Abnormal neutron star matter at ultrahigh densities

We consider three models, based on the mean field and sigma models, all of which fit the saturation properties and the symmetry energy of nuclear matter. None of the models yields an abnormal state of neutron star matter at supemuclear density even when pion condensation is taken into account.     

Few-body form factor measurements in Hall A of JLab

There is an active program of few-body form factor measurements in Hall A of Thomas Jefferson National Accelerator Facility (Jefferson Laboratory). Recent measurements of the deuteron elastic electric, A(Q²), and magnetic, B(Q²), structure functions will be presented. Planned measurements of the form factors of ³He and ⁴He will also be discussed.     

Laser Compton polarimetry at JLab and MAMI

For modern parity violation experiments it is crucial to measure and monitor the electron beam polarization continuously. In the recent years different high-luminosity concepts, for precision Compton backscattering polarimetry, have been developed, to be used at modern CW electron beam accelerator facilities. As Compton backscattering polarimetry is free of intrinsic systematic uncertainties, it can be a superior alternative to other polarimetry techniques such as M?ller and Mott scattering. State-of-the-art high-luminosity Compton backscattering designs currently in use and under development at JLab and Mainz are compared to each other. The latest results from the Mainz A4 Compton polarimeter are presented.     

The JLab polarization transfer measurements of proton elastic form factor

The ratio of the electric and magnetic proton form factors,G _Ep G _Mp , has been obtained in two Hall A experiments, from measurements of the longitudinal and transverse polarizations of the recoil proton,P _l andP _t , in the elastic scattering of polarized electrons, . Together these experiments cover theQ ² range of 0.5 to 5.6 GeV². A new experiment is currently being prepared, to extend theQ ² range to 9 GeV² in Hall C.     

Relativistic constituent quark model and experiments at JLab

Within the relativistic-quantum-mechanics version developed by the present authors in their previous studies, the pion electromagnetic form factor is calculated in the region of high momentum transfers reached and planned to be reached in experiments at the Thomas Jefferson Laboratory (JLab). An asymptotic expansion was obtained for the pion form factor for Q ² → ∞. This expansion describes well existing experimental values and the results of a QCD simulation of future experiments at JLab. It is shown that the region of experiments at JLab is an asymptotic region for the relativistic constituent quark model and that the behavior of the pion form factor, F _π (Q ²)Q ² = const, can be obtained within this model.     

Charge densities of the neutron and proton

A model-independent analysis of the infinite-momentum-frame charge density of partons in the transverse plane is presented for the nucleon. We find that the neutron-parton charge density is negative at the center, so that the square of the transverse charge radius is positive, in contrast with many expectations. Additionally, the proton's central d quark charge density is larger than that of the u quark by about 30%. The proton (neutron) charge density has a long range positively (negatively) charged component.     

Observations of neutron stars and the equation of state of matter at high densities

We summarize the constraints on the equation of state of high-density nuclear matter derived from neutron star observations. The most stringent constraints are provided by the largest mass, the largest radius, the highest rotational frequency, and the maximum surface gravity observed for neutron stars. The combination of these constraints allows only nuclear equations of state which are quite stiff.     

Kaon electro-production on protons at JLab in Hall A

The elementary reaction of kaon exclusive electro-production on protons has been studied in a broad kinematical range at Jefferson Lab in Hall A. Data have been taken at different values of the invariant center-of-mass energy W in the range W=1.8-2.2 GeV, for two values of the transferred 4-momentum Q² =1.9 and 2.4 (GeV/c)². Each kinematics was measured at different electron beam energies so as to separate the longitudinal (L) and transverse (T) contributions to the cross-section. The LT interference term has also been measured for a limited number of kinematics. The preliminary data are compared to results of different models developed in the framework of hadronic field and Regge theories.     

Transition Form Factors at JLab: Status and Outlook

The measurements of exclusive single-meson and double-pion electro-production cross sections off the proton to study nucleon resonances will be extended to higher momentum transfers with the CLAS12 detector and the energy upgraded CEBAF beam. Based on new theoretical developments to extract and interpret the electromagnetic transition form factors and on the experience gained from the most recent results, the newly formed collaboration of experimentalists and theorists shall enable us to provide unprecedented high- precision data, high-quality analyses, and state-of-the-art model and QCD based calculations in a Q2 domain up to 10 GeV2. For the first time nucleon resonance structures will be studied at still unexplored distance scales, where the dressed quark contributions are the dominating degrees of freedom and their strong interaction is responsible for the ground and excited nucleon state formation. These studies also open up a promising opportunity to understand the origin of more than 98% of the nucleon mass that is created by strong fields predominantly at these distance scales by dressing the current quarks.     

Dosimetry measurements at the fast neutron therapy facility in Seattle

The fast neutron therapy facility at the University of Washington has been in routine clinical use for 25 years. 50.5 MeV protons produce neutrons in a beryllium target mounted on an isocentric gantry. Beam shaping is accomplished with a 40-leaf collimator. Dosimetry measurements for treatment planning and calibration are performed with tissue equivalent ion chambers. A layered phantom of alternating Solid Water^® and Plastic Water^® slabs has been developed for rapid dose verification measurements. The neutron field in the room has been used for radiation testing of electronic components.     

Nucleon transition form factors at JLab: status and outlook

The measurements of exclusive single-meson and double-pion electro-production cross sections off the proton to study nucleon resonances will be extended to higher momentum transfers with the CLAS12 detector and the energy upgraded CEBAF beam. Based on new theoretical developments to extract and interpret the electromagnetic transition form factors and on the experience gained from the most recent results, the newly formed collaboration of experimentalists and theorists shall enable us to provide unprecedented high-precision data, high-quality analyses, and state-of-the-art model and QCD based calculations in a Q~2 domain up to 10 GeV~2. For the first time nucleon resonance structures will be studied at still unexplored distance scales, where the dressed quark contributions are the dominating degrees of freedom and their strong interaction is responsible for the ground and excited nucleon state formation. These studies also open up a promising opportunity to understand the origin of more than 98% of the nucleon mass that is created by strong fields predominantly at these distance scales by dressing the current quarks.     

Double-spin asymmetries in electron-nucleon scattering in Halls B and C at JLab

Three experiments at JLab have measured the double polarization asymmetries ) in the nucleon resonance region, using polarized electron beams incident on polarized proton and deuteron targets. The analysis for the first experiment, eg1a in Hall B, is nearly finished and preliminary values of the spin structure function g₁(x, Q²) and the first moment (x) have been extracted. The other two experiments, one in Hall B and one in Hall C, are still analysing data. Some results are presented.Received: 1 November 2002, Published online: 15 July 2003PACS: 24.70.+s Polarization phenomena in reactions     

Magnetoresistance measurements in Al-Ge alloys after neutron irradiation at 4.6 K

The influence of different structural defects, introduced by irradiation in a series of AlGe alloys is established by measuring the longitudinal magnetoresistance. The validity of Kohler's rule is absolute for both pure and alloyed samples that have been irradiated by neutrons at 4.6 K, while the rule breaks down after annealing at different temperatures.The origin of the breakdown of Kohler's rule appears to be the anisotropic scattering of the electrons on the clusters formed after annealing. This scattering depends on the size of the clusters which varies with the concentration of foreign atoms.     

Tests of the Electroweak Theory at LEP

LEP offers a rich choice of tests of the electroweak theory such as the measurement of hadronic and leptonic cross sections, leptonic forward-backward asymmetries, τ polarization asymmetries, partial widths and forward-backward asymmetries of heavy quark flavours, of the inclusive qq charge asymmetry and of final state radiation in hadronic events. We discuss experimental aspects of these measurements and their theoretical parametrization and summarize the results available so far. We present several analyses which reveal specific aspects of the results, such as their constraints on Standard Model parameters and on new particles, the sensitivity to deviations from the Standard Model multiplet structure and an analysis in a framework which provides a model independent search for new physics.     

The Electroweak Transition at Hot and Density Condition

The effective potential of the Weinbefg-Salam (WS) model is calculated at finite temperatureand in the chemical potential of top quarks according to the grand canonical ensembletemperature field theory. The electroweak transition is studied at hot and density conditions.It is indicated that the symmetry restoring transition can take place either by increasing thetemperature or chemical potential of top quarks, but at high temperature and in the lowchemical potential the transition is of the first order, and it becomes the second order at acold density condition. The phase diagrams are showed.     

Electroweak tri-boson couplings at LEP II and beyond

Possible non-standard model couplings of electroweak vector bosons are studied inW pair production ine ⁺ e ^? collisions. Helicity amplitudes are calculated in a factorized formalism; the choice of helicity basis suggested by this formalism is shown to increase sensitivity of angular correlations to anomalous couplings. In the course of this analysis, the chi-squared test for finite data samples is more carefully formulated. BothCP-conserving andCP-violating couplings are considered.     

Symmetry energy at subsaturation densities and the neutron skin thickness of ~(208)Pb

The mass-dependent symmetry energy coefficients asym(A) has been extracted by analysing the heavy nuclear mass differences reducing the uncertainties as far as possible in our previous work.Taking advantage of the obtained symmetry energy coefficient asym(A) and the density profiles obtained by switching off the Coulomb interaction in208 Pb,we calculated the slope parameter L0.11 of the symmetry energy at the density of 0.11 fm-3.The calculated L0.11 ranges from 40.5 Me V to 60.3 Me V.The slope parameter L0.11 of the symmetry energy at the density of 0.11 fm-3is also calculated directly with Skyrme interactions for nuclear matter and is found to have a fine linear relation with the neutron skin thickness of208 Pb,which is the difference of the neutron and proton rms radii of the nucleus.With the linear relation the neutron skin thickness Rn pof208 Pb is predicted to be 0.15–0.21 fm.