Determining the helicity structure of the nucleon at the Electron Ion Collider in China

Understanding how sea quarks behave inside a nucleon is one of the most important physics goals of the proposed Electron-Ion Collider in China (EicC), which is designed to have a 3.5 GeV polarized electron beam (80% polarization) colliding with a 20 GeV polarized proton beam (70% polarization) at instantaneous luminosity of 2 × 1033cm−2s−1. A specific topic at EicC is to understand the polarization of individual quarks inside a longitudinally polarized nucleon. The potential of various future EicC data, including the inclusive and semi-inclusive deep inelastic scattering data from both doubly polarized electron-proton and electron-3He collisions, to reduce the uncertainties of parton helicity distributions is explored at the next-to-leading order in QCD, using the Error PDF Updating Method Package (ePump) which is based on the Hessian profiling method. We show that the semi-inclusive data are well able to provide good separation between flavour distributions, and to constrain their uncertainties in the x > 0.005 region, especially when electron-3He collisions, acting as effective electron-neutron collisions, are taken into account. To enable this study, we have generated a Hessian representation of the DSSV14 set of PDF replicas, named DSSV14H PDFs.

The Sivers asymmetry in hadronic dijet production

We study the single spin asymmetry in the back-to-back dijet production in transversely polarized proton-proton collisions. Such an asymmetry is generated by the Sivers functions in the incoming polarized proton. We propose a QCD formalism in terms of the transverse momentum dependent parton distribution functions, which allow us to resum the large logarithms that arise in the perturbative calculations. We make predictions for the Sivers asymmetry of hadronic dijet production at the kinematic region that is relevant to the experiment at the Relativistic Heavy Ion Collider (RHIC). We further compute the spin asymmetries in the selected positive and negative jet charge bins, to separate the contributions from u- and d-quark Sivers functions. We find that both the sign and size of our numerical results are roughly consistent with the preliminary results from the STAR collaboration at the RHIC.

Polarized proton spin filter for epithermal neutrons based on dynamic nuclear polarization using photo-excited triplet electron spins

To polarize neutrons with energy beyond 0.1 eV, we developed a novel polarized proton spin filter based on dynamic nuclear polarization using photo-excited triplet electron spins. The spin filter consists of a single crystal of naphthalene doped with deuterated pentacene and has a size of $\varnothing15\times4 \, {\rm mm}^3$, allowing it to cover a wide beam diameter. It was operated in 0.35 T and at 90 K. We succeeded in polarizing neutrons in the energy range 0.1–10 eV using a RIKEN accelerator-driven compact neutron source. The averaged values of the proton and neutron polarization were $0.250\pm0.050$ and $0.076\pm0.015$, respectively.

Exploring nucleon structure and hadronization with dihadrons and hadrons in jets at STAR

Over the last decade, theoretical and experimental engagement of transverse-spin phenomena has unlocked tantalizing opportunities for new insights into nucleon structure and hadronization. Observables such as hadrons in jets and dihadron correlations from polarized proton collisions provide access to the transversity distribution function at a range of x complementary to existing semi-inclusive deep inelastic scattering (SIDIS) experiments but at a much higher range of Q 2. Moreover, these two observables give access through two different factorization frameworks–transverse-momentum-dependent (TMD) and collinear–enabling a unique path to address questions concerning factorization-breaking and the universality of TMD functions. Data collected by STAR have revealed the first observations of transverse single-spin asymmetries in the azimuthal distributions of dihadron correlations and hadrons within jets from polarized proton collisions at both s = 500 GeV and 200 GeV. The STAR 200 GeV dihadron data have recently been included in global analyses that for the first time include SIDIS, e + e −, and p + p data to extract the transversity distribution. The STAR hadron-in-jet data provide a unique opportunity to illuminate longstanding questions: Do factorization and universality extend to the TMD picture in proton-proton collisions, e.g. through the Collins mechanism? How do TMD functions evolve with changing kinematics? The STAR dihadron and hadron-in-jet data will be presented and discussed in context with the recent global analyses and model calculations.