Azimuthal Distributions of K + Mesons in Heavy-Ion Collisions

Strange mesons are considered to be sensitive to in-medium modifications. Theory predicts a repulsive K ⁺ N potential and an attractive K ^? N potential in dense matter. A repulsive K ⁺ N potential would repel the K ⁺ mesons from the bulk of the nucleons and therefore cause a preferred out-of-plane emission of K ⁺ mesons at midrapidity and a directed flow opposite to the nucleons at target and projectile rapidity. One of observables to probe in-medium effects is the azimuthal emission pattern of K ⁺ mesons in heavy ion collisions. KaoS collaboration has measured the azimuthal distributions of K ⁺ mesons in Au + Au reactions at 1.5 A GeV and Ni + Ni reactions at 1.93 A GeV. Data show that K ⁺ mesons exhibit a pronounced enhancement at ${\phi = {90}^\circ}$ , i.e. perpendicular to the reaction plane. The data have also been fitted using the first two components of a Fourier series to get the directed flow v ₁ and elliptic flow v ₂. We used the quantum molecular dynamics model based on the covariant kaon dynamics to simulate the Au + Au collisions at 1.5 A GeV and the Ni + Ni collisions at 1.93 A GeV, to analyze the azimuthal distributions of K ⁺ mesons, and to calculate v ₁ and v ₂ of K ⁺ mesons. Calculated results with a repulsive in-medium K ⁺ N potential can reasonably describe the features of KaoS data. This indicates that the azimuthal distribution is one of sensitive probes to extract information on in-medium properties at high densities.     

Proton dissociative ρ and elastic φ electroproduction at HERA

The electroproduction of ρ mesons with proton diffractive dissociation for Q ² > 7 GeV² and the elastic electroproduction of φ mesons for Q ² > 6 GeV² are studied in e ⁺ p collisions at HERA with the H1 detector, for an integrated luminosity of 2.8 pb^-1. The dependence of the cross sections on P _t ² and Q ² is measured, and the vector meson polarisation obtained. The cross section ratio between proton dissociative and elastic production of ρ mesons is measured and discussed in the framework of the factorisation hypothesis of diffractive vertices. The ratio of the elastic cross section for φ and ρ meson production is investigated as a function of Q ².     

Elastic and inelastic scattering of K+ mesons on deformed nuclei

Various aspects of the scattering of medium energy K⁺ mesons on deformed nuclei are investigated in the light of a specific example, viz. the scattering of 800 MeV/c positive kaons on ¹⁵²Sm. The effects of coupled channels are found to be significant despite the fact that the K⁺ meson is a rather weakly interacting hadronic probe. The localization of the reaction mechanism on a deformed target is discussed for both protons and K⁺ mesons to compare the extent of surface and volume probing capability of these two projectiles. The results show the remarkable sensitivity of the elastic and inelastic K⁺ differential cross sections to the differences between the neutron and proton density distributions in deformed nuclei.     

Parity violation in pion electroproduction and photoproduction with a proton target

Parity violation in pion electroproduction and photoproduction on a proton target is investigated as a possible means of elucidating the structure of the electronic and non-leptonic neutral weak currents. We calculate both parity-violating effects caused directly by Z-boson exchange, which contributes only to electron scattering, and those due to parity-violating electromagnetic and nuclear interactions. The asymmetry in electroproduction is of order 20^?5, whereas that in photoproduction is ～10^?7. The sensitivity to the parameter sin²θ_w is investigated; it is a maximum at backward electron scattering angles. In addition to the Born terms, contributions from the Δ(1232) resonance and the light vector mesons [?(776) and ω(782)] are included in the model. Fits to the observed π⁰ and π⁺ electroproduction and photoproduction cross sections indicate that the model accounts for the production data in the medium energy region.     

Meson electro-magnetic form factors in an extended Nambu–Jona-Lasinio model including heavy quark flavors

Based on an extended NJL model including heavy quark flavors, we calculate the form factors of pseudoscalar and vector mesons. After taking into account the vector-meson-dominance effect, which introduces a form factor correction to the quark vector coupling vertices, the form factors and electric radii of π+and K+pseudo-scalar mesons in the light flavor sector fit the experimental data well. The magnetic moments of the light vector mesonsρ+and K*+are comparable with other theoretical calculations. The form factors in the light-heavy flavor sector are presented to compare with future experiments or other theoretical calculations.     

Search for new SS states in the K− induced K+K− system

Results from the first PWA of the K⁺K^? system produced by incident K^?, are presented in the mass range from the threshold to 1.70 GeV. In the P and D waves only the φ and f′ mesons are observed and their production mechanism studied. A broad S wave peaking at 1.4 GeV is observed but the lack of information about its phase makes the search for new 0⁺⁺ mesons inconclusive.     

Timelike Compton Scattering at JLab

It is demonstrated, that with exclusive final state, data from electron scattering experiments that are recorded with loose trigger requirements can be used to analyze photoproduction reactions. A preliminary results on Timelike Compton Scattering using the electroproduction data from the CLAS detector at Jefferson Lab are presented. In particular, using final state (pe ^? e ⁺) photoproduction of vector mesons and timelike photon is studied. Angular asymmetries in Timelike Compton Scattering region is compared with model predictions in the framework of Generalized Parton Distribution.     

Deep processes in nuclei and in-medium dressing of the nucleons and mesons

K⁺ scattering and quasielastic electron scattering from nuclei are expected to provide information about the nucleons and mesons in the inner regions of nuclei. The K⁺- nucleus cross sections and the quasielastic electron-nucleus response functions have been calculated taking into account the same in-medium dressing of the nucleons and the same coupling of the σ and ω mesons to the polarization of nuclear matter. We obtain a good agreement with experimental data for the two processes.     

Effects of Final State Interactions in Pure Annihilation Decay of B+ → D+K0*

The decay of the B ⁺ meson to the D ⁺ and K ⁰* mesons is a pure annihilation decay. For this reason, in the framework of the quantum chromodynamics factorization (QCDF) approach, this decay has a small amplitude and a small branching ratio. In this research we find that, before the D ⁺ and K ⁰* mesons are produced in the final states, pair mesons such as D _s ⁺* and D _s ⁺ρ⁰ are produced. The intermediate-state mesons via the exchange of K ⁰(K ⁰*) and D ⁺(D ⁺*) go to the D ⁺ and K ⁰* final state mesons. However we calculate the B ₊ → D ⁺ K ⁰* decay in two different frameworks. The first framework is the QCDF method and the second one is final state interaction (FSI). The experimental branching ratio of B ₊ → D ₊ K ⁰* decay is less than 3 × 10^–6, and our results obtained by the QCDF method and FSI are (0.35 ± 0.04) × 10^–6 and (2.94 ± 0.10) × 10^–6, respectively.     

Study of the reaction e+e− → K+K− in the total energy range 1400–2060 MeV

The e⁺e^? → K⁺K^? cross section has been measured between 1400 and 2060 MeV. About 500 K⁺K^? events were detected in the magnetic detector DM1 at the Orsay storage rings DCI. The charged kaon form factor is appreciably higher than predicted by only the ?, ω, ø tails, suggesting contributions from higher vector mesons.     

Production properties ofD 0,D +,D *+ andD s + in 230 GeV/cπ − andK −-Cu interactions

We have studied the hadronic production of charmed mesons in the NA 32 experiment at CERN. A special trigger together with a high resolution vertex detector consisting of charge coupled devices and silicon microstrip detectors allowed the selection of very clean samples of charmed mesons. We have collected 852 fully reconstructed decays: 60D _s ⁺ →K ⁺ K ^?π⁺, 543D°→K ^?π⁺ andK ^?π⁺π^?π⁺ as well as 249D ⁺→K ^?π⁺π⁺ (or charge conjugate). 147 mesons out of our \({{D^0 } \mathord{\left/ {\vphantom {{D^0 } {\bar D^0 }}} \right. \kern-0em} {\bar D^0 }}\) sample were produced via chargedD ^* state. For all charmed mesons we determine the total production cross-section and study thex _F andp _t ² distributions.     

Coherent production of (K + π 0) pairs on nuclei in a Charged-Kaon beam

The cross section for the coherent production of (K ⁺ π ⁰) pairs that is associated with a chiral anomaly and with diagrams involving intermediate K*(892), ρ, ω, and ?(1020) mesons is calculated for the Coulomb interaction of K ⁺ mesons with nuclei. The number of such events that is expected for the OKA detector at the Institute for High Energy Physics (IHEP, Protvino) is presented.     

Subthreshold production ofK + mesons and the fragmentation of the target nucleus

The interplay between subthresholdK ⁺-production and the fragmentation of the target nucleus is considered in proton-nucleus interactions at projectile energies between 0.8 and 1 GeV. Inclusive data for the production ofK ⁺ mesons and of fragments are well described in the framework of the modified phase space model. For a coincidence measurement betweenK ⁺ mesons and fragments the model predicts a decrease of the relative yield of intermediate mass fragments by about four orders of magnitude. This strong decrease is a consequence of energy-momentum conservation, because at subthreshold energies a second endothermic process like multifragmentation can hardly proceed simultaneously with theK ⁺ production. AK ⁺ meson is, therefore, expected to be accompanied by a heavy target residue, which is so weakly excited that it may evaporate a few nucleons but cannot decay into fragments. Due to the large energy and momentum transfer in this process the strength of the predicted effect is supposed to be sensitive to the details of the reaction dynamics.The authors would like to thank H.W. Barz, F. Dönau and O. Schult for many valuable comments and discussions.     

New method for measurement of a T-violating muon polarization in K + decays

A new method is proposed for measuring a T-violating muon polarization in the decays K ⁺ → π⁰μ⁺ν and K ⁺ → μ⁺νγ. The method is based on a complete reconstruction of kinematics in these decays by using a high-resolution π⁰ detector, an active muon polarimeter, and a nearly 4π efficient photon veto system. A high acceptance of the detector allows one to reach a statistical sensitivity to the T-violating muon polarization of less than 10^?4 in an experiment with stopped K ⁺ mesons.     

Strange particles production and absorption in nuclei at high energies

The absorption of the secondary hadrons in nuclear matter is studied as a function of their flavour dependent inelastic cross section on nucleons. In particular the ratiosK ⁺/π⁺ andK ^?/π^? of particles produced in the proton-nucleus high energy interactions are examined and described in the very simple phenomenological model. The enhanced production ofK ⁺ mesons is explained by their relatively small interaction. The presence of the initial particle absorption is clearly demonstrated forx _F>0.5.     

New method of studying slow strange meson properties in nuclear matter

We suggest a new experimental method to explore the properties of slow strange mesons at normal nuclear matter density. We show that the K⁺ and K^? mesons with extremely small momenta relative to the surrounding medium rest frame can be produced in nucleus-nucleon collisions, and their production cross-sections are experimentally measurable. Experiments on the study of the momentum dependence of meson-nuclear potentials are discussed.     

In-Medium Kaon Potential and Nuclear Equation of State Measured in Nucleus–Nucleus Collisions

The kaon production in heavy ion collisions at intermediate energies provides a sensitive probe to study the in-medium properties and nuclear equation of state of hadrons. Properties of kaons in dense hadronic matter are important for a better understanding of both, the possible restoration of chiral symmetry in dense hadronic matter and the properties of nuclear matter at high densities. We investigated the in-medium kaon potential and nuclear equation of state by transverse mass spectra of K ⁺ mesons in heavy ion collisions. We use quantum molecular dynamics (QMD) models based on covariant kaon dynamics to simulate ${_{28}^{58}Ni +_{28}^{58}Ni}$ collisions at 1.93 A GeV, to analyze the transverse mass spectra of K ⁺. Calculated results with a repulsive in-medium K ⁺N potential can reasonably describe the features of KaoS data. They also shown that the transverse mass spectrum of K ⁺ mesons is a sensitive observable to probe the kaon in-medium potential in dense nuclear matter.     

Factorial moments and correlations in meson-nucleus interactions at 250 GeV/c

A sample of 8000 interactions of 250 GeV/c π⁺ andK ⁺ mesons on Al and Au nuclei, is used to search for intermittency effects by calculating the normalized factorial moments of order two to four. No significant effect is observed in the higher moments. Two-body rapidity correlations and Bose-Einstein correlations in these interactions are presented.     

Strange mesons in dense nuclear matter

Experimental data on the production of kaons and antikaons in heavy-ion collisions at relativistic energies are presented and discussed with respect to in-medium effects. The K ^?/K⁺ ratios measured in nucleus-nucleus collisions are 1–2 orders of magnitude larger than in proton-proton collisions. The azimuthal angle distributions of K ⁺ mesons indicate a repulsive kaon-nucleon potential. Microscopic transport calculations consistently explain both the yields and the emission patterns of kaons and antikaons when assuming that their properties are modified in dense nuclear matter. The K ⁺ production excitation functions measured in light and heavy collision systems provide evidence for a soft nuclear equation-of-state.