Double strangeness molecular-type pentaquarks from coupled channel dynamics J.A. Mars e-Valera V.K. Magas and A. Ramos Departament de F sica Qu antica i Astrof sica and Institut de Ci encies del Cosmos ICCUB

2025-04-27 0 0 359.36KB 5 页 10玖币

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Double strangeness molecular-type pentaquarks from coupled channel dynamics

J.A. Mars´e-Valera, V.K. Magas, and A. Ramos

Departament de F´ısica Qu`antica i Astrof´ısica and Institut de Ci`encies del Cosmos (ICCUB)

Universitat de Barcelona, Mart´ı i Franqu`es 1, 08028 Barcelona, Spain

(Dated: March 20, 2023)

The existence of pentaquarks with strangeness content zero and one are major discoveries of the

latest years in hadron physics. Most of these states can be understood as hadronic molecules and

were predicted prior to their discovery within a model based on unitarized meson-baryon amplitudes

obtained from vector meson exchange interactions. Contrary to earlier statements, we show this

model to also predict the existence of pentaquarks with double strangeness, at about 4500 MeV and

4600 MeV, which are generated in a very speciﬁc and unique mechanism, via an attraction induced

by a strong coupling between the two heaviest meson-baryon states.

I. INTRODUCTION

Since the turn of the millennium, an increasing amount

of data obtained by several collaborations (Belle, BaBar,

LHCb, BESII) has produced many exotic hadrons which

appear to be inconsistent with the predictions of the con-

ventional quark model [1, 2]. The discovery at LHCb [3,

4] of excited nucleon resonances (PN

Ψs(4312), PN

Ψs(4440)

and PN

Ψs(4457)), seen on the invariant mass distribution

of J/Ψppairs from the decay Λb→J/Ψp K−, has been

the ﬁrst clear evidence of the existence of pentaquark

baryons, as a c¯cpair is necessary to explain their high

mass. In a later experiment [5], the J/Ψ Λ spectrum, ob-

tained from the decay Ξ−

b→J/Ψ Λ K−, also provided

evidence for a pentaquark, the PΛ

Ψs(4459), this time with

one unit of strangeness content. More recently, an anal-

ysis of the B−→J/Ψ Λ ¯pdecay points at the exis-

tence of another narrow hidden-charm pentaquark with

strangeness, the PΛ

Ψs(4338) [6].

Among the various theoretical interpretations on the

nature of these pentaquarks, the possibility that they

could be structured as meson-baryon molecules was al-

ready predicted in [7–9], prior to their discovery, and

has gained interest ever since due to their proximity to

various charmed meson-baryon thresholds (see [10, 11]

and references therein). Many of these studies assume

a t-channel vector meson exchange interaction between

mesons and baryons, which is unitarized in coupled-

channels. However, a hidden charm pentaquark with

double strangeness was not found in this approach [8, 9].

From a hadronic molecular perspective, it is interesting

to note that the usually adopted alternative of molecu-

lar binding through a long-range interaction mediated by

the exchange of pions between the constituent hadrons is

not possible in the heavy part of strangeness S=−2

sector. In fact, a (no-pion) light meson exchange model

[12] ﬁnds doubly-strange hidden charm pentaquarks, but

requiring a unrealistically large regularization cut-oﬀ pa-

rameter. Let us ﬁnally mention that recent studies re-

lying on the quark substructure of the state also predict

double strangeness pentaquark candidates [13–15].

The unitarized coupled-channel hidden gauge formal-

ism has been a very successful approach in explaining

other exotic hadrons ﬁrst in the strange, and later in the

charm and hidden charm sectors (see [16] and references

therein). The most known example is the Λ(1405) res-

onance, whose mass was systematically predicted to be

too high by quark models, but it found a better expla-

nation as a resonant structure from a coupled-channel

KN interaction. This picture, which would consolidate

the Λ(1405) as the ﬁrst pentaquark ever, ﬁnds support

in its predicted double-pole nature [17, 18], conﬁrmed

later from the diﬀerent line shapes observed [19], and

now commonly accepted in the ﬁeld [20].

In this work, we revisit the unitarized coupled-channel

approach [8, 9] and demonstrate that, within realis-

tic model parameters, it does predict the existence of

strangeness S=−2 pentaquarks in a very unique way,

namely via an attraction generated by a strong coupling

between the two heaviest meson-baryon channels. This

ﬁnding not only complements the family of S= 0, and

S=−1 pentaquarks obtained within the same formal-

ism but, if conﬁrmed experimentally, it would strongly

support the validity of the unitarized t-channel vector-

meson exchange interaction models in explaining hadron

molecules, as the alternative pion-exchange mechanism

is forbidden in this sector.

II. FORMALISM

The model employed in this work relies on a meson-

baryon interaction in S-wave, which is built up from the

t-channel diagram of Fig. 1, where the mesons are de-

picted by dashed lines and the baryons by solid lines.

The external mesons in the diagram represent the ground

states of either pseudoscalar (JP(M) = 0−)- or vector

(JP(M)=1−)-type, while the baryons are the lowest-

energy ones with JP(B)=1/2+, all of them composed

out of u, d, s, c quarks and antiquarks. The indices i, j

label the diﬀerent meson-baryon channels with the same

spin-parity (JP), isospin and ﬂavor quantum numbers

that can be connected by the exchange of a vector meson

V∗.

The V P P (V V V ) and V BB vertices in the diagram

are described by eﬀective Lagrangians which are obtained

using the local hidden gauge formalism [21, 22] and as-

arXiv:2210.02792v2 [hep-ph] 17 Mar 2023

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Doublestrangenessmolecular-typepentaquarksfromcoupledchanneldynamicsJ.A.Marse-Valera,V.K.Magas,andA.RamosDepartamentdeFsicaQuanticaiAstrofsicaandInstitutdeCienciesdelCosmos(ICCUB)UniversitatdeBarcelona,MartiFranques1,08028Barcelona,Spain(Dated:March20,2023)Theexistenceofpentaquarkswithstra...

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Double strangeness molecular-type pentaquarks from coupled channel dynamics J.A. Mars e-Valera V.K. Magas and A. Ramos Departament de F sica Qu antica i Astrof sica and Institut de Ci encies del Cosmos ICCUB

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