Session FG: Mini-Symposium on the Spin Structure of the Nucleon III

Measurement of the net $\Lambda$ polarization in heavy-ion collisions from STAR

Non-central heavy-ion collisions provide a system with non-zero total angular momentum which can be transferred, in part, to the fireball via baryon stopping. It has been predicted that this angular momentum will lead to a net spin of emitted particles through coupling with the bulk material. Due to its parity violating decay the $\Lambda$ is self-analyzing, which allows us to associate the daughter proton decay direction with $\Lambda$ spin. Ultimately this allows us to use them as a probe of net-particle spin. I will present preliminary STAR measurements of the net $\Lambda$ polarization from Au+Au collisions at 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV.   

Sea Quark Contribution to the Nucleon Spin

The widespread belief is that proton and neutron, commonly known as nucleons, are each composed of three elementary particles called quarks. But in the last two decades experiments showed that the mass, momentum, spin and electromagnetic properties of the three quarks do not add up to the known proprieties of the nucleon. Theory predicts that a ``sea'' of virtual pairs of quarks and anti-quarks, along with the strong force carrier particles called gluons, should account for the difference. I will present ongoing work on the preparation of an experiment to isolate the contributions of the sea to the nucleon spin using semi-inclusive deep inelastic scattering technique at the Thomas Jefferson National Accelerator Facility.   

Accessing the Sea Quark Orbital Angular Momentum Contribution to the Proton's Spin

Past experimental measurements have shown that about half of the spin of the proton comes from the spin of its quarks and gluons. More recent theoretical and experimental efforts focus on how the orbital angular momentum (OAM) of the quarks and gluons contribute to the proton's spin. QCD calculations and indirect measurements indicate that the OAM contribution of the sea quarks could be large, but direct measurements remain inconclusive. Measurements accessing the sea quark Sivers distribution will provide a direct probe of the sea quark OAM contribution. The upcoming E1039 experiment at Fermilab will access this distribution via the Drell-Yan process using a 120 GeV unpolarized proton beam directed on a polarized target. At E1039 kinematics where the u-ubar process dominates the Drell-Yan cross section ($x_{Target}\,$=$\,$0.1$\,-\,$0.35), the measured Drell-Yan single-spin asymmetry should be zero if the ubar quark carries zero angular momentum, and vice versa. The E1039 experiment is a continuation of the currently running Seaquest experiment.   

Reconstruction of single-shell states for mid-heavy Sn isotopes

A great exact truncation to construct single-shell states for the shell model description of mid-heavy Sn isotopes is offered in the framework of the Drexel University shell model approach. It is based on the occurrence of only one-column Young diagrams in building the multi-shell model states [1]. This truncation allows us to calculate the coefficient of fractional parentage (CFP) for the most stable Sn isotopes, e.g., $^{116,118,120}$Sn, by reducing the calculation requirements. An application to $^{116,118,120}$Sn isotopes in the \textit{sdgh}-shell is presented.   

Exploring Nucleon Axial Structure at MicroBooNE

MicroBooNE is a new 170-ton liquid-argon time projection chamber located on the Booster neutrino beam line at Fermilab, being commissioned in 2015. Using a beam of neutrinos with a mean energy of approximately 1 GeV, MicroBooNE will explore neutrino oscillations, as well as measure a variety of neutrino-nucleon and neutrino-nucleus interaction cross sections in argon. One important goal is the measurement of the neutral-current elastic (NCE) $\nu p$ scattering cross section, $\nu p \rightarrow \nu p$. For $Q^2 < 1$ GeV$^2$, the NCE cross section is dominated by the proton elastic axial form factor, $G_A^Z(Q^2)$. The strangeness contribution to the axial form factor, $G_A^s(Q^2)$, is unknown below $Q^2=0.45$ GeV$^2$, and is of great interest since the strangeness contribution to the proton spin can be determined from it: $\Delta S = G_A^s(Q^2=0)$. This talk will discuss the capability of MicroBooNE to measure $G_A^s(Q^2)$, and present the current status of the experiment.   

Neutron Transverse Spin Structure using BigBite and Super BigBite Spectrometers in Jefferson Lab's Hall A

The Super BigBite Spectrometer (SBS), currently under construction for experiments in Jefferson Lab's Hall A, is a novel magnetic spectrometer designed for the detection of charged and neutral particles at forward scattering angles with large solid angle and momentum acceptance at the highest luminosities achievable using JLab's 11 GeV electron beam. Originally designed to facilitate precision measurements of nucleon electromagnetic form factors at large momentum transfers, the capabilities of SBS also make it suitable for the investigation of the nucleon's three-dimensional spin structure in semi-inclusive deep-inelastic scattering (SIDIS). The precision study of novel polarization phenomena such as target transverse single-spin asymmetries (SSA) in SIDIS, requires measurements with high statistical precision and wide coverage of the 4-dimensional kinematic phase space of the SIDIS process. This talk will present an overview of approved JLab experiment E12-09-018, that will use the SBS, the existing BigBite spectrometer and an upgraded high-luminosity polarized $^3$He target to map the transverse spin structure of the neutron in the valence region with unprecedented precision.   

An Opportunity for a Future Forward Jet Single Spin Asymmetry Measurements in p+p Collisions at RHIC

We explored possible measurements of transverse single spin asymmetries (SSA) in forward jet productions at RHIC, in transversely polarized $p+p$ collisions. Forward jets produced in $p+p$ carry a non-vanishing SSA, as observed by the AnDY experiment at RHIC. Although jet SSA is at 10$^{-3}$ level, it was interpreted due to cancellations of opposite sign contributions from valence up and down-quarks. This left-right bias in $p+p$ collision originates from a correlation between parton's transverse-momentum and the nucleon's transverse spin (Sivers effect), in co-linear twist-3 factorization framework, it can be related to the first moment of the Sivers distribution measured in semi-inclusive DIS. Gauge invariance predicts that the Sivers distribution is process-dependent, and the asymmetries of jet production in $p+p$ receive opposite sign contributions compared to those in semi-inclusive DIS. Through simulation studies, we show that valance quark contributions to jet production can be effectively flavor-ehanced with additional requirements on jet properties. Taking RHIC proposed new large acceptance jet-detector as an example, we show that with additional forward coverage, future jet SSA measurements at RHIC can be used to access valence quark Sivers effect at high-x.