Charmonium-Nucleon Dissociation Cross Sections in the Quark Model

Charmonium dissociation cross sections due to flavor-exchange charmonium-baryon scattering are computed in the constituent quark model. We present results for inelastic $J/\psi N$ and $\eta_c N$ scattering amplitudes and cross sections into 46 final channels, including final states composed of various combinations of $D$, $D^*$, $\Sigma_c$, and $\Lambda_c$. These results are relevant to experimental searches for the deconfined phase of quark matter, and may be useful in identifying the contribution of initial $c\bar c$ production to the open-charm final states observed at RHIC through the characteristic flavor ratios of certain channels. These results are also of interest to possible charmonium-nucleon bound states.Comment: 10 pages, 5 eps figures, revte

Mechanistic studies of nitrosation reactions of N-.O- and S-nitroso compounds

A kinetic study of the N-nitrosation of 2,3-diamlnonaphthalene in acid solution at 25 C was undertaken. Reaction occurred via both the protonated and unprotonated forms of 2,3-dlaminonaphthalene to yield 2,3-naphthotrlazole. The reaction is acid-catalysed and is also catalysed by added nucleophiles, The mechanism is consistent with the rate-limiting formation of the diazonium ion (N-nitrosation followed by rapid proton transfer and loss of a water molecule), which undergoes a rapid cyclisation process, to yield the product, Reactions of nitrosamines involving the N-N heterolytic cleavage with direct transfer of the nitroso group was also investigated. In particular, the denitrosation of N-nitrosoproline was studied. The reaction was carried out In the presence of an excess of nitrite trap to ensure irreversibility, in the presence of added nucleophlles, in high acidic conditions. All kinetic results are consistent with the mechanism involving a rapid reversible N-protonation followed by a rate-limiting attack by the nucleophile (added Br(^-), SCN(^-) or thiourea) giving the nitrosyl derivative, which is rapidly destroyed with the nitrite traps used in these experiments. However, at high nucleophile concentration and for reaction in ethanol, the reaction becomes Independent of added nucleophile. This is because the rate-limiting step is now the proton transfer to the nltrosamine rather than the attack of the nucleophile. N- nitrosopyrrolidine, a heterocycle which does not contain a β-electron withdrawing group reacted less readily in the denitrosation reaction. N- nitrososarcoslne, an acyclic compound containing a g-electron withdrawing group showed similar behaviour to NNP, suggesting that it is the β-electron withdrawing group, rather than the cyclic structure in NMP which is the dominant factor in the loss of the nitroso group. The reaction of N-nitroso compounds containing an electron-withdrawing group was studied. The high reactivity of N-methyl-N-nltrosotoluene-p- sulphonamide (MNTS) with nucleophlles, with the loss of the nitroso group has been explained in terms of either a rapid blmolecular reaction between the nucleophile and the more susceptible nitrosamine, due to the β-electron withdrawing substituent, or the weakening of the N-N bond by –S0(_2), resulting in extensive bond breaking. MNTS was reacted with powerful nucleophlles, L- cysteine, L-cystelne methyl and ethyl esters and N-acetyl-L-cystelne, In water at 25ºC in the pH range 6-13. The pH dependence of the rate constant Is consistent with a mechanism Involving a direct nitrosatlon by MNTS with the thiolate anion of the thiol. A quantitative kinetic analysis yielded microscopic pKa values for RSH ionlsatlon in good agreement with literature. Nitrosatlon by 0- and S-nitroso compounds were also studied. The substrates used in this case Include phenols, ascorbic acid and haems. Reaction of iso-amyl nitrite (IAN) (an alkyl nitrite) with phenols and ascorbic acid occurs via a rapid reversible acid-catalysed hydrolysis of iso-amyl nitrite giving nitrous acid, which then In Its protonated form effects nitrosatlon. Reaction of S-nitroso-N-acetylpenicillamine (SNAP) with phenols and ascorbic acid, however, showed different characteristics: a possible radical mechanism is suggested on the basis of e.s.r. experiments. Preliminary Investigations of the reactions of both IAN and SNAP with haems showed a complex reaction scheme: the reaction is not a simple single step reaction. The properties of the N-, 0- and S-nitroso compounds used in this study are also discussed

Interplay between Fermi surface topology and ordering in URu2_{2}Si2_2 revealed through abrupt Hall coefficient changes in strong magnetic fields

Temperature- and field-dependent measurements of the Hall effect of pure and 4 % Rh-doped URu$_{2}$Si$_{2}$ reveal low density (0.03 hole/U) high mobility carriers to be unique to the `hidden order' phase and consistent with an itinerant density-wave order parameter. The Fermi surface undergoes a series of abrupt changes as the magnetic field is increased. When combined with existing de Haas-van Alphen data, the Hall data expose a strong interplay between the stability of the `hidden order,' the degree of polarization of the Fermi liquid and the Fermi surface topology.Comment: 4 pages, 4 figures, Accepted to Phys. Rev. Let

Energy levels of the soliton--heavy-meson bound states

We investigate the bound states of heavy mesons with finite masses to a classical soliton solution in the Skyrme model. For a given model Lagrangian we solve the equations of motion exactly so that the heavy vector mesons are treated on the same footing as the heavy pseudoscalar mesons. All the energy levels of higher grand spin states as well as the ground state are given over a wide range of the heavy meson masses. We also examine the validity of the approximations used in the literatures. The recoil effect of finite mass soliton is naively estimated.Comment: 24 pages, REVTeX v3.0, 6 figures are available upon request

Determination of Intrinsic Ferroelectric Polarization in Orthorhombic Manganites with E-type Spin Order

By directly measuring electrical hysteresis loops using the Positive-Up Negative-Down (PUND) method, we accurately determined the remanent ferroelectric polarization Pr of orthorhombic RMnO3 (R = Ho, Tm, Yb, and Lu) compounds below their E-type spin ordering temperatures. We found that LuMnO3 has the largest Pr of 0.17 uC/cm^2 at 6 K in the series, indicating that its single-crystal form can produce a Pr of at least 0.6 \muuC/cm^2 at 0 K. Furthermore, at a fixed temperature, Pr decreases systematically with increasing rare earth ion radius from R = Lu to Ho, exhibiting a strong correlation with the variations in the in-plane Mn-O-Mn bond angle and Mn-O distances. Our experimental results suggest that the contribution of the Mn t2g orbitals dominates the ferroelectric polarization.Comment: 16 pages, 4 figure

Performance of a prototype active veto system using liquid scintillator for a dark matter search experiment

We report the performance of an active veto system using a liquid scintillator with NaI(Tl) crystals for use in a dark matter search experiment. When a NaI(Tl) crystal is immersed in the prototype detector, the detector tags 48% of the internal K-40 background in the 0-10 keV energy region. We also determined the tagging efficiency for events at 6-20 keV as 26.5 +/- 1.7% of the total events, which corresponds to 0.76 +/- 0.04 events/keV/kg/day. According to a simulation, approximately 60% of the background events from U, Th, and K radioisotopes in photomultiplier tubes are tagged at energies of 0-10 keV. Full shielding with a 40-cm-thick liquid scintillator can increase the tagging efficiency for both the internal K-40 and external background to approximately 80%.Comment: Submitted to Nuclear Instruments and Methods in Physics Research Section

Baryons with Two Heavy Quarks as Solitons

Using the chiral soliton model and heavy quark symmetry we study baryons containing two heavy quarks. If there exists a stable (under strong interactions) meson consisting of two heavy quarks and two light ones, then we find that there always exists a state of this meson bound to a chiral soliton and to a chiral anti-soliton, corresponding to a two heavy quark baryon and a baryon containing two heavy anti-quarks and five light quarks, or a ``heptaquark".Comment: 7 pages and 2 postscript figures appended, LaTex, UCI-TR 94-3

Coherent Vector Meson Photo-Production from Deuterium at Intermediate Energies

We analyze the cross section for vector meson photo-production off a deuteron for the intermediate range of photon energies starting at a few GeVs above the threshold and higher. We reproduce the steps in the derivation of the conventional non-relativistic Glauber expression based on an effective diagrammatic method while making corrections for Fermi motion and intermediate energy kinematic effects. We show that, for intermediate energy vector meson production, the usual Glauber factorization breaks down and we derive corrections to the usual Glauber method to linear order in longitudinal nucleon momentum. The purpose of our analysis is to establish methods for probing interesting physics in the production mechanism for phi-mesons and heavier vector mesons. We demonstrate how neglecting the breakdown of Glauber factorization can lead to errors in measurements of basic cross sections extracted from nuclear data.Comment: 41 pages, 13 figures, figure 9 is compressed from previous version, typos fixe