Charged jet cross sections and properties in proton-proton collisions at $\sqrt{s}=7$ TeV
ALICE Collaboration
TL;DR
This paper presents a detailed measurement of charged jet production, fragmentation, and jet shapes in pp collisions at $\sqrt{s}=7$ TeV with ALICE. Using anti-$k_{\rm T}$ (and cross-checked with $k_{\rm T}$ and SISCone) across $R=0.2$–0.6, and applying robust detector-correction techniques including Bayesian unfolding and UE subtraction, it provides a high-precision pp baseline for jet studies in heavy-ion environments. The results show that MC generators describe jet shapes and fragmentation with varying success: PYTHIA Perugia-2011 captures radial densities and $R_{80}$ well, while HERWIG better describes fragmentation at high $p_T$, with low-$p_T$ fragmentation generally underestimated by PYTHIA and PHOJET. The study also confirms consistency with ATLAS measurements and highlights areas for MC tuning, underscoring the importance of accurate UE treatment for jet-structure studies in hadronic collisions.
Abstract
The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at centre-of-mass energy $\sqrt{s}=7$ TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the mid-rapidity region using the sequential recombination $k_{\rm T}$ and anti-$k_{\rm T}$ as well as the SISCone jet finding algorithms with several resolution parameters in the range $R=0.2$ to $0.6$. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum ($p_{\rm T}$) interval $20<p_{\rm T}^{\rm jet,ch}<100$ GeV/$c$. They are also consistent with prior measurements carried out at the LHC by the ATLAS collaboration. The jet charged particle multiplicity rises monotonically with increasing jet $p_{\rm T}$, in qualitative agreement with prior observations at lower energies. The transverse profiles of leading jets are investigated using radial momentum density distributions as well as distributions of the average radius containing 80% ($\langle R_{\rm 80} \rangle$) of the reconstructed jet $p_{\rm T}$. The fragmentation of leading jets with $R=0.4$ using scaled $p_{\rm T}$ spectra of the jet constituents is studied. The measurements are compared to model calculations from event generators (PYTHIA, PHOJET, HERWIG). The measured radial density distributions and $\langle R_{\rm 80} \rangle$ distributions are well described by the PYTHIA model (tune Perugia-2011). The fragmentation distributions are better described by HERWIG.