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EXPERIMENTS WITH POLARIZED DEUTERON BEAMS AT SATURNE
J. Arvieux
To cite this version:
J. Arvieux. EXPERIMENTS WITH POLARIZED DEUTERON BEAMS AT SATURNE. Journal de Physique Colloques, 1985, 46 (C2), pp.C2-451-C2-453. �10.1051/jphyscol:1985253�. �jpa-00224568�
JOURNAL DE PHYSIQUE
Colloque C2, supplement au n°2, Tome 46, fevrier 1985 page C2-W1
EXPERIMENTS WITH POLARIZED DEUTERON BEAMS AT SATURNE
J . Arvieux
Laboratoire National Saturne, 91191 Gif-sur-lvette Cedex, France and
Institut des Sciences Nucleaires, 38026 Grenoble Cedex, France
Abstract - The Saturne synchrotron can accelerate up to 2.3 GeV beams of polarized deuterons with good intensity ( ISI 1010 d per pulse) and very high vector and tensor polarization. Some experiments which have been recently completed or are planned in a near future are described. Uses of intermediate energy polarized deuterons for polarimeter feasibility and for producing polarized neutrons are discussed.
I - INTRODUCTION
Polarized deuterons are interesting from many points of view :
1) in a reaction proceeding through a well understood mechanism they can be used to study properties of the deuteron itself (e.g. in d break-up reactions)
2) they may probe the structure of elementary systems (e.g. in the pp —»dfl and T\d—-*T\d reactions the tensor analyzing power is very sensitive to the excita- tion of dibaryons)
3) they can be used to study mechanisms in which polarization observables are very important (e.g. the d p - ^ tt\* reaction...)
4) they may be useful in probing nuclear structure effects (e.g. in d-nucleus scattering)
5) finally deuteron beams can be used as simple tools to produce polarized neu- trons or to calibrate polarimeters for measuring the polarization of recoil deu- terons (e.g. for measuring T in e-d scattering).
In fact there is a constant interplay between these different aspects which are being investigated at Saturne.
II - THE POLARIZED SOURCE
The polarized source is of the atomic beam type. It can produce either protons or deuterons. The gas and R.F. dissociation are pulsed during 3 ms per cycle and the dissociator nozzle is cooled to 70°K. Currents of 200 HA have been obtained after ionization. The polarization is produced by 3 R.F. transitions which give 8 combinations of polarized beams?
1) two are unpolarized
2) two are pure vector polarized (pz =-2/3)
3) four are vector (pz = ±1/3) and tensor (pzz = - 1 ) polarized.
The state of polarization is changed between each cycle. The polarization is measured in a low energy polarimeter between the source and the Linac which makes use of the cfd—*pt reaction at 400 keV. Vector polarization up to 95% and tensor polarization up to 80% of their maximum value are routinely obtained. There are no depolarizing resonances for deuterons in Saturne /l/.
III - SOME PROBLEMS STUDIED AT SATURNE
1) Backward dp scattering : The tensor analyzing power T has been measured around © = 180° from 0.3 to 2.3 GeV. Contrary to limited existing results
Résumé - Le synchrotron Saturne peut accélérer jusqu'à 2.3 GeV des faisceaux intenses de deutons polarisés ayant une polarisation vectorielle et tenso- rielle importante. Plusieurs expériences sont décrites. On discute aussi l'intérêt des deutons polarisés pour la réalisation d'un polariraètre et pour la production de neutrons polarisés.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985253
C2-45 2 JOURNAL DE PHYSIQUE
-0.5-
- l o
3000 3200 3400 6 WVI (above 1 GeV) by excitation of baryo-
Figure 1 nic resonances (N*) , dibaryon effects (or N h interactions) or more exotic phenomena (tribaryons etc ... ).
A more detailed account of this experiment will be given by A. Boudard /I/.
2) Elastic scattering of polarized deuterons by nuclei : The scattering of polari- zed deuterons by 160, 40~a and 5 8 ~ i has been studied at 200, 400 and 700 MeV /3/.
The 200 MeV data make a bridge with the low energy region (the highest energy for a polarized deuteron beam elsewhere is 80 MeV at IUCF). At 700 MeV one hopes to study relativistic effects (Dirac approach).
The tensor analyzing power A] = ( 4 ~ ~ 0 - &T2s) is shown in Fig. 2. Stan- dard optical models (with re1 tlvistic kinematics but without tensor interaction)
give a good account of the 58 Ni results but are much less satisfacto- ry for 160 (at 200 MeV the other situation prevails).
At 200 MeV we have observed the so called polarized nuclear rainbow effect for which Ay and Ayy satu- rate at their maximum value of 1, a property which can be used in a deuteron polarimeter.
- 5 - - . - - - - , - - 7OOMeV 1 3 ) Study of np scattering and pro-
0 . " 5. 1 0 . 1 . . 2s duction of polarized neutrons :
In a vector polarized deuteron the proton and neutron have about half the deuteron energy (corrected by
1.0 the Fermi energy) and their spins
are parallel. Then they have the
>, same polarization but it is smaller
2 . 9 than the deuteron polarization since
the spins in the S-state and in the D-state are opposite. This effect
0.0 is of the order of 1-3/2P where P
D D
is the D-state percentage. Then for a 6-7% D-state the relative decrease
-.S of neutron (and proton) polarization
0. is about 10% /4/. This property
8cm( d e g 1 can be used to produce polarized neutrons by breaking polarized deu- Figure 2 terons at small angles. It has also been used to compare quasi-free
I -
I { i i 4 f 1 4 4 1 ) I
f I
- r
'
-I I I I I I I
which were compatible with zero /2/, we find (fig. 1) a first negati- ve peak around 0.5 GeV and a second, less accentuated, structure around 1.4 GeV. The reaction mechanism changes drastically over such a wide energy range. Low energy (below pion production threshold) is domi- nated by one neutron exchange, the region around 0.6-1 GeV by A -
excitation and the higher range
pp and np scattering in a dp-r npp break-up. Knowing the pp analyzing power one -.
can deduce the np one, assuming that the ratio of quasi-elastic to free analyzing power is the same for pp and np (which is true to first order in the scattering diagrams).
The 1450 MeV results (725 MeV equivalent neutron energy) are shown in Fig. 3.
They agree well with phase-shift analysis predictions which fitted free np data at larger angles. Data have also been taken off quasi-free geometries to enhance higher order processes and to try to understand better their correction. Detailed results will be presented at this conference by F. Perrot.
0.8 , , , , , , , , 4) Studies for a deuteron polarimeter
F
A at intermediate energies : The tensor725 MaV polarization of the deuteron in e-d scat-
0 . 8 l I I I at this conference by B.H. Silverman.
0 40 80 I20 160
• EXP. - tering is a very sensitive test of the
o L A Y P ~ leso deuteron wave-function. This wave-function
- P S A is well known at small momentum transfer
but large discrepancies between nucleon- nucleon models exist for q & 5 fm-I where the D-state dominates over the S-state and measurements of TZ0 are crucial. For
Figure 3
0 2
0 4
IV - FUTURE PLANS
4 t 3
An experiment to measure T20 at O0 and 18c for dp --+ t n ( He TI*) to clarify the problem of the structures observed in dp-+pd and $d-+tn* reactions /6/ is planned in a near future. In particular we hope to pin down the different mecha- nisms contributing to the 3-nucleon interaction at intermediate energies whether they are due to excitation of single nucleons (A, N*), two nucleons ("dibaryons"
or N A interactions) or 3 nucleons ("tribaryons") .
A 8; elastic experiment at 1600 MeV will make use of a polarized deuteron beam and polarized proton target. It will complete single scattering results obtained earlier at Argonne and pd scattering data at 800 MeV from LAMPF to produce a com- plete set of pd elastic data.
\
- Aoono(n0I j: \ ,&f'
-
Finally the use of deuterons to produce polarized neutrons up to Tn = 1.15 GeV will intensify in the next few years to study the free np interaction in a comple- te experiment with a polarized proton target and recoil polarimeter.
the requested electron energies the recoil deuteron has an energy of a few hundreds
REFERENCES
- \ b ;* i- MeV which make the use of low energy pola- rimeter used so far /5/ out of question.
- We have studied elastic and inelastic
scattering of 200 and 400 MeV deuterons
- by various targets ( H , ~ H , Li, C, Ni, Pb) in order to find out the best polarimeter case. Detailed results will be uresented
/1/ More details about the formalism, polarized source and polarimeter will be found in a paper by J. Arvieux et al, accepted for publication in Nucl.Phys.
/2/ G. Igo et al, Phys. Rev. Lett. 43 (1979) 425
/3/ Nguyen Van Sen et al, contribution to PANIC, Heidelberg 1984 /4/ C. Wilkin, Journ6es dlEtudes Saturne, Roscoff 1979, p. 47 /5/ M.E. Schulze et al, Phys. Rev. Lett. 52 (1984) 597 /6/ R. Bertini et al, contribution to this conference.
