The angular dependence of the 16 O(e,e’K + ) 16  N and H(e,e’K + )  F. Garibaldi – Jlab December WATERFALL The WATERFALL target: reactions on 16 O and 1 H nuclei

1 H (e,e’K)  16 O(e,e’K) 16 N  1 H (e,e’K)  L S Energy Calibration Run Results on the WATERFALL target - 16 O and 1 H  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)

10/13/09 p(e,e'K + )  on Waterfall Production run Expected data from E07-012, study the angular dependence of p(e,e’K) L and 16 O(e,e’K) 16 N  at low Q 2 R esults on H target – The p(e,e’K) L C ross S ection p(e,e'K + )  on LH 2 Cryo Target Calibration run None of the models is able to describe the data over the entire range New data is electroproduction – could longitudinal amplitudes dominate? W =2.2 GeV

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

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

The cross section of (e,e’K) on a nuclear target and its angular dependence determined by: Transition operatorgiven by the modelelem. prod. on protons - Transition operator, which is given by the model used to describe the elem. prod. on protons Structuretarget nucleus - Structure (that is the many particle wave function) of the target nucleus and hypernuclear state Momentum transferred - Momentum transferred to the nucleus, q = p  - p K - Angular dependencemainlymomentum transferred via - Angular dependence determined mainly by the momentum transferred to the nucleus (q) via the transition form factorq is a rapidly increasing function of the kaon nucleus - hypernucleus transition form factor (q is a rapidly increasing function of the kaon scattering angle) scattering angle) - 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

Electroproduction on 16 O - angular distribution

- 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 hypernuclear physics AND discriminate Simultaneously measuring the electroproduction cross section on oxygen and hydrogen at a few kaon scattering angles will shed new light on problems of hypernuclear physics AND discriminate between groups of elementary models

The elementary process: The p(e,e’K + )  electromagnetic X-section ee kk  e e’ k pp Scattering plane (leptonic) Reaction plane (hadronic) e p K+K+ e’   * The appropriate set of propagators (particles) and coupling constants has to be established from the data and from theoretical guidelines (SU3 broken symmetry) At CEBAF energies non-perturbative QCD degrees of freedom have to be taken into account. - 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 ,( *,…)  * K+K+  p = K+K+  p P(N *, *,…) p  * K+K+  K(K1,…)  K+K+  * p s-channel t-channel u-channel ++

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 is poor in the kinematical region relevant for hypernuclear calculations 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. The elementary process: The p(e,e’K + )  electromagnetic X-section 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

The elementary process: The p(e,e’K + )  electromagnetic X-section K + -  electro-production cross section will be measured in an unexplored kinematical region typical of HYPERNUCLEAR experiments. 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. In the angular range proposed(  CM k  = 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. Q 2 =0.06 (GeV/c) 2 THIS EXPERIMENT PROJECTED DATA 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)

kinematics and counting rates Waterfall Target thicknes = 130 mg/cm 2 Beam current = 100  A beam time request SNR ≥ 6

beam time request With new setup in Hall A if 3 angles in one shot, a factor 3 in the yield (?) ~ 5 days

16 O(e,e’K) 16 N  16 O(  ,K + ) 16 O  16 O(K -,    ) 16 O  ~ 800 KeV similar discrepancy for elementary reaction this has to be understood !