Beam Spin Asymmetry in Semi-Inclusive Electroproduction of Hadron Pairs

International audienceA first measurement of the longitudinal beam spin asymmetry ALU in the semi-inclusive electroproduction of pairs of charged pions is reported. ALU is a higher-twist observable and offers the cleanest access to the nucleon twist-3 parton distribution function e(x). Data have been collected in the Hall-B at Jefferson Lab by impinging a 5.498-GeV electron beam on a liquid-hydrogen target, and reconstructing the scattered electron and the pion pair with the CLAS detector. One-dimensional projections of the ALUsinϕR moments are extracted for the kinematic variables of interest in the valence quark region. The understanding of dihadron production is essential for the interpretation of observables in single-hadron production in semi-inclusive DIS, and pioneering measurements of single-spin asymmetries in dihadron production open a new avenue in studies of QCD dynamics

Publisher's Note: Differential photoproduction cross sections of the \u3a3^{0}(1385), \u39b(1405), and \u39b(1520) [Phys. Rev. C 88, 045201 (2013)]

No abstract available

Exclusive electroproduction of \u3c6 mesons at 4.2 GeV

We studied the exclusive reaction ep\u20d7e\u2032p\u2032\u3c6 using the \u3c6\u20d7K+K- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in Q2 from 0.7 to 2.2 GeV2, and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of \u3c6 production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time c\u394\u3c4 below 2 fm. At \u3008c\u394\u3c4\u3009=0.6 fm, we measure b\u3c6=2.27\ub10.42 GeV-2. The cross section dependence on W as W0.2\ub10.1 at Q2=1.3 GeV2 was determined by comparison with \u3c6 production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction

Electroproduction of the \u39b(1520) hyperon

The reaction ep\u20d7e\u2032K+\u39b(1520) with \u39b(1520)\u2192p\u2032K- was studied at electron beam energies of 4.05, 4.25, and 4.46 GeV, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cos\u3b8K+, \u3c6K+, Q2, and W dependencies of \u39b(1520) electroproduction are presented for the kinematic region 0.9<Q2<2.4\u2002GeV2 and 1.95<W<2.65\u2002GeV. Also, the Q2 dependence of the \u39b(1520) decay angular distribution is presented for the first time. The cos\u3b8K+ angular distributions suggest t-channel diagrams dominate the production process. Fits to the \u39b(1520) t-channel helicity frame decay angular distributions indicate the mz=\ub11/2 parentage accounts for about 60% of the total yield, which suggests this reaction has a significant contribution from t-channel processes with either K+ exchange or longitudinal coupling to an exchanged K*. The Q2 dependence of the \u39b(1520) production cross section is the same as that observed for \u39b(1116) photo- and electroproduction

&#951; Photoproduction on the proton for photon energies from 0.75 to 1.95 GeV

Differential cross sections for \u3b3p\u2192\u3b7p have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W=1.75\u2009\u2009GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass 3c1.8\u2009\u2009GeV couples to the \u3b7N channel