Publications (28)106.8 Total impact
 [Show abstract] [Hide abstract]
ABSTRACT: We present a unitary multichannel model for $\bar{K}N$ scattering in the resonance region that fulfills unitarity. It has the correct analytical properties for the amplitudes once they are extended to the complex$s$ plane and the partial waves have the right threshold behavior. To determine the parameters of the model, we have fitted singleenergy partial waves up to $J=7/2$ and up to 2.15 GeV of energy in the centerofmass reference frame obtaining the poles of the $\Lambda^*$ and $\Sigma^*$ resonances, which are compared to previous analyses. We provide the most comprehensive picture of the $S=1$ hyperon spectrum to date. Important differences are found between the available analyses making the gathering of further experimental information on $\bar{K}N$ scattering mandatory to make progress in the assessment of the hyperon spectrum.  [Show abstract] [Hide abstract]
ABSTRACT: Polarisationdependent differential cross sections σT associated with the target asymmetry T have been measured for the reaction γp→→pπ0 with transverse target polarisation from π0 threshold to photon energies of 190 MeV. The data were obtained using a frozenspin butanol target with the Crystal Ball / TAPS detector setup and the Glasgow photon tagging system at the Mainz Microtron MAMI. Results for σT have been used in combination with our previous measurements of the unpolarised cross section σ0 and the beam asymmetry σ for a modelindependent determination of S and Pwave multipoles in the π0 threshold region, which includes for the first time a direct determination of the imaginary part of the E0+ multipole.  [Show abstract] [Hide abstract]
ABSTRACT: We compare the lowenergy partial wave analyses $\pi N$ scattering with a highenergy data via finite energy sum rules. We construct a new set of amplitudes by matching the imaginary part from the lowenergy analysis with the highenergy, Regge parametrization and reconstruct the real parts using dispersion relations.  [Show abstract] [Hide abstract]
ABSTRACT: New results are reported from a measurement of π^{0} electroproduction near threshold using the p(e,e^{'}p)π^{0} reaction. The experiment was designed to determine precisely the energy dependence of s and pwave electromagnetic multipoles as a stringent test of the predictions of chiral perturbation theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a twospectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the ϕ_{π}^{*} and θ_{π}^{*} angles in the pπ^{0} center of mass was obtained for invariant energies above threshold from 0.5 up to 15 MeV. The 4momentum transfer Q^{2} coverage ranges from 0.05 to 0.155 (GeV/c)^{2} in fine steps. A simple phenomenological analysis of our data shows strong disagreement with pwave predictions from ChPT for Q^{2}>0.07 (GeV/c)^{2}, while the swave predictions are in reasonable agreement.  [Show abstract] [Hide abstract]
ABSTRACT: We present an unitary dispersive model for the $\eta \to 3 \pi$ decay process based upon the KhuriTreiman equations which are solved by means of the Pasquier inversion method. The description of the hadronic finalstate interactions for the $\eta \to 3\pi$ decay is essential to reproduce the available data and to understand the existing discrepancies between Dalitz plot parameters from experiment and chiral perturbation theory. Our approach incorporates substraction constants that are fixed by fitting the recent highstatistics WASAatCOSY data for $\eta \to \pi^+ \pi^ \pi^0$. Based on the parameters obtained we predict the slope parameter for the neutral channel to be $\alpha=0.022\pm 0.004$. Through matching to nexttoleading order chiral perturbation theory we estimate the quark mass double ratio to be $Q=21.4 \pm 0.4$.  [Show abstract] [Hide abstract]
ABSTRACT: New results are reported from an experiment to measure $\pi^0$ electroproduction at and above threshold using the $p(e,e^{\prime} p)\pi^0$ reaction. The experiment was designed to precisely determine the energy dependence of $s$ and $p$wave electromagnetic multipoles as a stringent test of the predictions of Chiral Perturbation Theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a twospectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the $\phi^*_{\pi}$ and $\theta^*_{\pi}$ angles in the $p \pi^0$ centerofmass was obtained for invariant energies above threshold from 0.5~MeV up to 15~MeV. The 4momentum transfer $Q^2$ coverage ranges from 0.05 to 0.155 (GeV/c)$^2$ in fine steps. A simple phenomenological analysis of our data shows strong disagreement with $p$wave predictions from ChPT for $Q^2>0.07$ (GeV/c)$^2$, while the $s$wave predictions are in reasonable agreement.  [Show abstract] [Hide abstract]
ABSTRACT: We apply the generalized Veneziano model ($B_5$ model) in the doubleRegge exchange limit to the $\gamma p \to K^+ K^ p$ reaction. Four different cases defined by the possible combinations of the signature factors of leading Regge exchanges (($K^*,a_2/f_2$), ($K^*,\rho/\omega$), ($K_2^*,a_2/f_2$), and ($K_2^*,\rho/\omega$)) have been simulated through the Monte Carlo method. Suitable event candidates for the doubleRegge exchange highenergy limit were selected employing \textit{Van Hove} plots as a better alternative to kinematical cuts in the $K^+ K^ p$ Dalitz plot. In this way we predict and analyze the doubleRegge contribution to the $K^+ K^ p$ Dalitz plot, which constitutes one of the major backgrounds in the search for strangeonia, hybrids and exotics using $\gamma p\rightarrow K^+K^p$ reaction. We expect that data currently under analysis, and that to come in the future, will allow verification of the doubleRegge behavior and a better assessment of this component of the amplitude.  [Show abstract] [Hide abstract]
ABSTRACT: The decays $\omega/\phi \rightarrow 3\pi$ are considered in the dispersive framework that is based on the isobar decomposition and subenergy unitarity. The inelastic contributions are parametrized by the power series in a suitably chosen conformal variable that properly account for the analytic properties of the amplitude. The Dalitz plot distributions and integrated decay widths are presented. Our results indicate that the final state interactions may be sizable. As a further application of the formalism we also compute the electromagnetic transition form factors of $\omega/\phi \rightarrow \pi^0\gamma^*$.  [Show abstract] [Hide abstract]
ABSTRACT: A precision measurement of the differential cross sections dσ/dΩ and the linearly polarized photon asymmetry Σ≡(dσ_{⊥}dσ_{∥})/(dσ_{⊥}+dσ_{∥}) for the γ[over →]p→π^{0}p reaction in the nearthreshold region has been performed with a tagged photon beam and almost 4π detector at the Mainz Microtron. The GlasgowMainz photon tagging facility along with the Crystal Ball/TAPS multiphoton detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the S and all three Pwave amplitudes for the first time and provide the most stringent test to date of the predictions of chiral perturbation theory and its energy region of agreement with experiment. 
Article: PWA tools in Hadronic Spectroscopy
[Show abstract] [Hide abstract]
ABSTRACT: The miniproceedings of the Workshop on PWA tools in Hadronic Spectroscopy held in Mainz from February 18th to 20th, 2013. 
Article: Upper Energy Limit of Heavy Baryon Chiral Perturbation Theory in Neutral Pion Photoproduction
[Show abstract] [Hide abstract]
ABSTRACT: With the availability of the new neutral pion photoproduction from the proton data from the A2 and CBTAPS Collaborations at Mainz it is mandatory to revisit Heavy Baryon Chiral Perturbation Theory (HBChPT) and address the extraction of the partial waves as well as other issues such as the value of the lowenergy constants, the energy range where the calculation provides a good agreement with the data and the impact of unitarity. We find that, within the current experimental status, HBChPT with the fitted LECs gives a good agreement with the existing neutral pion photoproduction data up to $\sim$170 MeV and that imposing unitarity does not improve this picture. Above this energy the data call for further improvement in the theory such as the explicit inclusion of the \Delta (1232). We also find that data and multipoles can be well described up to $\sim$185 MeV with Taylor expansions in the partial waves up to first order in pion energy.  [Show abstract] [Hide abstract]
ABSTRACT: Quantum chaos is currently a well established discipline with outreach to many fields of physics. The most important signature of quantum chaos is the statistical analysis of the energy spectrum, which distinguishes between systems with integrable and chaotic classical analogues. The spectral statistical techniques inherited from quantum chaos have been applied to the baryon spectrum revealing its likely chaotic behavior in the low energy regime [1,2]. We present a robust analysis of the spectral fluctuations exhibited by the light meson spectrum. With this analysis we can obtain information about the degree of chaos in the spectrum getting insight on the properties of the underlying interactions. Our analysis unveils that the statistical properties of the light meson spectrum are close, but not exactly equal, to those of chaotic systems [3]. Besides the experimental spectrum, we have analyzed several theoretical spectra [47] including the latest lattice QCD calculation [8] finding out that, with the single exception of [5], their statistical properties are close to those of a generic integrable system, and thus incompatible with the experimental result. 
Article: Accurate Test of Chiral Dynamics in the \boldmath$\vec{\gamma} p \rightarrow \pi^0p$ Reaction
[Show abstract] [Hide abstract]
ABSTRACT: A precision measurement of the differential cross sections $d\sigma/d\Omega$ and the linearly polarized photon asymmetry $\Sigma \equiv (d\sigma_\perp  d\sigma_\parallel) \slash (d\sigma_\perp + d\sigma_\parallel)$ for the $\vec{\gamma} p \rightarrow \pi^0p$ reaction in the nearthreshold region has been performed with a tagged photon beam and almost $4\pi$ detector at the Mainz Microtron. The GlasgowMainz photon tagging facility along with the Crystal Ball/TAPS multiphoton detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the $S$ and all three $P$wave amplitudes for the first time and provide the most stringent test to date of the predictions of Chiral Perturbation Theory and its energy region of agreement with experiment. 
Article: Chaos in hadrons
[Show abstract] [Hide abstract]
ABSTRACT: In the last decade quantum chaos has become a well established discipline with outreach to different fields, from condensedmatter to nuclear physics. The most important signature of quantum chaos is the statistical analysis of the energy spectrum, which distinguishes between systems with integrable and chaotic classical analogues. In recent years, spectral statistical techniques inherited from quantum chaos have been applied successfully to the baryon spectrum revealing its likely chaotic behaviour even at the lowest energies. However, the theoretical spectra present a behaviour closer to the statistics of integrable systems which makes theory and experiment statistically incompatible. The usual statement of missing resonances in the experimental spectrum when compared to the theoretical ones cannot account for the discrepancies. In this communication we report an improved analysis of the baryon spectrum, taking into account the low statistics and the error bars associated with each resonance. Our findings give a major support to the previous conclusions. Besides, analogue analyses are performed in the experimental meson spectrum, with comparison to theoretical models.  [Show abstract] [Hide abstract]
ABSTRACT: We present a robust analysis of the spectral fluctuations exhibited by the light meson spectrum. This analysis provides information about the degree of chaos in light mesons and may be useful to get some insight on the underlying interactions. Our analysis unveils that the statistical properties of the light meson spectrum are close, but not exactly equal, to those of chaotic systems. In addition, we have analyzed several theoretical spectra including the latest lattice QCD calculation. With a single exception, their statistical properties are close to those of a generic integrable system, and thus incompatible with the experimental spectrum.  [Show abstract] [Hide abstract]
ABSTRACT: The electric form factor of the neutron was determined from studies of the reaction 3He(e,e'n)pp in quasielastic kinematics in Hall A at Jefferson Lab. Longitudinally polarized electrons were scattered off a polarized target in which the nuclear polarization was oriented perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons that were registered in a largesolidangle detector. More than doubling the Q2 range over which it is known, we find G(E)(n)=0.0236±0.0017(stat)±0.0026(syst), 0.0208±0.0024±0.0019, and 0.0147±0.0020±0.0014 for Q(2)=1.72, 2.48, and 3.41 GeV2, respectively.  [Show abstract] [Hide abstract]
ABSTRACT: Contributions of D waves to physical observables for neutral pion photoproduction from the proton in the nearthreshold region are studied and means to isolate them are proposed. Various approaches to describe the multipoles are employeda phenomenological one, a unitary one, and heavy baryon chiral perturbation theory. The results of these approaches are compared and found to yield essentially the same answers. D waves are seen to enter together with S waves in a way that any means which attempt to obtain the E{sub 0+} multipole accurately must rely on knowledge of D waves and that consequently the latter cannot be dismissed in analyses of lowenergy pion photoproduction. It is shown that D waves have a significant impact on doublepolarization observables that can be measured. This importance of D waves is due to the soft nature of the S wave and is a direct consequence of chiral symmetry and the NambuGoldstone nature of the pion. Fwave contributions are shown to be negligible in the nearthreshold region.  [Show abstract] [Hide abstract]
ABSTRACT: The contribution of D waves to physical observables for neutral pion photoproduction in the near threshold region is studied. Heavy Baryon Chiral Perturbation Theory to one loop, and up to ${\cal O}(q^4)$, is used to account for the S and P waves, while D waves are added in an almost modelindependent way using standard Born terms and vector mesons. It is found that the inclusion of D waves is necessary to extract the $E_{0+}$ multipole reliably from present and forthcoming data and to assess the lowenergy constants of Chiral Perturbation Theory. Arguments are presented demonstrating that Fwave contributions are negligible in the nearthreshold region. Comment: 10 pages, 5 figures  [Show abstract] [Hide abstract]
ABSTRACT: We present an optimization scheme that employs a Genetic Algorithm (GA) to determine the properties of lowlying nucleon excitations within a realistic photopion production model based upon an effective Lagrangian. We show that with this modern optimization technique it is possible to reliably assess the parameters of the resonances and the associated error bars as well as to identify weaknesses in the models. To illustrate the problems the optimization process may encounter, we provide results obtained for the nucleon resonances $\Delta$(1230) and $\Delta$(1700). The former can be easily isolated and thus has been studied in depth, while the latter is not as well known experimentally. 
Article: Spin asymmetry for the 16O() reaction in the Δ(1232) region within an effective Lagrangian approach
[Show abstract] [Hide abstract]
ABSTRACT: The spin asymmetry of the photon in the exclusive reaction is computed employing a recently developed fully relativistic model based on elementary pion production amplitudes that include a consistent treatment of the spin3/2 nucleon resonances. We compare the results of this model to the only available data on Oxygen [K. Hicks, et al., Phys. Rev. C 61 (2000) 054609] and find that, contrary to other models, the predicted spin asymmetry compares well to the available experimental data in the Δ(1232) region. Our results indicate that no major medium modifications in the Δ(1232) properties are needed in order to describe the measured spin asymmetries.
Publication Stats
200  Citations  
106.80  Total Impact Points  
Top Journals
 Physics Letters B (7)
 Physical Review C (4)
 Physical Review Letters (4)
 Physical Review D (2)
 Annals of Physics (1)
Institutions

20142015

Thomas Jefferson National Accelerator Facility
 Theoretical and Computational Physics Center
НьюпортНьюс, Virginia, United States


2012

European Centre for Theoretical Studies in Nuclear Physics and Related Areas
Trient, TrentinoAlto Adige, Italy


20082012

Complutense University of Madrid
 Department of Atomic, Molecular and Nuclear Physics
Madrid, Madrid, Spain 
Massachusetts Institute of Technology
 Center for Theoretical Physics
Cambridge, MA, United States


2007

Universidad de Sevilla
 Atomic, Molecular and Nuclear Physics
Hispalis, Andalusia, Spain 
Instituto de Estructura de la Materia
Madrid, Madrid, Spain


20052006

Spanish National Research Council
 Institute for the Structure of Matter
Madrid, Madrid, Spain
