Strange Mesons Research Articles

SU(3) symmetry-breaking corrections to meson distribution amplitudes

We consider constraints on the momentum fraction of the $K$ and $K^*$ meson carried by the strange quark that follow from exact operator identities, similar to those for the divergence of the quark part of the QCD energy-momentum tensor. The existing QCD sum rule estimates are reanalyzed in this context. Our conclusions essentially support the constituent quark-model picture where the momentum fraction is roughly proportional to the constituent quark mass, but the asymmetry turns out to be smaller compared to the naive quark model estimates. As a byproduct of this study, we calculate the SU(3)-breaking quark-antiquark-gluon matrix elements that determine the leading conformal spin contributions to the asymmetry in twist-four distribution amplitudes of strange mesons $K$ and $K^*$, and also update the estimate for the SU(3) breaking for the quark-antiquark-gluon vacuum condensate.

Heavy-quark symmetry and the electromagnetic decays of excited charmed strange mesons

Heavy-hadron chiral perturbation theory (HH$\chi$PT) is applied to the decays of the even-parity charmed strange mesons, D_{s0}(2317) and D_{s1}(2460). Heavy-quark spin symmetry predicts the branching fractions for the three electromagnetic decays of these states to the ground states D_s and D_s^* in terms of a single parameter. The resulting predictions for two of the branching fractions are significantly higher than current upper limits from the CLEO experiment. Leading corrections to the branching ratios from chiral loop diagrams and spin-symmetry violating operators in the HH$\chi$PT Lagrangian can naturally account for this discrepancy. Finally the proposal that the D_{s0}(2317) (D_{s1}(2460)) is a hadronic bound state of a D (D^*) meson and a kaon is considered. Leading order predictions for electromagnetic branching ratios in this molecular scenario are in very poor agreement with existing data.

Dynamics of strange, charm and high momentum hadrons in relativistic nucleus–nucleus collisions

We investigate hadron production and attenuation of hadrons with strange and charm quarks (or antiquarks) as well as high transverse momentum hadrons in relativistic nucleus–nucleus collisions from 2 A GeV to 21.3 A TeV within two independent transport approaches (UrQMD and HSD). Both transport models are based on quark, diquark, string and hadronic degrees of freedom, but do not include any explicit phase transition to a quark–gluon plasma. From our dynamical calculations we find that both models do not describe the maximum in the K +/ π + ratio at 20–30 A GeV in central Au+Au collisions found experimentally, though the excitation functions of strange mesons are reproduced well in HSD and UrQMD. Furthermore, the transport calculations show that the charmonium recreation by D+ D ̄ →J/Ψ+ meson reactions is comparable to the dissociation by ‘comoving’ mesons at RHIC energies contrary to SPS energies. This leads to the final result that the total J/ Ψ suppression as a function of centrality at RHIC should be less than the suppression seen at SPS energies where the ‘comover’ dissociation is substantial and the backward channels play no role. Furthermore, our transport calculations—in comparison to experimental data on transverse momentum spectra from pp, d+Au and Au+Au reactions—show that pre-hadronic effects are responsible for both the hardening of the hadron spectra for low transverse momenta (Cronin effect) as well as the suppression of high p T hadrons. The mutual interactions of formed hadrons are found to be negligible in central Au+Au collisions at s =200 GeV for p T ≥6 GeV/c and the sizeable suppression seen experimentally is attributed to a large extent to the interactions of ‘leading’ pre-hadrons with the dense environment.

The narrow width of the Θ+—a possible explanation

The narrow width of the exotic narrow baryon resonance Θ+ might be explained by mixing between the two nearly degenerate states that arise in models with two diquarks and an antiquark. The only open Θ+ decay channel is KN. When two states both coupled to a single dominant decay mode are mixed by the loop diagram via this decay mode, diagonalization of the loop diagram decouples one mass eigenstate from this decay mode as in some treatments of the ρ–π decay from the mixed singlet–octet ω–φ system, the K∗–π decay of the strange axial vector mesons and the NK couplings of some baryons. This mechanism can explain the narrow width and weak coupling of Θ+→KN while allowing a relatively large production cross section from K∗ exchange. Interesting tests are suggested in K−p reactions where backward kaon production must go by exotic baryon exchange.

Nuclear modification of identified strange particles at moderate pT in Au+Au collisions at at RHIC

We present the measurement of strange baryon and meson production for pT up to 5.0 GeV/c from Au+Au collisions at RHIC. Using decay topology reconstruction, we are able to identify and measure the production rate of strange baryons and mesons for pT up to 5.0 GeV/c from different centrality bins. The strange baryon and meson yield per binary collision for pT greater than 2 GeV/c from central collisions will be presented with respect to that from peripheral collisions. Strange baryons and mesons show a different suppression pattern. The suppression of unidentified charged hadrons and neutral pions at high pT from central Au+Au collisions at RHIC has already been reported by STAR and PHENIX. Theoretical calculations showed that the suppression is consistent with parton energy loss in high density medium created in nuclear collisions at RHIC. Our measurement would, in the same theoretical framework, indicate different dynamical behaviour in energy loss and/or fragmentation leading to strange baryon and meson production in the pT region from 2 to 5 GeV/c. The measurement of strange baryons and mesons at high pT can probe dynamics of nuclear medium effect on identified particle production in the soft-to-hard transition region.

Strange fluctuations at RHIC

Net charge fluctuations measured by the STAR experiment at RHIC agree with hadronic event generators, suggesting that more sensitive fluctuation observables are needed to extract information on collision dynamics. Important information on isospin fluctuations can be extracted from K0SK± measurements. Gavin and Kapusta proposed that disoriented chiral condensate can produce extraordinary isospin fluctuations in both strange and non-strange mesons. However, even in the absence of such a contribution, we argue that this observable is very sensitive to the collision dynamics.

System size dependence of strangeness production at 158 A GeV

An enhanced production of strange particles per pion in heavy ion collisions compared to elementary p + p interactions was observed in Pb + Pb reactions at the CERN SPS. New results obtained on small colliding systems, C + C and Si + Si, also show an enhancement. It increases steeply with system size and reaches in the larger system almost the level measured in Pb + Pb reactions. The shapes of the transverse mass spectra of strange mesons (K+, K−, ϕ) and baryons are consistent with the presence of collective transverse flow, which is already visible in small systems (C + C) and increases with the system size. The ratio together with the K+/K− ratio yields information about the baryochemical potential μB. The potential, determined at midrapidity, increases with the system size since the stronger stopping shifts baryons from near beam and projectile rapidity towards midrapidity. For the 4π yields μB is almost independent of the size of the colliding system.

Strange hadronic matter with a weakY−Yinteraction

A modified quark meson coupling (MQMC) model is extended to include $\ensuremath{\Lambda}$ hyperons and $\ensuremath{\Xi}$ hyperons. The extended model is then used to study the equation of state (EOS) for strange hadronic matter. A weak $\ensuremath{\Lambda}\text{\ensuremath{-}}\ensuremath{\Lambda}$ interaction deduced from recent observation of $_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{6}\mathrm{He}$ double hypernucleus is adopted in the calculation. The resultant EOS is compared with that deduced from a strong $\ensuremath{\Lambda}\text{\ensuremath{-}}\ensuremath{\Lambda}$ interaction. It is found that while the system with the strong $\ensuremath{\Lambda}\text{\ensuremath{-}}\ensuremath{\Lambda}$ interaction is more deeply bound than ordinary nuclear matter due to the opening of new degrees of freedom, the system with the weak $\ensuremath{\Lambda}\text{\ensuremath{-}}\ensuremath{\Lambda}$ interaction is rather loosely bound compared to the latter. It is necessary to introduce the strange mesons ${\ensuremath{\sigma}}^{*}$ and $\ensuremath{\phi}$ in the MQMC model to properly describe the interaction between the hyperons in either strong or weak $\ensuremath{\Lambda}\text{\ensuremath{-}}\ensuremath{\Lambda}$ interaction cases.

New method of studying slow strange meson properties in nuclear matter

We suggest the 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. The experiments on study of the momentum dependence of meson-nuclear potentials are discussed.

Strong decays of strange quarkonia

In this paper we evaluate strong decay amplitudes and partial widths of strange mesons (strangeonia and kaonia) in the 3P0 decay model. We give numerical results for all energetically allowed open-flavor two-body decay modes of all nsbar and ssbar strange mesons in the 1S, 2S, 3S, 1P, 2P, 1D and 1F multiplets, comprising strong decays of a total of 43 resonances into 525 two-body modes, with 891 numerically evaluated amplitudes. This set of resonances includes all strange qqbar states with allowed strong decays expected in the quark model up to ca. 2.2 GeV. We use standard nonrelativistic quark model SHO wavefunctions to evaluate these amplitudes, and quote numerical results for all amplitudes present in each decay mode. We also discuss the status of the associated experimental candidates, and note which states and decay modes would be especially interesting for future experimental study at hadronic, e+e- and photoproduction facilities. These results should also be useful in distinguishing conventional quark model mesons from exotica such as glueballs and hybrids through their strong decays.

Chiral symmetry restoration in linear sigma models with different numbers of quark flavors

Chiral symmetry restoration at nonzero temperature is studied in the framework of the O(4) linear sigma model and the U(N_f)_r x U(N_f)_l linear sigma model with N_f=2,3, and 4 quark flavors. We investigate the temperature dependence of the masses of the scalar and pseudoscalar mesons, and the non-strange, strange, and charm condensates within the Hartree approximation as derived from the Cornwall-Jackiw-Tomboulis formalism. We find that the masses of the non-strange and strange mesons at nonzero temperature depend sensitively on the particular symmetry of the model and the number of light quark flavors N_f. On the other hand, due to the large charm quark mass, neither do charmed mesons significantly affect the properties of the other mesons, nor do their masses change appreciably in the temperature range around the chiral symmetry restoration temperature. In the chiral limit, the transition temperatures for chiral symmetry restoration are surprisingly close to those found in lattice QCD.

Collision times in ππ and πK scattering and spectroscopy of meson resonances

Using the concept of collision time (time delay) introduced by Eisenbud and Wigner and its connection to on-shell intermediate unstable states, we study mesonic resonances in ππ and πK scattering. The time-delay method proves its usefulness by revealing the spectrum of the well known ρ- and K ∗ -mesons and by supporting some speculations on ρ-mesons in the 1200 MeV region. We use this method further to shed some light on more speculative meson resonances, among others the enigmatic scalars. We confirm the existence of chiralons below 1 GeV in the unflavoured and strange meson sector.

Indication of a low-mass scalar strange meson in D+ → K−π+π+ decay

Using a coherent amplitude analysis to fit the Dalitz plot of the D + → K − π + π + decay, we find evidence for a strange scalar resonance of mass 797 ± 19 ± 43 MeV/c 2 and width 410 ± 43 ± 87 MeV,/c 2, compatible with what is expected for the isoscalar meson κ. The D + → κπ + fraction accounts for approximately half of this decay of the D +, like the σ in D+ → π − π + π + and the ƒ 0(980) in D s + → π − π + π +.

Light hadron spectrum with two flavors of O(a) improved dynamical quarks: final results from JLQCD

We present the final results of the JLQCD calculation of the light hadron spectrum and quark masses with two flavors of dynamical quarks using the plaquette gauge action and fully O( a)-improved Wilson quark action at β = 5.2. We observe that sea quark effects lead to a closer agreement of the strange meson and baryon masses with experiment and a reduction of quark masses by 20–30%.

Strange Meson Radiative Capture on the Proton in Low Energy QCD Lagrangian**The project supported in part by National Natural Science Foundation of China under contract numbers 19975053, 19835010, and 10075081

Based on our low energy QCD Lagrangian description of strange meson photoproduction off the proton and the crossing symmetry, the strange meson radiative capture on the proton, , is investigated in the quark model of baryon structure with the same input parameter, the only strong coupling constant , as that in the strange meson photoproduction off the proton , a crossing channel of the capture reaction. A good agreement on the branching ratio between the predictions and data is obtained successfully. This excellent fit indicates that our low energy QCD Lagrangian theory with only one free parameter is an advanced and unified description of strange meson photoproduction and its associated radiative capture.

Kaon–nucleon and D–nucleon scattering in the quark model, including spin–orbit interactions

Interactions of charmed and strange mesons with baryonic matter can be calculated in the nonrelativistic quark potential model. For KN scattering data exist, and the theoretical results for S-waves are in approximate agreement with experiment. Here we apply the same model to the scattering of open-charm (D) mesons by nucleons, and give quark model predictions for DN scattering amplitudes. Spin–orbit forces in KN and DN will also be discussed.

Canonical constraints on particle production

We discuss the statistical model description of particle production in heavy-ion collisions. We put particular emphasis on the interpretation of the enhancement of particles that carry a non-vanishing quantum number related to U(1) internal symmetry. We argue that the basic features of experimental data showing enhancement of strange mesons and baryons are well described by the model.

Relating production and masses of the vector and P-wave mesons for light and heavy flavours at LEP

The production rates of primary vector and P-wave mesons in Z hadronic decays are analysed. The mass dependence of production rates for the bottom, charm, strange charm and three families of the light-flavour mesons is found to be very similar, allowing to relate the relative production rates for mesons with different flavours and, possibly, their masses. The strange axial mesons K_1(1273) and K_1(1402) might be assigned to the 1^+(1/2) and 1^+(3/2) levels degenerate with the 0^+(1/2) and 2^+(3/2) levels of the K^*_0(1430) and K^*_2(1430), respectively, if the observed K^*_0(1430) mass is replaced by its ``bare'' q\bar{q} mass corresponding to the K-matrix pole and close to the K_1(1273) mass. Then the 0^+(1/2) and 1^+(1/2) levels are below the 1^+(3/2) and 2^+(3/2) levels for the strange, charm and bottom mesons.

Formula omitted] symmetry breaking, scalar mesons and the nucleon spin problem in an effective chiral field theory

We establish a relationship between the scalar-meson spectrum and the U A(1) symmetry-breaking 't Hooft interaction on one hand and the constituent-quark flavor singlet axial coupling constant g A,Q (0) on the other, using an effective chiral quark field theory. This analysis leads to the new sum rule g A,Q (0)[m η′ 2+m η 2−2m K 2]≃−m f′ 0 2−m f 0 2+2m K 0 ∗ 2 , where η′,η,K are the observed pseudoscalar mesons, K 0 ∗ is the strange scalar meson at 1430 MeV and f 0,f′ 0 are “the eighth and the ninth” scalar mesons. We discuss the relationship between the constituent-quark flavor singlet axial coupling constant g A,Q (0) and the nucleon one g A,N (0) (“nucleon spin content”) in this effective field theory. We also relate g A,Q (0) as well as the flavour octet constituent-quark axial coupling constant g A,Q (1) to vector and axial-vector meson masses in general as well as in the tight-binding limit.

Strange mesons in dense nuclear matter

Experimental data on the production of kaons and antikaons in heavy ion collisions at relativistic energies are reviewed 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.