Multiplicity dependence of charged-particle production in pp, p-Pb, Xe-Xe and Pb-Pb collisions at the LHC

Multiplicity ($N_{\rm ch}$) distributions and transverse momentum ($p_{\rm T}$) spectra of inclusive primary charged particles in the kinematic range of $|\eta| <~ 0.8$ and 0.15 GeV/$c$ $<~ p_{T} <~$ 10 GeV/$c$ are reported for pp, p-Pb, Xe-Xe and Pb-Pb collisions at centre-of-mass energies per nucleon pair ranging from $\sqrt{s_{\rm NN}} = 2.76$ TeV up to $13$ TeV. A sequential two-dimensional unfolding procedure is used to extract the correlation between the transverse momentum of primary charged particles and the charged-particle multiplicity of the corresponding collision. This correlation sharply characterises important features of the final state of a collision and, therefore, can be used as a stringent test of theoretical models. The multiplicity distributions as well as the mean and standard deviation derived from the $p_{\rm T}$ spectra are compared to state-of-the-art model predictions. Providing these fundamental observables of bulk particle production consistently across a wide range of collision energies and system sizes can serve as an important input for tuning Monte Carlo event generators.

 

Phys. Lett. B 845 (2023) 138110
HEP Data
e-Print: arXiv:2211.15326 | PDF | inSPIRE
CERN-EP-2022-266
Figure group

Figure 2

The \nch dependence of the mean (left panel) and standard deviation (right panel) of the \pt distributions for (particle-composition corrected) Monte Carlo events in \pp, \ppb and \pbpb collisions at $\sqrsn = 5.02\tev$. Results propagated through a full GEANT model of ALICE and corrected with the sequential 2D unfolding (closed circles) procedure described in the text are compared with the generator-level (open squares) distributions and their ratios are shown in the bottom panels.

Figure 3

Top panel: the correlation of primary charged particle \pt spectra with multiplicity per $\nch > 0$ event for \pp collisions at $\sqrt{s} = 5.02\tev$ Bottom panels: the corresponding relative change of \pt (left) and \nch (right) distributions with respect to the inclusive ones. In the left panel, each of the curves represents a single \nch value, ranging from $\nch = 1$ (blue) to $\nch = 55$ (red). In the right panel, the colours represent the \pt intervals used in this analysis from the lowest in blue to the highest one in red.

Figure 5

Ratios of the KNO-scaled multiplicity distributions at various centre-of-mass energies per nucleon pair relative to $\sqrs = 13\tev$ for \pp collisions (top panel) and relative to $\sqrsn = 8.16\tev$ and $\sqrsn = 5.02\tev$ for \ppb and \pbpb collisions, respectively (left and right bottom panels). Statistical and systematic uncertainties are shown as bars and semi-transparent bands, respectively.

Figure 6

Mean (left) and standard deviation (right) of the charged-particle transverse momentum spectra as a function of the charged-particle multiplicity for \pp, \ppb, and \pbpb collisions at a centre-of-mass energy per nucleon pair of $\sqrsn = 5.02\tev$. Statistical and systematic uncertainties are shown as bars and semi-transparent bands, respectively.

Figure 8

Mean (left) and standard deviation (right) of the charged-particle transverse momentum spectra as a function of the charged-particle multiplicity (top) and relative multiplicity $\nch / \mnch$ (middle, bottom) for \pp, \ppb, \xexe and \pbpb collisions at various centre-of-mass energies per nucleon pair. The bottom panels show both quantities relative to their multiplicity-inclusive value. Statistical and systematic uncertainties are shown as bars and semi-transparent bands, respectively.

Figure 9

Relative standard deviation of the charged-particle transverse momentum spectra as a function of the absolute (left) and relative (right) charged-particle multiplicity for \pp, \ppb, \xexe and \pbpb collisions at various centre-of-mass energies per nucleon pair Statistical and systematic uncertainties are shown as bars and semi-transparent bands, respectively.

Figure 10

Ratio of model predictions to data for \pp collisions at various energies. The upper panels show it for the multiplicity distributions (left) and their KNO-scaling form (right), the bottom panels represent \mpt (left) and \sigmapt (right). The semi-transparent bands indicate the relative systematic uncertainties of the data.

Figure 11

Ratio of model predictions to data for \ppb collisions at various energies. The upper panels show it for the multiplicity distributions (left) and their KNO-scaling form (right), the bottom panels represent \mpt (left) and \sigmapt (right). The semi-transparent bands indicate the relative systematic uncertainties of the data.

Figure 12

Comparisons of \mpt as a function of \nch at $\sqrsn = 5.02\tev$ for \pp, \ppb, and \pbpb collisions to three different model predictions. Statistical and systematic uncertainties are shown as bars and semi-transparent bands, respectively.

Figure 13

Average transverse momentum \mpt as a function of the scaling variable $(W/W_0)^{\lambda/(\lambda + 2)} \sqrt{\nch / S_\textrm{T}}$  for \pp and \ppb collisions at various energies (left) and the ratio of all data sets to that in \pp collisions at 13 TeV (right). The reference energy $W_0$ corresponds to $\sqrs = 7 \mathrm{TeV}$ for \pp and $\sqrsn = 5.02 \mathrm{TeV}$ for \ppb collisions. Statistical and systematic uncertainties are shown as bars and semi-transparent bands, respectively.