Studying meson properties in nuclear matter from dilepton and decays

Gubler, P.; Bratkovskaya, E.*

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

https://doi.org/10.1051/epjconf/202227109004

There is presently no consensus on how the 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 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 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 spectra will be given and discussed.

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

https://doi.org/10.1007/JHEP06(2022)072

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 Hg, Xe, and Ra atoms, as well as those of H and He nuclei are finally given including comprehensive uncertainty analysis. While the leading contribution of the Hg EDM is given by the intrinsic nucleon EDM, that of 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 Hg atomic EDM, we obtain an upper limit on the Weinberg operator magnitude of if we assume that it is the only source of CP violation at the scale = 1 TeV.

The phi meson in nuclear matter in a transport approach

Gubler, P.

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

https://doi.org/10.22323/1.380.0215

最近の研究成果に基づき、有限密度における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、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。

The Negative-parity spin-1/2 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

https://doi.org/10.1016/j.physletb.2021.136473

The spectrum of the negative-parity spin-1/2 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 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 (1405)-poles and the (1670) resonance. The quark mass dependences of these two lattice QCD levels are in good agreement with their effective theory counterparts.

J/ near

Song, T.*; Gubler, P.; Hong, J.*; Lee, S. H.*; 森田 健司*

Physics Letters B, 813, p.136065_1 - 136065_5, 2021/02

https://doi.org/10.1016/j.physletb.2021.136065

We calculate the mass shift and thermal decay width of the J/ near the QCD transition temperature by imposing two independent constraints on these variables that can be obtained first by solving the Schrodinger equation and second from the QCD sum rule approach. While the real part of the potential is determined by comparing the QCD sum rule result for charmonium and the D meson to that from the potential model result, the imaginary potential is taken to be proportional to the perturbative form multiplied by a constant factor, which in turn can be determined by applying the two independent constraints. The result shows that the binding energy and the thermal width becomes similar in magnitude at around T = 1.09 , above which the sum rule analysis also becomes unstable, strongly suggesting that the J/ will melt slightly above .

Charmed baryon spectrum from lattice QCD near the physical point

Bahtiyar, H.*; Can, K. U.*; Erkol, G.*; Gubler, P.; 岡 眞; 高橋 徹*

Physical Review D, 102(5), p.054513_1 - 054513_18, 2020/09

AA2020-0041.pdf:2.4MB

https://doi.org/10.1103/PhysRevD.102.054513

格子QCDによる第一原理計算を用いて、正負パリティのチャームバリオンの基底および励起状態のスペクトルを求めた。チャームクォークを1個, 2個あるいは3個含むバリオンの正および負パリティ状態の質量を、第一原理計算から求めることで、これまでの実験データや模型計算結果との比較を行い、その物理的な意味を解析することが可能となる。今回の計算では、パイオンの質量が観測値に十分近い物理点に近い領域で、2+1フレーバーのゲージ配位を用いた解析を行った。ディラック行列などの配置の異なる複数の演算子を用意し、その交差相関関数を計算し、固有値を求める方法により、基底状態と励起状態のスペクトルを計算した。

Signatures of the vortical quark-gluon plasma in hadron yields

田屋 英俊*; Park, A.*; Cho, S.*; Gubler, P.; 服部 恒一*; Hong, J.*; Huang, X.-G.*; Lee, S. H.*; 門内 明彦*; 大西 明*; et al.

Physical Review C, 102(2), p.021901_1 - 021901_6, 2020/08

AA2020-0306.pdf:0.47MB

https://doi.org/10.1103/PhysRevC.102.021901

We investigate the hadron production from the vortical quark-gluon plasma created in heavy-ion collisions. Based on the quark-coalescence and statistical hadronization models, we show that total hadron yields summed over the spin components are enhanced by the local vorticity with quadratic dependence. The enhancement factor amounts to be a few percent and may be detectable within current experimental sensitivities. We also show that the effect is stronger for hadrons with larger spin, and thus propose a new signature of the local vorticity, which may be detected by the yield ratio of distinct hadron species having different spins such as and . The vorticity dependence of hadron yields seems robust, with consistent predictions in both of the hadron production mechanisms for reasonable values of the vorticity strength estimated for heavy-ion collisions.

meson mass and heavy quark potential at finite temperature

Gubler, P.; Song, T.*; Lee, S. H.*

Physical Review D, 101(11), p.114029_1 - 114029_10, 2020/06

https://doi.org/10.1103/PhysRevD.101.114029

Based on the observation that the heavy quark-antiquark potential value at infinity corresponds to twice the meson mass, we constrain the asymptotic value of the heavy quark potential in a hot medium through a QCD sum rule calculation of the meson at finite temperature. We find that to correctly reproduce the QCD sum rule results as well as a recent model calculation for the meson mass near the critical temperature, the heavy quark potential should be composed mostly of the free energy with an addition of a small but non-trivial fraction of the internal energy. Combined with a previous study comparing potential model results for the J/ to a QCD sum rule calculation, we conclude that the composition of the effective heavy quark potential should depend on the inter-quark distance. Namely, the potential is dominated by the free energy at short distance, while at larger separation, it has a fraction of about 20% of internal energy.

Exact vector channel sum rules at finite temperature

Gubler, P.; 佐藤 大輔*

JPS Conference Proceedings (Internet), 26, p.024023_1 - 024023_5, 2019/11

https://doi.org/10.7566/JPSCP.26.024023

本講演では最近の発表論文に基づき、vectorチャンネル(光子と同じ量子数を持つ状態)のスペクトル関数に関して導出したいくつかの厳密な和則を紹介する。摂動計算ではこの和則が成り立つことや、格子QCDへの応用についても議論する。

Compact pentaquark states predicted by a quark model

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

Physics Letters B, 798, p.135028_1 - 135028_8, 2019/11

https://doi.org/10.1016/j.physletb.2019.135028

Several compact pentaquark resonances are predicted in a potential quark model. The Hamiltonian is the best available one, which reproduces the masses of the low-lying charmed and strange hadrons well. Full five-body calculations are carried out by the use of the Gaussian expansion method, and the relevant baryon-meson thresholds are taken into account explicitly. Employing the real scaling method, we predict four sharp resonances, ( = 5180 MeV, = 20 MeV) and others. These are the candidates of compact pentaquark resonance states from the current best quark model, which should be confirmed either by experiments or lattice QCD calculations.