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1. Anisotropic flow of identified hadrons in Xe-Xe collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.44 TeV

   https://doi.org/10.1007/JHEP10(2021)152  

   Acharya, S. ; Adamová, D. ; Adler, A. ; Aglieri Rinella, G. ; Agnello, M. ; Agrawal, N. ; Ahammed, Z. ; Ahmad, S. ; Ahn, S. U. ; Ahuja, I. ; et al ( October 2021 , Journal of High Energy Physics)

   A bstract Measurements of elliptic ( v 2 ) and triangular ( v 3 ) flow coefficients of π ± , K ± , p+ $$ \overline{\mathrm{p}} $$ p ¯ , $$ {\mathrm{K}}_{\mathrm{S}}^0 $$ K S 0 , and Λ+ $$ \overline{\Lambda} $$ Λ ¯ obtained with the scalar product method in Xe-Xe collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 44 TeV are presented. The results are obtained in the rapidity range | y | < 0 . 5 and reported as a function of transverse momentum, p T , for several collision centrality classes. The flow coefficients exhibit a particle mass dependence for p T < 3 GeV/ c , while a grouping according to particle type (i.e., meson and baryon) is found at intermediate transverse momenta (3 < p T < 8 GeV/ c ). The magnitude of the baryon v 2 is larger than that of mesons up to p T = 6 GeV/ c . The centrality dependence of the shape evolution of the p T -differential v 2 is studied for the various hadron species. The v 2 coefficients of π ± , K ± , and p+ $$ \overline{\mathrm{p}} $$ pmore »¯ are reproduced by MUSIC hydrodynamic calculations coupled to a hadronic cascade model (UrQMD) for p T < 1 GeV/ c . A comparison with v n measurements in the corresponding centrality intervals in Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV yields an enhanced v 2 in central collisions and diminished value in semicentral collisions.« less
2. Prompt D0, D+, and D*+ production in Pb–Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV

   https://doi.org/10.1007/JHEP01(2022)174  

   Acharya, S. ; Adamová, D. ; Adler, A. ; Adolfsson, J. ; Aglieri Rinella, G. ; Agnello, M. ; Agrawal, N. ; Ahammed, Z. ; Ahmad, S. ; Ahn, S. U. ; et al ( January 2022 , Journal of High Energy Physics)

   A bstract The production of prompt D 0 , D + , and D *+ mesons was measured at midrapidity (| y | < 0.5) in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decay channels and their production yields were measured in central (0–10%) and semicentral (30–50%) collisions. The measurement was performed up to a transverse momentum ( p T ) of 36 or 50 GeV/c depending on the D meson species and the centrality interval. For the first time in Pb–Pb collisions at the LHC, the yield of D 0 mesons was measured down to p T = 0, which allowed a model-independent determination of the p T -integrated yield per unit of rapidity (d N/ d y ). A maximum suppression by a factor 5 and 2.5 was observed with the nuclear modification factor ( R AA ) of prompt D mesons at p T = 6–8 GeV/c for the 0–10% and 30–50% centrality classes, respectively. The D-meson R AA is compared with that of charged pions, charged hadrons, and Jmore »/ψ mesons as well as with theoretical predictions. The analysis of the agreement between the measured R AA , elliptic ( v 2 ) and triangular ( v 3 ) flow, and the model predictions allowed us to constrain the charm spatial diffusion coefficient D s . Furthermore the comparison of R AA and v 2 with different implementations of the same models provides an important insight into the role of radiative energy loss as well as charm quark recombination in the hadronisation mechanisms.« less
3. Charged-particle multiplicity fluctuations in Pb–Pb collisions at $$\sqrt{s_{\mathrm {NN}}}$$  = 2.76 TeV

   https://doi.org/10.1140/epjc/s10052-021-09784-4  

   Acharya, S. ; Adamová, D. ; Adler, A. ; Adolfsson, J. ; Aglieri Rinella, G. ; Agnello, M. ; Agrawal, N. ; Ahammed, Z. ; Ahmad, S. ; Ahn, S. U. ; et al ( November 2021 , 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 centrality 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.
4. Measurement of inclusive charged-particle b-jet production in pp and p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV

   https://doi.org/10.1007/JHEP01(2022)178  

   Acharya, S. ; Adamová, D. ; Adler, A. ; Adolfsson, J. ; Aglieri Rinella, G. ; Agnello, M. ; Agrawal, N. ; Ahammed, Z. ; Ahmad, S. ; Ahn, S. U. ; et al ( January 2022 , Journal of High Energy Physics)

   A bstract A measurement of the inclusive b-jet production cross section is presented in pp and p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV, using data collected with the ALICE detector at the LHC. The jets were reconstructed in the central rapidity region |η| < 0 . 5 from charged particles using the anti- k T algorithm with resolution parameter R = 0 . 4. Identification of b jets exploits the long lifetime of b hadrons, using the properties of secondary vertices and impact parameter distributions. The p T -differential inclusive production cross section of b jets, as well as the corresponding inclusive b-jet fraction, are reported for pp and p-Pb collisions in the jet transverse momentum range 10 ≤ p T , ch jet ≤ 100 GeV/ c , together with the nuclear modification factor, $$ {R}_{\mathrm{pPb}}^{\mathrm{b}-\mathrm{jet}} $$ R pPb b − jet . The analysis thus extends the lower p T limit of b-jet measurements at the LHC. The nuclear modification factor is found to be consistent with unity, indicating that the production of b jets in p-Pb at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5 . 02 TeV is not affected bymore »cold nuclear matter effects within the current precision. The measurements are well reproduced by POWHEG NLO pQCD calculations with PYTHIA fragmentation.« less
5. First measurements of N-subjettiness in central Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 2.76 TeV

   https://doi.org/10.1007/JHEP10(2021)003  

   Acharya, S. ; Adamová, D. ; Adler, A. ; Adolfsson, J. ; Aglieri Rinella, G. ; Agnello, M. ; Agrawal, N. ; Ahammed, Z. ; Ahmad, S. ; Ahn, S. U. ; et al ( October 2021 , 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 of 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 PYTHIA6more »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