Abstract
We present a study of the inclusive charged-particle transverse momentum (p_{mathrm{T}}) spectra as a function of charged-particle multiplicity density at mid-pseudorapidity, mathrm{d}N_{mathrm{ch}}/mathrm{d}eta , in pp collisions at sqrt{s}=5.02 and 13 TeV covering the kinematic range |eta |<0.8 and 0.15<p_{mathrm{T}} <20 GeV/c. The results are presented for events with at least one charged particle in |eta |<1 (INEL,>0). The p_mathrm{T} spectra are reported for two multiplicity estimators covering different pseudorapidity regions. The p_{mathrm{T}} spectra normalized to that for INEL,>0 show little energy dependence. Moreover, the high-p_{mathrm{T}} yields of charged particles increase faster than the charged-particle multiplicity density. The average { p}_{mathrm{T}} as a function of multiplicity and transverse spherocity is reported for pp collisions at sqrt{s}=13 TeV. For low- (high-) spherocity events, corresponding to jet-like (isotropic) events, the average p_mathrm{T} is higher (smaller) than that measured in INEL,>0 pp collisions. Within uncertainties, the functional form of langle p_{mathrm{T}} rangle (N_{mathrm{ch}}) is not affected by the spherocity selection. While EPOS LHC gives a good description of many features of data, PYTHIA overestimates the average p_{mathrm{T}} in jet-like events.
Highlights
The results are presented for events with at least one charged particle in |η| < 1 (INEL > 0)
The high- pT particle production is quantitatively well described by perturbative QCD calculations; on the other hand, the understanding of particle production at lowpT has to resort to phenomenological QCD inspired models
It is worth mentioning that a similar study has been performed by ALICE using p-Pb data; the results showed different modifications of the spectral shapes depending on the multiplicity estimators which were used [17]
Summary
The results are presented for events with at least one charged particle in |η| < 1 (INEL > 0). The pT spectra are reported for two multiplicity estimators covering different pseudorapidity regions. The forward multiplicity estimator is commonly used by the ALICE collaboration to minimize the possible autocorrelations induced by the use of the mid-pseudorapidity estimator One such examples is the “fragmentation bias” [15], which is the correlation between jet fragments and event multiplicity arising when the particle’s pT and event multiplicity are both measured within the same pseudorapidity interval [16]. Particle production from intermediate to high pT (> 4 GeV/c) is studied by fitting a power-law function to the invariant yield, and studying the multiplicity and energy dependence of the exponent. This has been proposed in Ref. [18] as a way to characterize the high- pT tails of different systems and energies in a convenient way that may make the comparison for the different systems more straightforward
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