The angular dependence of the 16 O(e,e’K + ) 16 N and H(e,e’K + ) F. Garibaldi – Jlab...
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Transcript of The angular dependence of the 16 O(e,e’K + ) 16 N and H(e,e’K + ) F. Garibaldi – Jlab...
The angular dependence of the 16O(e,e’K+)16LN and H(e,e’K+)L
F. Garibaldi – Jlab December 12-2012
The WATERFALL target: reactions on 16O and 1H nuclei
1H (e,e’K)L
16O(e,e’K)16NL
1H (e,e’K) ,L S
L
S
Energy Calibration Run
Results on the WATERFALL target - 16O and 1H
Water thickness from elastic cross section on H Precise determination of the particle momenta and beam energy using the Lambda and Sigma peak reconstruction (energy scale calibration)
10/13/09
p(e,e'K+)L on WaterfallProduction run
Expected data from E07-012, study the angular dependence of
p(e,e’K)L and 16O(e,e’K)16NL at low Q2
Results on H target – The p(e,e’K)L Cross Section
p(e,e'K+)L on LH2 Cryo Target
Calibration run
•None of the models is able to describe the data over the entire range•New data is electroproduction – could longitudinal amplitudes dominate?
W=2.2 GeV
The Proposal: studying, using waterfall target, different processes
The elementary process on the proton
Electroproduction of as function of Kaon angle
- Systematic study of reaction as function of A and neutron rich nuclei (E05-015)
- Understanding of the elementary reaction
- Angular distribution (momentum transfer)
what is missing ?
How?
The interpretation of the hypernuclear spectra is difficult because of the lack of relevant information about the elementary process.
Contains direct information on the target and hypernuclear structure, production mechanisms
Hall A experimental setup (septum magnets, waterfall target, excellent energy resolution AND Particle Identification ) give unique opportunity to measure, simultaneously, hypernuclear process AND elementary process
In this kinematical region models for the K+- electromagnetic production on protons differ drastically
The ratio of the hypernuclear and elementary cross section measured at the same kinematics is almost model independent at very forward kaon scattering angles
Why?
The cross section of (e,e’K) on a nuclear target and its angular dependence determined by:
- Transition operator, which is given by the model used to describe the elem. prod. on 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)
- The ratio of the hypernuclear and elementary cross section doesn’t depend strongly on the electroproducion model and contains direct information on hypercnulear structure and production mechanism
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 oxygen and hydrogen at a few kaon scattering angles will shed new light on problems of hypernuclear physics AND discriminate between groups of elementary models
The elementary process: The p(e,e’K+)L electromagnetic X-section
qeqk
Fe
e’k
pL
Scattering plane(leptonic) Reaction plane
(hadronic)
d5dE 'dedK
d *
dK
* p k
d *
dK
dT
dK
d L
dK
cos2dT
dK
2 1 cosd LT
dK
JHadr K ˆ J
Hadr p u p Ai s,t,Q2 Mi
i1
6
u P
e
p
K+
e’
L
g *LeptJ
The appropriate set of propagators (particles) and coupling constants has to be established from the data and from theoretical guidelines (SU3 broken symmetry)
At CEBAF energies non-perturbative QCD degrees of freedom have to be taken into account.
- IN PRINCIPLE: the amplitude can be calculated in QCD. IN PRACTICE: semi-phenomenological description Quantum HadronDynamics(QHD), degrees of freedom, nucleon, kaon, resonances.A diagrammatic semi-phenomenological approach based on hadronic field theories (effective hadronic Lagrangian - QHD) is likely well applicable in the description of the process
L,S(L*,…) g *
K+ L
p=
K+ L
p g *
P(N*,D*,…)
p g *
K+ L
K(K1,…)
L K+
g *p
s-channel t-channel u-channel
+ +
two groups of models differing by the treatment of hadronic vertices
show LARGE DIFFERENCES
Assumption for the hadronic form factor :- KMAID, Jansen, H2 : with h.f.f.- Saclay-Lyon, WiJiCo : without h.f.f.
The theoretical description is poor in the kinematical region
relevant for hypernuclear calculations
No dominant resonance contributes to the kaon electro and photo-production (like Delta for pion). a large number of possible resonances can contribute many free parameters, the coupling constants must be fixed by experiment. …many models on the market which differ just in the choice of the resonances.
The elementary process: The p(e,e’K+)L electromagnetic X-section
A phenomenon which can be addressed by the expected data:
The sharp damping of the cross section at very small kaon angles which is connected to the fundamental ingredients of the models, accounting for the hadronic form factors.
This is also very important in the hypernuclear calculations.
Photo-production existing data and model predictions
The elementary process: The p(e,e’K+)L electromagnetic X-section
K+-L electro-production cross section will be measured in an unexplored kinematical region typical of HYPERNUCLEAR experiments.In the angular range proposed(QCM
kg=5.4-18 deg) the electro-magnetic production models show a strong angular dependence. Measuring the elementary cross section in such an angular range will provide a set of data very important to constrain models and provide information on the use of hadronic form factors.
Q2=0.06 (GeV/c)2
THIS EXPERIMENTPROJECTED DATA
Electro-production model predictions
From electro-production to photo-production on hydrogen• Selection of a model• Eventually new fit on model parameters including these new data• Model dependent evaluation of interference terms w.r.t. the dominant transverse term (kinematics very close to the photon point)
kinematics and counting rates
Waterfall Target thicknes = 130 mg/cm2
Beam current = 100 A
beam time request
SNR ≥ 6
beam time request
With new setup in Hall A if 3 angles in one shot, a factor 3 in the yield (?)
~ 5 days
16O(e,e’K)16NL 16O(p+,K+)16OL16O(K-, p- g) 16OL
~ 800 KeV
similar discrepancy for elementary reaction
this has to be understood !