Transcript The Angular Dependence of O(e, e K )

The Angular Dependence of
proposal for PAC 31
- the electromagnetic approach
- recent results
- motivation
- the elementary reaction
- angular distribution
- the apparatus
- kinematics and counting rates
- summary and conclusion
O(e,eK  )16 N and H(e, eK+ )
(F. Garibaldi January 0507 - Hall A Collaboration meeting - Jlab)
- hypernuclear physics
- beam time request
16
HYPERNUCLEAR PHYSICS
Hypernuclei are bound states of nucleons with a strange baryon ( hyperon).
Extension of physics on N-N interaction to system with S#0
A hypernucleus is a
“laboratory” to study
nucleon-hyperon
interaction (-N
interaction)
Internal nuclear shell
are not Pauli-blocked
for hyperons
Spectroscopy
- 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.

Mass of hypernucleus
B (MeV)
 feels a weaker potential than nucleons
U = -30 MeV (c.f. UN = -50 MeV)
Hotchi et al., Phys.Rev.C 64 (2001) 044302
-> Attraction :
-N < N-N
Better energy resolution is necessary for
more studies on N interaction :
N spin-dependent forces, N-SN force, ..
Unified understanding of B-B interactions
in the quark (+meson) picture together
with
S
and

hypernuclear data
Present Status of
 Hypernuclear Spectroscopy
16

N
(p-,K+)
(e,e’K+)
O. Hashimoto and H. Tamura, Prog. Part. Nucl. Phys, in press.
N interaction
(r)
most of information is carried out by
the spin dependent part doublet
splitting determined by D, s, T
BNL 3 MeV(FWHM)
KEK336 2 MeV(FWHM)
Improving energy
resolution
1.45 MeV(FWHM)
635 KeV
and
using
electromagnetic
probe
≤ 500 KeV
Hall A
High resolution,
high yield, and
systematic study
is essential
12C(e,e’K)11B
B
11
6

12
6
C
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
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
angle (momentum transfer)
hypernucleus as function of scattering
2. elementary process on proton
sp= 4.47 nb/(GeV sr2
E94-107
th= 4.68 nb/(GeV sr2 )
(3+,2+)
good agreement with
theory
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+)
1/2
3/2
1/2
1-
3/2
1admixture
2-
2-
2+
2+
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
16O(e,e’K)16N

1H
Low counting levels
above Ethr.
(e,e’K)
16O(e,e’K)16N

16O(e,e’K)16N

16O(e,e’K)16N

pp 
1616
O(K
O(-,,K- + )1616OO

~ 800 KeV
elementary reaction: similar discrepancy
this has to be understood !
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
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
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
QuickTime™ and a
Motion JPEG OpenDML decompressor
are needed to see this picture.
1 (+1) Cherenkov
threshold aerogels +
RICH in the hadron
spectrometer +
septum magnet
PID
electron arm:gas Cherenkov + shower counter
--> 105 pion rejection
hadron arm
this proposal
RICH upgrade
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
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 E94107 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
ND
NF
NSC89
NSC97f
( “Quark”
Exp.
-0.048
0.072
1.052
0.754
S
SN
-0.131 -0.264
-0.175 -0.266
-0.173 -0.292
-0.140 -0.257
0.0
-0.4
-0.01
-0.4
T
(MeV)
0.018
0.033
0.036
0.054
G-matrix calc.
by Yamamoto
)
Strength equivalent to quark-model LS force by Fujiwara et al.
0.4
0.03
 Spin-orbit forces (S, SN) cannot be explained by meson models.
Data seems to favor quark models.
Consistent with Hiyama et al. PRL 85 (2000) 270
--but 9Be calculation by Fujiwara et al. (quark+meson) cannot reproduce it.

Tensor forces (T) is well explained by meson-exchange models.
Revised
Study of N interaction from  spectorscopy
BNL E930 (AGS D6 line + Hyperball)
Discovery of “Hypernuclear Fine Structure”
9Be
16O
(K-, p- ) 9Be
(K-, p- ) 16O
26.1±2.0 keV
43±5 keV
E
(keV)
E (keV)
MeV
MeV
Akikawa et al.,
PRL 88 (2002) 082501
N spin-orbit force: S= -0.01 MeV
=> agree with quark-model predictions
Ukai et al.,
PRL 93 (2004) 232501
N tensor force: T = 0.03 MeV
=> agree with meson-exchange
model predictions
HYPERNUCLEI and ASTROPHYSICS
Strange baryons may appear in neutral bstable matter through process like:
n  e-  S-   e

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.
-
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, …….
– S 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
1970  Now :
Spectrometers at accelerators:
Elementary reaction
on neutron :
CERN (up to 1980) BNL : (K-, p-)
K-  n  p -  
and (p+,K+), production methods KEK
p   n  K  
(K-, p-) and (p+, K+), production
methods
> 2000 :
> 2000 :
e.g.

Stopped kaons at DANE (FINUDA) :
(K-
stop,
p 
-)
The new electromagnetic way :

HYPERNUCLEAR production with
ELECTRON BEAM at JLAB
C 
12
12
C
Elementary reaction
on proton :
e  p  e K   
e.g.

C 
12
12
B
Production of MIRROR hypernuclei
: I=0, q=0  n = p
Spectroscopy of mirror hypernuclei reveal n ≠ p  S0 mixing
 and N-SN coupling