12 Search Results

Whether or not femto-scale droplets of quark-gluon plasma (QGP) are formed in so-called small systems at high-energy colliders is a pressing question in the phenomenology of the strong interaction. For proton-proton or proton-nucleus collisions the answer is inconclusive due to the large theoretical uncertainties plaguing the description of these processes. While upcoming data on collisions of ¹⁶O nuclei may mitigate these uncertainties in the near future, here we demonstrate the unique possibilities offered by complementing ¹⁶O + ¹⁶O data with collisions of ²⁰Ne ions. We couple both nuclear lattice effective field theory (NLEFT) and projected generator coordinate method (PGCM) abmore » initio descriptions of the structure of ²⁰Ne and ¹⁶O to hydrodynamic simulations of ¹⁶O + ¹⁶O and ²⁰Ne + ²⁰Ne collisions at high energy. We isolate the imprints of the bowling-pin shape of ²⁰Ne on the collective flow of hadrons, which can be used to perform quantitative tests of the hydrodynamic QGP paradigm. In particular, we predict that the elliptic flow of ²⁰Ne + ²⁰Ne collisions is enhanced by as much as 1.174⁢(8)_stat⁢(31)_syst for NLEFT and 1.139⁢(6)_stat⁢(39)_syst for PGCM relative to ¹⁶O + ¹⁶O collisions for the 1% most central events. At the same time, theoretical uncertainties largely cancel when studying relative variations of observables between two systems. This demonstrates a method based on experiments with two light-ion species for precision characterizations of the collective dynamics and its emergence in a small system.« less

The System for Measuring Overlap with Gas (SMOG2) at the LHCb detector enables the study of fixed-target ion-ion collisions at relativistic energies ($$\sqrt{𝑠_{NN}}$$ ∼ 100 GeV in the center of mass). Here, with input from ab initio calculations of the structure of ¹⁶O and ²⁰Ne , we compute 3+1⁢D hydrodynamic predictions for the anisotropic flow of Pb+Ne and Pb+O collisions to be tested with upcoming LHCb data. This will allow the detailed study of quark-gluon plasma formation as well as experimental tests of the predicted nuclear shapes. Elliptic flow (𝑣₂) in Pb + Ne collisions is greatly enhanced compared tomore » the Pb + O baseline due to the shape of ²⁰Ne , which is deformed in a bowling-pin geometry. Owing to the large ²⁰⁸Pb radius, this effect is seen in a broad centrality range, a unique feature of this collision configuration. Larger elliptic flow further enhances the quadrangular flow (𝑣₄) of Pb + Ne collisions via nonlinear coupling, and impacts the sign of the kurtosis of the elliptic flow vector distribution (𝑐₂⁡{4}). Exploiting the shape of ²⁰Ne proves thus an ideal method to investigate the formation of quark-gluon plasma in fixed-target experiments at LHCb, and demonstrates the power of System for Measuring Overlap with Gas as a tool to image nuclear ground states.« less

Investigating nucleon-nucleon correlations inherent to the strong nuclear force is one of the core goals in nuclear physics research. We showcase the unique opportunities offered by collisions of ¹⁶O nuclei at high-energy facilities to reveal detailed many-body properties of the nuclear ground state. We interface existing knowledge about the geometry of ¹⁶O coming from ab-initio calculations of nuclear structure with transport simulations of high-energy ¹⁶O+¹⁶O collisions. Bulk observables in these processes, such as the elliptic flow or the fluctuations of the mean transverse momentum, are found to depend significantly on the input nuclear model and to be sensitive to realisticmore » clustering and short-range repulsive correlations, effectively opening a new avenue to probe these features experimentally. This finding demonstrates collisions of oxygen nuclei as a tool to elucidate initial conditions of small collision systems while fostering connections with effective field theories of nuclei rooted in quantum chromodynamics (QCD).« less

State-of-the-art hydrodynamic simulations of the quark-gluon plasma are unable to reproduce the elliptic flow of particles observed at the BNL Relativistic Heavy Ion Collider (RHIC) in relativistic ²³⁸U + ²³⁸U collisions when they rely on information obtained from low-energy experiments for the implementation of deformation in the colliding ²³⁸U ions. Here, we show that this is due to an inappropriate treatment of well-deformed nuclei in the modeling of the initial conditions of the quark-gluon plasma. Past studies have identified the deformation of the nuclear surface with that of the nuclear volume, though these are different concepts. In particular, a volumemore » quadrupole moment can be generated by both a surface hexadecapole and a surface quadrupole moment. This feature was so far neglected in the modeling of heavy-ion collisions, and is particularly relevant for nuclei like ²³⁸U, which is both quadrupole deformed and hexadecapole deformed. With rigorous input from Skyrme density functional calculations, we show that correcting for such effects in the implementation of nuclear deformations in hydrodynamic simulations restores agreement with BNL RHIC data. This brings consistency to the results of nuclear experiments across energy scales, and demonstrates the impact of the hexadecapole deformation of ²³⁸U on high-energy collisions.« less

The notion of the "size" of nucleons and their constituents plays a pivotal role in the current paradigm of the formation and the fluctuations of the quark-gluon plasma produced in high-energy nuclear collision experiments. Here, we report on state-of-the-art hydrodynamic results showing that the correlation between anisotropic flow, $$v^{2}_{n}$$, and the mean transverse momentum of hadrons, [$$p_t$$], possesses a unique sensitivity to the nucleon size in off-central heavy-ion collisions. We argue that existing experimental measurements of this observable support a picture where the relevant length scale characterizing the colliding nucleons is of order 0.5 fm or smaller, and we discussmore » the broad implications of this finding for future global Bayesian analyses aimed at extracting initial state and medium properties from nucleus-nucleus collision data, including $$v^{2}_{n}$$-[$$p_t$$] correlations. Determinations of the nucleon size in heavy-ion collisions will provide a solid independent constraint on the initial state of small system collisions, and will establish a deep connection between collective flow data in nucleus-nucleus experiments and data on deep inelastic scattering on protons and nuclei.« less

In the hydrodynamic framework of heavy-ion collisions, elliptic flow v₂ is sensitive to the quadrupole deformation β of the colliding ions. This enables one to test whether the established knowledge on the low-energy structure of nuclei is consistent with collider data from high-energy experiments. We derive a formula based on generic scaling laws of hydrodynamics to relate the difference in v₂ measured between collision systems that are close in size to the value of β of the respective species. We validate our formula in simulations of ²³⁸U + ²³⁸U and ¹⁹⁷Au + ¹⁹⁷Au collisions at top Relativistic Heavy Ion Collidermore » (RHIC) energy, and subsequently apply it to experimental data. Using the deformation of ²³⁸U from low-energy experiments, we find that RHIC v₂ data implies 0.16 ≲ | β | ≲ 0.20 for ¹⁹⁷Au nuclei, i.e., significantly more deformed than reported in the literature, posing an interesting issue in nuclear phenomenology.« less

Abstract We show that an event-shape engineering based on the mean transverse momentum of charged hadrons, $$$$[p_t]$$$$ $\left[p_t\right]$ , provides an optimal handle on the strength of the magnetic field created in central heavy-ion collisions at high energy. This is established through quantitative evaluations of the correlation existing between the event-by-event magnetic field produced by the spectator protons in 5.02 TeV Pb + Pb collisions and the event-by-event $$$$[p_t]$$$$ $\left[p_t\right]$ at a given collision centrality. We argue that the event selection basedmore » on $$$$[p_t]$$$$ $\left[p_t\right]$ provides a better handle on the magnetic field than the more traditional selection based on the event ellipticities. Advantages brought by this new method for the experimental search of the chiral magnetic effect are discussed.« less

Nuclides sharing the same mass number (isobars) are observed ubiquitously along the stability line. While having nearly identical radii, stable isobars can differ in shape, and present different quadrupole deformations. We show that even small differences in these deformations can be probed by relativistic nuclear collisions experiments, where they manifest as deviations from unity in the ratios of elliptic flow coefficients taken between isobaric systems. Collider experiments with isobars represent, thus, a unique means to gain precise knowledge of the geometric shape of atomic nuclei.

The correlation between the mean transverse momentum of outgoing particles, $$\langle{p_t}\rangle$$, and the magnitude of anisotropic flow, v_n, has recently been measured in Pb+Pb collisions at the CERN Large Hadron Collider, as a function of the collision centrality. Here, we confirm the previous observation that event-by-event hydrodynamics predicts a correlation between v_n and $$\langle{p_t}\rangle$$ that is similar to that measured in data. We show that the magnitude of this correlation can be directly predicted from the initial condition of the hydrodynamic calculation, for n = 2, 3, if one replaces v_n by the corresponding initial-state anisotropy, ε_n, and $$\langle{p_t}\rangle$$ bymore » the total energy per unit rapidity of the fluid at the beginning of the hydrodynamic expansion.« less