arXiv subjects

Seung-Il Nam

Publications and source records attributed to Seung-Il Nam.

11 recordsLinked to original sources

arXiv2025

Approaching the continuum with anisotropic lattice thermodynamics

The FASTSUM collaboration has a long-standing programme of using anisotropic lattice QCD to investigate strong interaction thermodynamics, and in particular spectral quantities. Here we present first results from our new ensemble which has a temporal lattice spacing a_t=15am and anisotropy xi=a_s/a_t=7, giving unprecedented resolution in the temporal direction. We show results for the chiral transition, vector-axial-vector degeneracy, and heavy quarkonium, and compare them with earlier results with coarser time resolution.

hep-lat↗

arXiv2008

Production of the pentaquark exotic baryon Xi_5 in bar{K} N scattering : bar{K} N -> K Xi_5 and bar{K} N -> K* Xi_5

We investigate the production of the newly found pentaquark exotic baryon Xi_5 in the bar{K} N -> K Xi_5 and the bar{K} N -> K* Xi_5 reactions at the tree level. We consider both positive- and negative parities of the Xi_5. The reactions are dominated by the s- and u-channel processes, and the resulting cross sections depend very much on the parity of Xi_5 and on the type of form factor. We have seen that the cross sections for the positive-parity Xi_5 are generally about a hundred times larger than those of the negative-parity one. This large difference in the cross sections will be useful for further study of pentaquark baryons.

hep-ph↗

arXiv2006

Pentaquark Theta^+ production via gamma N ->K^*bar Theta^+(3/2^(+-))

We study the photoproduction of the exotic pentaquark Theta^+ baryon with the vector kaon, assuming that the quantum numbers of the Theta^+ to be J^P=3/2^(+-) and J^P=1/2^+. Scalar meson kappa(800)-exchange is also taken into account. In contrast with the gamma N -> Kbar Theta^+(3/2^(+-)) process, the large suppression from the proton target is not observed in the total cross sections. We also suggest a method to determine which meson exchange is the most dominant by analyzing the polarizations of incident photon and outgoing K^*. We find that kappa-exchange turns out to be prominent when the polarizations of the photon and K^* are aligned to be parallel, whereas K-exchange does when they are perpendicular to each other.

hep-ph↗

arXiv2005

Lambda(1520,3/2^-) photoproduction reaction via gamma N -> K Lambda(1520)

We investigate Lambda(1520,3/2^-,D_03) photoproduction via the gamma N -> K Lambda^* reaction process. Using effective Lagrangians, we compute the total and differential cross sections as well as the dependence on the momentum transfer for the photoproduction at the tree-level. We employ two different form factors: The four-dimensional gauge-invariant type and the three dimensional one depending on the external momenta. We find that the total cross sections for the proton target are well reproduced as compared with the experimental data. It turns out that the total cross sections for the neutron target are significantly smaller than those for the proton target. We also compare the present results with the gamma N -> bar{K} Theta^+ reaction in order to extract information of Theta^+. Finally the role of K^*--exchange in the production reaction is discussed.

hep-ph↗

arXiv2005

Suppression of Theta^+(J^P=3/2^(+,-)) photoproduction from the proton

We investigate the photoproduction of Theta^+ from the proton and neutron, gamma N -> Kbar Theta^+. Assuming that spin and parity of Theta^+ are J^P = 3/2^(+,-), it is shown that the production from the proton is strongly suppressed as compared with that from the neutron. This could provide a possible explanation for the null results of the recent CLAS experiment in finding Theta^+ via the reaction gamma p -> Kbar^0 Theta^+.

hep-ph↗

arXiv2005

Production of Lambda(1520)

We investigate the Lambda(1520) photoproduction via the reaction process, gamma N -> K Lambda(1520). We employ the Born approximation and the Rarita Schwinger formalism is used for Lambda(1520). We reproduce the total cross sections and the various angular distributions qualitatively well for the proton target and estimate them for the neutron one. We find that the contact term contributes much more to the process than the other kinematical channels. Taking into account this fact, we reanalyze the K^*--exchange dominance hypothesis suggested by the previous experiments.

hep-ph↗

arXiv2005

Photoproduction of Lambda(1520,3/2^-)

We investigate the photoproduction of Lambda(1520,3/2^-) via the gamma N -> K Lambda^* reaction using the Born approximation and the Rariata-Schwinger vector-spinor field for the spin 3/2 particle. We reproduce the experimental data of the total cross section and the angular dependence for the proton target qualitatively well and estimate them for the neutron target. For the neutron target, we find much smaller total cross section than that of the proton and the significant K^*-exchange contribution.

hep-ph↗

arXiv2005

Determination of the parity of the pentaquark baryons : Theta^+ and Xi_5

We study determination of the parity of the pentaquark baryons in two different processes. First, we investigate the Theta^+ production via the vec{p} vec{p} -> Sigma^+ Theta^+ reaction process which was proposed to determine unambiguously the parity of Theta^+. We observe the clear differences in the total cross sections and the spin observable A_{xx}. As for the Xi_5 in the bar{K} N -> K Xi_5 reaction process, the total cross section for the positive parity presents about one hundred times lager than that of the negative one due to the huge destructive interference.

hep-ph↗

arXiv2004

Theta^+ baryon production from gamma N and NN scattering

We investigate Theta^+ production via gamma N and NN reactions in order to obtain information on the structure of Theta^+, especially its parity. We observe that the positive parity. Theta^+production provides about ten times total cross sections than those of the negative parity one in both photon and nucleon induced reactions due to P-wave enhancement of the KNTheta vertex. We also consider the model independent method in the nucleon induced reaction to determine the parity of Theta^+ and show clearly distinguishable signals for the two parities.

nucl-th↗

arXiv2004

Photon and nucleon induced production of Theta^+

We investigate Theta^+ production via photon and nucleon induced reactions. We observe that the positive parity Theta^+ production provides about ten times larger total cross sections than those of the negative parity one in both photon and nucleon induced reactions due to P-wave enhancement of the K-N-Theta vertex. We also consider the model independent method in the nucleon induced reaction to determine the parity of Theta^+ and show clearly distinguishable signals for the two parities.

nucl-th↗

arXiv2004

Photo-production of the pentaquark $Θ^{+}$ with positive and negative parities

We investigate the production of the pentaquark $Θ^+$ baryon via the $γn\to K^-Θ^+$ and $γp\to \bar{K}^0 Θ^+$ processes, focusing on the parity of the $Θ^+$. Using the effective Lagrangians, we calculate the total and differential cross sections with the spin of the $Θ^+$ presumed to be 1/2. We employ the coupling constant of the $KNΘ$ vertex determined by assuming its mass and the decay width to be $1540 {\rm MeV}$ and $15 {\rm MeV}$. That of the $K^*NΘ$ is taken to be about a half of the $KNΘ$ coupling constant. We estimate the cutoff parameter by reproducing the total cross section of the $γp \to K^+ Λ$ reaction. It turns out that the total cross section for the $γn\to K^- Θ^+$ process is about four times larger than that of the $γp\to\bar{K}^0Θ^+$. We also find that the cross sections for the production of the positive-parity $Θ$ are about ten times as large as those for the negative-parity ones.

hep-ph↗