Multiplicity dependence of charged-particle jet production in pp collisions at $$\mathbf {\sqrt{s}}=\mathbf {13~TeV}$$

Abstract

The multiplicity dependence of jet production in pp collisions at the centre-of-mass energy of $$\sqrt{s} = 13\ {\mathrm {TeV}}$$ s = 13 TeV is studied for the first time. Jets are reconstructed from charged particles using the anti-$$k_\mathrm {T}$$ k T algorithm with resolution parameters R varying from 0.2 to 0.7. The jets are measured in the pseudorapidity range $$|\eta _{\mathrm{jet}}|< 0.9-R$$ | η jet | < 0.9 - R and in the transverse momentum range $$5<p_\mathrm {T,jet}^{\mathrm{ch}}<140\ {\mathrm {GeV}}/c$$ 5 < p T , jet ch < 140 GeV / c . The multiplicity intervals are categorised by the ALICE forward detector V0. The $$p_{\mathrm T}$$ p T differential cross section of charged-particle jets are compared to leading order (LO) and next-to-leading order (NLO) perturbative quantum chromodynamics (pQCD) calculations. It is found that the data are better described by the NLO calculation, although the NLO prediction overestimates the jet cross section below $$20\ {\mathrm {GeV}}/c$$ 20 GeV / c . The cross section ratios for different R are also measured and compared to model calculations. These measurements provide insights into the angular dependence of jet fragmentation. The jet yield increases with increasing self-normalised charged-particle multiplicity. This increase shows only a weak dependence on jet transverse momentum and resolution parameter at the highest multiplicity. While such behaviour is qualitatively described by the present version of PYTHIA, quantitative description may require implementing new mechanisms for multi-particle production in hadronic collisions.

Multiplicity dependence of charged-particle jet production in pp collisions at 13 TeV with ALICE

“…Furthermore, it is observed that the changes of these distributions in different multiplicity classes with respect to the minimum bias case are independent of the jet resolution parameter R and have a weak p T dependence, except for the very low p T domain. This indicates that jet production changes with event activity, but the slope of the spectrum stays similar to the one measured in MB events [6].…”

“…The analysis procedure for the measurement of the multiplicity dependence of jet production in pp collisions at s = 13 TeV is described in detail in Ref. [6].…”