Negative Kaons Research Articles

Laser-assisted kaon decay and CPT symmetry violation

In this paper, we have investigated the charged kaons decay at the lowest order in the presence of a circularly polarized laser field. To be more precise, we have examined the leptonic decay of both positive (matter) and negative (antimatter) kaon which weakly decay via the exchange of W boson. Indeed, we have derived the expression of the leptonic decay width, the leptonic branching ratio, the leptonic ratio and the charged kaon lifetime by using the decay matrix approach. In addition, by using numerical computation, we have presented and discussed how the laser field influences these physical quantities. Moreover, we have analyzed the effect of the laser field on the parameter associated to the CPT symmetry. Then, we have concluded that, in the presence of an electromagnetic field and based on this CPT symmetry parameter, it is possible to control the dominance of matter over antimatter or vice-versa by applying an external field to either violate or conserve the CPT symmetry.

Exploring hot and dense QCD matter with HADES

Experiments at snn 3 GeV provide the lowest energy point of the global effort made by the heavy-ion community in order to map the QCD phase diagram. This correspond to the highest baryon chemical potential, 700-900 MeV according to the universal freeze-out curve, and temperatures of the fireball of 60-80 MeV. The formed matter can be characterized in terms of particle spectra, fluctuations and correlations. The dilepton spectrum is dominated by thermal emission from the medium and it is sensitive to in medium hadron properties. Strangeness production occurs below the free nucleon-nucleon threshold and it is a sensitive probe to test models of strangeness propagation in matter and its coupling to baryons. Data show a common scaling of measured yields as a function of number of participating nucleons independently on the strangeness content or mass of the hadron. Strangeness propagation in cold nuclear matter produced in pion induced reactions on heavy and light targets shows a significant absorption of negative kaons in heavy targets as well as a similar behaviour of ϕ indicating a strong coupling of ϕ with nucleons. Two-pion correlations, flow harmonics, fluctuations are explored as well in order to further pin down the properties of the created matter.

The relative efficiency of 7LiF:Mg,Ti (MTS-7) and 7LiF:Mg,Cu,P (MCP-7) thermoluminescent detectors for muons, pions and kaons over a broad energy range (2 keV–1 GeV): theoretical calculations using the Microdosimetric d(z) Model

The relative efficiency of the two most commonly used 7LiF:Mg,Ti (MTS-7) and 7LiF:Mg,Cu,P (MCP-7) thermoluminescent detectors was calculated using the Microdosimetric d(z) Model for negative muons, positive muons, negative pions, positive pions, negative kaons, positive kaons and neutral kaons with energies spanning from 2 keV to 1 GeV. The needed microdosimetric specific energy probability density distributions were obtained by performing Monte Carlo radiation transport simulations using the computer code PHITS in the optimal 40 nm site size. The obtained efficiency values were found to be strongly affected by the particle type, its energy and the detector, ranging from 0.25 to 1.08. Possible correlations with average microdosimetric quantities such as the frequency- and dose-mean specific energy were discussed in detail. Finally, the effect of including the nominal dopant concentrations in the simulations used for the assessment of the microdosimetric spectra was proven to play a marginal role in the computation of the relative efficiency values, in agreement with what was found in previous studies for ions, photons, electrons, positrons and mixed particle fields.

Transverse momentum spectra of mesons in p+p collisions at CERN SPS energies from the UrQMD transport model

The UrQMD transport model, version 3.4, is used to study the new experimental data on total yields, rapidity distributions and transverse momentum spectra of π±, K±, p and $\bar p$ produced in inelastic p + p interactions at SPS energies, recently published by the NA61/SHINE Collaboration. The comparison of model predictions to these new measurements is presented as a function of collision energy. In addition, we compare with the experimental data the results on kaon-over-pion multiplicity ratio and the inverse slope parameter of negative kaons produced at midrapidity. A complicated pattern of discrepancies between the experimental data and the UrQMD transport model is apparent. We conclude that new experimental data analyzed in this contribution still constitute a challenge for the present version of the model.

Low energy interaction studies of negative kaons in light nuclear targets by AMADEUS

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, 4He, 9Be and 12C, 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.

Energy dependence of event-by-event kaon fluctuation in Au + Au collisions at $$\sqrt {^SNN} $$ = 19.6–200 GeV—a simulated study

A detailed study of energy dependence of event-by-event pseudorapidity fluctuations of the produced kaons in Au + Au collisions at \(\sqrt {^SNN} \) = 19.6–200 GeV in terms of the Φ measure has been carried out in the framework of the UrQMD model. The study of event-by-event kaon fluctuation in pseudorapidity space reveals energy dependence. It has been seen that as energy increases event-by-event fluctuation increases for both positive and negative kaons. Moreover, the positive kaons show larger event-by-event fluctuations than the negative kaons.

Kaon and pion parton distribution amplitudes to twist three

We compute all kaon and pion parton distribution amplitudes (PDAs) to twist three and find that only the pseudotensor PDA can reasonably be approximated by its conformal limit expression. At terrestrially accessible energy scales, the twist-two and pseudoscalar twist-three PDAs differ significantly from those functions commonly associated with their forms in QCD's conformal limit. In all amplitudes studied, $SU(3)$ flavor-symmetry breaking is typically a 13% effect. This scale is determined by nonperturbative dynamics; namely, the current-quark-mass dependence of dynamical chiral symmetry breaking. The heavier quark is favored by this distortion; for example, support is shifted to the $s$-quark in the negative kaon. It appears, therefore, that at energy scales accessible with existing and foreseeable facilities, one may obtain reliable expectations for experimental outcomes by using these ``strongly dressed'' PDAs in formulas for hard exclusive processes. Following this procedure, any discrepancies between experiment and theory will be significantly smaller than those produced by using the conformal-limit PDAs. Moreover, the magnitude of any disagreement will either be a better estimate of higher-order, higher-twist effects or provide more realistic constraints on the Standard Model.

Influence ofϕmesons on negative kaons in Ni + Ni collisions at1.91A GeV beam energy

$\phi$ and K$^-$ mesons from Ni+Ni collisions at the beam energy of 1.91A GeV have been measured by the FOPI spectrometer, with a trigger selecting central and semi-central events amounting to 51% of the total cross section. The phase space distributions, and the total yield of K$^-$, as well as the kinetic energy distribution and the total yield of $\phi$ mesons are presented. The $\phi$\K$^-$ ratio is found to be $0.44 \pm 0.07(\text{stat}) ^{+0.18}_{-0.12} (\text{syst})$, meaning that about 22% of K$^-$ mesons originate from the decays of $\phi$ mesons, occurring mostly in vacuum. The inverse slopes of direct kaons are up to about 15 MeV larger than the ones extracted within the one-source model, signalling that a considerable share of gap between the slopes of K$^+$ and K$^-$ could be explained by the contribution of $\phi$ mesons to negative kaons.

Performances of an Active Target GEM-Based TPC for the AMADEUS Experiment

In this paper, we present the R & D activity on a new GEM-based Time Projection Chamber (GEM-TPC) detector for the inner region of the AMADEUS experiment, which is aiming to perform measurements of low-energy negative kaon interactions in nuclei at the DAΦNE e+ e- collider at LNF-INFN. A novel idea of using a GEM-TPC as a low mass target and detector at the same time comes motivated by the need of studying the low energy interactions of K- with nuclei in a complete way, tracking and identifying all of the produced particles. Even more, what makes the experimental proposal revolutionary is the possibility of using different gaseous targets without any other substantial intervention on the experimental setup, making it a flexible multipurpose device. This new detection technique applied to the nuclear physics requires the use of low-radiation length materials and very pure light gases such as Hydrogen, Deuterium, Helium-3, Helium-4, etc. In order to evaluate the GEM-TPC performances, a 10 × 10 cm2 prototype with a drift gap of 15 cm has been realized. The detector was tested at the πM1 beam facility of the Paul Scherrer Institut (PSI) with low momentum pions and protons. Detection efficiency and spatial resolution, as a function of gas mixture, gas gain and ionazing particle, are reported and discussed.

Classical and semiclassical description of initial distributions of kaon capture by atomic hydrogen and deuterium

The moderation and capture of negative kaons by atomic hydrogen and deuterium were investigated by the classical trajectory Monte–Carlo (CTMC) and the semiclassical fermion molecular dynamics (FMD) methods. The dependence of ionization and capture cross sections on initial kaon energy was also studied. The initial populations of kaonic atom levels were calculated. The n distributions of kaonic atoms peaked close to the orbital giving optimum overlap with the displaced electronic orbital. The angular momentum distributions, l, are found to be approximately statistical but cut off at large l smaller than lmax = n − 1 in large n. The results are compared with the adiabatic ionization, diabatic states, and Born approximation methods. The FMD results were found to be in better agreement with quantum mechanical calculations than the ones from CTMC. The kaon kinetic energy spectrum prior to capture was calculated, which reveals that capture occurs at small collision energies up to the ionization energy. Also, the calculations show that kaonic hydrogen (deuterium) atoms have kinetic energies below 0.3 a.u. (0.15 a.u.) after formation.

Unlocking the secrets of the kaon–nucleon/nuclei interactions at low-energies: The SIDDHARTA(-2) and the AMADEUS experiments at the DAΦNE collider

The DAΦNE electron–positron collider at the Laboratori Nazionali di Frascati of INFN has made available a unique quality low-energy negative kaons “beam”, which is being used to unlock the secrets of the kaon–nucleon/nuclei interactions at low energies by the SIDDHARTA(-2) and the AMADEUS experiments. SIDDHARTA has already performed unprecedented precision measurements of kaonic atoms, and is being presently upgraded, as SIDDHARTA-2, to approach new frontiers. The AMADEUS experiment already started a data taking with a dedicated carbon target, plans to perform in the coming years precision measurements on kaon–nuclei interactions at low-energies, in particular to study the possible formation of kaonic nuclei and the Λ ( 1405 ) . The two experiments are briefly presented in this paper.

Kaonic helium X-ray measurement in the SIDDHARTA experiment

The SIDDHARTA (SIlicon Drift Detector for Hadronic Atom Research with Timing Application) collaboration performed X-ray spectroscopy measurement of kaonic atoms at the DAΦNE e+e−collider. Low energy negative kaons from DAΦNE ϕ-factory were stopped in gaseous targets to produce kaonic atoms. We employed specially designed Silicon Drift Detectors(SDDs) to detect the kaonic X-rays. Based on the energy of kaonic- 4He 3d → 2p transition, we determined a new value of the 2p level strong-interaction shift of kaonic- 4He: 0 ± 6 (stat.)± 2 (syst.) eV[1]. Together with the result of recent E570 experiment[2] at the KEK-PS, a small shift (if any) of kaonic- 4He 2p level has become well established.

Multidimensional study of hadronization in nuclei

Hadron multiplicities in semi-inclusive deep-inelastic scattering were measured on neon, krypton and xenon targets relative to deuterium at an electron(positron)-beam energy of 27.6 GeV at HERMES. These ratios were determined as a function of the virtual-photon energy nu, its virtuality Q2, the fractional hadron energy z and the transverse hadron momentum with respect to the virtual-photon direction pt . Dependences were analysed separately for positively and negatively charged pions and kaons as well as protons and antiprotons in a two-dimensional representation. Compared to the one-dimensional dependences, some new features were observed. In particular, when z > 0.4 positive kaons do not show the strong monotonic rise of the multiplicity ratio with nu as exhibited by pions and negative kaons. Protons were found to behave very differently from the other hadrons.

Hadronization in the Nuclear Media

The influence of the nuclear environment on the production of charged pions, kaons and (anti)protons in semi-inclusive deep inelastic scattering has been studied by the HERMES experiment at DESY using a 27.6 GeV positron beam. Identified hadron multiplicities have been measured for helium, neon, krypton and xenon relative to that of deuterium as a function of ν, z and \({p_{t}^{2}}\) . Dependences have been extracted in a one and two-dimensional representation, i.e. in the form of detailed binning over one variable and integrating over all other variable or three slices over the other variable. The most prominent feauteres compared to a one-dimensional analysis are changes of the ν-, \({p_{t}^{2}}\) two-dimensional dependences of ratios, in particular in case of protons. In general pions and negative kaons show similar dependences, however, positive kaons, protons and antiprotons behave quite differently.

X-RAY SPECTROSCOPY OF KAONIC ATOMS AT DAΦNE

The SIDDHARTA experiment aims a precise measurement of K -series kaonic hydrogen x-rays and the first-ever measurement of the kaonic deuterium x-rays to determine the strong-interaction energy-level shifts and widths of the lowest lying atomic states. These measurements offer a unique possibility to precisely determine the isospin-dependent kaon-nucleon ( KN ) scattering lengths [1] which are directly connected with the physics of the KN interaction. Kaonic Helium transitions to the 2p level ( L -lines) were as well measured. The experiment has been performed at the DAΦNE e+e- collider which produces the Φ-resonance. The resulting low energy negative charged kaons, coming from the Φ decay, are well suited to be stopped efficiently in a high density gas target for producing such kind of atoms. As x-ray detectors, we employed 144 Silicon Drift Detectors developed especially for this experiment, having good energy resolution of 140 eV FWHM at 6keV and time resolution of sub-micro seconds. The data taking was completed in November 2009. In this paper, an overview of this experiment and preliminary results are presented, together with future plans.

Kaon-nuclei interaction studies at low energies (the AMADEUS experiment)

The AMADEUS experiment aims to perform dedicated precision studies in the sector of low-energy kaon-nuclei interaction at the DAΦNE collider at LNF-INFN. In particular, the experiment plans to perform measurements of the so-called (very debated) deeply bound kaonic nuclei and, if existent, of their properties (binding energies and widths). Other important measurements proposed by AMADEUS are the low-energy interaction studies of negative kaons in various targets. The AMADEUS physics program and the proposed setup (consisting of dedicated additional items inserted in the central region of the KLOE detector) will be presented. Preliminary results from the analysis of the KLOE existing data and future plans will be discussed.

Low-Energy Kaon–Nucleon/Nuclei Interaction Studies at DAΦNE (SIDDHARTA and AMADEUS Experiments)

The DAΦNE electron–positron collider at the Laboratori Nazionali di Frascati of INFN has made available a unique quality low-energy negative kaons “beam”. The SIDDHARTA experiment used this beam to perform unprecedented precision measurements on kaonic atoms, while the AMADEUS experiment plans to perform in the coming years precision measurements on kaon–nuclei interactions at low-energies, in particular to study the kaonic nuclei. The two experiments are briefly presented in this paper.

Investigation ofKp- andKd-atom formation and their collisional processes with hydrogen and deuterium targets by the classical-trajectory Monte Carlo method

The classical-trajectory Monte Carlo method has been used to study the capture of negative kaons by hydrogen and deuterium atoms; subsequently, the elastic scattering, Stark mixing, and Coulomb deexcitation cross sections of $\mathit{Kp}$ and $\mathit{Kd}$ atoms have been determined. The results for kaonic atom formation confirm the initial conditions that have been parametrically applied by most atomic cascade models. Our results show that Coulomb deexcitation in $\mathit{Kp}$ and $\mathit{Kd}$ atoms with $\ensuremath{\Delta}n>1$ is important in addition to $n=1$. We have shown that the contribution of molecular structure effects to the cross sections of the collisional processes is larger than the isotopic effects of the targets. We have also compared our results with the semiclassical approaches.

Kaonic atoms measurements at the DAΦNE accelerator

The DAΦNE electron-positron collider at the Frascati National Laboratories has made available a unique “beam” of negative kaons. The SIDDHARTA (SIlicon Drift Detector for Hadronic Atom Research by Timing Application) experiment, successor of DEAR (DAΦNE Exotic Atom Research), aims 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 final goal is to extract the isospin dependent antikaon-nucleon scattering lengths which contribute to the understanding of aspects of non-perturbative QCD in the strangeness sector. Other possible hadronic atoms measurements at DAΦNE are under study.

Performances of a GEM-based TPC prototype for new high-rate particle experiments

Time projection chamber (TPC) has been successfully used as a central tracker and a particle identification device in a number of a high-energy physics experiments. However, the performance requirements on TPC for new high-rate particle experiments greatly exceed the abilities of traditional TPC readout by multi-wire proportional chamber (MWPC). Gas Electron Multiplier (GEM) detector has great potential to improve TPC performances when used as amplification device. In this paper we present the R&D activity on a new GEM-based TPC (TPG) detector for the inner part of the AMADEUS experiment, a new experimental proposal at DA Φ NE accelerator at LNF, aiming to perform measurements of the low-energy negative kaons interactions in nuclei. In order to evaluate the TPG feasibility, a 10 × 10 cm 2 prototype with a drift length up to 15 cm are designed. The performances of a 10 × 10 cm 2 pre-existing prototype with a reduced drift gap, operated with Ar / CO 2 / CF 4 (45/15/40) gas mixture and successfully tested at BTF facility, are presented. The gas mixture properties, such as the electron drift velocity and the diffusion, have been measured and they result comparable with those simulated with Garfield. A good resolution along the beam direction ( z-coordinate), sufficient for a more large scale TPG in AMADEUS, is achieved.