We use QCD spectral sum rules to test the nature of the meson X(3872), assumed to be an exotic four-quark (ccqq) state with J P C = 1 ++ . For definiteness, we work with the current proposed recently by Maiani et al [1], at leading order in αs, consider the contributions of higher dimension condensates and keep terms which are linear in the light quark mass mq. We find MX = (3925±127) MeV which is compatible, within the errors, with the experimental candidate X(3872), while the SU(3) breaking-terms lead to an unusual mass-splitting MXs − MX = −(61 ± 30) MeV. The massdifference between the neutral states due to isospin violation of about (2.6 ∼ 3.9) MeV is smaller than the value (8±3) MeV proposed in [1]. For the b-quark, we predict MX b = (10144±106) MeV for the X b (bbqq), which is much below theBB * threshold in contrast to theBB * molecule prediction [2], and for the X s b (bbss), a mass-splitting M X s b − MX b = −(121 ± 182) MeV. Our analysis also indicates that the mass-splitting between the ground state and the radial excitation of about (225 ∼ 250) MeV is much smaller than in the case of ordinary mesons and is (within the errors) flavour-independent. We also extract the decay constants, analogous to fπ, of such mesons, which are useful for further studies of their leptonic and hadronic decay widths. The uncertainties of our estimates are mainly due to the ones from the c and b quark masses.

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We use QCD sum rules to test the nature of the meson Xð3872Þ, assumed to be a mixture between charmonium and exotic molecular ½c "q½q " c states with J PC ¼ 1 þþ . We find that there is only a small range for the values of the mixing angle that can provide simultaneously good agreement with the experimental value of the mass and the decay width, and this range is 5 0 13 0 . In this range we get m X ¼ ð3:77 AE 0:18Þ GeV and ÀðX ! J=c þ À Þ ¼ ð9:3 AE 6:9Þ MeV, which are compatible, within the errors, with the experimental values. We, therefore, conclude that the Xð3872Þ is approximately 97% a charmonium state with 3% admixture of $88% D 0 D Ã0 molecule and $12% D þ D ÃÀ molecule.

Results are presented of an analysis of proton and charged pion azimuthal distributions measured with respect to the reaction plane in Au ϩ Au collisions at a beam momentum of about 11A GeV/c. The azimuthal anisotropy is studied as a function of particle rapidity and transverse momentum for different centralities of the collisions. The triple differential ͑in rapidity, transverse momentum, and azimuthal angle͒ distributions are reconstructed. A comparison of the results with a previous analysis of charged-particle and transverse energy flow as well as with model predictions are presented. ͓S0556-2813͑97͒05711-7͔ PACS number͑s͒: 25.75.Dw

Event shapes for Au + Au collisions at 11.4 GeV/c per nucleon were studied over nearly the full solid angle with the E877 apparatus. The analysis was performed by Fourier expansion of azimuthal distributions of the transverse energy (E T ) measured 1