LEDA / Lepton Scattering on
Hadrons
Member of the Hall A Collaboration at Jefferson Lab, leadership on:
• Hypernuclear Spectroscopy: 12C and 16O,9Be(preliminary) high quality
data available. First publication soon. Extension to heavier
hypernuclei under evaluation
• Good results on Parity (Happex) and Spin structure of neutron
• 3 experiments approved in January (high rate)
– PREX: measurement of neutron skin in Lead
– Transversity: one experiment approved on nucleon spin structure
– Correlation and relativistic effects (
nuclear medium
208Pb(e,e’p)207Tl)
in the
ELECTROproduction of Hypernuclei at Jefferson Lab
Hypernuclei are bound states of nucleons with a strange baryon (Lambda hyperon).
Hypernuclear physics accesses information on the nature of the force between nucleons
and strange baryons. A hypernucleus is a “laboratory” to study nucleon-hyperon
interaction (L-N interaction).
• The characteristics of the Jefferson
Lab. electron beam, and those of the
experimental equipments, offer a
unique opportunity to study
hypernuclear spectroscopy via
electromagnetic induced reactions. A
new experimental approach:
alternative to the hadronic induced
reactions studied so far.
• Hyperon formation in neutron stars is
controlled by the attractive hyperonnucleon interaction which can be
extracted from hypernuclear data
e
e’
p
K+
L
Hall A facility:
• Standard HRS spectrometers
• 2 Septum Magnets for small angle
• RICH detector for superior p / K /
identification
LEDA experiment is planning to complete a
systematic study of high resolution
spectroscopy on light and mediumheavy nuclei
First RESULTS on
12C(e,e’K)12B
12C
and
16O, 9Be
16O(e,e’K)16N
L
L
Signal
7
Bckgnd
nuclear targets:
~ 400 KeV

L-interaction here is in p-state, poorly known….
Data will help in improving the model parameters
(Spin-Orbit term of LN interaction potential)
9Be(e,e’p)9Li
L
Energy resolution ~ 700 KeV
-the best achieved in hypernuclear production
experiments, (improving) down to ~ 400 KeV
-first clear evidence of excited core states at ~2.5
and 6.5 MeV with high statistical significance
- possible thanks to the RICH detector and Septum
magnets (INFN contribution), important devices for
other experiments (parity, GDH..) and planned(Pb
Parity, Transversity..)
Models of elementary reactions fail in reproducing the data
(Red, Bennhold-Mart (K MAID)) (Blue Saclay-Lyon (SLA))
Happex: “strangeness content of proton”
Parity-violating electron scattering on proton and 4He
Interference with Electromagnetic amplitude
makes Neutral Current accessible
.
GEs = -0.12 ± 0.29
GMs = 0.62 ± 0.32
Strange form factors
Longitudinal spin asymmetry violates
parity (polarized e-, unpolarized p)
anticipated precision
Would imply that 7% of nucleon
magnetic moment is Strange
Improving precision
Q2~0.1 GeV2
LEDA contribution for experiments in Hall A
(performed and planned)
Superconducting Septum magnets
12.5°
6 ° (>Mott cross section)
QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.
RICH detector
unambiguous K identification
Pion rejection factor ~ 1000
PREX: Parity Violating Electron Scattering on Pb
Investigation of the nucleonic matter properties
• Equation of state of neutron rich matter
• Symmetry energy of dense matter
• Strong connection with neutron star properties
Clean Measurement of neutron skin of lead
by Left/Right Electroweak Cross Section Asymmetry:
2


e
+
Zz0
Fn Q 2 
 R   L PWIA
2
 ALR 
 1  4 sin W 
2 
 R  L
Fp Q 

e
As effective probe of neutron form factor Fn(Q2)
Accurate neutron radius determination
Experimental Aspects
• CEBAF 80% Polarized Electron Beam
• Lead Foil Target
• Hall A Standard Spectrometers + Septum Magnets
Single Spin Asymmetry of 3He(e,e’h±)X on DIS

h
K
First Time Measurement of neutron Transverse
Target Single Spin Asymmetry:

AUT hl , Sl

 

 

Sivers
Collins
 AUT
sin hl  Sl   AUT
sin hl  Sl 



l
l
l
l
1  h ,S  h ,S 
ST  hl ,Sl  hl ,Sl 
Physics Motivations:
• Nucleon Spin Structure: information on (poorly know) transverse quark spin and
(unknown) angular momentum contribution to the nucleon spin
• Non-perturbative QCD: non-singlet transverse quark distribution function provides a
clean Q2 evolution
Experimental Aspects
• CEBAF High Density Electron Beam
• High Density Transversely polarized 3He target
almost pure polarized neutron
• 26 International Institutions involved
• Approved experiment (Jlab) with highest
rating
• Expected to run 2 semester of 2007
• RICH Detector for scattered hadron (p/K)
for 1 month
identification
Complementary to existing data (HERMES and COMPASS mainly) and unique for the
coming years
nd
Impulse Approximation Limitation to
208Pb(e,e’p)207Tl
reaction
K. Aniol, A. Saha, J. M. Udias and G. Urciuoli Spokepersons
Identifying correlations and relativistic effects in the nuclear medium
The experiment will use 208Pb, a doubly magic, complex nuclei, a textbook case for the shell
model, measuring 208Pb(e,e’p)207Tl cross sections at true quasielastic kinematics and at both sides
of q.
This has never been done before for A>16 nucleus
Quasielastic kinematics:
xB = 1, q = 1 GeV/c , ω = 0.433
GeV/c
Determine momentum distributions:
0 < pmiss < 500 MeV/c
Determine Transverse-Longitudinal Asymmetry
ATL:
   0    
ATL 
Nikhef data at xB ~ 0.18
  

   0      
(1) First measurements in quasielastic kinematics on the paradigmatic shell model nucleus,
208Pb at high Q2. Accurate spectroscopic factors for separated shells will be obtained at
several values of Q2.
(2) Strength for pmiss > 300 MeV/c will give insight into nuclear structure issues and will settle
the long standing question about the amount of long range correlations. They will be seen
for the first time, if they are there.
(3) A new observable ATL for the five low lying states of 207Tl will be measured. ATL helps
distinguishing between relativistic and nonrelativistic structure of the wave
functions.
E94-107 Hall A Experiment Vs. KEK-E369
12C(e,e’K)12B
L

12C( ,K+)12C
L
H. Hotchi et al., Phys. Rev. C 64 (2001) 044302
Statistical significance of core excited states:
Signal
7
Bckgnd
E94-107 Hall A Experiment Vs. FINUDA (at Dane)
12C(e,e’K)12B
L
Statistical significance of core excited states:
Signal
7
Bckgnd
12C(K- ,
)12CL
E94-107 Hall A Experiment Vs. HallC E89-009
12C(e,e’K)12B
L
12C(e,e’K)12B
L
Miyoshi et al., PRL 90 (2003) 232502.
New analysis
Statistical significance of core excited states:
Signal
7
Bckgnd
E94-107 Hall A Experiment: status of
12C(e,e’K)12B
12B
L
data
L
Energy resolution is ~ 750 keV
with not fully optimized optics for
momenta reconstruction
Work is in progress to further
improve the resolution, hence the
signal/noise ratio
more checks and tuning have to be
done, …but :
the data are already of extremely
good quality
Statistical significance of core excited states:
Signal
7
Bckgnd
… to be published soon