Energy Dependence of the Entropy Production in Relativistic Heavy-Ion Collisions

홍병식 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4

We compile experimental data on the production yields of protons, deuterons, and pions from 1 to 200 GeV of psNN, and interpret them in the context of the nucleon density of a hot, dense fireball and the entropy production. The d/p yield ratio decreases with beam energy, implying that the nucleon density also decreases with beam energy. However, the entropy per nucleon increases with beam energy. In particular, the rate of the entropy increase changes dramatically at psNN ' 2 GeV, where nuclear stopping and sideward flow show their maxima. We conclude that disassembled nucleons are more effective for the entropy production than particle production. A big change in the energy dependence of the entropy production has not been observed between the Alternating Gradient Synchrotron (AGS) and the Relativistic Heavy Ion Collider (RHIC) energies.

Change of the Azimuthal Asymmetry at High Momentum with Different Parton Absorptions in a Quark-Gluon Plasma

홍병식 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III

We present simple geometrical model calculations for parton suppression at high momentum, where the fragmentation process is dominant, in relativistic heavy-ion collisions. Depending on the position of hard scattering, the pattern of the parton absorption changes because of the different pathlengths to escape the overlapped zone. The out-of-plane yield of partons is more suppressed than the in-plane yield in the overlap zone, especially for large impact parameters. In addition, the in-plane yield is expected to decrease as the parton absorption is increased because of the strong parton absorption even before they reach the geometrical boundary of the overlapped zone. The present result is in contrast to that of previous calculations in which the saturation effect was observed to occur at a rather small absorption coefficient.

Critical Evidence for Nucleon Coalescence in Heavy-Ion Collisions at 400 MeV per Nucleon

홍병식 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.5

We present two critical pieces of evidence for the coalescence of nucleons in heavy-ion collisions at 400 MeV per nucleon. The elliptic flow parameters of the proton and of the helium isotopes plotted as functions of the transverse momentum overlap each other when scaled by the number of nucleons. In addition, the shapes of the invariant spectra of deuterons can be reproduced by the proton spectra powered by the number of constituent nucleons. By using the density-matrix formalism, we extract the rapidity-dependent source radius of the excited zone at chemical freeze out. The source radius is maximum at midrapidity, and it decreases towards the target and projectile rapidities. The estimated chemical freeze-out radius at midrapidity is about 20 \% larger than the radius of the incident nuclei.

Effect of Longitudinal Momentum Unbalance on Nuclear Transparency

홍병식 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I

We present the effect of longitudinal momentum unbalance on nuclear transparency by using a simple geometrical model with momentum conservation. We find that the isospin-tracer parameters, deduced by using isospin symmetric and asymmetric isobaric collisions, do not depend on the collision centrality or the beam energy. The isospin-tracer parameters estimated by using a geometrical model cannot reproduce the experimental data. As a result, the observed effect must come from true nuclear transparency.

Expectation for the Density Dependence of Isoscaling Parameters at Rare Isotope Collisions

홍병식 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.5

We present the expected measurements of the isoscaling effect in rare isotope collisions with large isospin asymmetry at the future Korea rare-isotope accelerator. In particular, we explore the density dependence of the isoscaling parameters for various assumptions on the nuclear symmetry energy from super-soft to stiff forms. The magnitudes of the isoscaling parameters are expected to be larger for larger isospin asymmetric reactions. In addition, the density dependence of the ratio of the fragment yields is expected to be larger for larger proton-to-neutron ratio of the measured particle. The double ratio, which is ratio of any isobar yield ratios for different isospin compositions, can be another good probe for the nuclear symmetry energy. Since the double ratio depends on the neutron (or proton) number difference between two measured isobars, the potential candidates might be the pairs of (^9Be, ^9C), (^7Li, ^7Be), and (^(14)C, ^(14)N). The LAMPS detector system at the Korea rare-isotope accelerator is being optimized for measuring not only the isoscaling parameters but also other observables like the isospin tracing (or diffusion) parameters and the collective flow.

Endcap Resistive Plate Chambers for the Compact Muon Solenoid Experiment

홍병식,심광숙,이경세,홍성종,박성근 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.4

We review the development of the endcap resistive plate chambers for the Compact Muon Solenoid experiment at the Large Hadron Collider. The standard double gap geometry, which was designed and constructed by the Korea Detector Laboratory, satisfies all CMS requirements including the efficiency, the time resolution, and the working high-voltage plateau range. These results clearly demonstrate that the present design of the chamber is suitable for the muon trigger system in the endcap region of the Compact Muon Solenoid detector. We also discuss the possible applications of resistive plate chambers.n

Design of Wide-energy-range Neutron Calorimeter for Nuclear Collisions in the Korea Rare-isotope Accelerator

홍병식,Genie Jhang,주은아,이경세,심현하 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.2

We have designed a neutron calorimeter dedicated to the measurement of the nuclear symmetry energy in the planned Korea rare-isotope accelerator. The design was optimized to precisely measure the neutron energy with high efficiency in a wide energy range from about 30 to 300 MeV. The final configuration of the detector is a hybrid of the homogeneous and the sampling calorimeters with a veto counter in the front. The homogeneous part is ideal for measuring low-energy neutrons below ∼50 MeV whereas the sampling part is efficient for measuring high-energy neutrons. The detection efficiency is estimated to be about 88% for neutron energies larger than 50 MeV and decreases to ∼78% at 30 MeV.We have estimated the energy resolution as a function of the incident energy based on the time-of-flight method. Assuming an ideal detector performance with null time resolution, the relative energy resolution decreases as the incident neutron energy increases. However, under a more realistic situation with a finite time resolution for the detector, the energy resolution monotonically increases with increasing the neutron energy, following a logarithmic function. Imposing an energy resolution of better than 3% at the highest neutron energy, we find the nominal position of the hybrid calorimeter to be 15 m from the target for a time resolution of 1.0 ns, but the detector needs to be free to move closer to or farther from the target, depending on the physics goal.

Neutron-Detection Efficiency of Hybrid Resistive Plate Chambers as Estimated by Using the MC50 Cyclotron at KIRAMS

홍병식,B.I. Kim,H.C. Kim,J.H. Kim,K.B. Lee,K.S. Sim,K.S. Lee,M. Ito,M.S. Ryu,R. J. Hu,박성근,T.I. Kang 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4

We present the neutron-detection efficiencies of a Gd-coated single-gap resistive plate chamber (RPC) and a LiF-coated double-gap RPC. The experiments were performed by using indirect neutrons provided by the MC50 cyclotron at the Korea Institute of Radiological and Medical Science. Both RPCs show a decrease in the efficiency with increasing beam current, especially the Gd-coated RPC at the highest beam current (50 nA) that we received. Such a decrease in the efficiency could be understood in terms of a decrease in the effective electric field in the gas gap under high-particlerate environment. The operational plateaus start at about 8 kV for the Gd-coated RPC and at about 6.7 kV for the LiF-coated RPC. The neutron-detection efficiencies of the Gd-coated and the LiF-coated RPCs are about 2.5 and 1.8 %, respectively, at the operational high-voltage-plateau region. These results are completely consistent with the previous efficiencies obtained by using an intense 252Cf source.

중이온 충돌에서의 상태방정식 및 대칭에너지

홍병식 한국물리학회 2016 새물리 Vol.66 No.12

The RAON is expected to provide extremely rare isotope beams with unprecedented isospin asymmetry for studies of nuclear structure, nuclear astrophysics, and nuclear reaction dynamics. Neutron-rich isotope beams are useful for investigating in detail the nuclear equation of state and the symmetry energy, which are essential for understanding astronomical objects like neutron stars and supernovae. At the RAON, low beam energies below 18.5 MeV/u are suitable for symmetry-energy research at subsaturation densities, and high beam energies around 250 MeV/u are ideal for such research at supra-saturation densities. Some examples of representative observables for studying the symmetry energy are the electric dipole emission, isospin diffusion of charged hadrons, collective-flow parameters, and pion yield ratio. This review article describes a plan for studying the nuclear equation of state and the symmetry energy that can be pursued in heavy-ion collisions at the RAON. RAON은 핵의 구조와 핵천체물리, 핵반응 동역학 연구를 위하여 지금까지 생산한 적이 없는 매우 희귀한 아이소스핀 비대칭 동위원소 빔을 제공해 줄 것으로 기대된다. 중성자 과잉 동위원소 빔은 핵의 상태방정식과 대칭에너지 연구에 매우 유용하며, 이들은 중성자별이나 초신성과 같은 천체물리학적 대상을 이해하는데 필수적이다. RAON에서 낮은 빔에너지 영역인 핵자 당 18.5 MeV 이하는 정상 핵자밀도 이하의 대칭에너지 연구에 적당하며, 높은 빔에너지 영역인 핵자 당 250 MeV는 압축된 고밀도 핵물질의 대칭에너지를 연구하는데 매우 이상적인 조건을 제공해 준다. 대칭에너지 연구를 위한 대표적인 물리분석량의 예로써 이중극 감마선 방출, 하전 강입자의 전하확산 변수, 유체흐름 변수, 파이온 생성비 등을 들 수 있다. 이 해설논문은 RAON의 중이온 충돌에서 계획 중인 핵의 상태방정식과 대칭에너지 연구에 대해 기술한다.

유실물을 찾읍시다

홍병식 새가정사 1969 새가정 Vol.- No.-