4,954 research outputs found
Estimating decay rate of while assuming them to be molecular states
Discovery of brings up a tremendous interest because it is very
special, i.e. made of four different flavors. The D0 collaboration claimed that
they observed this resonance through portal , but
unfortunately, later the LHCb, CMS, CDF and ATLAS collaborations' reports
indicate that no such state was found. Almost on the Eve of 2017, the D0
collaboration reconfirmed existence of via the semileptonic decay of
. To further reveal the discrepancy, supposing as a molecular
state, we calculate the decay rate of in an
extended light front model. Numerically, the theoretically predicted decay
width of is MeV which is
consistent with the result of the D0 collaboration
( MeV). Since the
resonance is narrow, signals might be drowned in a messy background. In analog,
two open-charm molecular states and named as and , could
be in the same situation. The rates of and
are estimated as about 30 MeV and 20 MeV respectively. We suggest the
experimental collaborations round the world to search for these two modes and
accurate measurements may provide us with valuable information.Comment: 13 pages and 4 figures, accepted by EPJ
How can escape detection?
Multi-quark states were predicted by Gell-Mann when the quark model was first
formulated. Recently, numerous exotic states that are considered to be
multi-quark states have been experimentally confirmed (four-quark mesons and
five-quark baryons). Theoretical research indicates that the four-quark state
might comprise molecular and/or tetraquark structures. We consider that the
meson containing four different flavors should exist and decay
via the channel. However, except for the D0 collaboration,
all other experimental collaborations have reported negative observations for
in this golden portal. This contradiction has stimulated the interest
of both theorists and experimentalists. To address this discrepancy, we propose
that the assumed is a mixture of a molecular state and tetraquark,
which contributes destructively to . The cancellation may be
accidental and it should be incomplete. In this scenario, there should be two
physical states with the same flavor ingredients, with spectra of
and . lies in the error range of the first state. We
predict the width of the second state (designated as ) as
MeV. We strongly suggest searching for it
in future experiments.Comment: pages 4. Accepted by phys. lett.
Study on decays of and into
At the invariant mass spectrum of a new resonance
has been observed, however the previously confirmed does not show
up at this channel. In this paper we assume that and
are molecular states of and
respectively, then we calculate the transition rates of
and in the light front model. Our results show that the
partial width of is only three times smaller than that
of . seems to be a molecular state, so if
is also a molecular state it should be observed in the portal
as long as the database is sufficiently large, by
contrary if the future more precise measurements still cannot find
at channel, the molecular assignment to should be
ruled out.Comment: 15 pages, 4 figures, will be published in EPJ
A Constant-Factor Approximation for Multi-Covering with Disks
We consider variants of the following multi-covering problem with disks. We
are given two point sets (servers) and (clients) in the plane, a
coverage function , and a constant . Centered at each server is a single disk whose radius we are free to
set. The requirement is that each client be covered by at least
of the server disks. The objective function we wish to minimize is
the sum of the -th powers of the disk radii. We present a polynomial
time algorithm for this problem achieving an approximation
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