Strangeness and threshold of phase changes
Johann Rafelski, Inga Kuznetsova, Jean Letessier
我们探讨熵和奇异性作为QGP的签名顶部AGS能量和SPS的能量扫描。我们发现强子化动力学在20和30 $A$ GeV的射弹能量之间变化。高能区的结果与QGP一致。
We explore entropy and strangeness as signature of QGP for top AGS energy and the energy scan at SPS. We find that the hadronization dynamics changes between 20 and 30 $A$ GeV projectile energy. The high energy results are consistent with QGP.
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Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, the dynamics of strangeness (K$^{0,+}$, $Λ$ and $Σ^{-,0,+}$) production in heavy-ion collisions near threshold energies is investigated systematically, in which the strange particles are considered to be mainly produced by the inelastic collisions of baryon-baryon and pion-baryon. The collisions in the region of supra-saturation densities of the dense baryonic matter formed in heavy-ion collisions dominate the yields of strangeness production. The total multiplicities as functions of incident ener…
Associated Strangeness Production in the Threshold Region
接近临界值的相关奇异性产生是能量如何转化为强子物质的一个特别干净的例子。在LEAR/CERN完成的PS185合作实验的最终结果，使用反质子-质子相互作用产生反超子-超子对，表明这样的研究形成了一个强大的工具。本文介绍了COSY-11合作项目的第一批研究结果，并讨论了进一步研究的计划。最后，对动量大于5GeV/c的反质子束流与反质子-质子相互作用中奇异产生机制的未来研究提出了一个有趣的可能性。
We use the Isospin Quantum Molecular Dynamics approach supplemented with a phase space coalescence to study the properties of the production of hypertritons. We see strong influences of the hyperon rescattering on the yields. The hypertritons show up to be quite aligned to the properties of nuclear matter underlining the necessity of rescattering to transport the hyperons to the spectator matter.
On strangeness production in the reactions pp -> p Lambda^0 K^+ and pn -> n Lambda^0 K^+ near threshold
计算了pp -> p λ ^0 K ^+和pn -> n λ ^0 K ^+反应的截面。截面的理论比值R = sigma（pn -> n Lambda^0K^+）/ sigma（pp ->pΛ^0K^+）= 3表明，在奇异产生N Lambda^0K^+的阈值附近，pn相互作用相对于pp相互作用的增强。这种增强是由在同位旋单重态中的np相互作用的贡献引起的，其强于在同位旋三重态中的$pn$相互作用。为了证实这个结果，我们计算了反应pp -> pp pi ^0，pi ^0 p -> Lambda ^0 K^+和pi^-p -> Lambda ^0 K ^0在末态阈值附近的截面。理论截面与实验数据吻合较好。
We discuss strangeness production close to threshold in p+A and A+A collision. Comparing the body of available K+, K0, K-, and Lambda data with the IQMD transport code and for some key observables as well with the HSD transport code, we find good agreement for the large majority of the observables. The investigation of the reaction with help of these codes reveals the complicated interaction of the strange particles with hadronic matter which makes strangeness production in heavy-ion collisions very different from that in elementary interactions. We show how different strange particle observab…
Dynamics of strangeness production in the near threshold nucleon-nucleon collisions
在有效拉格朗日模型下研究了质子-质子碰撞中的奇异性λ K+和Σ 0 K+产生.两个核子之间的初始相互作用由π、ρ、ω和σ介子的交换来模拟，奇异度的产生通过N*（1650）、N*（1710）和N*（1720）重子共振的激发来进行。模型的参数在核子-核子-介子顶点处由核子-核子弹性散射与基于这四个介子交换的有效相互作用拟合确定，而共振顶点处的参数由已知的共振衰变宽度和矢量介子优势模型计算。COSY-11合作组最近的实验数据很好地描述了这种方法。在较高和较低的光束能量下，一π介子交换图主导着生产过程。在阈值能量附近，N*（1650）共振的激发主导两个产生通道。我们的模型与终态之间的相互作用的影响，包括在沃森-米格达尔近似，是能够解释所观察到的光束能量的依赖关系的总截面的比例，这两个反应。
Strangeness (K$^{0,+}$, $Λ$ and $Σ^{-,0,+}$) production in heavy-ion collisions near threshold energies has been investigated within the Lanzhou quantum molecular dynamics (LQMD) transport model. The kaon (anti-kaon)-nucleon and hyperon-nucleon potentials in dense nuclear matter are implemented in the model, which are computed from the chiral perturbation approach and the relativistic mean-field model, respectively. It is found that the in-medium potentials change the structure of transverse flow, and also affect the rapidity distributions and the inclusive spectra for strangeness production. …
We present results on deep sub threshold hyperon production in nuclear collisions, with the UrQMD transport model. Introducing anti-kaon+baryon and hyperon+hyperon strangeness exchange reactions we obtain a good description of experimental data on single strange hadron production in Ar+KCl reactions at $E_{lab}=1.76$ A GeV. We find that the hyperon strangeness exchange is the dominant process contributing to the $Ξ^-$ yield, however remains short of explaining the $Ξ^-/Λ$ ratio measured with the HADES experiment. We also discuss possible reasons for the discrepancy with previous studies and th…
I review the foundational motivation which led us to the ultra relativistic heavy ion collision research at SPS, RHIC and now LHC: the quantum vacuum structure; the deconfined nature of quark-gluon plasma (QGP) phase filling the Universe for the first 30$μ$s after the big-bang; the origin of stable matter mass; and of the origin of flavor. The special role of strangeness enhancement and strange antibaryon signature is highlighted. It is shown how hadron production can be used to determine the properties of QGP, and how the threshold energy for QGP formation is determined.
Strangeness Production Process $pp \to nK^ + Σ^ +$ within Resonance Model
基于COSY-11和COSY-ANKE发表的不一致的实验数据，我们探讨了$pp \to nK^ + Σ^ +$通道的产生机制和末态相互作用.在非相对论参数化研究中，$nΣ^ +$相互作用的散射参数$a> 0$被大的近阈值截面所支持，并且还表明了与$pp$相互作用相当的强$nΣ^ +$相互作用.在此基础上，计算了共振态$Δ^* (1920)$通过$π^ +$交换的贡献，计算结果表明，近阈值总截面很小，这与COSY-ANKE数据一致.通过引入亚阈值共振$Δ^*(1620)$，该模型对COSY-11公布的较大的近阈值总截面给出了更好的描述。
The details of the analysis of the near-threshold bump structure in the forward differential cross section of the ϕ-meson photoproduction to determine whether it is a signature of a resonance are presented. The analysis is carried out in an effective Lagrangian approach which includes Pomeron and (π,η) exchanges in the t channel, and contributions from the s- and u-channel excitations of a postulated nucleon resonance. In addition to the differential cross sections, we use the nine spin-density matrix elements (SDME) as recently measured, instead of the phi-meson decay angular distributions wh…
A novel, unorthodox picture of the dynamics of heavy ion collisions is developed using the concept of Hagedorn states. A prescription of the bootstrap of Hagedorn states respecting the conserved quantum numbers baryon number B, strangeness S, isospin I is implememted into the GiBUU transport model. Using a strangeness saturation suppression factor suitable for nucleon-nucleon-collisions, recent experimental data for the strangeness production by the HADES collaboration in Au+Au and Ar+KCl is reasonable well described. The experimental observed exponential slopes of the energy distributions are…
Strangeness Photoproduction with the Saphir Detector
用SAPHIR探测器在阈能至2.0 GeV的光子能量范围内收集了γp --> K^+ Λ和γp --> K^+ Λ ^0反应的总截面、微分截面角分布和超子反冲极化的统计改进数据。这里的总截面数据高达1.5 GeV。利用更高的统计量可以证实Λ和Λ偏振的符号相反以及前后方向的符号变化。观察到K^+ Λ总截面的陡峭阈值行为。
Impact of non-zero strangeness on thermodynamics of finite volume quark matter
该研究利用(2+1)味Polyakov夸克介子模型，探究有限体积与奇异数化学势对QCD临界点及手征相变边界的影响，明确了系统尺寸、奇异数化学势变化对应相变边界的不同偏移规律。
We study the in-medium effects in strangeness production in heavy-ion collisions at (sub-)\-threshold energies of 1 - 2 A GeV based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach. The in-medium modifications of the antikaon $(\bar K = K^-, \bar K^0)$ properties are described via the self-consistent coupled-channel unitarized scheme based on a SU(3) chiral Lagrangian which incorporates explicitly the $s-$ and $p-$ waves of the kaon-nucleon interaction. This scheme provides the antikaon potential, spectral functions and reaction cross sections as well as their depende…
High strangeness dibaryons in the extended quark delocalization, color screening model
利用扩展的夸克离域和色屏蔽模型研究了奇异度S=-2，-3，-4，-5，-6的候选重子.结果表明，只有少数几个有希望的低位双重子态：H和di-Omega可能是边缘强相互作用稳定的，但模型的不确定性太大，不允许任何明确的说法。SIJ=-3，1/2，2 N-Omega态比N-Omega阈值低62 MeV，比Lambda-Xi-pi阈值低24 MeV。它可能表现为一个窄的双重子共振，并通过重建Lambda-Xi两体衰变的顶点质量在RHIC探测器中被探测到。明确的K和η介子交换的影响进行了研究，发现在这个模型中可以忽略不计。讨论了夸克离域引起的有效中程吸引、σ介子交换和动能降低的机制。
Spectroscopy of excited baryons with strangeness $S=-2$ is stimulated by recent experimental developments. Here we focus on the $Ξ(1620)$ which locates close to the $\bar{K}Λ$ threshold. To take into account the threshold effects, we construct the coupled-channels meson-baryon scattering amplitude where the $Ξ(1620)$ appears as a resonance. We demonstrate that the $\bar{K}Λ$ threshold effects distort the peak of the $Ξ(1620)$ resonance from the simple Breit-Wigner distribution.
Comparison of Strangeness Production between A+A and p+p Reactions from 2 to 160 AGeV
测量的K $^+/π^+$比从重离子反应进行比较，从p+p反应的K $^+/π^+$比在能量范围2-160 AGeV。重离子反应中的K/ $π$增强在较低的能量下是最大的，与二次散射中的奇异性产生一致，在K介子产生阈值附近比初始碰撞变得相对更重要。从4到160 AGeV的增强稳步下降，这表明在整个能量范围内，强子再散射和弦衰变的增强机制可能是相同的。根据已有的数据，对40 AGeV/c的Pb+Pb反应，中快度$^+/π^+$比为$0.27\pm0.05$.
Pion and Strangeness Production as Signals of QCD Phase Transition
结果表明，在15 A GeV/c（BNL AGS）和160 A GeV/c（CERN SPS）碰撞能量范围内，中心核-核碰撞中π介子和奇异态的产生与形成夸克-胶子等离子体的假设是一致的.在统计方法的框架下解释的实验结果表明，在相变过程中，有效自由度增加了约3倍，并且在CERN SPS能量下产生的等离子体可能具有约280 MeV的温度（能量密度$\approx$ 10 GeV/fm^3）。为了局域化阈能和研究QCD相变的性质，迫切需要在20-160 A GeV/c能量范围内对中心Pb+Pb碰撞进行实验研究。
Strangeness and Pion Production as Signals of QCD Phase Transition
本文系统地分析了核子-核子和中心核-核碰撞中奇异性和π介子产生的实验数据。结果表明，在所有的碰撞能量的π/重子和奇异/π比表示饱和的碰撞核的大小。饱和能级的能量依赖性表明，跃迁到夸克-胶子等离子体发生在15 AGeV/c（BNL AGS）和160 AGeV/c（CERN SPS）碰撞能量之间。在统计方法的框架中解释的实验结果表明，在相变的过程中，自由度的有效数量增加，并且在CERN SPS能量下产生的等离子体可以具有约280 MeV（能量密度10 GeV/fm-3）的温度。相变的存在可以导致非单调的碰撞能量依赖的奇异/π比。在初始增加之后，比率应该下降到QGP的特征值。在过渡区以上，该比率预计与碰撞能量无关。为了局域化阈能和研究QCD相变的性质，迫切需要在能量范围为20- 160 AGeV/c的中心Pb+Pb碰撞实验研究。
We study the strangeness $S=-2$ baryon-baryon interactions in relativistic chiral effective field theory at leading order. Among the 15 relevant low energy constants, eight of them are determined by fitting to the state of the art lattice QCD data of the HAL QCD Collaboration (with $m_π=146$ MeV), and the rest are either taken from the study of the $S=-1$ hyperon-nucleon systems, assuming strict SU(3) flavor symmetry, or temporarily set equal to zero. Using the so-obtained low energy constants, we extrapolate the results to the physical point, and show that they are consistent with the availab…
Strange particles and hyperfragments in collisions of antiprotons and protons on nuclei have been investigated systematically within a microscopic transport model. The hyperons are produced from the annihilation in antibaryon-baryon collisions and strangeness exchange process in antiproton induced reactions. A coalescence approach is used for constructing the primary hyperfragments in phase space and the statistical model is modified for describing the decay of hyperfragments via evaporating hyperon, neutron, charged particles etc, in which the shell effect, binding energy and root-mean-square…
Lattice QCD Study of Positive Parity Dibaryons with Maximal Charm and Strangeness
本研究利用格点QCD方法，基于MILC系综计算了最大粲数、奇异数的单味双重子基态能谱，发现S=0道的Ωccc-Ωccc系统存在束缚态信号，为理解单味双重子性质提供了新结果。
We consider a physical scenario for ultra-relativistic heavy-ion collisions where, at the early stage, only transverse degrees of freedom of partons are thermalized, while the longitudinal motion is described by free streaming. When the energy density of the partonic system drops to a certain critical value, the partons hadronize and the newly formed hadronic system freezes out. This sudden change is described with the help of the Landau matching conditions followed by the simulations done with THERMINATOR. The proposed scenario reproduces well the transverse-momentum spectra, the elliptic flo…
The role of anti-kaons in the symmetry energy to be determined in heavy-ion collisions as for instance in such observables as the $π^-/π^+$ ratio is discussed using a simple chiral Lagrangian. It is shown, with some mild assumptions, that kaons, when present in the system, can affect the EoS appreciably for both symmetric and asymmetric nuclear matter. For nuclear matter with small asymmetry with which heavy-ion collisions are studied, it may be difficult to distinguish a stiff symmetry energy and the supersoft symmetry energy, even with kaons present. However the effect of kaon is found to be…
A combined study of the reactions $K^-p\rightarrow Σ^0π^0$, $Λπ^0$ and $\bar{K}^0n$ at low energies is carried out with a chiral quark-model approach. Good descriptions of the experimental observations are obtained. The roles of the low-lying strangeness $S=-1$ hyperon resonances in these processes are carefully analyzed. We find that: (i) In the $K^-p\rightarrow Σ^0π^0$ process, both $Λ(1405)S_{01}$ and $Λ(1520)D_{03}$ play dominant roles. Significant contributions of $Λ(1670)S_{01}$ and $Λ(1690)D_{03}$ could be seen around their threshold; (ii) In the $K^-p\rightarrow Λπ^0$ process, some obv…
Nucleon Resonances in Meson Nucleon Scattering with Strangeness Production
在耦合通道框架下，采用一种有效的拉格朗日模型来提取核子共振参数。在K矩阵近似下，我们同时分析了从π N到5种可能的介子-重子末态π N，pipi N，eta N，K λ和KSigma跃迁的所有数据，这些跃迁的能量范围从π N阈值到W = 2 GeV.在这项工作中，我们将重点放在K Sigma渠道上。特别是，我们包括一组1900 MeV附近的Delta共振：S31（1900），P31（1910）和P33（1920）状态。在大多数情况下，由拟合确定的核子共振参数与文献中普遍接受的值是一致的。我们发现在低能区，S11（1650），P11（1710）和P13（1720）态对p（pi-，K0）Sigma 0和p（pi-，K+）Sigma-过程是重要的，而P33（1600）和D33（1700）态对纯I = 3/2反应p（pi+，K+）Sigma+是重要的.在高能区，我们发现了一个在1945 MeV的D13态，这对p（pi-，K 0）Sigma 0反应是重要的，而在1900 MeV附近的Delta共振在p（pi-，K+）Sigma-和p（pi+，K+）Sigma+过程中显着。
Within the framework of quantum molecular dynamics transport model, the isospin and in-medium effects on the hyperon production in the reaction of $^{197}$Au + $^{197}$Au are investigated thoroughly. A repulsive hyperon-nucleon potential from the chiral effective field theory is implemented into the model, which is related to the hyperon momentum and baryon density. The correction on threshold energy of the elementary hyperon cross section is taken into account. It is found that the $Σ$ yields are suppressed in the domain of midrapidity and kinetic energy spectra with the potential. The hypero…
The reactions $pp\to pΛK^+$ and $pp\to pΣ^0K^+$ near their thresholds
在其阈值附近研究反应$pp\to pΛK^+$和$pp\to pΣ^0K^+$。奇异性产生过程由$π$ -和$K$交换机制描述。严格考虑了超子-核子系统中末态相互作用的影响。发现$Λ$的产生主要由$K$交换控制，而$K$ -以及$π$交换对于$Σ^0$情况起重要作用。它表明，实验观察到的强烈抑制$Σ^0$生产相比，$Λ$生产在相同的过剩能量可以解释由$π$和$K$之间的相消干涉交换反应$pp\to pΣ^0K^+$。指出了这种干扰对反应$pp\to nΣ^+K^+$的影响。
How strange: Phase diagrams with 3 critical points
本文证明手征平均场模型可产生含三个临界点的相图，涵盖核液-气相变、夸克退禁闭及奇异数驱动相变，并探讨其在重离子碰撞和中子星并合中的信号。
High-density symmetry energy from subthreshold hyperon production in heavy-ion collisions
该研究利用量子分子动力学输运模型分析阈下超子产生，表明 $Σ^{-}/Σ^{+}$ 可约束高密度对称能，而 $Ξ^{-}/Ξ^{0}$ 受其影响较弱。
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