Baryon anti-Baryon Photoproduction Cross Sections off the Proton

Afzal, F. ; Albrecht, M. ; Amaryan, M. ; et al.
2025.
Inspire Record 3075566 DOI 10.17182/hepdata.166629

The GlueX experiment at Jefferson Lab has observed $p\bar{p}$ and, for the first time, $Λ\barΛ$ and $p\barΛ$ photoproduction from a proton target at photon energies up to 11.6 GeV. The angular distributions are forward peaked for all produced pairs, consistent with Regge-like $t$-channel exchange. Asymmetric wide-angle anti-baryon distributions show the presence of additional processes. In a phenomenological model, we find consistency with a double $t$-channel exchange process where anti-baryons are created only at the middle vertex. The model matches all observed distributions with a small number of free parameters. In the hyperon channels, we observe a clear distinction between photoproduction of the $Λ\barΛ$ and $p\barΛ$ systems but general similarity to the $p\bar{p}$ system. We report both total cross sections and cross sections differential with respect to momentum transfer and the invariant masses of the created particle pairs. No narrow resonant structures were found in these reaction channels. The suppression of $s\bar{s}$ quark pairs relative to $d\bar{d}$ quark pairs is similar to what has been seen in other reactions.

10 data tables

Measured $\frac{d\sigma}{dm_{\Lambda\bar{\Lambda}}}~[\mathrm{nb/GeV}]$ for reaction $\gamma p\to \{\Lambda \bar{\Lambda}\} p$ including data of $6.5 \leq E_{\gamma} \leq 11.5$ [GeV], splitted in 10 energy bins (each as a column in the table). The observable $m_{\Lambda\bar{\Lambda}}$ is in unit of $[\mathrm{nb/GeV}]$ and is divided into bins of width 0.05 $[\mathrm{GeV}]$ (each as a row in the table). The global systematic uncertainty is 19% (not included in the table), with contributions of 5% from kinematic fitting, 10% from data selection, 5% from flux normalization, 13% from tracking efficiency, 3% from model dependence, and 6% from run-period variations.

Measured $\frac{d\sigma}{dm_{p\bar{\Lambda}}}~[\mathrm{nb/GeV}]$ for reaction $\gamma p\to \{p \bar{\Lambda}\} \Lambda$ including data of $6.5 \leq E_{\gamma} \leq 11.5$ [GeV], splitted in 10 energy bins (each as a column in the table). The observable $m_{p\bar{\Lambda}}$ is in unit of $[\mathrm{nb/GeV}]$ and is divided into bins of width 0.1 $[\mathrm{GeV}]$ (each as a row in the table). The global systematic uncertainty is 22% (not included in the table), with contributions of 2% from kinematic fitting, 10% from data selection, 5% from flux normalization, 15% from tracking efficiency, 3% from model dependence, and 10% from run-period variations.

Measured $\frac{d\sigma}{dm_{p\bar{p}}}~[\mathrm{nb/GeV}]$ for reaction $\gamma p\to \{p \bar{p}\} p$ including data of $3.5 \leq E_{\gamma} \leq 11.5$ [GeV], splitted in 15 energy bins (each as a column in the table). The observable $m_{p\bar{p}}$ is in unit of $[\mathrm{nb/GeV}]$ and is divided into bins of width 0.044 $[\mathrm{GeV}]$ (each as a row in the table). The global systematic uncertainty is 13% (not included in the table), with contributions of 8% from kinematic fitting, 4% from data selection, 5% from flux normalization, 8% from tracking efficiency, 3% from model dependence, and 1% from run-period variations.

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Imaging nuclear shape through anisotropic and radial flow in high-energy heavy-ion collisions

The EMAIL:star-publication@bnl.gov & STAR collaborations
Rept.Prog.Phys. 88 (2025) 108601, 2025.
Inspire Record 2937844 DOI 10.17182/hepdata.159930

Most atomic nuclei exhibit ellipsoidal shapes characterized by quadrupole deformation $β_2$ and triaxiality $γ$, and sometimes even a pear-like octupole deformation $β_3$. The STAR experiment introduced a new "imaging-by-smashing" technique [arXiv:2401.06625, arXiv:2501.16071] to image the nuclear global shape by colliding nuclei at ultra-relativistic speeds and analyzing outgoing debris. Features of nuclear shape manifest in collective observables like anisotropic flow $v_n$ and radial flow via mean transverse momentum $[p_{\mathrm{T}}]$. We present new measurements of the variances of $v_n$ ($n=2$, 3, and 4) and $[p_{\mathrm{T}}]$, and the covariance of $v_n^2$ with $[p_{\mathrm{T}}]$, in collisions of highly deformed $^{238}$U and nearly spherical $^{197}$Au. Ratios of these observables between the two systems effectively suppress common final-state effects, isolating the strong impact of uranium's deformation. By comparing results with state-of-the-art hydrodynamic model calculations, we extract $β_{2\mathrm{U}}$ and $γ_{\mathrm{U}}$ values consistent with those deduced from low-energy nuclear structure measurements. Measurements of $v_3$ and its correlation with $[p_{\mathrm{T}}]$ also provide the first experimental suggestion of a possible octupole deformation for $^{238}$U. These findings provide significant support for using high-energy collisions to explore nuclear shapes on femtosecond timescales, with implications for both nuclear structure and quark-gluon plasma studies.

169 data tables

Data from Figure 2, panel a, $p(N_{ch}^{rec})$

Data from Figure 2, panel b, $p(N_{ch}^{rec})$

Data from Figure 3, panel a, Au+Au

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Measurement of medium-induced acoplanarity in central Au-Au and pp collisions at $\sqrt{s_{\rm NN}}=200$ GeV using direct-photon+jet and $\pi^{0}$+jet correlations

The STAR collaboration
PRL; 3 figures+1 figure in End Matter, 2025.
Inspire Record 2919952 DOI 10.17182/hepdata.159953

The STAR Collaboration reports measurements of acoplanarity using semi-inclusive distributions of charged-particle jets recoiling from direct photon and $\pi^{0}$ triggers, in central Au-Au and pp collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Significant medium-induced acoplanarity broadening is observed for large but not small recoil jet resolution parameter, corresponding to recoil jet yield enhancement up to a factor of $\approx20$ for trigger-recoil azimuthal separation far from $\pi$. This phenomenology is indicative of the response of the Quark-Gluon Plasma to excitation, but not the scattering of jets off of its quasiparticles. The measurements are not well-described by current theoretical models which incorporate jet quenching.

18 data tables

Corrected Yield R=0.2 pi0+jet 10-15 pp at sqrt{s_{NN}}=200 GeV

Corrected Yield R=0.2 pi0+jet 15-20 pp at sqrt{s_{NN}}=200 GeV

Corrected Yield R=0.5 pi0+jet 10-15 pp at sqrt{s_{NN}}=200 GeV

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Observation of partonic flow in proton-proton and proton-nucleus collisions

The ALICE collaboration Acharya, Shreyasi ; Agarwal, Apar ; Aglieri Rinella, Gianluca ; et al.
CERN-EP-2024-299, 2024.
Inspire Record 2848254 DOI 10.17182/hepdata.165859

Quantum Chromodynamics predicts a phase transition from ordinary hadronic matter to the quark-gluon plasma (QGP) at high temperatures and energy densities, where quarks and gluons (partons) are not confined within hadrons. The QGP is generated in ultrarelativistic heavy-ion collisions. Anisotropic flow coefficients, quantifying the anisotropic azimuthal expansion of the produced matter, provide a unique tool to unravel QGP properties. Flow measurements in high-energy heavy-ion collisions show a distinctive grouping of anisotropic flow for baryons and mesons at intermediate transverse momentum, a feature associated with flow being imparted at the quark level, confirming the existence of the QGP. The observation of QGP-like features in relativistic proton-proton and proton-ion collisions has sparked debate about possible QGP formation in smaller collision systems, which remains unresolved. In this article, we demonstrate for the first time the distinctive grouping of anisotropic flow for baryons and mesons in high-multiplicity proton-lead and proton-proton collisions at the Large Hadron Collider (LHC). These results are described by a model that includes hydrodynamic flow followed by hadron formation via quark coalescence, replicating features observed in heavy-ion collisions. This observation is consistent with the formation of a partonic flowing system in proton-proton and proton-lead collisions at the LHC.

10 data tables

$v_2${2, $1.1<|\Delta\eta|< 7.8$} of $\mathrm{\pi}^{\pm}$ as a function of $p_{\mathrm{T}}$ in high-multiplicity p--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV.

$v_2${2, $1.1<|\Delta\eta|< 7.8$} of $\mathrm{K}^{\pm}$ as a function of $p_{\mathrm{T}}$ in high-multiplicity p--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV.

$v_2${2, $1.1<|\Delta\eta|< 7.8$} of p + $\rm\overline p$ as a function of $p_{\mathrm{T}}$ in high-multiplicity p--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV.

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Light Nuclei Femtoscopy and Baryon Interactions in 3 GeV Au+Au Collisions at RHIC

The STAR collaboration Aboona, B.E. ; Adam, J. ; Adamczyk, L. ; et al.
Phys.Lett.B 864 (2025) 139412, 2025.
Inspire Record 2837311 DOI 10.17182/hepdata.156057

We report the measurements of proton-deuteron ($p$-$d$) and deuteron-deuteron ($d$-$d$) correlation functions in Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ = 3 GeV using fixed-target mode with the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). For the first time, the source size ($R_{G}$), scattering length ($f_{0}$), and effective range ($d_{0}$) are extracted from the measured correlation functions with a simultaneous fit. The spin-averaged $f_0$ for $p$-$d$ and $d$-$d$ interactions are determined to be -5.28 $\pm$ 0.11(stat.) $\pm$ 0.82(syst.) fm and -2.62 $\pm$ 0.02(stat.) $\pm$ 0.24(syst.) fm, respectively. The measured $p$-$d$ interaction is consistent with theoretical calculations and low-energy scattering experiment results, demonstrating the feasibility of extracting interaction parameters using the femtoscopy technique. The reasonable agreement between the experimental data and the calculations from the transport model indicates that deuteron production in these collisions is primarily governed by nucleon coalescence.

3 data tables

Proton-Deuteron correlation function in 3 GeV Au+Au collisions.

Deuteron-Deuteron correlation function in 3 GeV Au+Au collisions.

Source size of p-d and d-d correlation function


Strangeness Production in $\sqrt{s_{\rm NN}}=3$ GeV Au+Au Collisions at RHIC

The STAR collaboration Abdulhamid, M.I. ; Aboona, B.E. ; Adam, J. ; et al.
JHEP 10 (2024) 139, 2024.
Inspire Record 2807679 DOI 10.17182/hepdata.153884

We report multi-differential measurements of strange hadron production ranging from mid- to target-rapidity in Au+Au collisions at a center-of-momentum energy per nucleon pair of $\sqrt{s_{\rm NN}}=3$ GeV with the STAR experiment at RHIC. $K^0_S$ meson and $\Lambda$ hyperon yields are measured via their weak decay channels. Collision centrality and rapidity dependences of the transverse momentum spectra and particle ratios are presented. Particle mass and centrality dependence of the average transverse momenta of $\Lambda$ and $K^0_S$ are compared with other strange particles, providing evidence of the development of hadronic rescattering in such collisions. The 4$\pi$ yields of each of these strange hadrons show a consistent centrality dependence. Discussions on radial flow, the strange hadron production mechanism, and properties of the medium created in such collisions are presented together with results from hadronic transport and thermal model calculations.

19 data tables

dN/dy of lambda for different centrality bins.

dN/dy of Ks0 for different centrality bins.

Rapidity dependence of Lambda/p for different centrality bins.

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Imaging Shapes of Atomic Nuclei in High-Energy Nuclear Collisions

The STAR collaboration Abdulhamid, M.I. ; Aboona, B.E. ; Adam, J. ; et al.
Nature 635 (2024) 67-72, 2024.
Inspire Record 2746294 DOI 10.17182/hepdata.147196

Atomic nuclei are self-organized, many-body quantum systems bound by strong nuclear forces within femtometer-scale space. These complex systems manifest a variety of shapes, traditionally explored using non-invasive spectroscopic techniques at low energies. However, at these energies, their instantaneous shapes are obscured by long-timescale quantum fluctuations, making direct observation challenging. Here we introduce the ``collective flow assisted nuclear shape imaging'' method, which images the nuclear global shape by colliding them at ultrarelativistic speeds and analyzing the collective response of outgoing debris. This technique captures a collision-specific snapshot of the spatial matter distribution within the nuclei, which, through the hydrodynamic expansion, imprints patterns on the particle momentum distribution observed in detectors. We benchmark this method in collisions of ground state Uranium-238 nuclei, known for their elongated, axial-symmetric shape. Our findings show a large deformation with a slight deviation from axial symmetry in the nuclear ground state, aligning broadly with previous low-energy experiments. This approach offers a new method for imaging nuclear shapes, enhances our understanding of the initial conditions in high-energy collisions and addresses the important issue of nuclear structure evolution across energy scales.

27 data tables

Data from Figure 2, panel a, Au+Au, 0-0.5% Centrality, 0.2<p_{T}<3 GeV/c, systematics include non-flow difference in the two systems, but correlated non-flow systematics with the value of $\delta \left\langle v_{2}^{2}\right\rangle$ =+-3.2e-5 included

Data from Figure 2, panel a, U+U, 0-0.5% Centrality, 0.2<p_{T}<3 GeV/c, systematics include non-flow difference in the two systems, but correlated non-flow systematics with the value of $\delta \left\langle v_{2}^{2}\right\rangle$ =+-3.2e-5 included

Data from Figure 2, panel b, Au+Au, 0-0.5% Centrality, 0.2<p_{T}<3 GeV/c

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Production of Protons and Light Nuclei in Au+Au Collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV with the STAR Detector

The STAR collaboration Abdulhamid, Muhammad ; Aboona, Bassam ; Adam, Jaroslav ; et al.
Phys.Rev.C 110 (2024) 054911, 2024.
Inspire Record 2724476 DOI 10.17182/hepdata.145837

We report the systematic measurement of protons and light nuclei production in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum ($p_{T}$) spectra of protons ($p$), deuterons ($d$), tritons ($t$), $^{3}\mathrm{He}$, and $^{4}\mathrm{He}$ are measured from mid-rapidity to target rapidity for different collision centralities. We present the rapidity and centrality dependence of particle yields ($dN/dy$), average transverse momentum ($\langle p_{T}\rangle$), yield ratios ($d/p$, $t/p$,$^{3}\mathrm{He}/p$, $^{4}\mathrm{He}/p$), as well as the coalescence parameters ($B_2$, $B_3$). The 4$\pi$ yields for various particles are determined by utilizing the measured rapidity distributions, $dN/dy$. Furthermore, we present the energy, centrality, and rapidity dependence of the compound yield ratios ($N_{p} \times N_{t} / N_{d}^{2}$) and compare them with various model calculations. The physics implications of those results on the production mechanism of light nuclei and on QCD phase structure are discussed.

53 data tables

Weak decay feed-down fraction of protons (%) at different centralities in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The statistical and systematic uncertainties are shown respectively.

Transverse momentum spectra of inclusive protons in 0-10% Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The statistical and systematic uncertainties are shown respectively.

Transverse momentum spectra of inclusive protons in 10-20% Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. The statistical and systematic uncertainties are shown respectively.

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Measurements of charged-particle multiplicity dependence of higher-order net-proton cumulants in $p$+$p$ collisions at $\sqrt{s} =$ 200 GeV from STAR at RHIC

The STAR collaboration Abdulhamid, Muhammad ; Aboona, Bassam ; Adam, Jaroslav ; et al.
Phys.Lett.B 857 (2024) 138966, 2024.
Inspire Record 2718013 DOI 10.17182/hepdata.145838

We report on the charged-particle multiplicity dependence of net-proton cumulant ratios up to sixth order from $\sqrt{s}=200$ GeV $p$+$p$ collisions at the Relativistic Heavy Ion Collider (RHIC). The measured ratios $C_{4}/C_{2}$, $C_{5}/C_{1}$, and $C_{6}/C_{2}$ decrease with increased charged-particle multiplicity and rapidity acceptance. Neither the Skellam baselines nor PYTHIA8 calculations account for the observed multiplicity dependence. In addition, the ratios $C_{5}/C_{1}$ and $C_{6}/C_{2}$ approach negative values in the highest-multiplicity events, which implies that thermalized QCD matter may be formed in $p$+$p$ collisions.

7 data tables

(c) Charged-particle multiplicity distribution.

(d) Event-by-event net-proton multiplicity distributions for $|y|<0.5$ and $0.4<p_{\rm{T}}<2.0$ GeV/$c$ at two ranges of charged particle multiplicity as indicated in the legend.

Net-proton cumulant ratios, (a) $C_{2}/C_{1}$, (b) $C_{3}/C_{2}$, (c) $C_{4}/C_{2}$, (d) $C_{5}/C_{1}$, and (e) $C_{6}/C_{2}$ as a function of charged-particle multiplicity from $\sqrt{s}=200$ GeV $p$+$p$ collisions. Black solid lines and red bands represent the statistical and systematic uncertainties, respectively. Cyan points represent event averages for $3 < m_{\rm ch}^{\rm TPC} < 30$, and they are plotted at the corresponding value of $m_{\rm ch}^{\rm TPC}$. The uncertainties on the cyan points are smaller than the marker size. The Skellam baselines are shown as dotted lines. The results of the PYTHIA8 calculations are shown by hatched-golden bands. The golden bands at $m_{\rm ch}^{\rm TPC}\approx 6$ are the results from the PYTHIA8 calculations averaged over multiplicities.

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Estimate of Background Baseline and Upper Limit on the Chiral Magnetic Effect in Isobar Collisions at $\sqrt{s_{\text{NN}}}=200$ GeV at the Relativistic Heavy-Ion Collider

The STAR collaboration Abdulhamid, M.I. ; Aboona, B.E. ; Adam, J. ; et al.
Phys.Rev.C 110 (2024) 014905, 2024.
Inspire Record 2713075 DOI 10.17182/hepdata.145133

For the search of the chiral magnetic effect (CME), STAR previously presented the results from isobar collisions (${^{96}_{44}\text{Ru}}+{^{96}_{44}\text{Ru}}$, ${^{96}_{40}\text{Zr}}+{^{96}_{40}\text{Zr}}$) obtained through a blind analysis. The ratio of results in Ru+Ru to Zr+Zr collisions for the CME-sensitive charge-dependent azimuthal correlator ($\Delta\gamma$), normalized by elliptic anisotropy ($v_{2}$), was observed to be close to but systematically larger than the inverse multiplicity ratio. The background baseline for the isobar ratio, $Y = \frac{(\Delta\gamma/v_{2})^{\text{Ru}}}{(\Delta\gamma/v_{2})^{\text{Zr}}}$, is naively expected to be $\frac{(1/N)^{\text{Ru}}}{(1/N)^{\text{Zr}}}$; however, genuine two- and three-particle correlations are expected to alter it. We estimate the contributions to $Y$ from those correlations, utilizing both the isobar data and HIJING simulations. After including those contributions, we arrive at a final background baseline for $Y$, which is consistent with the isobar data. We extract an upper limit for the CME fraction in the $\Delta\gamma$ measurement of approximately $10\%$ at a $95\%$ confidence level on in isobar collisions at $\sqrt{s_{\text{NN}}} = 200$ GeV, with an expected $15\%$ difference in their squared magnetic fields.

39 data tables

Figure 1a, upper panel, full-event

Figure 1a, lower panel, full-event

Figure 1b, upper panel, subevent

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