Dergi makalesi Açık Erişim

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

2024    CERN İşbirliği

The first measurement of the multiplicity dependence of intra-jet properties of leading charged-particle jets in proton–proton (pp) collisions is reported. The mean charged-particle multiplicity and jet fragmentation distributions are measured in minimum-bias and high-multiplicity pp collisions at center-of-mass energy $\sqrt{s}$ = 13 TeV using the ALICE detector. Jets are reconstructed from charged particles produced in the midrapidity region ( $|\eta |<0.9$ ) using the sequential recombination anti- ${k}_{\text{T}}$ algorithm with jet resolution parameters R = 0.2, 0.3, and 0.4 for the transverse momentum ( ${p}_{\text{T}}$ ) interval 5–110 GeV/c. The high-multiplicity events are selected by the forward V0 scintillator detectors. The mean charged-particle multiplicity inside the leading jet cone rises monotonically with increasing jet ${p}_{\text{T}}$ in qualitative agreement with previous measurements at lower energies. The distributions of jet fragmentation function variables ${z}^{\text{ch}}$ and ${\xi }^{\text{ch}}$ are measured for different jet- ${p}_{\text{T}}$ intervals. Jet- ${p}_{\text{T}}$ independent fragmentation of leading jets is observed for wider jets except at high- and low- ${z}^{\text{ch}}$ values. The observed "hump-backed plateau" structure in the ${\xi }^{\text{ch}}$ distribution indicates suppression of low- ${p}_{\text{T}}$ particles. In high-multiplicity events, an enhancement of the fragmentation probability of low- ${z}^{\text{ch}}$ particles accompanied by a suppression of high- ${z}^{\text{ch}}$ particles is observed compared to minimum-bias events. This behavior becomes more prominent for low- ${p}_{\text{T}}$ jets with larger jet radius. The results are compared with predictions of QCD-inspired event generators, PYTHIA 8 with Monash 2013 tune and EPOS LHC. It is found that PYTHIA 8 qualitatively reproduces the jet modification in high-multiplicity events except at high jet ${p}_{\text{T}}$ . These measurements provide important constraints to models of jet fragmentation.