High pressure effects in fluorinated HgBa2Ca2Cu3O(8+d)

We have measured the pressure sensitivity of Tc in fluorinated HgBa2Ca2Cu3O(8+d) (Hg-1223) ceramic samples with different F contents, applying pressures up to 30 GPa. We obtained that Tc increases with increasing pressure, reaching different maximum values, depending on the F doping level, and decreases for a further increase of pressure. A new high Tc record (166 K +/- 1 K) was achieved by applying pressure (23 GPa) in a fluorinated Hg-1223 sample near the optimum doping level. Our results show that all our samples are at the optimal doping, and that fluorine incorporation decreases the crystallographic $a$-parameter concomitantly increasing the maximum attainable Tc. This effect reveals that the compression of the $a$ axes is one of the keys that controls the Tc of high temperature superconductors.Comment: 4 pages, 4 figures, submitted to Phys. Rev.

On the Existence of Heavy Pentaquarks: The large Nc and Heavy Quark Limits and Beyond

We present a very general argument that the analogue of a heavy pentaquark (a state with the quantum numbers of a baryon combined with an additional light quark and a heavy antiquark) must exist as a particle stable under strong interactions in the combined heavy quark and large Nc limits of QCD. Moreover, in the combined limit these heavy pentaquark states fill multiplets of SU(4)xO(8)xSU(2). We explore the question of whether corrections in the combined 1/Nc and 1/mQ expansions are sufficiently small to maintain this qualitative result. Since no model-independent way is known to answer this question, we use a class of ``realistic'' hadronic models in which a pentaquark can be formed via nucleon-heavy meson binding through a pion-exchange potential. These models have the virtue that they necessarily yield the correct behavior in the combined limit, and the long-distance parts of the interactions are model independent. If the long-distance attraction in these models were to predict bound states in a robust way (i.e., largely insensitive to the details of the short-range interaction), then one could safely conclude that heavy pentaquarks do exist. However, in practice the binding does depend very strongly on the details of the short-distance physics, suggesting that the real world is not sufficiently near the combined large Nc, mQ limit to use it as a reliable guide. Whether stable heavy pentaquarks exist remains an open question.Comment: 11 pages; references adde

Radiative Corrections for Pion Polarizability Experiments

We use the semi-analytical program RCFORGV to evaluate radiative corrections to one-photon radiative emission in the high-energy scattering of pions in the Coulomb field of a nucleus with atomic number Z. It is shown that radiative corrections can simulate a pion polarizability effect. The average effect was estimated for pion energies 40-600 GeV. We also study the range of applicability of the equivalent photon approximation in describing one-photon radiative emission.Comment: 11 pages (LaTex), 6 figures, 1 table. No changes in the paper. New submission because old files are corrupted in arXi

Micro-canonical pentaquark production in \ee annihilations

The existence of pentaquarks, namely baryonic states made up of four quarks and one antiquark, became questionable, because the candidates, i.e. the $\Theta^+$ peak, are seen in certain reactions, i.e. p+p collisions, but not in others, i.e. \ee annihilations. In this paper, we estimate the production of $\Theta ^{+}(1540)$ and $\Xi^{--} (1860)$ in \ee annihilations at different energies using Fermi statistical model as originally proposed in its microcanonical form. The results is compared with that from pp collisions at SPS and RHIC energies. We find that, if pentaquark states exist, the production is highly possible in \ee annihilations. For example, at LEP energy $\sqrt{s}$=91.2 GeV, both $\Theta ^{+}(1540)$ and $\Xi^{--} (1860)$ yield more than in pp collisions at SPS and RHIC energy.Comment: 7 pages 2 figure

Search for the pentaquark resonance signature in lattice QCD

Claims concerning the possible discovery of the \Theta^+ pentaquark, with minimal quark content uudd\bar{s}, have motivated our comprehensive study into possible pentaquark states using lattice QCD. We review various pentaquark interpolating fields in the literature and create a new candidate ideal for lattice QCD simulations. Using these interpolating fields we attempt to isolate a signal for a five-quark resonance. Calculations are performed using improved actions on a large 20^3 x 40 lattice in the quenched approximation. The standard lattice resonance signal of increasing attraction between baryon constituents for increasing quark mass is not observed for spin-1/2 pentaquark states. We conclude that evidence supporting the existence of a spin-1/2 pentaquark resonance does not exist in quenched QCD.Comment: 42 pages, 28 figures, 11 table

Pion and Kaon Polarizabilities and Radiative Transitions

CERN COMPASS plans measurements of gamma-pi and gamma-K interactions using 50-280 GeV pion (kaon) beams and a virtual photon target. Pion (kaon) polarizabilities and radiative transitions will be measured via Primakoff effect reactions such as pi+gamma->pi'+gamma and pi+gamma->meson. The former can test a precise prediction of chiral symmetry; the latter for pi+gamma->a1(1260) is important for understanding the polarizability. The radiative transition of a pion to a low mass two-pion system, pi+gamma->pi+pi0, can also be studied to measure the chiral anomaly amplitude F(3pi) (characterizing gamma->3pi), arising from the effective Chiral Lagrangian. We review here the motivation for the above physics program. We describe the beam, target, detector, and trigger requirements for these experiments. We also describe FNAL SELEX attempts to study related physics via the interaction of 600 GeV pions with target electrons. Data analysis in progress aims to identify the reactions pi+e->pi'+e'+pi0 related to the chiral anomaly, and pi+e->pi'+e'+gamma related to pion polarizabilities.Comment: 16 pages, 6 figures, Latex Springer-Verlag style Tel Aviv U. Preprint TAUP-2469-97, Contribution to the Workshop on Chiral Dynamics Theory and Experiment, U. of Mainz, Sept. 1-5, 1997, to be published in Springer-Verlag, Eds. A. Bernstein, Th. Walcher, 199

The soft and the hard pomerons in hadron elastic scattering at small t

We consider simple-pole descriptions of soft elastic scattering for pp, pbar p, pi+ p, pi- p, K+ p and K- p. We work at t and s small enough for rescatterings to be neglected, and allow for the presence of a hard pomeron. After building and discussing an exhaustive dataset, we show that simple poles provide an excellent description of the data in the region - 0.5 GeV^2 < t < -0.1 GeV^2, 6 GeV<sqrt(s)< 63 GeV. We show that new form factors have to be used, and get information on the trajectories of the soft and hard pomerons.Comment: 27 pages, 9 figures, LaTeX. A few typos fixed, and references correcte

Pion Generalized Dipole Polarizabilities by Virtual Compton Scattering πe→πeγ\pi e \to \pi e\gamma

We present a calculation of the cross section and the event generator of the reaction $\pi e\to \pi e \gamma$. This reaction is sensitive to the pion generalized dipole polarizabilities, namely, the longitudinal electric $\alpha_L(q^2)$, the transverse electric $\alpha_T(q^2)$, and the magnetic $\beta(q^2)$ which, in the real-photon limit, reduce to the ordinary electric and magnetic polarizabilities $\bar{\alpha}$ and $\bar{\beta}$, respectively. The calculation of the cross section is done in the framework of chiral perturbation theory at ${\cal O}(p^4)$. A pion VCS event generator has been written which is ready for implementation in GEANT simulation codes or for independent use.Comment: 33 pages, Revtex, 15 figure