1,890 research outputs found
Analysis on Heavy Quarkonia Transitions with Pion Emission in Terms of the QCD Multipole Expansion and Determination of Mass Spectra of Hybrids
One of the most important tasks in high energy physics is search for the
exotic states, such as glueball, hybrid and multi-quark states. The transitions
and attract
great attentions because they may reveal characteristics of hybrids. In this
work, we analyze those transition modes in terms of the theoretical framework
established by Yan and Kuang. It is interesting to notice that the intermediate
states between the two gluon-emissions are hybrids, therefore by fitting the
data, we are able to determine the mass spectra of hybrids. The ground hybrid
states are predicted as 4.23 GeV (for charmonium) and 10.79 GeV (for bottonium)
which do not correspond to any states measured in recent experiments, thus it
may imply that very possibly, hybrids mix with regular quarkonia to constitute
physical states. Comprehensive comparisons of the potentials for hybrids whose
parameters are obtained in this scenario with the lattice results are
presented.Comment: 16 pages, 2 figur
Substrate entering and product leaving trajectories predict an engulfing dynamic for the major conformational change of the β-lactam acylase
It is still a major challenge to acquire insight into the conformational changes between the ground state and the transition state of an enzyme, although conformational fluctuation within interconverting conformers has been widely investigated (1-4). Here, we utilize different enzymatic reactions in b-lactam acylase to figure out the substrate/product trajectories in the enzyme, thereby probing the overall conformational changes in transition state. First, an auto-proteolytic intermediate of cephalosporin acylase (EC 3.5.1.11) with partial spacer segment was identified. As a final proteolytic step, the deletion of this spacer segment was revealed to be a first-order reaction, suggesting an intramolecular Ntn mechanism for the auto-proteolysis. Accordingly, the different proteolytic sites in the acylase precursor indicate a substrate entering pathway along the spacer peptide. Second, bromoacyl-7ACA can interact with penicillin G acylase (EC 3.5.1.11) in two distinguish aspects, to be hydrolyzed as a substrate analogue and to affinity alkylate the conserved Trpb4 as a product analogue. The kinetic correlation between these two reactions suggests a channel opening from Serb1 to Trpb4, responsible for the main product leaving. These two reaction trajectories relaying at the active centre, together with the crystal structures (5-10), predict an engulfing dynamic involving pocket constriction and channel opening
1-(3-ChloroÂbenzÂyloxy)urea
The asymmetric unit of the crystal structure of the title compound, C8H9ClN2O2, contains four independent molÂecules. The dihedral angles between the urea N—(C=O)—N planes and the benzene rings are 83.3 (3), 87.8 (1), 89.1 (1) and 17.5 (2)° in the four molÂecules. Extensive N—H⋯O hydrogen bonding is present in the crystal structure
Fully-strange tetraquark states with the exotic quantum numbers and
We study the fully-strange tetraquark states with the exotic quantum numbers
and . We construct their corresponding
diquark-antidiquark interpolating currents, and apply the QCD sum rule method
to calculate both their diagonal and off-diagonal correlation functions. The
obtained results are used to construct some mixing currents that are nearly
non-correlated, from which we extract the masses of the lowest-lying states to
be GeV and GeV. We apply the Fierz rearrangement to transform the
diquark-antidiquark currents to be the combinations of meson-meson currents,
and the obtained Fierz identities indicate that these two states may be
searched for in the -wave channels.Comment: 14 pages, 5 figures, 1 tables, revised version to be published in PR
- …