arXiv subjects

Muhammad Naeem Anwar

Publications and source records attributed to Muhammad Naeem Anwar.

13 recordsLinked to original sources

arXiv2026

Predictions for the scalar partner of the LHC tetraquark $X(6600)$

We consider how the recent CMS measurements of the masses and quantum numbers of $X(6600)$, $X(6900)$ and $X(7100)$ can help to reveal the internal structure of these apparent $cc\bar{c}\bar{c}$ tetraquark states. The measured $J^{PC} = 2^{++}$ quantum numbers of $X(6600)$ are consistent with our previous prediction, and imply the existence of lighter $0^{++}$ partner $X(6400)$ which also decays to $J/\psi J/\psi $. There may already be indications for this scalar partner in the recent CMS data fits, which include a Breit-Wigner peak with mass around 6400~MeV. We give predictions for the masses and decay properties of the scalar and other partner states, which are key experimental tests to discriminate between quark and diquark models. We urge closer experimental scrutiny in this mass region, to establish an S-wave multiplet of $cc \bar c \bar c$ states (the first of its kind), leading to a breakthrough in exotic hadron research and our understanding of exclusively heavy quark exotics.

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arXiv2025

Long-range interactions in double heavy tetraquarks $\bar Q \bar Q qq$

At the large distances compared to the chiral symmetry breaking scale, a four-quark system $\bar Q \bar Q qq$ (with $Q$ as heavy and $q$ as light quarks) can be treated as two asymptotic mesons interacting via strong residual forces. The static heavy quark assumption enables using the Born-Oppenheimer approximation, where one can compute the potential between two heavy antiquarks in the presence of two light quarks of finite mass -- a prescription utilized in several lattice QCD studies. To analyse the long-range strong force in a $\bar Q \bar Q qq$ system, we study the interaction between two bottom mesons in the heavy quark limit using chiral effective field theory and dispersion theory with unphysical pion mass. We present methods to obtain two-pion-exchange potential between two static heavy mesons at non-physical pion mass and compare our preliminary results with the corresponding lattice QCD potentials.

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arXiv2023

Tetraquark mass relations in quark and diquark models

We present new linear relations among the masses of S-wave tetraquarks with either one flavour ($QQ \bar Q \bar Q$) or two ($QQ\bar q \bar q$). Because the relations are sensitive to the hidden-colour, spin, and spatial degrees of freedom, comparison to experimental data can help to reveal the internal structure of tetraquarks, and discriminate among different theoretical models. Depending on the model, the relations are either exact, or valid in perturbation theory, and a thorough comparison with existing literature confirms their validity at the MeV level. Additionally, we explore the connections among tetraquark models, and show how those with effective (quark or diquark) masses are related to dynamical potential models. We also show how the spectrum of diquark models is effectively a limiting case of (more general) quark models, and in particular, that the diquark concept is most relevant in the particular combination $QQ\bar q \bar q$, where $Q$ is much heavier than $\bar q$.

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arXiv2023

Structure of $cc \bar c \bar c$ tetraquarks and interpretation of LHC states

Motivated by recent experimental evidence for apparent $cc\bar c \bar c$ states at LHCb, CMS and ATLAS, we consider how the mass spectrum and decays of such states can be used to discriminate among their possible theoretical interpretations, with a particular focus on identifying whether quarks or diquarks are the most relevant degrees of freedom. Our preferred scenario is that $X(6600)$ and its apparent partner state $X(6400)$ are the tensor $(2^{++})$ and scalar $(0^{++})$ states of an S-wave multiplet of $cc\bar c \bar c$ states. Using tetraquark mass relations which are independent of (or only weakly dependent on) model parameters, we give predictions for the masses of additional partner states with axial and scalar quantum numbers. Additionally, we give predictions for relations among decay branching fractions to $J/ψJ/ψ$, $J/ψη_c$, $η_cη_c$ and $D^{(*)} \bar{D}^{(*)}$ channels. The scenario we consider is consistent with existing experimental data on $J/ψJ/ψ$, and our predictions for partner states and their decays can be confronted with future experimental data, to discriminate between quark and diquark models.

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arXiv2021

Heavy quark spin partners of the $Y(4260)$ in coupled-channel formalism

The charmoniumlike state $Y(4260)$ is described as predominantly a $D_1 \bar{D}$ molecule in a coupled-channel quark model [Phys.\,Rev.\,D\,\textbf{96},\,114022\,(2017)]. The heavy quark spin symmetry (HQSS) thus implies the possible emergence of its heavy quark spin partners with molecular configuration as $D_1 \bar{D}^*$ and $D_2^* \bar{D}^*$ below these charmed mesons' thresholds. We analyze the probabilities of various intermediate charmed meson loops for $J^{PC}=1^{--}$ exotic state $Y(4360)$ and find that the channel $D_1 \bar{D}^*$ couples more strongly around its mass regime, and the coupling behavior remains the same even if the mass of $Y(4360)$ is pushed closer to $D_1 \bar{D}^*$ threshold. This enlightens that the most favorable molecular scenario for the $Y(4360)$ could be $D_1 \bar{D}^*$, and hence it can be interpreted as HQSS partner of the $Y(4260)$. We also find the strong coupling behavior of $D_2^* \bar{D}^*$ channel with the $ψ(4415)$, which makes it a good candidate for a dominant $D_2^* \bar{D}^*$ molecule. We discuss the important decay patterns of these resonances to disentangle their long- and short-distance structures.

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arXiv2019

$χ_{b}(3P)$ Multiplet Revisited: Ultrafine Mass Splitting and Radiative Transitions

Invoked by the recent CMS observation regarding candidates of the $χ_b(3P)$ multiplet, we analyze the ultrafine and mass splittings among $3P$ multiplet in our unquenched quark model (UQM) studies. The mass difference of $χ_{b2}$ and $χ_{b1}$ in $3P$ multiplet measured by CMS collaboration ($10.6 \pm 0.64 \pm 0.17$ MeV) is very close to our theoretical prediction ($12$ MeV). Our corresponding mass splitting of $χ_{b1}$ and $χ_{b0}$ enables us to predict more precisely the mass of $χ_{b0}(3P)$ to be ($10490\pm 3$) MeV. Moreover, we predict ratios of the radiative decays of $χ_{bJ}(nP)$ candidates, both in UQM and quark potential model. Our predicted relative branching fraction of $χ_{b0}(3P)\toΥ(3S)γ$ is one order of magnitude smaller than $χ_{b2}(3P)$, this naturally explains the non-observation of $χ_{b0}(3P)$ in recent CMS search. We hope these results might provide useful references for forthcoming experimental searches.

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arXiv2018

Spectroscopy and decays of the fully-heavy tetraquarks

We discuss the possible existence of the fully-heavy tetraquarks. We calculate the ground-state energy of the $bb \bar b \bar b$ bound state, where $b$ stands for the bottom quark, in a nonrelativistic effective field theory framework with one-gluon-exchange (OGE) color Coulomb interaction, and in a relativized diquark model characterized by OGE plus a confining potential. Our analysis advocates the existence of uni-flavor heavy four-quark bound states. The ground state $bb\bar b\bar b$ tetraquark mass is predicted to be $(18.72\pm0.02)$~GeV. Mass inequality relations among the lowest $QQ\bar{Q}\bar{Q}$ state, where $Q\in \{c, b\}$, and the corresponding heavy quarkonia are presented, which give the upper limit on the mass of ground state $QQ\bar{Q}\bar{Q}$. The possible decays of the lowest $bb\bar{b}\bar{b}$ are highlighted, which might provide useful references in the search for them in ongoing LHC experiments, and its width is estimated to be a few tens of MeV.

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arXiv2018

Spectroscopy of the hidden-charm $[qc][\bar q \bar c]$ and $[sc][\bar s \bar c]$ tetraquarks

We calculate the spectrum of $q\bar q c \bar c$ and $s\bar s c \bar c$ tetraquarks, where $q$, $s$ and $c$ stand for light ($u,d$), strange and charm quarks, respectively, in a relativized diquark model, characterized by one-gluon-exchange (OGE) plus confining potential. In the diquark model, a $q\bar q c \bar c$ ($s\bar s c \bar c$) tetraquark configuration is made up of a heavy-light diquark, $q c$ ($sc$), and anti-diquark, $\bar q \bar c$ ($\bar s \bar c$). According to our results, 13 charmonium-like observed states can be accommodated in the tetraquark picture, both in the hidden-charm ($q\bar q c \bar c$) and hidden-charm hidden-strange ($s\bar s c \bar c$) sectors.

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arXiv2017

$X(4260)$ Revisited: A Coupled Channel Perspective

We calculate the probabilities of various charmed meson molecules for $X(4260)$ under the framework of ${}^3P_0$ model. The results indicate that even though heavy quark spin symmetry forbids $S$ wave coupling of $D_1\bar{D}$ to the ${}^3S_1$ charmonia ($ψ(nS)$), the $D$ wave coupling is allowed and not negligible. Under this symmetry, the $D_1\bar{D}$ can couple to ${}^3D_1$ charmonia ($ψ(nD)$) via both $S$ and $D$ wave, and the overall coupling is around three times larger than that of $ψ(nS)$. The $X(4260)$ cannot be a pure molecule but a mixture of a charmonium and various charmed meson components. Since the $D_1\bar{D}$ couples strongly to $ψ(nD)$, our results suggest that in the $D_1\bar{D}$ molecular picture, the charmonium core of $X(4260)$ is $ψ(nD)$ instead of $ψ(nS)$. As a result, the experimental fact that the $R$ ratio has a dip around 4.26 GeV can be understood in the $D_1\bar{D}$ molecular picture of the $X(4260)$.

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arXiv2017

Heavy Quark Spin Symmetry Violating Hadronic Transitions of Higher Charmonia

In heavy quarkonia, hadronic transitions serve as an enlightened probe for the structure and help to establish the understanding of light quark coupling with a heavy degree of freedom. Moreover, in recent years, hadronic transitions revealed remarkable discoveries to identify the new conventional heavy quarkonia and extracting useful information about the so called "XYZ" exotic states. In this contribution, we present our predictions for heavy quark spin symmetry (HQSS) breaking hadronic transitions of higher $S$ and $D$ wave vector charmonia based on our recently proposed model (inspired by Nambu-Jona-Lasinio (NJL) model) to create light meson(s) in heavy quarkonium transitions. We also suggest spectroscopic quantum numbers $(^{2S+1}L_J)$ for several observed charmoniumlike states. Our analysis indicates that the $Y(4360)$ is most likely to be a $3D$ dominant state.

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arXiv2017

Modeling Charmonium-$η$ Decays of $J^{PC}=1^{--}$ Higher Charmonia

We propose a new model to create a light meson in the heavy quarkonium transition, which is inspired by the Nambu$-$Jona-Lasinio (NJL) model. Hadronic transitions of $J^{PC}=1^{--}$ higher charmonia with the emission of an $η$ meson are studied in the framework of the proposed model. The model shows its potential to reproduce the observed decay widths and make predictions for the unobserved channels. We present our predictions for the decay width of $Ψ\to J/ψη$ and $Ψ\to h_{c}(1P)η$, where $Ψ$ are higher $S$ and $D$ wave vector charmonia, which provide useful references to search for higher charmonia and determine their properties in forthcoming experiments. The predicted branching fraction $\mathcal B(ψ(4415)\to h_{c}(1P)η)=4.62\times 10^{-4}$ is one order of magnitude smaller than the $J/ψη$ channel. Estimates of partial decay width $Γ(Y \to J/ψη)$ are given for $Y(4360)$, $Y(4390)$ and $Y(4660)$ by assuming them as $c\bar{c}$ bound states with quantum numbers $3 ^3D_1$, $3 ^3D_1$ and $5 ^3S_1$, respectively. Our results are in favor of these assignments for $Y(4360)$ and $Y(4660)$. The corresponding experimental data for these $Y$ states has large statistical errors which do not provide any constraint on the mixing angle if we introduce $S-D$ mixing. To identify $Y(4390)$, precise measurements on its hadronic branching fraction are required which are eagerly awaited from BESIII.

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arXiv2017

How Large is the Contribution of Excited Mesons in Coupled-Channel Effects?

We study the excited $B$ mesons' contributions to the coupled-channel effects under the framework of ${}^3P_0$ model for the bottomonium. Contrary to what has been widely accepted, the contributions of $P$ wave $B$ mesons are generally the largest and this result is independent of the potential parameters to some extent. We also push the calculation beyond $B(1P)$ and carefully analyze the contributions of $B(2S)$. A form factor is a key ingredient to suppress the contributions of $B(2S)$ for low lying bottomonia. However, this suppression mechanism is not efficient for highly excited bottomonia such as $Υ(5S)$ and $Υ(6S)$. We give explanations why this difficulty happens to ${}^3P_0$ model and suggest analyzing flux-tube breaking model for the full calculation of coupled-channel effects.

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arXiv2016

Coupled-Channel Effects for the Bottomonium with Realistic Wave Functions

With Gaussian expansion method (GEM), realistic wave functions are used to calculate coupled-channel effects for the bottomonium under the framework of ${}^3P_0$ model. The simplicity and accuracy of GEM are explained. We calculate the mass shifts, probabilities of the $B$ meson continuum, $S-D$ mixing angles, strong and dielectric decay widths. Our calculation shows that both $S-D$ mixing and the $B$ meson continuum can contribute to the suppression of the vector meson's dielectric decay width. We suggest more precise measurements on the radiative decays of $Υ(10580)$ and $Υ(11020)$ to distinguish these two effects. The above quantities are also calculated with simple harmonic oscillator (SHO) wave function approximation for comparison. The deviation between GEM and SHO indicates that it is essential to treat the wave functions accurately for near threshold states.

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