arXiv subjects

Ayut Limphirat

Publications and source records attributed to Ayut Limphirat.

At least 37 records · Page 2Linked to original sources

arXiv2023

Group Theory Analysis of $P_c$ Resonances in Molecular Picture

Hidden-charm pentaquarks are analysed in Group Theory in the baryon-meson molecule picture within the framework of the constituent quark model. The investigation of strong decays of pentaquark resonances reveals that pentaquark states of all quark configurations can decay through the $N J/ψ$ channel while only five pentaquark states may decay in open-charm modes. The partial decay widths in the $pη_c$ channel are in the same order as in the $p J/ψ$ channel for $J^P=1/2^-$ baryon-meson pentaquark states, but the $pη_c$ channel is forbidden for $J^P=3/2^-$ states. The $p η_c$, $Σ_c\bar{D}$ and $Λ_c^+\bar{D}$ channels open for $J^P=1/2^-$ $P_c(4440)$ and $P_c(4457)$ while the $Σ_c^*\bar{D}$ channel opens for $J^P=3/2^-$ $P_c(4440)$ and $P_c(4457)$. For $P_c(4312)$, due to the mass threshold of $Σ_c\bar{D}$ and $Σ_c^*\bar{D}$ higher than 4312 MeV, the $p η_c$ and $Λ_c^+\bar{D}$ channels are open for $J^P=1/2^-$ but no open-charm channel open for $J^P=3/2^-$. We strongly suggest that the spin of the $P_c$ resonances may be determined in experiments by investigating the $p η_c$ and open-charm channels.

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arXiv2023

Harmonic flow correlations in Au+Au reactions at 1.23 AGeV: A new testing ground for the Equation-of-State and expansion geometry

Correlations between the harmonic flow coefficients $v_1$, $v_2$, $v_3$ and $v_4$ of nucleons in semi-peripheral Au+Au collisions at a beam energy of 1.23~AGeV are investigated within the hadronic transport approach Ultra-relativistic Quantum Molecular Dynamics (UrQMD). In contrast to ultra-relativistic collision energies (where the flow coefficients are evaluated with respect to the respective event plane), we predict strong correlations between the flow harmonics with respect to the reaction plane. Based on an event-by-event selection of the midrapidity final state elliptic flow of protons we show that as a function of rapidity, I) the sign of the triangular flow changes, II) that the shape of $v_4$ changes from convex to concave, and III) that $v_3\propto v_1v_2$ and $v_4\propto v_2^2$ for all different event classes, indicating strong correlations between all investigated harmonic flow coefficients.

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arXiv2022

A possible interpretation of $Λ$ baryon spectrum with pentaquark components

The $Λ$ baryon spectrum is studied within the SU(3) flavor symmetry in a constituent quark model. We found that it is rather difficult to accommodate some negative-parity $Λ$ resonances as single $q^2s$ ($q = u,\,d$ quarks) states in the conventional three-quark picture. The ground $q^3s\bar q$ pentaquark mass spectrum is evaluated and a possible interpretation is proposed in the work: the observed $Λ(1405)1/2^{-}$, $Λ(1670)1/2^{-}$ and $Λ(1800)1/2^{-}$ are three-state mixtures of two $p$-wave $q^2s$ states and one ground $q^3s\bar q$ pentaquark state, so are the $Λ(1520)3/2^{-}$, $Λ(1690)3/2^{-}$ and $Λ(2050)3/2^{-}$ resonances.

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arXiv2022

Enhanced pion-to-proton ratio at the onset of the QCD phase transition

The pion-to-proton ratio is identified as a potential signal for a non-equilibrium first-order chiral phase transition in heavy-ion collisions, as the pion multiplicity is directly related to entropy production. To showcase this effect, a non-equilibrium Bjorken expansion starting from realistic initial conditions along a Taub adiabat is used to simulate the entropy production. Different dynamical criteria to determine the final entropy-per-baryon number are investigated and matched to a hadron resonance gas model along the chemical freeze out curve to obtain the final pion and proton numbers. We detect a strong enhancement of their multiplicity ratio at the energies where the system experiences a strong phase transition as compared to a smooth crossover which shows almost no enhancement.

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arXiv2022

Correcting the $B_A$ coalescence factor at GSI-HADES and RHIC-BES energies

We investigate the coalescence factors $B_2$ and $B_3$ at low collision energies ($\sqrt{s_\mathrm{NN}}<6$ GeV) with special focus on the HADES and RHIC-BES experiments. It is shown that, in order to properly interpret the coalescence factors $B_A$, two important corrections are necessary: I) $B_2$ has to be calculated using the proton $\times$ neutron yields in the denominator, instead of the square of the proton yield, and II) the primordial proton (neutron) densities have to be used for the normalization and not the final state (free) protons (neutrons). Both effects lead to a drastic reduction of $B_2$ and $B_3$ at low energies. This reduction decreases the discrepancy between the volumes extracted from HBT measurements and the volumes extracted from the coalescence factor ($V\propto 1/B_2$). While at HADES and low RHIC-BES energies these corrections are substantial, they become irrelevant above $\sqrt{s_\mathrm{NN}}>6$ GeV. The proposed correction method is model independent and is only based on the measurement of protons, clusters and charged pions.

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arXiv2022

Net-proton number cumulant ratios as function of beam energy from an expanding nonequilibrium chiral fluid

The beam energy scan program at RHIC provides data on net-proton number fluctuations with the goal to detect the QCD critical end point and first-order phase transition. Interpreting these experimental signals requires a vital understanding of the interplay of critical phenomena and the nonequilibrium dynamics of the rapidly expanding fireball. We study these aspects with a fluid dynamic expansion coupled to the explicit propagation of the chiral order parameter sigma via a Langevin equation. Assuming a sigma-proton coupling through an effective proton mass, we relate cumulants of the order parameter and the net-proton number at freeze-out and obtain observable cumulant ratios as a function of beam energy. We emphasize the role of the nonequilibrium first-order phase transition where a mixed phase with gradual freeze-out can significantly alter the cumulants. We find that the presence of a critical end point is clearly visible in the cumulant ratios for a relatively wide range of center-of-mass energies.

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arXiv2022

Cumulants of the chiral order parameter at lower RHIC energies

We study cumulants of the chiral order parameter as function of beam energy as a possible signal for the presence of a critical end point and first-order phase transition in the QCD phase diagram. We model the expansion of a heavy-ion collision by a fluid dynamic expansion coupled to the explicit propagation of the chiral order parameter sigma via a Langevin equation. We evolve the medium until a parametrized freeze-out condition is met where we calculate event-by-event fluctuations and cumulants of sigma which are expected to follow the trend of net-proton number cumulants. We emphasize the role of a nonequilibrium first-order phase transition: The presence of an unstable phase causes the well-known bending of the trajectories in the space of temperature and baryochemical potential. For these cases at lower beam energies, the system crosses the freeze-out line more than once, allowing us to calculate a range of cumulants for each initial condition which are overall enhanced for the second hit of the freeze-out line. We thus find not only the critical end point but also the phase transition of the underlying model clearly reflected in the cumulants. The impact of volume fluctuations is demonstrated to play a measurable role for fluid dynamical evolutions that last significantly long.

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arXiv2021

Study of charmonium-like and fully-charm tetraquark spectroscopy

The masses of tetraquark states of all $qc\bar q \bar c$ and $cc\bar c \bar c$ quark configurations are evaluated in a constituent quark model, where the Cornell-like potential and one-gluon exchange spin-spin coupling are employed. All model parameters are predetermined by comparing the theoretical and experimental masses of light, charmed and bottom mesons. The theoretical predictions of the charmoniumlike tetraquarks are compared with the observed $XYZ$ states, and one tentative assignment is suggested. The work suggests that the $X(6900)$ observed by LHCb is likely to be the first radial excited fully-charm tetraquark state with $J^{PC} = 1^{+-}$ in the $\bar 3_c \otimes 3_c$ configuration, and the ground and second radial excited states of fully-charm tetraquark are around $6494$ and $7253$ MeV respectively.

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arXiv2021

Deuteron production from phase-space coalescence in the UrQMD approach

UrQMD phase-space coalescence calculations for the production of deuterons are compared with available data for various reactions from the GSI/FAIR energy regime up to LHC. It is found that the production process of deuterons, as reflected in their rapidity and transverse momentum distributions in p+p, p+A and A+A collisions at a beam energies starting from the GSI energy regime around 1 AGeV and up to the LHC, are in good agreement with experimental data. We further explore the energy and centrality dependence of the d/p ratios. Finally, we discuss anti-deuteron production for selected systems. Overall, a good description of the experimental data is observed. The results are also compatible with thermal model estimates. Most importantly this good description is based only on a single set of coalescence parameters that is independent of energy system size and can also be applied for anti-deuterons.

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arXiv2021

$P_c$ Resonances in the Compact Pentaquark Picture

$P_c$ resonances are studied in the approach of quark model and group theory. It is found that there are totally 17 possible pentaquark states with the quark contents $q^3Q \bar Q$ ($q$ are $u$ and $d$ quarks; $Q$ is $c$ quark) in the compact pentaquark picture, where the hidden heavy pentaquark states may take the color singlet-singlet ($[111]_{qqq}\otimes [111]_{c \bar c}$) and color octet-octet ($[21]_{qqq}\otimes [21]_{c \bar c}$) configurations. The partial decay widths of hidden heavy pentaquark states are calculated for all possible decay channels. The results show that the $pJ/ψ$ is the dominant decay channel for both the spin $3/2$ and $1/2$ pentaquark states, and indicate that the $P_c(4440)$ may not be a compact pentaquark state while $P_c(4312)$ and $P_c(4457)$ could be the spin-$\frac{1}{2}$ and spin-$\frac{3}{2}$ pentaquark states, respectively.

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arXiv2021

Modeling (anti)deuteron formation at RHIC with a geometric coalescence model

We study (anti)deuteron formation rates in heavy-ion collisions in the framework of a wave-function based coalescence model. The main feature of our model is that nucleons are emitted from the whole spherically symmetric fireball volume, while antinucleons are emitted only from a spherical shell close to the surface. In this way, the model accounts for nucleon-antinucleon annihilations in the center of the reaction at lower beam energies. Comparison with experimental data on the coalescence parameter in the range $\sqrt{s_{NN}}= 4.7-200$ GeV allows us to extract radii of the respective source geometries. Our results are qualitatively supported by data from the UrQMD transport model which shows a comparable trend in the geometric radii as a function of beam energy. In line with our expectations, we find that at lower energies, the central region of the fireball experiences stronger annihilation than at higher energies.

hep-ph↗

arXiv2020

Deuteron and Antideuteron Coalescence in Heavy-Ion Collisions: Energy Dependence of the Formation Geometry

We investigate the collision energy dependence of deuteron and antideuteron emission in the RHIC-BES low- to mid-energy range $\sqrt{s_{NN}} = 4.6-200$ GeV where the formation rate of antinuclei compared to nuclei is strongly suppressed. In the coalescence picture, this can be understood as bulk emission for nuclei in contrast to surface emission for antinuclei. By comparison with experimental data on the coalescence parameter $B_2$, we are able to extract the respective source geometries. This interpretation is further supported by results from the UrQMD transport model, and establishes the following picture: At low energies, nucleons freeze out over the total fireball volume, while antinucleons are annihilated inside the nucleon-rich fireball and can only freeze out on its surface. Towards higher energies, this annihilation effect becomes irrelevant (due to the decreasing baryochemical potential) and the system's freeze-out is driven by the mesons. Thus, the nucleon and antinucleon freeze-out distributions become similar with increasing energy.

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arXiv2020

Pentaquark components in low-lying baryon resonances

We study pentaquark states of both light $q^4\bar q$ and hidden heavy $q^3 Q\bar Q$ (q = u,d,s quark in SU(3) flavor symmetry; Q = c, b quark) systems with a general group theory approach in the constituent quark model, and the spectrum of light baryon resonances in the ansatz that the $l=1$ baryon states may consist of the $q^3$ as well as $q^4\bar q$ pentaquark component. The model is fitted to ground state baryons and light baryon resonances which are believed to be normal three-quark states. The work reveals that the $N(1535)1/2^{-}$ and $N(1520)3/2^-$ may consist of a large $q^4\bar q$ component while the $N(1895)1/2^{-}$ and $N(1875)3/2^-$ are respectively their partners, and the $N^+(1685)$ might be a $q^4\bar q$ state. By the way, a new set of color-spin-flavor-spatial wave function for $q^3 Q\bar Q$ systems in the compact pentaquark picture are constructed systematically for studying hidden charm pentaquark states.

hep-ph↗

arXiv2020

Influence of centrality definition and detector efficiency on the net-proton kurtosis

We study the influence of the centrality definition and detector efficiency on the net-proton kurtosis for minimum bias Au+Au collisions at a beam energy of $\sqrt{s_{\mathrm{NN}}}= 7.7$ GeV by using the UrQMD model. We find that different ways of defining the centrality lead to different cumulant ratios. Moreover, we demonstrate that the kurtosis is suppressed for central collisions when a wider transverse momentum acceptance is used. Finally, the influence of a detector efficiency on the measured cumulant ratios is estimated.

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arXiv2019

Forward and backward comparative study of jet properties in pp collisions at \sqrt{s}=7 TeV

We propose a forward method, based on the PYTHIA6.4, to study theoretically the jet properties in the ultra-relativistic pp collisions. In the forward method, the partonic initial states are first generated with PYTHIA6.4 and then hadronized in the Lund srting fragmentation regime, and finally hadronic jets are constructed from the created hadrons. Jet properties calculated in the forward method for pp collisions at \sqrt{s}=7 TeV are comparable with the corresponding ones calculated with usual anti-k_t algorithm (backward method) in the PYTHIA6.4. The comparison between the results in the backward and forward methods may bring benefit to the understanding of the partonic origin of jets in the backward method.

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arXiv2019

Complete basis for the pentaquark wave function in a group theory approach

Permutation groups are applied to analyze the symmetries of pentaquark states. All possible quark configurations of the color, flavor, spin and spatial degrees of freedom are worked out in the language of permutation groups, and the corresponding wave functions are constructed systematically in the form of a Yamanouchi basis. The pentaquark spatial wave functions of various symmetries, which are derived in the harmonic-oscillator interaction, are applied as complete bases to evaluate the low-lying light $q^4\overline q$ pentaquark mass of all configurations, where the Cornell-like potential is employed.

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arXiv2019

Contributions of box diagrams and $Δ(1940)$ resonance to $K^0Σ^+$ photoproduction

We study first the box-diagram contribution to the $γp\,\rightarrow \,K^0Σ^+$ process to understand the anomaly of the kaon photoproduction cross section from CBELSA/TAPS experiment at Electron Stretcher Accelerator (ELSA), where the imaginary part of the scattering amplitude from the box-diagrams is calculated by using Cutkosky's rules in the on-shell approximation while the real part of the amplitude is derived by dispersion relation calculations. Together with the results of the K-MAID model, the contribution of the box-diagrams fails to provide the sudden drop of the differential cross-section between the $K^*\,Λ$ and $K^*\,Σ$ thresholds. In addition, we include the $Δ(1940)$ resonance in the process to complete the description of the differential cross-section. Combining the contributions from the K-MAID model, the box-diagrams and the $Δ(1940)$ resonance, we have obtained the theoretical differential cross-section the $γp\,\rightarrow \,K^0Σ^+$ process, which is compatible with the CBELSA/TAPS experimental data.

hep-ph↗

arXiv2019

Delta mass shift as a thermometer of kinetic decoupling in Au+Au reactions at 1.23 AGeV

The HADES experiment at GSI will soon provide data on the production and properties of $Δ$(1232) baryons from Au+Au reactions at 1.23 AGeV. Using the UrQMD model, we predict the yield and spectra of $Δ$(1232) resonances. In addition we show that one expects to observe a mass shift of the $Δ$(1232) resonance on the order of 50 MeV in the reconstructable $Δ$(1232) mass distribution. This mass shift can be understood in terms of late stage $Δ$(1232) formation with limited kinetic energy. We show how the mass shift can be used to constrain the kinetic decoupling temperature of the system.

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