This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Bacher, A.D.

Lisantti, J.

Olmer, C.

Opper, A.K.

Rinckel, T.

Sawafta, R.

Stephenson, E.J.

Wells, S.

Wissink, S.W.

English

IUScholarWorks

INELASTIC SCATTERING 
MEASUREMENTS OF THE SPIN OBSERVABLES DNNl AND P IN 
INELASTIC PROTON SCATTERING FROM 12C AND 160 AT 200 MeV 
A.D. Bacher, J. Lisantti, C. Olmer, A.K. Opper, T. Rinckel, 
R. Sawafta, E.J. Stephenson, S. Wells, and S.W. Wissink 
Indiana University Cyclotron Facility, Bloornington, Indiana 47408 
We have recently measured the normal-component spin observables DNNl, P, and A, 
at 200 MeV for the 1+, T=O (12.71 MeV) and T = l  (15.11 MeV) states in 12c and for the 
4-, T=O (17.79 and 19.80 MeV) and T = l  (18.98 MeV) states in 160. The data represent 
the first physics measurements performed using the newly commissioned K600 Focal Plane 
Polarimeter, which is described elsewhere in this report.'l2 These spin observables were 
determined at five angles for the l2 c 1+ transitions, corresponding to center-of-mass 
momentum transfers between 80 and 250 MeV/c, and at three angles for the 4- transitions 
in 160, at momentum transfers of 225 to 400 MeV/c. The angles were chosen to match 
those at which the in-plane spin transfer observables had been measured previously for 
these same transitions in experiment E24L3 During the 39 shifts allocated for this run, 
we completed all of the measurements originally proposed (E306) and in fact added two 
additional points to the l2 C angular distributions, despite a loss of approximately six shifts 
to various machine instabilities or failures in the cyclotron RF, polarized ion source, or 
other systems. 
The primary motivation for this work is to exploit the increased sensitivity predicted 
for the polarization transfer observables to some of the spin-dependent (and generally 
weaker) terms of the effective interaction used to describe nucleon-nucleus scattering at 
intermediate energies. Within the context of the impulse approximation, this process 
can be related to the free N-N scattering amplitudes, albeit in a model-dependent way. 
Comparison of measured observables to their calculated values thus tests not only our 
understanding of the nuclear response for these transitions, but our ability to efficiently 
parameterize the N-N interaction and then modify it appropriately to compensate for 
the many effects that arise when the scattering occurs within the nuclear medium. If 
discrepancies are found between measured and calculated values, one must search for some 
clue as to where the calculation erred. Cross-sections and analyzing powers represent 
sums over many terms in this process, making it difficult to isolate specific shortcomings 
in either the interaction or the nuclear structure. A very promising approach involves 
measurement of a complete set of inelastic proton scattering spin observables for a variety 
of nuclear transitions. 
This is most easily demonstrated in a static, plane-wave impulse approximation in 
which only direct terms are included. In this approximation, each of the five spin trans- 
fer coefficients, denoted by DG1, can be expressed in terms of sums of interaction and 
structure products. By adding and subtracting thesi spin observables from one another 
in particular combinations, certain components of the interaction and structure can be 
effectively isolated. One finds that for unnatural parity  transition^:^ 
where (i, i, k )  = (A x i, i ,  A). C is the spin-orbit and B, E, and F are tensor amplitudes 
of the free N-N force, and XT and XL are respectively the transverse and longitudional 
nuclear form factors as developed by Kerman, McManus and Thaler.' Note that complete 
sets of spin observables are required to isolate individual terms in the interaction. There is a 
similar factorization of interaction and structure terms in a relativistic plane-wave impulse 
approximation framework? Though the above relationships are rigorously true only in a 
static PWIA without exchange, previous investigations suggest6 that these should serve 
as useful guides to our intuition at typical IUCF energies, at least near the peak of the 
transition form factors. 
Experimental sensitivity to the spin-orbit and tensor terms of the effective interac- 
tion is enhanced between 200 and 300 MeV, where the relative strength of the central 
interaction is minimized. In selecting the excited states for this work, we have chosen 
strong, unnatural-parity, spin-flip transitions, which should serve to emphasize the spin- 
dependent terms of the interaction, yet are states for which the nuclear structure has been 
carefully studied. In particular, different aspects of the if states in 12c have been studied 
by a wide variety of probes, though possible ambiguities in the nuclear wave functions have 
still not been satisfactorily resolved. The 4- transitions in 160, being "stretched" states, 
can only be excited (via a lp-lh mechanism) when a single value of angular momentum 
is transferred to the target nucleus. This results in a simple proportionality between the 
transverse and longitudinal form factors, which greatly simplifies the nuclear structure. 
By chosing transitions with fairly well-determined nuclear structure, we hope to gain in- 
sight into the effective interaction amplitudes. The combination of low and high spin data 
will allow us to examine the isoscaler and isovector q dependences over a large range of 
momentum transfer, though the large exchange contributions predicted for excitation of 
some of these states will significantly complicate the relationship between the momentum 
transfer of the (p,pf) reaction and the effective momentum transfer at which the N-N 
scattering occurs within the nucleus. 
Before taking data, we thoroughly tested all of the changes and improvements we had 
made to the focal plane polarimeter system since our last run.' These changes included 
the addition of new and more sophisticated algorithms and sorting conditions in the online 
analysis. We also developed diagnostic software to calculate various ratios and sums based 
on either cumulative or incremental scaler values to aid in rapidly noting and identifying 
possible hardware problems. We also had made a number of hardware changes, such as 
isolating the scintillator high voltage power supply to reduce noise in the scintillator signals, 
and changing the ADC delay-lines to coaxial cables to eliminate cross-talk found in the 
twisted-pair cables we had been using. As a final check on the whole system, we began 
our production run by repeating a calibration point from our November calibration run.2 
This was done by elastically scattering the 200 MeV proton beam from 12c at 24.26O, 
which is where we had found the p + 12c analyzing power to be nearly equal to zero. 
The calibration point was found to be in agreement with our earlier determinations of the 
FPP 's effective analyzing power and efficiency. 
Three shifts were then required to optimize the beamline for dispersion matching, 
and approximately half a shift was used to alter the focal plane of the K600 to improve 
our data rate. Since the medium dispersion mode of the K600 Spectrometer has a 9% 
momentum bite, which corresponds to approximately a 36 MeV energy bite at 200 MeV, 
approximately 60% of our momentum acceptance (and - 75% of our event rate) was in 
energy regimes that were not the primary focus of this investigation. We were able to 
eliminate these events from our data stream by stopping the ground state on a copper 
block mounted on a movable track inside the K600 vacuum box, and disabling particular 
pre-amp cards on the VDC's of the K600 focal plane. By doing this, elastic scattering 
events did not produce any first-level triggers, while regions of either very low or very high 
excitation were vetoed at a second-level in hardware, leaving us with a 14 MeV energy 
bite. Throughout the run, resolution of the carbon and oxygen states was about 30 keV 
and 70 keV, respectively, as shown in Figs. 1 and 2. Fig. 1 is a 200 MeV 12C(p, p') 12c* 
Figure 1. Typical spectrum for the reaction 1 2 ~ ( p ,  ' ) 1 2 ~ *  at 200 MeV for Blab = 16O. 
The I+, T=O state (12.71 MeV), the I+, T = l  state (15.11 MeV), and the 2+, T = l  state 
(16.11 MeV) are readily apparent. The experimental resolution for these states is less than 
30 keV. 
Figure 2. Typical spectrum for the reaction 160 (p, 160* at 200 MeV for O l a b  = 28O. 
A H3 " ~ 0 3  target was used. The 4- states at 17.79 MeV (T=O), 18.98 MeV (T=l), and 
19.80 MeV (T=o) have experimental resolutions of about 60-70 keV. 
spectrum taken with a natural carbon target at Olab  = 16O. The I+, T=O state at 12.71 
MeV is centered near channel 4700, while the I+, T = l  state (15.11 MeV) is seen near 
channel 5300. At this angle, the state at 16.11 MeV (2+, T=l)  is also strong and easily 
resolved near channel 5550. Fig. 2 shows inelastic proton scattering from a H3 1°~03 
target at Blab  = 28O, which is near the peak of the cross section for the 160 4- states. 
The states of interest, at 17.79 MeV (T=O), 18.98 MeV (T=l) and 19.80 MeV (T=O), are 
centered near channels 6150, 6450 and 6650, respectively. 
Because the cyclotrons had been shut down for 11 days prior to our run, it took 
several days for the magnets to stabilize and for the beam tune to remain constant at 
the level needed for high resolution data acquisition on the K600. We had a number of 
failures of the polarized ion source and the RF system throughout the run, usually lasting 
between one and six hours. Once beam returned, we could generally start taking data 
almost immediately, since the dispersion matching conditions would remain stable over 
time scales of several days. The K600 focal plane and focal plane polarimeter worked 
smoothly and consistently throughout the run, though about a week and a half into the 
run the communication system of the wire chamber high voltage power supply failed, 
and we had to replace it with manually controlled supplies. The only component of the 
polarimeter system that failed was a single LeCroy 2731A Latch and Delay PCOS module. 
The statistical quality and angular range of our measurements is demonstrated in 
Figs. 3, 4, and 5, in which preliminary values for the spin observables (P - Ay) and DNNt 
are shown for the strong isoscalar and isovector 1+ states in 12C and for the isovector 
4- state in 160. We want to emphasize that the data points shown in these figures are 
based upon on-line analyses with crude peak-summing, and the error bars reflect only 
statistical uncertainties. Though detailed comparisons with various theoretical predictions 
would therefore be very premature at this point, it is useful to point out that in many 
cases the discrepancies between the data and most of the calculations are greater than the 
variations among the different calculations. For the 12C 1+ states (Figs. 3 and 4), we show 
three distorted-wave impulse approximation (D WIA)  calculation^,^ each of which uses 
Cohen-Kurath wave functions8 and the same distorted waves, the latter based on optical 
model parameters adjusted to simultaneously fit elastic scattering cross section, analyzing 
power, and spin rotation coefficient data.' For the 4- isovector state in 160 (Fig. 4), the 
wave function is described by a d5/2P$ configuration which is almost a pure T = l  state, 
as suggested by earlier pion scattering experiments. lo Distortions for the l6 0 states were 
obtained in a manner similar to that of the 12c work.' In both cases, the three effective 
interactions shown are the ~ove-Franeyl' and ~ o n n ' ~  interactions, based on the free N-N 
CFIRBON 12.7 MeV, I+. T=0 CFIRBON 12.7 MeV. l+, T=0 
- FRANEY-LOVE; RWTL ; 12.70MEV 
,, FREEBOW; W T L ;  12.70MEV 
------- DD BONN; RUNTLi 12.70t€V 
8 LP
r( I I I I I I 
P NIMJS A I 
- FRANEY-LOVE; RLHTLi 12.70MEV 
- - , - FREE BOW; RUNTL; 12.70MEV 
--,,,,. DD BONN; RUNTL; 12.78PEV 
E 
0 . 0 0  1 0 . 0 0  2 0 . 8 8  3 0 . 0 0  
NOENTUN TRANSFER <HEV/C> 
Figure 3. Preliminary results for the spin observables (P - A,) and DNNt for the isoscalar 
I+ state (12.71 MeV) in 12c. The curves correspond to three D WIA calculations based on 
the effective interactions indicated at the top of the figures. 
CARBON 15. 11 MeV, I+, T=l CClRBON 15. 11 MeV, 1+, T = l  
- FRANEY-WVE; RWT1; 1 5 . 1  1HEV - FRANEY-LOVE; R l N T l ;  1 5 . 1  lMEV 
,,,. FREE BOW; RUNTL; 15.1lMEV , , , . FREE BOW; RUNTL; 1 5 . 1  LMEV 
,,,,,,. DD BONN; RUNTI; 15.11PEV , , , , , , . DD BONN; RUNT I; 1 5 . 1  1PEV 
8 8 
8 8 
WOHENl'UW TRFINSFER <flEV/C> HOPENTUN TRANSFER <flEV/C) 
Figure 4. Preliminary results for the spin observables (P -A,)  and D N N ~  for the isovector 
lf state (15.11 MeV) in 12c. The curves correspond to three DWIA calculations based on 
the effective interactions indicated at the top of the figures. 
scattering amplitudes, and a modified Bonn interaction in which nuclear medium effects 
have been incorporated in a density-dependent way.12 
Though more detailed off-line analysis and yield-extraction techniques will need to be 
developed, the statistical quality of the data is readily apparent, as are the general trends 
of the angular distributions. As stated above, we have completed all of the measurements 
that were proposed, as well as two additional angles for the carbon data. We expect the 
final statistical uncertainty in these measurements to be better than 0.05 for DNNt and 
0.03 for P at most angles. A second-pass analysis is currently underway, with the goal of 
obtaining final results by late summer. 
1. S.W. Wissink et al., "Experimental Facilities Development - the K600 Focal Plane 
Polarimeter", IUCF Scientific and Technical Report, 1988. 
2. E.J. Stephenson et al., "Calibration of the K600 Focal Plane Polarimeter" , IUCF 
Scientific and Technical Report, 1988. 
3. C. Olmer, in Antinucleon- and Nucleon-Nucleus Interactions, ed. G.E. Walker, C.D. 
Goodman, and C. Olmer (Plenum Press, New York, 1985) p. 261. 
4. J.M. Moss, Phys. Rev. C 26, 727 (1982). 
5.  A.K. Kerman, H. McManus, and R.M. Thaler, Ann. Phys. 8, 551 (1959). 
6. T. Carey, in Proc. Sixth Int. Symp. Polar. Phenom. in Nucl. Phys., Osaka, 1985 
7. R. Schaeffer and J. Raynal, Saclay Report CEA-R4000 (1970); modifications by J. 
Comfort and W. Bauhoff. 
8. S. Cohen and D. Kurath, Nucl. Phys. A101, 1 (1967). 
9. P. Schwandt, private communication. 
10. J.A. Carr, F. Petrovich, D. Halderson, D.B. Holtcamp, and W.B. Cottingame, Phys. 
Rev. C 27, 1636 (1983). 
11. W.G. Love and M.A. Franey, Phys. Rev. C 24,1073 (1981). 
12. R. Machleit , private communication 
OXYGEN 19.0 MeV, 4-, T = l  OXYGEN 19.0 MeV, 4-, T = l  
- FRANEY-UIVE; RUJTL ; L8.978NEV - FRANEY-WVE; RLNTL ; L8.978NEV 
- - - - FREE BOW; RUNT1 ; 18. 97BHEV , - - . FREE BOW; RUNTL; 18.978HEV 
------. a BONN; RUNTli 18.978nEV ------. DD BONN; RUNTL; 18.978nEV 
8 
8 8 
NOPIENTUN TRCINSFER <HEV/C) 
20.80 40.80 
NOHENTUN TRCINSFER <HEV/C> 
Figure 5. Preliminary results for the spin observables (P - A,) and DNNt for the isovector 
4- state (18.98 MeV) in 160. The curves correspond to three DWIA calculations based 
on the effective interactions indicated at the top of the figures. 


Measurements of the Spin Observables D_NN' and P in the Inelastic Proton Scattering from 12-C and 16-O at 200 MeV

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Measurements of the Spin Observables D_NN' and P in the Inelastic Proton Scattering from 12-C and 16-O at 200 MeV

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