Multiplicity dependence of $π$, K, and p production in pp collisions at $\sqrt{s} = 13$ TeV

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This paper presents the measurements of $\pi^{\pm}$, $\rm{K}^{\pm}$, $\rm{p}$ and $\bar{\rm{p}}$ transverse momentum ($p_{\rm{T}}$) spectra as a function of charged-particle multiplicity density in proton-proton (pp) collisions at $\sqrt{s}$ = 13 TeV with the ALICE detector at the LHC. Such study allows us to isolate the center-of-mass energy dependence of light-flavour particle production. The measurements reported here cover a $p_{\rm{T}}$ range from 0.1 GeV/$c$ to 20 GeV/$c$ and are done in the rapidity interval $|y|<~0.5$. The $p_{\rm{T}}$-differential particle ratios exhibit an evolution with multiplicity, similar to that observed in pp collisions at $\sqrt{s}$ = 7 TeV, which is qualitatively described by some of the hydrodynamical and pQCD-inspired models discussed in this paper. Furthermore, the $p_{\rm{T}}$-integrated hadron-to-pion yield ratios measured in pp collisions at two different center-of-mass energies are consistent when compared at similar multiplicities. This also extends to strange and multi-strange hadrons, suggesting that, at LHC energies, particle hadrochemistry scales with particle multiplicity the same way under different collision energies and colliding systems.

 

Eur. Phys. J. C 80, 693 (2020)
HEP Data
e-Print: arXiv:2003.02394 | PDF | inSPIRE
CERN-EP-2020-024

Figure 1

Transverse momentum spectra of \pion, \kaon, and \pr for different multiplicity event classes. Spectra are scaled by powers of 2 in order to improve visibility. The corresponding ratios to INEL$>$0 spectra are shown in the bottom panels.

Figure 2

Multiplicity dependence of \pT-differential \kaon/\pion (upper panels) and \pr/\pion (lower panels) ratios measured in pp collisions at $\sqrt{s}$ = 7 TeV \cite{Acharya:2018orn} and 13 TeV (blue and red, respectively). Lines represent different MC generator predictions for pp collisions at \cme{13}. Left to right: low-, intermediate-, and high-transverse momenta. Vertical bars, open, and shaded bands represent statistical, total systematic, and multiplicity uncorrelated systematic uncertainties, respectively.

Figure 3

Correlation of kinetic freeze-out temperature \Tkin and average expansion velocity \mbeta, extracted from simultaneous Blast-Wave fits to \pion, \kaon, and \pr spectra measured in pp, p--Pb, and Pb--Pb collisions. Contours represent 1$\sigma$ uncertainty. The shaded ellipses represent the \Tkin-\mbeta correlation calculated from Blast-Wave fit to \kaon, \pr, and $\Lambda$ spectra~\cite{Acharya:2019kyh} measured in pp collisions at \cme{13}. The empty circles represent Blast-Wave fits with resonance decays~\cite{Mazeliauskas:2019ifr}. References from~\cite{Abelev:2013haa,Acharya:2018orn,Mazeliauskas:2019ifr,ALICE:2017jyt}.

Figure 5

Integrated \kaon/\pion (top) and \pr/\pion (bottom) yield ratios as a function of charged-particle multiplicity density measured in pp, p--Pb, and Pb--Pb collisions at different center-of-mass energies. Empty (shaded) boxes represent total (multiplicity uncorrelated) systematic uncertainties. Black lines represent predictions from different MC generators for pp collisions at \cme{13}. References from~\cite{Acharya:2018orn,Adam:2016dau,Abelev:2013vea,Acharya:2019yoi}.

Figure 6

Integrated strange hadron-to-pion ratios as a function of \mdNde measured in pp, p--Pb, and Pb--Pb collisions. The open (shaded) boxes around markers represent full (multiplicity uncorrelated) systematic uncertainties. Different lines represent predictions from different MC generators for pp collisions at \cme{13}. References from~\cite{Adam:2015vsf,ALICE:2017jyt,Acharya:2018orn,Acharya:2019kyh}.

Figure 7

Upper panels: average transverse momenta of \pion, \kaon, and \pr as a function of charged-particle multiplicity density measured in pp collisions at \cme{\textrm{7 and 13}}. The red solid line represents $a-b(c-\mdNde)^{-1}$ fit to the 13~TeV data to guide the eye. Open (shaded) boxes represent total (multiplicity uncorrelated) systematic uncertainties. Black lines represent predictions from different MC generators for pp collisions at \cme{13}. Bottom panels: ratios of \mpT to the fits. Data at \cme{7} are from~\cite{Acharya:2018orn}.