Home | << 1 2 3 4 5 6 7 8 9 10 >> [11–20] |
![]() |
Penalva, N., Hernandez, E., & Nieves, J. (2019). Further tests of lepton flavor universality from the charged lepton energy distribution in b -> c semileptonic decays: The case of Lambda(b) -> Lambda(c) l(v)over-bar(l). Phys. Rev. D, 100(11), 113007–11pp.
Abstract: In a general framework, valid for any H -> H' l(-)(v) over bar (l) semileptonic decay, we analyze the d(2)Gamma/(d omega d cos theta(l)) and d(2)Gamma/(d omega dE(l)) distributions, with omega being the product of the hadron four-velocities, theta(l) the angle made by the three-momenta of the charged lepton and the final hadron in the W- center of mass frame and E-l the charged lepton energy in the decaying hadron rest frame. Within the Standard Model (SM), d(2)Gamma/(d omega dE(l)) proportional to (c(0) (omega) c(1) (omega)E-l/M + c(2) (omega)E-l(2)/M-2), with M the initial hadron mass. We find that c(2) (omega) is independent of the lepton flavor and thus it is an ideal candidate to look for lepton flavor universality (LFU) violations. We also find a correlation between the a(2) (omega) structure function, which governs the (cos theta(l))(2) dependence of d(2)Gamma/(d omega d cos theta(l)), and c(2) (omega). Apart from trivial kinematical and mass factors, the ratio of a(2) (omega)/c(2) (omega) is a universal function that can be measured in any semileptonic decay, involving not only b -> c transitions. These two SM predictions can be used as new tests in the present search for signatures of LFU violations. We also generalize the formalism to account for some new physics (NP) terms, and show that neither c(2) nor a(2) are modified by left and right scalar NP terms, being however sensitive to left and right vector corrections. We also find that the a(2)/c(2) ratio is not modified by these latter NP contributions. Finally, and in order to illustrate our findings, we apply our general framework to the Lambda(b) -> Lambda(c)l (v) over bar (l) decay. We show that a measurement of c(2) (or a(2)) for tau decay would not only be a direct measurement of the possible existence of NP, but it would also allow to distinguish from NP fits to b -> c tau(v) over bar (tau) anomalies in the meson sector, which otherwise give the same total and differential d Gamma/d omega widths. We show that the same occurs for the other two terms, c(0) and c(1), that appear in d(2)Gamma/(d omega dE(l)), and for the cos theta(l) linear term of the angular distribution.
|
Nieves, J., & Pavao, R. (2020). Nature of the lowest-lying odd parity charmed baryon Lambda(c)(2595) and Lambda(c)(2625) resonances. Phys. Rev. D, 101(1), 014018–17pp.
Abstract: We study the structure of the Lambda(c) (2595) and Lambda(c) (2625) resonances in the framework of an effective field theory consistent with heavy quark spin and chiral symmetries, which incorporates the interplay between Sigma(()(c)*() )pi – ND(*()) baryon-meson degrees of freedom (d.o.f.) and bare P-wave c (u) over bard quark-model states. We show that these two resonances are not heavy quark spin symmetry partners. The J(P) = 3/2(-) Lambda(c) (2625) should be viewed mostly as a dressed three-quark state, whose origin is determined by a bare state, predicted to lie very close to the mass of the resonance. The J(P) = 1/2(-) Lambda(c) (2595) seems to have, however, a predominant molecular structure. This is because it is either the result of the chiral Sigma(c)pi interaction, whose threshold is located much closer than the mass of the bare three-quark state, or because the light d.o.f. in its inner structure are coupled to the unnatural 0(-) quantum numbers. We show that both situations can occur depending on the renormalization procedure used. We find some additional states, but the classification of the spectrum in terms of heavy quark spin symmetry is difficult, despite having used interactions that respect this symmetry. This is because the bare quark-model state and the Sigma(c)pi threshold are located extraordinarily close to the Lambda(c) (2625) and Lambda(c) (2595), respectively, and hence they play totally different roles in each sector.
|
Yao, D. L., Fernandez-Soler, P., Guo, F. K., & Nieves, J. (2020). New parametrization of the form factors in (B)over-bar -> Dl(nu)over-bar(l) decays. Phys. Rev. D, 101(3), 034014–7pp.
Abstract: A new model-independent parametrization is proposed for the hadronic form factors in the semileptonic (B) over bar -> Dl (nu) over bar (l) decay. By a combined consideration of the recent experimental and lattice QCD data, we determine precisely the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar = 41.01(75) x 10(-3) and the ratio R-D = BR((B) over bar -> D tau(nu) over bar (tau))/BR((B) over bar -> Dl (nu) over bar (l)) = 0.301(5). The coefficients in this parametrization, related to phase shifts by sumrulelike dispersion relations and hence called phase moments, encode important scattering information of the (B) over bar (D) over bar interactions which are poorly known so far. Thus, we give strong hints about the existence of at least one bound and one virtual (B) over bar (D) over bar S-wave 0(+) states, subject to uncertainties produced by potentially sizable inelastic effects. This formalism is also applicable for any other semileptonic processes induced by the weak b -> c transition.
|
Penalva, N., Hernandez, E., & Nieves, J. (2020). (B)over-bar(c) ->eta(c),(B)over-bar(c) -> J/psi and (B)over-bar -> D-(*()) semileptonic decays including new physics. Phys. Rev. D, 102(9), 096016–27pp.
Abstract: We apply the general formalism derived by Penalva et al. [Phys. Rev. D 101, 113004 (2020)] to the semileptonic decay of pseudoscalar mesons containing a b quark. While present (B) over bar -> D-(*()) data give the strongest evidence in favor of lepton flavor universality violation, the observables that are normally considered are not able to distinguish between different new physics (NP) scenarios. In the above reference we discussed the relevant role that the various contributions to the double differential decay widths d(2)Gamma (d omega d cos theta(l)) and d(2)Gamma (d omega dE(l)) could play to this end. Here omega is the product of the two hadron fourvelocities, theta(l) is the angle made by the final lepton and final hadron three-momenta in the center of mass of the final two-lepton system, and E-l is the final charged lepton energy in the laboratory system. The formalism was applied by Penalva et al. to the analysis of the Lambda(b) -> Lambda(c) semileptonic decay, showing the new observables were able to tell apart different NP scenarios. Here we analyze the (B) over barc -> eta(c)tau(nu) over bar (tau), (B) over barc -> J/psi tau(nu) over bar (tau), (B) over bar -> D tau(nu) over bar (tau) and (B) over bar -> D*tau(nu) over bar (tau) , semileptonic decays. We find that, as a general rule, the (B) over barc -> J/psi observables, even including (tau) polarization, are less optimal for distinguishing between NP scenarios than those obtained from (B) over barc -> eta(c) decays, or those presented by Penalva et al. for the related Lambda(b) -> Lambda(c) semileptonic decay. Finally, we show that (B) over bar -> D and (B) over barc -> eta(c) , and (B) over bar -> D* and (B) over barc -> J/psi decay observables exhibit similar behaviors.
|
Yang, Z., Cao, X., Guo, F. K., Nieves, J., & Pavon Valderrama, M. (2021). Strange molecular partners of the Z(c)(3900) and Z(c)(4020). Phys. Rev. D, 103(7), 074029–8pp.
Abstract: Quantum chromodynamics presents a series of exact and approximate symmetries which can be exploited to predict new hadrons from previously known ones. The Z(c)(3900) and Z(c)(4020), which have been theorized to be isovector D*(D) over bar and D*(D) over bar* molecules [I-G(J(PC)) = 1(-)(1)(+-))], are no exception. Here we argue that from SU(3)-flavor symmetry, we should expect the existence of strange partners of the Z(c)'s with hadronic molecular configurations D*(D) over bar (s) – D (D) over bar*(s) and D*(D) over bar*(s) (or, equivalently, quark content c (c) over bars (q) over bar, with q = u, d). The quantum numbers of these Z(cs) and Z(cs)* structures would be I(J(P)) = 1/2 (1(+)). The predicted masses of these partners depend on the details of the theoretical scheme used, but they should be around the D*(D) over bar (s) – D (D) over bar*(s) and D*(D) over bar*(s) thresholds, respectively. Moreover, any of these states could be either a virtual pole or a resonance. We show that, together with a possible triangle singularity contribution, such a picture nicely agrees with the very recent BESIII data of the e(+)e(-) -> K+((Ds-D*0) + D*D--(s)0).
|