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Abstract A systematic investigation of Planacon MCP-PMTs was performed using 64 XP85002/ FIT-Q photosensors. These devices are equipped with microchannel plates of reduced resistance. Results of a study of their gain stability over time and saturation level in terms of the average anode current are presented. This information allows one to determine the lower limit of the MCP resistance for stable Planacon operation. The spread of the electron multiplication characteristics for the entire production batch is also presented, indicating the remarkably low voltage requirements of these MCP-PMTs. Detection efficiency and noise characteristics, such as dark count rate and afterpulsing level, are also reviewed.more » « less
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Free, publicly-accessible full text available September 1, 2025
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The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high) charged hadron, inand central Pb-Pb collisions at center-of-mass energy per nucleon–nucleon collisionTeV. The large uncorrelated background in central Pb-Pb collisions is corrected using a data-driven statistical approach which enables precise measurement of recoil jet distributions over a broad range inand jet resolution parameter. Recoil jet yields are reported for, 0.4, and 0.5 in the rangeand, whereis the azimuthal angular separation between hadron trigger and recoil jet. The low-reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark–gluon plasma generated in high-energy nuclear collisions. Comparison ofdistributions fromand central Pb-Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching.
©2024 CERN, for the ALICE Collaboration 2024 CERN Free, publicly-accessible full text available July 1, 2025 -
The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high transverse momentum (high) hadron trigger in proton-proton and central Pb-Pb collisions at. A data-driven statistical method is used to mitigate the large uncorrelated background in central Pb-Pb collisions. Recoil jet distributions are reported for jet resolution parameter, 0.4, and 0.5 in the rangeand trigger-recoil jet azimuthal separation. The measurements exhibit a marked medium-induced jet yield enhancement at lowand at large azimuthal deviation from. The enhancement is characterized by its dependence on, which has a slope that differs from zero by. Comparisons to model calculations incorporating different formulations of jet quenching are reported. These comparisons indicate that the observed yield enhancement arises from the response of the QGP medium to jet propagation.
© 2024 CERN, for the ALICE Collaboration 2024 CERN Free, publicly-accessible full text available July 1, 2025 -
Free, publicly-accessible full text available June 1, 2025
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A bstract Results on the transverse spherocity dependence of light-flavor particle production (
π , K, p,ϕ , K*0, , Λ, Ξ) at midrapidity in high-multiplicity pp collisions at$$ {\textrm{K}}_{\textrm{S}}^0 $$ = 13 TeV were obtained with the ALICE apparatus. The transverse spherocity estimator$$ \sqrt{s} $$ categorizes events by their azimuthal topology. Utilizing narrow selections on$$ \left({S}_{\textrm{O}}^{p_{\textrm{T}}=1}\right) $$ , it is possible to contrast particle production in collisions dominated by many soft initial interactions with that observed in collisions dominated by one or more hard scatterings. Results are reported for two multiplicity estimators covering different pseudorapidity regions. The$$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ estimator is found to effectively constrain the hardness of the events when the midrapidity (|$$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ η | < 0.8) estimator is used.The production rates of strange particles are found to be slightly higher for soft isotropic topologies, and severely suppressed in hard jet-like topologies. These effects are more pronounced for hadrons with larger mass and strangeness content, and observed when the topological selection is done within a narrow multiplicity interval. This demonstrates that an important aspect of the universal scaling of strangeness enhancement with final-state multiplicity is that high-multiplicity collisions are dominated by soft, isotropic processes. On the contrary, strangeness production in events with jet-like processes is significantly reduced.
The results presented in this article are compared with several QCD-inspired Monte Carlo event generators. Models that incorporate a two-component phenomenology, either through mechanisms accounting for string density, or thermal production, are able to describe the observed strangeness enhancement as a function of
.$$ {S}_{\textrm{O}}^{p_{\textrm{T}}=1} $$ Free, publicly-accessible full text available May 1, 2025 -
A bstract The production yields of the Σ(1385)
± and Ξ(1530)0resonances are measured in pp collisions at = 13 TeV with ALICE. The measurements are performed as a function of the charged-particle multiplicity ⟨d$$ \sqrt{s} $$ N ch/ dη ⟩, which is related to the energy density produced in the collision. The results include transverse momentum (p T) distributions,p T-integrated yields, mean transverse momenta of Σ(1385)± and Ξ(1530)0, as well as ratios of thep T-integrated resonance yields relative to yields of other hadron species. The Σ(1385)± /π ± and Ξ(1530)0/π ± yield ratios are consistent with the trend of the enhancement of strangeness production from low to high multiplicity pp collisions, which was previously observed for strange and multi-strange baryons. The yield ratio between the measured resonances and the long-lived baryons with the same strangeness content exhibits a hint of a mild increasing trend at low multiplicity, despite too large uncertainties to exclude the flat behaviour. The results are compared with predictions from models such as EPOS-LHC and PYTHIA 8 with Rope shoving. The latter provides the best description of the multiplicity dependence of the Σ(1385)± and Ξ(1530)0production in pp collisions at = 13 TeV.$$ \sqrt{s} $$ Free, publicly-accessible full text available May 1, 2025 -
pairs may be produced in photonuclear collisions, either from the decays of photoproducedmesons or directly as nonresonantpairs. Measurements ofphotoproduction probe the couplings between theand charged kaons with photons and nuclear targets. The kaon-proton scattering occurs at energies far above those available elsewhere. We present the first measurement of coherent photoproduction ofpairs on lead ions in ultraperipheral collisions using the ALICE detector, including the first investigation of directproduction. There is significantproduction at low transverse momentum, consistent with coherent photoproduction on lead targets. In the mass rangeabove theresonance, for rapidityand, the measured coherent photoproduction cross section is. The center-of-mass energy per nucleon of the photon-nucleus (Pb) systemranges from 33 to 188 GeV, far higher than previous measurements on heavy-nucleus targets. The cross section is larger than expected forphotoproduction alone. The mass spectrum is fit to a cocktail consisting ofdecays, directphotoproduction, and interference between the two. The confidence regions for the amplitude and relative phase angle for directphotoproduction are presented.
© 2024 CERN, for the ALICE Collaboration 2024 CERN Free, publicly-accessible full text available May 1, 2025 -
A bstract Measurements of inclusive charged-particle jet production in pp and p-Pb collisions at center-of-mass energy per nucleon-nucleon collision
= 5$$ \sqrt{s_{\textrm{NN}}} $$ . 02 TeV and the corresponding nuclear modification factor are presented, using data collected with the ALICE detector at the LHC. Jets are reconstructed in the central rapidity region |$$ {R}_{\textrm{pPb}}^{\textrm{ch}\ \textrm{jet}} $$ η jet|< 0. 5 from charged particles using the anti-k Talgorithm with resolution parametersR = 0. 2, 0. 3, and 0. 4. Thep T-differential inclusive production cross section of charged-particle jets, as well as the corresponding cross section ratios, are reported for pp and p-Pb collisions in the transverse momentum range 10< $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ < 140 GeV/c and 10< $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ < 160 GeV/c , respectively, together with the nuclear modification factor in the range 10$$ {R}_{\textrm{pPb}}^{\textrm{ch}\ \textrm{jet}} $$ < $$ {p}_{\textrm{T},\textrm{jet}}^{\textrm{ch}} $$ < 140 GeV/c . The analysis extends thep Trange of the previously-reported charged-particle jet measurements by the ALICE Collaboration. The nuclear modification factor is found to be consistent with one and independent of the jet resolution parameter with the improved precision of this study, indicating that the possible influence of cold nuclear matter effects on the production cross section of charged-particle jets in p-Pb collisions at = 5$$ \sqrt{s_{\textrm{NN}}} $$ . 02 TeV is smaller than the current precision. The obtained results are in agreement with other minimum bias jet measurements available for RHIC and LHC energies, and are well reproduced by the NLO perturbative QCD Powheg calculations with parton shower provided by Pythia 8 as well as by Jetscape simulations.Free, publicly-accessible full text available May 1, 2025