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D*-Meson Photoproduction off the Proton Target with the Regge Contribution
남승일 한국물리학회 2020 New Physics: Sae Mulli Vol.70 No.1
We investigate the four individual photoproduction channels off the proton target, corresponding to the isospin single and triplet charmed baryons, p ! D 0+c and p ! (D +0c ;D 0+c ;D ++ c ). In this work, we estimate the unpolarized total cross sections as guidance for possible future J-PARC experiments. For this purpose, we employ the effective Lagrangian approach at the tree-level Born approximation with the t-channel D and D meson Reggized propagators. In addition, phenomenological form factors are taken into account for considering the spatial extension of the hadrons involved. From the numerical calculations, we observed that cross sections of tens of nanobarns for +c production and a few nanobarns for the ++ c ones, which are in the detectable range of cross sections in presently available high-energy experiments.
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비섭동 영역에서의 제트-담금질 매개변수 $\hat{q}$
남승일 한국물리학회 2016 새물리 Vol.66 No.6
We investigate the jet-quenching parameter $\hat{q}$ for the quark-gluon plasma (QGP) for $N_c=3$, defined nonperturbatively with the Wilson loop in the light-cone (LC) coordinate, at finite temperature $(T)$. Considering the effective static (heavy) quark-antiquark potential $V_{\bar{Q}Q}=\sigma L+C-A/L$, where $L$ indicates the LC transverse separation between the quarks, we obtain $\hat{q}\approx8V_{\bar{Q}Q}/L^2$. The $T$ dependences for $L$ and other relevant parameters are extracted from the $T$-dependent instanton (trivial-holonomy caloron) length parameters and the lattice quantum chromodynamics (QCD) data. By choosing $L\approx{a}\approx\bar{\rho}_T$, in which $a$ and $\bar{\rho}_T$ denote the lattice spacing and the $T$-dependent average (anti)instanton size, respectively, we find numerically that $\hat{q}=(5\sim25)\,\mathrm{GeV/fm}$ for $T= 0\sim 0.6$ GeV, these values are consistent with other estimates from AdS/CFT and experimental analyses. $\hat{q}$ is produced almost completely by the Coulomb and constant potentials of $V_{\bar{Q}Q}$. We also observe that the ratio $T^3/\hat{q}$ saturates at $\sim4.45\times10^{-2}$ for $T ≳ 0.4$ GeV, indicating a strongly-coupled QGP, and that $\hat{q}$ is proportional to $T^3$ for high $T$. 본 연구는 유한온도 쿼크-글루온 플라즈마에서 중요한 역할을 하는 비섭동 영역에서의 제트-담금질 매개변수($\hat{q}$)를 $N_c=3$의 경우에 대하여, 광원추상의 윌슨 루프를 이용하여 연구하였다. 무거운 쿼크간 광원추상에서 거리가 $L$ 일때, 유효 포텐셜이 $V_{\bar{Q}Q}=\sigma L+C-A/L$로 주어지는 것을 고려하면, $\hat{q}\approx8V_{\bar{Q}Q}/L^2$이 됨을 보인다. $L$과 다른 모형 변수들의 온도 의존성은 자명한 홀로노미(trivial-holonomy)를 가진 칼로론(caloron)과 격자 QCD로부터 결정되어진다. $a$ and $\bar{\rho}_T$를 각각 격자 QCD 간격과 온도에 의존하는 평균적인 인스탄톤의 크기라 하고, 차원 분석을 통해 $L\approx{a}\approx\bar{\rho}_T$를 가정하면, $T=(0\sim0.6)$에서 $\hat{q}=(5\sim25)\,\mathrm{GeV/fm}$로 주어진다. 이 값 은 AdS/CFT 및 실험 분석에서의 다른 추정과 잘 일치한다. 수치결과의 분석을 통해, 포텐셜 $V_{\bar{Q}Q}$중 쿨롱 및 상수 부분의 기여가 가장 중요함을 알 수 있었다. 또한 $T\gtrsim0.4$ GeV의 영역에서 비율 $T^3/\hat{q}$는 약 $4.45\times10^{-2}$에 근접하며, 이는 $\hat{q}$ 가 높은 온도에서 $T^3$의 형태로 거동함을 보여준다.
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Photoproduction of <i>K<sup>*</sup></i> Meson off the Proton Target with the Regge Contributions
남승일,유병길 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.6
We investigate the <i>K<sup>*</sup></i>Λ(1116) photoproduction off the proton target by employing the treelevel Born approximation within the effective Lagrangian approach. We take into account the κ, <i>K</i>, and <i>K<sup>*</sup></i> exchanges in the <i>t</i> channel in addition to the ground-state nucleon- and hyperon-pole contributions in the s and the <i>u</i> channels with the gauge-invariant form-factor scheme. The nucleon and the hyperon resonances, <i>D</i><sub>13</sub>(2080) and Σ<sup>*</sup>(1385), are also included. We take into account the Regge trajectories of the strange mesons for the t-channel contributions in such a way that the Feynman and Regge propagators are interpolated smoothly for the relevant photon energy region. We provide numerical results for the differential cross sections, which result in qualitatively good agreement with the presently available experimental data from the CLAS collaboration at Jefferson laboratory. The Feynman-Regge interpolation for the meson exchanges turns out to play a critical role in reproducing the data simultaneously for the low and the relatively high energy regions. We also compute the total cross sections, momentum-transfer dependence of the differential cross sections in the <i>t</i>-channel, and the photon-beam asymmetry as useful guides for future experiments.
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남승일,Hyun-Chul Kim,Atsushi Hosaka,Daisuke Jido,Tetsuo Hyodo 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
We investigate the dependences of the s-wave meson-baryon scattering amplitudes on dierent regularizations within the framework of the chiral unitary model. We employ two dierent regularization schemes, i.e., dimensional and form-factor regularizations, to tame the divergences in the model. We also use those regularization schemes to study the analytic structures of the T-matrices. We nd that while the form-factor regularizaion produces almost the same results as the dimensional regularization does, the on-shell approximation is to some extent limited in the case of the form-factor regularization. Having chosen parameters properly, we show that the regularization dependences can be minimized.
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인스탄톤 모형을 이용한 $N_f=2$ 양자색소역학 위상구조 연구
남승일 한국물리학회 2017 새물리 Vol.67 No.3
In this work, we investigate the phase diagram of quantum chromodynamics (QCD) for $N_f=2$ as a function of the temperature and the density by employing the liquid-instanton model. For this purpose, we take into account two cases, one with zero and one with finite current-quark masses. The instanton parameters, such as the average (anti)instanton size $\bar{\rho}$ and the inter-(anti)instanton distance $\bar{R}$, are given as functions of the temperature $T$ via the trivial-holonomy caloron solution. From the numerical calculations, we confirm that the phase-transition patterns follow the appropriate universal class, $i.e.$, the second-order phase transition for the massless quarks and the crossover for the finite-mass quarks. The critical-end point (CEP) are found to be (187,92) MeV and (232,72) MeV for the massless and the finite-mass quarks. Our results are compared with other theoretical results from the Nambu—Jona-Lasinio model (NJL). 본 연구에서는 인스탄톤 진공을 이용한 유효 모형인 액체-인스탄톤 모형 (liquid-instanton model, LIM)을 이용하여 $N_f=2$ 에서의 양자색소역학적 위상구조를 온도($T$)와 쿼크 화학 포텐셜($\mu$)의 함수로서 연구하고자 한다. 이를 위해 쿼크의 전류 질량(current-quark mass, $m$)이 0인 경우와 유한한 경우 $m_q$ = 5 MeV를 고려한다. 인스탄톤의 평균 크기($\bar{\rho}$), 인스탄톤간 평균 거리($\bar{R}$) 등의 모형 매개변수들은 자명한 홀로노미의 칼로론해(trivial-caloron solution)를 이용하여 계산되었다. 수치계산으로부터 쿼크 전류 질량에 의한 정확한 상전이(phase transition) 패턴이 확인되었으며, 상전이의 변화가 일어나는 임계 종말점(critical-end point, CEP)은 쿼크 전류 질량 $m$ = (0,5) MeV에 대해 각각 (187,92) MeV과 (232,72) MeV로 주어진다. 또한 본 이론 계산 결과를 다른 유효 모형인 남부-요나-라시니오(Nambu-Jona-Lasinio, NJL)모형의 결과와 비교하였다.
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