1. Spectroscopy of -Hypernuclei by Electroproduction HNSS/HKS Experiments at JLAB L. Tang Hampton University & JLAB
SNP2006, Zhangjiajie, Sept 5-8, 2006

2. Introduction – YN Interaction
,0
(uds) n
(udd) p+
(uud) +
(uus) -
(dds) -
(dss) 0
(uss) S Q I
S = 0
S = -1
S = -2
JP=1/2+
B-B interactions are fundamental in our understanding on the formation of the world – Nuclear Matter, Neutron Stars, …
Our current knowledge is basically limited at the level of S = 0 (n and p)
Study S ≠ 0 B-B interactions (YN and YY) is a MUST in order to extend our knowledge to include as well as reach beyond strangeness and seek an unified description of B-B interaction
Due to the short lifetime of Y, direct study of YN interactions is almost impossible

3. Introduction – Hypernuclei
Hypernucleus – A nucleus with one or more nucleons replaced by hyperon, Λ, Σ, …, through elementary production process
Unique gate way to study S ≠ 0 B-B interaction: YN interaction embedded in a nuclear mean field, a rich laboratory to study YN interactions with the method of NUCLEAR PHYSICS
New degree of freedom in nucleus – Strangeness Challenges the limit of conventional nuclear models of hadronic many-body system but also open doors to new or hidden aspects in the “traditional” nuclear physics

4. Introduction – -Hypernuclei
-hypernuclei are the most stable ones (S = -1)
Novel features of -hypernucleus – N Interaction
Absence of long range OPE between Λ and N due to conservaison of isospin in strong interaction, thus it signifies
- Higher mass meson exchanges that are over shadowed by the
dominant OPE force in N-N interactions in the traditional nuclear
nuclear physics
- Sizable charge asymmetry (p and n)
- Intermediate Λ-Σ coupling and significant three-body forces
(ΛNN) with two-pions exchange

5. In terms of mesons and nucleons: Or in terms of quarks and gluons:
Understanding the N-N Force
In terms of mesons and nucleons:
Or in terms of quarks and gluons:
V =

6. -Hypernuclei Provide Essential Clues
For the N-N System:
For the L-N System: Long Range Terms Suppressed
(by Isospin)

7. Introduction – -Hypernuclei
Absence of Pauli Blocking – , like an “impurity”, has full access to all levels of nuclear interior structures, thus a better illumination to explore the nuclear interior
Stabilized states with narrow width –  decays weakly, thus allowing precision spectroscopy and theory descriptions
Opening issues:
- Precise description of -Nucleus potential (spin dependent
interactions)
VΛN(r) = Vc(r) + Vs(r)(SΛ*SN) + VΛ(r)(lΛN*SΛ) + VN(r)(lΛN*SN) + VT(r)S12
- To what extend the  remains as a single particle, effective vs
exact models
- Short range nature of N interaction and density dependency

8. Model Productions of -hypernucleiOR S P
Particle hole
Particle
(K-, -) – Nature parity, low spin substitutional
states due to low momentum transfer,
high yield
(+, K+) – Nature parity, high spin stretched states
due to high momentum transfer
(e, e’K+) – Unnature parity, high spin stretched
states due to high momentum transfer
and the spin covered by the virtual
photons

9. Spectroscopy – Low lying A=12 system ( in s shell)
(π+, K+) Reaction
(e,e’K+) Reaction 1- 1-
4.80
3/2-
5.02
3/2- 2- 2-
4.32 2-
4.45
5/2- 2-
5/2- 0- 0-
2.00
1/2-
2.12
1/2- 1- 1-
~0.1
~0.1 2- 2-
0.00
0.00
3/2-
3/2- 1- 1-
0.0
0.0 JP
MeV JP
MeV
11C 
12C
11B 
12B
Complementary and charge symmetry breaking

10. L single particle potential
Energy resolution is very limited by using hadronic beam – 1.5 MeV FWHM
Hotchi et al., PRC 64 (2001)
Hasegawa et. al., PRC 53 (1996)1210
KEK E140a
Textbook example of
Single-particle orbits in nucleus
L Single particle states
→ L-nuclear potential
depth = -30 MeV → VLN < VNN

11. Existing 12C(p+,K+)12LC spectra
BNL 3 MeV(FWHM)
KEK E MeV(FWHM)
High resolution, high yield, and systematic study is essential and is the key to
unlock the “gate”
KEK MeV(FWHM)

12. Thomas Jefferson National
Accelerator Facility
(TJNAF or JLAB)
Location in U.S.A.
Virginia

13. Continuous Electron Beam Accelerator Facility (CEBAF)
MCC CH
North
Linac
+400MeV
South
Injector
FEL
East Arc
West Arc

14. Electroproduction of -hypernuclei in Hall C at JLAB
High precision beam → high resolution spectroscopy
High intensity and 100% duty factor → Overcome low cross section for high yield which is essential to study heavy hypernuclei
Advantage: High resolution and high yield
Challenges: Extremely high particle rates

15. d2σ/dΩk is completely transverse as Q2 → 0
Key Considerations in Electroproduction A   N A e e’
→ Coincidence of e’ and K+
→ Keep ω=E-E’ low (K+ background)
→ Maximize Γ –- e’ at forward angle
→ Maximize yield –- K+ at forward
angle K+
d2σ/dΩk is completely transverse as Q2 → 0

16. First Pioneer Experiment - HNSS
Beam Dump
Target
Enge
Split-Pole
Spectrometer
Electron Beam
1.864 GeV
Focal Plane
( SSD + Hodoscope )
Splitter
Magnet K+
SOS Spectrometer(QDD) Q D _ 1m
Side View
0.3GeV/c
1.2GeV/c e’
Local Beam Dump
Year 2000
Tagged e’ at 0o!

17. HNSS: A Great Challenge
Low resolution of the existing SOS spectrometer (p/p ~7x10-4 FWHM only)
Small solid angle acceptance (SOS has 4.5 msr)
Extremely high electron rate (200 MHz) at 0o
Can only use extremely low luminosity (20mg/cm2 target and 0.6A beam current)
High accidental coincidence background rate
Goal: Aim to the future and learn experiences

18. Λ (Σ0) Spectrum for Energy Calibration
p(e,e’K+)Λ
p(e,e’K+)Σ0
12C(e,e’K+)(Q.F.)
Accidentals
Beam time: 170 hours

19. Achievement: 12C(e,eK+)12LB (HNSS)
11B(gs)×L(0s)
11B(gs)×L(0p)
Resolution
1.5 MeV FWHM
by (p+,K+)
750 keV FWHM
by (e,e’K+)
a month data
Beam time: 450 hrs
Calc. by Motoba & Miliner

20. Spectroscopy of A=7 Systems – 7LHe (neutron rich)
~240 hrs test
Bound g.s. !?

21. Jlab HKS experiment (2005)
High-resolution ~400 keV (factor of 2 improvement)
High yield rates High yield
Better S/A ratio ~5 times improvement
Explore hadronic many-body systems with strangeness
through the reaction spectroscopy by the (e,e’K+) reaction
Immediate Physics goals
12C(e,eK+)12LB
demonstrate the mass resolution & hypernuclear yield.
core excited states and splitting of the pL-state of 12LB….
Mirror symmetric L hypernuclei 12LC vs. 12LB
28Si(e,e’K+)28LAl
Prove the (e,e’K+) spectroscopy is possible for the medium-heavy target possible.
precision 28LAl hypernuclear structure and ls splitting of p-state….

22. Key Technical Approaches of HKS
Electron arm
Tilt method for the electron arm
Suppress Brems electrons by 104 times
Need higher order terms of the transfer matrix
Kaon arm (Replace SOS by HKS)
High Resolution Kaon Spectrometer (HKS)
High resolution (2 times) & Large solid angle (3 times)
Good particle ID in both trigger and analysis
Need sophisticated calibrations and analyses

23. 5 times Target thickness
Scattered electrons (0.2 to 0.4 GeV/c)
(1)from bremsstrahlung
(2)associate with virtual photons
(3) from Møller scattering
Tilt Method
(1) Brems e’
(3) Moeller
scattering
(2) Virtual photon
Associated e’
(1/1000)
Tilt e-arm by 7.75 deg. vertically
with respect to splitter & K-arm
Singles rate of e-arm
200 MHz → 3 MHz
with
5 times Target thickness
50 times Beam intensity
Compared to E89-009
Better Yield and S/A
Medium-heavy hypernuclei can be studied

24. Layout of the HKS setup 2005 2 x 10-4(FWHM) 16 msr with splitter
Tilt 7.75 degrees

26. HKS: 2005 -  &  production (CH2, calibration)
Installed in 4 months (Feb. to May)
Commissioning in 1.5 months
Data taking in 2 months (near end of Sept)
Data taken for
-  &  production (CH2, calibration)
- 12B spectroscopy (C, calibration and physics)
- 28Al spectroscopy (28Si, primary physics)
- 6,7He, 9Li, and 10,11Be (short runs, yield test)
- 51Ti and 89Sr (short runs, yield test)

27. HKS: Analysis Still preliminary
Current stage focuses on calibration and optimization of kinematics and optics
Future stages include (1) target straggling loss corrections for all targets and fine optical tune and (2) beam energy and on target position studies and possible corrections

28. p(e,e’K+)&0 used for kinematics and optics calibration
HKS-JLAB
CH2 target
~ 70 hours 
15 times more yield
6 times better S/A
Preliminary
M = 1.43 MeV (FWHM)
M = (MR - M0) = - 44 keV
M = 1.47 MeV (FWHM)
M = (MR - M0) = - 83 keV
Counts (0.4MeV/bin)
Events from C 0
Accidentals
B (MeV)

29. 12C(e,e’K+)12B used for kinematics and optics calibration
Preliminary
JLAB – HKS
~ 90 hrs w/ 30A
s(g.s.)
Ground State (2-/1-):
 = 670 keV (FWHM)
B = MeV p
C.E. #1
15 times more yield
4 times better S/A
Counts (0.2 MeV/bin)
C.E. #2
or more
Accidentals
B (MeV)

30. 28Si(e,e’K+)28Al – First Spectroscopy of 28Al
Preliminary
JLAB – HKS ~140 hrs w/ 13A s p
C.E. ?
C.E. ?
Ground State:
 = 745 keV (FWHM)
B = MeV
Yield = ~5/hr (30A)
Counts (0.25 MeV/bin)
Accidentals
B (MeV)

31. 7Li(e,e’K+)7He – First Observation of ½+ G.S. of 7He
Preliminary
JLAB – HKS ~ 30 hrs
s (1/2+)
Ex. state?
Ground State:
 = 940 keV (FWHM)
B = MeV
(Threshold: 6He+)
Counts (0.4 MeV/bin)

32. HKS-HES (E05-115) - Heavy Hypernuclei
NEXT & FUTURE
HKS-HES (E05-115) - Heavy Hypernuclei
Replace Enge by new HES spectrometer with larger acceptance
Use higher beam energy (> 2.1 GeV)
Obtain 30 times more yield gain over HKS experiment but the same background rate
Improve another 5 times better S/A ratio for clean spectroscopy
Study 51Ti and 89Sr in detail
Study p-shell systems with high statistics in very short running time
Current schedule: installation starts in summer of all equipment will be ready by the end of 2007

33. New Era of Hypernuclear Spectroscopy !
Summary
The first experiment HNSS proved the potential to study hypernuclear spectroscopy with high precision using the CEBAF beam and (e,e’K+) reaction at JLAB
The HKS experiment has successfully demonstrated that such a high precision study can be carried out with high yield and heavy systems can be studied with an optimized experiment design
The next phase experiment HKS/HES will be carried out in the period of
The new system and the hypernuclear program will continue after the 12 GeV upgrade in Hall A
New Era of Hypernuclear Spectroscopy !

34. p(e,e’K+)&0 used for kinematics and optics calibration
HKS-JLAB
CH2 target
~ 70 hours 
Preliminary
Counts (0.4MeV/bin)
B < 150keV/77 MeV 0
Events from C
Accidentals
B (MeV)

35. Preliminary Accidentals
12C(e,e’K+)12B used for kinematics and optics calibration
JLAB – HKS
~ 90 hrs w/ 30A s
Preliminary p
C.E. #1
C.E. #2
Counts (0.2 MeV/bin)
Current width:
670 keV FWHM
Accidentals
B- Binding Energy (MeV)

36. Preliminary Accidentals
28Si(e,e’K+)28Al – First Spectroscopy of 28Al
Preliminary
JLAB – HKS ~ 140 hrs w/ 13A s
d ? p
C.E. ?
Counts (0.25 MeV/bin)
Accidentals
B- Binding Energy (MeV)

37. Preliminary Accidentals
7Li(e,e’K+)7He – First Observation of ½+ G.S. of 7He
Preliminary
JLAB – HKS ~ 30 hrs
B (g.s.) = -4 MeV
1 to 1.4 MeV less bound than theory prediction!
s (1/2+)
Counts (0.4 MeV/bin)
Accidentals
B- Binding Energy (MeV)