Search

We discuss recent advances of the HADES collaboration in the sector of in-medium strangeness physics, in particular the measurement of neutral kaons produced in proton-niobium reactions at 3.5 GeV. [ABSTRACT FROM AUTHOR]

The behavior of the ϕ meson at finite density is studied, making use of a QCD sum rule approaeh in eombination with the maximum entropy method. It is demonstrated that a possible mass shift of the ϕ in nuelear matter is strongly eorrelated to the strangeness eontent of the nueleon, whieh is proportional to the strange sigma term, σsN. In eontrast to earlier studies, our results show that, depending on the value of σsN, the ϕ meson eould reeeive both a positive or negative mass shift at nuelear matter density. We find that these results depend only weakly on potential modifieations of the width of the ϕ meson peak and on assumptions made on the behavior of four-quark eondensates at finite density. [ABSTRACT FROM AUTHOR]

The role played by baryonic resonances in the production of final states containing strangeness for proton-proton reactions at 3.5 GeV measured by HADES is discussed by means of several very different measurements. First the associate production of Δ resonances accompanying final states with strange hadrons is presented, then the role of interferences among N* resonances, as measured by HADES for the first time, is summarised. Last but not least the role played by heavy resonances, with a mass larger than 2 GeV/c2 in the production of strange and non-strange hadrons is discussed. Experimental evidence for the presence of a Δ(2000)++ are presented and hypotheses are discussed employing the contribution of similar objects to populate the excesses measured by HADES for the Ξ in A+A and p+A collisions and in the dilepton sector for A+A collisions. This extensive set of results helps to better understand the dynamic underlaying particle production in elementary reactions and sets a more solid basis for the understanding of heavy ion collisions at the same energies and even higher as planned at the FAIR facility. [ABSTRACT FROM AUTHOR]

The behavior of the Ф meson at finite density is studied, making use of a QCD sum rule approach in combination with the maximum entropy method. It is demonstrated that a possible mass shift of the Ф in nuclear matter is strongly correlated to the strangeness content of the nucleón, which is proportional to the strange sigma term, σsN. In contrast to earlier studies, our results show that, depending on the value of σsN, the Ф meson could receive both a positive or negative mass shift at nuclear matter density. We find that these results depend only weakly on potential modifications of the width of the Ф meson peak and on assumptions made on the behavior of four-quark condensates at finite density. [ABSTRACT FROM AUTHOR]

We discuss recent advances of the HADES collaboration in the sector of in-medium strangeness physics, in particular the measurement of neutral kaons produced in proton-niobium reactions at 3.5 GeV. [ABSTRACT FROM AUTHOR]

The role played by baryonic resonances in the production of final states containing strangeness for proton-proton reactions at 3.5 GeV measured by HADES is discussed by means of several very different measurements. First the associate production of Δ resonances accompanying final states with strange hadrons is presented, then the role of interferences among N∗ resonances, as measured by HADES for the first time, is summarised. Last but not least the role played by heavy resonances, with a mass larger than 2 GeV/c² in the production of strange and non-strange hadrons is discussed. Experimental evidence for the presence of a Δ(2000)++ are presented and hypotheses are discussed employing the contribution of similar objects to populate the excesses measured by HADES for the Ξ in A+A and p+A collisions and in the dilepton sector for A+A collisions. This extensive set of results helps to better understand the dynamic underlaying particle production in elementary reactions and sets a more solid basis for the understanding of heavy ion collisions at the same energies and even higher as planned at the FAIR facility. [ABSTRACT FROM AUTHOR]

Realistic description of core-collapsing supernovae evolution and structure of proto-neutron stars chiefly depends on microphysics input in terms of equations of state, chemical composition and weak interaction rates. At sub-saturation densities the main uncertainty comes from the symmetry energy. Within a nuclear statistical equilibrium (NSE) model with consistent treatment of clusterized and unbound components we investigate the meaning of symmetry energy in the case of dis-homogeneous systems, as the one thought to constitute the neutron star crust, and its sensitivity to the isovector properties of the effective interaction. At supra-saturation densities the situation is much more difficult because of the poor knowledge of nucleon-hyperon and hyperon-hyperon interactions and thermodynamic behavior in terms of phase transitions. Within a simple (np?) model we show that compressed baryonic matter with strangeness manifests a complex phase diagram with first and second order phase transitions. The fact that both are explored under strangeness chemical equilibrium and survive Coulomb suggests that they might have sizable consequences on star evolution. An example in this sense is the drastic reduction of the neutrino-mean free path in the vicinity of the critical point obtained within RPA which would lead to a less rapid star cooling. [ABSTRACT FROM AUTHOR]

Albeit quark models explain the known baryon spectrum reasonably well, they all overpredict the number of states significantly. This is often called the “missing resonance” problem. It is speculated, that some of these resonances remained undetected in pi-induced reactions, but have a sizeable coupling to channels with strangeness involved. This provided our motivation to measure cross sections and polarisation observables in associated Kaon-Hyperon photoproduction with the focus on the ∑+Ks0 channel. Up to now, for this particular channel only limited data exists from the SAPHIR-, CLAS- and CBELSA/TAPS-collaboration for total and differential cross sections, and for recoil polarisation. Using the linearly polarised, energy tagged photon beam at the ELSA particle accelerator of Bonn University, data were taken with the combined photon spectrometers Crystal Barrel and TAPS. This setup is well suited to detect multi photon final states and therefore ideal to measure the reaction channel γp→∑+Ks0→pπ0π0π0→p6γ. Here the extraction of cross sections, the recoil polarisation P and the photon asymmetry ∑, which is measured for the first time, will be discussed. [ABSTRACT FROM AUTHOR]

We describe a few-body calculation of ΛΛ5H as well as ΛΛ4H and ΛΛ6He taking account fully coupled-channel two-baryon potentials acting among the octet of baryons. The wave function includes not only pnnΛΛ and ppnnΞ- components but also pnnΛΣ0, ppnΛΣ-, pnnΣ0Σ0 and ppnΣ0Σ-. An effective YY potential based on Nijmegen model D is used. We find that the pnnλΣ0 and ppnΛΣ- components play an important role in producing the ΛΛ5H bound state. The present result requires the introduction of a new coupled-channel three-body-force, NΛΛ—NNΞ, if the intermediate pnnλσ0 and ppnΛΣ- states are eliminated from the model space. [ABSTRACT FROM AUTHOR]

Results of the parity violating asymmetry APV for longitudinally polarized 3 GeV electrons from both hydrogen and helium cryogenic targets, at small scatteting angle [phonetic_theta]lab∼6 ° are presented. The asymmetry for hydrogen is a function of a linear combination of GEs and GMs, the strange quark contributions to the electric and magnetic form factors of the nucleon respectively, and that for 4He is a function solely of GEs. The combination of the two results therefore allows GEs and GMs to be separately determined. [ABSTRACT FROM AUTHOR]

The experimental data from 2m propane bubble chamber have been analyzed to search of scalar meson κ(800) in Ks0π± spectra for the reaction p+A at 10 GeV/c. The Ks0π± invariant mass spectra has shown similarly resonant structures with MKs0π=720,780 and 890 MeV/c2. The M(890) peak is identified as the well known resonance K* from PDG. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Experimental data from the 2m propane bubble chamber have been analyzed for exotic baryon states search. A number of peculiarities were found in the effective mass spectra of: Λπ+(Σ*+(1382),PDG), Λp and Λpp subsystems. A few events detected on the photographs of the propane bubble chamber exposed to a 10 GeV/c proton beam, were interpreted as S=-2 H0 light(

Hyperon enhancements at 160 and 40 A Gev/c are presented and compared. The momentum spectra are analysed in the framework of the blast wave model and freeze-out temperature, transverse and longitudinal flows are extracted. Nuclear modification factors are presented and discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The experimental data from the 2 m propane bubble chamber have been analyzed for pC→ Λ(Ks0)X reactions at 10 GeV/c. The estimation of experimental inclusive cross sections for Lgr; and Ks0 production in the p12C collision is equal to σΛ= 13.3±1.7 mb and σKs0= 3.8±0.6 mb, respectively. The measured Λ/π+ ratio from pC reactions is equal to (5.3±0.8) * 10-2. The experimental Λ/π+ ratio in the pC reaction is approximately two times larger than the Λ/π+ ratio from pp reactions. There is a significant enhancement specially in the Λ/π+ ratio for p+C and C+C collisions at 10 A·GeV/c. The investigation has been performed at the Veksler and Baldin Laboratory of High Energies, JINR. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Experimental data from the 2m propane bubble chamber have been analyzed to search for an exotic baryon states, in the Ks0p, Ks0Λ and Λp decay mode for the reaction p+C3H8 at 10 GeV/c. In the invariant mass spectrum ΛKs0 narrow peaks are observed at 1750, 1795, 1850 MeV/c2. The statistical significance of these peaks has been estimated as 5.6, 3.3 and 3.0 S.D., respectively. There are small enhancements in mass regions of (1650–1675) and (1925–1950) MeV/c2. These would be candidates for the N0 or the [cap_xi]0 pentaquark states. The pKs0 invariant mass spectrum shows resonant structures with MKs0p=1540, 1613, 1821 MeV/c2. The statistical significance of these peaks have been estimated as 5.5,4.8 and 5.0 s.d., respectively. There are also small peaks in 1487 (3 s.d.), 1690 (3.6 s.d.), 1750 (2.3 s.d.) and 1980 (3.0 s.d.) MeV/c2 mass regions. In the invariant mass spectrum S=-1 Λp narrow peaks at 2100, 2175, 2285 and 2353 MeV/c2 are observed. Their excess above background by the second method is 6.9, 4.9, 3.8 and 2.9 S.D., respectively. There is also a small peak in 2225 (2.2 s.d.) MeV/c2 mass region. The investigation has been performed at the Veksler and Baldin Laboratory of High Energies, JINR. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We discuss experimental features of identified particle production from nucleus-nucleus collisions. These features reflect hadronization from a deconfined partonic matter whose particle formation scheme is distinctly different from fragmentation phenomenology in elementary collisions. Multi-parton dynamics, such as quark coalescences or recombinations, appear to be essential to explain the experimental measurements at the intermediate transverse momentum of 2–5 GeV/c. Constituent quarks seem to be the dominant degrees of freedom at hadronization. Heavy quark production should help quantify deconfined matter properties. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present a systematic study of the sensitivity of quasielastic neutrino-nucleus cross sections at intermediate energies to the strange quark sea of the nucleon. To this end, we investigate the impact of the weak strangeness form factors on the ratio of proton-to neutron knockout, the ratio of neutral-to-charged current cross sections, on the Paschos-Wolfenstein relation, and on the longitudinal helicity asymmetry. [ABSTRACT FROM AUTHOR]

The results from the G0 forward angle experiment are reported in this talk. The parity-violating asymmetry of elastic e-p scattering has been measured within the range of the four-momentum transfer (Q2) from 0.12 to 1.0 (GeV/c)2, which yields linear combinations of the strange electric and magnetic form factors of the nucleon, GEs + ηGMs, in the same Q2 range. The G0 results, combined with the measurements from other experiments, indicate that GEs and GMs are both likely non-zero. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The implications of the empirical indications for a positive strangeness magnetic moment on the possible configurations of the uudss component of the proton are analysed. A positive value for μs is obtained in the ss configuration where the uuds subsystem is in an orbitally excited state with [4]FS[22]F[22]S flavor-spin symmetry, which is likely to have the lowest energy. The configurations in which the s is orbitally excited, which include the conventional K+Λ0 configuration, with exception of that in which the uuds component has spin 2, yield negative values for μs. The hidden strangeness analogues of recently proposed quark cluster models for the θ+ pentaquark give differing signs for μs. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present measurements of strange and multi-strange hadrons in p+p collisions at √s = 200 GeV measured by STAR. We will compare these preliminary results to leading-order (LO) and next-to-leading order (NLO) perturbative QCD models widely believed to describe the production mechanisms. In particular we will point out recent changes of the model calculations which improve the agreement with our data significantly and will discuss the physics consequences. In larger collision systems, produced with heavy ions at RHIC, we observe the centrality dependence of strange and multi-strange particle production. The non-linear dependency between (anti)-hyperon yields and the system size Npart seems to indicate that the correlation volume does not scale exactly with Npart in contradiction to previous assumptions by thermal models. [ABSTRACT FROM AUTHOR]

The WA97 experiment at CERN has collected data aiming to study strangeness production in heavy ion collisions at 158 A GeV/c; p-Be data were also taken as reference data. Here we show some results of an analysis of these p-Be data in order to check for evidence of a recently claimed pentaquark state. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Neutrino scattering on the nucleon, and charged lepton scattering on the nucleon provide information on the parton (quark and gluon) distributions in the nucleon. Unpolarized parton distributions represent how the nucleon's linear momentum is shared with quarks and gluons. Recently, the spin structure of the nucleon has also been studied. Polarized parton distributions show how the nucleon spin, 1/2, is constituted by quarks and gluons. Neutrino-nucleon elastic scattering can contribute to the study of the strangeness-quark spin in the nucleon. [ABSTRACT FROM AUTHOR]