1. - motivation - angular distribution - the elementary reaction -kinematics and counting rates - beam time request - the apparatus - summary and conclusion (F. Garibaldi – Hall A – Hall C joint meeting - Jefferson Lab – May 15 2008 - hypernuclear physics - the electromagnetic approach - recent results

2. 16 O(e,e’K) 16 Λ N I : 100  A Targ. thick: ~100 mg/cm2 Counting Rates: 0.1 – 10 counts/peak/hr  e =  K = 6° Q 2 = 0.079 (GeV/c) 2 E beam = 4.016 GeV P k = 1.96 GeV/c P e = 1.8 GeV/c ω = E γ = 2.2 GeV

3. - energy resolution ~ 635 KeV, the best achieved in hypernuclear production experiments - work is in progress to further improve the resolution - first clear evidence of excited core states at ~2.5 and 6.5 MeV with high statistical significance - the width of the strong p  peak and the distribution of strength within several MeV on either side of this peak can put constraints on the hypernuclear structure calculations - hint for a peak at 9.65 MeV excitation energy (admixture) 1/2 1- 3/2 2- (3+,2+) 2+ admixture  sp = 4.47 nb/(GeV sr 2  th = 4.68 nb/(GeV sr 2 ) good agreement with theory 1/2 1- 3/2 2- admixture (3+,2+) 2+ Red line: Fit to the dataBlue line: Theoretical curve: Saghai Saclay-Lyon (SLA) used for the elementary K-  electroproduction on proton.Hypernuclear wave function obtained by M.Sotona and J.Millener E94-107 12 C(e,e’K) 11  B

4. 1 H (e,e’K)  16 O(e,e’K) 16 N  1 H (e,e’K)    Energy Calibration Run Preliminary Results on the WATERFALL target - 16 O and H spectra Excitation Energy (MeV) Nb/sr2 GeV MeV  Water thickness from elastic cross section on H  Fine determination of the particle momenta and beam energy using the Lambda peak reconstruction (resolution vs position)

5.  Fit to the data (red line): Fit 4 regions with 4 Voigt functions  2 /ndf = 1.19  Theoretical model (blu line) superimposed curve based on : i)SLA p(e,e’K+) (elementary process) ii)N interaction fixed parameters from KEK and BNL 16  O spectra R esults on 16 O target – Hypernuclear Spectrum of 16 N  - Peak Search : Identified 4 regions with excess counts above background Binding Energy B  =13.68 ± 0.16 (stat) ± 0.05 (sys) MeV Measured for the first time with this level of accuracy (ambiguous interpretation from emulsion data; interaction involving  production on n more difficult to normalize) Binding Energy (MeV) Cross Section [nb/(sr 2 MeV GeV)]

6. R esults on 16 O target – Hypernuclear Spectrum of 16 N  E94-107 (  +,K + ) (K -,  - ) (K stop,  - ) [2] O. Hashimoto, H. Tamura, Part Nucl Phys 57, 564 (2006) [3] private communication from D. H. Davis, D. N. Dovee, fit of data from Phys Lett B 79, 157 (1978) [4] private communication from H. Tamura, erratum on Prog Theor Phys Suppl 117, 1 (1994) [2 ] [3 ] [4 ] Comparison with the mirror nucleus 16 O  Difference expected with respect to mirror nucleus: 400 – 500 keV (M. Sotona)

7. p(e,e'K + )  on Waterfall Production run p(e,e'K + )  on LH2 Cryo Target Calibration run Work on normalizations, acceptances, efficiencies still underway Expected data from the Experiment E07-012 to study the angular dependence of p(e,e’K) and 16 O(e,e’K) 16 N  at Low Q 2 (approved January, 2007) R esults on H target – The p(e,e’K)  C ross S ection

8. 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 ?

9. 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 process AND 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?

10. 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

11. Electroproduction on 16 O - angular distribution

12. - 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

13. 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 ++

14. 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

15. 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  =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. 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)

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

17. Measurement and Feasibility: This measurement is a larger-angle version of E94-107, which has already run successfully in Hall A. If the cross sections drop rapidly with angle, the signal might become difficult to see, but given the range of models this appears to still provide a sufficient result. Issues: The PAC was convinced that the measurement of the elementary p(e,e'K + )L process is of sufficient interest to warrant measurement at both angles. The PAC did not find the argument for the measurement of 16 O(e,e'K + ) 16 N L at all angles equally compelling. PAC 31 Report

18. Something new We might be able to have 5 degrees Ei=3.660 GeV; Ef=1.450 GeV; teta = 6 teta = 5 theta(gamma-e) 3.91 3.26 theta(K-gamma) = 2.09 1.74 virtual photon flux = 0.0172 0.0250 Pk (GeV/c) 1.970 1.970 q (GeV.c) 0.264 0.257 16O(e,e'K+) (nb/sr^2/GeV) = 1.45 2.55 1H(e,e'K+) (nb/sr^2/GeV) = 36.2 55.9

19. Hall A - Two High Resolution Spectrometers QDQ - Momentum Range: 0.3 –4 GeV/c  p/p : 1 x 10-4 –  p = =-5% -  –  mr 1 (+1) Cherenkov threshold aerogels + RICH in the hadron spectrometer + septum magnet

20. PID electron arm:gas Cherenkov + shower counter --> 10 5 pion rejection hadron arm 2 aerogel detectors (n=1.015 and n=1.025) RICH detector pion rejection ~ 10.000 !! RICH upgrade this proposal

23. Summary and Conclusions - Understanding the elementary cross section in an unexplored kinematical region fundamental for the hypernuclear spectroscopy experiments region fundamental for the hypernuclear spectroscopy experiments - Obtaining information about the importance of hadron f.f. - Is the concept of the hadronic form factors used in the isobaric models correct? - Is the hypernuclear angular dependence the same as the elementary dependence? - What is the angular dependence of the hypernuclear form factor at forward angles? - The ratio of the hypernuclear and elementary cross section is only weakly sensitive to -> direct access to the hypernuclear structure the models of elementary production -> direct access to the hypernuclear structure in a model independent way (unique feature of this experiment) in a model independent way (unique feature of this experiment) - These questions are very important for our understanding of dynamics of the process and vital for the hypernuclear calculations and interpretation of the process and vital for the hypernuclear calculations and interpretation of the data data - The proposed experimental technique has been fully and successfully proven in the previous experiment, E94-107, where very clean, background free, high resolution spectra have been obtained. Measuring simultaneously the angular dependence of electroproduction on Oxygen and Hydrogen is important