Nuclear Physics at RCNP

1
Nuclear Physics at RCNP
International Workshop on Nuclear Physics with
RIB August 28-31, 2001, Lanzhou, China
Yasuhiro Sakemi Research Center for Nuclear
Physics, Osaka University e-mail
sakemi_at_rcnp.osaka-u.ac.jp
2
Contents

• Overview of the Experimental Facility
• Overview of the Physics Programs
• Physics Topics at RCNP
• Modification of the nuclear interaction in the
  nuclear
• medium studied by (p,2p) reaction
• Quenching of Gamow-Teller strength and
• Pionic nuclear collectivity studied by (p,n)
  reaction
• Construction of High resolution beam line for
• the study of the 0- (pionic) state in 16O
• 4. Planned experiment Coherent Pion Production
  
• Summary

3
Physics Activities at RCNP
Cyclotron Laboratory Nucleon, Meson, Hadron
Physics AVF cyclotron with K0.14 GeV and Ring
cyclotron with K0.4 GeV Polarized p,d light
heavy ion with Ep0.01 0.4 GeV , E/A0.01 0.1
GeV
West Harima, Spring8, Hyogo
Suita, Osaka
Tentsuji-tunnel in Ohto, Nara
Laser Electron Photon Laboratory Quark Nuclear
Physics 1 3.5 GeV Polarized Photon Beams by
Back Scattering of Laser Photons (2 6 eV) from
8 GeV electrons at Spring8
Ohto Cosmo Observatory Lepton Nuclear Physics
Underground laboratory with low background (500
m depth, 10 Bq/m3 Rn 410-3/m2/s cosmic µ
4
Overview of RCNP Facility
Neutron Course
Ring Cyclotron
East experimental hall
West experimental hall
AVF Cyclotron

• Polarized proton/deuteron beam
• High resolution beam/spectrometer
• Two arm spectrometers
• Focal Plane Polarimeter to measure the
  polarization transfer
• Neutron Polarimeter

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Accelerators

• AVF cyclotron Used as injector of Ring
  Cyclotron
• Magnet
• Pole diameter 3.3 m
• Pole gap 20.6 cm 34.7 cm
• Averaged field 1.6 T
• Trim coils 16 sets
• Valley coils 3 5 sets
• Weight 400 tons
• Acceleration system
• Dee Single 180 degrees type
• Resonator Moving short
• Frequency 6 19 MHz
• Max. acceleration voltage 80 kV
• Extraction system Electrostatic deflector
• Ion Sources
• Internal ion source Oak Ridge Type
• External ion source Atomic beam type polarized
  ion source
• ECR ion source
• RING cyclotron

6
Physics Programs at RCNP
Unique Points

• Nucleon and Nuclear Interactions in Nuclear
  Medium .
• (p,2p) reaction
• K.Hatanaka et al. Phys. Rev. Lett. 78 (1997)
  1014
• Modification of the nuclear interaction in the
  nuclear medium..
• Proton Elastic Scattering Polarization transfer
  measurements
• Medium modification of the exchanged mesons
  masses in the N-N interaction.
• Proton Inelastic Scattering Polarization
  transfer measurements
• Study the isoscalar spin-dependent central
  interaction.
• Spin Isospin Excitations .
• (p,n) reaction
• T. Wakasa et al. Phys. Lett. B426 (1998) 257,
  Phys. Rev. C59 (1999) 3177
• Study the quenching problem of the Gamow-Teller
  (GT) transion
• (3He,t) reaction Gamow-Teller resonance
• (n,p) reaction The construction of the (n,p)
  experimental facility
• was completed, now experiment is in progress.
• Giant Resonance.
• (p,p) / (a,a) / (7Li,7Be) reactions
• Fragmentation of Deep Hole States in Light Nuclei
  .
• Proton-proton Bremsstrahlung (p,p?) Reaction .

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Topics 1 Physics Modification of the nuclear
interaction in the nuclear medium
T. Noro and H.P.Yoshida et al.
Physics Motivation Partial restoration of Chiral
Symmetry in the nuclear medium ?Modification of
hadron properties hadron mass reduction
m(?)/m f(?)
lt0qq0gt (-250 MeV)3 at free
lt0qq0gt ? 0 at high density
Exchanged meson mass reduction ? Nucleon
Nucleon (NN) interaction modification

• Physics Goal
• Extract NN interaction in the nuclear medium and
  compare it with free NN int.
• Obtain the information on hadron mass change in
  the nuclear medium via NN int.
• Unique Points of Experimental Technique
• Exclusive measurements measure knockout proton
  together with scattered one
• Polarization transfer measurements sensitive to
  the meson mass
• Study the density dependence of the
• hadron properties such as meson mass
• reduction in the nuclear medium

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High resolution two arm spectrometer
M.Fujiwara, N.Matsuoka et al.

• Two arm spectrometer
• High resolution spectrometer Grand Raiden
• Large Acceptance Spectrometer LAS
• Grand Raiden LAS
• Maximum Magnetic Rigidity (B?) 5.4 Tm 3.2 Tm
• 1st Order Momentum Resolution (M/D) 2.7
  10-5 1.7 10-4
• Confirmed Momentum Resolution (?P/P) 4.7
  10-5 5 10-4
• Momentum Bite (Pmax/Pmin) 1.05 1.35
• Acceptance (?O) 5.6 msr 20 msr
• Total Weight 600 t 150 t

DSR

• Dipole magnet for Spin Rotator (DSR)
• Used to perform the complete measurements
• of the polarization transfer Dij
• ?Scattered proton spin is precessed by DSR,
• and the polarization is determined from the
• combination of the measurements with DSR
• excited positively/negatively.

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Experiment
M.Yosoi et al.

• Beam Energy Ep 392 MeV
• Beam Intensity 0.1 100 nA (depend on the
  background condition)
• Targets 6Li, 12C, 16O, 40Ca
• Observed Reaction 1s1/2(6Li, 12C, 16O),
  2s1/2(40Ca)
• Energy Resolution 350 keV (beam energy
  distribution dominant)
• Measured Observable Analyzing power (Ay),
• Polarization Transfer (Dij, where i,j n, l,
  s)

2nd level trigger ?Use FPGA (Field
Programmable Gate Array) Reject the events
scattered at forward angles which is not
necessary to determine Dij
10
Unique Points
T. Noro and H.P.Yoshida et al.

• Measurement condition
• Knockout of s1/2 nucleons knockout of the
  nucleon at rest in the plane wave
• Advantage
• The cross section of the s1/2 knockout maximum
  at zero recoil condition.
• Bound nucleons are regarded to be unpolarized
  simple relation between
• the spin observable of (p,2p) reaction and of
  the NN scattering.
• Obtained spectrum
• s1/2 state observed clearly
• Events in s1/2 state (black area) selected and
  used to determine the polarization
• Energy resolution about 350 keV beam energy
  distribution dominant

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Nuclear Density
T. Noro and H.P.Yoshida et al.

• Evaluation of the averaged nuclear density seen
  through the reaction
• non-relativisitic DWIA with factorized and local
  density approximation
• NN amplitude t (r,?) t0 t1?(r) assuming
  the linear density dependence

• 12C 1s1/2 knockout reaction see the nuclear
  density 40 of saturated density
• Averaged density ? ranged from 7 to 40
• Nuclear density dependence of various observable
  can be observed

12
Results
T. Noro and H.P.Yoshida et al.

• Observed features
• Ay and Dij shows the density dependence
  decreased with density
• Ay significant difference from the theoretical
  calculations (PWIA/DWIA)
• Dij sell reproduced by DWIA
• Difference of PWIA and DWIA small distortion
  effects can be neglected
• Ay monotonically decreasing with nuclear density
  
• some medium effects in the NN interaction
• Possible medium effects
• Multi step process but can not be seen in Dij
  not likely
• detailed theoretical calculation
  shows the contribution
• to the cross section within a few
  
• Distortion effects negligible (almost no
  difference between DWIA/PWIA)
• Modification of the NN interaction most
  likely ?

13
Medium Effects observed in Ay
T. Noro and H.P.Yoshida et al.

• Medium effects
• g-matrix (NN interaction in the nuclear filed)
  include Pauli Blocking effects
• Amos group completely microscopic
• reproduce data of elastic and inelastic
  scattering from 65 to 400 MeV
• Kelly group empirical g-matrix
• Both calculations not reproduce the density
  dependent reduction of Ay
• Hadron mass reduction in the nuclear medium
• T-matrix (T) in the framework of relativistic
  impulse approximation
• where ?i(r) is 4 component wave function
  (i0incidence and i1,2outgoing) F(r) is wave
  function of knockout nucleon,
• F is Lorentz-invariant NN ampilitude, and Fk is
  kinematical factor.
• ? nucleon mass reduction M ?
• where S(r) scalar potential
• ? meson mass reduction F parameterize NN
  interaction with OBEP shape
• modification of the meson mass(m) momentum
  transfer (q) dependence of a relevant component
  of NN amplitudes

at saturated density Value used by ref. G.Krein
et al., Phys. Rev. C51 (1995)2646
Reproduce the density dependence of Ay well by
the meson mass reduction
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Polarization Transfer and Next Step
T. Noro and H.P.Yoshida et al.

• Dij universal scaling (m g) such as
• not reproduce all the Dij well
• Only one meson mass (m?) reduction 0.9
  significant change of Dij
• Dij sensitive to each meson mass reductions
• Spin observable (Dij) for (p,2p) reactions good
  probe to study the
• possible modification of the NN interaction and
  meson mass reduction
• in the nuclear medium

Outlook To observe the mass modification for each
kind of mesons in the nuclear medium ? Complete
measurements Cross section Analyzing
power exists Polarization transfer
for the scattered and knockout particles
exists/planned
Grand RAIDEN Polarimeter
Polarized beam
2nd polarimeter construction
LAS Polarimeter
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Topics 2 PhysicsQuenching of Gamow-Teller
Strength and Pionic Nuclear Collectivity
H.Sakai and T.Wakasa et al.

• Physics Motivation
• Pionic nuclear collectivity enhancement
• Strong attraction produced by pions
• ? leads to various interesting phenomena
• such as pion condensation and its precursor
• Interaction of nucleon, pion, and ? in the
  nucleus
• This phenomena is related to short range
  correlation of Nucleon-Nucleon interaction.
• Experimental Observation of
• Quenching of Gamow-Teller strength
• Enhancement of Longitudinal Spin Response
• ? access the Pionic Collectivity in the nucleus
  at different kinematics region
• Physics Goal
• 1. Determine the short range correlation of NN
  interaction
• (Landau-Migdal parameters) from the
  measurements of
• the quenching factor for Gamow-Teller strength by
  (p,n) reaction
• Longitudinal spin response function by (p,n)
  quasi-elastic scattering
• 2. Investigate the enhancement of the pionic
  collectivity (pion condensation)

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Spin-Isospin Correlation

• Spin-Isospin Response Function
• Longitudinal
• Transverse
• p?g model
• NN effective interaction of ts channel
• where
• Characteristics of interaction
• Shift to repulsive force due to g short range
  correlation
• Difference of VL and VT due to the mass
  difference of pand ?meson

One p exchange
One ? exchange
g Short range correlation of NN interaction

• If g large
• Coupling of ? and N strong
• GT strength absorbed by ?
• transition
• Reason of Quenching of B(GT)
• If g small
• Attractive force of VL strong
• Coupling of ? and N strong
• Enhancement of pionic mode
• Experimental g determination
• Important

17
Experiment
H.Sakai and T.Wakasa et al.
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Neutron Polarimeter NPOL2
H.Sakai and T.Wakasa et al.

• Position sensitive neutron counters 6 layers
• Size 1 m 1 m 0.1 m for 1 layer
• 4 layers liquid scintillator 2 layers
  plastic scintillator
• Figure of Merit (FOM) ed.s.ltAygt2
• where ed.s. (scattering probability from
  analyzer) (detection efficiency)
• Ay is effective analyzing powers
  of analyzer
• Comparison of the specification of neutron
  polarimeter
• lt Facility gt lt Construction gt lt Beam Energy gt lt
  FOM gt
• IUCF 1985 160 MeV 4.610-5
• LAMPF / NTOF 1992 500 MeV 2.310-4
• RCNP / NPOL2 1992 300 MeV 4.910-4
• ? High FOM neutron polarimeter at RCNP

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(p,n) Experimental Topics 1Quenching of the GT
strength
T.Wakasa et al.

• Motivation to search the missing strength at
  continuum region
• Ikedas sum rule for GT strength Sß Sß
  3(Z - N)
• Missing strength in terms of the sum rule
  Quenching of the GT strength
• In the previous experiment Large quenching
  value 40 50
• ? derived from the (p,n) reaction at IUCF (beam
  energy 100 200 MeV)
• Well explained by using the Landau-Migdal
  parameters g 0.6 0.8
• assuming the universality ansatz with
  g(gNNgN?g??)
• ? large gN? value suggests pion condensation
  and its precursor are unlikely
• Possible explanations
• 1. Contribution from ? excitation
• Fragmentation of GT strength to higher excitation
  energy due to higher
• configuration mixing such as 2p-2h state
• Experimentally, it was not well known how much is
  contained in small amplitudes
• at excitation energies higher in the continuum as
  a tail of the GT resonance

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Results of the GT strength
T.Wakasa et al.

• What is new on the experiment at RCNP
• GT strength search in the continuum by the (p,n)
  reaction at 300 MeV
• Polarization transfer measurement to confirm spin
  flip ?S1
• Multipole decomposition analysis to extract ?L0
• Obtained data shows
• Observe the GT resonance at Ex 9 MeV
• Total spin transfer S 0.99 for GT resonance
  region (6 lt Ex lt 16 MeV)
• S 0.86 for continuum region (Ex 50
  MeV)
• ? event at higher excitation region, confirm
  spin transfer reaction ?S1
• GT resonance
• 1. at peak area all the yield contributes GT
  transition
• 2. GT strength contribution exists at higher
  excitation energy up to 50 MeV

Extraction of GT strength B(GT) s?L0(q,?)sGTF(
q, ?) B(GT) (measured) (calculated)
(extract) Quenching Factor Q

• Quenching of the GT strength
• Mainly due to the configuration mixing
• ?-h admixture into 1p-1h GT small

21
Extraction of Landau-Migdal parameters
T.Suzuki and H.Sakai et al.
New Landau-Migdal parameters g N? 0.2 / g
NN 0.6 / m0.8m In the previous values
(universal Assumption) g N? g NN 0.6
0.8
22
(p,n) Experimental Topics 2Longitudinal
Response Functionfrom (p,n) Quasi-elastic
scattering
T.Wakasa et al.

• Quasi-Elastic Scattering (QES) (q 1 3 fm-1)
• Momentum transfer q
• Energy transfer ?
• Spin transfer ?S (longitudinalp/ transverse?)
• Isospin transfer ?T
• Transferred by NN scattering from the nucleon in
  the nucleus
• Simple reaction mechanism
• ? information of nuclear spin response
• Factorized impulse approximation model
• Cross sectionsQES(q,?) NeffsNN(q, ?) R (q,?)
  
• Spin transfer Dij?(distortion)(NN
  scattering)(Response)

• Experiment
• Ep346 MeV, q1.7fm-1
• Longitudinal cross section IDq
• Transverse cross section Idp
• Analysis
• Continuum RPA DWIA
• g N? 0.3 / g NN 0.7 /
• g ? ? 0.5 / m0.7m
• Conclusion
• Small g N? enhance IDq
• Reproduce data well
• Consistent with the LM
• parameters extracted from
• GT strength quenching factor

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Enhancement of Pionic Nuclear Collectivity
T.Suzuki and H.Sakai et al.
Attractive

• Next Step
• Other evidence of enhancement of Pionic Nuclear
  Collectivity 0- state study
• Landau-Migdal parameter determination
  independently Coherent Pion Production

24
Next step to study pion collectivity
Pion Collectivity in the Nucleus
25
Layout of new beam line
T.Wakasa et al.
26
Dispersion Matching
T.Wakasa et al.
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Dispersion Matching with Spectrometer
T.Wakasa et al.
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Results of the Dispersion Matching
T.Wakasa et al.
Lateral and Angular dispersion matching between
WS-BL and Grand RAIDEN Quite high resolution
beam with ?E 12.8 keV is achieved in this new
beam line.
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Status of the Measurement
T.Wakasa et al.
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Topics 4 Planed ExperimentCoherent Pion
Production

• Coherent Pion Production (CPP)
• Virtual pion, emitted from proton (spin
  longitudinal part of transferred quantum),
  propagates through the nucleus by mixing with
  -hole states.
• 2. ends up on-shell pion with the target nucleus
  
• recoiling with the difference in momentum
  between
• the off-shell and on-shell pion.
• 3. target nucleus is left in the ground state
• Physics Goal
• Study the production process of the coherent
  pions.
• Investigate the longitudinal part of the
  spin-isospin interaction involving the ?
  excitation.
• Extract g ?? to get information on the property
  of the predicted pion condensation phase.

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Unique Points
Cross section
where

• The cross section depends on
• the phase factor pn/pp
• Longitudinal / Transverse response function VL
  / VT
• distortion of incoming/outgoing particles

• The angular distribution of the coherent pion
  production on
• 12C at Ep 400 MeV.
• has a forward peak angular correlation due to the
  dominant
• contribution of the longitudinal component.

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Extraction of g??

• The magnitude and the shape of the cross sections
  are
• sensitive to the g??.
• Energy shift is proportional to the change of g
  ??
• ?E ?g ??(hcfpN?2/2pmp2)?0

Pion coincidence Spectrum for the 12C(3He,t)
reaction at E 2 GeV.
g ?? 0.4 1.5
g ?? 1/3

• Limit the value of g ?? experimentally from the
  CPP ,
• g ?? is important for the study of the
  condensation phase.

• p 12C ? n p 12C (g.s.)
• Proton incidence energy 400 MeV
• Scattered neutron 180 MeV
• Produced pions 70 MeV

33
Summary
International Workshop on Nuclear Physics with
RIB August 28-31, 2001, Lanzhou, China

• 1. The RCNP is unique facility for
• High resolution beam and High resolution detector
  
• Polarized beam and polarization transfer
  measurements
• Double arm spectrometer to measure the scattered
  particle correlation
• 2. Nuclear Physics to investigate
• Modification of nuclear interaction in the
  nuclear medium
• Spin-Isospin excitations in Nuclei
• have been/are now performed actively.
• 3. The hadron properties in the nuclear medium
  such as
• Meson mass reduction in the nucleus
• Enhancement of Pionic Nuclear Collectivity (Pion
  Condensation)
• are understood experimentally in more detail.
  
• Further experimental study is in progress.
• High resolution beam line to study pionic state
  construction
• Coherent Pion Production to determine g??