| Nuclear Physics Group
Experimental Intermediate Energy Nuclear Physics Group
The intermediate energy group (R. Ransome and R. Gilman)
research is supported by the U. S. National
Science Foundation under grant PHY 06-52713. We investigate
strong QCD (mostly the structure of the proton and neutron), nuclear
structure, and physics beyond the standard model. We are mainly
involved in experiments at the Thomas Jefferson National
Accelerator Facility (JLAB)
6 GeV accelerator, CEBAF,
in Virginia (where I am currently the chair of the Users Group Board of
Directors) and at Fermilab, in Batavia Illinois.
Our JLab research is centered on studies of spin physics, studying
nucleons and subnucleonic effects in light nuclei using polarized
electron beams, targets, and recoil polarimeters. Our research at
Fermilab uses neutrino beams. We generally work in
international collaborations of 50 - 100
physicists from 10 - 20 institutions.
Our largest construction project, which has led to a significant
portion of our research program from the late 1990s through now, was
building the focal plane proton polarimeter in Jefferson
Lab Hall A, with colleagues from William & Mary and elsewhere.
The prject ws funded by the U. S. National Science Foundation, grants PHY
9213864 (C. F. Perdrisat, College of William & Mary, et al.),
and PHY 9213869 (R. Gilman, Rutgers University, et al.).
See Ron Gilman's Focal Plane
Polarimeter for CEBAF Hall A Home Page.
We are now involved in a much bigger project to build the MINERνA
experiment at Fermilab.
Following is a list of ongoing projects (most recent work first):
Following is a list of important experimental programs
from the past
- We are now in the construction phase for a major
nucleon and nuclei with neutrino beams at Fermilab.
The experiment is expected to run from about 2010 - 2012.
MINERVA home page.
- Fermilab experiment 906, expected
to run 2010 - 2011, will use the ``Drell-Yan'' process (q + antiquark
μ+μ-) on hydrogen, deuterium, and other targets
to investigate the
anti-u and anti-d
quark distributions in the proton, hadronization of quarks, etc.
- We are currently involved in detector upgrades for the
upcoming (late 2008-early 2009) ``Big Family'' round of polarized 3He
experiments in Jefferson Lab Hall A. One example is the
transversity experiment investigates the quark spin distributions
of the neutron,
when the neutron's spin orientation is perpendicular to the momentum
direction. The experiments inve.tigate a wide range of physics,
including the structure of 3He, two-photon exchange
effects, the color polarizibility of the neutron, etc
- In May 2008 we will run a new low Q2 proton form
experiment in Jefferson Lab Hall A, which will determine the form
unprecedented precision, investigating a range of issues including
proposed fine structures in the form factors, the isoscalar and
isovector form factors, the u and d quark form factors, the role of
strange quarks in the proton, the electric vs. magnetic radii of the
proton, and theoretical uncertainties in the hydrogren hyperfine
- We are currently running a series of experiments in
Jefferson Lab Hall C to investigate the proton electric and magnetic
distributions at high momentum transfer, to put experimental
constraints on the possible two-photon corrections to these
measurements, and to study high energy real Compton scattering on the
proton, which provides a complementary set of data on the quark
distributions in the proton.
- The Jefferson Lab Hall A 3He / two-proton
(ran mid 2007), in combination with our previous deuteron
photodisintegration results, investigates the quark structure of light
nuclei and the reaction mechanism in the difficult transition region,
where there are at present no good methods of solving QCD. (There is
recent promising work from ads/CFT.) The analysis is approaching final.
- The Jefferson Lab Hall A Li/B elastic scattering experiment
investigates the radii of these light nuclei. They are needed to anchor
isotope differences measured with atomis physics techniques, for
comparison to modern ab initio nuclear structure calculations.
- The Jefferson Lab Hall A 4He polarization
(most recent run in late 2006) investigates the issue of whether
it is sensible to consider nucleon properties to be modified in the
nuclear medium. The analysis is underway.
- The Jefferson Lab Hall A electron-deuteron elastic
(ran mid 2006) is intended to put effective
field theories derived from QCD, or relativity in conventional hadronic
on a firmer basis by resolving some issues in existing data sets.
Analysis is progressing.
- Measurements of low-energy deuteron photodisintegration,
run in 2006 in Jefferson Lab Hall A, show the limits in our ability to
describe reactions using hadronic degrees of freedom. The results are
- Proton charge distribution :
The probability of elastically scattering an electron from the proton
depends on the
proton charge and magnetic distributions.
These distributions also lead to an orientation of the proton's spin,
if the electron
spin is oriented along its momentum direction.
Previously, the best experiments, based on scattering probabilities,
charge and magnetic distributions of the proton are essentially the
Our measurements of the spin orientations are a superior technique, and
show a clear difference between the two distributions.
(Jones et al., Gayou et al., or see
E93-027 home page)
A new higher precision scattering probability measurement in which we
is in agreement with earlier data, indicating some difference in the
Both experiments are based on the idea that the electron and proton
by exchanging a single photon.
There is now excitement about the possibility of explaining the
between the techniques from two photon exchange. Two experiments are
currently running, the GEp-III/GEp-2g
experiments. The first pushes measurments to a much higher momentum
transfer / much finer resolution, while the second checks for possible
two-photon exchange effects.
- The proton charge distribution, in the
From the perspective that quarks make up the nucleon, the
interactions in the nucleus modify the quark distributions, and thus
charge and magnetic distributions, of the nucleon.
To some degree these effects are already incorporated
in the nucleon-nucleon force, and to date experiments have
largely put limits on possible effects; claims of modifications
have been controversial. In what are perhaps the cleanest measurements
to date, we have compared measurements of charge and magnetic
of the proton in the nucleus to those of the free proton, using the
proton spin technique.
The most complete theory suggests only about 2-3 % conventional
but our data show about 8 % effects. The 5 % difference is consistent
with estimates of changes in the charge and magnetic distributions.
(Strauch et al.)
- Deuteron photodisintegration experiments :
High-energy deuteron photodisintegration probes the quark structure
of the deuteron.
Over the past decade, we have shown that cross sections are consistent
with simple scaling rules expected from the quark picture. (Bochna et
Schulte et al.)
We have also performed the highest energy polarization measurements,
which further suggest the appropriateness of quark models. (Wijesooriya
et al., and Jiang et al.)
At present there are several contending quark models, all in
agreement with existingcross section data. Only two seem to have
qualitative predicting power for the polarization observables. To
further stress these models,
we measureed two proton disintegration in 3He.
See the 1999
experiments home page or the 2002 experiment
or the Gilman and Gross review article.
- Spin structure of the neutron (in 3He):
There has been a series of polarized 3He experiments,
looking at different aspects of the neutron spin structure (since the
two protons in 3He are largely coupled to spin 0).
Two examples follow.
- The extended Gerasimov-Drell-Hearn sum rule
was studied at moderate Q2 in 1998, followed by a very low Q2
measurement during 2003.
The sum rule (at Q2 = 0) relates the difference of total
spin-dependent scattering to the anomalous magnetic moment, and can be
from fundamental theories based on QCD over almost the entire range of Q2
= 0 to infinity.
We performed the first measurements in the difficult region of 0.1 to
which show a smooth variation from effective field theory region to the
See the E94-010 home page .
(Amarian et al.)
The data are also being used to determine the proton polarizibility,
the deformation due to the applied electromagnetic fields, and other
quantities of interest.
- The A1n asymmetry and g2n
were measured during 2001.
The first measurement gives the alignment of quark spins to the nucleon
We found for the first time that A1n is positive,
the quark and
nucleon spins are aligned, when the proton u quark has a large fraction
of the nucleon's
momentum. However, the proton d quark remains anti-aligned to the
(X. Zheng et al.)
- Elastic electron deuteron scattering :
These experiments measure the charge distributions of the deuteron.
Quantum mechanically, since the deuteron has spin 1, it has three
charge distribution, the electric, magnetic, and quadrupole
The JLab Hall C t20
experiment and the JLab Hall
A cross section experiment allowed
these quantities to be determined with good accuracy to high momentum
The experiments present clean indications that understanding nuclear
structure at large momentum requires special relativisitic effects.
Unlike the photodisintegration measurements, the electron elastic
is not sensitive to the underlying quarks.
Experimental Nuclear Structure Physics Group
Gerfried Kumbartzki maintains online documentation
spectrum analysis code SA .