Example reconstructed $M(\gamma\gamma)$ distributions in forward $p{\rm Pb}$ collisions at $\sqrt{s_{\rm NN}}=8.16 {\rm TeV}$ with $2.5<y_{\rm c.m.}<3.5$. Distributions are shown for (left) $1.5<p_{\rm T}<1.6\text{ Ge V} {}$ and (right) $3.0<p_{\rm T}<3.2\text{ Ge V} {}$. Fit results are overlaid, including the mixed event and correlated combinatorial background templates. The lower panels show the background-subtracted mass distributions with the fit results overlaid.

Example reconstructed $M(\pi^+\pi^-\eta)$ distributions in forward $p{\rm Pb}$ collisions at $\sqrt{s_{\rm NN}}=8.16 {\rm TeV}$ with $2.5<y_{\rm c.m.}<3.5$. Distributions are shown for (left) $3<p_{\rm T}<4\text{ Ge V} {}$ and (right) $7<p_{\rm T}<10\text{ Ge V} {}$. Fit results are overlaid, including the mixed event and correlated combinatorial background templates. The lower panels show the background-subtracted mass distributions with the fit results overlaid.

Measured $\eta$ and $\eta'$ differential cross sections in the (left) backward and (right) forward regions. The $pp$ cross sections are scaled by the atomic mass of the lead ion, $A=208$. The $\eta'$ cross sections are scaled down by a factor of $10$ for visual clarity. Statistical uncertainties are shown as error bars, while systematic uncertainties are shown as error boxes.

Measured $\eta$ and $\eta'$ nuclear modification factors in the (top) backward and (bottom) forward regions. Error bars show the statistical uncertainties, while the boxes show the systematic uncertainties except for the uncertainty associated with the luminosity, which is fully correlated between measurements. The luminosity uncertainty is shown as a dark gray shaded box. The $\eta$ and $\eta'$ results are compared to the $\pi^0$ data from Ref. [19].

Measured $R^{\eta'}_{p{\rm Pb}}/R^{\eta}_{p{\rm Pb}}$ in the (left) backward and (right) forward regions. Error bars show the statistical uncertainties, while the boxes show the systematic uncertainties. The systematic uncertainties are approximately fully correlated in $p_{\rm T}$. The results are compared to predictions from EPOS4 with and without QGP-like effects. The shaded and hatched regions show the statistical 68% confidence-level regions of the predictions.

Measured $\eta$ differential cross sections in the (left) backward and (right) forward regions. Results are shown for $pp$ collisions at (top) $\sqrt{s}=5.02$ and (middle) $13 {\rm TeV}$ and (bottom) for $p{\rm Pb}$ collisions at $\sqrt{s_{\rm NN}}=8.16 {\rm TeV}$. Results are compared to predictions from EPOS4 and Pythia {}8. The lower panels show the ratios of the predictions to the measured results. The statistical uncertainties are shown by error bars, while systematic uncertainties are shown by boxes.

Measured $\eta'$ differential cross sections in the (left) backward and (right) forward regions. Results are shown for $pp$ collisions at (top) $\sqrt{s}=5.02$ and (middle) $13 {\rm TeV}$ and (bottom) for $p{\rm Pb}$ collisions at $\sqrt{s_{\rm NN}}=8.16 {\rm TeV}$. Results are compared to predictions from EPOS4 and Pythia {}8. The lower panels show the ratios of the predictions to the measured results. The statistical uncertainties are shown by error bars, while systematic uncertainties are shown by boxes.

Measured $\eta/\pi^0$ cross section ratios in the (left) backward and (right) forward regions. Results are shown for $pp$ collisions at (top) $\sqrt{s}=5.02$ and (middle) $13 {\rm TeV}$ and (bottom) for $p{\rm Pb}$ collisions at $\sqrt{s_{\rm NN}}=8.16 {\rm TeV}$. Results are compared to predictions from EPOS4 and Pythia {}8. The statistical uncertainties are shown by error bars, while systematic uncertainties are shown by boxes. The systematic uncertainties are approximately fully correlated between $p_{\rm T}$ regions. The black dashed line and the gray shaded region show the central value of $C^{\eta/\pi^0}$ and its uncertainty, respectively, where $C^{\eta/\pi^0}$ is calculated for $p_{\rm T}>3\text{ Ge V} {}$.

Animated gif made out of all figures.

Relative systematic and statistical uncertainties in $d\sigma^{\eta}/dp_{\rm T}$, $R^{\eta}_{p{\rm Pb}}$, $d\sigma^{\eta'}/dp_{\rm T}$, and $R^{\eta'}_{p{\rm Pb}}$, where the superscript denotes the hadron species. The uncertainties are reported in percent, and the ranges correspond to the minimum and maximum values of the associated uncertainties across all $p_{\rm T}$ intervals, $y_{\rm c.m.}$ regions, and data sets. All sources of systematic uncertainty are approximately fully correlated across $p_{\rm T}$ intervals.

Measured $C^{\eta/\pi^0}$ for each data set and rapidity region. The first uncertainty is statistical and the second is systematic. The systematic uncertainties are approximately 90% positively correlated between data sets.

Measured $d\sigma/dp_{\rm T}$ of $\eta$ production in $pp$ collisions at $\sqrt{s}=5.02 {\rm TeV}$. Results and uncertainties are given in ${\rm mb/GeV}$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ intervals, while the systematic uncertainty is approximately fully correlated.

Measured $d\sigma/dp_{\rm T}$ of $\eta$ production in $pp$ collisions at $\sqrt{s}=13 {\rm TeV}$. Results and uncertainties are given in ${\rm mb/GeV}$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ intervals, while the systematic uncertainty is approximately fully correlated.

Measured $d\sigma/dp_{\rm T}$ of $\eta$ production in $p{\rm Pb}$ collisions at $\sqrt{s_{\rm NN}}=8.16 {\rm TeV}$. Results and uncertainties are given in ${\rm mb/GeV}$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ intervals, while the systematic uncertainty is approximately fully correlated.

Measured $d\sigma/dp_{\rm T}$ of $\eta'$ production in $pp$ collisions at $\sqrt{s}=5.02 {\rm TeV}$. Results and uncertainties are given in ${\rm mb/GeV}$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ bins, while the systematic uncertainty is approximately fully correlated.

Measured $d\sigma/dp_{\rm T}$ of $\eta'$ production in $pp$ collisions at $\sqrt{s}=13 {\rm TeV}$. Results and uncertainties are given in ${\rm mb/GeV}$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ bins, while the systematic uncertainty is approximately fully correlated.

Measured $d\sigma/dp_{\rm T}$ of $\eta'$ production in $p{\rm Pb}$ collisions at $\sqrt{s_{\rm NN}}=8.16 {\rm TeV}$. Results and uncertainties are given in ${\rm mb/GeV}$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ bins, while the systematic uncertainty is approximately fully correlated.

Measured $\eta/\pi^0$ cross section ratio for $2.5<y_{\rm c.m.}<3.5$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ bins, while the systematic uncertainty is approximately fully correlated.

Measured $\eta/\pi^0$ cross section ratio for $-4.0<y_{\rm c.m.}<-3.0$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ bins, while the systematic uncertainty is approximately fully correlated.

Measured $\eta$ nuclear modification factor $R_{p{\rm Pb}}$ as a function of $p_{\rm T}$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ bins, while the systematic uncertainty is approximately fully correlated.

Measured $\eta'$ nuclear modification factor $R_{p{\rm Pb}}$ as a function of $p_{\rm T}$. The first uncertainty is statistical and the second is systematic. The statistical uncertainty is uncorrelated between $p_{\rm T}$ bins, while the systematic uncertainty is approximately fully correlated.