Negative Kaons Research Articles

Kaonic atoms and nuclei search at the DAΦNE accelerator

The DAΦNE electron-positron collider at the Laboratori Nazionali di Frascati dell'INFN has made available a unique quality low-energy negative kaons “beam”. Two experiments, SIDDHARTA and AMADEUS, will use this kaon source to perform unprecedented precision measurements on kaonic atoms and kaonic nuclei. The scientific cases, together with the experimental setups, are briefly presented in this paper.

The calibration of a Meson Spectrometer with a Least Squares Minimization technique

The task of calibration and analysis of the Neutral Meson Spectrometer (NMS) was undertaken with the help of negative kaon (κ−) data from the Brookhaven laboratory E931 experiment. A useful least squares minimization technique, using Chi-Squared Minimization, was developed and implemented to determine the coefficients for 120 Cesium-Iodide crystals in NMS. This short paper reports the details of this technique which finds application in a number of areas, especially electromagnetic and meson spectrometry/calorimetry, where a least squares estimation method is required for calibration of multi-channel instruments.

KAONIC ATOMS/NUCLEI MEASUREMENTS AT DAΦNE: SIDDHARTA AND AMADEUS

The DAΦNE electron-positron collider at the Laboratori Nazionali di Frascati dell'INFN has made available a unique quality negative kaons “beam”. Two experiments, SIDDHARTA and AMADEUS, will use this beam to perform unprecedented precision measurements on kaonic atoms and kaonic nuclei. The scientific cases, together with the experimental setups, are briefly presented in this paper.

Correlated Λd pairs from the [formula omitted] reaction

Correlated Λd pairs emitted after the absorption of negative kaons at rest Kstop−A→ΛdA′ in light nuclei 6Li and 12C are studied. Λ-hyperons and deuterons are found to be preferentially emitted in opposite directions. The Λd invariant mass spectrum of 6Li shows a bump whose mass is 3251±6 MeV/c2. The bump mass (binding energy), width and yield are reported. The appearance of a bump is discussed in the realm of the [K¯3N] clustering process in nuclei. The experiment was performed with the FINUDA spectrometer at DAΦNE (LNF).

Precision measurements of kaonic atoms at DA ΦNE and future perspectives

The DAΦNE electron-positron collider at the Frascati National Laboratories has made available a unique “beam" of negative kaons providing unprecedented conditions for the study of the low-energy kaon-nucleon interaction, a field still largely unexplored. The DEAR (DAΦNE Exotic Atom Research) experiment at DAΦNE and its successor SIDDHARTA (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) aim at a precision measurement of the strong-interaction shift and width of the fundamental 1s level, via the measurement of the X-ray transitions to this level, for kaonic hydrogen and kaonic deuterium. The aim is to extract the isospin-dependent antikaon-nucleon scattering lengths and to contribute to the understanding of aspects of chiral symmetry breaking in the strangeness sector.

First results on 12ΛC production at DAΦNE

Λ-hypernuclei are produced and studied, with the FINUDA spectrometer, for the first time at an e+e− collider: DAΦNE, the Frascati ϕ-factory. The slow negative kaons from ϕ(1020) decay are stopped in thin (0.2 g/cm2) nuclear targets, and Λ-hypernuclei formation is detected by measuring the momentum of the outgoing π−. A preliminary analysis on 12ΛC shows an energy resolution of 1.29 MeV FWHM on the hypernuclear levels, the best obtained so far with magnetic spectrometers at hadron facilities. Capture rates for the ground state and the excited ones are reported, and compared with previous experiments.

Chemical reaction of negative particles [formula omitted], K −, and μ − with molecular ions

Rearrangement processes of the exotic system, X − + H 2 + → X −p + H, where X −= p ̄ (antiproton), K − (negative kaon), and μ − (negative muon), can be treated as a familiar type of chemical reaction, i.e., collisions on a single Born–Oppenheimer potential energy surface. The cross-section for this reaction and the state distribution of the formed exotic atoms X −p are calculated by the classical trajectory Monte Carlo method. The reaction dynamics is investigated by comparison with the X − + H and H 2 systems.

Minimal color-flavor-locked–nuclear interface

At nuclear matter density, electrically neutral strongly interacting matter in weak equilibrium is made of neutrons, protons, and electrons. At sufficiently high density, such matter is made of up, down, and strange quarks in the color-flavor-locked (CFL) phase, with no electrons. As a function of increasing density (or, perhaps, increasing depth in a compact star) other phases may intervene between these two phases, which are guaranteed to be present. The simplest possibility, however, is a single first order phase transition between CFL and nuclear matter. Such a transition, in space, could take place either through a mixed phase region or at a single sharp interface with electron-free CFL and electron-rich nuclear matter in stable contact. Here we construct a model for such an interface. It is characterized by a region of separated charge, similar to an inversion layer at a metal-insulator boundary. On the CFL side, the charged boundary layer is dominated by a condensate of negative kaons. We then consider the energetics of the mixed phase alternative. We find that the mixed phase will occur only if the nuclear-CFL surface tension is significantly smaller than dimensional analysis would indicate.

Kaon condensation in high-density quark matter.

We point out that the problem of kaon condensation in dense hadronic matter can be addressed in perturbative QCD. Indeed, perturbative calculations suggest that negative kaons are condensed in high-density quark matter if the presence of electrons is taken into account. This observation sheds new light on the proposal that the low-density hyperon and high-density quark matter phases of QCD are continuously connected.

Kaonic hydrogen - past puzzles

The experimental study of low energy kaon–nucleon interactions began in the ’50s when accelerators reached an energy at which kaons could first be produced in the laboratory. Hydrogen-, deuterium-, and helium-filled bubble chambers were used to study both negative and positive kaon scattering and absorption reactions. Where available, beams of negative kaons were stopped in targets ranging from helium to carbon – and later up to uranium – for the purpose of studying the X-rays resulting from the de-excitation of the kaon from a high capture orbit down to the lowest orbit reached. The energy of this lowest orbit of these so-called exotic atoms was shifted in energy and absorption-broadened by the kaon–nucleus strong interaction. Hence, the X-ray spectrum could be used to measure both the shift and width of this lowest level. X-ray intensity ratios of the feeding transition to this lowest transition could also be used to deduce the absorption width of the higher level. However, in the late ’70s, no experimental data yet existed for the simplest and most fundamental of these – the exotic kaonic hydrogen isotopes – for reasons discussed below. The optical model theory of exotic hadronic atoms relating low-energy scattering data to shifts and widths was well developed for pions in the ’60s by the Ericsons [1], thus the formalism for kaons, which are also spinless particles, was put in place. Knowing the shift and width, the complex scattering length could then be deduced and compared with scattering data. Physicists embroiled in the excitement of both the experiments and the theoretical underpinnings prepared many excellent reviews. They do far better justice to this period of kaonic hydrogen pre-history than would I. The reader is referred to Burhop [2] and the references therein for the early period up to the late ’60s, and to Seki and Wiegand for kaonic and other exotic atom data up to the mid-’70s [3]. Chris Batty reviewed both theory and experimental results on a broad range of exotic atoms in the late ’70s (and updated it recently [4]). H. Poth [5] provided a valuable compilation of hadronic atom data in 1979. A bibliography of exotic atoms from 1939 to 1982 was produced by Dezso Horvath and Richard Lambrecht [6] in 1984. The state of theory up to the early ’80s has been well presented by Florian Scheck [7].

Inclusive φ meson production in neutron–carbon interactions at 20–70 GeV

φ mesons have been reconstructed from their decay to positive and negative kaons, using the data obtained from interaction of neutrons at 20–70 GeV with a carbon target collected by EXCHARM experiment at the Serpukhov accelerator. The analysis relies on the use of reconstructing trajectories and particle identification. From about 45 million events (19600 ± 350) φ mesons were found. The φ meson mass is measured to be (1019.4 ± 0.1)MeV/c 2; the φ meson width is measured to be (4.9 ± 0.3)MeV/c 2. The investigation has been performed at the Joint Institute for Nuclear Research at the Laboratory of Super High Energies.

K − and $$\bar p$$ Production in Au + Pb Collisions at 11.5 A GeV/cProduction in Au + Pb Collisions at 11.5 A GeV/c

I will present the first results from the E864 collaboration on the production of negative kaons and antiprotons in 10% central 11.5 A GeV/c Au+Pb nucleus collisions at the Brookhaven AGS. E864 is a high rate, open geometry spectrometer, capable of measuring particle production in a range of rapidities and transverse momenta at a single setting of the spectrometer magnets. The results are derived from the analysis of over 20 million central interactions collected in the Fall 1994 run. I will report onK − production in a rapidity range from 1.9<y<2.2 (y cm=1.6) and 25<pT<150 MeV/c, and $$\bar p$$ production from 1.2<y<2.2 and 50<pT<400 MeV/c. A comparison with previously published results from E878 is presented and the implications for $$\bar \Lambda $$ production are discussed.

Kaon production in Si+Al and Si+Au collisions at 14.6 [formula omitted

AGS experiment E859 is a follow-on to experiment E802 that uses a second-level trigger based on particle identification to enhance the collection of rare species. We now have high statistics spectra over a broad range in rapidity and transverse momentum for both positive and negative kaons, allowing a detailed comparison of these particles for the first time in AGS heavy-ion experiments. The K − are seen to have a narrower rapidity distribution than the K +, a difference which may be due to the way in which resonances contribute to the yield of K − and K +.

A new 1–2 GeV/c separated beam for BNL

Abstract A 1–2 GeV/c beam line has been constructed at the Brookhaven National Laboratory alternating gradient synchrotron (BNL AGS). The beam line is optimized to deliver an intense clean beam of 1.8 GeV/c negative kaons for an H particle search experiment and incorporates two stages of velocity selection with the magnetic optics corrected to third order. Details of the beam line design as well as results of the commissioning will be discussed.

Strangeness production in proton and heavy-ion collisions at 14.6A GeV.

Rapidity and transverse momentum distributions of ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$, ${\mathit{K}}^{\ifmmode\pm\else\textpm\fi{}}$, and p have been computed for p+Be, p+Au, and Si+Au collisions at 14.6A GeV with the Monte Carlo quark-gluon string model (QGSM). The calculations are compared to experimental data at the same energy. The QGSM reproduced the shapes and approximately absolute values of the minimum bias rapidity distribution for all particles except the pions in p+Au data. The model also reproduced the rapidity distribution for protons and ${\mathit{K}}^{+}$ in the central Si+Au collisions. However, we overestimated the enhancement at low ${\mathit{p}}_{\mathit{t}}$ for pions and negative kaons. As a consequence, the QGSM also produces an excess of pions and ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ in the rapidity distribution below y=2, and predicted an overall ${\mathit{K}}^{+}$/${\mathrm{\ensuremath{\pi}}}^{+}$ enhancement by a factor of 1.4--1.9 as compared to pp data, instead of a factor of 4 as obtained by the E802 Collaboration.

Trapping of negative kaons by metastable states during the atomic cascade in liquid helium.

We observed two distinct peaks, 205-MeV/c ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ and 235-MeV/c ${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$, associated with ${K}_{\ensuremath{\pi}2}^{\mathrm{\ensuremath{-}}}$ and ${K}_{\ensuremath{\mu}2}^{\mathrm{\ensuremath{-}}}$ decays at rest, respectively, from negative kaons stopped in liquid helium. These peaks were found to be delayed with respect to the stopping ${K}^{\mathrm{\ensuremath{-}}}$, showing that stopped ${K}^{\mathrm{\ensuremath{-}}}$ mesons of about 2% fraction are trapped in metastable states with an overall lifetime of about 40 nsec. This observation provides a direct evidence for Condo's trapping hypothesis for the at-rest decay components of ${K}^{\mathrm{\ensuremath{-}}}$ and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ in liquid helium.

Exotic-atom measurement of the magnetic dipole moment of theΣ−hyperon

The magnetic dipole moment of the ..sigma../sup -/ hyperon has been determined from ..sigma../sup -/-atom x-ray transitions in natural lead and tungsten. Negative kaons were stopped in a target which consisted of sheets of W or Pb immersed in liquid hydrogen. The ..sigma../sup -/ resulting from the reaction K/sup -/p..--> sigma../sup -/..pi../sup +/ were tagged by observing the monoenergetic ..pi../sup +/. X rays from ..sigma../sup -/ atoms were detected by intrinsic Ge detectors. The x-ray lines were analyzed for fine-structure splitting and the magnetic moment was determined from the measured splitting. The value obtained for the magnetic moment is ..mu..(..sigma../sup -/) = (-1.105 +- 0.029 +- 0.010)..mu../sub N/ where the first error is statistical and the second systematic. This value is in reasonable agreement with measurements that used precession techniques and with the theoretical predictions of simple quark models.

A measurement of the kaon charge radius

The negative kaon electromagnetic form factor has been measured in the space-like q 2 range 0.015–0.10 (GeV/ c ) 2 by the direct scattering of 250 GeV kaons from electrons at the CERN SPS. It is found that the kaon mean square charge radius 〈 r 2 K 〉 = 0.34 ± 0.05 fm 2 . From data collected simultaneously for πe scattering, the difference between the charged pion and kaon mean square radii (which is less sensitive to systematic errors) is found to be 〈 r 2 π 〉 − 〈 r 2 K = 0.1 0 ± 0.045 fm 2 .

Beams for kaon research

A proposed 1–2 GeV/c kaon beam line for BNL, designed to deliver momentum analyzed negative kaon beams with intensities above 10 6 per spill, is discussed. The beam intensity is expected to be about an order of magnitude greater than presently available and it is expected to be a clean beam with no more than 1:1 ( π −, μ −, e −)/K −. The beam line will allow a detailed investigation of strangeness −2 systems as well as continued investigations of strangeness −1 systems.

The (K −, π+) strangeness exchange reaction on 16O

Using negative kaons of 450 MeV/ c momentum, Σ hypernuclear states have been produced in the (K −, π +) reaction on 16O. The observed states are interpreted as the recoilless production of Σ − particles in the p 3 2 and p 1 2 orbits of the Σ 16C hypernucleus. Their energy splitting gives a constraint to the magnitude of the spin-orbit coupling for the Σ − particles in the nucleus.