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Physics with CLAS
No full textThe authors describe the physics program and the experimental equipment of the CEBAF Large Acceptance Spectrometer, CLAS. The spectrometer is located in Hall B, one of the three experimental areas at the Continuous Electron Beam Accelerator Facility (CEBAF) operated by the Thomas Jefferson National Accelerator Facility. They review the program to study baryon resonances to demonstrate the multi-particle detection capabilities of the CLAS detector
Bayesian Analysis of Pentaquark Signals from CLAS Data
No full textWe examine the results of two measurements by the CLAS collaboration, one of which claimed evidence for a Θ+ pentaquark, while the other found no such evidence. The unique feature of these two experiments was that they were performed with the same experimental setup. Using a Bayesian analysis, we find that the results of the two experiments are in fact compatible with each other, but that the first measurement did not contain sufficient information to determine unambiguously the existence of a Θ+. Further, we suggest a means by which the existence of a new candidate particle can be tested in a rigorous manner
Differential Cross Sections for Λ (1520) Using Photoproduction at CLAS
No full textThe reaction p → K+Λ (1520) using photoproduction data from the CLAS g12 experiment at Jefferson Lab is studied. The decay of Λ(1520) into two exclusive channels, Σπ+π- and Σ-π+, is studied from the detected K+, π+, and π- particles. A good agreement is established for the Λ(1520) differential cross sections with the previous CLAS measurements. The differential cross sections as a function of center-of-mass angle are extended to higher photon energies. Newly added are the differential cross sections as a function of invariant four-momentum transfer t, which is the natural variable to use for a theoretical model based on a Regge-exchange reaction mechanism. No new N* resonances decaying into the K+Λ (1520) final state are found
Ovisnost kutnih raspodjela o helicitetu u fototvorbi parova nabijenih piona
No full textTwo-pion photoproduction in the reaction γp → pπ +π − has been studied at Jefferson Lab Hall B using a circularly polarized tagged-photon beam in the energy range between 0.6 GeV and 2.3 GeV. Owing to the large angular acceptance of the CLAS detector, complete beam-helicity-dependent angular distributions of the final-state particles were measured. The large cross-section asymmetries exhibit strong sensitivity to the kinematics of the reaction and provide valuable information on the reaction dynamics. Preliminary results are presented.Istraživali smo dvopionsku fototvorbu u reakciji γp → pπ +π − pomoću cirkularno polariziranog snopa obilježenih fotona na energijama između 0.6 GeV i 2.3 GeV u Hali B Jeffersonovog Laba. Zahvaljujući velikom prihvatnom kutu detektora CLAS, izmjerili smo potpune kutne raspodjele čestica u konačnom stanju u ovisnosti o helicitetu snopa. Velike asimetrije udarnih presjeka pokazuju jaku ovisnost o kinematici reakcije i pružaju važne podatke o njenoj dinamici. Predstavljaju se prethodni ishodi mjerenja
Suppression of neutral pion production in deep-inelastic scattering off nuclei with the CLAS detector
No full textWe present the first three-fold differential measurement for neutral pion multiplicity ratios produced in semi-inclusive deep-inelastic electron scattering on carbon, iron and lead nuclei normalized to deuterium from CLAS at Jefferson Lab. We found that the neutral pion multiplicity ratio is maximally suppressed for the leading hadrons (energy fraction z approaching unity), suppression varying from 25% in carbon up to 75% in lead. An enhancement of the multiplicity ratio at low z and high p2T is observed, suggesting an interconnection between these two variables. This behavior is qualitatively similar to the previous two-fold differential measurement of charged pions by the HERMES Collaboration and recently - by CLAS Collaboration. The largest enhancement was observed at high pT2 for heavier nuclei, namely iron and lead, while the smallest enhancement was observed for the lightest nucleus, carbon. This behavior suggests a competition between partonic multiple scattering, which causes enhancement, and hadronic inelastic scattering, which causes suppression
Ovisnost kutnih raspodjela o helicitetu u fototvorbi parova nabijenih piona
No full textTwo-pion photoproduction in the reaction γp → pπ +π − has been studied at Jefferson Lab Hall B using a circularly polarized tagged-photon beam in the energy range between 0.6 GeV and 2.3 GeV. Owing to the large angular acceptance of the CLAS detector, complete beam-helicity-dependent angular distributions of the final-state particles were measured. The large cross-section asymmetries exhibit strong sensitivity to the kinematics of the reaction and provide valuable information on the reaction dynamics. Preliminary results are presented.Istraživali smo dvopionsku fototvorbu u reakciji γp → pπ +π − pomoću cirkularno polariziranog snopa obilježenih fotona na energijama između 0.6 GeV i 2.3 GeV u Hali B Jeffersonovog Laba. Zahvaljujući velikom prihvatnom kutu detektora CLAS, izmjerili smo potpune kutne raspodjele čestica u konačnom stanju u ovisnosti o helicitetu snopa. Velike asimetrije udarnih presjeka pokazuju jaku ovisnost o kinematici reakcije i pružaju važne podatke o njenoj dinamici. Predstavljaju se prethodni ishodi mjerenja
Search for the Θ^{+} Pentaquark in the γd→ ΛnK^{+} Reaction Measured with the CLAS Spectrometer
No full textFor the first time, the reaction γd→ΛnK+ has been analyzed in order to search for the exotic pentaquark baryon Θ+(1540). The data were taken at Jefferson Laboratory, using the Hall-B tagged-photon beam of energy between 0.8 and 3.6 GeV and the CEBAF Large Acceptance Spectrometer (CLAS). No statistically significant structures were observed in the nK+ invariant-mass distribution. The upper limit on the γd→ΛΘ+ integrated cross section has been calculated and found to be between 5 and 25 nb, depending on the production model assumed. The upper limit on the differential cross section is also reported
Differential cross section and recoil polarization measurements for the γp→K+Λ reaction using CLAS at Jefferson Lab
No full textWe present measurements of the differential cross section and Λ recoil polarization for the γp→K+Λ reaction made using the CLAS detector at Jefferson Lab. These measurements cover the center-of-mass energy range from 1.62 to 2.84 GeV and a wide range of center-of-mass K+ production angles. Independent analyses were performed using the K+pπ− and K+p (missing π−) final-state topologies; results from these analyses were found to exhibit good agreement. These differential-cross-section measurements show excellent agreement with previous CLAS and LEPS results and offer increased precision and a 300-MeV increase in energy coverage. The recoil polarization data agree well with previous results and offer a large increase in precision and a 500-MeV extension in energy range. The increased center-of-mass energy range that these data represent will allow for independent study of nonresonant K+Λ photoproduction mechanisms at all production angles
Measurement of the nuclear multiplicity ratio for K0 s hadronization at CLAS
No full textThe influence of cold nuclear matter on lepto-production of hadrons in semi-inclusive deep inelastic scattering is measured using the CLAS detector in Hall B at Jefferson Lab and a 5.014 GeV electron beam. We report the Kos multiplicity ratios for targets of C, Fe, and Pb relative to deuterium as a function of the fractional virtual photon energy z transferred to the Kos and the transverse momentum squared P2T of the Kos. We find that the multiplicity ratios for Kos are reduced in the nuclear medium at high z and low P2T, with a trend for the Kos transverse momentum to be broadened in the nucleus for large P2T
Suppression of neutral pion production in deep-inelastic scattering off nuclei with the CLAS detector
No full textWe present the first three-fold differential measurement for neutral pion
multiplicity ratios produced in semi-inclusive deep-inelastic electron
scattering on carbon, iron and lead nuclei normalized to deuterium from CLAS at
Jefferson Lab. We found that the neutral pion multiplicity ratio is maximally
suppressed for the leading hadrons (energy fraction z approaching unity),
suppression varying from 25% in carbon up to 75% in lead. An enhancement of the
multiplicity ratio at low z and high p2T is observed, suggesting an
interconnection between these two variables. This behavior is qualitatively
similar to the previous two-fold differential measurement of charged pions by
the HERMES Collaboration and recently - by CLAS Collaboration. The largest
enhancement was observed at high pT2 for heavier nuclei, namely iron and lead,
while the smallest enhancement was observed for the lightest nucleus, carbon.
This behavior suggests a competition between partonic multiple scattering,
which causes enhancement, and hadronic inelastic scattering, which causes
suppression
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