Medium Energy Physics
The goals of the Medium Energy Physics group in the Physics Division of Argonne National Laboratory are to test our understanding of the structure of hadrons and the structure of nuclei, and to develop and exploit new technologies for high-impact applications in nuclear physics, tests of fundamental symmetries and other national priorities. The key components of the program are described below.
JLAB ExperimentsAt Jefferson Lab (JLab) we are focusing on the structure of the hadrons, exotic structures in nuclei, and the study of the Standard Model. More specifically, we lead a variety of experiments at JLab including measurements of elastic form factors the proton and neutron, studies of exotic configurations of matter in nuclei, color transparency in proton, pion, and rho production, high energy photoreactions, and tests of the Standard Model. These experiments are or will be performed in Hall A, Hall B and Hall C. In the JLab 6 GeV era, the MEP group proposed and ran 23 experiments. As of 2013, have 14 approved experiments that will run after the 12 GeV upgrade (beginning in 2014).
Our earlier measurements included elastic e-p scattering, A(e,e'p), A(e,e'pi), and A(e,e'K) reactions as well as a series of cross section and polarization measurements of real photon reactions (gamma+d-->p+n and gamma+N-->pi+N). More recently, we completed a search for color transparency, led experiments to study two-photon exchange effects and the proton form factors, and studied the connection between the modification of quark distributions in nuclei and the presence of high-density, highly-excited two-nucleon configurations in nuclei.
Our initial 12 GeV program begins in Hall A with proton form factor measurements, measurements of the d-quark to u-quark ratio at large Bjorken-x in the proton (through comparison of inclusive scattering from 3H and 3He), and studies of short-range correlations and their isospin dependence in 3H and 3He. Measurements in Hall B include further studies of color transparency in rho production, quark propagation in nuclei, and GPD/TMD studies with an emphasis on strange quark contributions. In Hall C, we will study Charge-Symmetry Violation, the EMC effect, and short-range correlations in nuclei.
Trapping and Probing Atoms of Rare Isotopes with Laser Light
We are developing new methods and improvements to existing techniques for controlling atoms of rare isotopes, which we are using to study new problems in nuclear physics and to develop novel applications based on Atom Trap Trace Analysis (ATTA). See the ATTA homepage for details on the many nuclear physics applications developed by the Argonne MEP group.
Tests of Fundamental Symmetries
The optical trapping method is being applied to test the time reversal symmetry, and thereby search for new physics beyond the standard model. Other Standard Model tests we are currently pursuing include the PV-DIS program at Jefferson Lab. We are currently leading the program of testing the Standard Model via parity violation in deep inelastic scattering (PV-DIS) using both the currently available 6 GeV beam (E05-007) and at the future 12 GeV upgrade of JLab. In addition, we are participating in searches for physics beyond the standard model in parity-violating moller scattering.
Drell-Yan Measurements of Proton Structure
We are conducting a series of fixed target Drell-Yan experiments designed to measure the quark and antiquark structure of the nucleon and the modifications to that structure which occur when the nucleon is embedded in a nucleus. With these measurements, we are also able to quantify the energy loss of a colored parton (quark) travelling through cold, strongly-interacting matter.
The first of these expeirments, E866/NuSea took place at Fermilab. The primary focus of this experiment was to measured the asymmetry of down and up antiquarks in the nucleon sea using Drell-Yan di-muons produced in 800 GeV proton interactions with hydrogen and deuterium targets. It has also made measurements of the suppression of the production of J/Psi's in nuclei over a broad range in xF and pT as well as angular distributions for Drell-Yan, J/Psi and Upsilon production.
To extend these measurements to larger Bjorken-x, E906/Drell-Yan has been approved by Fermilab. It will use a 120 GeV proton beam extracted from the Fermilab Main Injector. In addition to extending the down to up antiquark measurements, the experiment will also examine the modifications to the antiquark structure of the proton from nuclear binding. This experiment currently being assembled at Fermilab. It is expected to be comissioned in 2010 and collect data for two years.
Following the completion of E906/Drell-Yan, we have stage-1 approved experiments at FNAL to explore polarized proton-induced Drell-Yan experiments with a polarized target and/or a polarized beam (E1027 and E1039).
HERMES: The HERMES experiment measured the interaction of polarized 25-30 GeV positrons with polarized internal targets of hydrogen, deuterium and Helium-3. The measurements focus on the deep inelastic spin structure functions of the nucleon. In 2002, the transverse polarized hydrogen target was installed. One of the goals is to provide the first measurement of the transversity structure function of the proton, The polarization of the quark sea will be measured using asymmetries of events with charged hadrons detected in coincidence with the scattered positrons. A list of HERMES publications is available on SPIRES.