A proximity focusing RICH detector for kaon physics at Jefferson lab hall A

Abstract

Important information on the AN interaction can be obtained from High Resolution Hypenuclear Spectroscopy experiments with electromagnetic probes. A challenging experiment on electroproduction of hypernuclei is scheduled for 2003 in Hall A at Jefferson Lab. One of the challenges is the high performance particle identification system needed. The signal is expected to be rare compared to the very high pion and proton backgrounds due to the small electron and kaon detection angles. The "standard" Hall A PID apparatus (TOF and two aerogel threshold Cherenkov detectors) does not provide sufficient suppression of the background. Simulations and calculations have shown that a RICH detector would solve the problem. A proximity focusing fluorocarbon/CsI detector similar to the ALICE RICH detector has been designed, built, tested and commissioned. The results show that the detector performs as expected. (C) 2003 Published by Elsevier Science B.V

High-Resolution Spectroscopy ofNΛ16by Electroproduction

“…Λ B, 15 Λ N, and 16 Λ O using an array of germanium detectors called the Hyperball [2,3,4,5] and interpreted in terms of shell-model calculations that include both Λ and Σ hypernuclear configurations [6]. For 16 Λ O, the ground-state is found to have J π = 0 − with excited states at 26 keV (1 − ), 6562 keV (1 − ), and 6782 keV (2 − ) [4,5] (the 2 − state is weakly populated and its existence less certain).…”

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An experimental study of the 16 O(e, e ′ K + ) 16 Λ N reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target.

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“…For 16 Λ O, the ground-state is found to have J π = 0 − with excited states at 26 keV (1 − ), 6562 keV (1 − ), and 6782 keV (2 − ) [4,5] (the 2 − state is weakly populated and its existence less certain).…”

“…In fact, 16 O targets have been extensively used in hypernuclear studies with the (K − , π − ), (π + , K + ), and (K − stop , π − ) reactions with dominant non-spin-flip reaction mechanisms that excite natural-parity states [2]. In all cases, four peaks are seen with the excited states at ≈ 6.2, ≈ 10.6, and ≈ 17.1 MeV corresponding to Λ's in s and p orbits coupled to the p −1 1/2 ground state and the 6.176-MeV p −1 3/2 states of 15 O.…”

“…In the present case, 1 − , 2 − , 1 + , 2 + , and 3 + particle-hole states can be excited with significant cross sections. In addition, the K + Λ associated production occurs on a proton making 16 Λ N, the mirror to 16 Λ O. After taking into account that the p 3/2 -hole state is 148 keV higher in 15 N than 15 O, comparison of the energy spectra (and especially of Λ binding energies) of these mirror hypernuclei can, in principle, shed light on charge-dependent effects in hyperon-nucleon interactions.…”