1. Florida International University, Miami, FLγ e´ p Λ
Z–1 A Z K+
Spectroscopy of
Λhypernuclei
in the (e,e´K+) reaction at Jefferson Lab
For E01-011(HKS) Collaboration
Paul Baturin
Florida International University, Miami, FL
XIII International Conference on Hadron Spectroscopy, Tallahassee, Florida, USA – Nov. 29 – Dec. 4, 2009
HADRON 2009

2. Physics Motivation
# 1
Hypernucleus: complex nuclear system containing at least one bound hyperon
strongly interacting with the nucleons. Λ Λ
Λ,…,…,…
(p , n) nucleus
Λ hypernucleus
Λ Λ hypernucleus
Complex hypernucleus
Why to Study Hypernuclei ?
- Test the NN interaction models beyond S=0 realm ;
- Λ brings new degree of freedom – strangeness ;
- Λ is free of Pauli Blocking ;
- Access to deeply bound states ;
- Evidence of single particle orbits deep in the nucleus
(cannot be seen by nucleons) ;
- Central and spin dependent ΛN interactions ;
- Possibility to study three body forces (3BF), which have
sizable effect due to NΛ – N coupling channel ;
- Charge Symmetry Breaking (CSB) ;
- Precise lifetime measurements at different masses
via non-mesonic weak decay NΛ  NN ;
- Strangeness in Neutron stars ;
Properties of Λ Hypernuclei
Λ feels weaker potential than N
VΛN (≈-30MeV) <VNN (≈-50MeV) 1s
1p3/2 p n Λ
30 MeV
50 MeV
Narrow width of excited states (≈ 100 keV)
Requires High Resolution Spectroscopy

3. Hypernuclear Electroproduction
# 2
Meso-production (with K or π beams): n(K-,π -)Λ and n(π+,K+)Λ  BNL, KEK
- Both low and high momentum transfer to Λ
- Large cross sections  10-3 and 10-6 b/sr
- Limited Energy Resolution  1.45 MeV
(due to energy resolution of secondary meson beam)
Electroproduction (electron beam): p(e,e´K+)Λ  JLAB
- High momentum transfer to Λ
- Small cross sections  10-9 b/sr
(compensated by high intensity of electron beam)
- Possibility of high resolution  400 keV (FWHM)
- Spin-flip amplitude (unnatural parity hypernuclear states)
- Neutron rich Λ hypernuclei
H. Bando et al. Int. Jour. of Mod. Phys
Schematic representation of electroproduction
Quark flow schematic diagram (associated production mechanism)

4. Previous Experiment (HNSS - 2000)
# 3
11B(gs)×L(s)
11B(gs)×L(p)
12C(e,e´K+)12LB
Binding Energy: BL(s) = 11.40.5 MeV
(emulsion data BL(s) = MeV)
Resolution: 720 keV (FWHM)
0 degree tagging geometry in electron
spectrometer ;
Large background rate associated with
Bremsstrahlung and Moller scatterings ;
Current limitation due to high background rate
I = 1.6 A for C12 target
(1-,2-)
(2+,3+)
core-excited
states
(1-,0-)
(2-,1-)
Needed to improve:
1. Spectrometer resolution
2. Reduce background
12C(e,e´K+)12LB HNSS, JLab, Hall-C, 2000

5. E01-011 (HKS) Experiment - 2005 HKS Experimental Setup HKS ENGE
# 4
1. ENGE spectrometer is vertically tilted to avoid background associated with Bremsstrahlung and Møller scattering events
2. HKS (high-resolution Kaon Spectrometer).
High acceptance &
high resolution.
- Tilt Angle = 7.750
Reduced Bremss. rate
Signal/Noise (S/N) ratio
increased by 10 times
Momentum resolution:
GeV/c
Acceptance: 12.5%
Flight path ~ 10 m
HKS Experimental Setup
Splitter Magnet
HKS (QQD) & ENGE (D) spectrometers
HKS: Vacuum chamber
Two Drift Chambers (DC)
Set of Scintillators (1X, 1Y, 2X)
Three Aerogel Cherenkov detectors
Two Water Cherenkov Detectors
ENGE: Two layers of hodoscopes
Drift Chamber
HKS
ENGE
SPLITTER

6. Targets and Trigger Conditions
# 5
Targets
Hypernucleus
Thickness (mg/cm2)
Current
Purpose
CH2
Λ, 
460
1.5 A
calibration
6Li
6He
164
30 A
production
7Li
7He
189
27 A
9Be
9Li
19 A
10B
10Be
100
26 A
12C
12B
101.7
28Si
28Al 50
18 A
51V
51Ti
59.6
rate study
89Y
89Sr 56
13 A
208Pb
208Tl
283
0.3 A
Trigger Conditions
HKS
1X & 1Y & 2X & AC & WC
Rate 12 KHz
ENGE
1X & 2X
Rate  1.0 ÷1.2 MHz (HNSS  100MHz)
COIN
K+ and e´ in coincidence
Rate  0.5 ÷ 1.0 kHz

7. Particle Identification (for Kaons)
# 6
Two approaches were utilized:
Standard “hard cuts” method  ( ∑AC < 10 & ∑WC > 75 & abs(beta-betak)<0.06 )
Likelihood approach  (using the normalized pdfs for each detector and combining into final
likelihood values)

8. 12C(e,e´K+)12LB accidental Preliminary 12B 12C KEK E369 (2001) # 7
Hall-A, JLab E (2004)
12B
gs~650 keV
S (1-,2-)
p (2+,3+)
Yield (Counts/150 keV)
gs~470 keV
S 
p 
core-excited
(1-,0-)
(2-,1-)
core-excited
accidental
Excitation Energy(MeV)
-B  MeV
12C
KEK E369 (2001)
gs~1.5 MeV
12B (Theor.) T. Motoba
Mirror hypernucleus 12C (p=6, n=5)

9. 28Si(e,e´K+)28LAl accidental Preliminary 28Al
# 8
28Al
Preliminary
p (4-,3-)
d (5+,4+)
S (2+,3+)
 First time a high resolution of d state.
Yield (Counts/150 keV)
gs~435 keV
KEK E140a (1995)
28Si
accidental
-B  MeV
Theor. Motoba, 2003
Mirror hypernucleus 28Si (p=14, n=13)

10. 7Li(e,e´K+)7He accidental Preliminary
# 9
Preliminary
7He
“Gluelike role” of  in 7He (neutron halo)
6He
7He 0+
+n+n
++n+n ½+
-0.69
<r-n>=4.6 fm
-6.12
<rcore-n>=3.55 fm
E. Hiyama, et al., Phys. Rev. C53, 2075,(1997)
S (1/2+)
Yield (Counts/150 keV) α n α n Λ
gs~450 keV
E (MeV)
accidental -5
-B  MeV
-10
First experimental observation of 1/2+ state

11. Summary
# 10
The hypernuclear experiments at Jefferson Lab aimed to obtain high precision hypernuclear spectroscopy in a wide mass range via electroproduction reaction.
New high resolution, large acceptance spectrometers: ENGE and HKS. New experimental techniques: on-target splitter, tilted ENGE.
Achieved the best resolution hypernuclear reaction spectroscopy for
12B, 7LHe and 28LAl ( keV FWHM)
12LB spectrum consistent with HNSS and Hall A experiment.
28LAl spectrum obtained first time with high energy resolution. It contains Λ in s, p, and d shells.
7LHe spectrum contains first time measurement of ½+ ground state binding energy.