The H dibaryon on the lattice

We present our final results for the mass of the six quark flavor singlet state (J^P=0^+, S=-2) called H dibaryon, which would be the lightest possible strangelet in the context of strange quark matter. The calculations are performed in quenched QCD on (8-24)^3 x 30 lattices with the (1,2) Symanzik improved gauge action and the clover fermion action. Furthermore the fuzzing technique for the fermion fields and smearing of the gauge fields is applied in order to enhance the overlap with the ground state. Depending on the lattice size we observe an H mass slightly above or comparable with the \Lambda\Lambda threshold for strong decay. Therefore a bound H dibaryon state seemed to be ruled out by our simulation.Comment: Lattice2002(spectrum), 3 pages, 2 figures, Proceedings of the XX International Symposium on Lattice Field Theory, June 24-29, 2002 (MIT, Cambridge, USA

Testing MEM with Diquark and thermal Meson Correlation Functions

When applying the maximum entropy method (MEM) to the analysis of hadron correlation functions in QCD a central issue is to understand to what extent this method can distinguish bound states, resonances and continuum contributions to spectral functions. We discuss these issues by analyzing meson and diquark correlation functions at zero temperature as well as free quark anti-quark correlators. The latter test the applicability of MEM to high temperature QCD.Comment: 6 pages, 6 figures. Contribution to the proceedings of the Conference on Strong and Electroweak Matter (SEWM 2000), Marseille, France, 14-17 June 2000; Figure 3(b) change

Further Evidence for an unstable H-Dibaryon?

We present preliminary results for the mass of the 6q flavor-singlet state ($J^P=0^+$, $S=-2$) called H-dibaryon, calculated in quenched QCD on $16^3$x30 and $24^3$x30 lattices with improved gauge and fermion actions (Symanzik improvement, Clover action). For both lattice sizes we applied the fuzzing technique to enhance the overlap with the ground state. We observe a H-mass above the $\Lambda\Lambda$ threshold for strong decay. The difference in mass, $m_H - 2m_\Lambda$, increases with increasing lattice size.Comment: Poster at LATTICE99 (QCD Spectrum and Quark Masses), 3 pages, 4 figures, LaTeX2e using espcrc2.st

Meson Spectral Functions at finite Temperature

The Maximum Entropy Method provides a Bayesian approach to reconstruct the spectral functions from discrete points in Euclidean time. The applicability of the approach at finite temperature is probed with the thermal meson correlation function. Furthermore the influence of fuzzing/smearing techniques on the spectral shape is investigated. We present first results for meson spectral functions at several temperatures below and above $T_c$. The correlation functions were obtained from quenched calculations with Clover fermions on large isotropic lattices of the size $(24-64)^3 \times 16$. We compare the resulting pole masses with the ones obtained from standard 2-exponential fits of spatial and temporal correlation functions at finite temperature and in the vacuum. The deviation of the meson spectral functions from free spectral functions is examined above the critical temperature.Comment: Lattice2001(hightemp), 3 pages, 6 figure

Meson correlators above deconfinement

We review recent progress in studying spectral functions for mesonic observables at finite temperatures, by analysis of imaginary time correlators directly calculated on isotropic lattices. Special attention is paid to the lattice artifacts present in such calculations.Comment: Latex, 3 figures uses iopart.cls, talk presented at Hot Quarks 2004, July 18-24, 2004, Taos Valley New Mexico, US

A Lattice Calculation of Thermal Dilepton Rates

Using clover improved Wilson fermions we calculate thermal vector meson correlation functions above the deconfinement phase transition of quenched QCD. At temperatures 1.5 Tc and 3Tc they are found to differ by less than 15% from that of a freely propagating quark anti-quark pair. This puts severe constraints on the dilepton production rate and in particular rules out a strong divergence of the dilepton rate at low energies. The vector spectral function, which has been reconstructed using the Maximum Entropy Method, yields an enhancement of the dilepton rate over the Born rate of at most a factor two in the energy interval 4 < E/T < 8 and suggests that the spectrum is cut-off at low energies by a thermal mass threshold of about (2-3)T.Comment: 9 pages, LaTeX2e File, 5 EPS files; minor corrections, modified error bins in Fig.2

H-Dibaryon from Lattice QCD with Improved Anisotropic Actions

The six quark state(uuddss) called H dibaryon($J^P=0^+$,$S=-2$) has been calculated to study its existence and stability. The simulations are performed in quenched QCD on $8^3 \times 24$ and $16^3 \times 48$ anisotropic lattices with Symanzik improved gauge action and Clover fermion action. The gauge coupling is $\beta=2.0$ and aspect ratio $\xi=a_s/a_t=3.0$. Preliminary results indicate that mass of H dibaryon is 2134(100)Mev on $8^3 \times 24$ lattice and 2167(59)Mev on $16^3 \times 48$ respectively. It seems that the radius of H dibaryon is very large and the finite size effect is very obvious

Scaling test of quenched Wilson twisted mass QCD at maximal twist

We present the results of an extended scaling test of quenched Wilson twisted mass QCD. We fix the twist angle by using two definitions of the critical mass, the first obtained by requiring the vanishing of the pseudoscalar meson mass m_PS for standard Wilson fermions and the second by requiring restoration of parity at non-zero value of the twisted mass mu and subsequently extrapolating to mu=0. Depending on the choice of the critical mass we simulate at values of beta in [5.7,6.45], for a range of pseudoscalar meson masses 250 MeV < m_PS < 1 GeV and we perform the continuum limit for the pseudoscalar meson decay constant f_PS and various hadron masses (vector meson m_V, baryon octet m_oct and baryon decuplet m_dec) at fixed value of r_0 m_PS. For both definitions of the critical mass, lattice artifacts are consistent with O(a) improvement. However, with the second definition, large O(a^2) discretization errors present at small quark mass with the first definition are strongly suppressed. The results in the continuum limit are in very good agreement with those from the Alpha and CP-PACS Collaborations.Comment: 6 pages, Talk presented at Lattice 2005, Dublin, 25-30 July 200