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Nuclear Science Division

Relativistic Nuclear Collisions

Program Head: John Arrington

The Relativistic Nuclear Collisions (RNC) program in the Nuclear Science Division at LBNL carries out experimental research in Nuclear Physics, with participation in STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, and in the ALICE experiment at the Large Hadron Collider (LHC) at CERN. Our interests focus mainly on two areas of Quantum Chromo-dynamics (QCD): the nature of strongly interacting matter and exploration of the QCD phase diagram; and the spin structure of the nucleon.

High Energy Heavy Ion Collisions

Numerical QCD calculations on the lattice indicate that, above a temperature of about 170 MeV, strongly interacting nuclear matter dissolves into a plasma of quarks and gluons, called the Quark-Gluon Plasma (QGP). The QGP filled the universe 10 microseconds after the Big Bang, and may exist today in the cores of neutron stars. However, the QGP can only be studied experimentally via the collision of heavy atomic nuclear at very high energy, and both RHIC and the LHC have vigorous, ongoing programs in this area. The picture of the QGP that has emerged from these experimental studies is quite different from initial theoretical expectations of a rather featureless gas of non-interacting quarks and gluons at high temperature. Rather, the QGP displays complex and fascinating collective behavior, whose basic constituents (“quasi-particles”) are quite different from undressed quarks and gluons and appear to interact with the lowest specific viscosity allowed by nature. Experimental study of the QGP has attracted attention from neighboring fields of physics, including condensed matter, plasma physics, and even string theory.

The RNC has played a central role in the STAR experiment at RHIC throughout its history, constructing the STAR central detector (the Time Projection Chamber, or TPC), and leading fundamental discoveries by STAR about the QGP, in particular the collective dynamical behavior of the QGP and the interaction and modification of hard QCD jets in the QGP. The latter effect, known as “jet quenching”, was predicted by our theory colleagues in the NSD. More recently, members of the RNC STAR group have turned their attention to questions about the behavior of heavy quarks in the QGP, as well as to an experimental search for the QGP critical point via a beam energy scan (BES), utilizing the tremendous flexibility of the RHIC collider complex to provide collisions of heavy nuclei at center of mass energy per nucleon pair from 5 to 200 GeV.

The RNC also plays a key role in the ALICE experiment at the LHC. The RNC, together with collaborators at other US institutions, led the construction and commissioning of the ALICE EMCal, a large electromagnetic calorimeter that enables ALICE to carry out unique measurements of jets and other hard probes in nuclear collisions. To date there have been two successful heavy ion running periods at the LHC. Members of the RNC are focusing on the analysis with ALICE data of jets (shown in the picture above), photons, and high momentum light meson and heavy flavor production which together will provide deep insight into the nature of jet quenching at the LHC.

Spin of the Nucleon

A profound, long-standing problem in QCD is the nature of the spin of the nucleon. The quark and anti-quark spins are known to carry only a small fraction of the proton spin, whereas the distribution of the remaining fraction amongst gluon spin and orbital angular momenta is not well understood. RHIC is not only the world’s first and most flexible heavy ion collider, but is also the world’s only polarized proton collider, enabling unique studies of proton spin structure. Members of the RNC are focusing on world-leading measurements of nucleon spin structure and spin in QCD, through measurements with STAR of jets and other probes.

Computing

Analyzing the large amount of data accumulated by the STAR and ALICE detectors is a formidable challenge. RNC provides significant computing capabilities for both experiments, primarily through the PDSF analysis center at NERSC, and is the Host Institution for the ALICE-USA computing project. Grid technologies for highly distributed computing play a key role in efficient usage of these resources, as does the high capacity HPSS mass storage system at NERSC. RNC is collaborating with NERSC to develop the next generation of computing facility for large collider detectors, through exploratory usage of massively interconnected computing facilities at NERSC.
Experimental Upgrades and Future Projects

Looking Ahead

Looking to the future, the RNC is playing a central role in the Heavy Flavor Tracker (HFT) upgrade for STAR. The HFT, an ultra-high precision silicon vertex detector for heavy flavor measurements, is based on next-generation MAPS sensors together with a revolutionary mechanical support structure that was developed by RNC. Upgrades to the ALICE detector, for the period 2017 and beyond, are currently under active discussion. The RNC also has strong interest and is an active participant in the development of the Electron-Ion Collider project.

Nuclear Theory

Program Head: Feng Yuan

The Nuclear Theory Program at LBNL covers a wide spectrum of nuclear physics, ranging from high-energy heavy-ion physics to nuclear structure, nuclear astrophysics and QCD in hadronic physics. The research program is particularly focused on the study of the physical properties of nuclear matter under extreme conditions- from the formation of the quark-gluon plasma in high-energy heavy-ion collisions to dense matter in neutron stars, from effective field theories for few-body systems to macroscopic properties of super-deformed nuclei and production of superheavy elements. We seek theoretical understanding of properties of nuclear matter under different conditions from both fundamental and effective theories of the strong interaction by developing phenomenological methods for the analysis and interpretation of experimental data.

Neutrinos and Nuclear Astrophysics

Program Head: Alan Poon

The Neutrinos and Nuclear Astrophysics program focuses its research on the properties of neutrinos.  The program has been a major player in key international experiments of the last two decades, including the Sudbury Neutrino Observatory (SNO) and KamLAND.  SNO was recognized in the Nobel Prize of Physics in 2015, and, along with the KamLAND experiment, in the Breakthrough Prize in Fundamental Physics in 2016.  Our current program has significant roles in three current-generation neutrinoless double-beta decay experiments: CUORE, MAJORANA DEMONSTRATOR, and SNO+; and in the next-generation experiments and beyond: CUPID, LEGEND, and THEIA.   The observation of neutrinoless double-beta decay would answer the fundamental question of whether neutrinos are their own antiparticles.  The program operates a Low-Background Counting Facility to qualify the purity of materials used in these experiments and other low-background experiments in the community. We are a partner in KATRIN, currently the most sensitive direct neutrino mass experiment.
 
The Neutrinos and Nuclear Astrophysics program is part of the Institute of Nuclear and Particle Astrophysics (INPA).  INPA is sponsored by the Nuclear Science Division and the Physics Division at Berkeley Lab. While participants in INPA are predominantly from these two Divisions, the Physics Department and the Space Sciences Laboratory at UC Berkeley are also represented.  The research areas at the Institute are broad and have a strong interdisciplinary flavor, yet a common purpose connects them – to use the science and the technologies of nuclear physics and particle physics to address fundamental questions bearing on the nature of the universe: past, present, and future.  Research and education are combined not only through the participation of students and postdoctoral researchers, but also at the high school level through summer programs for teachers and students.

Accelerator-Based Low-Energy Research

Program Head: Paul Fallon

The study of atomic nuclei is central to our understanding of the world around us.  Comprising 99.9% of the visible matter in the universe nuclei are, in multiple aspects, central to fundamental questions in physics, such as our understanding of the origin of the elements and how complex many-body quantum systems organize.  Their properties depend sensitively on the number of protons (Z) and neutrons (N), and much of what we know about them comes from the measurement and characterization of their excitation modes and energy levels. Understanding nuclear properties, their role within the cosmos, and more broadly their application for society, requires measurements on elements and isotopes at the limits of their mass (N+Z), charge (Z), and β-decay stability (N-Z).

Our program is focused on measuring the properties of the heaviest elements to establish the limits of their existence and their structure, and on investigating the effects of weakly bound nucleons and large neutron excess (or deficiency) on nuclear shell structure and collective degrees of freedom. We also carry out a wide range of experimental and nuclear data evaluation activities to address the needs of the basic and applied nuclear science community.

We develop, construct, and utilize advanced instrumentation for this work including the gamma-ray tracking arrays GRETINA and GRETA, and the heavy element mass separators BGS and FIONA.

Research is carried out locally at the 88-Inch Cyclotron (LBNL’s high-intensity stable-beam accelerator), at the ATLAS/CARIBU facility, and at the rare-isotope beam facilities FRIB at Michigan State University, the Rare Isotope Beam Factory (RIBF) at RIKEN, and the ISAC Facility at TRIUMF. Our program has close connections to the U.C. Berkeley Nuclear Engineering Department and the 88-Inch Cyclotron is an ideal facility for attracting and training students in basic nuclear and applied nuclear science.

Details on our research activities can be found at: