/tau(Ab0). The value r(tau)= 1.076 +/- 0.013 +/- 0.006 is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain r(tau)(Rrun 1,2) = 1.078 +/- 0.012 +/- 0.007. Multiplying by the world -average value of the A(b)(0) lifetime yields r(Xi b-)(Rrun 1,2) = 1.578 +/- 0.018 +/- 0.010 +/- 0.011 ps, where the uncertainties are statistical, systematic, and due to the limited knowledge of the A(b)(0), lifetime. This measurement improves the precision of the current world average of the Xi(-)(b) lifetime by about a factor of 2, and is in good agreement with the most recent theoretical predictions.
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LHCb Collaboration(Aaij, R. et al), Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Martinez-Vidal, F., Oyanguren, A., et al. (2024). Observation of New Charmonium or Charmoniumlike States in B+ → D*±D∓K+ Decays. Phys. Rev. Lett., 133(13), 131902–14pp.
Abstract: A study of resonant structures in B+ -> D*(DK+)-D-+/--K--/+ and B+ -> D*(DK+)-D-+/--K--/+ decays is performed, using proton-proton collision data at center-of-mass energies of root s = 7, 8, and 13 TeV recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb(-1). A simultaneous amplitude fit is performed to the two channels with contributions from resonances decaying to D*D-+/-(+) and D*D-+/-(-) states linked by C parity. This procedure allows the C parities of resonances in the D*D-+/-(-/+) mass spectra to be determined. Four charmonium or charmoniumlike states are observed decaying into D*D-+/-(-/+): eta(c)(3945), h(c)(4000), chi(c1)(4010), and h(c)(4300), with quantum numbers J(PC) equal to 0(-+), 1(+-), 1(+-), and 1(+-), respectively. At least three of these states have not been observed previously. In addition, the existence of the T-(c) over bar(s) over bar0*(2870)(0) and T-(c) over bar(s) over bar1*(2900)(0) resonances in the D-K+ mass spectrum, already observed in the B+ -> D+D-K+ decay, is confirmed in a different production channel.
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