Hypertriton production in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV

The study of nuclei and antinuclei production has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. The first measurement of the production of ${\rm ^{3}_{\Lambda}\rm H}$ in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV is presented in this Letter. Its production yield measured in the rapidity interval $-1 <~ y <~ 0$ for the 40% highest multiplicity p-Pb collisions is ${\rm d} N /{\rm d} y =[\mathrm{6.3 \pm 1.8 (stat.) \pm 1.2 (syst.) ] \times 10^{-7}}$. The measurement is compared with the expectations of statistical hadronisation and coalescence models, which describe the nucleosynthesis in hadronic collisions. These two models predict very different yields of the hypertriton in small collision systems such as p-Pb and therefore the measurement of ${\rm d} N /{\rm d} y$ is crucial to distinguish between them. The precision of this measurement leads to the exclusion with a significance larger than 6$\sigma$ of some configurations of the statistical hadronisation, thus constraining the production mechanism of loosely bound states.


Submitted to: PRL
e-Print: arXiv:2107.10627 | PDF | inSPIRE
Figure group

Figure 1

Invariant mass distribution of the selected $\Hee + \pi^{-}$ and charge conjugate pairs. Vertical lines represent the statistical poissonian uncertainties. The invariant mass spectrum is fitted with a two component model: the blue line represents the total fit while the orange dashed line shows the background component only.

Figure 2

\hyp/$\Lambda$ (on the left) and $S_3$ (on the right) measurements in p--Pb (in red) and Pb--Pb collisions (in blue) as a function of mean charged-particle multiplicity. The vertical lines and boxes are the statistical and systematic uncertainties (including the uncertainty on the B.R.), respectively. The expectations for the canonical statistical hadronization and coalescence models are shown .

Figure 3

\hyp/$\Lambda$ times branching ratio as a function of branching ratio. The horizontal line is the measured value and the band represents statistical and systematic uncertainties added in quadrature. The expectations for the canonical statistical hadronization and coalescence models are shown .