| Spin as a fundamental degree of freedom of the particle is a powerful tool to study the strong interaction. The spin physics is always important in particle physics. In particular, the spin structure of nucleon is one of the hot topics in this area. There are still many unsolved problems in this area. One of these problem is the strange sea quark's spin structure in nucleon. At first, the information about the spin structure of nucleon were mainly from polarized lepton-hadron deep inelastic scattering(DIS). In these experiments, people use longitudinal polarized lepton beam strike the polarized target and measure the polarized nucleon structure function and its first moment. Com-bined these results with the data from hyperon's decay and the SU(3) flavor symmetry, people can get the contribution from different quark flavor to the total spin of nucleon,△U,△D and△S. So far, a lot of this kind of experiments had been done and a vast body of data had been collected. The results show that strange sea quark's contribution is negative,△S< 0. Recently, HERMES experiment had measured the contribution from strange sea quark to nucleon from semi-inclusive deep inelastic scattering(SIDIS) more directly. The results may show that△S> 0. This is not consistent with the result from inclusive deep inelastic scattering. These situations indicate that our knowledge about the spin structure of sea quark in nucleon is still very limited. Therefore, the measurement of△S from other high energy reaction is become very important. A(A) hyperon has been studied extensively in different aspects of spin physics, because their polarization can be easily measured by their self-analyzing weak decay. The longitu-dinal polarization of A(A) hyperon has been studied in e+e- annihilation and lepton-nucleon deep inelastic scattering with polarized beam and/or target. In these reaction, the significant polarization has been measured. Recently detailed phenomenological study indicated that the longitudinal polarization of A is very sensitive to the polar-ized parton distribution of strange sea quark. Therefore, the polarization of A(A) in pp collision give us another method to study the polarization of sea quark in nucleon. The Relativistic Heavy Ion Collider(RHIC) at Brookhaven National Laboratory of America is also the first polarized high energy pp collider. This experiment pro-vides us a good opportunity to understand the spin structure of nucleon. Many related studies have been developed at RHIC recently. For example, measurement of the lon-gitudinal double spin asymmetry(ALL) of jets and hadrons which can give a constrain on the gluon's contribution to the spin of nucleon; measurement the longitudinal single spin asymmetry(AL) of W bosons which can give an insight about the polarized parton distribution functions of u, d, u and d quark. In this dissertation, we report the first measurement of longitudinal spin transfer DLL to A and A hyperons in proton-proton collisions at (?)=200GeV at the RHIC. In this measurement, we use the polarized pp collision data taken by STAR detector at 2005. The measurements cover pseudo-rapidity,η, in the range |η|< 1.2 and transverse momenta, pT, up to 4GeV/c. The longitudinal spin transfer is found to be DLL=-0.03±0.13(stat)±0.04(syst) for inclusive A and DLL= 0.12±0.08(stat)±0.03(syst) for inclusive A hyperons with (η)= 0.5 and (pT)= 3.7GeV/c. The dependence onηand pT is presented.In analysis, we used the data with three different triggers:MB trigger, HT trigger and JP trigger. The MB trigger data mainly covers low pT region, meanwhile the HT and JP trigger data can cover higher pT.In this dissertation, we report the reconstruc-tion of A and A for these three trigger data separately which include:data set selection, reconstruction method and Monte-Carlo simulation, etc. The longitudinal spin transfer DLL is determined from the asymmetry of reconstructed A and A counts with different beam polarization configuration. With this new analysis method we developed, the systematic uncertainty can be reduced because the detector acceptance mostly cancels. Then we give some cross checks to our analysis method and result with KS0 and simu-lation data. We also discussed the possible systematic uncertainty in this measurement, especially the uncertainty from pile-up effect and trigger bias. Then we give the result and a discussion of longitudinal spin transfer DLL to A and A at (?)=200GeV pp collision.On the other hand, the available experimental and theoretical studies about the polarization of hyperons in pp collisions mostly focused on the midrapidity region. The STAR experiment has proposed a detector upgrade in the near future, which may enable hyperon polarization measurement in the forward range of pp collisions. Com-pared with hyperons at midrapidity, the forward hyperons carry a larger momentum fraction of the beam and their polarizations may have different properties. Therefore, it is of practical importance to see the behaviors of hyperon polarization in this kine-matic region. In this thesis, we also study the longitudinal polarization of hyperons and antihyperons at forward pseudorapidity,2.5<η< 4, in singly polarized pp collisions at RHIC energies by using different parameterizations of the polarized parton densities and different models for polarized fragmentation functions. The results show that the∑+ polarization is able to distinguish different pictures on spin transfer in high energy fragmentation processes; and the polarization of∧and∧can provide sensitivity to the helicity distribution of strange sea quarks. The influence from beam remnant to hyperon polarization in the forward region is also discussed.
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