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meson spectrum through kaons in proton-nucleus reactionsBalassa, G.*; 青木 和也*; Gubler, P.; Lee, S. H.*; 佐甲 博之; Wolf, G.*
Progress of Theoretical and Experimental Physics (Internet), 2025(11), p.113C01_1 - 113C01_20, 2025/11
被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)Exploring the mass modifications of mesons in nuclei provides insights into the nature of strongly interacting matter. Specifically, meson mass shifts can be related to the in-medium modification of the strange quark condensate. Therefore, the partial restoration of chiral symmetry can be studied by observing the mass shifts through the decay channels 
, and 
. In this paper, we examine the possibility of observing the meson mass modifications of the mesons in 30 GeV proton-nucleus (C, Cu, Pb) collisions, to be studied at the J-PARC E88 experiment, through the kaonic decay channel, with the off-shell Budapest Boltzmann-Uehling-Uhlenbeck (BuBUU) transport model. By applying different mean fields to the kaons, we examine their effects on the invariant mass spectra.
江島 廉*; Gubler, P.; 佐々木 千尋*; 志垣 賢太*
Physical Review C, 111(5), p.055201_1 - 055201_12, 2025/05
被引用回数：2 パーセンタイル：82.52(Physics, Nuclear)The degeneracy of chiral partners is an ideal signal for measuring the restoration of the spontaneously broken chiral symmetry in QCD. In this work, we investigate the observability of the -f(1420) degeneracy in the J-PARC E16 experiment, which measures di-electrons emitted from 30 GeV pA collisions. We for this purpose make use of an effective Lagrangian approach, which naturally incorporates the broken charge-conjugation symmetry in nuclear matter and the ensuing anomaly-induced mixing between vector and axial-vector mesons, to compute the spectral function relevant for the experimental measurement. The real-time dynamics of the pA collision is obtained from a transport simulation. Including experimental background and resolution effects on top of that, we find that a signal of the -f(1420) mixing can be observed around 2.5 
with the Run2 statistics planned for the J-PARC E16 experiment with an ideal mixing strength.
mesons in proton-nucleus reactions from a transport approachGubler, 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：4 パーセンタイル：94.12(Physics, Nuclear)Production and in-medium modification of hidden strange 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 meson in the reactions studied. Different in-medium scenarios for the modification of the 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 meson production in p+A reactions occurs only at densities around or below normal nuclear matter density 
, we find visible modifications of the generated dilepton spectra for the in-medium scenarios compared to the vacuum distribution.
correlation functionAbreu, L. M.*; Gubler, P.; Khemchandani, K. P.*; Mart
nez Torres, A.*; 保坂 淳
Physics Letters B, 860, p.139175_1 - 139175_7, 2025/01
被引用回数：9 パーセンタイル：84.06(Astronomy & Astrophysics)The femtoscopic 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 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 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 
*(1895) nucleon resonance.
, 
, 
and 
mesons through their angular-dependent two-body decay modesPark, 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 , 
, 
, and 
(
) decays. Concerning and 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.
Kumar, A.*; Yang, D.-L.*; Gubler, P.
Physical Review D, 109(5), p.054038_1 - 054038_16, 2024/03
被引用回数：23 パーセンタイル：95.60(Astronomy & Astrophysics)Starting with the polarization dependent Wigner function of vector mesons, we derive an expression for the 00-component (
) 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 for and 
mesons resulting from distribution gradients in Au-Au collisions with 
GeV at midrapidity. Our results for the transverse momentum dependence indicate that the deviations of 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 
dependence suggest that such deviations have a 
structure with opposite sign for and . Our finding may be considered as a baseline for probing spin-alignment mechanisms beyond hydrodynamic gradients.
meson through dilepton and kaon decaysPark, 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：13 パーセンタイル：74.61(Astronomy & Astrophysics)Angular distributions of meson decay amplitudes of 
and 
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 meson and discuss advantages and disadvantages of employing either the leptonic or hadronic decay modes for this task.
meson with finite momentum in a dense mediumKim, H.-J.*; Gubler, P.
Physics Letters B, 805, p.135412_1 - 135412_8, 2020/06
被引用回数：27 パーセンタイル：90.09(Astronomy & Astrophysics)QCD和則を利用し、核物質におけるメソンの分散関係を調べる。敗れたLorentz対称性により、有限密度中ではベクター粒子のlongitudinal及びtransverseモードが異なる振る舞いを示しえる。次元6までの可能な演算子及びそのWilson係数をすべて用い、様々な密度及び運動量におけるメソンの分散関係を解析する。その結果、longitudinal及びtransverseモードが逆の振る舞いを示すことが分かった。実際、運動量1GeVでは、longitudinalモードでは質量が5MeVほど下り、transverseモードでは7MeVほど上がることが分かった。longitudinal及びtransverseモードを区別しない実験では、この現象が二つの分離されたピークとして観測される可能性がある。
modification with high-statistics 
decay measurements in 30-GeV proton-nucleus collisions佐甲 博之
no journal, ,
meson is a good probe to explore mass modification inside the nucleus due to partial restoration of chiral condensate with its narrow width. In particular, modification of meson mass is sensitive to strange quark condensate. J-PARC E88 is proposed as an experiment to study modification of meson mass inside nuclei in p+A collisions. Complementary to 
decay measurements at J-PARC E16, E88 will measure high-statistics 
decays of 
M in p+C, p+Cu, and p+Pb. Utilizing high-statistics data, we will measure the momentum dependence of mass modification (dispersion relation), which is used to extrapolate to zero momentum to evaluate strange quark condensate. Also, we will measure the dispersion relations for longitudinal and transverse polarized 's with 
decay angle, which are predicted to be different in QCD sum rules. In this presentation, we will discuss physics goals, the experimental design, and the preparation status.
decaysGubler, P.
no journal, ,
While the meson vacuum properties, such as mass and width, are well known, it is not clear how these properties will change once it is put in a dense environment such as nuclear matter. Theoretically, many works have been conducted with the aim of studying the meson in nuclear matter. Connecting theoretical results with experimental measurements is, however, not a trivial task, as the meson in nuclear matter is usually produced in relatively 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.
Gubler, P.; Kim, H. J.*; Lee, S. H.*
no journal, ,
有限運動量を持つ核物質中のphiメソンの振る舞いについての最近の研究の進捗状況について報告する。J-PARCのE16実験との関連についても議論する。
Gubler, P.
no journal, ,
本講演の前半では核物質中でのカイラル対称性の部分的回復の現状を概観する。後半では自分がここ数年取り組んでいる核物質中のメソンの振る舞いに関する研究を紹介し、特にJ-PARCのE16実験との関連を議論する。
Gubler, P.
no journal, ,
We present recent results of numerical simulations of the 12 GeV pA reactions probed at the KEK E325 experiment using a transport approach. Furthermore, we discuss how the simulation results can be used to interpret the experimental data in terms of the modification of the phi meson at finite density. Finally, we will give an outlook to the presently ongoing J-PARC E16 experiment.
meson in nuclear matter; Interpreting the E325 data in a transport approachGubler, P.
no journal, ,
We present recent results of numerical simulations of the 12 GeV pA reactions probed at the KEK E325 experiment using a transport approach. Furthermore, we discuss how the simulation results can be used to interpret the experimental data in terms of the modification of the phi meson at finite density.
Gubler, P.
no journal, ,
While the phi meson vacuum properties, such as mass and width, are well known, it is not clear how these properties will change once it is put in a dense environment such as nuclear matter. To study how the phi meson behaves at finite density has been the goal of several past and near future experiments at KEK, COSY-ANKE and J-PARC. Recently, ALICE has obtained novel experimental data constraining the phi-N interaction, at the same time as new lattice QCD calculations about the phi-N potential are also becoming available. In this talk, I will discuss how these data can be interpreted from a theoretical point of view, and how they possibly can be used to constrain the nuclear matter properties of the phi meson and its longitudinal and transverse polarization modes. I will review theoretical predictions for the in-medium modifications of these quantities and discuss how they could be measured at the future J-PARC E16 and E88 experiments.
