A hot and dense state of nuclear matter, known as the quark-gluon plasma, is created in collisions of ultrarelativistic heavy nuclei. Highly energetic quarks and gluons, collectively referred to as partons, lose energy as they travel through this matter, leading to suppressed production of particles with large transverse momenta ($p_\mathrm{T}$). Conversely, high-$p_\mathrm{T}$ particle suppression has not been seen in proton-lead collisions, raising questions regarding the minimum system size required to observe parton energy loss. Oxygen-oxygen (OO) collisions examine a region of effective system size that lies between these two extreme cases. The CMS detector at the CERN LHC has been used to quantify charged-particle production in inclusive OO collisions for the first time via measurements of the nuclear modification factor ($R_\mathrm{AA}$). The $R_\mathrm{AA}$ is derived by comparing particle production to expectations based on proton-proton (pp) data and has a value of unity in the absence of nuclear effects. The data for OO and pp collisions at a nucleon-nucleon center-of-mass energy $\sqrt{s_\mathrm{NN}}$ = 5.36 TeV correspond to integrated luminosities of 6.1 nb$^{-1}$ and 1.02 pb$^{-1}$, respectively. The $R_\mathrm{AA}$ is below unity with a minimum of 0.69 $\pm$ 0.04 around $p_\mathrm{T}$ = 6 GeV. The data exhibit better agreement with theoretical models incorporating parton energy loss as compared to baseline models without energy loss.
Inclusive charged particle spectra for pp collisions at 5.36 TeV for $3 < p_{T} (GeV) <103.6$. The errors represent statistical, systematics and normalization uncertainties.
Inclusive charged particle spectra for OO collisions at 5.36 TeV for $3 < p_{T} (GeV) <103.6$. The errors represent statistical, systematics and normalization uncertainties.
Inclusive charged particle R_{AA} for 5.36 TeV OO collisions for $3 < p_{T} (GeV) <103.6$. The errors represent statistical, systematics and normalization uncertainties.
The production of prompt $\mathrm {\Lambda_{c}^{+}}$ baryons has been measured at midrapidity in the transverse momentum interval $0<p_{\rm T}<1$ GeV/$c$ for the first time, in pp and p-Pb collisions at a centre-of-mass energy per nucleon-nucleon collision $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. The measurement was performed in the decay channel ${\rm \Lambda_{c}^{+}\to p K^{0}_{S}}$ by applying new decay reconstruction techniques using a Kalman-Filter vertexing algorithm and adopting a machine-learning approach for the candidate selection. The $p_{\rm T}$-integrated $\mathrm {\Lambda_{c}^{+}}$ production cross sections in both collision systems were determined and used along with the measured yields in Pb-Pb collisions to compute the $p_{\rm T}$-integrated nuclear modification factors $R_{\rm pPb}$ and $R_\mathrm{AA}$ of $\mathrm{\Lambda_{c}^{+}}$ baryons, which are compared to model calculations that consider nuclear modification of the parton distribution functions. The $\mathrm{\Lambda_{c}^{+}/D^0}$ baryon-to-meson yield ratio is reported for pp and p-Pb collisions. Comparisons with models that include modified hadronisation processes are presented, and the implications of the results on the understanding of charm hadronisation in hadronic collisions are discussed. A significant ($3.7\sigma$) modification of the mean transverse momentum of $\mathrm {\Lambda_{c}^{+}}$ baryons is seen in p-Pb collisions with respect to pp collisions, while the $p_{\rm T}$-integrated $\mathrm{\Lambda_{c}^{+}/D^0}$ yield ratio was found to be consistent between the two collision systems within the uncertainties.
The $p_\mathrm{T}$-differential prompt $\Lambda_\mathrm{c}^{+}$ production cross sections per unit rapidity in pp collisions for $|y| < 0.5$, at $\sqrt{s} = 5.02$ TeV. Data for $1<p_\mathrm{T} < 12$ GeV/$c$ from Phys.Rev.Lett. 127 (2021) 202301, 2021, https://www.hepdata.net/record/ins1829739.
The $p_\mathrm{T}$-differential prompt $\Lambda_\mathrm{c}^{+}$ production cross sections per unit rapidity in p-Pb collisions for $-0.96<y_\mathrm{cms}<0.04$, at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. Data for $1<p_\mathrm{T} < 24$ GeV/$c$ from Phys.Rev.Lett. 127 (2021) 202301, 2021, https://www.hepdata.net/record/ins1829739.
The $p_\mathrm{T}$-integrated production cross sections per unit rapidity for prompt $\Lambda_\mathrm{c}^{+}$ baryons in pp and p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV.
We report on the observed differences in production rates of strange and multi-strange baryons in Au+Au collisions at sqrts = 200 GeV compared to pp interactions at the same energy. The strange baryon yields in Au+Au collisions, then scaled down by the number of participating nucleons, are enhanced relative to those measured in pp reactions. The enhancement observed increases with the strangeness content of the baryon, and increases for all strange baryons with collision centrality. The enhancement is qualitatively similar to that observed at lower collision energy sqrts =17.3 GeV. The previous observations are for the bulk production, while at intermediate pT, 1 < pT< 4 GeV/c, the strange baryons even exceed binary scaling from pp yields.
Midrapidity E(i) as a function of $<N_{part}>$ for $\Lambda$, $\bar{\Lambda}$ ($|y| < 1.0$), $\Xi^{-}$, $\bar{\Xi}^{+}$ ($|y| < 0.75$). Error bars on the data points represent those from the heavy ions. Stat. and syst. errors added in quadrature. Grand Canonical Model arrows(values in brackets), for $\Lambda$ E(2.6) and T(165 MeV) for $\bar{\Lambda}$ E(2.2) and T(170 MeV), for $\Xi$ E(10.7) and T(165 MeV), for anti-$\Xi$ E(7.5) and T(170 MeV).
Midrapidity E(i) as a function of $<N_{part}>$ for $\Omega^{-}+\bar{\Omega}^{+}$ ($|y| < 0.75$). Error bars on the data points represent those from the heavy ions. Stat. and syst. errors added in quadrature.
Midrapidity E(i) as a function of $<N_{part}>$ for inclusive $p$ ($|y| < 0.5$). Error bars on the data points represent those from the heavy ions. Stat. and syst. errors added in quadrature.
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