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Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Aglieri Rinella, G.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; et al(
, Journal of High Energy Physics)
A bstract A measurement of inclusive, prompt, and non-prompt J/ ψ production in p-Pb collisions at a nucleon-nucleon centre-of-mass energy $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV is presented. The inclusive J/ ψ mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum p T = 0. The inclusive J/ ψ nuclear modification factor R pPb is calculated by comparing the new results in p-Pb collisions to a recently measured proton-proton reference at the same centre-of-mass energy. Non-prompt J/ ψ mesons, which originate from the decay of beauty hadrons, are separated frommore »promptly produced J/ ψ on a statistical basis for p T larger than 1.0 GeV/ c . These results are based on the data sample collected by the ALICE detector during the 2016 LHC p-Pb run, corresponding to an integrated luminosity $$ \mathcal{L} $$ L int = 292 ± 11 μ b − 1 , which is six times larger than the previous publications. The total uncertainty on the p T -integrated inclusive J/ ψ and non-prompt J/ ψ cross section are reduced by a factor 1.7 and 2.2, respectively. The measured cross sections and R pPb are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt J/ ψ production cross section, the $$ \mathrm{b}\overline{\mathrm{b}} $$ b b ¯ production cross section at midrapidity, $$ {\mathrm{d}\sigma}_{\mathrm{b}\overline{\mathrm{b}}} $$ d σ b b ¯ / d y , and the total cross section extrapolated over full phase space, $$ {\sigma}_{\mathrm{b}\overline{\mathrm{b}}} $$ σ b b ¯ , are derived.« less
Free, publicly-accessible full text available June 1, 2023
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Aglieri Rinella, G.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; et al(
, The European Physical Journal C)
Abstract Measurements of event-by-event fluctuations of charged-particle multiplicities in Pb–Pb collisions at $$\sqrt{s_{\mathrm {NN}}}$$ s NN $$=$$ = 2.76 TeV using the ALICE detector at the CERN Large Hadron Collider (LHC) are presented in the pseudorapidity range $$|\eta |<0.8$$ | η | < 0.8 and transverse momentum $$0.2< p_{\mathrm{T}} < 2.0$$ 0.2 < p T < 2.0 GeV/ c . The amplitude of the fluctuations is expressed in terms of the variance normalized by the mean of the multiplicity distribution. The $$\eta $$ η and $$p_{\mathrm{T}}$$ p T dependences of the fluctuations and their evolution with respect to collision centralitymore »are investigated. The multiplicity fluctuations tend to decrease from peripheral to central collisions. The results are compared to those obtained from HIJING and AMPT Monte Carlo event generators as well as to experimental data at lower collision energies. Additionally, the measured multiplicity fluctuations are discussed in the context of the isothermal compressibility of the high-density strongly-interacting system formed in central Pb–Pb collisions.« less
Free, publicly-accessible full text available November 1, 2022
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Aglieri Rinella, G.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; et al(
, Journal of High Energy Physics)
A bstract The transverse momentum ( p T ) differential cross section of the charm-strange baryon $$ {\Xi}_{\mathrm{c}}^0 $$ Ξ c 0 is measured at midrapidity (| y | < 0.5) via its semileptonic decay into e + Ξ − ν e in pp collisions at $$ \sqrt{s} $$ s = 5 . 02 TeV with the ALICE detector at the LHC. The ratio of the p T -differential $$ {\Xi}_{\mathrm{c}}^0 $$ Ξ c 0 -baryon and D 0 -meson production cross sections is also reported. The measurements are compared with simulations with different tunes of the PYTHIA 8 eventmore »generator, with predictions from a statistical hadronisation model (SHM) with a largely augmented set of charm-baryon states beyond the current lists of the Particle Data Group, and with models including hadronisation via quark coalescence. The p T -integrated cross section of prompt $$ {\Xi}_{\mathrm{c}}^0 $$ Ξ c 0 -baryon production at midrapidity is also reported, which is used to calculate the baryon-to-meson ratio $$ {\Xi}_{\mathrm{c}}^0 $$ Ξ c 0 / D 0 = 0 . 20 ± 0 . 04 $$ {\left(\mathrm{stat}.\right)}_{-0.07}^{+0.08} $$ stat . − 0.07 + 0.08 (syst . ). These results provide an additional indication of a modification of the charm fragmentation from e + e − and e − p collisions to pp collisions.« less
Free, publicly-accessible full text available October 1, 2022
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Aglieri Rinella, G.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; et al(
, Journal of High Energy Physics)
A bstract The ALICE Collaboration reports the first fully-corrected measurements of the N -subjettiness observable for track-based jets in heavy-ion collisions. This study is performed using data recorded in pp and Pb-Pb collisions at centre-of-mass energies of $$ \sqrt{s} $$ s = 7 TeV and $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 2 . 76 TeV, respectively. In particular the ratio of 2-subjettiness to 1-subjettiness, τ 2 /τ 1 , which is sensitive to the rate of two-pronged jet substructure, is presented. Energy loss of jets traversing the strongly interacting medium in heavy-ion collisions is expected to change the rate ofmore »two-pronged substructure relative to vacuum. The results are presented for jets with a resolution parameter of R = 0 . 4 and charged jet transverse momentum of 40 ≤ p T , jet ≤ 60 GeV/ c , which constitute a larger jet resolution and lower jet transverse momentum interval than previous measurements in heavy-ion collisions. This has been achieved by utilising a semi-inclusive hadron-jet coincidence technique to suppress the larger jet combinatorial background in this kinematic region. No significant modification of the τ 2 /τ 1 observable for track-based jets in Pb-Pb collisions is observed relative to vacuum PYTHIA6 and PYTHIA8 references at the same collision energy. The measurements of τ 2 /τ 1 , together with the splitting aperture angle ∆ R , are also performed in pp collisions at $$ \sqrt{s} $$ s = 7 TeV for inclusive jets. These results are compared with PYTHIA calculations at $$ \sqrt{s} $$ s = 7 TeV, in order to validate the model as a vacuum reference for the Pb-Pb centre-of-mass energy. The PYTHIA references for τ 2 /τ 1 are shifted to larger values compared to the measurement in pp collisions. This hints at a reduction in the rate of two-pronged jets in Pb-Pb collisions compared to pp collisions.« less
Free, publicly-accessible full text available October 1, 2022
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Aglieri Rinella, G.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; et al(
, Journal of High Energy Physics)
A bstract Jet fragmentation transverse momentum ( j T ) distributions are measured in proton-proton (pp) and proton-lead (p-Pb) collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV with the ALICE experiment at the LHC. Jets are reconstructed with the ALICE tracking detectors and electromagnetic calorimeter using the anti- k T algorithm with resolution parameter R = 0 . 4 in the pseudorapidity range |η| < 0 . 25. The j T values are calculated for charged particles inside a fixed cone with a radius R = 0 . 4 around the reconstructed jet axis. The measuredmore »j T distributions are compared with a variety of parton-shower models. Herwig and P ythia 8 based models describe the data well for the higher j T region, while they underestimate the lower j T region. The j T distributions are further characterised by fitting them with a function composed of an inverse gamma function for higher j T values (called the “wide component”), related to the perturbative component of the fragmentation process, and with a Gaussian for lower j T values (called the “narrow component”), predominantly connected to the hadronisation process. The width of the Gaussian has only a weak dependence on jet transverse momentum, while that of the inverse gamma function increases with increasing jet transverse momentum. For the narrow component, the measured trends are successfully described by all models except for Herwig. For the wide component, Herwig and PYTHIA 8 based models slightly underestimate the data for the higher jet transverse momentum region. These measurements set constraints on models of jet fragmentation and hadronisation.« less
Free, publicly-accessible full text available September 1, 2022
Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Rinella, G. Aglieri; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; et al(
, The European Physical Journal C)
Abstract The coherent photoproduction of $$\mathrm{J}/\psi $$ J / ψ and $${\uppsi '}$$ ψ ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy $$\sqrt{s_{\mathrm {NN}}}~=~5.02$$ s NN = 5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The $$\mathrm{J}/\psi $$ J / ψ is reconstructed using the dilepton ( $$l^{+} l^{-}$$ l + l - ) and proton–antiproton decay channels, while for the $${\uppsi '}$$ ψ ′ the dilepton and the $$l^{+} l^{-} \pi ^{+} \pi ^{-}$$ l + l - πmore »+ π - decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 $$\mu {\mathrm{b}}^{-1}$$ μ b - 1 . The results are compared with theoretical models for coherent $$\mathrm{J}/\psi $$ J / ψ and $${\uppsi '}$$ ψ ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken- x of around $$6\times 10^{-4}$$ 6 × 10 - 4 , such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent $$\mathrm{J}/\psi $$ J / ψ cross section including ALICE measurements at forward rapidity. The ratio of $${\uppsi '}$$ ψ ′ to $$\mathrm{J}/\psi $$ J / ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.« less
