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Sökning: LAR1:lu > Lunds universitet > Stenlund Evert

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1.
  • A, Lebedev, et al. (författare)
  • Direct photons in WA98.
  • 2002
  • Ingår i: Nuclear Physics A. - Elsevier. ; 698, s. 135-135
  • Tidskriftsartikel (refereegranskat)
  •  
2.
  • Acharya, S, et al. (författare)
  • Anisotropic flow in Xe–Xe collisions at sNN=5.44 TeV
  • 2018
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - Elsevier. - 0370-2693. ; 784, s. 82-95
  • Tidskriftsartikel (refereegranskat)abstract
    • The first measurements of anisotropic flow coefficients vn for mid-rapidity charged particles in Xe–Xe collisions at sNN=5.44 TeV are presented. Comparing these measurements to those from Pb–Pb collisions at sNN=5.02 TeV, v2 is found to be suppressed for mid-central collisions at the same centrality, and enhanced for central collisions. The values of v3 are generally larger in Xe–Xe than in Pb–Pb at a given centrality. These observations are consistent with expectations from hydrodynamic predictions. When both v2 and v3 are divided by their corresponding eccentricities for a variety of initial state models, they generally scale with transverse density when comparing Xe–Xe and Pb–Pb, with some deviations observed in central Xe–Xe and Pb–Pb collisions. These results assist in placing strong constraints on both the initial state geometry and medium response for relativistic heavy-ion collisions. © 2018 European Organization for Nuclear Research
3.
  • Acharya, S, et al. (författare)
  • Anisotropic flow of identified particles in Pb-Pb collisions at √sNN=5.02 TeV
  • 2018
  • Ingår i: Journal of High Energy Physics. - Springer. - 1126-6708. ; 2018:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The elliptic (v2), triangular (v3), and quadrangular (v4) flow coefficients of π±, K±, p+p¯,Λ+Λ¯,KS0, and the ϕ-meson are measured in Pb-Pb collisions at sNN=5.02 TeV. Results obtained with the scalar product method are reported for the rapidity range |y| < 0.5 as a function of transverse momentum, pT, at different collision centrality intervals between 0–70%, including ultra-central (0–1%) collisions for π±, K±, and p + p ¯. For pT< 3 GeV/c, the flow coefficients exhibit a particle mass dependence. At intermediate transverse momenta (3 < pT < 8–10 GeV/c), particles show an approximate grouping according to their type (i.e., mesons and baryons). The ϕ-meson v2, which tests both particle mass dependence and type scaling, follows p + p ¯ v2 at low pT and π±v2 at intermediate pT. The evolution of the shape of vn(pT) as a function of centrality and harmonic number n is studied for the various particle species. Flow coefficients of π±, K±, and p + p ¯ for pT < 3 GeV/c are compared to iEBE-VISHNU and MUSIC hydrodynamical calculations coupled to a hadronic cascade model (UrQMD). The iEBE-VISHNU calculations describe the results fairly well for pT < 2.5 GeV/c, while MUSIC calculations reproduce the measurements for pT < 1 GeV/c. A comparison to vn coefficients measured in Pb-Pb collisions at sNN=2.76 TeV is also provided.[Figure not available: see fulltext.]. © 2018, The Author(s).
4.
  • Acharya, S, et al. (författare)
  • Azimuthally-differential pion femtoscopy relative to the third harmonic event plane in Pb–Pb collisions at sNN=2.76TeV
  • 2018
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - Elsevier. - 0370-2693. ; 785, s. 320-331
  • Tidskriftsartikel (refereegranskat)abstract
    • Azimuthally-differential femtoscopic measurements, being sensitive to spatio-temporal characteristics of the source as well as to the collective velocity fields at freeze out, provide very important information on the nature and dynamics of the system evolution. While the HBT radii oscillations relative to the second harmonic event plane measured recently reflect mostly the spatial geometry of the source, model studies have shown that the HBT radii oscillations relative to the third harmonic event plane are predominantly defined by the velocity fields. In this Letter, we present the first results on azimuthally-differential pion femtoscopy relative to the third harmonic event plane as a function of the pion pair transverse momentum kT for different collision centralities in Pb–Pb collisions at sNN=2.76 TeV. We find that the Rside and Rout radii, which characterize the pion source size in the directions perpendicular and parallel to the pion transverse momentum, oscillate in phase relative to the third harmonic event plane, similar to the results from 3+1D hydrodynamical calculations. The observed radii oscillations unambiguously signal a collective expansion and anisotropy in the velocity fields. A comparison of the measured radii oscillations with the Blast-Wave model calculations indicate that the initial state triangularity is washed-out at freeze out. © 2018 European Organization for Nuclear Research
5.
  • Acharya, S, et al. (författare)
  • Charged-particle multiplicity distributions over a wide pseudorapidity range in proton-proton collisions at √s= 0.9, 7, and 8 TeV
  • 2017
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 77:12
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the charged-particle multiplicity distributions over a wide pseudorapidity range (-3.45.0) for pp collisions at s=0.9,7, and 8 TeV at the LHC. Results are based on information from the Silicon Pixel Detector and the Forward Multiplicity Detector of ALICE, extending the pseudorapidity coverage of the earlier publications and the high-multiplicity reach. The measurements are compared to results from the CMS experiment and to PYTHIA, PHOJET and EPOS LHC event generators, as well as IP-Glasma calculations. © 2017, CERN for the benefit of the ALICE collaboration.
6.
  • Acharya, S, et al. (författare)
  • Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in Pb–Pb collisions at sNN=2.76 TeV
  • 2018
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - Elsevier. - 0370-2693. ; 777, s. 151-162
  • Tidskriftsartikel (refereegranskat)abstract
    • In ultrarelativistic heavy-ion collisions, the event-by-event variation of the elliptic flow v2 reflects fluctuations in the shape of the initial state of the system. This allows to select events with the same centrality but different initial geometry. This selection technique, Event Shape Engineering, has been used in the analysis of charge-dependent two- and three-particle correlations in Pb–Pb collisions at sNN=2.76 TeV. The two-particle correlator 〈cos⁡(φα−φβ)〉 calculated for different combinations of charges α and β is almost independent of v2 (for a given centrality), while the three-particle correlator 〈cos⁡(φα+φβ−2Ψ2)〉 scales almost linearly both with the event v2 and charged-particle pseudorapidity density. The charge dependence of the three-particle correlator is often interpreted as evidence for the Chiral Magnetic Effect (CME), a parity violating effect of the strong interaction. However, its measured dependence on v2 points to a large non-CME contribution to the correlator. Comparing the results with Monte Carlo calculations including a magnetic field due to the spectators, the upper limit of the CME signal contribution to the three-particle correlator in the 10–50% centrality interval is found to be 26–33% at 95% confidence level. © 2017 The Author(s)
7.
  • Acharya, S, et al. (författare)
  • Constraints on jet quenching in p–Pb collisions at sNN=5.02 TeV measured by the event-activity dependence of semi-inclusive hadron-jet distributions
  • 2018
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - Elsevier. - 0370-2693. ; 783, s. 95-113
  • Tidskriftsartikel (refereegranskat)abstract
    • The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high-transverse momentum trigger hadron in p–Pb collisions at sNN=5.02 TeV. Jets are reconstructed from charged-particle tracks using the anti-kT algorithm with resolution parameter R=0.2 and 0.4. A data-driven statistical approach is used to correct the uncorrelated background jet yield. Recoil jet distributions are reported for jet transverse momentum 15<pT,jet ch<50GeV/c and are compared in various intervals of p–Pb event activity, based on charged-particle multiplicity and zero-degree neutral energy in the forward (Pb-going) direction. The semi-inclusive observable is self-normalized and such comparisons do not require the interpretation of p–Pb event activity in terms of collision geometry, in contrast to inclusive jet observables. These measurements provide new constraints on the magnitude of jet quenching in small systems at the LHC. In p–Pb collisions with high event activity, the average medium-induced out-of-cone energy transport for jets with R=0.4 and 15<pT,jet ch<50GeV/c is measured to be less than 0.4 GeV/c at 90% confidence, which is over an order of magnitude smaller than a similar measurement for central Pb–Pb collisions at sNN=2.76TeV. Comparison is made to theoretical calculations of jet quenching in small systems, and to inclusive jet measurements in p–Pb collisions selected by event activity at the LHC and in d–Au collisions at RHIC. © 2018 European Organization for Nuclear Research
8.
  • Acharya, S, et al. (författare)
  • D-Meson Azimuthal Anisotropy in Midcentral Pb-Pb Collisions at s NN=5.02 TeV
  • 2018
  • Ingår i: Physical Review Letters. - American Physical Society. - 1079-7114. ; 120:10
  • Tidskriftsartikel (refereegranskat)abstract
    • The azimuthal anisotropy coefficient v2 of prompt D0, D+, D∗+, and Ds+ mesons was measured in midcentral (30%-50% centrality class) Pb-Pb collisions at a center-of-mass energy per nucleon pair sNN=5.02 TeV, with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decays at midrapidity, |y|
9.
  • Acharya, S, et al. (författare)
  • Dielectron and heavy-quark production in inelastic and high-multiplicity proton–proton collisions at s=13TeV
  • 2019
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - Elsevier. - 0370-2693. ; 788, s. 505-518
  • Tidskriftsartikel (refereegranskat)abstract
    • The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye|<0.8) in proton–proton (pp) collisions at a centre-of-mass energy of s=13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at s=7 TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: dσcc¯/dy|y=0=974±138(stat.)±140(syst.)±214(BR)μb and dσbb¯/dy|y=0=79±14(stat.)±11(syst.)±5(BR)μb using PYTHIA simulations and dσcc¯/dy|y=0=1417±184(stat.)±204(syst.)±312(BR)μb and dσbb¯/dy|y=0=48±14(stat.)±7(syst.)±3(BR)μb for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various pT intervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of pT. Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations. © 2018 The Author
10.
  • Acharya, S, et al. (författare)
  • Dielectron production in proton-proton collisions at √s=7 TeV
  • 2018
  • Ingår i: Journal of High Energy Physics. - Springer. - 1126-6708. ; 2018:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The first measurement of e+e− pair production at mid-rapidity (|ηe| < 0.8) in pp collisions at s=7 TeV with ALICE at the LHC is presented. The dielectron production is studied as a function of the invariant mass (mee < 3.3 GeV/c2), the pair transverse momentum (pT,ee < 8 GeV/c), and the pair transverse impact parameter (DCAee), i.e., the average distance of closest approach of the reconstructed electron and positron tracks to the collision vertex, normalised to its resolution. The results are compared with the expectations from a cocktail of known hadronic sources and are well described when PYTHIA is used to generate the heavy-flavour contributions. In the low-mass region (0.14 < mee < 1.1 GeV/c2), prompt and non-prompt e+e− sources can be separated via the DCAee. In the intermediate-mass region (1.1 < mee < 2.7 GeV/c2), a double-differential fit to the data in mee and pT,ee and a fit of the DCAee distribution allow the total c c ¯ and b b ¯ cross sections to be extracted. Two different event generators, PYTHIA and POWHEG, can reproduce the shape of the two-dimensional mee and pT,ee spectra, as well as the shape of the DCAee distribution, reasonably well. However, differences in the c c ¯ and b b ¯ cross sections are observed when using the generators to extrapolate to full phase space. Finally, the ratio of inclusive to decay photons is studied via the measurement of virtual direct photons in the transverse-momentum range 1 < pT < 8 GeV/c. This is found to be unity within the statistical and systematic uncertainties and consistent with expectations from next-to-leading order perturbative quantum chromodynamic calculations.[Figure not available: see fulltext.]. © 2018, The Author(s).
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