Publications (24)80.81 Total impact
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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.Physical Review Letters 08/2013; 111(6):062004. · 7.73 Impact Factor 
Article: PWA tools in Hadronic Spectroscopy
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ABSTRACT: The miniproceedings of the Workshop on PWA tools in Hadronic Spectroscopy held in Mainz from February 18th to 20th, 2013.04/2013; 
Article: Upper Energy Limit of Heavy Baryon Chiral Perturbation Theory in Neutral Pion Photoproduction
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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$185 MeV with Taylor expansions in the partial waves up to first order in pion energy.Physics Letters B 12/2012; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Quantum chaos is currently a well established discipline with outreach to many fields of physics. The most important signature of quantum chaos is the statistical analysis of the energy spectrum, which distinguishes between systems with integrable and chaotic classical analogues. The spectral statistical techniques inherited from quantum chaos have been applied to the baryon spectrum revealing its likely chaotic behavior in the low energy regime [1,2]. We present a robust analysis of the spectral fluctuations exhibited by the light meson spectrum. With this analysis we can obtain information about the degree of chaos in the spectrum getting insight on the properties of the underlying interactions. Our analysis unveils that the statistical properties of the light meson spectrum are close, but not exactly equal, to those of chaotic systems [3]. Besides the experimental spectrum, we have analyzed several theoretical spectra [47] including the latest lattice QCD calculation [8] finding out that, with the single exception of [5], their statistical properties are close to those of a generic integrable system, and thus incompatible with the experimental result.12/2012; 
Article: Accurate Test of Chiral Dynamics in the \boldmath$\vec{\gamma} p \rightarrow \pi^0p$ Reaction
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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.Physical Review Letters 11/2012; 111(062004). · 7.73 Impact Factor 
Article: Chaos in hadrons
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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.Journal of Physics Conference Series 09/2012; 381(1):2031.  [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.Physics Letters B 03/2012; 710(1). · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The electronion scattering experiment ELISe is part of the installations envisaged at the new experimental storage ring at the international Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany.It offers an unique opportunity to use electrons as probe ininvestigations of the structure of exotic nuclei. The conceptual design and the scientific challenges of ELISe are presented.Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2011; · 1.14 Impact Factor  [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.Physical Review Letters 12/2010; 105(26):262302. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The electric form factor of the neutron was determined from studies of the reaction He3(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 Q2range over which it is known, we find GEn = 0.0225 +/ 0.0017 (stat) +/ 0.0024 (syst), 0.0200 +/ 0.0023 +/ 0.0018, and 0.0142 +/ 0.0019 +/ 0.0013 for Q2 = 1.72, 2.48, and 3.41 GeV2, respectively.Physical Review Letters 08/2010; 105(26). · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: It has been commonly assumed that lowenergy neutral pion photoproduction from the proton can be described accounting only for S and P waves, and that higher partial waves are irrelevant. We have found that this assumption is not correct and that the inclusion of D waves is necessary to obtain a reliable extraction of the $E_{0+}$ multipole from experimental data. This is due in large measure to the spontaneous breaking of chiral symmetry in QCD which leads to very small Swave contributions. This makes the usual partial wave expansion less accurate and although D waves are small, their contribution is enhanced through the interference with P waves, which compromises the Swave extraction from data if D waves are not taken into account. In our work we have used Heavy Baryon Chiral Perturbation Theory to one loop, and up to ${\cal O}(q^4)$, 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. We also show that higher partial waves do not play an important role. Comment: Talk presented in the 6th International Workshop on Chiral Dynamics, July 610 2009, Bern, Switzerland. To be published in Proceedings of Science. Uses class Pos.cls (included). 6 pages and 3 figures12/2009;  [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.Physical Review C 12/2009; 80(6). · 3.72 Impact Factor  [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 figuresPhysics Letters B 02/2009; · 4.57 Impact Factor  [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.Physical Review C 06/2008; 78(6):65212. · 3.72 Impact Factor 
Article: Spin asymmetry for the 16O() reaction in the Δ(1232) region within an effective Lagrangian approach
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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.Physics Letters B 06/2008; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Recent results are presented for quasifree pion photoproduction off the deuteron in the energy region from threshold up to the Delta(1232)resonance with inclusion of all leading piNN effects. Finalstate interaction effects are investigated and their role in polarized and unpolarized observables are found to be significant. The sensitivity of results to the elementary N(gamma,pi)N operator is discussed and considerable dependence is found. We expect that these results may be useful to interpret the recent measurements from LEGS, A2 and GDH Collaborations.AIP Conference Proceedings. 04/2008; 1006(1).  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the importance of crossing symmetry in effective field models and the effects of phenomenological nucleon resonance widths on the paradigmatic case of pion photoproduction. We use reaction models containing four star resonances up to 1.8 Gev ($\Delta$(1232), N(1440), N(1520), N(1535), $\Delta$(1620), N(1650), $\Delta$(1700), and N(1720)) with different prescriptions for crossed terms and widths, to fit the latest world database on pion photoproduction. We compare $\chi^2$ results from selected multipoles and fits. The $\chi^2$ is highly dependent on the fulfillment of crossing symmetry and the inclusion of $u$ channels.02/2008;  [Show abstract] [Hide abstract]
ABSTRACT: We analyze the γp→ηp process from threshold up to 1.2 GeV, employing an effective Lagrangian approach that allows for a mixing of eta couplings of pseudoscalar and pseudovector nature. The mixing ratio of the couplings may serve as a quantitative estimation of the SUL(3)×SUR(3) extended chiral symmetry violation in this energy regime. The data analyzed (differential cross sections and asymmetries) show a preference for the pseudoscalar coupling—91% of pseudoscalar coupling component for the best fit. We stress that a more conclusive answer to this question requires a more complete electromagnetic multipole database than the presently available one.Physics Letters B 07/2007; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study the lowlying baryon spectrum (up to 2.2 GeV) provided by experiments and different quark models using statistical tools which allow us to postulate the existence of missing levels in spectra. We confirm that the experimental spectrum is compatible with random matrix theory, the paradigmatic model of quantum chaos, and we find that the quark models are more similar to a Poisson distribution, which is not compatible with what should be expected in a correlated spectrum. From our analysis it stems that the spectral fluctuation properties of quarkmodel spectra are incompatible with experimental data. This result can be used to enlighten the problem of missing resonances.Physical Review Letters 03/2007; 98(6):062001. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The helicity dependence of the γ d → π − pp, γ d → π + nn, and γ d → π 0 np reaction channels is studied for incident photon energies from threshold up to the (1232) resonance with inclusion of leading πNN effects. The doubly polarized total and differential cross sections for parallel and antiparallel helicity states are predicted. Then the contribution of various channels to the deuteron spin asymmetry and the double polarization E asymmetry is calculated. In addition, the contribution to the GerasimovDrellHearn (GDH) integral from separate channels is evaluated by explicit integration up to a photon lab energy of 350 MeV. Sizeable effects from finalstate interactions, specially for π 0 production, are found. The sensitivity of the results to the elementary pion photoproduction operator is also investigated. Considerable dependence of the results on the elementary amplitude is found. We expect that these results may be useful to interpret the recent measurements from LEGS@BNL, A2, and GDH@MAMI Collaborations.01/2007;
Publication Stats
72  Citations  
80.81  Total Impact Points  
Top Journals
Institutions

2012

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


2005–2012

Complutense University of Madrid
 Facultad de Ciencias Físicas
Madrid, Madrid, Spain


2008–2009

Massachusetts Institute of Technology
 Center for Theoretical Physics
Cambridge, MA, United States


2005–2007

Instituto de Estructura de la Materia
Madrid, Madrid, Spain
