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 major thrusts of the program are:

Jefferson Lab (JLab) Program

Hall A HRSAt Jefferson Lab (JLab) we are focusing on the structure of the hadrons, exotic features of nuclei, as well as the study of the Standard Model. In particular, we are involved in a variety of experiments at JLab, including measurements of elastic form factors of the pion and the proton, the search for exotic states of matter in nuclei, high energy photoreactions, the effect of color transparency in rho production, and tests of the Standard Model. These experiments are or will be performed in Hall A, Hall B and Hall C.

Completed experiments include measurements of (e,e'p), (e,e'pi), and (e,e'K) reactions and a series of cross section and polarization measurements of real photon reactions (gamma+d-->p+n and gamma+N-->pi+N). We have recently completed data taking for a proton form factor measurement, and for a search for color transparency. We are leaders of the next high momentum transfer elastic nucleon form factor measurements to take place at Jefferson Lab in Hall A in the Super Bigbite program and in Hall C measuring GEn through recoil polarimetry.

We are currently involved with several parity-violation programs at Jefferson Lab. These include the measurement of the neutron skin thickenss of 208Pb, PREX-II, and of 48Ca, CREX, using elastic elastic nuclear scattering. These experiments will provide precise data to constrain the neutron-rich nuclear matter equation of state and will impact on our understanding of neutron star structure and the observable neutron star merger graviational wave signals from LIGO. We have completed experiments measuring in parity-violating deep inelastic scattering (PV-DIS) with the 6 GeV beam and are developing the future 12 GeV measurements with a new high intensity, large acceptance solenoidal spectrometer, SoLID. These measurements will reveal the valence parton flavor structure of the proton and neutron in a new light as well as provide tests of the weak interaction in the standard model. We are also involved with MOLLER, which will provide one of the most precise measurements of sin2θW ever performed and search for new interactions which would be beyond the reach of even the LHC.

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 taking data at Fermilab. Following the completion of E906/Drell-Yan, we are exploring possibilities of continuing the Drell-Yan scattering program using the 50 GeV proton ring at the J-PARC Nuclear and Particle Physics Facility.

Electron-Ion Collider

We have been involved in developing the case for the EIC for several years. More recently, we have initiated a major effort, in collaboration with the HEP division, to apply our combined expertise in nuclear physics, colliders, and detector and accelerator design to enhance the physics case and capabilities of a future EIC.

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).

.He468Time reversal Symmetry

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.

Paul E. Reimer
2 April 2018