Neutral Kaon Production Research Articles

Kaon photoproduction from the deuteron in a Regge-plus-resonance approach

We present a Regge-inspired effective-Lagrangian framework for kaon photoproduction from the deuteron. Quasi-free kaon production is investigated using the Regge-plus-resonance (RPR) elementary operator within the relativistic plane-wave impulse approximation. The RPR model was developed to describe photoinduced and electroinduced charged-kaon production off protons. We show how this elementary operator can be transformed in order to account for the production of neutral kaons from both protons and neutrons. The model results for kaon photoproduction from the deuteron compare favourably to the 2H(g,K)YN data published to date.

Neutral kaon production in p $+$ p and p $+$ Nb collisions

The kaon nucleus (KN) interaction in dense nuclear matter is predicted to be repulsive and increasing with density. However, determined values for this potential are not yet consistent with each other (Benabderrahmane et al., Phys Rev Lett 102:182501, 2009; Agakishiev et al., Phys Rev C 82:044907, 2010; Buscher et al., Eur Phys J A 22:301–317, 2004). We analyze \(K^0_S\) mesons identified with the HADES detector in p+p and p+ 93Nb reactions at 3.5 GeV kinetic beam energy. To determine the KN potential at normal nuclear density we propose to compare the \(K^0_S\) differential distributions in p+ 93Nb and p+p collisions. High statistics of low p t -kaons (p t < 100 MeV/c) ensure the sensitivity of our measurements to the nuclear matter effects. We present the data analysis method and first results.

Nonsinglet kaon fragmentation function frome+e−kaon production

We perform fits to the available charged and neutral kaon production data in $e^++e^-\to K+X$, $K=K^\pm and K^0_S$, and determine the non-singlet combination of kaon fragmentation functions $D_u^{K^\pm}-D_d^{K^\pm}$ in a model independent way and without any correlations to the other fragmentation functions. Only nuclear isospin invariance is assumed. Working with non-singlets allows us to include the data at very low momentum fractions, which have so far been excluded in global fits, and to perform a first NNLO fit to fragmentation functions. We find that the kaon non-singlet fragmentation function at large $z$ is larger than that obtained by the other collaborations from global fit analysis and differs significantly at low $z$.

Annihilation at rest of antiprotons and protons into neutral particles

Annihilation of antiprotons and protons at rest into neutral particles has been studied with the Crystal Barrel detector at LEAR. Annihilation frequencies are determined for final states containing π 0, η, η′ and ω mesons using a liquid and a room temperature, 12 bar, gaseous hydrogen target. Including annihilation frequencies for production of neutral kaons from other experiments, the identified reactions for annihilation in liquid hydrogen add up to a branching fraction of (3.56±0.28)% per annihilation compared to the frequency of (3.50±0.30)% with which we observe the all-neutral decay modes inclusively. Since the exclusive final states are normalized to the Crystal Barrel measurement of the π 0 π 0 branching ratio, the latter result is strongly supported by this present study.

Kaon production in S+nucleus and Pb+Pb collisions at CERN SPS

Charged and neutral kaon production in S-nucleus and Pb-Pb collisions has been measured at CERN in the NA35 and NA49 experiments, close to mid-rapidity. The production ofK± in S+S, Ag, Au at 200 GeV/nucleon was measured via their one-prong (kink) topology inside a Time Projection Chamber (TPC). The resulting charged kaon yields are in agreement with other measurements done in the same experiment. TheK+/K− ratio was found to be 1.30±0.15 in central S+Au interactions. The production ofKS0 in Pb+Pb collisions was measured using the NA49’s large (Main) TPCs outside the magnetic field. The resulting yields are compatible with other measurements performed in the same experiment, within the quoted systematic errors. The preliminary rapidity distribution in Pb+Pb scales with the number of participants if compared to S+S collisions. From this we conclude that no further strangeness enhancement (relative to nucleon-nucleon collisions) is observed in going from S+S to Pb+Pb.

The production of neutral kaons in Z0 decays and their Bose-Einstein correlations

The production of neutral kaons in e+e− annihilation at centre-of-mass energies in the region of the Z0 mass and their Bose-Einstein correlations are investigated with the OPAL detector at LEP. A total of about 1.26×106 Z0 hadronic decay events are used in the analysis. The production rate of K0 mesons is found to be 1.99±0.01±0.04 per hadronic event, where the first error is statistical and the second systematic. Both the rate and the differential cross section for K0 production are compared to the predictions of Monte Carlo generators. This comparison indicates that the fragmentation is too soft in bothJetset andHerwig. Bose-Einstein correlations in Ks0Ks0 pairs are measured through the quantityQ, the four momentum difference of the pair. A threshold enhancement is observed in Ks0Ks0 pairs originating from a mixed sample of\(K^0 \bar K^0\) and K0K0 (\(\bar K^0 \bar K^0\)) pairs. For the strength of the effect and for the radius of the emitting source we find values of λ=1.14±0.23±0.32 andR0=(0.76±0.10±0.11) fm respectively. The first error is statistical and the second systematic.

InclusiveK s 0 , Λ and $$\bar \Lambda$$ -production in $$\bar p$$ p-interactions at 22.4 GeV/c

InclusiveKs0, Λ and\(\bar \Lambda\)-production has been investigated in\(\bar p\)p-interactions at 22.4 GeV/c. Total and topological cross sections and multiplicity characteristics of neutral strange particles have been determined. DifferentialKs0 and Λ-cross sections and also characteristics of annihilation processes with neutral kaon production have been studied. It is shown that the difference of the shapes of the invariantx-distributions forK-mesons in the fragmentation region for annihilation and non-annihilation processes can be described in the framework of the “dual” valon model, but not by considering the current (undressed) quark recombination mechanisms only. The polarization of Λ and\(\bar \Lambda\)-hyperons has been measured.

Charged particle and neutral kaon production ine + e − annihilation at PETRA

The mean charged multiplicity as well as its distribution has been measured as a function of c.m. energy in the reactione+e−→hadrons. Fragmentation models are compared with the data. After applying radiative corrections the mean charged multiplicity is measured to be 8.4±0.3±0.6 at 12 GeV, 13.1±0.3±0.6 at 30 GeV and 13.6±0.3±0.6 at 35 GeV. The ratio of mean charged multiplicity to the dispersion ( /Dch) is almost constant in the energy range studied, indicating KNO scaling of the charged multiplicity. The inclusive differential cross sections(dσ/dx p ) shows scaling violation in the highx p region (x p >0.15). The absolute value of the scaling violation is consistent with the result of 2nd order QCD calculations. The production of neutral kaons has been investigated by identifying the decayK S 0 →π+π−. The production probability for a strange quark relative to that of au ord quark in the fragmentation, γ s , has been determined to be 0.27±0.03±0.05 averaged over c.m. energies from 12 to 35 GeV. Momentum spectra for neutral kaons are presented and are compared with model predictions.

Inclusive neutral kaon production in 70 GeV/c K +p interactions

The inclusive production of neutral kaons in 70 GeV/ c K +p interactions is studied with the CERN BEBC bubble chamber. The (semi-)inclusive cross sections are interpreted in terms of the various strangeness channels leading to neutral kaon production. The invariant inclusive cross section for kaon production is studied as a function of p t 2 and the Feynman variable x. The latter distributions are considered both “raw” and corrected for the presence of K 0's resulting from K ∗ decay. They are compared with the predictions expected from the Regge-Mueller formalism, the recombination model and fragmentation models.

InclusiveK *+(892) andK *0(892) production inK + p interactions at 32 GeV/c

Total and semi-inclusive cross sections, longitudinal and transverse momentum distributions and spin density matrix elements of theK*+(892) andK*0(892) produced in the inclusive reactionsK+p→K*+(892)+X andK+p→K*0(892)+X at 32 GeV/c are studied in detail. The inclusive spectra of theK*(892) and their decay products are compared with pion and neutral kaon production. TheK*+(892) andK*+(892) are dominantly produced by kaon fragmentation processes. The dependence of average transverse momentum vs.x for resonances has been investigated for the first time.

Neutral kaon production in K +p interactions at 32 GeV/ c

The production of neutral kaons in the reaction K +p → K n + X is studied at the incident momentum of 32 GeV/ c. Inclusive cross sections and single-particle distributions are presented and compared with the data at lower energies. The total inclusive cross section amounts to 7.9 ± 0.3 mb at 32 GeV/ c and is significantly higher than at lower energies due to the rapid rise of multikaon production. The fraction of K n's coming from the decay of the K ∗ resonances stays roughly constant with energy between 8.2 and 32 GeV/ c. In the central and beam fragmentation regions the single-particle distributions reveal no energy dependence between the 16 and 32 GeV/ c data in contrast with the behaviour at lower energies, while in the proton fragmentation region the data are compatible with the trend observed at lower energies and with theoretical expectations.

Neutral hadrons in EAS: an energy threshold above 105GeV?

The authors compare measurements of charged/neutral hadrons in extensive air showers with calculations that include production of neutral kaons and nucleon-antinucleon pairs. At approximately 2*105 GeV, observation and calculation agree; above approximately 3*105 GeV, a different experiment appears to be significantly lower than calculation. If confirmed, the latter experiment will require a threshold in the nuclear physics around this energy.

Inclusive production of lambda and neutral kaon in K−p interactions at 3.93 GeV/c and 14.3 GeV/c

Lambda and neutral-kaon production is studied in K−p interactions at 3.93 and 14.3 GeV/c. Topological inclusive cross-sections are given at both energies. Invariant cross-sections for lambdas and neutral kaons are presented as a function of the Feynmanx-variable and are found to decrease in magnitude and vary their shapes with energy. The\(AK\overline K \) production, which represents (9±2)% and (29±3)% of the lambda inclusive cross-section at 3.93 GeV/c and 14.3 GeV/c respectively, yields mainly backward lambdas. The shapes of the transverse-momentum invariant distributions vary withx, but are roughly independent of energy. The lambda polarization is studied as a function ofx at both incident momenta: for fast lambdas it is negative, as observed in reactions where nucleon exchange is dominant.