Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2509.12399

Unveiling the shape of the $^{20}$Ne nucleus by measuring the flow coefficients with cumulants in PbNe and PbAr collisions at $\sqrt{s_{NN}} = 70.9$ GeV

LHCb collaboration
View original source ↗Read source document ↗Export metadata ↓

Abstract

The anisotropic flow coefficients $v_n$ quantify the collective medium response to the initial spatial anisotropy of the overlapping region in ion collisions and serve as sensitive probes of both the medium properties and shape of nuclear initial states. In this analysis, the $v_2$ and $v_3$ parameters of prompt charged particles are measured using the multiparticle cumulant method in fixed-target PbNe and PbAr collisions at $\sqrt{s_{NN}} = 70.9$ GeV, collected by LHCb using the SMOG2 gas-target system during the 2024 LHC lead-beam run. The cumulant method is first validated using 2018 PbPb collision data, successfully reproducing previous measurements obtained via the two-particle correlation method. Results for the fixed-target collisions are then presented, showing a significantly larger value of the elliptic flow coefficient $v_2$ in central PbNe with respect to PbAr collisions. This is qualitatively consistent with 3+1D hydrodynamic predictions including ab-initio descriptions of the nuclear structure. The results provide the first experimental confirmation of the distinctive bowling-pin shape of the ground-state $^{20}$Ne nucleus, validating at the same time the hydrodynamic description of the hot medium formed in high-energy collisions involving light ions.

Explore related subjects

nucl-exhep-ex

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

LHCb collaboration. 2025-09-15. Unveiling the shape of the $^{20}$Ne nucleus by measuring the flow coefficients with cumulants in PbNe and PbAr collisions at $\sqrt{s_{NN}} = 70.9$ GeV. https://arxiv.org/abs/2509.12399

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Jet-like di-hadron correlations in pO, OO, and Ne--Ne collisions

Heavy-ion collisions are primarily studied to investigate the properties of hot and dense nuclear matter, known as the quark--gluon plasma (QGP). However, recent observations of hydrodynamic flow-like behaviour in pp and p--Pb collisions at the LHC suggest the possible formation of QGP droplets even in small collision systems. To bridge the multiplicity gap between small and large systems and to examine the applicability of hydrodynamic descriptions, light-ion collisions were performed for the first time at the LHC in 2025. This contribution presents measurements of the near-side peak width of di-hadron correlations in pO, OO, and Ne--Ne collisions with ALICE, used to search for medium effects. The width of the near-side correlation peak is studied as a function of the average charged-particle multiplicity at midrapidity. At low transverse momentum ($p_{\rm T}$), the near-side peak is broader in OO and Ne--Ne collisions than in pp and pO collisions, and in central collisions its width approaches that measured in Pb--Pb collisions. At higher $p_{\rm T}$ the peak narrows modestly with increasing multiplicity. The results are compared with PYTHIA, AMPT, and JETSCAPE calculations, none of which reproduces the measured widths over the full kinematic range.

nucl-ex↗
arXiv2026

Electromagnetic transition strength in $^{53}$Ca: the lifetime of the $5/2^{-}$ state

High-resolution in-beam $γ$-ray spectroscopy of $^{53}$Ca was performed at the Radioactive Isotope Beam Factory (RIBF) at RIKEN. Excited states in $^{53}$Ca were populated via one-neutron and one-proton removal reactions from a $^{55}$Sc radioactive beam, and the emitted $γ$ rays were detected using the HiCARI hybrid germanium detector array. The lifetime of the first excited $5/2^{-}$ state in $^{53}$Ca was measured for the first time through an analysis of Doppler-roadened $γ$-ray line shapes arising from relativistic recoil velocities. A lifetime of $τ = 11.3_{-11.3}^{+5.3(stat)+3(sys)}$ ps was deduced, corresponding to a reduced transition probability of $B(E2;5/2^{-}{\rightarrow}1/2^{-}) > 2.6 e^{2}fm^{4}$ at the 1$σ$ level, with a best-fit value of $4.5 e^{2}fm^{4}$. The measured transition strength is compared with state-of-the-art shell-model and ab initio calculations, providing a stringent benchmark for shell-model Hamiltonians and effective charges and modern ab initio descriptions of the neutron-rich calcium isotopes approaching the potential $N$ = 40 shell closure.

nucl-ex↗
arXiv2026

Measurements of $γ_v p \to π^+ π^-p'$ Cross Sections with the CLAS12 Detector for $Q^2$ from 2.4-8.0 GeV$^2$ and $W$ from 1.4-2.1 GeV

This paper reports exclusive cross sections for the $ep \to e'π^+π^-p'$ reaction using the CLAS12 detector at Jefferson Laboratory. The extractions of fully integrated and nine single-differential cross sections are presented for the first time for photon virtualities $Q^2$ from 2.4 to 8.0 GeV$^2$ and center-of-mass energies $W$ from 1.4 to 2.1 GeV, which covers a large part of the nucleon resonance region. These data considerably extend the kinematic reach of previous measurements from CLAS that covered $Q^2$ up to 5.0 GeV$^2$. Exclusive $γ_v p \to π^+ π^-p'$ cross section measurements are of particular importance for the extraction of $γ_vpN^*$ resonance electrocouplings across the $N^*$ spectrum, especially in the mass range above 1.6 GeV where several resonances decay preferentially to the $ππN$ final states. The electrocouplings with extended $Q^2$ coverage expected from these new data will enable an improved understanding of the emergence of $N^*$ mass and structure in the transition from the strongly coupled toward the perturbative QCD regime.

nucl-ex↗