14632156
Plans for a Neutron EDM Experiment at SNS
The electric dipole moment of the neutron, leptons, and atoms provide a unique window to Physics Beyond the Standard Model. We are currently developing a new neutron EDM experiment (the nEDM Experiment) [4]. This experiment, which will be run at the 8.9 A Neutron Line at the Fundamental Neutron Physics Beamline (FNPB) at the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory, will search for the neutron EDM with a sensitivity two orders of magnitude better than the present limit. In this paper, the motivation for the experiment, the experimental method, and the present status of the experiment are discussed.
42563880
Parity Violating Electron Scattering on the Proton and Deuteron at Backward Angles
The parity violating asymmetry in quasielastic electron scattering from the deuteron at backward scattering angles has been recently measured for the first time. Combined with the previously performed similar measurement on the proton, this measurement provides a determination of both the proton's strange magnetic form factor G^(a)_(M) and the axial vector e-N form factor G^(a)_(A). A preliminary analysis indicates that G^(a)_(M) is slightly positive but consistent with zero and that G^(e)_(A)(T=1) is in substantial disagreement with the theoretical estimate.
121871688
Antiproton trapping in various helium media: report of the HELIUMTRAP experiment at LEAR
Abstract HELIUMTRAP (PS205) investigates the recently discovered anomalously long-lived states of antiprotons in various helium media. An overview is given of experiments stopping antiprotons in several phases of helium performed at LEAR in the last two years.
122256238
Kaonic hydrogen X-ray experiment at KEK
Abstract For the further understanding of the K -N interaction in the low energy region, we are performing a measurement of K − p X rays at KEK which adopts a new technique to improve the signal-to-background ratio (S/N); specifying the final state of the K − p reaction and using a gaseous hydrogen target (4 atm at 100 K). With this technique three orders of magnitude better S/N and one order higher statistics are expected as compared to previous experiments.
119214299
Effect of an electric field on superfluid helium scintillation produced by $\alpha$-particle sources
We report a study of the intensity and time dependence of scintillation produced by weak alpha particle sources in superfluid helium in the presence of an electric field (0 - 45 kV/cm) in the temperature range of 0.2 K to 1.1 K at the saturated vapor pressure. Both the prompt and the delayed components of the scintillation exhibit a reduction in intensity with the application of an electric field. The reduction in the intensity of the prompt component is well approximated by a linear dependence on the electric field strength with a reduction of 15% at 45 kV/cm. When analyzed using the Kramers theory of columnar recombination, this electric field dependence leads to the conclusion that roughly 40% of the scintillation results from species formed from atoms originally promoted to excited states and 60% from excimers created by ionization and subsequent recombination with the charges initially having a cylindrical Gaussian distribution about the alpha track of 60 nm radius. The intensity of the delayed component of the scintillation has a stronger dependence on the electric field strength and on temperature. The implications of these data on the mechanisms affecting scintillation in liquid helium are discussed.
14917200
Phase and density dependence of the delayed annihilation of metastable antiprotonic helium atoms in gas, liquid, and solid helium.
Systematic studies of the phase and density dependence of the delayed annihilation time spectra of antiprotons (DATS) in gaseous, liquid, and solid helium have been performed using the low energy antiproton ring at CERN. The results show a small but significant dependence of DATS on the phase and density of the helium medium. The average lifetime of antiprotons ([ital T][sub [ital a][ital v]]) in gas at 10--30 K was found to be 4.03[plus minus]0.02 [mu]s. In liquid helium [ital T][sub [ital a][ital v]] decreases with density from 3.0 [mu]s at 1 bar to 2.5 [mu]s at 60 bars, while in solid helium its value is 2.14[plus minus]0.03 [mu]s, 20% shorter than that in liquid helium of the same density. There is no change of DATS betweeen normal 1-bar liquid and superfluid helium. An isotope effect between [sup 4]He and [sup 3]He similar to the one previously observed in the gas phase has also been found for liquid helium. All the data can be fitted fairly well with a simple three-level chain decay model with describes the general structure of DATS, characterized by downaward curving behavior on a logarithmic scale at later times and by the presence of a short-lived component.more » No delayed annihilation was observed in lithium.« less
15584025
Polarized structure functions of nucleons and nuclei
We determine the quark distributions and structure functions for both unpolarized and polarized DIS of leptons on nucleons and nuclei. The scalar and vector mean fields in the nucleus modify the motion of the quarks inside the nucleons. By taking into account this medium modification, we are able to reproduce the experimental data on the unpolarized EMC effect, and to make predictions for the polarized EMC effect. We discuss examples of nuclei where the polarized EMC effect could be measured. We finally present an extension of our model to describe fragmentation functions.
122821193
The NJL‐jet model for quark fragmentation functions
A description of fragmentation functions which satisfy the momentum and isospin sum rules is presented. We concentrate on the pion fragmentation function, taking into account cascade‐like processes in a generalized jet‐model approach. Numerical results obtained in this NJL‐jet model are presented.
18357270
Quark distributions in nucleons and nuclei
We discuss the medium modifications of quark distributions and structure functions in the framework of a chiral effective quark theory. Particular emphasis is put on the isospin dependence of the in-medium quark distributions. As an interesting application, we discuss a possible solution of the so called NuTeV anomaly. Possible extensions of the model to describe fragmentation functions are also discussed.
119264092
Spin-dependent parton distributions and structure functions
Nuclear parton distributions and structure functions are determined in an effective chiral quark theory. We also discuss an extension of our model to fragmentation functions.
120047394
Quark fragmentation to pions and kaons in the NJL‐jet model
We describe the quark fragmentation functions to pions and kaons in the NJL‐jet model and compare the results with empirical parametrizations. By including cascade‐like fragmentation processes, the momentum and isospin sum rules can be satisfied naturally without introducing new parameters into the theory. We associate a low energy scale with the NJL model, and perform the Q2 evolution in leading order. The results are in reasonable agreement with the empirical fragmentation functions.