Current Research / Experiments

 

Belle / HERMES / PHENIX / G0 / RCS / nPOL / JLab Transversity
Muon g-2 / MuLan / MuCap / nEDM

 

Strong Interaction Physics
     
Belle Belle
KEK - Tsukuba, Japan
Matthias Grosse-Perdekamp, David Hertzog
   
The Japanese B-factory KEKB in Tsukuba has produced an enormous data sample for e+e- - annihilation into quark-anti quark pairs. We utilize these data to measure subtle spin effects in the fragmentation process of the quarks. The knowledge of spin effects in quark fragmentation is important input to our program to study transverse proton spin structure in the HERMES and PHENIX experiments, and at Jefferson Laboratory. In addition, we carry out analysis in Belle which will lead to improved knowledge of the contribution from hadronic loops to the anomalous magnetic moment of the muon. This analysis is critical input for the interpretation of the
g-2 experiment E821 at Brookhaven National Laboratory.
     
HERMES HERMES
DESY - Hamburg, Germany
Naomi Makins (analysis coordinator)
   
HERMES is an experiment investigating the quark-gluon structure of matter: we study the spin structure of the nucleon. By nucleon, we refer to the protons and neutrons which are the fundamental components of all atomic nuclei. However, if you look a little closer, you find that these nucleons are not as fundamental as they might appear... in fact, they are bound states, composite systems composed of even more fundamental constituents, namely quarks and gluons, held together by the strong force. And all of these particles have an important property called spin. The quarks have spin 1/2, the gluons have spin 1, and the nucleon itself has spin 1/2. The question we seek to answer at HERMES goes roughly like this: "How do the constituents of the nucleon conspire to produce its overall spin of 1/2?" Our first data-taking run started in 1995, and ended in September, 2000. HERMES run 2 started in 2001 and will last up to summer 2007.
[ref]
     
PHENIX PHENIX
BNL - Long Island, NY
Jen-Chieh Peng, Matthias Grosse-Perdekamp (deputy spokesperson)
   
Our understanding of proton sub-structure is closely connected to the physics of the quantum chromodynamics (QCD) vacuum at high energy densities: the properties of the proton cannot be understood without taking into account the complex "sea" of virtual quark, anti-quark pairs and gluons inside the proton. In PHENIX, we study the sub-structure of protons in proton-nucleus and polarized proton-proton collisions leading to a very broad and rigorous program in the physics of hadrons and QCD as the theory describing their interactions and structure.
     
G0 G0
Jefferson Lab - Newport News, VA
Doug Beck (spokesperson), Peter Kammel, Steve Williamson (project manager)
   
The goal of the G0 experiment is to learn more about the quark substructure of protons and neutrons (nucleons). Our interest is in the distributions of charge and magnetization in the nucleon and how it is built up out of the different types of quarks. We are particularly interested in whether these distributions have any contribution from strange quarks as this type exists only "virtually" in nucleons as the result of the quantum mechanical interplay between mass and energy. [ref]
     
RCS RCS (Real Photon Scattering)
Jefferson Lab - Newport News, VA
Alan Nathan (co-spokesperson)
   
The Real Compton Scattering (RCS) experiment measured the cross sections for RCS from the proton in the energy range 3-6 GeV and over a wide angular range, and measured the longitudinal and transverse components of the polarization transfer to the recoil proton at a single kinematic point. Together, these measurements test models of the reaction mechanism and determine new structure functions of the proton that are related to the same nonforward parton densities that determine the elastic electron scattering form factors and the parton densities. [ref]
     
  nPOL
MAX-lab - Lund, Sweden
Alan Nathan
   
We are attempting to measure the electromagnetic polarizabilities of the neutron by deuteron elastic Compton scattering. By covering a wide range of angles and energies we will reduce the model dependence while still having a smaller statistical uncertainty than previous measurements. Recent theoretical developments in accounting for meson exchange currents inside the deuteron and improvement of the Baldin sum rule should provide us with the ability to accurately determine the electric and magnetic polarizabilities.
     
JLab JLab Transversity
Jefferson Lab - Newport News, VA
Jen-Chieh Peng (co-spokesperson of E-06-010)
   
The goal of the JLab Transversity experiment is to provide the first measurement of the neutron transverse target single spin asymmetry (SSA) complementary to the recent HERMES and COMPASS measurements on the proton and deuteron. SSA data on transversely polarized neutrons will provide crucial new information on the flavor dependence of various structure and fragmentation functions probed by the SSA experiments. This first measurement focuses on the valence quark region. Data from this experiment, when combined with the world proton and deuteron data, will provide powerful constraints on the transversity distributions and Sivers function for both u-quark and d-quark in the valence region. [ref]

Fundamental Symmetries

     
muon g-2 Muon g-2
BNL - Long Island, NY
Paul Debevec, Dave Hertzog (co-spokesperson), Peter Kammel
   
The muon anomalous magnetic moment, measured by the E821 Collaboration to a precision of 0.54 ppm, represents a stringent test of the Standard Model. Current (2007) comparison with theory indicates a 3.4 standard deviation, arguably the strongest experimental hint of new physics apart from the recent revolution in the neutrino sector. The implications are profound as the magnitude of the deviation locks squarely with predictions by many supersymmetric models and implies mass scales that are quite accessible at the Large Hadron Collider. Toward a more sensitive experiment, we have strongly pushed the new E969 experiment at BNL, which aims to reduce the experimental uncertainty by a factor of 2 - 3. The UIUC group has designed a new beamline concept and has built prototype W/SciFi calorimeters as part of our R & D efforts for E969.
     
MuLan MuLan
PSI - Villigen, Switzerland
Paul Debevec, Dave Hertzog (co-spokesperson), Peter Kammel
   
The Muon Lifetime Analysis (MuLan) experiment will measure the positive muon lifetime to a precision of one part per million (ppm). The muon lifetime provides the most precise determination of the Fermi coupling constant, which is one of the fundamental inputs to the Standard Model. Recent advances in theory have reduced the theoretical uncertainty on the Fermi coupling constant as calculated from the muon lifetime to a few tenths of a ppm. The remaining uncertainty on the Fermi constant is entirely experimental, and is dominated by the uncertainty on the muon lifetime. The MuLan experiment will use an innovative pulsed beam, a symmetric detector, and modern data-taking methods to reduce the uncertainty on the muon lifetime to 1 ppm.
     
MuCap MuCap
PSI - Villigen, Switzerland
Dave Hertzog, Peter Kammel (co-spokesperson)
   
The goal of the µCap experiment is a 1% precision measurement of the muon capture rate on the proton. From the capture rate the pseudoscalar form factor gP of the nucleon will be extracted with 7% precision. This basic quantity is predicted theoretically with high precision, but the experimental situation is quite controversial. The new experiment should yield an unambiguous value for gP and a sensitive test of the chiral symmetry of QCD at low energies.
     
EDM Neutron Electric Dipole Moment
SNS - Oak Ridge, Tennessee
Doug Beck, Jen-Chieh Peng, Steve Williamson
   
The possible existence of a non-zero electric dipole moment of the neutron is of great fundamental interest and directly impacts our understanding of the nature of electro-weak and strong interactions. The experimental search for this moment has the potential to reveal new sources of T and CP violation and to challenge calcuations that propose extensions to the Standard Model. In addition, the small value for the neutron EDM continues to raise the issue of why the strength of the CP-violating terms in the QCD Lagrangian are so small. This seems to suggest the existence of a new fundamental symmetry that blocks strong CP-violating processes.

NSF
This material is based upon work supported by the National Science Foundation under Grant No. NSF PHY 06-01067.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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