ЯДРА
STATUS OF THE INVESTIGATION OF THE SPIN STRUCTURE OF d, 3H, AND 3He AT VBLHE USING POLARIZED AND UNPOLARIZED DEUTERON BEAM
© 2008 M. Janek1),2)*, V. P. Ladygin1)**, L. S. Azhgirey1), T. Uesaka3), Yu. V. Gurchin1), M. Hatano4), K. Itoh5), A. Yu. Isupov1), J.-T. Karachuk1),6), H. Kato4), T. Kawabata3), V. A. Krasnov1),7), A. N. Khrenov1), A. S. Kiselev1), V. A. Kizka1), J. Kliman1),8), A. K. Kurilkin1), P. K. Kurilkin1), N. B. Ladygina1), A. N. Livanov1),7), Y. Maeda3), A. I. Malakhov1), V. Matousek8), M. Morhach1),8), J. Nishikawa5), Yu. K. Pilipenko1), T. Ohnishi9), H. Okamura10), S. M. Piyadin1), S. G. Reznikov1), T. Saito4), S. Sakaguchi3), H. Sakai3),4), N. Sakamoto9), S. Sakoda4), Y. Sasamoto3), Y. Satou11), K. Sekiguchi9), K. Suda3), M. A. Shikhalev1), A. Tamii12), I. Turzo8), N. Uchigashima4), T. A. Vasiliev1), K.Yako4), L. S. Zolin1)
Received March 14, 2008
The investigation of the spin structure of d, 3H, and 3He has been performed at RIKEN acceleration research facility and VBLHE. Vector Ay and tensor Ayy, Axx, Axz analyzing powers for the dd ^ 3Hen and dd ^ 3Hp are presented at 270 MeV. The mirror channels (3Hen and 3Hp) are compared to each other in order to find possible manifestation of charge symmetry breaking. The preliminary results on the polarization observables for dd ^ 3Hp at 200 MeV are also presented. The obtained data are compared with One-Nucleon-Exchange calculations. As a byproduct, dd ^ pX and dí2C ^ pX breakup reactions are investigated at 140, 200, and 270 MeV. The experimental data on dp elastic scattering were obtained at 270, 880, and 2000 MeV at Nuclotron. The polarization of deuteron beam was measured at 270 MeV at Internal Target Station. The preliminary data on the vector Ay and tensor Ayy, Axx analyzing powers for
the dp elastic scattering at 880 MeV are presented. The calculations on Ay, Ayy, and Axx analyzing powers for the dp elastic scattering at 880 MeV were performed in the framework of multiple-scattering model.
PACS:24.70.+s, 25.10.+s, 21.45.-v
'Joint Institute for Nuclear Research, Dubna, Russia.
2)P.J.Safarik University, Kosice, Slovakia.
3)Center for Nuclear Study, University of Tokyo, Japan.
4)Department of Physics, University of Tokyo, Japan.
5)Department of Physics, Saitama University, Urawa, Japan.
6)Advanced Research Institute for Electrical Engineering, Bucharest, Romania.
7)Institute for Nuclear Research, Russian Academy of Sciences, Moscow.
8)Instituteof Physics, Slovak Academy of Sciences, Bratislava.
9)RIKEN (the Institute for Physical and Chemical Research), Saitama, Japan.
10)CYRIC, Tohoku University, Sendai, Japan. n)Department of Physics, Tokyo Institute of Technology,
Japan.
12)Research Center for Nuclear Physics, Osaka University, Ibaraki, Japan.
E-mail: janek@sunhe.jinr.ru E-mail: ladygin@sunhe.jinr.ru
1. INTRODUCTION
To describe the attributes of a few-nucleon systems, the different models of NN potentials (CD-Bonn, Nijmegen, AV-18, etc.) are used. They reproduce data on the nucleon—nucleon scattering up to 350 MeV very well. It was investigated that the binding energy of the three-nucleon bound systems and also data on nonpolarized dp elastic and breakup reaction cannot be described based only on NN potentials. Binding energy of three-nucleon systems and also data on nonpolarized deuteron proton reaction can be described, if three-nucleon forces (3NF) are included into calculations [1]. But, the inclusion of 3NF does not improve description of polarization observables for deuteron—proton reactions. Problem can be in inadequate description of spin structure of 3NF, poor knowledge of wave functions at short
1525
distances or in relativistic effects which can play substantial role above the pion threshold.
The fundamental degrees of freedom begin to play a role at the internucleonic distances comparable with the size of the nucleon. The constituent counting rules (CCR) [2] works at high energies s and large transverse momenta pT. These rules predict the dependence of the cross section of the binary reactions at the fixed scattering angle in the c.m.s. as a power-law in s.
The tensor analyzing power T20 in deuteron breakup with proton emission at zero angle has been measured recently up to internal momenta k ~ ~ 1 GeV/c [3] defined in the light-cone dynamics [4]. Neither considering of the additional mechanisms, nor taking into account non-nucleonic degrees of freedom in the deuteron reproduce the T20 data in the whole range of k. The measurements of the tensor analyzing power Ayy in deuteron breakup on nuclear targets at large transverse momenta of protons at 9 GeV/c [5], have shown a significant variation of Ayy versus the transverse proton momentum at a fixed value of the longitudinal proton momentum. This finding indicates that the deuteron structure may depend on two variables.
Another interest of few-nucleon systems is the investigation of charge symmetry breaking affected by strong interaction. Mass splitting [6], differences in nucleon—nucleon scattering lengths [7], p—u [8] or n—n—n' mixing [9] are affected quark mass difference. The ground state of mirror nuclei would have the same binding energy, if the charge symmetry holds. The difference in binding energies of 3H and 3He with correction on electromagnetic effect is about 70 keV. The contribution of p—u mixing fills this gap, but not completely.
Three-nucleon forces, non-nucleonic degrees of freedom, relativistic effects and charge symmetry breaking can be investigated in experiments in which the light nuclei are participating.
2. ANALYZING POWERS AT 140, 200, AND 270 MeV
The experiment with polarized deuteron beam was performed at RIKEN Accelerator Research Facility (RARF). One can find the detailed description of the experiment in [10].
2.1. Analyzing Powers for the dd — 3Hen
anddd — 3Hp Reactions at 200 and270MeV
The angular dependence of the vector Ay and tensor Ayy, Axx, and Axz analyzing powers for the
dd — 3Hen and dd — 3Hp reactions at 270 and 200 MeV are presented in Figs. 1a and 16. The errors of the analyzing powers include both the statistical and systematic errors due to the uncertainty in the beam polarization.
The negative tensor analyzing powers can be understood in terms of the ratio of the D- and S-wave component of the 3He wave function by means of ONE calculations. It has been found [11] that the tensor analyzing powers due to polarization of the deuteron beam are sensitive to the ratio of the D- and S-wave component of the 3He (3H) and deuteron wave function, when 3He (3H) is emitted in the forward and backward directions in the c.m., respectively.
The solid, dashed, and dotted curves in Figs. 1 a and 16 are the results of nonrelativistic ONE calculations [12] using Urbana [ 13], Paris [14], and RSC [15] (with the parametrization from [16]) wave functions of3He. The Paris parametrization [17] was applied for the deuteron wave function.
The negative sign of the tensor analyzing powers Ayy and Axx at small scattering angles reflects the positive sign of the ratio of the D/S-wave component of the 3He wave function in the momentum space. However, the trend of the tensor analyzing powers Ayy and Axx at the angles below 15° in the c.m. is opposite to the ONE calculations.
The strong disagreement of the experimental data from the nonrelativistic ONE calculations is observed at angles larger than 15° in the c.m. The discrepancy between the data and the calculations shown in Fig. 1 can be explained by the reaction mechanism which differs from ONE (A-isobar excitation, ...) and/or by the nonadequate description of the short-range 3He spin structure. Our data on the vector analyzing power Ay have values of ^—0.35 at the angles larger than 50°, while ONE predicts vanishing vector analyzing powers. Thus, our data have clearly indicated that the additional processes are important in this angular region.
The analysis of the experimental data on the cross sections for the dp — pd and dd — 3Hen reactions [18] has shown that non-nucleonic degrees of freedom can occur already at Td ~ 500 MeV. On the other hand, the discrepancy between the data on the tensor analyzing powers and ONE calculations [12] can be caused by the relativistic effects. Relativity in 3He wave function was taken into account in [10] by the minimal relativization scheme [4]. But, this approximation does not allow to reproduce Ayy data. The structure of 3He can be more complicated and depends on more than one variable as in the case of the deuteron where the strong dependence of the spin structure on two variables was observed [ 19].
^c.m.' deg
Fig. 1. The results on the vector Ay and tensor Ayy, Axx, and Axz analyzing powers (a)for the dd ^ 3Hp (filled symbols) and dd ^ 3Hen (open symbols) reactions at energy 270 MeV, (b) for the dd ^ 3Hp reaction at energy 200 MeV. The curves are explained in the text.
The results on the analyzing powers differences for the 3Hen—3Hp channels, AT-t, are shown in Fig. 2 as a function of the scattering angle in c.m.s. The AT-t values demonstrate no dependence on the scattering angle for all the analyzing powers. Therefore, the differences of the analyzing powers AT-t in Fig. 2 were fitted by constants. The averaged values of AT-t are comparable with zero within the achieved experimental accuracy. Therefore, one can conclude that the effect of CSB at the nuclear level in the analyzing
powers of the dd ^ 3Hp and dd ^ 3Hen reactions at 270 MeV, has not been observed. This confirms the results of the earlier experiments performed at lower energies [20].
2.2. Analyzing Power for the dd — p3 H and dd — pX Reactions at 270 MeV
The experimental results on the vector Ay and tensor Ayy, Axx, and Axz analyzing powers for the
dd — p3 H reaction at energy 270 MeV are presented by the filled symbols in Fig. 3a. The solid, dashed, and dotted curves are the results of ONE calculations using Paris [17], Bonn B [21], and Bonn C [21] deuteron wave fu
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