Tue·Jun 7, 2022Tuesday·June 7, 2022

1. 01*

   Ratios of collective flow observables in high-energy isobar collisions are insensitive to final state interactions

   Chunjian Zhang🇺🇸 · Somadutta Bhatta🇺🇸 · Jiangyong Jia🇺🇸

   The ratios of bulk observables, such as harmonic flow $v_2$ and $v_3$, between high-energy ${}^{96}$Ru+${}^{96}$Ru and ${}^{96}$Zr+${}^{96}$Zr collisions were recently argued to be a clean probe of the nuclear structure differences between ${}^{96}$Ru and ${}^{96}$Zr. Using a transport model simulation of isobar collisions, we quantify this claim from the dependence of the ratios $v_{2,\mathrm{Ru}}/v_{2,\mathrm{Zr}}$ and $v_{3,\mathrm{Ru}}/v_{3,\mathrm{Zr}}$ on various final state effects, such as the shear viscosity, hadronization and hadronic cascade. Although the $v_2$ and $v_3$ change by more than 50% when varying the final state effects, the ratios are unchanged. In addition, these ratios are independent of the transverse momentum $p_{\mathrm{T}}$ and hadron species, despite of up to a factor of two change in $v_n$. The ratio of mean transverse momentum $⟨p_{\mathrm{T}}⟩$ is found to be controlled by the nuclear skin and nuclear radius, but is only slightly impacted by the final state effects. Therefore, these isobar ratios serve as a clean probe of the initial condition of the quark-gluon plasma, which in turn is controlled by the collective structure of the colliding nuclei.

   ↳ nucl-thhep-exhep-phnucl-exPRC(2022)·42 citations
2. 02*

   Extended optimal Fermi averaging for near-recoilless $\Lambda$ production in the ($K^{-}$, ${\pi }^{-}$) reaction on nuclei

   Toru Harada🇯🇵 · Yoshiharu Hirabayashi🇯🇵

   We propose to extend the optimal Fermi averaging procedure theoretically in order to calculate an in-medium $K^{-}n\to {\pi }^{-}\Lambda$ amplitude for the exothermic ($K^{-}$, ${\pi }^{-}$) reaction on nuclei in the framework of a distorted-wave impulse approximation, taking into account the local momentum transfer generated by semiclassical distorted waves for $K^{-}$ and ${\pi }^{-}$ mesons. Angular distributions for the ${}^{12}$C($K^{-}$, ${\pi }^{-}$)${}_{\Lambda }^{12}$C reaction in which a momentum transfer is $q\lesssim$ 80 MeV/$c$ at $p_K=$ 800 MeV/$c$ in the ${\pi }^{-}$ forward direction, are estimated by applying the extended procedure. The result shows that the calculated angular distributions are in good agreement with those of the data, and this extension is a successful prescription making it possible to describe the reaction cross sections in near-recoilless reactions such as ($K^{-}$, ${\pi }^{-}$) in our framework.

   ↳ nucl-thnucl-exPRC(2022)·4 citations
3. 03*

   Relation to a property of the angular momentum zero space of states of four fermions in an angular momentum $j=9/2$ shell unexpectedly found to be stationary for any rotationally invariant two-body interaction

   K. Neergård

   The existence of states with angular momenta $I=4$ and~6 of four fermions in an angular momentum $j=9/2$ shell that are stationary for any rotationally invariant two-body interaction despite the presence of other states with the same angular momentum, the Escuderos-Zamick states, is shown to be equivalent to the invariance to any such interaction of the span of states generated from $I=0$ states by one-body operators. This invariance is verified by exact calculation independently of previous verifications of the equivalent statement. It explains the occurrence of the Escuderos-Zamick states for just $I=4$ and 6. The action of an arbitrary interaction on the invariant space and its orthogonal complement is analyzed, leading to a relation of the Escuderos-Zamick energy levels to levels with $I=10$ and 12. Parts of the observed spectra of ${}^{72}$Ni, ${}^{74}$Ni, ${}^{94}$Ru, ${}^{96}$Pd, ${}^{212}$Rn, and ${}^{214}$Ra are discussed in the light of this relation.

   ↳ nucl-thnucl-exPRC(2022)·4 citations
4. 04*

   A unified picture of medium-induced radiation

   Johannes Hamre Isaksen🇳🇴 · Adam Takacs🇳🇴 · Konrad Tywoniuk🇳🇴

   We revisit the picture of jets propagating in the quark-gluon plasma. In addition to vacuum radiation, partons scatter on the medium constituents resulting in induced emissions. Analytical approaches to including these interactions have traditionally dealt separately with multiple, soft, or rare, hard scatterings. A full description has so far only been available using numerical methods. We achieve full analytical control of the relevant scales and map out the dominant physical processes in the full phase space. To this aim, we extend existing expansion schemes for the medium-induced spectrum to the Bethe--Heitler regime. This covers the whole phase space from early to late times, and from hard splittings to emissions below the thermal scale. Based on the separation of scales, a space-time picture naturally emerges: at early times, induced emissions start to build from rare scatterings with the medium. At a later stage, induced emissions due to multiple soft scatterings result in a turbulent cascade that rapidly degrades energy down to, and including, the Bethe--Heitler regime. We quantify the impact of such an improved picture, compared to the current state-of-the-art factorization that includes only soft scatterings, by both analytical and numerical methods for the medium-induced energy distribution function. Our work serves to improve our understanding of jet quenching from small to large systems and for future upgrades of Monte Carlo generators.

   ↳ hep-phhep-exnucl-exnucl-thJHEP(2023)·25 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.