Strangeness production and other recent results from Hall B at Jefferson Lab

Recent results using the CLAS detector at Jefferson Lab are discussed. We emphasize strangeness photo- and electro-production in the baryon resonance region between W = 1.6 and 2.3 GeV, where indications of s-channel structure are suggestive of high-mass baryon resonances coupling to kaons and hyperons in the final state. Other CLAS results, for the E _{1 +} /M _{1 +} transition form factor at the first -resonance, two-pion electroproduction, and photoproduction are also briefly mentioned.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.30.-a Decays of baryons - 13.30.Eg Hadronic decays - 13.40.-f Electromagnetic processes and properties - 13.60.-r Photon and charged-lepton interactions with hadronsR.A. Schumacher: For the CLAS Collaboration     

Density measurement through elastic electron scattering with a gaseous target at the Jefferson Lab

We report the density measurement through e-³He elastic scattering with a 1.23 GeV electron beam in Jefferson Lab experiment E06-010. The extracted ³He density is (9.26±0.06) amagats and the N₂/³He ratio is (1.49±0.08)%. In addition, these results are consistent with the deduced target densities based on pressure broadening measurement.     

Recent results of two-boson-exchange effects in the parity-violating elastic electron-proton scattering

The results of two-boson-exchange effects in the parity-violating elastic electron-proton scattering are reported based on a simple hadronic model. The corrections are calculated including the nucleon and △（1232） intermediate states. And the numerical results are also compared with the recent results reported by other group and other methods.     

Recent results of two-boson-exchange effects in the parity-violating elastic electron-proton scattering

The results of two-boson-exchange effects in the parity-violating elastic electron-proton scattering are reported based on a simple hadronic model. The corrections are calculated including the nucleon and △(1232) intermediate states. And the numerical results are also compared with the recent results reported by other group and other methods.     

Evolution of the high power THz source program at Jefferson Lab

We report the evolution of the high power THz source program at Jefferson Lab. The source is based on coherent synchrotron radiation in which short bunches of relativistic electrons radiate when traversing a dipolar magnetic field. In our first accelerator we produced 20 W of broadband THz light. Our upgraded accelerator with higher current and improved THz extraction optics will considerably enhance the output power to >100 W. In this paper we describe the source in some detail and present theoretical calculations for the upgrade.     

The proton form factor measurements at Jefferson Lab, past and future

Use of the double-polarization technique to obtain the elastic nucleon form factors has resulted in a dramatic improvement of the quality of two of the four nucleon electromagnetic form factors, G _Ep and G _En . It has also changed our understanding of the proton structure, having resulted in a distinctly different Q ²-dependence for both G _Ep and G _Mp , contradicting the prevailing wisdom of the 1990’s based on cross section measurements, namely that G _Ep and G _Mp obey a “scaling” relation μG _Ep ～ G _Mp . A related consequence of the faster decrease of G _Ep revealed by the Jefferson Lab (JLab) polarization results was the disappearance of the early scaling F ₂/F ₁ ～ 1/Q ² predicted by perturbative QCD. In three experiments, GEp(1), GEp(2) and GEp(3), in Halls A and C at JLab, the ratio of the proton’s electromagnetic elastic form factors, G _Ep /G _Mp , was measured up to four momentum transfer Q ² of 8.5 GeV² with high precision, using the recoil polarization technique. The initial discovery that the proton form factor ratio measured in these three experiments decreases approximately linearly with four-momentum transfer, Q ², for values above ～ 1 GeV², was modified by the GEp(3) results, which suggests a slowing down of this decrease. There is an approved experiment, GEp(5), to continue these measurements to 15 GeV². A dedicated experimental setup, the super bigbite spectrometer (SBS), will be built for this purpose. It will be equipped with a new focal plane polarimeter to measure the polarization of the recoil protons. In this presentation, I will review the status of the proton elastic electromagnetic form factors, mention succinctly a number of theoretical approaches to describe results and show some features required for the future GEp(5) experiment.     

Status of the N<Superscript>*</Superscript> program at Jefferson Lab

Recent results in electromagnetic excitation of nucleon resonance are presented, and confronted with theoretical predictions. Preliminary data in the search for missing states are discussed as well.Received: 1 November 2002, Published online: 15 July 2003PACS: 13.60.Le Meson production - 13.88.+e Polarization in interactions and scattering     

QCD confinement and the GlueX experiment at Jefferson Lab

An understanding of the confinement mechanism in QCD requires a detailed mapping of the spectrum of hybrid mesons.Understanding confinement means understanding the role of gluons and it is in hybrid mesons that the gluonic degrees of freedom are manifest.High statistics searches for such states with π and p beams have resulted in some tantalizing signals.There is good reason to expect beams of photons to yield hybrid mesons with J P C quantum numbers not possible within the conventional picture of mesons as qq bound states.Meager data currently exist on the photoproduction of light quark mesons.This talk represents an overview of the available data and what has been learned.In looking toward the future,the GlueX experiment at Jefferson Laboratory represents a new initiative that will perform detailed spectroscopy of the light-quark meson spectrum.This experiment and its capabilities will be reviewed.     

QCD confinement and the GlueX experiment at Jefferson Lab

An understanding of the confinement mechanism in QCD requires a detailed mapping of the spectrum of hybrid mesons.Understanding confinement means understanding the role of gluons and it is in hybrid mesons that the gluonic degrees of freedom are manifest.High statistics searches for such states with π and p beams have resulted in some tantalizing signals.There is good reason to expect beams of photons to yield hybrid mesons with J P C quantum numbers not possible within the conventional picture of mesons as qq bound states.Meager data currently exist on the photoproduction of light quark mesons.This talk represents an overview of the available data and what has been learned.In looking toward the future,the GlueX experiment at Jefferson Laboratory represents a new initiative that will perform detailed spectroscopy of the light-quark meson spectrum.This experiment and its capabilities will be reviewed.     

Studies of the neutron spin structure at Jefferson Lab

The polarized ³He program of Hall A at Jefferson Lab will be described. Results on the generalized Gerasimov-Drell-Hearn integral for the neutron in a Q² range between 0.02 GeV²/c² < Q² < 0.9 GeV²/c² will be presented. Preliminary results of the virtual photon asymmetry A₁ⁿ(x, Q²) and the spin structure function g₂ⁿ(x, Q²) at large values of Bjorken x and low Q², respectively, will be discussed.Received: 1 November 2002, Published online: 15 July 2003PACS: 11.55.Hx Sum rules - 13.40.Gp Electromagnetic form factors - 13.88.+e Polarization in interactions and scattering - 29.25.Pj Polarized and other targets     

Electro- and photoproduction of vector mesons at Jefferson Lab

The total and differential cross section for exclusive electro- and photoproduction of vector mesons in the resonance region and above (1.6 < W < 2.9 GeV) was measured at Jefferson Laboratory in a wide kinematic range (0 < Q ² < 4 GeV² and 0 < —t < 5 GeV²). The measurement of the total and differential cross section down to 100 pb/GeV² with the full kinematic coverage, was possible for the first time thanks to the combination of the 100% duty cycle of CEBAF and the large acceptance of the CLAS detector. The main results from the CLAS Collaboration activity in this field will be presented and discussed.     

Preservation and control of the proton and deuteron polarizations in the proposed electron-ion collider at Jefferson Lab

We propose a scheme of preserving the proton and deuteron beam polarizations during acceleration and storage in the proposed electron-ion collider at Jefferson Lab. This scheme allows one to provide both the longitudinal and transverse polarization orientations of the proton and deuteron beams at the interaction points of the figure-8 ion collider ring. We discuss questions of matching the polarization direction at all stages of the beam transport including the pre-booster, large booster and ion collider ring.     

Radiation and ionization energy loss simulation for the GDHsum rule experiment in Hall-A at Jefferson Lab

The radiation and ionization energy loss are presented for single arm Monte Carlo simulation for the GDH sum rule experiment in Hall-A at the Jefferson Lab. Radiation and ionization energy loss are discussed for ¹²C elastic scattering simulation. The relative momentum ratio Δp/p and ¹²C elastic cross section are compared without and with radiative energy loss and a reasonable shape is obtained by the simulation. The total energy loss distribution is obtained, showing a Landau shape for ¹²C elastic scattering. This simulation work will give good support for radiation correction analysis of the GDH sum rule experiment.     

Measuring the weak charge of the proton at Jefferson Lab: A search for physics beyond the standard model

The JLab Q _weak Collaboration is designing and constructing an experiment to measure the proton’s weak charge, Q _W ^p , by measuring the parity violating asymmetry in elastic electron-proton scattering at very low momentum transfer. The standard model predicts Q _W ^p = 1 ? 4 sin² θ _w from the running of the weak mixing angle sin² θ _w , corresponding to a 10σ effect in the experiment. The experiment will determine Q _W ^p with 4% combined statistical and systematic uncertainties, which leads to 0.3% uncertainty in sin² θ _w . Installation of the experiment will begin in September 2009.     

Radiation and ionization energy loss simulation for the GDH sum rule experiment in Hall-A at Jefferson Lab

The radiation and ionization energy loss are presented for single arm Monte Carlo simulation for the GDH sum rule experiment in Hall-A at the Jefferson Lab. Radiation and ionization energy loss are discussed for12 C elastic scattering simulation. The relative momentum ratio△p pand12 C elastic cross section are compared without and with radiative energy loss and a reasonable shape is obtained by the simulation. The total energy loss distribution is obtained, showing a Landau shape for12 C elastic scattering. This simulation work will give good support for radiation correction analysis of the GDH sum rule experiment.     

Recent results and future prospects of laser fusion research at ILE, Osaka

Reviewed are the present status of the fast ignition researches. Since 1997, the fast ignition experiment and theory researches have been extensively continued at the Institute of Laser Engineering of Osaka University. In particular, the cone-shell target experiments and simulation research have been progressing. In order to demonstrate heating of imploded high density plasma to the ignition temperature, in the April of 2003, the construction of heating laser of 10 kJ/10 ps/1.06 μm (Laser for Fusion Experiment; LFEX), for FIREX-I (Fast Ignition Realization Experiment) has started. The fabrication of DT foam cryogenic cone target is also under development as a collaboration program between Osaka University and NIFS (National Institute for Fusion Science). The LFEX will be completed in 2008. After the completion of LFEX, the foam cryogenic cone shell target experiment will start in 2008. As a new approach toward a compact ignition, an impact fusion has been proposed, where the ablative acceleration to the order of 10⁸ cm/s is the key issue. The ablation acceleration related to the impact fusion has been explored by experiments.     

Dynamically polarized target for the g 2 p and G E p experiments at Jefferson Lab

Recently, two experiments were concluded in Hall A at Jefferson Lab which utilized a newly assembled, solid, polarized hydrogen target. The primary components of the target are a new, high cooling power ⁴He evaporation refrigerator, and a re-purposed, superconducting split-coil magnet. It has been used to polarize protons in irradiated NH₃ at a temperature of 1 K and at fields of 2.5 and 5.0 tesla. Maximum polarizations of 55% and 95% were obtained at those fields, respectively. To satisfy the requirements of both experiments, the magnet had to be routinely rotated between angles of 0°, 6°, and 90° with respect to the incident electron beam.