We have developed a new method, based on the ballistic transfer of preaccumulated plasmas, to obtain large and dense positron plasmas in a cryogenic environment. The method involves transferring ...plasmas emanating from a region with a low magnetic field (0.14 T) and relatively high pressure (10(-9) mbar) into a 15 K Penning-Malmberg trap immersed in a 3 T magnetic field with a base pressure better than 10(-13) mbar. The achieved positron accumulation rate in the high field cryogenic trap is more than one and a half orders of magnitude higher than the previous most efficient UHV compatible scheme. Subsequent stacking resulted in a plasma containing more than 1.2 x 10(9) positrons, which is a factor 4 higher than previously reported. Using a rotating wall electric field, plasmas containing about 20 x 10(6) positrons were compressed to a density of 2.6 x 10(10) cm(-3). This is a factor of 6 improvement over earlier measurements.
The nuclear physics program of the ASACUSA experiment at the Antiproton Decelerator (AD) at CERN is concerned with the measurements of antiproton-nuclei cross-sections at low energies (from 5.3MeV ...down to the 100keV region). These measurements are expected to contribute to understand the dynamics of the annihilation process. We give here a full description of the experimental apparatus used for the measurements at 5.3MeV.
The study of the K¯N system at very low energies plays a key role for the understanding of the strong interaction between hadrons in the strangeness sector. At the DAΦNE electron–positron collider of ...Laboratori Nazionali di Frascati we studied kaonic atoms with Z=1 and Z=2, taking advantage of the low-energy charged kaons from Φ-mesons decaying nearly at rest. The SIDDHARTA experiment used X-ray spectroscopy of the kaonic atoms to determine the transition yields and the strong interaction induced shift and width of the lowest experimentally accessible level (1s for H and D and 2p for He). Shift and width are connected to the real and imaginary part of the scattering length. To disentangle the isospin dependent scattering lengths of the antikaon–nucleon interaction, measurements of K−p and of K−d are needed. We report here on an exploratory deuterium measurement, from which a limit for the yield of the K-series transitions was derived: Y(Ktot)<0.0143 and Y(Kα)<0.0039 (CL 90%). Also, the upcoming SIDDHARTA-2 kaonic deuterium experiment is introduced.
The antikaon-nucleon interaction close to threshold provides crucial information on the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. In this context, the ...importance of kaonic deuterium x-ray spectroscopy has been well recognized, but no experimental results have yet been obtained due to the difficulty of the measurement. To measure the shift and width of the kaonic deuterium 1s state with an accuracy of 30 eV and 75 eV, respectively, an apparatus is under construction at the Laboratori Nazionali di Frascati. A detailed Monte Carlo simulation has shown that an increase of the signal to background ratio by a factor of ten will be required compared to the successfully performed kaonic hydrogen measurement (SIDDHARTA). Three pillars are essential for the newly developed experimental apparatus: a large area x-ray detector system (consisting of Silicon Drift Detectors), a lightweight cryogenic target system and a veto system, consisting of an outer veto detector (Veto-1) for active shielding and an inner veto detector (Veto-2) for charged particle suppression. For both veto systems, an excellent time resolution is required to distinguish kaons stopping in gas from direct kaon stops in the entrance window or side wall of the target. First test measurements on the Veto-2 system were performed. An average time resolution of (54 ± 2) ps and detection efficiencies of ~ 99 % were achieved.
The physics program at the super-conducting fragment separator (Super-FRS) at FAIR, being operated in a multiple-stage, high-resolution spectrometer mode, is discussed. The Super-FRS will produce, ...separate and transport radioactive beams at high energies up to 1.5 AGeV, and it can be also used as a stand-alone experimental device together with ancillary detectors. Various combinations of the magnetic sections of the Super-FRS can be operated in dispersive, achromatic or dispersion-matched spectrometer ion-optical modes, which allow measurements of momentum distributions of secondary-reaction products with high resolution and precision. A number of unique experiments in atomic, nuclear and hadron physics are suggested with the Super-FRS as a stand-alone device, in particular searches for new isotopes, studies of hypernuclei, delta-resonances in exotic nuclei and spectroscopy of atoms characterized by bound mesons. Rare decay modes like multiple-proton or neutron emission and the nuclear tensor force observed in high-momentum regime can be also addressed. The in-flight radioactivity measurements as well as fusion, transfer and deep-inelastic reaction mechanisms with the slowed-down and energy-bunched fragment beams are proposed for the high-resolution and energy buncher modes at the Super-FRS.
Cold, two-body antiprotonic helium ions p 4He2+ and p 3He2+ with 100-ns-scale lifetimes, occupying circular states with the quantum numbers ni=28-32 and li=ni-1 have been observed. They were produced ...by cooling three-body antiprotonic helium atoms in an ultra-low-density helium target at temperature T approximately 10 K by atomic collisions, and then removing their electrons by inducing a laser transition to an autoionizing state. The lifetimes of p 3He2+ against annihilation induced by collisions were shorter than those of p 4He2+, and decreased for larger-ni states.
We describe some acrylic Cherenkov detectors read out by gateable fine-mesh photomultipliers, used in laser spectroscopy experiments of metastable antiprotonic helium
(
p
̄
He
+)
atoms carried out at ...the LEAR and AD facilities at CERN. The atoms were produced by stopping pulsed antiproton beams in a helium target. Charged particles emerging from the antiproton annihilations produced Cherenkov light in the detector, the time envelope of which consisted of a strong flash from the promptly-annihilating antiprotons, followed by a much longer but less intense tail from the delayed annihilations of the metastable atoms. The photomultiplier was turned off during the initial light flash by reversing the electric potential on its dynodes, thus allowing only the delayed annihilations to be recorded as an analog pulse. The atoms were irradiated with a laser pulse tuned to the characteristic wavelength which stimulated antiproton transitions from a metastable state to a state with a short lifetime against annihilation. The resonance condition between the laser beam and the atom was thus revealed as a sharp spike superimposed on the Cherenkov light pulse. We tested Cherenkov radiators of various sizes and different types of photomultipliers in order to (i) suppress the spurious afterpulsing in the photomultiplier signal caused by the strong flash of Cherenkov light during the prompt annihilation, (ii) evaluate the background caused by π
+→μ
+→e
+ decay, and (iii) optimize the linearity, dynamic range, and response time of the detector.
The AMADEUS collaboration is performing experimental investigations in the sector of the low energy strangeness hadron physics by taking advantage of the DAΦNE collider, which provides a unique ...source of monochromatic low-momentum kaons and exploiting the KLOE detector as an active target. The
K
−
single and multi-nuclear absorption on H,
4
He,
9
Be and
12
C, both at-rest and in-flight, are studied with the aim to determine the nature of the controversial Λ(1405), the non-resonant hyperon pion formation amplitude below the
K̅N
threshold, the yield and cross sections of
K
−
multi-nucleon absorptions intimately connected to the antikaon multi-nucleon clusters properties and the
K
−
scattering cross sections on light nuclear targets.
These studies have a strong impact on the non-perturbative strangeness QCD with implications ranging from nuclear physics to the equation of state of neutron stars.
The kaonic deuterium measurement at J-PARC and DAΦNE will provide a piece of information still missing to the antikaon-nucleon interaction close to threshold, providing valuable information to answer ...one of the most fundamental problems in hadron physics today - to the yet unsolved puzzle of how the hadron mass is generated. For this a new X-ray detector system has been developed to measure the shift and width of the 2p → 1s transition of kaonic deuterium with a precision of 60 eV and 140 eV, respectively.
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