Light Hadron Spectroscopy: Theory and Experiment

Rapporteur talk at the Lepton-Photon Conference, Rome, July 2001: reviewing the evidence and strategies for understanding scalar mesons, glueballs and hybrids, the gluonic Pomeron and the interplay of heavy flavours and light hadron dynamics. Dedicated to the memory of Nathan Isgur, long-time collaborator and friend, whose original ideas in hadron spectroscopy formed the basis for much of the talk.Comment: to be published in "Lepton Photon 2001 Conference Proceedings" (World Scientific Publishing), 19 pages with 6 figure

Dynamics and Decay of Heavy-Light Hadrons

Recent signals for narrow hadrons containing heavy and light flavours are compared with quark model predictions for spectroscopy, strong decays, and radiative transitions. In particular, the production and identification of excited charmed and cs states are examined with emphasis on elucidating the nature of $0^+$ and $1^+$ states. Roughly 200 strong decay amplitudes of $D$ and $D_s$ states up to 3.3 GeV are presented. Applications include determining flavour content in $\eta$ mesons and the mixing angle in $P$ and $D$ wave states and probes of putative molecular states. We advocate searching for radially excited $D_s^*$ states in B decays.Comment: 19 pages, 7 figures, revtex. A numerical error is corrected. Some strong decay rates have change

Spin of ground state baryons

We calculate the quark spin contribution to the total angular momentum of flavor octet and flavor decuplet ground state baryons using a spin-flavor symmetry based parametrization method of quantum chromodynamics. We find that third order SU(6) symmetry breaking three-quark operators are necessary to explain the experimental result Sigma_1=0.32(10). For spin 3/2 decuplet baryons we predict that the quark spin contribution is Sigma_3=3.93(22), i.e. considerably larger than their total angular momentum.Comment: 8 page

The First Direct Distance and Luminosity Determination for a Self-Luminous Giant Exoplanet: The Trigonometric Parallax to 2MASS1207334-393254Ab

We present the first trigonometric parallax and distance for a young planetary mass object. A likely TW Hya cluster member, 2MASSW J1207334-393254Ab (hereafter 2M1207Ab) is an M8 brown dwarf with a mid to late L type planetary mass companion. Recent observations of spectral variability have uncovered clear signs of disk accretion and outflow, constraining the age of the system to <10 Myr. Because of its late spectral type and the clearly youthful nature of the system, 2M1207b is very likely a planetary mass object. We have measured the first accurate distance and luminosity for a self-luminous planetary mass object. Our parallax measurements are accurate to <2 mas (1sigma) for 2M1207Ab. With 11 total epochs of data taken from January 2006 through April 2 007 (475 images for 2M1207Ab), we determine a distance of 58.8+-7.0 pc (17.0{+2.3}{-1.8} mas, 1.28sigma) to 2M1207Ab and a calculated luminosity of 0.68-2.2x10^-5 Lsun for 2M1207b. Hence 2M1207Ab is a clear member of the TW Hya cluster in terms of its distance, proper motions, and youthful nature. However, as previously noted by Mohanty and co-workers, 2M1207b's luminosity appears low compared to its temperature according to evolutionary models.Comment: 12 pages, 3 figures, accepted to ApJ Letter

Mixing of scalar tetraquark and quarkonia states in a chiral approach

A chiral invariant Lagrangian describing the tetraquark-quarkonia interaction is considered at the leading and subleading order in the large-$N_{c}$ expansion. Spontaneous chiral symmetry breaking generates mixing of scalar tetraquark and quarkonia states and non-vanishing tetraquark condensates. In particular, the mixing strength is related to the decay strengths of tetraquark states into pseudoscalar mesons. The results show that scalar states below 1 GeV are mainly four-quark states and the scalars between 1 and 2 GeV quark-antiquark states, probably mixed with the scalar glueball in the isoscalar sector.Comment: 30 pages, 3 figures, 6 tables, to appear in Phys. Rev.

Decisive Search for a Diquark-Antidiquark Meson with Hidden Strangeness

Diquark-antidiquark states are expected to exist as a natural complement of mesons and baryons. Although they were predicted long ago, and some candidates were found experimentally, none has, as yet, been reliably identified. We suggest that the search for the so-called $C(1480)$-meson in reactions such as photoproduction $\gamma N\rightarrow\phi\pi N$ and $K N \rightarrow \phi \pi \Lambda$ should provide a decisive way to settle this issue. Estimates of the cross sections are given using present experimental information on the C-meson and assuming its diquark-antidiquark structure. Sizable cross sections are predicted (of the order of 0.1 $\mu$b for photoproduction and of the order of 0.1 mb for $KN$ at the maximum with an insignificant background). Failure to find this kind of signal would imply that the C-meson is {\it not} a diquark-antidiquark state.Comment: 9 pages in LATex + 6 figs. (available from authers upon request), IUHET-269/9

Open-charm meson spectroscopy

We present a theoretical framework that accounts for the new $D_J$ and $D_{sJ}$ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional $P-$wave quark-antiquark states and four-quark components. The narrowest states are basically $P-$wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold, being broad resonances. We study the electromagnetic decay widths as basic tools to scrutiny their nature. The proposed explanation incorporates in a natural way the most recently discovered mesons in charmonium spectroscopy.Comment: 15 pages, 5 tables. Accepted for publication in Phys. Rev.

Isospin breaking in scalar and pseudoscalar channels of radiative J/ψJ/\psi-decays

In the framework of simple assumption on factorizing a mixing of vector state with isoscalar components in effective amplitudes of isospin breaking caused by the electromagnetic quark current, a branching fraction of radiative $J/\psi\to a_0$ transition is evaluated at the level of $3\cdot 10^{-3}$.Comment: 3 pages, revtex4 class, 2 eps-figures; reference, comment and acknowledgement adde

Neutrino induced threshold production of two pions and N^*(1440) electroweak form factors

We study the threshold production of two pions induced by neutrinos in nucleon targets. The contribution of nucleon, pion and contact terms are calculated using a chiral Lagrangian. The contribution of the Roper resonance, neglected in earlier studies, has also been taken into account. The numerical results for the cross sections are presented and compared with the available experimental data. It has been found that in the two pion channels with $\pi^+\pi^-$ and $\pi^0\pi^0$ in the final state, the contribution of the $N^*(1440)$ is quite important and could be used to determine the $N^*(1440)$ electroweak transition form factors if experimental data with better statistics become available in the future.Comment: This version corrects a mistake on the helicity amplitudes sign. Additional comments on resonance-background relative sign are added. Other minor corrections. Matches published version. 17 pages, 7 figure

The \rho\rho interaction in the hidden gauge formalism and the f_0(1370) and f_2(1270) resonances

We have studied the interaction of vectors mesons within the hidden gauge formalism and applied it to the particular case of the $\rho \rho$ interaction. We find a strong attraction in the isospin, spin channels I,S=0,0 and 0,2, which is enough to bind the $\rho \rho$ system. We also find that the attraction in the I,S=0,2 channel is much stronger than in the 0,0 case. The states develop a width when the $\rho$ mass distribution is considered, and particularly when the $\pi \pi$ decay channel is turned on. Using a regularization scheme with cut offs of natural size, we obtain results in fair agreement with the mass and the width of the $f_0(1370)$ and $f_2(1270)$ meson states, providing a natural explanation of why the tensor state is more bound than the scalar and offering a new picture for these states, which would be dynamically generated from the $\rho \rho$ interaction or, in simpler words, $\rho \rho$ molecular states.Comment: Version accepted for publicatio