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論文

Analysis of spectral modification in nuclei using the PHSD transport approach

市川 真也; Gubler, P.; 成木 恵; 四日市 悟*

Journal of Subatomic Particles and Cosmology (Internet), 3, p.100018_1 - 100018_5, 2025/06

It is important to measure the hadron spectrum at finite density to explore the origin of hadron masses. At the KEK-PS E325 experiment, $$phi$$ mesons inside and outside nuclei were measured by using 12GeV pA reactions and significant spectral modification was observed. In order to accurately estimate the density that the $$phi$$ mesons felt during the reaction, a PHSD transport calculation of the respective reaction is currently ongoing. In this paper, PHSD and the current status of its implementation are reported.

論文

Production and in-medium modification of $$phi$$ mesons in proton-nucleus reactions from a transport approach

Gubler, P.; 市川 真也; Song, T.*; Bratkovskaya, E.*

Physical Review C, 111(3), p.034908_1 - 034908_12, 2025/03

 被引用回数:0

Production and in-medium modification of hidden strange $$phi$$ mesons are studied in proton-nucleus reactions: p+C, p+Cu, and p+Pb at 12 GeV/c, partially measured by the KEK E325 Collaboration via the dilepton decay mode. This work is based on the off-shell microscopic parton-hadron-string dynamics transport approach, and especially makes it possible to simulate in-medium off-shell dynamics of the $$phi$$ meson in the reactions studied. Different in-medium scenarios for the modification of the $$phi$$ meson spectral function in nuclear matter are investigated: (i) dropping pole mass, (ii) collisional broadening, and (iii) simultaneous dropping pole mass and collisional broadening. Even though the $$phi$$ meson production in p+A reactions occurs only at densities around or below normal nuclear matter density $$rho_0$$, we find visible modifications of the generated dilepton spectra for the in-medium scenarios compared to the vacuum distribution.

論文

A Study of the $$phi N$$ correlation function

Abreu, L. M.*; Gubler, P.; Khemchandani, K. P.*; Mart$'i$nez Torres, A.*; 保坂 淳

Physics Letters B, 860, p.139175_1 - 139175_7, 2025/01

 被引用回数:1 パーセンタイル:0.00(Astronomy & Astrophysics)

The femtoscopic $$phi N$$ correlation function is studied within a hadronic effective Lagrangian approach with coupled channels, based on hidden local symmetry. The results are compared with the data recently reported by the ALICE collaboration. We find that the correlation function has very different features for the $$phi N$$ system in the spin 1/2 and 3/2 configurations, with the spin-averaged combination matching well with the experimental data. A strong attraction, leading to the formation of a $$phi N$$ bound state or a very prominent cusp is found in the spin 3/2 case. The correlation function for spin 1/2, on the other hand, is strongly impacted by the negative parity $$N$$*(1895) nucleon resonance.

論文

Investigation on the $$Omega(2012)$$ from QCD sum rules

Su, N.*; Chen, H.-X.*; Gubler, P.; 保坂 淳

Nuclear and Particle Physics Proceedings, 347, p.2 - 5, 2024/12

We investigate the recently observed $$Omega(2012)$$ baryon using QCD sum rules. By constructing P-wave $$Omega$$ baryon currents and performing spin projection and parity projection, we obtain the masses of the $$J^P = 1/2^{-}$$ and $$3/2^{-}$$ states as $$M_{1/2^-} = 2.07^{+0.07}_{-0.07}$$ GeV and $$M_{3/2^-} = 2.05^{+0.09}_{-0.10}$$ GeV, in good agreement with experiment. This suggests that $$Omega(2012)$$ is likely to be a negative parity P-wave excited state, though its spin remains undetermined and requires further study of its decay properties.

論文

Studies on the $$phi$$ meson production in nuclear matter and the $$phi N$$ correlation function

Gubler, P.

Journal of Subatomic Particles and Cosmology (Internet), 1-2, p.100007_1 - 100007_4, 2024/11

We first review results of transport simulations of 12 GeV pA reactions to study the $$phi$$ meson in nuclear matter, especially focusing on the production mechanism of the $$phi$$ meson in such reactions and on the generated dilepton spectrum. Next, we discuss a recent study calculating the $$phi N$$ correlation function, making use of a hadronic effective Lagrangian approach with coupled channels and comparing the result with the recent measurement of the same quantity by the ALICE collaboration.

論文

Separating the transverse and longitudinal modes of $$phi$$, $$rho$$, $$K^{ast}$$ and $$K_1$$ mesons through their angular-dependent two-body decay modes

Park, I. W.*; 佐甲 博之; 青木 和也*; Gubler, P.; Lee, S. H.*

Journal of Subatomic Particles and Cosmology (Internet), 1-2, p.100014_1 - 100014_11, 2024/11

The mass shift a spin-1 particle moving in the nuclear medium will depend on its polarization direction. To study polarization-independent mass shifts in the medium, we explore methods to isolate each polarization direction of spin-1 mesons through the angular-dependent two-body decay modes. Specifically, we study $$phi to K^+ K^-$$, $$rho to pi pi$$, $$K^{ast} to K pi$$, $$phi to e^+ e^-$$ and $$K_1 to rho K$$ ($$K^{ast} pi$$) decays. Concerning $$K^{ast}$$ and $$K_1$$ mesons, since both particles have vacuum widths smaller than 100 MeV, they are ideal candidates for experimentally measuring chiral partners. The simultaneous observation of mass shifts of these chiral partners would provide valuable insights into the contribution of chiral symmetry breaking to the generation of hadron masses.

論文

Investigation on the $$Omega(2012)$$ from QCD sum rules

Su, N.*; Chen, H.-X.*; Gubler, P.; 保坂 淳

Physical Review D, 110(3), p.034007_1 - 034007_9, 2024/08

 被引用回数:0 パーセンタイル:0.00(Astronomy & Astrophysics)

We study the recently observed $$Omega(2012)$$ baryon in quantum chromodynamics (QCD) sum rules. We construct the P-wave $$Omega$$ baryon currents with a covariant derivative, and perform spin projection to obtain the currents with total spin 1/2 and 3/2. We then apply the parity-projected QCD sum rules to separate the contributions of the positive and negative parity states. We extract the masses of $$J^P = 1/2^{-}$$ and $$3/2^{-}$$ states to be $$M_{1/2^-} = 2.07^{+0.07}_{-0.07}$$ GeV and $$M_{3/2^-} = 2.05^{+0.09}_{-0.10}$$ GeV. Both results are in good agreement with the experimental result. Therefore, it is likely that the $$Omega(2012)$$ is a negative parity state, which is interpreted as a P-wave excited state in the quark model. However, its spin is not determined in the present analysis, which can be done by detailed study on its decay properties.

論文

Identifying the transverse and longitudinal modes of the $$K^{ast}$$ and $$K_1$$ mesons through their angular-dependent decay modes

Park, I. W.*; 佐甲 博之; 青木 和也*; Gubler, P.; Lee, S. H.*

Physical Review D, 109(11), p.114042_1 - 114042_10, 2024/06

 被引用回数:0 パーセンタイル:0.00(Astronomy & Astrophysics)

Observing the mass shifts of chiral partners will provide invaluable insight into the role of chiral symmetry breaking in the generation of hadron masses. Because both the $$K^{ast}$$ and $$K_1$$ mesons have vacuum widths smaller than 100 MeV, they are ideal candidates for realizing mass shift measurements. On the other hand, the different momentum dependence of the longitudinal and transverse modes smear the peak positions. In this work, we analyze the angular dependence of the two-body decays of both the $$K^{ast}$$ and $$K_1$$. It is found that the longitudinal and transverse modes of the $$K^{ast}$$ can be isolated by observing the pseudoscalar decay in either the forward or perpendicular directions, respectively. For the $$K_1$$ decaying into a vector meson and a pseudoscalar meson, one can accomplish the same goal by further observing the polarization of the vector meson through its angular dependence on the two pseudoscalar meson decay.

論文

Spin alignment of vector mesons by second-order hydrodynamic gradients

Kumar, A.*; Yang, D.-L.*; Gubler, P.

Physical Review D, 109(5), p.054038_1 - 054038_16, 2024/03

 被引用回数:11 パーセンタイル:90.93(Astronomy & Astrophysics)

Starting with the polarization dependent Wigner function of vector mesons, we derive an expression for the 00-component ($$rho_{00}$$) of spin density matrix in terms of the second order gradients of the vector meson distribution functions. We further apply a thermal model to analyze the transverse momentum and the azimuthal angle dependence of $$rho_{00}$$ for $$phi$$ and $$K^{ast,0}$$ mesons resulting from distribution gradients in Au-Au collisions with $$sqrt{s_{NN}} = 130$$ GeV at midrapidity. Our results for the transverse momentum dependence indicate that the deviations of $$rho_{00}$$ from 1/3 as the signal for spin alignment are greatly enhanced at large transverse momenta and have a strong centrality dependence while analysis of the azimuthal angle $$(phi_q)$$ dependence suggest that such deviations have a $$cos(2phi_q)$$ structure with opposite sign for $$phi$$ and $$K^{ast,0}$$. Our finding may be considered as a baseline for probing spin-alignment mechanisms beyond hydrodynamic gradients.

論文

The $$phi$$ meson in nuclear matter from theory and experimental data

Gubler, P.; Bratkovskaya, E.*; 市川 真也; Song, T.*

EPJ Web of Conferences, 291, p.04003_1 - 04003_4, 2024/02

核物質における$$phi$$中間子の性質変化に関する最近の理論的及び実験的な研究を総括し、今後の展望について議論する。われわれの研究の最近の結果についても紹介する。

論文

Disentangling longitudinal and transverse modes of the $$phi$$ meson through dilepton and kaon decays

Park, I. W.*; 佐甲 博之; 青木 和也*; Gubler, P.; Lee, S. H.*

Physical Review D, 107(7), p.074033_1 - 074033_9, 2023/04

 被引用回数:9 パーセンタイル:72.04(Astronomy & Astrophysics)

Angular distributions of $$phi$$ meson decay amplitudes of $$e^+e^-$$ and $$K^+K^-$$ channels are computed using both specific interaction Lagrangians and simple arguments relying on angular momentum conservation. Based on the obtained results, we assess methods to experimentally disentangle the longitudinal and transverse polarization modes of the $$phi$$ meson and discuss advantages and disadvantages of employing either the leptonic or hadronic decay modes for this task.

論文

$$phi$$ meson properties in nuclear matter from dilepton spectra in a transport approach

Gubler, P.; Bratkovskaya, E.*; Song, T.*

EPJ Web of Conferences, 274, p.07015_1 - 07015_6, 2022/12

There is presently no consensus on how the $$phi$$ meson mass and width will change once it is put in a dense environment such as nuclear matter. While many theoretical works exist, connecting them with experimental measurements remains non-trivial task, as the $$phi$$ meson in nuclear matter is usually produced in relatively high-energy pA (p: proton, A: nucleus) reactions, which are generally non-equilibrium processes. In this presentation I will report on an ongoing project, attempting to simulate pA reactions in which the $$phi$$ meson is produced in nuclei, making use of a transport approach. Results of simulations of 12 GeV/30 GeV p+C and p+Cu reactions will be presented and comparisons between obtained dilepton spectra and experimental data of the E325 experiment at KEK will be made. Furthermore, predictions for the ongoing J-PARC E16 experiment for both dilepton and $$K^+K^-$$ spectra will be given and discussed.

論文

Studying $$phi$$ meson properties in nuclear matter from dilepton and $$K^+K^-$$ decays

Gubler, P.; Bratkovskaya, E.*

EPJ Web of Conferences, 271, p.09004_1 - 09004_4, 2022/11

There is presently no consensus on how the $$phi$$ meson mass and width will change once it is put in a dense environment such as nuclear matter. While many theoretical works exist, connecting them with experimental measurements remains non-trivial task, as the $$phi$$ meson in nuclear matter is usually produced in high-energy pA reactions, which are generally non-equilibrium processes. In this presentation I will report on an ongoing project, attempting to simulate pA reactions in which the $$phi$$ meson is produced in nuclei, making use of a transport approach. Results of simulations of 12 GeV/30 GeV p+C and p+Cu reactions will be presented and comparisons between obtained dilepton spectra and experimental data of the E325 experiment at KEK will be made. Furthermore, predictions for the ongoing J-PARC E16 experiment for both dilepton and $$K^{+}K^{-}$$ spectra will be given and discussed.

論文

Chiral gravitational waves from thermalized neutrinos in the early Universe

Gubler, P.; 山本 直希*; Yang, D.-L.*

Journal of Cosmology and Astroparticle Physics (Internet), 2022(9), p.025_1 - 025_36, 2022/09

 被引用回数:3 パーセンタイル:30.25(Astronomy & Astrophysics)

We investigate polarized gravitational waves generated by chiral fermions in the early Universe. In particular, we focus on the contribution from left-handed neutrinos in thermal equilibrium with finite temperature and chemical potential in the radiation dominated era. We compute the correlation functions of gravitational fields pertinent to the Stokes parameter V characterizing the circular polarization of gravitational waves in the Minkowski and expanding spacetime backgrounds. In the expanding universe, we find that the thermalized neutrinos induce a non-vanishing V linear to the neutrino degeneracy parameter and wavenumber of gravitational waves in the long wavelength region. While the magnitude of the gravitational waves generated by thermal neutrinos is too small to be detectable by current and planned third generation gravitational wave detectors, their observations by future generation detectors for ultra-high frequency regimes could provide information on the neutrino degeneracy parameter in the early Universe.

論文

Contribution of the Weinberg-type operator to atomic and nuclear electric dipole moments

長村 尚弘*; Gubler, P.; 山中 長閑*

Journal of High Energy Physics (Internet), 2022(6), p.072_1 - 072_30, 2022/06

 被引用回数:6 パーセンタイル:51.32(Physics, Particles & Fields)

The contribution of the CP violating three-gluon Weinberg operator to the atomic and nuclear EDMs is estimated using QCD sum rules. After calculating the transition matrix element between the pion and the vacuum through the Weinberg operator, we obtain the long-range CP-odd nuclear force by determining the isovector CP-odd pion-nucleon vertex, using chiral perturbation theory at NLO. The EDMs of $$^{199}$$Hg, $$^{129}$$Xe, and $$^{225}$$Ra atoms, as well as those of $$^{2}$$H and $$^{3}$$He nuclei are finally given including comprehensive uncertainty analysis. While the leading contribution of the $$^{199}$$Hg EDM is given by the intrinsic nucleon EDM, that of $$^{129}$$Xe atom may be dominated by the one-pion exchange CP-odd nuclear force generated by the Weinberg operator. From current experimental data of the $$^{199}$$Hg atomic EDM, we obtain an upper limit on the Weinberg operator magnitude of $$|omega| < 4times10^{-10}mathrm{GeV}^{-2}$$ if we assume that it is the only source of CP violation at the scale $$mu$$ = 1 TeV.

論文

$$phi$$ meson properties in nuclear matter from QCD sum rules with chirally separated four-quark condensates

Kim, J.*; Gubler, P.; Lee, S. H.*

Physical Review D, 105(11), p.114053_1 - 114053_9, 2022/06

 被引用回数:4 パーセンタイル:30.25(Astronomy & Astrophysics)

The modification of the $$phi$$ meson spectrum in nuclear matter is studied in an updated QCD sum rule analysis, taking into account recent improvements in properly treating the chiral invariant and breaking components of four-quark condensates. Allowing both mass and decay width to change at finite density, the QCD sum rule analysis determines certain combinations of changes for these parameters that satisfy the sum rules equally well. A comprehensive error analysis, including uncertainties related to the behavior of various condensates at linear order in density, the employed renormalization scale and perturbative corrections of the Wilson coefficients, is used to compute the allowed ranges of these parameter combinations. We find that the $$phi$$ meson mass shift in nuclear matter is especially sensitive to the strange sigma term $$sigma_{sN}$$, which determines the decrease of the strange quark condensate in nuclear matter.

論文

The Phi meson in nuclear matter in a transport approach

Gubler, P.

Proceedings of Science (Internet), 380, p.215_1 - 215_5, 2022/05

最近の研究成果に基づき、有限密度における$$phi$$メソンを実験的に調べるためのpA(p:陽子、A:原子核)反応の数値シミュレーションについて解説する。特に、$$phi$$メソンのスペクトル関数の核物質中における変形が実験的に観測されるdi-leptonのスペクトルにいかに反映されるかについて詳しく議論する。

論文

Prediction of Double-heavy Tetraquarks Bound States in Quark Model

Meng, Q.*; 肥山 詠美子; 保坂 淳; 岡 眞; Gubler, P.; Can, K. U.*; 高橋 徹*; Zong, H. S.*

Few-Body Systems, 62(4), p.79_1 - 79_5, 2021/12

 被引用回数:2 パーセンタイル:22.52(Physics, Multidisciplinary)

Bound states of double-heavy tetraquarks are studied in a constituent quark model. Two bound states are found for isospin and spin-parity $$I(J^P) = 0(1^+)$$ in the $$bbbar{u}bar{d}$$ channel. One is deeply bound and compact made of colored diquarks, while the other is shallow and extended as a $$BB^{ast}$$ molecule. The former agrees well with lattice QCD results. A systematic decrease in the binding energy is seen by replacing one of the heavy quarks to a lighter one. Altogether we find ten bound states. It is shown for the first time that hadrons with totally different natures emerge from a single Hamiltonian.

論文

Studying the phi meson in nuclear matter by simulating pA reactions in a transport approach

Gubler, P.

Few-Body Systems, 62(3), p.53_1 - 53_5, 2021/09

 被引用回数:1 パーセンタイル:12.01(Physics, Multidisciplinary)

最近の研究成果に基づき、有限密度における$$phi$$メソンを実験的に調べるためのpA(p:陽子, A:原子核)反応の数値シミュレーションについて解説する。特に、$$phi$$メソンのスペクトル関数の核物質中における変形が実験的に観測されるdi-leptonのスペクトルにいかに反映されるかについて詳しく議論する。

論文

The Negative-parity spin-1/2 $$Lambda$$ baryon spectrum from lattice QCD and effective theory

Pavao, R.*; Gubler, P.; Fernandez-Soler, P.*; Nieves, J.*; 岡 眞; 高橋 徹*

Physics Letters B, 820, p.136473_1 - 136473_8, 2021/09

 被引用回数:5 パーセンタイル:52.80(Astronomy & Astrophysics)

The spectrum of the negative-parity spin-1/2 $$Lambda$$ baryons is studied using lattice QCD and hadronic effective theory in a unitarized coupled-channel framework. A direct comparison between the two approaches is possible by considering the hadronic effective theory in a finite volume and with hadron masses and mesonic decay constants that correspond to the situation studied on the lattice. Comparing the energy level spectrum and $$SU(3)$$ flavor decompositions of the individual states, itis found that the lowest two states extracted from lattice QCD can be identified with one of the two $$Lambda$$(1405)-poles and the $$Lambda$$(1670) resonance. The quark mass dependences of these two lattice QCD levels are in good agreement with their effective theory counterparts.

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