Garcia-Recio, C., Nieves, J., Romanets, O., Salcedo, L. L., & Tolos, L. (2013). Hidden charm N and Delta resonances with heavy-quark symmetry. Phys. Rev. D, 87(7), 074034–23pp.
Abstract: A model is developed to describe odd-parity baryon resonances generated dynamically through a unitary baryon-meson coupled-channels approach. The scheme applies to channels with light- and/or heavy-quark content. Distinct features of the model are that i) the interaction is an S-wave contact one, ii) it reduces to the SU(3) Weinberg-Tomozawa Hamiltonian when light pseudoscalar mesons are involved, thus respecting chiral symmetry, iii) spin-flavor is preserved in the light-quark sector, and iv) heavy-quark spin symmetry is fulfilled in the heavy-quark sector. In particular, baryon-meson states with different content in c or in (c) over bar do not mix. The model is a minimal one and it contains no free parameters. In this work, we focus on baryon resonances with hidden charm (at least one (c) over bar and one c quark). We analyze several possible sectors and, for the sector with zero net charm, we write down the most general Lagrangian consistent with SU(3) and heavy-quark spin symmetry. We explicitly study the N and Delta states, which are produced from the S-wave interaction of pseudoscalar and vector mesons with 1/2(+) and 3/2(+) baryons within the charmless and strangeless hidden-charm sector. We predict seven odd-parity N-like and five Delta-like states with masses around 4 GeV, most of them as bound states. These states form heavy-quark spin multiplets, which are almost degenerate in mass. The predicted new resonances definitely cannot be accommodated by quark models with three constituent quarks and they might be looked for in the forthcoming PANDA experiment at the future FAIR facility.
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LHCb Collaboration(Aaij, R. et al), Oyanguren, A., & Ruiz Valls, P. (2013). Observation of the decay B-c(+) -> psi(2S)pi(+). Phys. Rev. D, 87(7), 071103–7pp.
Abstract: The decay B-c(+) -> psi(2S)pi(+) with psi(2S) -> mu(+)mu(-) is observed with a significance of 5.2 sigma using pp collision data corresponding to an integrated luminosity of 1.0 fb(-1) collected by the LHCb experiment. The branching fraction of B-c(+) -> psi(2S)pi(+) decays relative to that of the B-c(+) -> J/psi pi(+) mode is measured to be B(B-c(+) -> psi(2S)pi(+))/B(B-c(+) -> J/psi pi(+)) = 0.250 +/- 0.068(stat) +/- 0.014(syst) +/- 0.006(B). The last term is the uncertainty on the ratio B(psi(2S) -> mu(+)mu(-))/B(J/psi -> mu(+)mu(-)).
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Search for single b*-quark production with the ATLAS detector at root s=7 TeV. Phys. Lett. B, 721(4-5), 171–189.
Abstract: The results of a search for an excited bottom-quark b* in pp collisions at root s = 7 TeV, using 4.7 fb(-1) of data collected by the ATLAS detector at the LHC are presented. In the model studied, a single b*-quark is produced through a chromomagnetic interaction and subsequently decays to a W boson and a top quark. The search is performed in the dilepton and lepton + jets final states, which are combined to set limits on b*-quark couplings for a range of b*-quark masses. For a benchmark with unit size chromomagnetic and Standard Model-like electroweak b* couplings, b* quarks with masses less than 870 GeV are excluded at the 95% credibility level.
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Guastalla, G. et al, Algora, A., & Domingo-Pardo, C. (2013). Coulomb Excitation of Sn-104 and the Strength of the Sn-100 Shell Closure. Phys. Rev. Lett., 110(17), 172501–5pp.
Abstract: A measurement of the reduced transition probability for the excitation of the ground state to the first 2(+) state in Sn-104 has been performed using relativistic Coulomb excitation at GSI. Sn-104 is the lightest isotope in the Sn chain for which this quantity has been measured. The result is a key point in the discussion of the evolution of nuclear structure in the proximity of the doubly magic nucleus Sn-100. The value B(E2; 0(+) -> 2(+)) = 0.10(4) e(2)b(2) is significantly lower than earlier results for Sn-106 and heavier isotopes. The result is well reproduced by shell model predictions and therefore indicates a robust N = Z = 50 shell closure.
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LHCb Collaboration(Aaij, R. et al), Oyanguren, A., & Ruiz Valls, P. (2013). Search for the decay B-s(0) -> D*(-/+)pi(+/-). Phys. Rev. D, 87(7), 071101–8pp.
Abstract: A search for the decay B-s(0) -> D*(-/+)pi(+/-) is presented using a data sample corresponding to an integrated luminosity of 1.0 fb(-1) of pp collisions collected by LHCb. This decay is expected to be mediated by a W-exchange diagram, with little contribution from rescattering processes, and therefore a measurement of the branching fraction will help us to understand the mechanism behind related decays such as B-s(0) -> pi(+)pi(-) and B-s(0) -> D (D) over bar. Systematic uncertainties are minimized by using B-0 -> D*(-/+)pi(+/-) as a normalization channel. We find no evidence for a signal, and set an upper limit on the branching fraction of B(B-s(0) -> D*(-/+)pi(+/-) < 6.1(7.8) x 10(-6) at 90% (95%) confidence level.
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Chachamis, G., Hentschinski, M., Madrigal Martinez, J. D., & Sabio Vera, A. (2013). Next-to-leading order corrections to the gluon-induced forward jet vertex from the high energy effective action. Phys. Rev. D, 87(7), 076009–11pp.
Abstract: We determine both real and virtual next-to-leading order corrections to the gluon-induced forward jet vertex from the high energy effective action proposed by Lipatov. For these calculations we employ the same regularization and subtraction formalism developed in our previous work on the quark-initiated vertex. We find agreement with previous results in the literature.
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Navarro, J., & Polls, A. (2013). Spin instabilities of infinite nuclear matter and effective tensor interactions. Phys. Rev. C, 87(4), 044329–11pp.
Abstract: We study the effects of the tensor force, present in modern effective nucleon-nucleon interactions, in the spin instability of nuclear and neutron matter. Stability conditions of the system against certain very low energy excitation modes are expressed in terms of Landau parameters. It is shown that in the spin case, the stability conditions are equivalent to the condition derived from the spin susceptibility, which is obtained as the zero-frequency and long-wavelength limit of the spin response function calculated in the random phase approximation. Zero-range forces of the Skyrme type and finite-range forces of M3Y and Gogny type are analyzed. It is shown that for the Skyrme forces considered, the tensor effects are sizable and tend to increase the spin instability, which appears at smaller densities than in the case that the tensor is not taken into account. On the contrary, the tensor contribution of finite-range forces to the spin susceptibility is small or negligible for both isospin channels of symmetric nuclear matter as well as for neutron matter. A comparison with the spin susceptibility provided by realistic interactions is also presented.
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Zheng, Y. et al, & Gadea, A. (2013). gamma-ray linear polarization measurements and (g(9/2))(-3) neutron alignment in Ru-91. Phys. Rev. C, 87(4), 044328–10pp.
Abstract: Linear polarization measurements have been performed for gamma rays in Ru-91 produced with the Ni-58(Ar-36,2p1n gamma)Ru-91 reaction at a beam energy of 111 MeV. The EXOGAM Ge clover array has been used to measure the gamma-gamma coincidences, gamma-ray linear polarization, and gamma-ray angular distributions. The polarization sensitivity of the EXOGAM clover detectors acting as Compton polarimeters has been determined in the energy range 0.3-1.3 MeV. Several transitions have been observed for the first time. Measurements of linear polarization and angular distribution have led to the firm assignments of spin differences and parity of high-spin states in Ru-91. More specifically, calculations using a semiempirical shell model were performed to understand the structures of the first and second (21/2(+)) and (17/2(+)) levels. The results are in good agreement with the experimental data, supporting the interpretation of the nonyrast (21/2(+)) and (17/2(+)) states in terms of the J(max) and J(max) – 2 members of the seniority-three nu(g(9/2))(-3) multiplet.
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HADES Collaboration(Agakishiev, G. et al), Diaz, J., & Gil, A. (2013). Deep sub-threshold K*(892)(0) production in collisions of Ar + KCl at 1.76A GeV. Eur. Phys. J. A, 49(3), 34–7pp.
Abstract: Results on the deep sub-threshold production of the short-lived hadronic resonance K*(892)(0) are reported for collisions of Ar + KCl at 1.76 A GeV beam energy, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. The K*(892)(0) production probability per central collision of P-K*0 = (4.4 +/- 1.1 +/- 0.5) x 10(-4) and the K*(892)(0)/K-0 ratio of P-K*0/P-K0 = (1.9 +/- 0.5 +/- 0.3) x 10(-2) are determined at the lowest energy so far (i.e. deep below the threshold for the corresponding production in nucleon-nucleon collisions, root s(NN)-root s(thr) = -340MeV). The K*(0)/K-0 ratio is compared with results of other experiments and with the predictions of the UrQMD transport approach and of the statistical hadronization model. The experimental K*(0) yield and the K-*0/K-0 ratio are overestimated by the transport model by factors of about five and two, respectively. In a chemically equilibrated medium the ratio corresponds to a temperature of the thermalized system being systematically lower than the value determined by the yields of the stable and long-lived hadrons produced in Ar + KCl collisions. From the present measurement, we conclude that sub-threshold K* production either cannot be considered to proceed in a system being in thermal equilibrium or these short-lived resonances appear undersaturated, for example as a result of the rescattering of the decay particles in the ambient hadronic medium.
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Oset, E. (2013). On the ambiguities of sign determination of the S-matrix from energy levels in a finite box. Eur. Phys. J. A, 49(3), 32–4pp.
Abstract: In a recent paper the authors make a study on the determination of the S-matrix elements for scattering of particles in the infinite volume from the energy levels in a finite box for the case of multiple channels. The study is done with a toy model in 1+1 dimension and the authors find that there is some ambiguity in the sign of nondiagonal matrix elements, casting doubts on whether the needed observables in the infinite volume can be obtained from the energy levels of the box. In this paper I present an easy derivation, confirming the ambiguity of the sign and argue that this, however, does not put restrictions in the determination of observables.
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