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A<sc>bstract</sc> Measurements of charged-particle production in pp, p–Pb, and Pb–Pb collisions in the toward, away, and transverse regions with the ALICE detector are discussed. These regions are defined event-by-event relative to the azimuthal direction of the charged trigger particle, which is the reconstructed particle with the largest transverse momentum$$ \left({p}_{\textrm{T}}^{\textrm{trig}}\right) $$ in the range 8<$$ {p}_{\textrm{T}}^{\textrm{trig}} $$ <15 GeV/c. The toward and away regions contain the primary and recoil jets, respectively; both regions are accompanied by the underlying event (UE). In contrast, the transverse region perpendicular to the direction of the trigger particle is dominated by the so-called UE dynamics, and includes also contributions from initial- and final-state radiation. The relative transverse activity classifier,$$ {R}_{\textrm{T}}={N}_{\textrm{ch}}^{\textrm{T}}/\left\langle {N}_{\textrm{ch}}^{\textrm{T}}\right\rangle $$ , is used to group events according to their UE activity, where$$ {N}_{\textrm{ch}}^{\textrm{T}} $$ is the charged-particle multiplicity per event in the transverse region and$$ \left\langle {N}_{\textrm{ch}}^{\textrm{T}}\right\rangle $$ is the mean value over the whole analysed sample. The energy dependence of theRTdistributions in pp collisions at$$ \sqrt{s} $$ = 2.76, 5.02, 7, and 13 TeV is reported, exploring the Koba-Nielsen-Olesen (KNO) scaling properties of the multiplicity distributions. The first measurements of charged-particlepTspectra as a function ofRTin the three azimuthal regions in pp, p–Pb, and Pb–Pb collisions at$$ \sqrt{s_{\textrm{NN}}} $$ = 5.02 TeV are also reported. Data are compared with predictions obtained from the event generators PYTHIA 8 and EPOS LHC. This set of measurements is expected to contribute to the understanding of the origin of collective-like effects in small collision systems (pp and p–Pb).
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This content will become publicly available on July 1, 2026
System size and energy dependence of the mean transverse momentum fluctuations at the LHC
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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- Award ID(s):
- 2012154
- PAR ID:
- 10627353
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- The European Physical Journal C
- Volume:
- 85
- Issue:
- 7
- ISSN:
- 1434-6052
- Page Range / eLocation ID:
- 76
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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