Overview on (p,2p) reactions

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Overview on (p,2p) reactions what did we learn?
A A Cowley
Stellenbosch University and iThemba LABS South
Africa
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outline of talk

• brief outline of DWIA theory

• (p,2p) knockout results for light target at low
  energy

cross sections
analyzing power
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Gottschalk (1967)
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Gottschalk (1967)
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Gottschalk (1967)
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early concerns
worries about

• validity of impulse approximation

• distortions

• off-shell effects

- different off-shell results for equivalent on
shell sets

• factorisation of cross section

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Roos 1977
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input quantities required for DWIA calculations
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Distorted waves
from proton elastic scattering (optical
potentials)
Bound state
from electron scattering (bound state potential)
Nuclear density
affects intranuclear nucleon-nucleon interaction
(theoretical estimate phenomenology)
Occupation numbers
extracted from experiment compare with theory
(e,ep)
Half-shell cross section
on-shell approximations initial / final

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• choice of kinematic arrangement
• (incident energy, angles) affects
• the validity of approximations in
• the theory

• this is now understood reasonably well

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coplanar symmetric equal energy geometry
p1 p2
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coplanar symmetric equal energy geometry
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coplanar symmetric equal energy geometry
eliminates Maris effect
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Coplanar symmetric geometry
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208Pb(p,2p) Ep 200 MeV
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quasifree energy-sharing distribution
p1
p0
p2
T1T2 T0 Eb Trecoil 0
kinematically possible
minimized off-shell effect
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quasifree energy-sharing distribution
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quasifree
Coplanar symmetric geometry
not problems anyway
eliminated or avoided
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208Pb(p,2p) Ep 200 MeV
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12C(p,2p) Ep 100 MeV
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12C(p,2p) Ep 100 MeV
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16O(p,2p) Ep 150 MeV
spectroscopic factor 1.1 - 1.5
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test of factorization approximation
12C(p,2p) Ep 100 MeV
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test of (extreme) factorization approximation
208Pb(p,2p) at 200 MeV
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typical effect of choices of input quantities
Distorting potentials
Density /no density effect
knockout at low nuclear density
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spectroscopic factor
theory 0.63 0.70
(e,ep) 0.65 0.73
(p,2p) 0.5 0.9
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DWIA gives a good description of the (p2p)
knockout reaction
energy sharing cross section distribution energy
sharing analyzing power distribution spectroscopi
c factor (absolute yield) energy-dependent
distortion (shape)
(p,2p) yield is only 5 of the plane-wave limit
for 208Pb
what happens to the rest?
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binding energy EbT1T2
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what fraction of the inclusive (p,p/) yield is
included in (p,p/ p//)?
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sp,p/ sp,p/p// dWp//
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inclusive 40Ca(p,p) E p390 MeV
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conclusions
DWIA reproduces (p2p) knockout
rescattering initiated by knockout as (p,p/p//)
inclusive (p,p/) consistent with knockout
rescattering
future refined coherent theory containing the
basic reaction mechanisms