Observation of the Antimatter Hypernucleus $^4_{\bar{\Lambda}}\overline{\hbox{H}}$

The STAR collaboration
Nature 632 (2024) 1026-1031, 2024.

Abstract (data abstract)
Matter-antimatter asymmetry is a research topic of fundamental interest, as it is the basis for the existence of the matter world, which survived annihilation with antimatter in the early Universe. High energy nuclear collisions create conditions similar to the Universe microseconds after the Big Bang, with comparable amounts of matter and antimatter. Much of the antimatter created escapes the rapidly expanding fireball without annihilation, making such collisions an effective experimental tool to create heavy antimatter nuclear objects and study their properties. In this paper, we report the first observation of the antimatter hypernucleus \hbox{$^4_{\bar{\Lambda}}\overline{\hbox{H}}$}, composed of an $\bar{\Lambda}$, an antiproton and two antineutrons. The discovery was made through its two-body decay after production in ultrarelativistic heavy ion collisions by the STAR experiment at the Relativistic Heavy Ion Collider. In total, 15.6 candidate \hbox{$^4_{\bar{\Lambda}}\overline{\hbox{H}}$} \ antimatter hypernuclei are obtained with an estimated background count of 6.4. Lifetimes of the antihypernuclei \hbox{$^3_{\bar{\Lambda}}\overline{\hbox{H}}$} \ and \hbox{$^4_{\bar{\Lambda}}\overline{\hbox{H}}$} \ are measured and compared with lifetimes of their corresponding hypernuclei, testing the symmetry between matter and antimatter. Various production yield ratios among (anti)hypernuclei and (anti)nuclei are also measured and compared with theoretical model predictions, shedding light on their production mechanism.

  • Fig3 (A) $^3_{\Lambda}H$

    Data from Figure 3

    10.17182/hepdata.145132.v1/t1

    Invariant mass distributions of $^3\hbox{He}+\pi^-$ (A), $^3\overline{\hbox{He}}+\pi^+$ (B), $^4\hbox{He}+\pi^-$ (C) and $^4\overline{\hbox{He}}+\pi^+$ (D). The solid bands mark the signal invariant...

  • Fig3 (B) $^3_{\bar{\Lambda}}\overline{H}$

    Data from Figure 3

    10.17182/hepdata.145132.v1/t2

    Invariant mass distributions of $^3\hbox{He}+\pi^-$ (A), $^3\overline{\hbox{He}}+\pi^+$ (B), $^4\hbox{He}+\pi^-$ (C) and $^4\overline{\hbox{He}}+\pi^+$ (D). The solid bands mark the signal invariant...

  • Fig3 (C) $^4_{\Lambda}H$

    Data from Figure 3

    10.17182/hepdata.145132.v1/t3

    Invariant mass distributions of $^3\hbox{He}+\pi^-$ (A), $^3\overline{\hbox{He}}+\pi^+$ (B), $^4\hbox{He}+\pi^-$ (C) and $^4\overline{\hbox{He}}+\pi^+$ (D). The solid bands mark the signal invariant...

  • Fig3 (D) $^4_{\bar{\Lambda}}\overline{H}$

    Data from Figure 3

    10.17182/hepdata.145132.v1/t4

    Invariant mass distributions of $^3\hbox{He}+\pi^-$ (A), $^3\overline{\hbox{He}}+\pi^+$ (B), $^4\hbox{He}+\pi^-$ (C) and $^4\overline{\hbox{He}}+\pi^+$ (D). The solid bands mark the signal invariant...

  • Fig4 (A) A=3 particle

    Data from Figure 4

    10.17182/hepdata.145132.v1/t5

    (A) (anti)hypernuclei yields versus $L/\beta\gamma$. The vertical error bars represent the statistical error only.

  • Fig4 (A) A=4 particle

    Data from Figure 4

    10.17182/hepdata.145132.v1/t6

    (A) (anti)hypernuclei yields versus $L/\beta\gamma$. The vertical error bars represent the statistical error only.

  • Fig4 (B) Lifetime

    Data from Figure 4

    10.17182/hepdata.145132.v1/t7

    Our measured (anti)hypernuclei lifetimes compared with world data and theoretical predictions (solid triangles). Error bars and boxes represent statistical and...

  • Fig5 This Analysis Au+Au, U+U, Zr+Zr, Ru+Ru

    Data from Figure 5

    10.17182/hepdata.145132.v1/t8

    Production yield ratios of various particles with the same baryon number. Results combining all collision systems in this work are...

  • Fig5 This Analysis Au+Au, U+U

    Data from Figure 5

    10.17182/hepdata.145132.v1/t9

    Production yield ratios of various particles with the same baryon number. Results combining all collision systems in this work are...

  • Fig5 This Analysis Zr+Zr, Ru+Ru

    Data from Figure 5

    10.17182/hepdata.145132.v1/t10

    Production yield ratios of various particles with the same baryon number. Results combining all collision systems in this work are...

  • Fig5 Thermal Model

    Data from Figure 5

    10.17182/hepdata.145132.v1/t11

    Production yield ratios of various particles with the same baryon number. Results combining all collision systems in this work are...

  • Fig2 Tau Bin Efficiency for A=3 Particle

    Data from Method Figure 2

    10.17182/hepdata.145132.v1/t12

    Reconstruction efficiency as a function of $L/(\beta\gamma)$ obtained from the embedding Monte Carlo technique. Hypernuclei have stricter topological cuts than...

  • Fig2 Tau Bin Efficiency for A=4 Particle

    Data from Method Figure 2

    10.17182/hepdata.145132.v1/t13

    Reconstruction efficiency as a function of $L/(\beta\gamma)$ obtained from the embedding Monte Carlo technique. Hypernuclei have stricter topological cuts than...

  • Fig3, invariant-mass distributions for each tau bin of H3L

    Data from Method Figure 3

    10.17182/hepdata.145132.v1/t14

    H3L, antiH3L, H4L and antiH4L candidate invariant-mass distributions in different $L/\beta\gamma$ intervals.

  • Fig3, invariant-mass distributions for each tau bin of antiH3L

    Data from Method Figure 3

    10.17182/hepdata.145132.v1/t15

    H3L, antiH3L, H4L and antiH4L candidate invariant-mass distributions in different $L/\beta\gamma$ intervals.

  • Fig3, invariant-mass distributions for each tau bin of H4L

    Data from Method Figure 3

    10.17182/hepdata.145132.v1/t16

    H3L, antiH3L, H4L and antiH4L candidate invariant-mass distributions in different $L/\beta\gamma$ intervals.

  • Fig3, invariant-mass distributions for each tau bin of antiH4L

    Data from Method Figure 3

    10.17182/hepdata.145132.v1/t17

    H3L, antiH3L, H4L and antiH4L candidate invariant-mass distributions in different $L/\beta\gamma$ intervals.

  • Fig4 Lambda and anti-Lambda

    Data from Method Figure 4

    10.17182/hepdata.145132.v1/t18

    $dN/d(L/\beta\gamma)$ as a function of $L/\beta\gamma$ for $\Lambda$ and $\bar{\Lambda}$, and exponential fits to obtain their lifetimes.

  • Fig5 pT spectra of He3 and anti-He3

    Data from Method Figure 5

    10.17182/hepdata.145132.v1/t19

    Efficiency corrected $p_{T}$ spectra for $^3\hbox{He}$, $^3\overline{\hbox{He}}$, \htl, and \ahtl. The spectra are in the phase space of $|y|<0.7$ with...

  • Fig5 pT spectra of H3L and anti-H3L

    Data from Method Figure 4

    10.17182/hepdata.145132.v1/t20

    Efficiency corrected $p_{T}$ spectra for $^3\hbox{He}$, $^3\overline{\hbox{He}}$, \htl, and \ahtl. The spectra are in the phase space of $|y|<0.7$ with...

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