Abstract
Hypernuclear research will be one of the main topics addressed by the PANDA experiment at the planned Facility for Antiproton and Ion Research FAIR at Darmstadt (Germany). [1, 2] Thanks to the use of stored p beams, copious production of double Λ hypernuclei is expected at the PANDA experiment, which will enable high precision γ spectroscopy of such nuclei for the first time, and consequently a unique chance to explore the hyperon-hyperon interaction. In particular, ambiguities of past experiments in determining the strength of the ΛΛ interaction will be avoided thanks to the excellent energy precision of a few keV (FWHM) achieved by germanium detectors. Such a resolution capability is particularly needed to resolve the small energy spacing of the order of (10–100) keV, which is characteristic from the spin doublet in hypernuclei the so –called “hypernuclear fine structure”.In comparison to previous experiments, PANDA will benefit from a novel technique to assign the various observable γ -transitions in a unique way to specific double hypernuclei by exploring various light targets. Nevertheless, the ability to carry out unique assignments requires a devoted hypernuclear detector setup. This consists of a primary nuclear target for the production of Ξ− + pairs, a secondary active target for the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform γ spectroscopy.Moreover, one of the most challenging issues of this project is the fact that all detector systems need to operate in the presence of a high magnetic field and a large hadronic background. Accordingly, the need of an innovative detector concept will require dramatic improvements to fulfil these conditions and that will likely lead to a new generation of detectors. In the present work details concerning the current status of the activities related to the detector developments for this challenging programme will be given.Among these improvements is the new concept for a cooling system for the germanium detector based on a electro-mechanical device. In the present work, the cooling efficiency of such devices has been successfully tested, showing their capability to reach liquid nitrogen temperatures and therefore the possibility to use them as a good alternative to the standard liquid nitrogen dewars. Furthermore, since the momentum resolution of low momentum particles is crucial for the unique identification of hypernuclei, an analysis procedure for improving the momentum resolution in few layer silicon based trackers is presented.
Highlights
The simultaneous production and implementation of two Λ particles into a nucleus is intricate
While the double pionic decay of light double hypernuclei can be used as an effective experimental filter to reduce the background [13] the unique identification of hypernuclei ground states only via their pionic decay is usually hampered by the limited resolution
The tracking of pions emitted from the hypernuclei decay with a momentum ranging between 70 MeV/c and 140 MeV/c will require a reduction of the magnetic field strength.The momentum resolution of low momentum pions have been studied by using the tracking package GenFit [20, 21], which takes care of effects due to energy losses and multi-scattering process inside the detector material
Summary
The simultaneous production and implementation of two Λ particles into a nucleus is intricate. To produce double hypernuclei in a more ’controlled’ way the conversion of a captured Ξ− and a proton into two Λ particles can be used. This process releases, ignoring binding energy effects, only 28 MeV. The advantage as compared to the kaon induced reaction is that antiprotons are stable and can be retained in a storage ring This allows a rather high luminosity even with very thin primary targets. Spectroscopic information on double hypernuclei can only be obtained via their decay products. Γ-rays emitted via the sequential decay of excited double hypernuclei may provide precise information on the level structure [14, 15]
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