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Cross-section and analyzing-power measurements for the 2H(n,pn)n reaction at 189 MeV
_A
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ELSEVIER
Nuclear Physics A663&664 (2000) 545c-548c www.elsevier.nlllocate/npe
Cross-Section and Analyzing-Power Measurements for the 2H(n,pn)n Reaction at 189 MeV B.D. Anderson", O. Osadchy", J. Sowinski", A.R. Baldwin", W. Franklin'v", J.W. Watson", S. Wissink", M. Wolanski'', G. Yang", W. Glockle", H. Witalad "Physics Department, Kent State University, Kent, Ohio 44242 USA bIndiana University Cyclotron Facility, Bloomington, Indiana 47405 USA CInstitute for Theoretical Physics, Ruhr-Univ. Bochum, D-44780 Bochum, Germany dInstitute of Physics, Jagellonian University, PL-30059 Cracow, Poland We measured cross sections and analyzing powers for the 2H(n,n)2H and 2H(n,pn)n reactions at 189 MeV at the Indiana University Cyclotron Facility (IUCF). These measurements are designed to search for evidence of three-body forces in the nuclear force and have the advantage that the Coulomb force is not involved. The analyzing-power measurements for the 2H(n,n)2H reaction are in close agreement with those from the analog 2H(p,p)2H reaction at nearby energies and do not agree quantiatively with available three-body, Faddeev calculations, either with or without three-body forces included. The 2H(n,pn)n measurements are still under analysis.
1. Introduction It is generally acknowledged that three-body forces must exist in nature, including in the nuclear force. Many different diagrams can be drawn which are normally considered to represent a three-body interaction, and which can be present in the nuclear interaction; however, the evidence for such forces in nuclear reaction studies is very limited. At this time, the best evidence for three-body forces in nuclei comes from studies of the binding energies for A = 3 nuclei, viz., 3H and 3He. One finds it necessary to include some 3-body forces in order to explain the observed binding energies in terms of specific models of the nuclear force. At the same time, it is observed that one can do this using different possible 3-body forces and that the binding-energy information cannot distinguish between such forces. It is hoped that nuclear reactions could help to identify specifically which 3-body force diagrams are most important. So far, low-energy «100 MeV) reaction studies have provided no experimental results which have clearly required 3-body forces in order to be described accurately. More recently, measurements by Sagai et al.! for the 2H(n,n)2H reaction at 135 MeV and by Cadman et al. 2 for the 2H(p,p)2H reaction at 200 MeV show effects in spin observable measurements which are described somewhat better when a 3body force is included in the nuclear force assumed; however, some of the spin observables measured by Cadman et al. are not described well by any available calculations, with or without, 3-body forces. 0375-9474/00/$ - see front matter © 2000 Elsevier Science B.Y. All rights reserved. PH S0375-9474(99)00652-l
546c
B.D. Anderson et al.!Nuclear Physics A663&664 (2000) 545c-548c
This experiment is designed to look for possible 3-body force effects in reactions with polarized neutrons incident upon deuterium. These reactions have the advantage that only one charged particle is present so that the Coulomb force is not involved. This is important because the 3-body, Faddeev calculations used to describe these reactions cannot include the infinite-ranged Coulomb force; thus, the comparisons of the experimental results for these measurements with the calculations are more unambiguous. The availablilty of 3body Faddeev calculations above 100 MeV is recent. Witala and Glockle have made such calculations now" and these calculations were used in designing this experiment. These calculations indicate that the effects of the nuclear 3-body force may be strong in the breakup reaction on deuterium in a geometry which picks out the final-state interaction of the emitted proton with one of the neutrons in the ISO state. Two basic geometries were studied in this experiment. One geometry produced the detected proton and the undetected neutron in the ISO final-state interaction and is predicted to be strongly sensitive to possible three-body forces. This geometry allows us also to measure the elastic-scattering reaction 2H(n,n)2H, which was observed to show possible 3-body force effects by Sakai et al. at 135 MeV. The other geometry studied corresponds to quasifree scattering kinematics and is predicted to not be sensitive to such forces, and will provide a test of the general validity of the calculations at this energy.. The predictions were performed using exact, three-body, Faddeev calculations using a realistic nucleon-nucleon (NN) interaction plus an assumed three-body interaction.i'
2. Experimental Procedure The measurements were performed with the upgraded polarized neutron facility at IUCF. The polarized neutrons were produced with polarized protons from the highintensity polarized source incident upon a liquid deuterium (LD2) target. The emitted neutrons were then collimated by a path through a shielding wall into a beam 5cm X 7cm with an intensity of about 107 neutrons/sec. The neutron beam had a polarization of about 0.6. The neutrons were then incident upon a second LD2 target in order to study the reaction of interest. The emitted protons were detected in a stack containing multiwire drift chambers and plastic scintillators. Both the angles and energies of the emitted protons were determined. The emitted neutrons were detected in coincidence with segmented, position-sensitive plastic scintillators. Six detectors, each 1m long by IDem X IDem in cross section were used. Each neutron detector was divided into 5 slabs, each 2cm thick. The timing and position from each neutron detector was obtained with IDem phototubes mounted on each end of the 1m long detectors. The slab information was obtained from wave-shifting fibers run along the top of each slab and viewed by separate 2.5 em diam. phototubes. The flight path to the neutron detectors was about 2m. Overall energy resolutions of about 5 to 10 MeV were obtained in the experiment, sufficient for the study of this reaction. Various requirements are impressed upon the data. Time-of-flight from the production target to the secondary target was measured using a fast plastic scintillator detecting the emitted protons or deuterons and located near the secondary target. A fiducial timing mark was obained from the cyclotron RF indicating the time of arrival of the proton beam on the production target. Particle identification was performed using E - !:i.E scintillators
B.D. Anderson et al./Nuclear Physics A663&664 (2000) 545c-5 48c
547c
in the charged-pa rt icle stac k. The angle informat ion from both the charged-particle stac k and the position-sensitive neutr on detectors was used to require co-planarity and correct kinematic opening angle. The final cuts are then placed on the measur ed charged-particle and neutron energies .
3. Results Results have been obtained for analyzing powers for th e 2H(n,n)2H elastic-scattering reaction and compared wit h earlier measurements of th e analog p-d elasti c-scat tering analyzing-powers at nearby energies.V' The results for th e deuteron breakup reaction into the final-state and quasifree-scat tering geometries is in progress and results will be present ed later in comparison with Faddeev calculations. The result s for the 2H(n,n)2 analy zing power measurements are shown in Fig. 1, compared with analog measurements for th e 2H(p,p yH reaction at nearby energies . It can be seen that all of these results are in good agreement, indicating that Coulomb effects are apparently small at this energy. Thi s is an important result in that it indicates that one can use the analog reaction, even though two charged particles are involved, to look for possible 3-body force effects without concern that the Coulomb force will significantly affect th e measurements.
n/p+d Elastic Scattering • 08
~
p+d at 200 MeV (IUCF, Ref. 4) p+d at 198 MeV (Adelberger, Ref. 5)
'" p+d at 191 MeV (IUCF unpub.) • n+d at 187 MeV (this exp.)
0 .6 0.'
4i ~
0.2
o
DOl
c
]. - 0.2
c; e
et - 0.' -0.6 - 0 ,1:5
20
40
60
80
100
120
1040
160
180
NeutronIProton Angle (deg)
Figure 1. Analyzing powers for th e 2H(n, n)2H reaction at 189 MeV as a function of the angle of the emitted neutron compared with analog measur ement s for the 2H(p, py n reaction at nearby energies.
548c
B.D. Anderson et al. / Nuclear Physics A 663&664 (2000) 545c-548c
Figure 2 shows the comparison of the results of these measurements for the 2H(n,n)2H reaction compared to 3-body, Faddeev calculations, with and without a 3-body force included. It can be seen that although the calculations clearly describe the measurements qualitatively, they are not accurate quantitatively. Neither of the calculations accurately describe the data, which as seen in Fig. 1, agree with several analog reaction results at this energy. The theoretical effort is now concerned that calculations at this energy may require the calculations to be performed relativistically.
n+d Elastic Scattering 0.8
CD Bonn +TM3NF .... CDBonn
0.6
•
n+d at 186 MeV (this exp.)
0.4
~
0.2
~
Cll C
~
iii
-0.2
C
<
-0.4
-0.6
-0.8
20
40
60
80
100
eM Neutron Angle
120
140
160
180
(deg)
Figure 2. Analyzing powers for the 2H(n, n)2H reaction at 189 MeV as a function of the angle of the emitted neutron compared to three-body, Faddeev calculations. (See text.)
References 1. Sakai et al., RIKEN, unpublished.
2. 3. 4. 5.
Cadman et al., Bull Am Phys Soc 44 (1999) 1407. Witala H, Glockle W, and Cornelius Th, Few-Body Syst 6 (1989) 79. S.P. Wells et al., Nuc!. lnstr. Meth. A325 (1993) 205. R.E. Adelberger and C.N. Brown, Phys. Rev. D (1972) 2139.
This work was supported in part by the U.S. National Science Foundation.
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~
ELSEVIER
Nuclear Physics A663&664 (2000) 545c-548c www.elsevier.nlllocate/npe
Cross-Section and Analyzing-Power Measurements for the 2H(n,pn)n Reaction at 189 MeV B.D. Anderson", O. Osadchy", J. Sowinski", A.R. Baldwin", W. Franklin'v", J.W. Watson", S. Wissink", M. Wolanski'', G. Yang", W. Glockle", H. Witalad "Physics Department, Kent State University, Kent, Ohio 44242 USA bIndiana University Cyclotron Facility, Bloomington, Indiana 47405 USA CInstitute for Theoretical Physics, Ruhr-Univ. Bochum, D-44780 Bochum, Germany dInstitute of Physics, Jagellonian University, PL-30059 Cracow, Poland We measured cross sections and analyzing powers for the 2H(n,n)2H and 2H(n,pn)n reactions at 189 MeV at the Indiana University Cyclotron Facility (IUCF). These measurements are designed to search for evidence of three-body forces in the nuclear force and have the advantage that the Coulomb force is not involved. The analyzing-power measurements for the 2H(n,n)2H reaction are in close agreement with those from the analog 2H(p,p)2H reaction at nearby energies and do not agree quantiatively with available three-body, Faddeev calculations, either with or without three-body forces included. The 2H(n,pn)n measurements are still under analysis.
1. Introduction It is generally acknowledged that three-body forces must exist in nature, including in the nuclear force. Many different diagrams can be drawn which are normally considered to represent a three-body interaction, and which can be present in the nuclear interaction; however, the evidence for such forces in nuclear reaction studies is very limited. At this time, the best evidence for three-body forces in nuclei comes from studies of the binding energies for A = 3 nuclei, viz., 3H and 3He. One finds it necessary to include some 3-body forces in order to explain the observed binding energies in terms of specific models of the nuclear force. At the same time, it is observed that one can do this using different possible 3-body forces and that the binding-energy information cannot distinguish between such forces. It is hoped that nuclear reactions could help to identify specifically which 3-body force diagrams are most important. So far, low-energy «100 MeV) reaction studies have provided no experimental results which have clearly required 3-body forces in order to be described accurately. More recently, measurements by Sagai et al.! for the 2H(n,n)2H reaction at 135 MeV and by Cadman et al. 2 for the 2H(p,p)2H reaction at 200 MeV show effects in spin observable measurements which are described somewhat better when a 3body force is included in the nuclear force assumed; however, some of the spin observables measured by Cadman et al. are not described well by any available calculations, with or without, 3-body forces. 0375-9474/00/$ - see front matter © 2000 Elsevier Science B.Y. All rights reserved. PH S0375-9474(99)00652-l
546c
B.D. Anderson et al.!Nuclear Physics A663&664 (2000) 545c-548c
This experiment is designed to look for possible 3-body force effects in reactions with polarized neutrons incident upon deuterium. These reactions have the advantage that only one charged particle is present so that the Coulomb force is not involved. This is important because the 3-body, Faddeev calculations used to describe these reactions cannot include the infinite-ranged Coulomb force; thus, the comparisons of the experimental results for these measurements with the calculations are more unambiguous. The availablilty of 3body Faddeev calculations above 100 MeV is recent. Witala and Glockle have made such calculations now" and these calculations were used in designing this experiment. These calculations indicate that the effects of the nuclear 3-body force may be strong in the breakup reaction on deuterium in a geometry which picks out the final-state interaction of the emitted proton with one of the neutrons in the ISO state. Two basic geometries were studied in this experiment. One geometry produced the detected proton and the undetected neutron in the ISO final-state interaction and is predicted to be strongly sensitive to possible three-body forces. This geometry allows us also to measure the elastic-scattering reaction 2H(n,n)2H, which was observed to show possible 3-body force effects by Sakai et al. at 135 MeV. The other geometry studied corresponds to quasifree scattering kinematics and is predicted to not be sensitive to such forces, and will provide a test of the general validity of the calculations at this energy.. The predictions were performed using exact, three-body, Faddeev calculations using a realistic nucleon-nucleon (NN) interaction plus an assumed three-body interaction.i'
2. Experimental Procedure The measurements were performed with the upgraded polarized neutron facility at IUCF. The polarized neutrons were produced with polarized protons from the highintensity polarized source incident upon a liquid deuterium (LD2) target. The emitted neutrons were then collimated by a path through a shielding wall into a beam 5cm X 7cm with an intensity of about 107 neutrons/sec. The neutron beam had a polarization of about 0.6. The neutrons were then incident upon a second LD2 target in order to study the reaction of interest. The emitted protons were detected in a stack containing multiwire drift chambers and plastic scintillators. Both the angles and energies of the emitted protons were determined. The emitted neutrons were detected in coincidence with segmented, position-sensitive plastic scintillators. Six detectors, each 1m long by IDem X IDem in cross section were used. Each neutron detector was divided into 5 slabs, each 2cm thick. The timing and position from each neutron detector was obtained with IDem phototubes mounted on each end of the 1m long detectors. The slab information was obtained from wave-shifting fibers run along the top of each slab and viewed by separate 2.5 em diam. phototubes. The flight path to the neutron detectors was about 2m. Overall energy resolutions of about 5 to 10 MeV were obtained in the experiment, sufficient for the study of this reaction. Various requirements are impressed upon the data. Time-of-flight from the production target to the secondary target was measured using a fast plastic scintillator detecting the emitted protons or deuterons and located near the secondary target. A fiducial timing mark was obained from the cyclotron RF indicating the time of arrival of the proton beam on the production target. Particle identification was performed using E - !:i.E scintillators
B.D. Anderson et al./Nuclear Physics A663&664 (2000) 545c-5 48c
547c
in the charged-pa rt icle stac k. The angle informat ion from both the charged-particle stac k and the position-sensitive neutr on detectors was used to require co-planarity and correct kinematic opening angle. The final cuts are then placed on the measur ed charged-particle and neutron energies .
3. Results Results have been obtained for analyzing powers for th e 2H(n,n)2H elastic-scattering reaction and compared wit h earlier measurements of th e analog p-d elasti c-scat tering analyzing-powers at nearby energies.V' The results for th e deuteron breakup reaction into the final-state and quasifree-scat tering geometries is in progress and results will be present ed later in comparison with Faddeev calculations. The result s for the 2H(n,n)2 analy zing power measurements are shown in Fig. 1, compared with analog measurements for th e 2H(p,p yH reaction at nearby energies . It can be seen that all of these results are in good agreement, indicating that Coulomb effects are apparently small at this energy. Thi s is an important result in that it indicates that one can use the analog reaction, even though two charged particles are involved, to look for possible 3-body force effects without concern that the Coulomb force will significantly affect th e measurements.
n/p+d Elastic Scattering • 08
~
p+d at 200 MeV (IUCF, Ref. 4) p+d at 198 MeV (Adelberger, Ref. 5)
'" p+d at 191 MeV (IUCF unpub.) • n+d at 187 MeV (this exp.)
0 .6 0.'
4i ~
0.2
o
DOl
c
]. - 0.2
c; e
et - 0.' -0.6 - 0 ,1:5
20
40
60
80
100
120
1040
160
180
NeutronIProton Angle (deg)
Figure 1. Analyzing powers for th e 2H(n, n)2H reaction at 189 MeV as a function of the angle of the emitted neutron compared with analog measur ement s for the 2H(p, py n reaction at nearby energies.
548c
B.D. Anderson et al. / Nuclear Physics A 663&664 (2000) 545c-548c
Figure 2 shows the comparison of the results of these measurements for the 2H(n,n)2H reaction compared to 3-body, Faddeev calculations, with and without a 3-body force included. It can be seen that although the calculations clearly describe the measurements qualitatively, they are not accurate quantitatively. Neither of the calculations accurately describe the data, which as seen in Fig. 1, agree with several analog reaction results at this energy. The theoretical effort is now concerned that calculations at this energy may require the calculations to be performed relativistically.
n+d Elastic Scattering 0.8
CD Bonn +TM3NF .... CDBonn
0.6
•
n+d at 186 MeV (this exp.)
0.4
~
0.2
~
Cll C
~
iii
-0.2
C
<
-0.4
-0.6
-0.8
20
40
60
80
100
eM Neutron Angle
120
140
160
180
(deg)
Figure 2. Analyzing powers for the 2H(n, n)2H reaction at 189 MeV as a function of the angle of the emitted neutron compared to three-body, Faddeev calculations. (See text.)
References 1. Sakai et al., RIKEN, unpublished.
2. 3. 4. 5.
Cadman et al., Bull Am Phys Soc 44 (1999) 1407. Witala H, Glockle W, and Cornelius Th, Few-Body Syst 6 (1989) 79. S.P. Wells et al., Nuc!. lnstr. Meth. A325 (1993) 205. R.E. Adelberger and C.N. Brown, Phys. Rev. D (1972) 2139.
This work was supported in part by the U.S. National Science Foundation.