Session E11: Minisymposium: Connections Between Nuclear PDFs and Nuclear Structure II

Tagged DIS measurements of high-momentum bound nucleons

For over 50 years, deep inelastic scattering (DIS) has been used to study the quark structure of hadronic matter. One of the most puzzling discoveries made by DIS is the difference in quark structure between a nucleus and its component nucleons. This difference, called the EMC effect, is attributed to the modification of the internal structure of nucleons bound in nuclei. Forty years after its discovery, there remains no consensus on the origin of the EMC effect. While existing inclusive DIS data have characterized the EMC effect over a wide range of nuclei, they have limited ability to discriminate between different hypotheses of bound nucleon modification. In the emerging technique of tagged DIS (TDIS), the DIS reaction off of a bound nucleon is "tagged" by the detection of a second spectator nucleon, which carries information on the initial configuration of the nucleus. TDIS measurements are sensitive to the momentum dependence of bound nucleon structure, and can discriminate between different EMC effect hypotheses. This talk will summarize current and future TDIS experiments, including preliminary results from measurements of the structure of high-momentum protons bound in deuterium.   

Modification of Quark-Gluon Distributions in Nuclei by Correlated Nucleons Pairs

Analyzing data from nuclear lepton Deep-Inelastic Scattering, Drell-Yan processes, and W and Z boson production, we show that factorizing nuclear structure into quasi-free nucleons and universally modified close-proximity Short Range Correlated (SRC) nucleon pairs allows us to fully describe the quark-gluon structure of nuclei down to very-low momentum fractions. This is the first combined extraction of the universal distribution of quarks and gluons inside SRC pairs, and the nucleus-specific fraction of nucleons in SRC pairs. The extracted SRC fractions are in good agreement with previous nuclear structure calculations and measurements. This extraction of nuclear structure information from quark-gluon distributions thus represents a significant development toward understanding the structure of nuclei in terms of their fundamental quark-gluon constituents. At the same time such obtained nuclear PDFs are in very good agreement with fits using conventional framework of global nuclear PDF analysis.   

Short-Range Correlation Studies in Inverse Kinematics to access unstable nuclei

Nucleon-nucleon short-range correlations (SRC) in atomic nuclei have traditionally been investigated using electron scattering. Surprisingly, we have observed indications that protons become more correlated in neutron-rich nuclei. To overcome fundamental limitations of scattering in normal kinematics on stable targets, we have extended our studies to experiments in inverse kinematics at JINR and GSI-FAIR by scattering high energy ion beams off a proton target. By utilizing nucleon-knockout reactions in fully exclusive kinematics at JINR, we gain unique insight into SRC properties in 12C. Moreover, the R3B S522 experiment at GSI-FAIR studied SRCs for the first time in the very neutron-rich short-lived nucleus 16C. In this talk, I will give an overview of the experimental efforts at JINR and GSI-FAIR and present results for SRC studies in 12C and 16C from inverse kinematics experiments.   

Angular Distribution of Dimuons from Drell-Yan Production in p+Fe Interactions at 120 GeV Beam Energy

In the naive Drell--Yan model, the angular distribution of the Drell--Yan process has zero $cos2phi$ modulation, where $phi$ denotes the azimuthal angle of dimuons in the Collins--Soper frame. However, a sizable $cos 2phi$ dependence was observed in pion-induced Drell--Yan experiments, such as the NA10 and E615 experiments. The Boer--Mulders function is a transverse momentum dependent distribution that represents the correlation between the transverse spin and the transverse momentum of the quark. A non-zero Boer--Mulders function can produce a $cos2phi$ modulation in Drell--Yan angular distribution. We present an update on the measurement of the $cos2phi$ modulation of proton-induced Drell--Yan dimuons produced at the SeaQuest/E906 Fermilab experiment, using a 120 GeV proton beam on an Fe beam dump upstream of the dimuon spectrometer. Our analysis of SeaQuest data provides an opportunity to extract the Boer--Mulders function for the Fe nucleus. To extract the Drell-Yan signal, we developed both an improved method for subtracting the combinatoric background, and also an iterative technique for unfolding the angular distributions in order to remove inefficiencies, acceptance effects and bin migration. The unfolding technique improves the response matrix based on the outcome of the previous unfolding step, leading to good convergence without exaggeration of uncertainties.