Measurement Of Transverse Spin Transfer To ? And (?) In Transversely Polarized Proton-Proton Collisions At RHIC-STAR

Spin is one of the intrinsic property for elementany particles and it is an important approach to study the strong interaction.In the study of the strong interaction,the spin structure of the nucleon is one of the most popular fields.In the parton model,spin structures of the nucleon with longitudinal and transverse polarizations are de-scribed by the helicity distribution and the transversity distribution,respectively.We have obtained rich knowledge about the helicity distribution after decades of study.The measurements of the helicity distributions for the value quarks with flavors u and d are already precise,relatively.The pictures of sea quarks are also obtained based on the accumulation of experimental data in recent years.The contribution from the gluon spin has been investigated actively and the recent global analysis indicated significant contribution to proton spin.The study of the transversity distribution began later than the helicity distribu-tion due to its chiral-odd nature.This nature makes the transversity distribution can only be probed in processes with chirality flipped.Hadron production is usually re-quired in these kinds of process,which means the effect of transverse polarization is determined both of the transversity distribution and the transversely polarized frag-mentation function.The transverse polarization effect is studied via the spin asym-metry measurement in SIDIS and hadron-hadron collisions.The transversity distribu-tion and the fragmentation function can be extracted simultaneously from SIDIS and hadron-hadron collisions data,together with the fragmentation function measured in e+e-annihilation.So far,the transversity distributions of value quarks with flavors u and d have been extracted initially.For sea quarks,especially the strange quark,there is no any constraints,yet.It is expected that the measurement of the transverse spin transfer,DTT,to A and A in transversely polarized proton-proton collisions can provide the information of the transversity distribution and the transversely polarized fragmentation function of the strange sea quark.The Relativistic Heavy Ion Collider,RHIC,is the first and only collider running the polarized proton-proton collisions.It provides unique opportunity to study the spin structure of the nucleon.A number of measurements on the spin effect have been made at RHIC,such as the study on the spin of sea quarks via the measure-ment of W boson single spin asymmetry and the gluon polarization via the jet double spin asymmetry.In this thesis,we report the first measurement of the transverse spin transfer,DTT to A and A hyperons in transversely polarized proton-proton collisions with ?s = 200 GeV taken with the STAR detectors in 2012.In this analysis,the jet-patch triggered data sample is selected in order to improve the sampling efficiency for events with high momenta transferred.Firstly,we intro-duce the quality assurance process of the data sample.Then A and A hyperons were reconstructed via their weak decay channels,??p?-and ??p?+.We also re-constructed jets from the fragmenting parton in order to determine the polarization direction of the fragmenting parton.Thus the polarization direction in each of the A(A)events was obtained via the correlation between hyperons and jets.We devel-oped and applied Cross-Ratio method in the process of extracting DTT and thus can-celed the detector acceptance and the relative luminosity ratio in the extraction.In this way,the systematic uncertainties from the relative luminosity ratio and detector acceptance were cancelled.We also used different approaches to check the extraction method and obtained good agreement between them.The simulation sample was generated with PYTHIA and GEANT in order to help us check and understand the reconstruction.The trigger bias was studied and discussed based on the simulation data sample together with the theoretical model calculation.The contribution from feed-down was firstly studied in spin transfer measurement.Other systematic uncer-tainties in our measurement were also studied,which include contributions from the pile-up effect and the estimation of the background fraction.The hyperon sample covers transverse momenta pT up to 8 GeV/c and the pseu-dorapidity range |?|<1.2,We measured the DTT dependence on hyperon pT.In the highest pT bin,the results cure found to be DTT = 0.031 ± 0.033(stat.)± 0.008(syst.)for A and DTT =-0.034 ± 0.040(stat.)± 0.009(syst.)for ? with(pT)= 6.7GeV/c and...