Showing papers on "Meson published in 2022"
TL;DR: In this article , an updated review of the recent experimental and theoretical progresses in the active field of hadron physics has been provided, including the recently observed open heavy flavor tetraquark states X(2900) and Tcc+(3875) as well as the hidden heavy flavor multiquark states.
Abstract: The past decades witnessed the golden era of hadron physics. Many excited open heavy flavor mesons and baryons have been observed since 2017. We shall provide an updated review of the recent experimental and theoretical progresses in this active field. Besides the conventional heavy hadrons, we shall also review the recently observed open heavy flavor tetraquark states X(2900) and Tcc+(3875) as well as the hidden heavy flavor multiquark states X(6900), Pcs(4459)0 , Zcs(3985)− , Zcs(4000)+ , and Zcs(4220)+ . We will also cover the recent progresses on the glueballs and light hybrid mesons, which are the direct manifestations of the non-Abelian SU(3) gauge interaction of the Quantum Chromodynamics in the low-energy region.
109 citations
TL;DR: The tetraquark as discussed by the authors contains two charm quarks, a $$\overline{{{{{u}}}}} and a $$/overline{{d}}}}}, and has a mass of approximately 3,875 MeV.
Abstract: Abstract Conventional, hadronic matter consists of baryons and mesons made of three quarks and a quark–antiquark pair, respectively 1,2 . Here, we report the observation of a hadronic state containing four quarks in the Large Hadron Collider beauty experiment. This so-called tetraquark contains two charm quarks, a $$\overline{{{{{u}}}}}$$ u ¯ and a $$\overline{{{{{d}}}}}$$ d ¯ quark. This exotic state has a mass of approximately 3,875 MeV and manifests as a narrow peak in the mass spectrum of D 0 D 0 π + mesons just below the D *+ D 0 mass threshold. The near-threshold mass together with the narrow width reveals the resonance nature of the state.
79 citations
TL;DR: In this article , the authors summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels and identify new search strategies for under-explored signatures, and demonstrate that improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.
Abstract: Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.
40 citations
TL;DR: In this paper , a doubly charmed four-quark state was treated as an axial-vector tetraquark and its mass and current coupling were derived by means of the QCD two-point sum rule method by taking into account quark, gluon and mixed condensates up to dimension 10.
29 citations
TL;DR: In this paper , an extensive review of the progress on the heavy hadronic molecular states within the framework of the chiral perturbation theory is presented, in which the same chiral dynamics not only govern the nuclei and forms the deuteron, but also dictates the shallow bound states or resonances composed of two heavy hadrons.
26 citations
TL;DR: In this article , the authors show that the SU(3) flavor octet and singlet mixing is non-negligible and apparently deviates from the flavor ideal mixing.
Abstract:
The observation of the light hybrid candidate $\eta_1(1855)$ by the BESIII Collaboration brings great opportunities for advancing our knowledges about exotic hadrons in the light flavor sector. We show that this observation provides a crucial clue for establishing the $J^{P(C)}=1^{-(+)}$ hybrid nonet. Based on the flux tube model picture, the production and decay mechanisms for the $J^{P(C)}=1^{-(+)}$ hybrid nonet in the $J/\psi$ radiative decays into two pseudoscalar mesons are investigated. In the $I=0$ sector, we find that the SU(3) flavor octet and singlet mixing is non-negligible and apparently deviates from the flavor ideal mixing. Since only signals for one isoscalar $\eta_1(1855)$ are observed in the $\eta\eta'$ channel, we investigate two schemes of the nonet structure in which $\eta_1(1855)$ can be either the higher or lower mass state that strongly couples to $\eta\eta'$. Possible channels for detecting the multiplets are suggested. In particular, a combined analysis of the hybrid production in $J/\psi\to VH$, where $V$ and $H$ stand for the light vector mesons and $1^{-(+)}$ hybrid states, may provide further evidence for this nonet structure and finally establish these mysterious exotic species in experiment. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.
25 citations
TL;DR: In this article , the authors investigated the doubly heavy tetraquark states with the molecule configuration $[Q_1\bar{q}_2][Q_3\bar}q]_4]$ in a nonrelativistic quark model, which involves a color screening confinement potential, meson-exchange interactions and one-gluon exchange interactions.
Abstract: Inspired by the $T^+_{cc}$ signal discovered by the LHCb Collaboration, we systematically investigate the doubly heavy tetraquark states with the molecule configuration $[Q_1\bar{q}_2][Q_3\bar{q}_4]$ ($Q=c$ and $b$, $q=u$, $d$ and $s$) in a nonrelativistic quark model. The model involves a color screening confinement potential, meson-exchange interactions and one-gluon-exchange interactions. The $T^+_{cc}$ state with $IJ^P=01^+$ is a very loosely bound deuteron-like state with a binding energy around 0.34 MeV and a huge size of 4.32 fm. Both the meson exchange force and the coupled channel effect play a pivotal role. Without the meson exchange force, there does not exist the $T^+_{cc}$ molecular state. In strong contrast, the QCD valence bond forms clearly in the $T^+_{bb}$ system when we turn off the meson-exchange force, which is very similar to the hydrogen molecule in QED. Moreover, the $T^+_{bb}$ becomes a helium-like QCD-atom if we increase the bottom quark mass by a factor of three. Especially, the $T^+_{bb}$ states with $01^+$, $T^+_{bc}$ with $00^+$ and $01^+$ and the $V$-spin antisymmetric states $T^+_{bbs}$ with $\frac{1}{2}1^+$, $T^+_{bcs}$ with $\frac{1}{2}0^+$ and $\frac{1}{2}1^+$ can form a compact, hydrogen molecule-like or deuteron-like bound state with different binding dynamics. The high-spin states $T^+_{bc}$ with $02^+$ and $T^+_{bcs}$ with $\frac{1}{2}2^+$ can decay into $D$-wave $\bar{B}D$ and $\bar{B}_sD$ although they are below the thresholds $\bar{B}^*D^*$ and $\bar{B}^*_sD^*$, respectively. The isospin and $V$-spin symmetric states are unbound. We also calculate their magnetic moments and axial charges.
22 citations
TL;DR: In this paper , neutral pion and meson production cross sections were measured up to unprecedentedly high transverse momenta in p-Pb collisions at $\sqrt{s}$ = 8.16 TeV.
19 citations
TL;DR: In this article , a simple model that realizes resonant self-interaction (analogous to the ϕ-K-K system) and thermal freeze-out was proposed.
Abstract: We present new models utilizing QCD-like dark sectors to resolve small-scale structure problems. These models of resonant self-interacting dark matter in a dark sector with QCD are based on analogies to the meson spectra in standard model QCD. We introduce a simple model that realizes resonant self-interaction (analogous to the ϕ-K-K system) and thermal freeze-out, in which dark mesons are made of two light quarks. We also consider asymmetric dark matter composed of heavy and light dark quarks to realize a resonant self-interaction (analogous to the ϒ(4S)-B-B system) and discuss the experimental probes of both setups. Finally, we comment on the possible resonant self-interactions already built into SIMP and ELDER mechanisms while using lattice results to determine feasibility.
18 citations
TL;DR: In this article , analytical expressions of energy eigenvalues and eigen functions for a generalized Cornell potential are obtained by solving the non-relativistic Schrodinger equation using the Nikiforov-Uvarov functional analysis method along with Greene-Aldrich approximation.
Abstract: Here, analytical expressions of energy eigenvalues and eigen functions for a generalized Cornell potential are obtained by solving the non-relativistic Schrodinger equation using the Nikiforov–Uvarov functional analysis method along with Greene–Aldrich approximation. Energy spectra of three physically important potentials viz the pseudoharmonic, the Kratzer and the Coulomb perturbed potentials are derived from the general results. Further, within the framework of the Kratzer potential, energy eigenvalue spectra of diatomic molecules [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] are computed. The mass spectra of two heavy mesons are also investigated using the Coulomb perturbed potential, a form of the generalized Cornell potential. The obtained results are in good agreement with the results of others studies. The study is further extended to calculate and draw the partition function and other associated thermodynamic quantities for heavy mesons.
16 citations
TL;DR: In this article , the authors explore the spectrum and structure of the excited states of the nucleon from experiments with electromagnetic probes on proton targets, and discuss the impact of these results on the insight into the strong interaction dynamics that underlie the generation of the full spectrum of nucleon resonances of distinctively different structure.
Abstract: Advances in the exploration of the spectrum and structure of the excited states of the nucleon from experiments with electromagnetic probes on proton targets are presented. Impressive progress has been achieved in the studies of exclusive meson photoproduction in experiments with continuous electron beams and with detectors of almost $$4\pi $$ acceptance. The high-quality data, coupled with the advances in the amplitude analyses of exclusive photo- and hadroproduction data, allow for the observation of several long-awaited new baryon states known previously as the “missing” resonances. Studies of exclusive meson electroproduction in the resonance region with the CLAS detector at JLab have provided the dominant part of the available world information on exclusive meson electroproduction observables. These data offer unique information on the structure of most well-established excited nucleon states in the mass region up to 1.8 GeV in terms of the evolution of their electroexcitation amplitudes with momentum transfer of the virtual photon. We discuss the impact of these results on the insight into the strong interaction dynamics that underlie the generation of the full spectrum of nucleon resonances of distinctively different structure. These results shed light on the emergence of hadron mass, which is one of the most important and still open problems in the Standard Model. The extension of the nucleon resonance studies in the experiments of the 12-GeV era at JLab with the CLAS12 detector are outlined.
TL;DR: In this paper , it was shown that in relativistic heavy-ion collisions, where quarks and gluons are set free over an extended volume, two species of produced vector (spin-1) mesons emerge with a surprising pattern of global spin alignment.
Abstract: Notwithstanding decades of progress since Yukawa first developed a description of the force between nucleons in terms of meson exchange, a full understanding of the strong interaction remains a major challenge in modern science. One remaining difficulty arises from the non-perturbative nature of the strong force, which leads to the phenomenon of quark confinement at distances on the order of the size of the proton. Here we show that in relativistic heavy-ion collisions, where quarks and gluons are set free over an extended volume, two species of produced vector (spin-1) mesons, namely $\phi$ and $K^{*0}$, emerge with a surprising pattern of global spin alignment. In particular, the global spin alignment for $\phi$ is unexpectedly large, while that for $K^{*0}$ is consistent with zero. The observed spin-alignment pattern and magnitude for the $\phi$ cannot be explained by conventional mechanisms, while a model with a connection to strong force fields, i.e. an effective proxy description within the Standard Model and Quantum Chromodynamics, accommodates the current data. This connection, if fully established, will open a potential new avenue for studying the behaviour of strong force fields.
TL;DR: In this article , the authors presented improved estimates of the couplings, masses and mass ratios of the ZQ, XQ and TQQq¯q¯ q¯′ states (Q≡c,b;q,q′≡u,d,s) using (inverse) QCD Laplace sum rules (LSR), their ratios R and double ratios DRSR within stability criteria, where the NLO factorized PT QCD corrections are included.
TL;DR: In this article , the authors investigated the production and decay mechanisms for the hybrid nonet in the radiative decays into two pseudoscalar mesons and deduced that the SU(3) flavor octet and singlet mixing is non-negligible and apparently deviates from the flavor ideal mixing.
Abstract: The observation of the light hybrid candidate by the BESIII Collaboration offers great opportunities for advancing our knowledge on exotic hadrons in terms of flavor sector. We demonstrate that this observation provides a crucial clue for establishing the hybrid nonet. Based on the flux tube model picture, the production and decay mechanisms for the hybrid nonet in the radiative decays into two pseudoscalar mesons are investigated. In the sector, we deduce that the SU(3) flavor octet and singlet mixing is non-negligible and apparently deviates from the flavor ideal mixing. Because only signals for one isoscalar are observed in the channel, we investigate two schemes of the nonet structure in which can either be the higher or lower mass state that strongly couples to . Possible channels for detecting the multiplets are suggested. In particular, a combined analysis of the hybrid production in , where and denote the light vector mesons and hybrid states, respectively, may provide further evidence for this nonet structure and ultimately establish these mysterious exotic species in the experiment.
TL;DR: In this article , the light meson mass spectroscopy from the light-front quantum chromodynamics (QCD) Hamiltonian was obtained for their constituent quark-antiquark and quarkantiquarks-gluon Fock components, together with a three-dimensional confinement.
TL;DR: In this article , the absorption and production processes of a new state in a hadronic medium were investigated, considering the reactions $T{cc}+ \pi, T_{cc}^+ \rho \rightarrow D^{(*)} D^{ (*)} $ and the corresponding inverse reactions.
Abstract: We investigate the absorption and production processes of this new state in a hadronic medium, considering the reactions $T_{cc}^+ \pi, T_{cc}^+ \rho \rightarrow D^{(*)} D^{(*)} $ and the corresponding inverse reactions. We use effective field Lagrangians to account for the couplings between light and heavy mesons, and give special attention to the form factors in the vertices. We calculate here for the first time the $ T_{cc}^+ - D - D^*$ form factor derived from QCD sum rules. The results are also obtained by testing widely utilized empirical form factors. The absorption cross sections are found to be larger than the production ones. We compare our results with the only existing estimate of these quantities, presented in a work of J.~Hong, S.~Cho, T.~Song and S.~H.~Lee, in which the authors employed the quasi-free approximation. We find cross sections which are one order of magnitude smaller.
TL;DR: In this article , the ground-state charm mesons and baryons, D0, D+, Ds+, Λc+, and Ξc0, are used to evaluate the charm fragmentation fractions and production cross section per unit of rapidity at midrapidity (|y|<0.5), in pp collisions at s=5.02 TeV at the LHC.
Abstract: Recent pT-integrated cross-section measurements of the ground-state charm mesons and baryons, D0, D+, Ds+, Λc+, and Ξc0, are used to evaluate the charm fragmentation fractions and production cross section per unit of rapidity at midrapidity (|y|<0.5), in pp collisions at s=5.02 TeV at the LHC. The latter is dσcc¯/dy||y|<0.5=1165±44(stat)−101+134(syst) μb. These measurements were obtained for the first time in hadronic collisions at the LHC, including the charm baryon states, recently measured by ALICE at midrapidity. The charm fragmentation fractions differ significantly from the values measured in e+e− and ep collisions, providing evidence of the dependence of the parton-to-hadron fragmentation fractions on the collision system, indicating that the assumption of their universality is not supported by the measured cross sections. An increase of a factor of about 3.3 for the fragmentation fraction for the Λc+ with a significance of 5σ between the values obtained in pp collisions and those obtained in e+e− (ep) collisions is reported. The fragmentation fraction for the Ξc0 was obtained for the first time in any collision system. The measured fragmentation fractions were used to update the cc¯ cross sections per unit of rapidity at |y|<0.5 at s=2.76 and 7 TeV, which are about 40% higher than the previously published results. The data were compared with perturbative-QCD calculations and lie at the upper edge of the theoretical bands.Received 2 August 2021Accepted 16 December 2021DOI:https://doi.org/10.1103/PhysRevD.105.L011103Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.© 2022 CERN, for the ALICE CollaborationPhysics Subject Headings (PhySH)Research AreasHadron-hadron interactionsAccelerators & Beams
TL;DR: In this paper , the decay modes of the $D_s^+ \to \pi^+ K^+ k+ K+ K + K^- , \pi+ K_s+ K-s^0 K+K + K_S^0$ reactions producing two vector mesons and one pseudoscalar were identified and two acceptable scenarios were given for the ratio of the branching ratios of these two reactions in agreement with experiment.
Abstract: We have identified the decay modes of the $D_s^+ \to \pi^+ K^+ K^- , \pi^+ K_s^0 K_s^0$ reactions producing two vector mesons and one pseudoscalar. The posterior vector-vector interaction generates two resonances that we associate to the $f_0(1710)$ and the $a_0(1710)$ recently claimed. We find two acceptable scenarios that give results for the ratio of the branching ratios of these two reactions in agreement with experiment. With these two scenarios we make predictions for the branching ratios of the $D_s^+ \to \pi^0 K^+ K_s^0$ reaction, finding values within the range of $(2.0 \pm 0.7)\times 10^{-3}$. Comparison of these predictions with coming experimental results on that latter reaction will be very most useful to deepen our understanding on the nature of these two resonances.
TL;DR: Based on Weinberg's compositeness criterion, together with a theorem by Smorodinsky, it follows that the $X$ has to have a compact hidden charm structure, most likely a tetraquark, interacting with unbound $D\bar{D}^*$ pairs via short-distance color forces as mentioned in this paper .
Abstract: From a study of the lineshape of the $X(3872)$, the LHCb collaboration measures a sizeable negative effective range. This cannot be reconciled with a shallow $D\bar{D}^*$ bound state hypothesis. Based on Weinberg's compositeness criterion, together with a theorem by Smorodinsky, it follows that the $X$ has to have a compact hidden charm structure, most likely a tetraquark, interacting with unbound $D\bar{D}^*$ pairs via short-distance color forces. This conclusion is strengthened by the general pattern recently emerging for exotic mesons.
TL;DR: In this article , the authors calculated the exclusive production of light vector mesons in deep inelastic scattering in the limit of high photon virtuality, and the resulting expression is free of any divergences and suitable for numerical evaluations.
Abstract: Exclusive production of light vector mesons in deep inelastic scattering is calculated at next-to-leading order in the dipole picture in the limit of high photon virtuality. The resulting expression is free of any divergences and suitable for numerical evaluations. The higher-order corrections are found to be numerically important, but they can be mostly captured by the nonperturbative fit parameters describing the initial condition for the small-$x$ evolution of the dipole scattering amplitude. The vector meson production cross section is shown to depend only weakly on the meson distribution amplitude and the factorization scale. We also present phenomenological comparisons of our result to the existing exclusive $\phi$ and $\rho$ production data from HERA and find an excellent agreement at high virtualities.
TL;DR: In this article , the authors proposed a scheme of constructing the scalar meson family based on the reported scalar states and predicted the third radial excitation of the $a_0(980)$ trajectory.
Abstract: Stimulated by the newly observed $a_0(1817)$ by the BESIII Collaboration, we find a perfect Regge trajectory composed of the $a_0(980)$, $a_0(1450)$, and $a_0(1817)$, which leads us to categorize the $a_0(980)$, $a_0(1450)$, and $a_0(1817)$ into the isovector scalar meson family. This scenario is supported by their two-body Okubo-Zweig-Iizuka allowed strong decay behaviors. In this scheme, we also predict the third radial excitation of the $a_0(980)$, which is denoted as the $a_0(2115)$, accessible at future experiment as a direct test of this assignment. We find another Regge trajectory which contains three isoscalar scalar states $f_0(980)$, $X(1812)$, and $f_0(2100)$. We investigate their two-body Okubo-Zweig-Iizuka allowed strong decay patterns, which are roughly consistent with the experimental data. The $f_0(980)$, $X(1812)$, and $f_0(2100)$ can be well grouped into the isoscalar scalar meson family. We want to emphasize that these two Regge trajectories have a similar slope. In summary, the present work provides a scheme of constructing the scalar meson family based on these reported scalar states. The possibility of the $f_0(1710)$ as the candidate of the scalar glueball cannot be excluded by the observation of the $a_0(1817)$ since the $a_0(1817)$ is more suitable as the isovector partner of the $X(1812)$.
20 Jan 2022
TL;DR: In this paper , it was shown that the rate of the axion decays to multiple charged leptons as a probe of light dark particles (X) is 1.0 times the Standard Model expectation.
Abstract: We point out kaon decays to multiple charged leptons as a novel probe of light dark particles $X$. Previously neglected channels, such as ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}(XX\ensuremath{\rightarrow}2({e}^{+}{e}^{\ensuremath{-}}))$, ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}(XX\ensuremath{\rightarrow}2({e}^{+}{e}^{\ensuremath{-}}))$, and ${K}_{S}\ensuremath{\rightarrow}(XX\ensuremath{\rightarrow}2({e}^{+}{e}^{\ensuremath{-}}))$ may have very large rates, exceeding not only the Standard Model expectations but also possible backgrounds, such as Dalitz decays of neutral pions. We apply this idea to dark sector models where the production of dark Higgses or heavy neutral leptons leads to final states with several visible dark photons. We also investigate a recently proposed model of an MeV-scale QCD axion, where the rates for kaon decays to multiple axion states are large due to the nonlinear interactions of the axion with the light mesons. In addition, we point out new probes of this axion in pion decays, such as the single production of $a$ in ${\ensuremath{\pi}}^{+}\ensuremath{\rightarrow}\ensuremath{
u}(({e}^{+}{)}^{*}\ensuremath{\rightarrow}{e}^{+}a\ensuremath{\rightarrow}{e}^{+}{e}^{+}{e}^{\ensuremath{-}})$, double production in pion capture ${\ensuremath{\pi}}^{\ensuremath{-}}+(p\text{ }\text{or}\text{ }\mathrm{D})\ensuremath{\rightarrow}aa+(n\text{ }\mathrm{or}\text{ }nn)\ensuremath{\rightarrow}\phantom{\rule{0ex}{0ex}}2({e}^{+}{e}^{\ensuremath{-}})+(n\text{ }\mathrm{or}\text{ }nn)$, as well as ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}aaa\ensuremath{\rightarrow}3({e}^{+}{e}^{\ensuremath{-}})$. The latter decay is fixed at $\mathcal{B}({\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}aaa)=1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ for a 17 MeV axion.
TL;DR: In this article , the authors studied the scattering amplitudes of the LHCb coupled channels based on the $K$ matrix within the Chew-Mandelstam formalism.
Abstract: In this paper, we study the scattering amplitudes of ${D}^{0}{D}^{0}{\ensuremath{\pi}}^{+}\text{\ensuremath{-}}{D}^{*+}{D}^{0}$ coupled channels based on the $K$ matrix within the Chew-Mandelstam formalism. The ${D}^{0}{D}^{0}{\ensuremath{\pi}}^{+}$ invariant mass spectrum of LHCb is fitted, and the pole parameters of the ${T}_{cc}^{+}$ are extracted. The analysis of pole behavior suggests that the ${T}_{cc}^{+}$ may originate from a ${D}^{*+}{D}^{0}$ virtual state and is formed as a result of an interplay between an attractive interaction between ${D}^{0}$ and ${D}^{*+}$ and coupling to ${D}^{0}{D}^{0}{\ensuremath{\pi}}^{+}$ channel.
TL;DR: In this article , the mixing angles between scalar isoscalar resonances and a scalar glueball are determined from their decays into two pseudoscalars mesons, and the summation of all observed glueball fractions up to 2100\,MeV yields (78\er18)\%.
TL;DR: In this article , an analytically solvable 3D light-front Hamiltonian model for hadrons was presented, which extends light- front holography by including finite mass quarks and a longitudinal confinement term.
TL;DR: In this article , the production yields of D mesons were measured at midrapidity (| y | < 0.5) in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair.
Abstract: A bstract The production of prompt D 0 , D + , and D *+ mesons was measured at midrapidity (| y | < 0.5) in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decay channels and their production yields were measured in central (0–10%) and semicentral (30–50%) collisions. The measurement was performed up to a transverse momentum ( p T ) of 36 or 50 GeV/c depending on the D meson species and the centrality interval. For the first time in Pb–Pb collisions at the LHC, the yield of D 0 mesons was measured down to p T = 0, which allowed a model-independent determination of the p T -integrated yield per unit of rapidity (d N/ d y ). A maximum suppression by a factor 5 and 2.5 was observed with the nuclear modification factor ( R AA ) of prompt D mesons at p T = 6–8 GeV/c for the 0–10% and 30–50% centrality classes, respectively. The D-meson R AA is compared with that of charged pions, charged hadrons, and J /ψ mesons as well as with theoretical predictions. The analysis of the agreement between the measured R AA , elliptic ( v 2 ) and triangular ( v 3 ) flow, and the model predictions allowed us to constrain the charm spatial diffusion coefficient D s . Furthermore the comparison of R AA and v 2 with different implementations of the same models provides an important insight into the role of radiative energy loss as well as charm quark recombination in the hadronisation mechanisms.
TL;DR: In this paper , the authors studied the stiffening of dense matter in two color QCD (QC$_2$D) where hadrons are mesons and diquark baryons.
Abstract: We discuss stiffening of dense matter in two color QCD (QC$_2$D) where hadrons are mesons and diquark baryons. We study two models which describe a transition of matter from the Bose-Einstein-Condensation regime at low density to the Bardeen-Cooper-Schrieffer regime at high density. The first model is based on coherent states of diquarks, and the second is the Nambu-Jona-Lasinio model with diquark pairing terms. We particularly focus on how quark states are occupied as baryon density increases. We find that, due to the occupied quark levels, the ideal gas picture of diquarks breaks down at density significantly less than the density where baryon cores overlap. The saturation of quark states at low momenta stiffens equations of state. We also study the effects of interactions which depend on the quark occupation probability. We argue that equations of state become very stiff when the bulk part of the quark Fermi sea has the effective repulsion but the Fermi surface enjoys the attractive correlations. This disparity for different momentum domains is possible due to the strong channel dependence in gluon exchanges with momentum transfer of $0.2-1$ GeV. These concepts can be transferred from QC$_2$D to QCD in any numbers of colors.
TL;DR: In this article , the nucleon's D-term in a holographic QCD model was calculated in five dimensions, and it was shown that the form factor is saturated by the exchanges of infinitely many 0++ and 2++ glueballs dual to transverse-traceless metric fluctuations.
Abstract:
The D-term is one of the conserved charges of hadrons defined as the forward limit of the gravitational form factor D(t). We calculate the nucleon’s D-term in a holographic QCD model in which the nucleon is described as a soliton in five dimensions. We show that the form factor D(t) is saturated by the exchanges of infinitely many 0++ and 2++ glueballs dual to transverse-traceless metric fluctuations on the Wick rotated AdS7 black hole geometry. We refer to this phenomenon as ‘glueball dominance’, in perfect analogy to the vector meson dominance of the electromagnetic form factors. However, the value at vanishing momentum transfer D(t = 0) can be interpreted as due to the exchange of pairs of pions and infinitely many vector and axial-vector mesons without any reference to glueballs. We find that the D-term is slightly negative as a result of a cancellation between the isovector and isoscalar meson contributions.