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The angular dependence of the 16 O(e,e’ K + ) 16 L N and H (e,e’ K + ) L

The angular dependence of the 16 O(e,e’ K + ) 16 L N and H (e,e’ K + ) L F. Garibaldi – Jlab December 12-2012. The WATERFALL target: reactions on 16 O and 1 H nuclei. Results on the WATERFALL target - 16 O and 1 H. 1 H (e,e’K) L. 1 H (e,e’K) L,S. L. Energy Calibration Run. S.

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The angular dependence of the 16 O(e,e’ K + ) 16 L N and H (e,e’ K + ) L

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  1. The angulardependenceof the 16O(e,e’K+)16LN and H(e,e’K+)L F. Garibaldi –JlabDecember 12-2012 TheWATERFALLtarget: reactions on 16O and 1H nuclei

  2. Results on the WATERFALLtarget - 16O and 1H 1H(e,e’K)L 1H(e,e’K)L,S L Energy Calibration Run S 16O(e,e’K)16NL • Water thickness from elastic cross section on H • Precise determination of the particle momenta and beam energy • using the Lambda and Sigma peak reconstruction (energy scale calibration)

  3. Results on H target – The p(e,e’K)LCross Section p(e,e'K+)Lon Waterfall Production run W=2.2 GeV p(e,e'K+)L on LH2CryoTarget Calibrationrun Expected data fromE07-012, study the angular dependence of p(e,e’K)Land 16O(e,e’K)16NL at low Q2 • None of the models is able to describe the data over the entire range • New data is electroproduction – could longitudinal amplitudes dominate? 10/13/09

  4. Electroproduction of as function of Kaon angle what is missing ? - Systematic study of reaction as function of A and neutron rich nuclei (E05-015) - Angular distribution (momentum transfer) - Understanding of the elementary reaction The Proposal: studying, using waterfall target, different processes The elementary process on the proton

  5. Why? In this kinematical region models for the K+- electromagnetic production on protons differ drastically The interpretation of the hypernuclear spectra is difficult because of the lack of relevant information about the elementary process. The ratio of the hypernuclear and elementary cross section measured at the same kinematics is almost model independent at very forward kaon scattering angles Contains direct information on the target and hypernuclear structure, production mechanisms How? Hall A experimental setup (septummagnets, waterfall target, excellent energy resolutionANDParticle Identification) give unique opportunity to measure, simultaneously,hypernuclear processANDelementary process

  6. The cross section of (e,e’K) on a nuclear target and its angular dependence determined by: - The ratio of the hypernuclear and elementary cross section doesn’t depend strongly on the electroproducion model and contains direct information on hypercnulear structure and production mechanism • - Transition operator, which is given by the model used to describe the elem. prod. on protons • - Structure (that is the many particle wave function) of the target nucleus and hypernuclear state • Momentum transferred to the nucleus, q = p - pK • Angular dependence determined mainly by the momentum transferred to the nucleus (q) via the • nucleus - hypernucleus transition form factor (q is a rapidly increasing function of the kaon • scattering angle)

  7. Electroproduction on 16O - angular distribution

  8. - The slope depends on the spin of hypernuclear state - Excitation of hypernuclear states brings in a different combinations of the elementary amplitudes for different final states - The nuclear structure for a specific final state can emphasize either spin-flip or non-spin flip amplitudes, as well as combinations of them with different phases. - Deviations from an exponential decreases of cross sections with q could be caused by interference between the different amplitudes Simultaneously measuring the electroproduction cross section on oxygen and hydrogen at a few kaon scattering angles will shed new light on problems of hypernuclear physicsANDdiscriminatebetweengroups of elementary models

  9. The elementary process:Thep(e,e’K+)L electromagnetic X-section L L K+ K+ L L K+ K+ = P(N*,D*,…) + + g * L,S(L*,…) K(K1,…) p p p p g * g * g * s-channel u-channel t-channel k qe e’ qk pL e F L Scattering plane (leptonic) K+ Reaction plane (hadronic) e’ g * At CEBAF energies non-perturbative QCD degrees of freedom have to be taken into account. p e - IN PRINCIPLE: the amplitude can be calculated in QCD. IN PRACTICE: semi-phenomenological description Quantum HadronDynamics(QHD), degrees of freedom, nucleon, kaon, resonances. A diagrammatic semi-phenomenological approach based on hadronic field theories (effective hadronic Lagrangian - QHD) is likely well applicable in the description of the process The appropriate set of propagators (particles) and coupling constants has to be established from the data and from theoretical guidelines (SU3 broken symmetry)

  10. The elementary process:Thep(e,e’K+)L electromagnetic X-section No dominant resonance contributes to the kaon electro and photo-production (like Delta for pion).  a large number of possible resonances can contribute  many free parameters, the coupling constants must be fixed by experiment. …many models on the market which differ just in the choice of the resonances. • two groups of models differing by the treatment of hadronic vertices show LARGE DIFFERENCES • Assumption for the hadronic form factor : • KMAID, Jansen, H2 : with h.f.f. • Saclay-Lyon, WiJiCo : without h.f.f. The theoretical description ispoor in the kinematical region relevant for hypernuclear calculations A phenomenon which can be addressed by the expected data: The sharp damping of the cross section at very small kaon angles which is connected to the fundamental ingredients of the models, accounting for the hadronic form factors. This is also very important in the hypernuclear calculations. Photo-production existing data and model predictions

  11. The elementary process:Thep(e,e’K+)L electromagnetic X-section Electro-production model predictions From electro-production to photo-production on hydrogen • Selection of a model • Eventually new fit on model parameters including these new data • Model dependent evaluation of interference terms w.r.t. the dominant transverse term (kinematics very close to the photon point) K+-L electro-production cross section will be measured in an unexplored kinematical regiontypical of HYPERNUCLEAR experiments. In the angular range proposed(QCMkg=5.4-18 deg) the electro-magnetic production models show a strong angular dependence. Measuring the elementary cross section in such an angular range will provide a set of data very important to constrain models and provide information on the use of hadronic form factors. THIS EXPERIMENT PROJECTED DATA Q2=0.06 (GeV/c)2

  12. beam time request kinematics and counting rates Waterfall Target thicknes = 130 mg/cm2 Beam current = 100 A SNR ≥ 6

  13. beam time request Withnewsetup in Hall A if3angles in oneshot, a factor3 in the yield (?) ~ 5days

  14. 16O(e,e’K)16NL Preliminary 16O(K-, p- g) 16OL 16O(p+,K+)16OL ~ 800 KeV this has to be understood ! similar discrepancy for elementary reaction

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