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Abstract Event-by-event fluctuations of the event-wise mean transverse momentum,$$\langle p_{\textrm{T}}\rangle $$ , of charged particles produced in proton–proton (pp) collisions at$$\sqrt{s}$$ = 5.02 TeV, Xe–Xe collisions at$$\sqrt{s_{\textrm{NN}}}$$ = 5.44 TeV, and Pb–Pb collisions at$$\sqrt{s_{\textrm{NN}}}$$ = 5.02 TeV are studied using the ALICE detector based on the integral correlator$$\langle \!\langle \Delta p_\textrm{T}\Delta p_\textrm{T}\rangle \!\rangle $$ . The correlator strength is found to decrease monotonically with increasing produced charged-particle multiplicity measured at midrapidity in all three systems. In Xe–Xe and Pb–Pb collisions, the multiplicity dependence of the correlator deviates significantly from a simple power-law scaling as well as from the predictions of the HIJING and AMPT models. The observed deviation from power-law scaling is expected from transverse radial flow in semicentral to central Xe–Xe and Pb–Pb collisions. In pp collisions, the correlation strength is also studied by classifying the events based on the transverse spherocity,$$S_0$$ , of the particle production at midrapidity, used as a proxy for the presence of a pronounced back-to-back jet topology. Low-spherocity (jetty) events feature a larger correlation strength than those with high spherocity (isotropic). The strength and multiplicity dependence of jetty and isotropic events are well reproduced by calculations with the PYTHIA 8 and EPOS LHC models.
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Multiplicity dependence of charged-particle intra-jet properties in pp collisions at $$\sqrt{{{\varvec{s}}}}$$ = 13 TeV
Abstract 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-$$k_{\textrm{T}}$$ algorithm with jet resolution parametersR= 0.2, 0.3, and 0.4 for the transverse momentum ($$p_\textrm{T}$$ ) 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$$p_\textrm{T}$$ in qualitative agreement with previous measurements at lower energies. The distributions of jet fragmentation function variables$$z^{\textrm{ch}}$$ and$$\xi ^{\textrm{ch}}$$ are measured for different jet-$$p_\textrm{T}$$ intervals. Jet-$$p_\textrm{T}$$ independent fragmentation of leading jets is observed for wider jets except at high- and low-$$z^{\textrm{ch}}$$ values. The observed “hump-backed plateau” structure in the$$\xi ^{\textrm{ch}}$$ distribution indicates suppression of low-$$p_\textrm{T}$$ particles. In high-multiplicity events, an enhancement of the fragmentation probability of low-$$z^{\textrm{ch}}$$ particles accompanied by a suppression of high-$$z^{\textrm{ch}}$$ particles is observed compared to minimum-bias events. This behavior becomes more prominent for low-$$p_\textrm{T}$$ 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$$p_\textrm{T}$$ . These measurements provide important constraints to models of jet fragmentation.
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- PAR ID:
- 10599258
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- The European Physical Journal C
- Volume:
- 84
- Issue:
- 10
- ISSN:
- 1434-6052
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1140/epjc/s10052-024-13228-0
