Julián Pacomio - Academia.edu (original) (raw)
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Papers by Julián Pacomio
Photoproduction of the cascade resonances has been investigated in the reactions γp → K + K + (X)... more Photoproduction of the cascade resonances has been investigated in the reactions γp → K + K + (X) and γp → K + K + π − (X). The mass splitting of the ground state (Ξ − , Ξ 0) doublet is measured to be 5.4 ± 1.8 MeV/c 2 , consistent with existing measurements. The differential (total) cross sections for the Ξ − have been determined for photon beam energies from 2.75 to 3.85 (4.75) GeV, and are consistent with a production mechanism of Y * → K + Ξ − through a t-channel process. The reaction γp → K + K + π − [Ξ 0 ] has also been investigated in search of excited cascade resonances. No significant signal of excited cascade states other than the Ξ − (1530) is observed. The cross section results of the Ξ − (1530) have also been obtained for photon beam energies from 3.35 to 4.75 GeV.
Physical Review Letters, 2010
We report the first measurement of the transverse momentum dependence of double spin asymmetries ... more We report the first measurement of the transverse momentum dependence of double spin asymmetries in semi-inclusive production of pions in deep inelastic scattering off the longitudinally polarized proton. Data have been obtained using a polarized electron beam of 5.7 GeV with the CLAS detector at the Thomas Jefferson National Accelerator Facility (JLab). A significant non-zero sin 2φ single spin asymmetry was also observed for the first time indicating strong spin-orbit correlations for transversely polarized quarks in the longitudinally polarized proton. The azimuthal modulations of single spin asymmetries have been measured over a wide kinematic range.
Physical Review C, 2009
We present results on the electroexcitation of the low mass resonances ∆(1232)P33, N (1440)P11, N... more We present results on the electroexcitation of the low mass resonances ∆(1232)P33, N (1440)P11, N (1520)D13, and N (1535)S11 in a wide range of Q 2. The results were obtained in the comprehensive analysis of JLab-CLAS data on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for π electroproduction off the proton. The data were analysed using two conceptually different approaches, fixed-t dispersion relations and a unitary isobar model, allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the ∆(1232)P33 show the importance of a mesoncloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q 2 ≤ 6 GeV 2. For the Roper resonance, N (1440)P11, the data provide strong evidence for this state as a predominantly radial excitation of a 3-quark ground state. Measured in pion electroproduction, the transverse helicity amplitude for the N (1535)S11 allowed us to obtain the branching ratios of this state to the πN and ηN channels via comparison to the results extracted from η electroproduction. The extensive CLAS data also enabled the extraction of the γ * p → N (1520)D13 and N (1535)S11 longitudinal helicity amplitudes with good precision. For the N (1535)S11, these results became a challenge for quark models, and may be indicative of large meson-cloud contributions or of representations of this state different from a 3q excitation. The transverse amplitudes for the N (1520)D13 clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q 2 > 1 GeV 2 , confirming a long-standing prediction of the constituent quark model.
Physical Review C, 2009
Differential cross sections for the reaction γ p → n π + have been measured with the CEBAF Large ... more Differential cross sections for the reaction γ p → n π + have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.725 to 2.875 GeV. Where available, the results obtained here compare well with previously published results for the reaction. Agreement with the SAID and MAID analyses is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been made up to 2.7 GeV. Resonance couplings have been extracted and compared to previous determinations. With the addition of these cross sections to the world data set, significant changes have occurred in the high-energy behavior of the SAID cross-section predictions and amplitudes.
Photoproduction of the cascade resonances has been investigated in the reactions γp → K + K + (X)... more Photoproduction of the cascade resonances has been investigated in the reactions γp → K + K + (X) and γp → K + K + π − (X). The mass splitting of the ground state (Ξ − , Ξ 0) doublet is measured to be 5.4 ± 1.8 MeV/c 2 , consistent with existing measurements. The differential (total) cross sections for the Ξ − have been determined for photon beam energies from 2.75 to 3.85 (4.75) GeV, and are consistent with a production mechanism of Y * → K + Ξ − through a t-channel process. The reaction γp → K + K + π − [Ξ 0 ] has also been investigated in search of excited cascade resonances. No significant signal of excited cascade states other than the Ξ − (1530) is observed. The cross section results of the Ξ − (1530) have also been obtained for photon beam energies from 3.35 to 4.75 GeV.
Physical Review Letters, 2010
We report the first measurement of the transverse momentum dependence of double spin asymmetries ... more We report the first measurement of the transverse momentum dependence of double spin asymmetries in semi-inclusive production of pions in deep inelastic scattering off the longitudinally polarized proton. Data have been obtained using a polarized electron beam of 5.7 GeV with the CLAS detector at the Thomas Jefferson National Accelerator Facility (JLab). A significant non-zero sin 2φ single spin asymmetry was also observed for the first time indicating strong spin-orbit correlations for transversely polarized quarks in the longitudinally polarized proton. The azimuthal modulations of single spin asymmetries have been measured over a wide kinematic range.
Physical Review C, 2009
We present results on the electroexcitation of the low mass resonances ∆(1232)P33, N (1440)P11, N... more We present results on the electroexcitation of the low mass resonances ∆(1232)P33, N (1440)P11, N (1520)D13, and N (1535)S11 in a wide range of Q 2. The results were obtained in the comprehensive analysis of JLab-CLAS data on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for π electroproduction off the proton. The data were analysed using two conceptually different approaches, fixed-t dispersion relations and a unitary isobar model, allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the ∆(1232)P33 show the importance of a mesoncloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q 2 ≤ 6 GeV 2. For the Roper resonance, N (1440)P11, the data provide strong evidence for this state as a predominantly radial excitation of a 3-quark ground state. Measured in pion electroproduction, the transverse helicity amplitude for the N (1535)S11 allowed us to obtain the branching ratios of this state to the πN and ηN channels via comparison to the results extracted from η electroproduction. The extensive CLAS data also enabled the extraction of the γ * p → N (1520)D13 and N (1535)S11 longitudinal helicity amplitudes with good precision. For the N (1535)S11, these results became a challenge for quark models, and may be indicative of large meson-cloud contributions or of representations of this state different from a 3q excitation. The transverse amplitudes for the N (1520)D13 clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q 2 > 1 GeV 2 , confirming a long-standing prediction of the constituent quark model.
Physical Review C, 2009
Differential cross sections for the reaction γ p → n π + have been measured with the CEBAF Large ... more Differential cross sections for the reaction γ p → n π + have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.725 to 2.875 GeV. Where available, the results obtained here compare well with previously published results for the reaction. Agreement with the SAID and MAID analyses is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been made up to 2.7 GeV. Resonance couplings have been extracted and compared to previous determinations. With the addition of these cross sections to the world data set, significant changes have occurred in the high-energy behavior of the SAID cross-section predictions and amplitudes.