| Extensive experimental and theoretical explorations over the last decades showed that nucleon is not just a simple system composed of 3 quarks bound by gluons,but more complex.To understand how the properties of these colored building blocks are related to the basic properties of the nucleon like its mass,its spin or its charge,a full understanding of three dimensional nucleon structure is required.In addition to the longitudinal momentum fraction,the intrinsic transverse motion of partons should also be considered.The transverse momentum dependent parton distribution functions(TMDs)are distribution densities to find a parton carrying a longitudinal momentum fraction x and transverse momentum k⊥ inside a nucleon.TMDs are essential to access the three dimensional images of nucleons.At the leading twist,there are eight independent TMDs in terms of the polarization states of quark and nucleon,one of which is BoerMulders function,h1⊥(x,k⊥2).Boer-Mulders fu1ction signifies the relation between the transverse momentum and transverse spin of the quark in an unpolarized nucleon.Boer-Mulders function can be accessed from the ν which is the cosφ modulation coefficient of di-lepton angular distribution in the Drell-Yan process.At leading order,the coefficient is proportional to the product of quark and anti-quark Boer-Mulders functions—one for each initial state hadron.By now,angular distributions have been measured in pion induced Drell-Yan proce.ss like NA10 experiment and E615 experiment,as well as proton induced Drell-Yan process like E866/NuSea experiment.The angular distribution in proton induced Drell-Yan process has only been measured by E866/NuSea experiment with 800 GeV proton beam so far.E906/SeaQuest experiment will present another set of data points:we use high statistics data from 120 GeV proton beam reacting with LH2(proton)and LD2(deuteron)targets at E906/SeaQuest experiment in year 2014-2015 to perform dimuon angular distribution measurements in the proton induced Drell-Yan process.Compared with E866/NuSea,E906/SeaQuest uses lower beam energy covering larger Bjorken-x region.The measurements from both LH2 and LD2 targets make it possible to investigate flavor dependence of Boer-Mulders function.Compared to LH2 target,the additional neutron in LD2 target increases the sensitivity to d under the assumption of iso-spin symmetry,which puts constriants on the u and d flavor dependence.At E906/SeaQuest experiment,dimuon tracks are reconstructed by hits collected from the tracking system.Dimuon selection criteria is applied afterwards to remove background.The remaining dimuons are composed of several sources including charmonium decay.Drell-Yan process,random coincidence combination and empty flask reaction.Those dinuons not related to Drell-Yan process are subtracted.To obtain the two dimensional(cosθ.o)angular distribution,where θ and o are polar angle and azimuthal angle in Collins-Soper frame respectively,detector acceptance and rate dependent tracking efficiency are corrected.Detector acceptance is studied by the ratio of Two MC simulations.with one representing Drell-Ya.n events at generator level and another one representing detector level operated by GEANT4 packages.Rate dependent tracking efficiency depends on beam intensity,which is correlated with measurable drift chamber oceupaney,so it can be interpreted as functions of drift chamler occupaney,and corrected accordingly.Two dimensional(cosθ,φ)angular distribution fitting is performed via unbinned maximum likelihood method and the angular distribution coefficients λ,μ and ν are extracted,where ν is the cos2ν modulation coefficient.proportional to Boer-Mulders function.The angular distribution results for LH2 data are:μ=0.007±0.080(stat.)±0.049(syst.),ν=0.208±0.050(stat.)±0.024(syst.)with λ being fixed to 1.For LD2 data are:μ=-0.110±0.063(stat.)±0.054(syst.),ν=0.158±0.041(stat.)±0.035(syst)with λ being fixed to 1.The obtained results of the polar angle dependence μ from E906/SeaQuest are consistent with E866/NuSea within uncertainties.The obtained results of the azimuthal angular dependence v for both LH2 and LD2 data have been found to be larger than E866/NuSea results in the measured transverse momentum ranges,at the similar level as NA10 and E165 experiments,indicating there might be other nechanisim(e.g.QCD effect)contributing to the cos2φ angular dependence.These results play an important role in constraining the extraction of Boer-Mulders funciton.The results of LH2 and LD2 are consistent within uncertainty,indicating similar Boer-Mulders funcitons for u and d,as predicted by various models like lattice QCD model and quark-spectator-diquark model.In addition to the angular distribution analysis,we also perform a study on Λ polarization simulation in semi-inclusive deep inelastic scattering(SIDIS)process.SIDIS is a golden process to investigate the three dimensional image of the spin related parton structure of nucleons.In the lepton-nucleon scattering.A polarization can be measured through its self-analyzing weak decay Λ→pπ-,making it an ideal candidate for probing the polarized parton distribution functions(PDFs)and the polarized fragmentation functions(FFs).Λ production and reconstruction is simulated under 3.5 GeV×20 GeV e-p collision at electron-ion collider in China(EicC).In the framework constructed by EicC fast simulation,predictions based on two parameterized models and statistical projections based on one month data taking is given for Λ spontaneous transverse polarization,providing valuable insights into future research prospects. |
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