1. 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

2. 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

3. 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)
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

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

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

6. 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

7. 12C(e,e’K)11B KINEMATICS Ebeam = 4.016 — 3.777 — 3.656 GeV
Pe= 1.80 — 1.56 — 1.44 GeV/c
Pk= GeV/c
e = K = 6°
= E ~ 2.2 GeV – Q2 = (GeV/c)2
Beam current : 100 A
Target thickness : ~100 mg/cm2
Counting Rates ~ 0.1 – 10 counts/peak/hour

8. 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

9. 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)

10. 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

11. 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

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

13. 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

14. 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

15. 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

16. elementary process; angular distribution

17. electroproduction on 16O; angular distribution

18. - 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

19. 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

20. 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

21. 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 ~ !!

22. 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

23. 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.

24. 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 E 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 E 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?

25. Comparison with BB interaction models
D SL SN T (MeV) ND NF
NSC
NSC97f
( “Quark” )
Exp
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.

26. 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)
Ukai et al.,
PRL 93 (2004)
LN spin-orbit force: SL = MeV
=> agree with quark-model predictions
LN tensor force: T = 0.03 MeV
=> agree with meson-exchange
model predictions

27. 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.

28. 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

29. 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

30. 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.
> : Stopped kaons at DANE (FINUDA) : (K-stop, p-)
Elementary reaction
on proton :
> : 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