We report measurements of the $π^- p \to π^o n$ differential cross sections at six momenta (104-143 MeV/c) and four angles (0-40 deg) by detection of $γ$-ray pairs from $π^o \to γγ$ decays using the TRIUMF RMC spectrometer. This region exhibits a vanishing zero-degree cross section from destructive interference between s-- and p--waves, thus yielding special sensitivity to pion-nucleon dynamics and isospin symmetry breaking. Our data and previous data do not agree, with important implications for earlier claims of large isospin violating effects in low energy pion-nucleon interactions.
The strong interactions among nucleons have an approximate spin-isospin exchange symmetry that arises from the properties of quantum chromodynamics in the limit of many colors, $N_c$. However this large-$N_c$ symmetry is well hidden and reveals itself only when averaging over intrinsic spin orientations. Furthermore, the symmetry is obscured unless the momentum resolution scale is close to an optimal scale that we call $Λ_{{\rm large-}N_c}$. We show that the large-$N_c$ derivation requires a momentum resolution scale of $Λ_{{\rm large-}N_c} \sim 500$ MeV. We derive a set of spin-isospin exchan…
We have studied the possible isospin corrections on the skewness and kurtosis of net-baryon and net-charge fluctuations in the isospin asymmetric matter formed in relativistic heavy-ion collisions at RHIC-BES energies, based on a 3-flavor polyakov-looped Nambu-Jona-Lasinio model. With typical scalar-isovector and vector-isovector couplings leading to the splitting of $u$ and $d$ quark chiral phase transition boundaries and critical points, we have observed dramatic isospin effects on the susceptibilities, especially those of net-charge fluctuations. Reliable experimental measurements at even l…
Dipolar degrees of freedom and Isospin equilibration processes in Heavy Ion collisions
背景资料：在费米能级的重离子碰撞中，当不同荷质不对称性的核相互作用时，会发生同位旋平衡过程，从而得到核子-核子等矢量有效相互作用的信息。目的：本文对40 MeV/核子的48 Ca +27 Al系统，利用一个与同位旋平衡过程密切相关的、对碰撞动力学阶段敏感的可观测过程，研究了这一过程.从与动力学模型计算的比较中，我们还希望获得关于等矢量有效微观相互作用的信息。方法：的平均时间导数的总偶极子与所有发射的带电粒子和碎片的相对运动已确定从测量的电荷和速度，通过使用4？多探测器嵌合体半周边碰撞和不同的电荷Zb的最大产生的碎片的平均值已被确定。本文还讨论了在40 MeV/核子的27 Al +48 Ca和27 Al +40 Ca系统中所收集的实验证据。
用大阵列硅条探测器测量了入射能量为E/A=50 MeV的112 Sn +112 Sn和124 Sn +124 Sn碰撞中轻带电粒子和中等质量碎片的能谱。我们使用带电粒子的多重性检测到的阵列与近4 π的覆盖范围，以选择数据的中心碰撞事件。我们研究类似的比率的中子和质子谱，包括双比和产率比的t/3 He和Z=3至Z=8的碎片构建的不对称性的同位旋观测。利用能谱，我们可以把这些观测量构造成动能的函数。大多数碎片不对称观测值对连续衰变有很大的敏感性。
Isospin symmetry breaking (ISB) effects in the charge radius difference $ΔR_{\rm ch}$ of mirror nuclei are studied using the test example of ${}^{48}$Ca and ${}^{48}$Ni. This choice allows for a transparent study of ISB contributions since paring and deformation effects, commonly required for the study of mirror nuclei, can be neglected in this specific pair. The connection of $ΔR_{\rm ch}$ with the nuclear Equation of State and the effect of ISB on such a relation are discussed according to an Energy Density Functional approach. We find that nuclear ISB effects may shift the estimated value f…
Spin-isospin transitions in nuclei away from the valley of stability are essential for the description of astrophysically relevant weak interaction processes. While they remain mainly beyond the reach of experiment, theoretical modeling provides important insight into their properties. In order to describe the spin-isospin response,vcthe proton-neutron relativistic quasiparticle random phase approximation (PN-RQRPA) is formulated using the relativistic density-dependent point coupling interaction, and separable pairing interaction in both the $T=1$ and $T=0$ pairing channels. By implementing r…
We study isoscalar (IS) and isovector (IV) densities in ${}^{40} \mathrm{Ca}$ in comparison with theoretical densities calculated by Skyrme Hartree-Fock (HF) models. The charge symmetry breaking and the charge independence breaking forces are introduced to study the effect on the IV density. The effect of isospin mixing in the ground-state density is examined by using the particle-vibration coupling model taking into account the collective IV giant monopole excitation. We show a clear correlations in the IV density and isospin impurity of ${}^{40} \mathrm{Ca}$ within the HF and the particle-vi…
We investigate the isospin transport with 40,48 Ca+ 40,48 Ca reactions at 35 MeV/nucleon, measured with the coupling of the VAMOS high acceptance spectrometer and the INDRA charged particle multidetector. Using the quasi-projectile remnant measured with VAMOS and carefully selected light-charged-particles measured in coincidence with INDRA, a reconstruction method is applied to estimate the excited quasi-projectile (QP) on an event-by-event basis. The isospin diffusion is investigated using the isospin transport ratio with the asymmetry $δ$ = (N -- Z)/A of the projectile as an isospin-sensitiv…
Evidence of isospin-symmetry violation in high-energy collisions of atomic nuclei: Theoretical and Phenomenological considerations
Warsaw University of Technology（华沙理工大学）；Jan Kochanowski University（扬·科哈诺夫斯基大学）；Bogolyubov Institute for Theoretical Physics（博戈柳博夫理论物理研究所）；University of Houston（休斯顿大学）；Kalinga Institute of Industrial Technology（卡林加工业技术学院）
The $Λ$ separation energies in the mirror hypernuclei ${_Λ^4}{\rm H}-{_Λ^4}{\rm He}$ exhibit large charge symmetry breaking (CSB). Analyzing this CSB within pionless effective field theory while using partially conserved baryon-baryon SU(3) flavor symmetry, we deduce a $Λ-Σ^0$ induced in-medium admixture amplitude ${\cal A}_{I=1}\approx 1.5\%$ in the dominantly isospin $I=0$ $Λ$ hyperon. Our results confirm the free-space value ${\cal A}^{(0)}_{I=1}$ inferred directly within the SU(3) baryon octet by Dalitz and von-Hippel in 1964 and reaffirmed in a recent QCD+QED lattice calculation. Furtherm…
