Fig 7 - available via license: Creative Commons Attribution 4.0 International
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(Colour online.) Space-time diagram of a heavy-ion collision of two nuclei colliding at time t=0 and longitudinal position z=0 (transverse direction not shown). The evolution goes from a hot-fireball in a pre-equilibrium phase through the formation of a QGP, followed by a cross-over phase transition to a hadron gas. The fireball formed in the collision emits different kinds of particles (indicated by the arrows). The temperatures crossed during the evolution are T c , T chem and T kin . For further details see text. (Figure courtesy of Boris Hippolyte).
Source publication
Loosely-bound objects such as light nuclei are copiously produced in proton-proton and nuclear collisions at the Large Hadron Collider (LHC), despite the fact that typical energy scales in such collisions exceed the binding energy of the objects by orders of magnitude. In this review we summarise the experimental observations, put them into context...
Context in source publication
Context 1
... schematic picture of the evolution through the different phases of a collision of two relativistic nuclei is displayed in Fig. 7. It displays the collision of two nuclei traveling with (nearly) the speed of light and exhibits the different phases of the created fireball while cooling down. In fact, the expansion in z-direction (beam direction) is the main cooling mechanism in these collisions, and this one-dimensional space-time picture is fully analytically ...
Citations
... This qualitative behavior disfavors the magnetic field, although the errors are still large. It should be noted, however, that this analysis is based on the assumption of the thermal production mechanism for light nuclei (see, e.g., [49] for an overview) and may not apply if another mechanism, such as coalescence, is assumed instead. ...
We study the influence of an external magnetic field on hadron yields and fluctuations in a hadron resonance gas by performing calculations within an updated version of the open-source Thermal-FIST package. The presence of the magnetic field has a sizable influence on certain hadron yield ratios. Most notably, it leads to enhanced $ p/pi$ and suppressed $n/p$ ratios, which may serve as a magnetometer in heavy-ion collisions. By attributing the centrality dependence of the $p/\pi$ ratio in Pb-Pb collisions at 5.02 TeV measured by the ALICE Collaboration entirely to the magnetic field, we estimate its maximal strength at freeze-out to be $eB \simeq 0.12$~GeV$^2 \simeq 6.3 m_\pi^2$ in peripheral collisions. The magnetic field also enhances various conserved charge susceptibilities, which is qualitatively consistent with recent lattice QCD data and is driven in the HRG model by the increase of hadron densities. However, the variances of hadrons do not show any enhancement when normalized by the means, therefore, measurements of second-order fluctuations in heavy-ion collisions do not appear to offer additional information about the magnetic field relative to mean multiplicities.
... The study of light nuclei production in heavy-ion collisions has received increased interest both experimentally [1][2][3][4][5][6] and theoretically [7][8][9][10][11][12][13] due to its relevance in probing the critical point of strongly interacting matter [14][15][16][17][18][19][20][21][22][23][24] and indirect dark matter searches [25,26]. ...
The production of light nuclei in isobaric $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr collisions, ranging from $\sqrt{s_{NN}}$ = 7.7 to 200 GeV, are studied using the string melting version of A Multi Phase Transport (AMPT) model in combination with a coalescence approach to light nuclei production. From the calculated yields, transverse momentum $p_{T}$ spectra, and rapidity dependences of light nuclei $p$, $n$, $d$, $t$, ${}^{3}$He, we find that the Ru+Ru/Zr+Zr ratios for the yields of these particles exceed unity with the inclusion of a quadrupole deformation $\beta_{ 2 }$ and octupole deformation $\beta_{ 3 }$ as well as the neutron skins. We also find that heavier particles have a larger deviation from unity. Furthermore, we find that as the collision energy increases, the influence of isospin effects on the production of light nuclei in isobar collisions gradually decreases, while the influence of nuclear structure becomes more significant, particularly evident from the energy dependence of the deuteron ratio, which is unaffected by isospin effects.
... As a specific group of observables in relativistic heavy ion collisions [1][2][3][4][5][6][7][8][9][10][11][12], light nuclei such as the deuteron (d), triton (t), helium-3 ( 3 He), and helium-4 ( 4 He) have been under active investigation in recent decades both in experiment [13][14][15][16][17][18][19][20][21][22][23] and theory [24][25][26][27][28][29]. The STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC) and the ALICE experiment at the CERN Large Hadron Collider (LHC) have collected a wealth of data on light nucleus production. ...
... The STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC) and the ALICE experiment at the CERN Large Hadron Collider (LHC) have collected a wealth of data on light nucleus production. These data exhibit some fascinating features, especially their non-trivial energydependent behaviors in a wide collision energy range from the GeV to TeV scale [17][18][19][20][21][22][23]. Theoretical studies have also made significant progress. ...
... cent nucleons in the phase space, possesses unique characteristics. Many current experimental observations at high RHIC and LHC energies favor nucleon coalescence [18,19,22,23,[49][50][51]. Recently, the STAR collaboration extended the beam energy scan program to lower collision energies and published the data of both hadrons and light nuclei in Au-Au collisions at GeV [52][53][54][55]. ...
We study the production of light nuclei in the coalescence mechanism of Au-Au collisions at midrapidity at GeV. We derive analytic formulas of the momentum distributions of two bodies, three bodies, and four nucleons coalescing into light nuclei and naturally explain the transverse momentum spectra of the deuteron ( d ), triton ( t ), helium-3 ( ³ He), and helium-4 ( ⁴ He). We reproduce data on the yield rapidity densities, yield ratios, and averaged transverse momenta of d , t , ³ He, and ⁴ He and provide the proportions of contributions from different coalescence sources for t , ³ He, and ⁴ He in their production. We find that besides nucleon coalescence, nucleon+nucleus coalescence and nucleus+nucleus coalescence may play requisite roles in light nucleus production in Au-Au collisions at GeV.
... The hypertriton ( 3 H) is a bound state of a proton, a neutron, and a hyperon, which can be produced via coalescence in collisions [10,11]. Hypernuclei provide experimental access to the hyperon-nucleon interaction through the measurement of their lifetimes and of their binding energies [12,13]. ...
... A related problem is the production of loosely bound nuclei and antinuclei in heavy-ion collisions [13][14][15]. The deuteron has a binding energy of only 2.2 MeV. ...
A bstract
The thermal corrections to the propagator of a loosely bound charm-meson molecule in a pion gas are calculated to next-to-leading order in the heavy-meson expansion using a zero-range effective field theory. Ultraviolet divergences in the charm-meson-pair self energy are canceled by corrections to the charm-meson-pair contact vertex. Terms that are singular at the charm-meson-pair threshold can be absorbed into thermal corrections to the rest energies and kinetic masses of the charm-meson constituents. The remaining terms reduce to a thermal correction to the binding momentum that is proportional to the pion number density and suppressed by the pion/charm-meson mass ratio. The correction gives a tiny decrease in the binding energy of the charm-meson molecule relative to the charm-meson-pair threshold in the pion gas and a change in its thermal width that is small compared to the thermal widths of the charm-meson constituents. These results are encouraging for the prospects of observing X (3872) and $$ {T}_{cc}^{+}(3875) $$ T cc + 3875 in the expanding hadron gas produced by heavy-ion collisions.
... Since the Λ separation energy (B Λ = 0.162±0.044 MeV [15] is so small it is often imagined as a deuteron core with a Λ with a distance of about ⟨r 2 dΛ ⟩ ≈ 10.6 fm [17,18]. If one does a more sophisticated calculation [16,18,19] one can also determine the rms radius ( ⟨r 2 ⟩) of the whole object. ...
... One might say that from the current most situation is cleared up, but taking all measurements (also the new preliminary result from HADES [40]) into account and building an average (visible from the blue dashed line in Fig. 4 and the resulting uncertainty in the blue shaded band) one gets a 4.2σ distance even taking the uncertainty of the PDG value of the Λ [39] into account. So from that perspective the "hypertriton puzzle" [17] is not solved yet. ...
This article summarizes some of the current theoretical developments and the experimental status of hypernuclei in relativistic heavy-ion collisions and elementary collisions. In particular, the most recent results of hyperhydrogen of mass A = 3 and 4 are discussed. The highlight at SQM2022 in this perspective was the discovery of the anti-hyperhydrogen-4 by the STAR Collaboration, in a large data set consisting of different collision systems. Furthermore, the production yields of hyperhydrogen-4 and hyperhelium-4 from the STAR Collaboration can be described nicely by the thermal model when the excited states of these hypernuclei are taken into account. In contrast, the production measurements in small systems (pp and p–Pb) from the ALICE Collaboration tends to favour the coalescence model over the thermal description. New measurements from STAR, ALICE and HADES Collaborations of the properties, e.g. lifetime, of A = 3 and 4 hypernuclei give similar results of these properties. Also the anti-hyperhydrogen-4 lifetime is in rather good agreement with previous measurements. Interestingly, the new STAR measurement on the R3 value, that is connected to the branching ratio, points to a Λ separation energy that is below 100 keV but definitely consistent with the value of 130 keV assumed since the 70s.
... Figure 10 derived from Refs. [109,110] highlights the expected yield for light hypernuclei at the collision energies covered by NA60+, according to the Statistical Hadronisation Model (SHM). Thanks to the large integrated luminosity, a copious amount of hypernuclei is expected to be detected in NA60+. ...
... Statistical Hadronisation Model predictions[109,110] for the yield of nuclei, antinuclei and antinuclei in 10% most central Pb-Pb collisions as a function of the collision energy. The green box highlights the energy region explored by NA60+. ...
We propose a new fixed-target experiment for the study of electromagnetic and hard probes of the Quark-Gluon Plasma (QGP) in heavy-ion collisions at the CERN SPS. The experiment aims at performing measurements of the dimuon spectrum from threshold up to the charmonium region, and of hadronic decays of charm and strange hadrons. It is based on a muon spectrometer, which includes a toroidal magnet and six planes of tracking detectors, coupled to a vertex spectrometer, equipped with Si MAPS immersed in a dipole field. High luminosity is an essential requirement for the experiment, with the goal of taking data with 10$^6$ incident ions/s, at collision energies ranging from $\sqrt{s_{\rm NN}} = 6.3$ GeV ($E_{\rm lab}= 20$ A GeV) to top SPS energy ($\sqrt{s_{\rm NN}} = 17.3$ GeV, $E_{\rm lab}= 158$ A GeV). This document presents the physics motivation, the foreseen experimental set-up including integration and radioprotection studies, the current detector choices together with the status of the corresponding R&D, and the outcome of physics performance studies. A preliminary cost evaluation is also carried out.
... State-of-the-art SHM and coalescence model provide similar predictions for the yields of (anti)nuclei [41][42][43]. Possibilities to discriminate between the two approaches could come from the study of the production yields of different nuclei that differ in size. The coalescence model, indeed, is sensitive to the size of the nucleus, in particular to the relation between nuclear size and emission source size [36,38]. ...
... In order to investigate the dependence of the coalescence probability on the size of the particle emitting source, as suggested by state-of-the-art coalescence models [41][42][43], the B 2 parameters extracted in several collision systems and LHC energies [2, 4-7, 9, 10, 13, 14, 52, 83-85] are compared as a function of the charged-particle multiplicity for a fixed value of p T /A in Fig. 3. The measurements show a smooth transition from low to high charged-particle multiplicity densities, which correspond to an increasing system size. ...
Measurements of (anti)proton, (anti)deuteron, and (anti)$^3$He production in the rapidity range $-1<y< 0$ as a function of the transverse momentum and event multiplicity in p-Pb collisions at a center-of-mass energy per nucleon-nucleon pair $\sqrt{s_{\rm NN}} = 8.16$ TeV are presented. The coalescence parameters $B_2$ and $B_3$, measured as a function of the transverse momentum per nucleon and of the mean charged-particle multiplicity density, confirm a smooth evolution from low to high multiplicity across different collision systems and energies. The ratios between (anti)deuteron and (anti)$^3$He yields and those of (anti)protons are also reported as a function of the mean charged-particle multiplicity density. A comparison with the predictions of the statistical hadronization and coalescence models for different collision systems and center-of-mass energies favors the coalescence description for the deuteron-to-proton yield ratio with respect to the canonical statistical model.
... The formation probability of light antinuclei (up to mass number A = 4) is currently studied at accelerators. By now, several models successfully describe light-antinuclei production yields [33][34][35][36][37] . Such models are based on either the statistical hadronization 12,[38][39][40] or coalescence approach 41-45 . ...
In our Galaxy, light antinuclei composed of antiprotons and antineutrons can be produced through high-energy cosmic-ray collisions with the interstellar medium or could also originate from the annihilation of dark-matter particles that have not yet been discovered. On Earth, the only way to produce and study antinuclei with high precision is to create them at high-energy particle accelerators. Although the properties of elementary antiparticles have been studied in detail, the knowledge of the interaction of light antinuclei with matter is limited. We determine the disappearance probability of 3He¯ when it encounters matter particles and annihilates or disintegrates within the ALICE detector at the Large Hadron Collider. We extract the inelastic interaction cross section, which is then used as an input to the calculations of the transparency of our Galaxy to the propagation of 3He¯ stemming from dark-matter annihilation and cosmic-ray interactions within the interstellar medium. For a specific dark-matter profile, we estimate a transparency of about 50%, whereas it varies with increasing 3He¯ momentum from 25% to 90% for cosmic-ray sources. The results indicate that 3He¯ nuclei can travel long distances in the Galaxy, and can be used to study cosmic-ray interactions and dark-matter annihilation. Measurements of the inelastic cross section of anti-3He allow the estimation of the transparency of the Milky Way to the propagation of these light antinuclei produced in either cosmic-ray collisions or annihilation of dark-matter particles.
... The coalescence scenario can be tested by computing the coalescence parameter B A (see for instance Ref. [80] and references therein). Under the assumption of equal production of protons and neutrons, it is defined as ...
The measurement of the production of deuterons, tritons and $^{3}\mathrm{He}$ and their antiparticles in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV is presented in this article. The measurements are carried out at midrapidity ($|y| < $ 0.5) as a function of collision centrality using the ALICE detector. The $p_{\rm T}$-integrated yields, the coalescence parameters and the ratios to protons are reported and compared with nucleosynthesis models. The comparison of these results in different collision systems at different centre-of-mass collision energies reveals a suppression of nucleus production in small systems. In the Statistical Hadronisation Model framework, this can be explained by a small correlation volume where the baryon number is conserved, as already shown in previous fluctuation analyses. However, a different size of the correlation volume is required to describe the proton yields in the same data sets. The coalescence model can describe this suppression by the fact that the wave functions of the nuclei are large and the fireball size starts to become comparable and even much smaller than the actual nucleus at low multiplicities.
