Hypernuclear Physics at Jefferson Lab

Hypernuclear Physics at Jefferson Lab
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Release: 2005
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The Continuous Electron Beam Accelerator Facility (CEBAF) has been successfully carrying out hadronic physics studies since 1996 at the Thomas Jefferson National Accelerator Facility (JLab) in Virginia, USA. The characteristics of this electron beam, together with those of the experimental equipment, offer a unique opportunity to study the electro-production of hypernuclei through the reaction A(e, e[prime]K[sup +])B[sub [Lambda]], where the hypernuclear production is tagged by the detection of the scattered electron in coincidence with the produced kaon. The kaon is a part of the associated strangeness pair production with a [Lambda] hyperon remaining embedded in the nuclear medium to form the hypernucleus. The hypernuclear physics program will cover an important part of the JLab experimental program over the next few years. This short review will focus mainly on a few subjects, and some experimental details of the Hall A experiment, where the authors have primarily responsibilities, will be presented.

Hypernuclear Physics Programs Via Electroproduction in Hall C at Jefferson Lab

Hypernuclear Physics Programs Via Electroproduction in Hall C at Jefferson Lab
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Hypernuclei with strangeness -1 have been intensively studied both theoretically and experimentally using hadronic probes and reactions, (K, [pi]) and ([pi], K), for many years since the first discovery of such formation in the earlier nuclear emulsion and bubble chamber experiments. Many recent review papers exist on the status of hypernuclear physics, such as the recent one written by B.F. Gibson and Ed V. Hungerford in which one can find detailed discussion on all aspects of hypernuclear physics and more complete reference list. The unique feature of this field can be summarized, in general, into three categories: (1) Strong Interaction Involving Strangeness, (2) Weak Interaction with [Delta]S = -1, and (3) Medium Modifications. For strong interaction, it is commonly believed that a hyperon can be treated as an ''impurity'' to probe deep interior of the nuclear medium to explore fundamental issues such as the changes in size and shape due to the short range feature of YN interactions, limit of conventional nuclear model (shell or cluster) in solving for many body systems with new degree of freedom, spin dependent forces (spin-spin, spin-orbital, tensor), new symmetry and explicit QCD effect in nuclear media. Many of such issues are impossible or very difficult to be studied in the ordinary nuclear physics. The keys for success in this part of field includes good energy resolution and wide ranged spectroscopy. Until now, many important issues are still unresolved or remained to be resolved in more consistent and satisfactory fashion, such as spin dependent forces. This is due to luck of high quality experimental facilities. Recent experiments at KEK using ([pi][sup +], K[sup +]) reaction with a dedicated new SKS spectrometer have demonstrated the importance of improving the energy resolution. New structures were found as resolution improved only from 3 MeV to 2 MeV.

Recent Results on High Resolution Hypernuclear Spectroscopy by Electroproduction at Jefferson Lab, Hall A.

Recent Results on High Resolution Hypernuclear Spectroscopy by Electroproduction at Jefferson Lab, Hall A.
Author: G. Chang
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Release: 2005
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The first ''systematic'' study of 1 p shell hypernuclei with electromagnetic probes has started in Hall A at Jefferson Lab . The aim is to perform hypernuclear high resolution spectroscopy by the electroproduction of strangeness on four 1p-shell targets: 12C, 9Be, 16O, 7Li. The first part of the experiment on 12C and 9Be has been performed in 2004, the second part (16O and 7Li) is scheduled for June 2005. To overcome the major experimental difficulties, namely the low counting rate and the challenging Particle IDentification (PID), two septum magnets and a Ring Imaging CHerenkov (RICH) detector had to be added to the existing apparatus. After underlining the particular role the electroproduction reaction plays in hypernuclear physics we describe the challenging modifications of the Hall A apparatus. Preliminary results on 12C and 9Be are presented.

Feasibility Test Run of C-12(e, E'K[sup +] Reaction at Thomas Jefferson National Accelerator Facility

Feasibility Test Run of C-12(e, E'K[sup +] Reaction at Thomas Jefferson National Accelerator Facility
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The high quality and high duty factor (100%) electron beam at Jefferson Lab offers an opportunity to broaden their view of hypernuclear physics by studying the (e, e[prime]K[sup +]) reaction with high resolution. The present data represent a feasibility study of such a reaction on a carbon target. The test run was carried out during experiments E91-16 (Electroproduction of Kaons and Light Hypernuclei) and E93-18 (Kaon Electroproduction on p(e, e[prime]K[sup +])Y). These two experiments used liquid deuterium and hydrogen targets, respectively. There exist data on an aluminum target for the background calibration of the liquid targets which are suitable also for a feasibility study of electroproduction of hypernuclei. These data are still under analysis. The goal of this test run is to evaluate issues concerned with the electroproduction of hypernuclei. These issues include: (1) the quasi-free production rate, which had not been measured previously, (2) random coincidence background, (3) keon identification over a possibly large hadronic background, and (4) possible evaluation of the production rate of the bound hypernuclear structures. This test run will supply significant knowledge for running high quality hypernuclear experiments at Jefferson Lab. The spectroscopy of hypernuclei has been studied mainly in two ways: the strangeness-exchange reaction (K[sup -], [pi][sup -]), and associated strangeness production ([pi][sup +], K[sup +]). The (e, e[prime]K[sup +]) reaction has the advantage of exciting both natural- and unnatural-parity states and the possibility of obtaining good energy resolution. The cross section for the (e, e[prime]K[sup +]) reaction is about a hundred times smaller than for the corresponding hadronic production reactions but it is compensated for by the availability of high intensity and high duty factor electron beams. In order to optimize the production rate, the kinematic setting requires both the scattered electron and kaon to be detected at very forward angles. The test run was not optimized for hypernuclear production, but it serves as an important technical evaluation for future hypernuclear programs at Jefferson Lab. The first high-resolution spectroscopy experiment on p-shell lambda hypernuclei is tentatively scheduled to run in 1999 in Hall C at Jefferson Lab.

High Resolution Hypernuclear Spectroscopy at Jefferson Lab Hall A.

High Resolution Hypernuclear Spectroscopy at Jefferson Lab Hall A.
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The characteristics of the Jefferson Lab electron beam, together with those of the experimental equipment, offer a unique opportunity to study hypernuclear spectroscopy via electromagnetic induced reactions. Experiment 94-107 started a systematic study on 1p-shell targets, $Ĉ$, ${̂9}Be$ and $Ô$. For $Ĉ$ for the first time measurable strength in the core-excited part of the spectrum between the ground state and the p state was shown in $_̂{\Lambda}B$ spectrum. A high-quality $_̂{\Lambda}N$ spectrum was produced for the first time with sub-MeV energy resolution. A very precise $\Lambda$ binding energy value for $_̂{\Lambda}N$, calibrated against the elementary $(e, e'K+̂)$ reaction on hydrogen, has also been obtained. ${̂9}_{\Lambda}Li$ spectrum shows some disagreement in strength for the second and third doublet with respect to the theory.

Electron Induced Hypernuclear Spectroscopy. Results in Hall A at Jefferson Lab

Electron Induced Hypernuclear Spectroscopy. Results in Hall A at Jefferson Lab
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The characteristics of the Jefferson LAB electron beam, together with those of the experimental equipments, offer a unique opportunity to study hypernuclear spectroscopy via electromagnetic induced reactions. Results are presented on 12C, 16O and 9Be targets. In the hypernuclear missing-mass spectrum the experiment achieves sub-MeV energy resolution by exploiting the characteristics of the High Resolution Spectrometer pair and the beam quality available at JLab. These studies have provided, among other things, the first quantitative information on core-excited states in hypernuclei, as well as the precise determination of Lambda binding energy in the Lambda16N hypernucleus. For the experiment on oxygen, a waterfall target has been employed, allowing simultaneous measurement of the elementary reaction on protons: a crucial measurement to disentangle the contribution of the elementary reaction from the measured hypernuclear production cross section, yielding direct access to the nucleus-hypernucleus transition structure.

First Experiment on Spectroscopy of Lambda-Hypernuclei by Electroproduction at Jlab

First Experiment on Spectroscopy of Lambda-Hypernuclei by Electroproduction at Jlab
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Release: 2001
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The first experiment in Lambda-hypernuclear spectroscopy using the high precision electron beam at Jefferson laboratory (Jlab) has been carried out. The hypernuclear spectrometer system (HNSS) was used to measure spectra from the 12C(e, e(prime)K)12{sub {Lambda}}B reaction with sub-1 MeV resolution, the best energy resolution obtained thus far in hypernuclear spectroscopy with magnetic spectrometers. This paper describes the HNSS and the preliminary results for the 12{sub {Lambda}}B system. The experimental spectrum is consistent with the expected strong spin-flip excitations of unnatural parity states. A program of hypernuclear physics experiments is planned for the future with much higher yield and even better energy resolution.