Note on Shadowing and Diffraction in Deep-Inelastic Lepton Scattering

We discuss the close relation between shadowing in deep-inelastic lepton-nucleus scattering and diffractive photo- and leptoproduction of hadrons from free nucleons. We show that the magnitude of nuclear shadowing at small Bjorken-x, as measured by the E665 and NMC collaborations, is directly related to HERA data on the amount of diffraction in the scattering from free nucleons.Comment: 6 pages, Latex, to be published in Eur. Phys. J.

Scattering lengths of Nambu-Goldstone bosons off DD mesons and dynamically generated heavy-light mesons

Recent lattice QCD simulations of the scattering lengths of Nambu-Goldstone bosons off the $D$ mesons are studied using unitary chiral perturbation theory. We show that the Lattice QCD data are better described in the covariant formulation than in the heavy-meson formulation. The $D^*_{s0}(2317)$ can be dynamically generated from the coupled-channels $DK$ interaction without \textit{a priori} assumption of its existence. A new renormalization scheme is proposed which manifestly satisfies chiral power counting rules and has well-defined behavior in the infinite heavy-quark mass limit. Using this scheme we predict the heavy-quark spin and flavor symmetry counterparts of the $D^*_{s0}(2317)$.Comment: 22 pages, 5 figures; to appear in Physical Review

Open-charm enhancement at FAIR?

We have calculated the D-meson spectral density at finite temperature within a self-consistent coupled-channel approach that generates dynamically the $\Lambda_c$ (2593) resonance. We find a small mass shift for the D-meson in this hot and dense medium while the spectral density develops a sizeable width. The reduced attraction felt by the D-meson in hot and dense matter together with the large width observed have important consequences for the D-meson production in the future CBM experiment at FAIR.Comment: 4 pages, 2 figures, to appear in the proceedings of 9th International Conference on Strangeness in Quark Matter (SQM2006), Los Angeles, USA, March 26-31, 200

Chiral Dynamics of Deeply Bound Pionic Atoms

We present and discuss a systematic calculation, based on two-loop chiral perturbation theory, of the pion-nuclear s-wave optical potential. A proper treatment of the explicit energy dependence of the off-shell pion self-energy together with (electromagnetic) gauge invariance of the Klein-Gordon equation turns out to be crucial. Accurate data for the binding energies and widths of the 1s and 2p levels in pionic ^{205}Pb and ^{207}Pb are well reproduced, and the notorious "missing repulsion" in the pion-nuclear s-wave optical potential is accounted for. The connection with the in-medium change of the pion decay constant is clarified.Comment: preprint ECT*-02-16, 4 pages, 3 figure

Low-energy interactions of Nambu-Goldstone bosons with DD mesons in covariant chiral perturbation theory

We calculate the scattering lengths of Nambu-Goldstone bosons interacting with $D$ mesons in a covariant formulation of chiral perturbation theory, which satisfies heavy-quark spin symmetry and analytical properties of loop amplitudes. We compare our results with previous studies performed using heavy meson chiral perturbation theory and show that recoil corrections are sizable in most cases.Comment: 3 figures and 4 table

Nuclear Quark and Gluon Distributions in Coordinate Space

In coordinate space, quark and gluon distributions of the nucleon are defined as correlation functions involving two field operators separated by a light-cone distance $y^+ = 2l$. We study the nuclear modifications of these distributions. The largest effect is a strong depletion of parton distributions (shadowing) at large longitudinal distances, which starts for all parton species at $l=2$ fm, i.e. at the average nucleon-nucleon separation in nuclei. On the other hand, the nuclear radius does not play a significant role. At $l intrinsic structure of individual nucleons is evidently not very much affected by nuclear binding. In particular, there is no evidence for a significant increase of the quark or gluon correlation length in bound nucleons

Stochastic optimization of a cold atom experiment using a genetic algorithm

We employ an evolutionary algorithm to automatically optimize different stages of a cold atom experiment without human intervention. This approach closes the loop between computer based experimental control systems and automatic real time analysis and can be applied to a wide range of experimental situations. The genetic algorithm quickly and reliably converges to the most performing parameter set independent of the starting population. Especially in many-dimensional or connected parameter spaces the automatic optimization outperforms a manual search.Comment: 4 pages, 3 figure

Spectrum of the excited N∗N^* and Δ∗\Delta^* baryons in a relativistic chiral quark model

The spectrum of the SU(2) flavor baryons is studied in the frame of a relativistic chiral quark potential model based on the one-pion and one-gluon exchange mechanisms. It is argued that the N* and Delta* resonances strongly coupled to the pi-N channel are identified with the orbital configurations $(1S_{1/2})^2(nlj)$ with a single valence quark in the excited state (nlj). With the obtained selection rules based on the "chiral constraint", we show that it is possible to construct a schematic periodic table of baryon resonances, consistent with the experimental data and yielding no "missing resonances". A new original method for the treatment of the center of mass problem is suggested, which is based on the separation of the three-quark Dirac Hamiltonian into the parts, corresponding to the Jacobi coordinates. The numerical estimations for the energy positions of the Nucleon and Delta baryons (up to and including F-wave resonances), obtained within the field-theoretical framework by using time ordered perturbation theory, yield an overall good description of the experimental data at the level of the relativized CQM of S. Capstick and W. Roberts without any fitting parameters. The Delta(1232) is well reproduced. However, N g. s. and most of the radially excited baryon resonances (including Roper) are overestimated. Contrary, the first band of the orbitally excited baryon resonances with a negative parity are underestimated. At the same time, the second band of the orbitally excited Delta* states with the negative parity are mostly overestimated, while the N* states are close to the experimental boxes. The positive parity baryon resonances with J=5/2, 7/2 are close to the experimental data. At higher energies, where the experimental data are poor, we can extend our model schematically and predict an existence of seven N* and four Delta* new states with larger spin values.Comment: 19 pages, 6 figures, 2 tables. The results and text have been updated. arXiv admin note: text overlap with arXiv:1103.366

The 157 nm Photodissociation of OCS

The photodissociation of OCS at 157 nm has been investigated by using tunable vacuum ultraviolet radiation to probe the CO and S photoproducts. Sulfur is produced almost entirely in the 1S state, while CO is produced in its ground electronic state and in vibrational levels from v=0-3 in the appropriate ratio (v=0):(v=1):(v=2):(v=3) = (1.0):(1.0):(0.5):(0.3). The rotational distribution for each vibrational level is found to be near Boltzmann, with temperatures that decrease from 1350 K for v=0 to 780 K for v=3. Measurements of the CO Doppler profiles demonstrate that the dissociation takes place from a transition of predominantly parallel character (β=1.8±0.2) and that the CO velocity and angular momentum vectors are perpendicular to one another

Nuclear Shadowing and the Optics of Hadronic Fluctuations

A coordinate space description of shadowing in deep-inelastic lepton-nucleus scattering is presented. The picture in the laboratory frame is that of quark-gluon fluctuations of the high-energy virtual photon, propagating coherently over large light-cone distances in the nuclear medium. We discuss the detailed dependence of the coherence effects on the invariant mass of the fluctuation. We comment on the issue of possible saturation in the shadowing effects at very small Bjorken-$x$.Comment: 11 pages, 5 figure