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@MISC{Collaboration:348368,
      author       = {{ALICE Collaboration}},
      title        = {{E}lliptic flow of charged particles at midrapidity
                      relative to the spectator plane in {P}b-{P}b and {X}e-{X}e
                      collisions},
      reportid     = {GSI-2024-00204},
      year         = {2022},
      note         = {Journal Article GSI record: GSI-2024-00203},
      abstract     = {Measurements of the elliptic flow coefficient relative to
                      the collision plane defined by the spectator neutrons
                      $v_2\{\Psi_\mathrm{SP}\}$ in collisions of Pb ions at
                      center-of-mass energy per nucleon-nucleon pair
                      $\sqrt{s_\mathrm{NN}}=2.76$ TeV and Xe ions at
                      $\sqrt{s_\mathrm{NN}}=5.44$ TeV are reported. The results
                      are presented for charged particles produced at midrapidity
                      as a function of centrality and transverse momentum for the
                      $5-70\\%$ and $0.2-6\ \mathrm{GeV}/c$ ranges, respectively.
                      The ratio between $v_2\{\Psi_\mathrm{SP}\}$ and the elliptic
                      flow coefficient relative to the participant plane
                      $v_2\{4\}$, estimated using four-particle correlations,
                      deviates by up to $20\\%$ from unity depending on
                      centrality. This observation differs strongly from the
                      magnitude of the corresponding eccentricity ratios predicted
                      by the TRENTo and the elliptic power models of initial state
                      fluctuations that are tuned to describe the participant
                      plane anisotropies. The differences can be interpreted as a
                      decorrelation of the neutron spectator plane and the
                      reaction plane because of fragmentation of the remnants from
                      the colliding nuclei, which points to an incompleteness of
                      current models describing the initial state fluctuations. A
                      significant transverse momentum dependence of the ratio
                      $v_2\{\Psi_\mathrm{SP}\}/v_2\{4\}$ is observed in all but
                      the most central collisions, which may help to understand
                      whether momentum anisotropies at low and intermediate
                      transverse momentum have a common origin in initial state
                      fluctuations. The ratios of $v_2\{\Psi_\mathrm{SP}\}$ and
                      $v_2\{4\}$ to the corresponding initial state eccentricities
                      for Xe--Xe and Pb--Pb collisions at similar initial entropy
                      density show a difference of $(7.0\pm0.9)\\%$ with an
                      additional variation of $+1.8\\%$ when including RHIC data
                      in the TRENTo parameter extraction. These observations
                      provide new experimental constraints for viscous effects in
                      the hydrodynamic modeling of the expanding quark--gluon
                      plasma produced in heavy-ion collisions at the LHC.},
      cin          = {ALI / DTL / CIT / EXM / ALICE@CERN},
      cid          = {I:(DE-Ds200)ALI-20080822OR105 /
                      I:(DE-Ds200)DTL-20051214OR031 /
                      I:(DE-Ds200)CIT-20110310OR121 /
                      I:(DE-Ds200)EXM-20080818OR100 / I:(DE-Ds200)Coll-CERN-ALICE},
      pnm          = {612 - Cosmic Matter in the Laboratory (POF4-612) / HGS-HIRe
                      - HGS-HIRe for FAIR (HGS-HIRe) / SUC-GSI-Heidelberg -
                      Strategic university cooperation GSI-U Heidelberg
                      (SUC-GSI-HE) / SUC-GSI-Frankfurt - Strategic university
                      cooperation GSI-U Frankfurt/M (SUC-GSI-FR) /
                      SUC-GSI-Darmstadt - Strategic university cooperation GSI-TU
                      Darmstadt (SUC-GSI-DA)},
      pid          = {G:(DE-HGF)POF4-612 / G:(DE-Ds200)HGS-HIRe /
                      G:(DE-Ds200)SUC-GSI-HE / G:(DE-Ds200)SUC-GSI-FR /
                      G:(DE-Ds200)SUC-GSI-DA},
      experiment   = {EXP:(DE-H253)LHC-Exp-ALICE-20150101},
      typ          = {PUB:(DE-HGF)32},
      doi          = {10.17182/HEPDATA.134258},
      url          = {https://repository.gsi.de/record/348368},
}