Session F4: Nuclear Physics and Fusion

Polarization of prompt $J/\psi$ and $\Upsilon$(1S) production in the color evaporation model using the $k_T$-factorization approach

Quarkonium prodcution is strong test of high energy QCD phenomenology but its production mechanism is still not well understood. The color evaporation model (CEM) and Nonrelativistic QCD (NRQCD) can describe production yields rather well but spin-related measurements like the polarization are stronger tests. So far no model can describe the yields and the polarization simutaneously. In this talk, I will outline the recent challenges to NRQCD and present the first $p_T$-dependent prediction of the polarization of prompt $J/\psi$ and $\Upsilon$(1S) in the CEM using the $k_T$-factorization approach, which integrates over all color states and takes the off-shell properties of the incoming-gluons and feed down mechanism into account.   

Computing the Dimension 6 Chromomagnetic Contribution to the Neutron EDM using the Feynman-Hellmann Method and Lattice QCD

The universe is observed to be in a matter anti-matter asymmetric state, with an observed baryon dominance on the order of one part per billion. A necessary condition for the generation of this asymmetry is the violation of the combined symmetries of charge conjugation (C) and parity (P). CP violation within the standard model of particle physics is orders of magnitude too small to account for this asymmetry, leading to the search for beyond standard model sources. Beyond standard model sources of CP violation invariably give rise to new interactions between standard model particles that can, in principle, be detected. Lattice QCD is uniquely suited for investigating these contributions in the strong sector, as it allows a non-perturbative solution of the low-energy, strong coupling, region of QCD with fully controllable systematics. In this talk I will present Lattice QCD measurements of the leading beyond standard model contribution to the Neutron Electric Dipole moment using a method which has been shown to provide increased control over systematics as compared to previous measurement methods.   

A new paradigm about strong interaction and weak interaction

The paradigm of modern physics can be stated as three aspects: (1) Particle is the form of material existence in point space, fundamental particle is the smallest unit of nature, it is usually abstracted as point-like particle with mass, electricity, flavor, and color. (2) Particle takes classical relative displacement motion or quantum motion of duality of wave-particle in the form of continuity. (3) Particles have interaction between them by means of classical fields or quantum fields. This paradigm of physics can be called the particle model of modern physics. This author assumes that, fundamental matter flavor and color don't exist in the form of particle, instead, they exist in the form of volume field. Such that, a new paradigm of strong and weak interaction is proposed: (a) Volume field is the form of material existence in plane space, fundamental body (such as quark) is composed of fundamental particle (fundamental matter mass and electricity) and fundamental volume field (fundamental matter flavor and color) which exists in the form of limited volume. (b) Volume field takes absolute volume motion. (c) Volume fields have strong or weak interaction between them by means of overlapping volume fields. With these concepts under the new paradigm, this author further formulates a classic-like formula of color field force as classical static electric force, and by introducing deformation force of volume field, the author reinterprets the mechanism of ``asymptotic freedom'' and ``quark confinement'' in hadron.   

The Design and Performance of the ALICE ITS Upgrade

The ALICE (A Large Ion Collider Experiment) detector at the LHC (Large Hadron Collider) was designed to characterize a state of matter known as the QGP (Quark Gluon Plasma) formed in the aftermath of heavy-ion collisions. New detector technologies aim to more accurately measure the physics observables needed to address the many questions concerning the properties of this strongly interacting medium. An upgrade to the current ALICE ITS (Inner Tracking System) is scheduled for the next LHC run in 2021. Consisting of seven layers of silicon pixel detectors, the ITS upgrade will incorporate new MAPS (Monolithic Active Pixel Sensor) technology that reduces the material budget in the interaction region. The upgrade will improve resolution and tracking efficiency, particularly at low transverse momentum. These improvements are necessary to be able to precisely reconstruct the decay vertices of heavy flavor hadrons, which are an effective probe since they are produced in the early stages of the collision and therefore experience the full evolution of this strongly coupled medium. This talk will focus on the detector design and the expected physics capabilities of the ITS upgrade.   

Analysis of Lambda-Proton Elastic Scattering in CLAS

Lambda-Proton elastic scattering offers multiple insights on problems in nuclear physics. SU(3)-flavor symmetry implies a close agreement between the Lambda-proton and proton-proton scattering cross sections. The Lambda-Proton elastic scattering cross section can also illuminate the structure of neutron stars. A data-mining project was started using CLAS data taken to look for exotic quark matter with a high-energy photon beam on a long liquid hydrogen target. A Lambda produced in a process such as gamma p-->K+ Lambda can interact with a second proton inside the target before either decaying or leaving the target. The good angular acceptance and momentum resolution of CLAS make it well-suited for this type of analysis, even though it was not designed for a measurement such as this. The scattered Lambda can be found in the pi- proton invariant mass. The four-vector of the initial Lambda is then reconstructed in the process Xp-->Lambda p, which shows a strong peak at the Lambda mass with roughly twice the number of events as the existing world data sample. This observation opens up the possibility of other measurements using secondary beams of short-lived particles. This talk will discuss the current status of the analysis, and our plans for future work on this project.   

Simulation of Lambda-Proton Elastic Scattering in CLAS

The cross section for Lambda-Proton elastic scattering is complicated. The cross section formula is well-known, and depends on the numbers of detected events, beam particles, and target particles, the acceptance, and the detector and analysis efficiencies. For Lambda-Proton elastic scattering, the beam particle is a secondary particle with a short mean life, complicating this calculation. This study made use of the CLAS simulation program GSIM, which includes a complete description of the CLAS detector. The first step is to simulate the energy and angular spectrum of the beam Lambda. Also, the Lambda's short mean life makes it necessary to study the effect of its decay on the luminosity. The energy and angular spectrum of the beam Lambda is simulated with the process gamma p --> K+ Lambda. Using this energy and angular spectrum, we then determine the luminosity of our Lambda-Proton measurement by generating Lambdas based upon the simulated results, with a second pass of the simulation. We can then determine the geometrical acceptance for the Lambda-Proton elastic scattering process with a third pass of the simulation. This talk will discuss the status of the simulation project, and will present the initial results of the Lambda spectrum simulation.   

Proton Spectra of Fixed-Target Au + Au $\sqrt{s_{NN}}$ = 4.5 GeV collisions

In this talk, results are presented from the fixed-target (FXT) run at STAR which is an extension of the RHIC beam energy scan (BES). The BES program was proposed to look for turn-off signatures of the quark-gluon plasma and search for a possible QCD critical point. We shall present the FXT study of Au + Au collisions at $\sqrt{s_{NN}} $ = 4.5 GeV. An overview of particle identification for proton spectra is discussed. The details of several analysis techniques are presented including detector performance and background corrections for FXT in STAR. The results demonstrate that STAR has a good particle identification and event reconstruction in the fixed-target configuration.   

Pion spectra from Al+Au collisions at $\sqrt{s_{NN}}$ = 4.9 GeV}

The STAR experiment at RHIC has demonstrated to have good event reconstruction and particle identification capabilities for fixed-target (FXT) configurations. The goal of the FXT program is to extend the Beam Energy Scan II (BES-II) to energies below 7 GeV as well as baryon chemical potential $\mu_{B}$ up to 720 MeV and, based on the results from BES-I, improve our understanding of a transition between a QGP and a hadronic gas. Using the time projection chamber (TPC) and time of flight (TOF) detectors along with particle identification (PID) techniques, pion spectra are measured from the events in the Al+Au FXT runs taken in 2015. Understanding the yields of the pions and the shape of the spectra are useful for a variety of analyses. These spectra are presented across different centralities ranging from central to peripheral types of collisions at various rapidities.