proposal for PAC 31 (F. Garibaldi January 0507 - Hall A Collaboration meeting - Jlab) hypernuclear physics the electromagnetic approach recent results motivation the elementary reaction angular distribution the apparatus kinematics and counting rates beam time request summary and conclusion

HYPERNUCLEAR PHYSICS - N interaction Hypernuclei are bound states of nucleons with a strange baryon ( hyperon). Extension of physics on N-N interaction to system with S#0 Internal nuclear shell are not Pauli-blocked for hyperons Spectroscopy A hypernucleus is a “laboratory” to study nucleon-hyperon interaction (-N interaction) - N interaction Unique aspects of strangeness many body problems Importance for astrophysics

What do we find from  hypernuclear data? SKS at KEK-PS Experimental evidence for single particle orbits deep in nucleus They cannot be seen by nucleons Only hyperons () which are free from Pauli blocking make it possible.  feels a weaker potential than nucleons U = -30 MeV (c.f. UN = -50 MeV) 　 -> Attraction : -N < N-N Mass of hypernucleus　 B (MeV) Hotchi et al., Phys.Rev.C 64 (2001) 044302 Better energy resolution is necessary for more studies on N interaction : LN spin-dependent forces, LN-SN force, .. Unified understanding of B-B interactions in the quark (+meson) picture　 together with  and  hypernuclear data

Present Status of  Hypernuclear Spectroscopy 16LN (e,e’K+) (p-,K+) O. Hashimoto and H. Tamura, Prog. Part. Nucl. Phys, in press.

LN interaction (r) most of information is carried out by the spin dependent part doublet splitting determined by D, sL, T

and Improving energy resolution using electromagnetic probe BNL 3 MeV(FWHM) KEK336 2 MeV(FWHM) Improving energy resolution 1.45 MeV(FWHM) and 635 KeV using electromagnetic probe High resolution, high yield, and systematic study is essential Hall A ≤ 500 KeV

12C(e,e’K)11B KINEMATICS Ebeam = 4.016 — 3.777 — 3.656 GeV Pe= 1.80 — 1.56 — 1.44 GeV/c Pk= 1.96 GeV/c e = K = 6° = E ~ 2.2 GeV – Q2 = 0.079 (GeV/c)2 Beam current : 100 A Target thickness : ~100 mg/cm2 Counting Rates ~ 0.1 – 10 counts/peak/hour

the proposal: studying, using waterfall target, different processes what is missing ? - systematic study of reaction as function of A and neutron rich nuclei - better understanding of the elementary reaction - cross section as funtion of angle (momentum transfer (w. function)) the proposal: studying, using waterfall target, different processes 1. electroproduction of hypernucleus as function of scattering angle (momentum transfer) 2. elementary process on proton

good agreement with theory sp= 4.47 nb/(GeV sr2 th= 4.68 nb/(GeV sr2 ) good agreement with theory E94-107 Red line: Fit to the dataBlue line: Theoretical curve: Sagay Saclay-Lyon (SLA) used for the elementary K- electroproduction on proton.Hypernuclear wave function obtained by M.Sotona and J.Millener (3+,2+) (3+,2+) 1/2 1- 3/2 2- 1/2 1- 2+ 2+ 3/2 2- admixture admixture 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)

E-94107: Preliminary spectra of missing energy Low counting levels above Ethr. 16O(e,e’K)16NL 1H (e,e’K)L 16O(e,e’K)16NL 16O(e,e’K)16NL

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

E-94107: Very Preliminary Results on 9Be target Can we get info also about 9B angular distribution?

why in this kinematical region models for the K+- electromagnetic production on protons differ drastically lack of relevant information about the elementary process makes an interpretation of obtained hypernuclear spectra difficult the ratio of the hypernuclear and elementary cross section measured at the same kinematics should be 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 (septum magnets, waterfall target, excellent energy resolution and PID) give unique opportunity to measure, at the same time, elementary process and hypernuclear process

dependence of hypernuclear cross section on angle determined mainly by the following factors - transition operator, which is given by the model used to describe the elementary production on individual 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 elementary process

two group of models according to the assumption for h.f.f. elementary process - in principle, the amplitude can be calculated in QCD, in practice semifenomenological description Quantum HadronDynamics(QHD), degrees of freedom, nucleon, kaon, resonances. parameters of the Lagrangian taken from other processes or from fit to data taking into account general principles (SU(2), SU(3)) elm. structure of hadrons by f.f.(important at Eg>1.5 GeV for suppression of X-section) - non pointilike structure of hadrons in the strong vertex, only recently in some models two group of models according to the assumption for h.f.f. KMAID, Jansen, H2 Saclay-Lyon, WiJiCo description very bad in the kinematical region relevant for hypernuclear calculations

elementary process; angular distribution

electroproduction on 16O; 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 Simultaneously measuring the electroproduction cross section on hydrogen and oxygen targets at a few kaon scattering angles can therefore not only discriminate between two groups of elementary models but it can shed new light also on some problems of hypernuclear physics

beam time request SNR = 5 - 6 kinematics and counting rates Waterfall Target thicknes = 130 mg/cm2 Beam current = 100 A beam time request SNR = 5 - 6

Hall A - Two High Resolution Spectrometers QDQ - Momentum Range: 0.3 –4 GeV/c Dp/p : 1 x 10-4 – Dp = =-5% - DW = 5 –6 mr 1 (+1) Cherenkov threshold aerogels + RICH in the hadron spectrometer + septum magnet

PID this proposal RICH upgrade electron arm:gas Cherenkov + shower counter --> 105 pion rejection RICH upgrade hadron arm 2 aerogel detectors (n=1.015 and n=1.025) RICH detector pion rejection ~ 10.000 !!

Summary and conclusions the proposed experiment will answer the following questions • does the cross section for the photo-production continue in rising as the kaon angle goes to zero or is there a plateau or even a dip like for the high-energy data?(relationship with CLASS data) • is the concept of the hadronic form factors as it is used in the isobaric models still correct? What is the angular dependence of the hypernuclear form factor at forward angle? . is the hypernuclear angular dependence the same as the hypernuclear process? • which of the models describes better the reality at forward angles and can be therefore used in analysis of hypernuclear data without introducing an additional uncertainty? . the success of the previous experiment (very “clean” (background free) data) guarantees for the experimental equipment (optics, PID), analysis, rates (beam time) evaluation to be under control. (extrapolations “easy”). “unique possibility” for this experiment in Hall A with waterfall target, septa and PID these questions are very important for our understanding of dynamics of the process and vital for the hypernuclear calculations and interpretation of the data, they urge to be answered also for “building” the hypernuclear program at Jlab in the future

The scientific case for these measurements is well made. The elementary production reaction may help shed light on striking discrepancies between current models of this reaction at small angles. At this time, the small-angle behavior of the p(e,e'K+)Lambda cross-section is essentially unknown and difficult to access experimentally. The study of the angular dependence would be of great use to distinguish between the several competing models available to-date. Hence, JLab can make a significant contribution to basic hyperon physics. In addition, the small-angle regime of the elementary cross section is essential input for hypernuclear production calculations. Comparison of elementary and hypernuclear production data at the same kinematics may allow conclusions about the hypernuclear reaction dynamics. The simultaneous acquisition of data for each of these two types of reaction with a water target is particularly appealing. While the scientific case is compelling, the discussion raises a few concerns. Furthermore, the experimental part of the proposal appears somewhat thin. The proposal would clearly gain from some clarificationsand a more thorough experimental discussion. The two main concerns I have are Extraction of the photoproduction cross section from the electroproduction data may not be unambiguous; - The signal-to-noise ratio in the hypernuclear channel may become too poor to obtain a clear signal at the proposed angles Given the scarcity of hypernuclear data, there is significant discovery potential.

The status of the "already measured" (p. 14) E94-107 data point at theta_CM = 5.4 degrees is only briefly discussed on pp. 7-9, and a discrepancy of a factor of 2 with the SLA model is noted. It remains somewhat vague how final these results are. Even so, it would be illustrative to add these (presumably preliminary) data to Figs. 7 and 9. A discussion of the current uncertainty and main source of error would likewise help. On p. 13/Fig. 6: "Moreover, the CLAS and SAPHIR data are not fully consistent at the forward angles...". This should be "... the LEPS and SAPHIR data..." (red triangles and blue squares). Interestingly, these data _are_ consistent in Fig 7, which shows different kinematics. On p. 10 and 16, the authors discuss the possibility of extracting the photoproduction cross-section from electroproduction data. On p. 10, they claim that longitudinal and interference terms "should be negligible". On p. 16, they state that "LT and TT interference terms can contribute significantly". This is confusing. In same line of discussion, on p. 16, a claim is made that "we believe that [by] utilizing the data distribution in the azimuthal angle ... it will be possible to estimate the contribution of the interference terms". This is highly unconvincing. The acceptance of the HRS in the out-of-plane direction in these kinematics is very small (a few degrees). It appears nearly impossible to obtain data as a function of azimuth, especially with sufficient statistics and coverage to perform a Fourier decomposition. Since contributions from interference terms increase with angle, it is not unlikely that the proposed measurements will only yield meaningful electroproduction results. Best suited for extracting a photoproduction cross section are the already existing data from E94-107. Should it not be possible to extract photoproduction data reliably, how useful is the measurement of the elementary process then? On p. 21, Table 5, there is an estimate of rates. There is no word as to how these estimates were obtained. Since calculations differ in their cross section predictions by up to an order of magnitude, it would be very useful to provide somewhat more detail. For instance, If the SLA model was used, which E94-107 already suggests to be over-predicting cross sections, these estimates might be significantly too optimistic. Since the signal-to-noise ratio in the hypernuclear channel is poor, it is essential to convince the PAC that this is not a potential show-stopper. In the same vein, a discussion of expected statistics and systematics in the 16N-Lambda channel is missing. Also completely missing is a discussion of how the two reaction channels can be separated in the analysis. On p. 22, it would help to elaborate what property of the RICH will improve with the upgrade. Is it just a larger pad area and so a wider geometric acceptance? How, then, the better resolution?

Comparison with BB interaction models D SL SN T (MeV) ND -0.048 -0.131 -0.264 0.018 NF 0.072 -0.175 -0.266 0.033 NSC89 1.052 -0.173 -0.292 0.036 NSC97f 0.754 -0.140 -0.257 0.054 ( “Quark” 0.0 -0.4 ) Exp. 0.4 -0.01 -0.4 0.03 G-matrix calc. by Yamamoto Strength equivalent to quark-model LS force by Fujiwara et al. 　Spin-orbit forces (SL , SN) cannot be explained by meson models. Data seems to favor quark models. Consistent with Hiyama et al. --but 9LBe calculation by Fujiwara et al. (quark+meson) cannot reproduce it. PRL 85 (2000) 270 Tensor forces (T) is well explained by meson-exchange models.

Revised Study of LN interaction from g spectorscopy BNL E930　 (AGS D6 line + Hyperball) Discovery of “Hypernuclear Fine Structure” 16O (K-, p- g) 16LO 9Be (K-, p- g) 9LBe 26.1±2.0 keV 43±5 keV Eg (keV) Eg (keV) MeV MeV Akikawa et al., PRL 88 (2002) 082501 Ukai et al., PRL 93 (2004) 232501 LN spin-orbit force: SL = -0.01 MeV => agree with quark-model predictions LN tensor force: T = 0.03 MeV => agree with meson-exchange model predictions

HYPERNUCLEI and ASTROPHYSICS Strange baryons may appear in neutral b-stable matter through process like: The presence of strange baryons in neutron stars strongly affect their properties. Example: mass-central density relation for a non-rotating (left) and a rotating (right) star The effect strongly depends upon the poorly known interactions of strange baryons More data needed to constrain theoretical models.

large evident differences in their predictions for neutron star both potential sets are fitted equally well to hyperon-nucleon data large evident differences in their predictions for neutron star structure the onset density and concentration of the lambda are quite different with both models need for more experimental constraints on these potentials evident

Hypernuclear investigation (1) Few-body aspects and YN, YY interaction Flavor SU(3) extended nuclear interaction BB interaction Spin dependent interactions Spin-orbit interaction, ……. LS mixing or the three-body interaction Mean field aspects of nuclear matter A baryon deep inside a nucleus distinguishable as a baryon ? Medium effect ? Tensor interaction in normal nuclei and hypernuclei Astrophysical aspect Role of strangeness in compact stars Hyperon-matter, SU(3) quark-matter, … YN, YY interaction information

Hypernuclei: historical background - experimental techniques 1953  1970 : hypernuclear identification with visualizing techniques emulsions, bubble chambers Elementary reaction on neutron : 1970  Now : Spectrometers at accelerators: CERN (up to 1980) BNL : (K-, p-) and (p+,K+), production methods KEK (K-, p-) and (p+, K+), production methods e.g. > 2000 : Stopped kaons at DANE (FINUDA) : (K-stop, p-) Elementary reaction on proton : > 2000 : The new electromagnetic way : HYPERNUCLEAR production with ELECTRON BEAM at JLAB e.g. Production of MIRROR hypernuclei L: I=0, q=0  Ln = Lp Spectroscopy of mirror hypernuclei reveal Ln ≠ Lp  LS0 mixing and LN-SN coupling