arXiv subjects
Publications and source records attributed to Kenji Morita.
We report recent progress on theoretical investigations of quarkonia at finite temperature. We discuss medium modification of charmonia and bottomonia from a viewpoint of local operators and point out that while charmonia are sensitive to the deconfinement transition bottomonia will be modified at much higher temperatures.
The phase structure of Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model is explored at imaginary chemical potential, with particular emphasis on the deconfinement transition. We point out that the statistical confinement nature of the model naturally leads to characteristic dependence of the chiral condensate $<\bar{q}q>$ on $θ=μ_I/T$. We introduce a dual parameter for the deconfinement transition by making use of this dependence. By changing a four-fermion coupling constant, we tune the location of the critical endpoint of the deconfinement transition.
We explore the thermodynamics and phase structure of the Polyakov loop-extended two flavor chiral quark--meson (PQM) model beyond the mean-field approximation at imaginary chemical potential. Our approach is based on the functional renormalization group (FRG) method. At finite temperature and imaginary chemical potential, we solve the renormalization group flow equation for a scale-dependent thermodynamic potential in the presence of the gluonic background field. We determine behavior of order parameters of the PQM model in the FRG approach and compute the phase diagram. We compare our FRG results with that obtained in the mean-field approximation at imaginary chemical potential.
The phase structure of the two-flavor Polyakov-loop extended Nambu-Jona-Lashinio model is explored at finite temperature and imaginary chemical potential with a particular emphasis on the confinement-deconfinement transition. We point out that the confined phase is characterized by a $\cos3μ_I/T$ dependence of the chiral condensate on the imaginary chemical potential while in the deconfined phase this dependence is given by $\cosμ_I/T$ and accompanied by a cusp structure induced by the Z(3) transition. We demonstrate that the phase structure of the model strongly depends on the choice of the Polyakov loop potential $\mathcal{U}$. Furthermore, we find that by changing the four fermion coupling constant $G_s$, the location of the critical endpoint of the deconfinement transition can be moved into the real chemical potential region. We propose a new parameter characterizing the confinement-deconfinement transition.
Charmonia spectral functions at finite temperature are studied using QCD sum rules in combination with the maximum entropy method. This approach enables us to directly obtain the spectral function from the sum rules, without having to introduce any specific assumption about its functional form. As a result, it is found that while J/psi and eta_c manifest themselves as significant peaks in the spectral function below the deconfinement temperature T_c, they quickly dissolve into the continuum and almost completely disappear at temperatures between 1.0 T_c and 1.1 T_c.
We investigate the properties of heavy quarkonia at finite temperature in detail using QCD sum rules. Extending previous analyses, we take into account a temperature dependent effective continuum threshold and derive constraints on the mass, the width, and the varying effective continuum threshold. We find that at least one of these quantities of a charmonium changes abruptly in the vicinity of the phase transition. We also calculate the ratio of the imaginary time correlator to its reconstructed one, $G/G_{\text{rec}}$, by constructing a model spectral function and compare it to the corresponding lattice QCD results. We demonstrate that the almost constant unity of $G/G_{\text{rec}}$ can be obtained from the destructive interplay of the changes in each part of the spectral modification which are extracted from QCD sum rules.
We study the $σ$ meson in QCD sum rules using a two quark interpolating field with derivatives. In the constituent quark model, the $σ$ meson is composed of a quark and an antiquark in the relative p-wave state and is thus expected to have a larger overlap with an interpolating field that measures the derivative of the relative quark wave-function. While the sum rule with a current without derivatives gives a pole mass of around 1 GeV, the present sum rule with a derivative current gives a mass of around 550 MeV and a width of 400 MeV, that could be identified with the $σ$ meson.
We investigate the changes of the masses and widths of $χ_{c0}$ and $χ_{c1}$ in hot gluonic matter near $T_c$ and in nuclear medium using QCD sum rules. As in the previous works for the $J/ψ$ and $η_c$, in-medium effects are incorporated through the changes of gluon condensates. Twist-2 terms for the $^3 P_0 (χ_{c0})$ and $^3 P_1 (χ_{c1})$ are also included for the first time. The results show that larger mass shifts and width broadenings take place as compared to the $S$-wave states. As the critical change take place near $T_c$, related measurements can reveal critical phenomenon in QCD.
Starting from the temperature dependence of the energy density and pressure from lattice QCD calculation, we extract the temperature dependence of the electric and magnetic condensate near $T_c$. While the magnetic condensate hardly changes across $T_c$, we find that the electric condensate increases abruptly above $T_c$. This induces a small but an equally abrupt decrease in the mass of $J/ψ$, can be calculated through the second-order Stark effect. Combining the present result with the previously determined QCD sum rule constraint, we extract the thermal width of $J/ψ$ above $T_c$, which also increases fast. These changes can be identified as the critical behavior of $J/ψ$ across $T_c$ associated with the phase transition. We find that the mass shift and with broadening of $J/ψ$ at 1.05 $T_c$ will be around -100 MeV and 100 MeV respectively.
We use QCD sum rules to study the recently observed resonance-like structures in the $π^+χ_{c1}$ mass distribution, $Z_1^+(4050)$ and $Z_2^+(4250)$, considered as $D^{*+}\bar{D}^{*0}$ and $D_1^+\bar{D}^0+ D^+\bar{D}_1^0$ molecules with the quantum number $J^P=0^+$ and $J^P=1^-$ respectively. We consider the contributions of condensates up to dimension eight and work at leading order in $α_s$. We obtain $m_{D^*D^*}=(4.15\pm0.12) \GeV$, around 100 MeV above the $D^*D^*$ threshold, and $m_{D_1D}=(4.19\pm 0.22) \GeV$, around 100 MeV below the $D_1D$ threshold. We conclude that the $D^{*+}\bar{D}^{*0}$ state is probably a virtual state that is not related with the $Z_1^+(4050)$ resonance-like structure. In the case of the $D_1D$ molecular state, considering the errors, its mass is consistent with both $Z_1^+(4050)$ and $Z_2^+(4250)$ resonance-like structures. Therefore, we conclude that no definite conclusion can be drawn for this state from the present analysis.
We investigate the widths of the recently observed charmonium like resonances X(3872), Z(4430) and Z_2(4250) using QCD sum rules. Extending previous analyses regarding these states as diquark-antiquark states or molecules of D mesons, we introduce the Breit-Wigner function in the pole term. We find that introducing the width increases the mass at small Borel window region. Using the OPE up to dimension eight, we find that the sum rules based on interpolating current with molecular components give a stable Borel curve from which both the masses and widths of these resonances can be well obtained. Thus the QCD sum rule approach strongly favors the molecular description of these states.
We study behavior of J/psi in hot gluonic matter using QCD sum rules. Taking into account temperature dependences of the gluon condensates extracted from lattice thermodynamics for the pure SU(3) system, we find that the mass and width of J/psi exhibit rapid change across the critical temperature.
We investigate medium-induced change of mass and width of J/psi and eta_c across the phase transition in hot gluonic matter using QCD sum rules. In the QCD sum rule approach, the medium effect on heavy quarkonia is induced by the change of both scalar and twist-2 gluon condensates, whose temperature dependences are extracted from the lattice calculations of energy density and pressure. Although the stability of the operator product expansion side seems to break down at T > 1.06Tc for the vector channel and T>1.04Tc for the pseudoscalar channel, we find a sudden change of the spectral property across the critical temperature Tc, which originates from an equally rapid change of the scalar gluon condensate characterized by e-3p. By parameterizing the ground state of the spectral density by the Breit-Wigner form, we find that for both J/psi and eta_c, the masses suddenly decrease maximally by a few hundreds of MeV and the widths broaden to ~100 MeV slightly above Tc. Implications for recent and future heavy ion experiments are discussed. We also carry out a similar analysis for charmonia in nuclear matter, which could serve as a testing ground for observing the precursor phenomena of the QCD phase transition. We finally discuss the possibility of observing the mass shift at nuclear matter at the FAIR project at GSI.
We discuss how the spectral changes of quarkonia at T_c can reflect the ``critical'' behaviour of QCD phase transition. Starting from the temperature dependencies of the energy density and pressure from lattice QCD calculation, we extract the temperature dependencies of the scalar and spin 2 gluon condensates near T_c. We also parameterize these changes into the electric and magnetic condensate near T_c. While the magnetic condensate hardly changes across T_c, we find that the electric condensate increases abruptly above T_c. Similar abrupt change is also seen in the scalar condensate. Using the QCD second-order Stark effect and QCD sum rules, we show that these sudden changes induce equally abrupt changes in the mass and width of J/psi, both of which are larger than 100 MeV at slightly above T_c.
We investigate possible mass shift and width broadening of J/psi in hot gluonic matter using QCD sum rule. Input values of gluon condensates at finite temperature are extracted from lattice QCD data for the energy density and pressure. Although stability of the moment ratio is achieved only up to T/Tc ~ 1.05, the gluon condensates cause a decrease of the moment ratio, which results in change of spectral properties. Using the Breit-Wigner form for the phenomenological side, we find that mass shift of J/psi just above Tc can reach maximally 200 MeV and width can broaden to dozens of MeV.
After five years of running at RHIC, and on the eve of the LHC heavy-ion program, we highlight the status of femtoscopic measurements. We emphasize the role interferometry plays in addressing fundamental questions about the state of matter created in such collisions, and present an enumerated list of measurements, analyses and calculations that are needed to advance the field in the coming years.
We investigate degree of coherence of pion sources produced in relativistic heavy ion collisions using multi-particle interferometry. In order to obtain ``true'' chaoticity, lambda^true from two-pion correlation functions measured in experiments, we make a correction for long-lived resonance decay contributions. Using this lambda^true and the weight factor which are obtained from parameter fitted to two- and three-pion correlation function, we calculate a chaotic fraction epsilon and the number of coherent sources alpha for different colliding energies. The result gives constraints on the source and shows an increase of the minimum number of alpha with multiplicity, although multiplicity independent chaoticity is not excluded.
We calculate two-pion correlation functions at finite rapidities based on a hydrodynamical model which does not assume explicit boost invariance along the collision axis. Extracting the HBT radii through $χ^2$ fits in both Cartesian and Yano-Koonin-Podgoretski\uı parametrizations, we compare them with the experimental results obtained by the PHOBOS. Based on the results, we discuss longitudinal expansion dynamics.