ANALYZING POWER MEASUREMENTS IN πd ELASTIC SCATTERING AT 50 MeV

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ANALYZING POWER MEASUREMENTS IN π d ELASTIC SCATTERING AT 50 MeV

N. Stevenson, R. Schubank, Y. Shin, P. Amaudruz, P. Delheij, D. Healey, B.

Jennings, D. Ottewell, G. Sheffer, G. Smith, et al.

To cite this version:

N. Stevenson, R. Schubank, Y. Shin, P. Amaudruz, P. Delheij, et al.. ANALYZING POWER MEA-

SUREMENTS IN πd ELASTIC SCATTERING AT 50 MeV. Journal de Physique Colloques, 1990,

51 (C6), pp.C1-391-C1-394. �10.1051/jphyscol:1990636�. �jpa-00230903�

N.R. STEVENSON, R.B. SCHUBANK, Y.M. SHIN, P. AMAUDRUZ*,

P.P.J. DELHEIJ", D.C. HEALEY*, B.K. JENNINGS*, D.F. OTTEWELL*, G. SHEFFER*, G.R. SMITH*, G.D. WAIT*, N. GRION*", R. RUI"*, J.T. BRACK'**, A. FELTHAM"**, M. HANNA***, R.R. JOHNSON'**,

F.M. ROZON***, V. SOSSI*"*, D. VETTERLI*"", P. W E B E R * * * , M. K O H L E R * * * * , R.A. RISTINEN**** E.L. MATHIE**""* R. TACIK*** * * , M. Y E O M A N S * * * * * , C.A. GOSSETT*****'

,

Department of Physics, University of Saskatchewan, Saskatoon, Sask.,

?7N OWO, Canada

TRIUMF, 4004 Wesbrook Mall, Vancouver, B.C., V6T 2A3, Canada

f * Istituto Nazionale di Fisica Nucleare and Dipartimento di Fisica, yf:versita di Trieste, Trieste, I-34127, Italy

Department of Physics, University of Bristish Columbia, Vancouver, B. C. , V6T 1W5. Canada

t X * *

Department of Physics, University of Colorado, Boulder, CO 80309,

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Nuclear Physics Lab., University of Washington, Seattle, WA

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Physikalisches Institut der Universitaet Tuebingen, f;l?fgf?f:elle, 0-7400 Tuebingen. F.R.G.

Department of Physics, Simon Fraser University, Burnaby, B.C., V5A 1S6. Canada

Rksumb - Nos mesures du pouvoir d'analyse vectoriel dans la diffusion 6lastique nd B 50 MeV sont en accord avec les prkdictions des modMes qui incluent la partie Pll du potentiel n N integral mais sont en d6saccord avec ceux qui ornettent ou suppriment cette composante.

Abstract - Measurements of the vector analyzing power in nd elastic scattering at 50 MeV are found to agree well with model calculations that include the full nN Pll potential and disagree when this is omitted or suppressed.

The n N N system has been the subject of attention for many theorists and experimenters over the last few decades. Due to its fundamental nature and importance in the interactions within complex nuclei and, more recently, by its association with possible dibaryon effects this system has come under close scrutiny. Initially, basic Nucleon-Nucleon scattering served as the launching platform via the N N - n N N interaction. In recent years, as meson factories came onto the scene, the complimentary nd system (see Fig. 1) has come more into focus. In particular, ~ d elastic scattering has been highlighted as a channel that is sensitive to many of the remaining outstanding problems such as the effect of the n N PI, potential [I] the degree of Pauli Blocking in the N N * intermediate state [2], and the possibility of exotic structures (such as the speculated dibaryon) [3].

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990636

COLLOQUE DE PHYSIQUE

Figure 1: Reactions used to investigate the x N N system.

Measurements of cross-sections, analyzing powers, and polarizations have been quite extensive over the resonance region (134-294 MeV). Spin-transfer measurements are also planned in the near future [4] thereby allowing the reconstruction of the amplitudes or partial waves [5]. At this point in time, significant discrepancies persist between theoretical models and experimental measurements defying a complete understanding. At the heart of the xd dilemma seems to be the a N Pll potential. One unex- pected observation is that omitting the Pll [6], or reducing its magnitude [7] brings model calculations more in line with data around the resonance region. At TRIUMF progress towards reconciling this problem has been achieved by Jennings and Rinat [8] who calculated the effect of higher order r a N N terms which seem to offset these PI1 effects thereby restoring the agreement between theory and exper- iment. Ferreira et al. [9] have also concluded that short-range A-N interactions can account for some discrepancies observed between cross-section and vector analyzing power measurements and theoretical calculations.

At lower energies, effectively outside the dominance of the P 3 , the Pll sensitivity it amplified thereby presenting a more suitable arena in which to investigate this contribution. A program is un- derway a t TRIUMF to measure analyzing powers at 50 MeV. The experimental layout of these mea- surements performed in the TRIUMF M13 channel is shown in Fig. 2 and consists of wire chambers (PCOS, W2-5), scintillators ( ~ 1 4 , B1, B2, A-D, E l , EZ), polarized target (PDT), and spectrometer magnets (Q2, BT). The polarized target material consists of deutrated butanol arranged on a ladder system with an identical H-butanol background target so that the spectra observed from both materials can be sequentially measured at each angle. A comparison of the spectra allows the a d elastic reaction to be isolated. Calculating the relative yields for a d elastic scattering when the deuterium target is polarized positively (a+), negatively (a-), and when it is unpolarized (a0) provides the basis for the calculation of analyzing powers. For example, the vector analyzing power iTll, is given by :

where p~ is the average magnitude of the target vector ~olarization and b(iTl1) is a small correction factor to take into account unequal positive and negative target polarization values. Preliminary results for some of the iTll measurements, shown in Fig. 3, are compared with recent model predictions. In contrast to spin measurements at higher energies we find better agreement with model calculations that include the full Pll potential, rather than when it is omitted or suppressed. Since there is good agreement with the calculations of Jennings and Rinat [8] both here and with data a t higher energies it suggests that the remaining discrepancies between theory and experiment are caused not by the improper handling of the Pl1 but rather because of an incomplete description of other contributions. To further understand this system further measurements of vector and tensor analyzing powers are underway in both a + d and a-d systems so that other effects, such as Coulomb and charge symmetry breaking [lo], can be investigated.

Figure 2: Layout of the experiment in the TRIUMF M13 beamline.

COLLOQUE DE PHYSIQUE

REFERENCES

[I] S. Morioka and I.R. Afnan, Phys. Rev. C26, 1148 (1982).

[2] I.R. Afnan and R.J. McLeod, Phys. Rev. C31, 1821 (1985).

[3] M.P. Locher and M.E. Sainio, Phys. Lett. 24B, 227 (1983).

[4] Y.M. Shin et al., TRIUMF proposal 360, PSI proposal R-87-04.

[5] N.R. Stevenson and Y.M. Shin, Phys. Rev. (236, 1221 (1987).

[6] B. Blankleider and I.R. Afnan, Phys. Rev. C31, 1380 (1985).

[7] H. Garcilazo, Phys. Rev. C35, 1804 (1987).

[8] B.K. Jennings and A.S. Rinat, Nucl. Phys. A485, 421 (1988).

[9] E. Ferreira et al., Phys. Rev. C40, 1750 (1989).

[lo] J. Frohlich et al., Nucl. Phys. A435, 738 (1985).

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(deg.)

Figure 3: Preliminary iTll measurements in x+d elastic scattering a t 50 MeV.