Search for a new gauge boson in electron-nucleus fixed-target scattering by the APEX experiment.

We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α' to electrons. Such a particle A' can be produced in electron-nucleus fixed-target scattering and then decay to an e + e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175-250 MeV, found no evidence for an A'→ e+ e- reaction, and set an upper limit of α'/α ~/= 10(-6). Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.

High-resolution spectroscopy of Lambda16N by electroproduction.

An experimental study of the (16)O(e,e'K(+))(Lambda)(16)N reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target. This permitted a simultaneous measurement of the p(e,e'K(+))Lambda, Sigma(0) exclusive reactions and a precise calibration of the energy scale. A ground-state binding energy of 13.76+/-0.16 MeV was obtained for (Lambda)(16)N with better precision than previous measurements on the mirror hypernucleus (Lambda)(16)O. Precise energies have been determined for peaks arising from a Lambda in s and p orbits coupled to the p(1/2) and p(3/2) hole states of the (15)N core nucleus.

[Our experience with chordoma treatment]. / Nase zkusenosti s lécbou chordomu.

PURPOSE OF THE STUDY: The aim of the study was to evaluate the group of patients operated on for chordoma at our department. We present diagnostic and surgical management options relevant to the localisation of chordoma in the spine, and evaluate the results in terms of post-operative complications, tumour recurrence and patient survival. MATERIAL AND METHODS: Between 1989 and 2002 a total of 20 patients diagnosed with chordoma were treated. There were 15 men and five women with an average age of 53 years. The cervical spine was affected in 20 %, thoracic in 15%, lumbar in 25 % and sacral in 40 % of the patients. All of them suffered from back pain, and nine patients (45 %) had neurological symptoms. The average time from the onset of complaints till disease diagnosis was 7.2 months. RESULTS: The average survival time was 63 months, with eight patients (40 %) surviving for more than five years. Of the patients with chordoma of the mobile spine, 66 % were treated by a combined antero-posterior procedure involving somatectomy, vertebral body replacement and posterior stabilisation; for sacral spine chordoma, a dorsal approach was always used. Of 11 patients (55 %) who required repeat surgery, eight had recurrent tumour and three had wound infection. DISCUSSION: Chordomas are rare, slow-growing tumours usually diagnosed with a delay, particularly when localised in the sacral spi- ne. At present magnetic resonance imaging is the essential diagnostic method allowing us to plan the appropriate surgical management.When the mobile spine is affected, a combined antero-posterior procedure including somatectomy, vertebral body replacement with a graft or implant and posterior stabilisation is used.When the sacral spine is involved, some authors prefer en bloc resection from the posterior approach, others use a combined antero-posterior procedure. Chordomas are known to have a high risk of local recurrence. Post-operative radiotherapy, which makes the disease-free interval longer, is recommendedúúú chemotherapy has no effect. CONCLUSIONS: Chordomas are associated with serious diagnostic and therapeutic problems, with frequent local recurrence. Prognosis is good if early diagnosis is made, and en bloc resection is performed.

High resolution spectroscopy of (lambda)(12)B by electroproduction.

An experiment measuring electroproduction of hypernuclei has been performed in hall A at Jefferson Lab on a 12C target. In order to increase counting rates and provide unambiguous kaon identification two superconducting septum magnets and a ring imaging Cherenkov detector were added to the hall A standard equipment. An unprecedented energy resolution of less than 700 keV FWHM has been achieved. Thus, the observed (Lambda)(12)B spectrum shows for the first time identifiable strength in the core-excited region between the ground-state s-wave Lambda peak and the 11 MeV p-wave Lambda peak.

Measurement of tensor polarization in elastic electron-deuteron scattering at large momentum transfer

Tensor polarization observables ( t(20), t(21), and t(22)) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c)(2). The experiment was performed at the Jefferson Laboratory in Hall C using the electron High Momentum Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q2 the deuteron charge form factors G(C) and G(Q). They are in good agreement with relativistic calculations and disagree with perturbative QCD predictions.

Measurement of the electric form factor of the neutron through d-->(e-->,e(')n)p at Q2 = 0.5 (GeV/c)(2).

We report the first measurement using a solid polarized target of the neutron electric form factor G(n)(E) via d-->(e-->,e(')n)p. G(n)(E) was determined from the beam-target asymmetry in the scattering of longitudinally polarized electrons from polarized deuterated ammonia ( 15ND3). The measurement was performed in Hall C at Thomas Jefferson National Accelerator Facility in quasifree kinematics with the target polarization perpendicular to the momentum transfer. The electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle segmented detector. We find G(n)(E) = 0.04632+/-0.00616(stat)+/-0.00341(syst) at Q2 = 0.495 (GeV/c)(2).