G.M. Urciuoli

Quantum efficiency measurement system for large area CsI photodetectors

A proximity focusing freon/CsI RICH detector has been built for kaon physics at Thomas Jefferson National Accelerator Facility (TJNAF or Jefferson Lab), Hall A. The Cherenkov photons are detected by a UV photosensitive CsI film which has been obtained by vacuum evaporation. A dedicated evaporation facility for large area photocathodes has been built for this task. A measuring system has been built to allow the evaluation of the absolute quantum efficiency (QE) just after the evaporation. The evaporation facility is described here, as well as the quantum efficiency measurement device. Results of the QE on-line measurements, for the first time on large area photocathodes, are reported.

Update of High Resolution (e,e'K^+) Hypernuclear Spectroscopy at Jefferson Lab's Hall A

Abstract Updated results of the experiment E94-107 hypernuclear spectroscopy in Hall A of the Thomas Jefferson National Accelerator Facility (Jefferson Lab), are presented. The experiment provides high resolution spectra of excitation energy for 12ΛB, 16ΛN, and 9ΛLi hypernuclei obtained by electroproduction of strangeness. A new theoretical calculation for 12ΛB, final results for 16ΛN, and discussion of the preliminary results of 9ΛLi are reported.

Hybrid silicon μstrip and GEM tracker for JLab hall-a high luminosity experiments

A new hybrid silicon μstrip and large area GEM (Gas Electron Multiplier) tracker is under development for the upcoming high luminosity (up to 1039 /s/cm2) experiments at the Hall-A of the JLab 12 GeV electron beam facility. The system consists of 2 small 10×20 cm2 silicon planes placed near the scattering chamber and 18 40×50 cm2 GEM modules that form larger chambers with variable active area depending on the experimental needs. Rather general purpose readout electronics has been designed for both detectors and can be adopted in other equipment. It consists of two active components: front-end cards, directly connected to the detector channels and a multi-purpose digitizer board (MPD). The front-end is based on existing 128 channels APV25-S1 chip developed in the framework of LHC experiments. The MPD handles 16 front-end cards (for a total of 2048 channels) and can be used in VME environments (also VME64x or VXS). It also provides: optical, Ethernet, USB. These resources permit to use MPD cards in different frameworks, ranging from small bench-top to large on-detector distributed systems. The GEM project is part of the CERN/RD51 collaboration activities. The system has been beam tested in late 2010 and 2011, some results are presented here.

Performance of the Two Aerogel Cherenkov Detectors of the JLab Hall A Hadron Spectrometer

We report on the design and commissioning of two silica aerogel Cherenkov detectors with different refractive indices. In particular, extraordinary performance in terms of the number of detected photoelectrons was achieved through an appropriate choice of PMT type and reflector, along with some design considerations. After four years of operation, the number of detected photoelectrons was found to be noticeably reduced in both detectors as a result of contamination, yellowing, of the aerogel material. Along with the details of the set-up, we illustrate the characteristics of the detectors during different time periods and the probable causes of the contamination. In particular we show that the replacement of the contaminated aerogel and parts of the reflecting material has almost restored the initial performance of the detectors.

High-resolution hypernuclear spectroscopy electron scattering at JLab, Hall A

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. Experiment 94-107 started a systematic study on 1p-shell targets, 12C, 9Be and 16O. We present the results from 12C, 16O and very preliminary results from 9Be. For 12C for the first time measurable strength in the core-excited part of the spectrum between the ground state and the pΛ state was shown in for the first time. A high-quality 16ΛN spectrum was produced for the first time with sub-MeV Energy resolution. A very precise BΛ value for 16ΛN, calibrated against the elementary (e, e′K+) reaction on hydrogen, has also been obtained. Final data on 9Be will be available soon. The missing energy resolution is the best ever obtained in hypernuclear production experiments.

Instrumentation for Δ photoproduction experiments on nuclei with high-energy resolution

Abstract A technique has been developed to perform photo-induced experiments in the region of the Δ(1232) resonance with a sufficiently good energy resolution to separate excited states of the final nucleus. The technique utilizes developments in accelerator technology (high-duty factor electron beams), target technology (multi-layer waterfall targets), and detector technology (diffusely reflective aerogel Cherenkov systems). Taken together, these developments have enabled studies of the reaction 16 O( γ , π − p) with an energy resolution of less than 1 MeV. This represents an order of magnitude improvement in energy resolution over previous experiments of this kind.

High resolution hypernuclear spectroscopy at Jefferson Lab, Hall A: The experimental challenge

The E94-107 experiment in Hall A at Jefferson Lab has started a systematic study of 1p-shell hypernuclei. Data have been taken on C-12, Be-9 and O-16 targets. The counting rate for hypernuclear electroproduction decreases dramatically as the scattering angle increases. Therefore, the electron scattering angle has to be as forward as possible to get high virtual photon flux and kaon angle has to be as close as possible to the virtual photon direction to minimize momentum transfer. In order to allow experiments at very forward angle in Hall A, two superconducting septum magnets were added to the High Resolution Spectrometers (HRS). The two magnets bend particles scattered at 6° into each HRS, introducing only a small perturbation on the HRS optics thus preserving the excellent momentum resolution of the HRS. With the new setup a momentum resolution of 10−4 FWHM on both HRS arms was obtained. One of the challenges of the experiment at very forward angle is the identification of very small peaks in the missingenergy spectrum; this requires a powerful Particle Identification (PID) system that provides unambiguous kaon selection.