1,459 research outputs found
Baryons with two heavy quarks: Masses, production, decays, and detection
The large number of mesons observed by LHCb suggests a sizable cross
section for producing doubly-heavy baryons in the same experiment. Motivated by
this, we estimate masses of the doubly-heavy baryons ,
, and , and their hyperfine partners, using a
method which accurately predicts the masses of ground-state baryons with a
single heavy quark. We obtain MeV, MeV, MeV, MeV, MeV, MeV, and
MeV. As a byproduct, we estimate the hyperfine
splitting between and mesons to be MeV. We discuss
P-wave excitations, production mechanisms, decay modes, lifetimes, and
prospects for detection of the doubly heavy baryons.Comment: 29 pages, no figures. More text and references added. To be published
in Phys. Rev.
Exotic resonances due to exchange
The meson and several related states appear to be, at least in
part, hadronic molecules in which a heavy flavored meson (such as ) is
bound to another heavy meson (such as ). Although not the only
effect contributing to the binding, pion exchange seems to play a crucial role
in generating the longest-range force between constituents. Mesons without
and light quarks (such as ) cannot exchange pions, but under suitable
circumstances can bind as a result of exchange. Channels in which this
mechanism is possible are identified, and suggestions are made for searches for
the corresponding molecular states, including a manifestly exotic baryonic
resonance decaying into .Comment: 6 pages, 1 figur
photoproduction on deuterium as a test for exotic baryons
We extend a previous study of photoproduction of exotic baryon resonances to
the reaction , which permits simultaneous
investigation of the reactions \hbox{(
spectator)} and \hbox{( spectator).}
Here is an exotic baryon with quark content , and
is its hypothetical isospin partner with quark content . We find:
\hbox{(1) The} cross section for photoproduction should be equal to
that for photoproduction if these processes are dominated by the
photon coupling to a pair. In that case the two processes are equal
by isospin reflection. (2) If a candidate is a genuine
resonance, its isospin partner should have the same
mass (again by isospin reflection). (3) In the absence of Fermi motion, the
cross section for photoproduction of off a deuteron should be nearly the
sum of two equal cross sections: (spectator )
and (spectator ). (4) The effects of Fermi
motion are significant. They include smearing, form-factor suppression and
offshellness. The upshot is that the resonance is significantly wider and the
peak cross section off a deuteron is expected to be considerably less than
twice that in .Comment: 5 pages, 2 figures. To be submitted to Physics Letters
New Exotic Meson and Baryon Resonances from Doubly-Heavy Hadronic Molecules
We predict several new exotic doubly-heavy hadronic resonances, inferring
from the observed exotic bottomonium-like and charmonium-like narrow states
, , , , and . We
interpret the binding mechanism as mostly molecular-like isospin-exchange
attraction between two heavy-light mesons in a relative S-wave state. We then
generalize it to other systems containing two heavy hadrons which can couple
through isospin exchange. The new predicted states include resonances in
meson-meson, meson-baryon, baryon-baryon, and baryon-antibaryon channels. These
include those giving rise to final states involving a heavy quark and
antiquark , namely , , , , , , ,
, , , , , , , and , as well as corresponding S-wave
states giving rise to or .Comment: 8 pages, no figures, additional text and references, to be published
in Phys. Rev. Letter
Discovery of doubly-charmed Xi_{cc} baryon implies a stable (b b ubar dbar) tetraquark
Recently LHCb discovered the first doubly-charmed baryon at MeV, very close to our theoretical prediction. We
use the same methods to predict a doubly-bottom tetraquark
with at MeV, 215 MeV below the
threshold and 170 MeV below threshold for decay to . The
is therefore stable under strong and electromagnetic (EM)
interactions and can only decay weakly, the first exotic hadron with such a
property. On the other hand, the mass of with
is predicted to be MeV, 7 MeV above the threshold and
148 MeV above threshold. with
is predicted at MeV, 11 MeV below the threshold. Our
precision is not sufficient to determine whether is actually
above or below the threshold. It could manifest itself as a narrow resonance
just at threshold.Comment: References added, typos corrected, plot updated. Conclusions
unchange
Very narrow excited baryons
Recently LHCb reported the discovery of five extremely narrow excited
baryons decaying into . We interpret these baryons as
bound states of a -quark and a -wave -diquark. For such a system
there are exactly five possible combinations of spin and orbital angular
momentum. The narrowness of the states could be a signal that it is hard to
pull apart the two -quarks in a diquark. We predict two of spin 1/2, two of
spin 3/2, and one of spin 5/2, all with negative parity. Of the five states two
can decay in -wave and three can decay in -wave. Some of the -wave
states might be narrower than the -wave states. We discuss relations among
the five masses expected in the quark model and the likely spin assignments and
compare with the data. A similar pattern is expected for negative-parity
excited states. An alternative interpretation is noted in which the
heaviest two states are excitations with and , while
the lightest three are those with expected to decay
via -waves. In this case we expect states around
2904 and 2978 MeV.Comment: 18 pages, 4 figures (expanded text, appendices, and references
Scaling of P-wave excitation energies in heavy-quark systems
A simple regularity in anticipating P-wave excitation energies of states with
heavy quarks is noted. It can apply to systems such as the negative-parity
, , and , quarkonia, and the
bottom-charmed meson . When one subtracts a term accounting for
phenomenological energies of heavy quarks binding with one another in S-waves,
the residual excitation energies display an approximately linear behavior in
the reduced mass of constituents, all the way from the to the
.Comment: 10 pages, 1 figure, discussion of B_s added, to be submitted to Phys.
Rev. D. Third paragraph of last section modifie
Quark-level analogue of nuclear fusion with doubly-heavy baryons
The recent discovery by LHCb of the first doubly-charmed baryon
at MeV implies a large binding energy
MeV between the two quarks. This strong binding enables a
quark-rearrangement exothermic reaction with MeV, which is a quark-level analogue of
deuterium-tritium nuclear fusion reaction . Due to much
larger binding energy between two quarks MeV, the analogous
reaction with quarks, is expected
to have a dramatically larger -value, MeV.Comment: 5 pages, 1 figur
Multiquark States
Why do we see certain types of strongly interacting elementary particles and
not others? This question was posed over 50 years ago in the context of the
quark model. M. Gell-Mann and G. Zweig proposed that the known mesons were and baryons , with quarks known at the time ("up"),
("down"), and ("strange") having charges (2/3,-1/3,-1/3). Mesons and
baryons would then have integral charges. Mesons such as and
baryons such as would also have integral charges. Why weren't
they seen? They have now been seen, but only with additional heavy quarks and
under conditions which tell us a lot about the strong interactions and how they
manifest themselves. The present article describes recent progress in our
understanding of such "exotic" mesons and baryons
Radiative Return Capabilities of a High-Energy, High-Luminosity Collider
An electron-positron collider operating at a center-of-mass energy
can collect events at all lower energies through initial-state radiation (ISR
or radiative return). We explore the capabilities for radiative return studies
by a proposed high-luminosity collider at = 250 or 90 GeV, to fill in
gaps left by lower-energy colliders such as PEP, PETRA, TRISTAN, and LEP. These
capabilities are compared with those of the lower-energy colliders as
well as hadron colliders such as the Tevatron and the CERN Large Hadron
Collider (LHC). Some examples of accessible questions in dark photon searches
and heavy flavor spectroscopy are given.Comment: 26 pages, 11 figures, 5 table
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