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Open Access Publications from the University of California

Scholarly Works (145 results)

  • Article
  • Peer Reviewed
UC Berkeley Previously Published Works (2020)
The production of the Λ (1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at s=7TeV and in p–Pb collisions at sNN=5.02TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel Λ (1520) → pK - and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p–Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (π, K, KS0, p, Λ) describes the shape of the Λ (1520) transverse momentum distribution up to 3.5GeV/c in p–Pb collisions. In the framework of this model, this observation suggests that the Λ (1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of Λ (1520) to the yield of the ground state particle Λ remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p–Pb collisions on the Λ (1520) yield.
    Cover page: Measurement of Λ(1520) production in pp collisions at s=7TeV and p–Pb collisions at sNN=5.02TeV
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2016)
    We present results of a search for two hypothetical strange dibaryon states, i.e. the H-dibaryon and the possible Λn‾ bound state. The search is performed with the ALICE detector in central (0–10%) Pb–Pb collisions at sNN=2.76 TeV, by invariant mass analysis in the decay modes Λn‾→d‾π+ and H-dibaryon →Λpπ−. No evidence for these bound states is observed. Upper limits are determined at 99% confidence level for a wide range of lifetimes and for the full range of branching ratios. The results are compared to thermal, coalescence and hybrid UrQMD model expectations, which describe correctly the production of other loosely bound states, like the deuteron and the hypertriton.
      Cover page: Search for weakly decaying Λn‾ and ΛΛ exotic bound states in central Pb–Pb collisions at sNN=2.76 TeV
      • Article
      • Peer Reviewed
      LBL Publications (2019)
      The production of the ρ(770)0 meson has been measured at midrapidity (|y|<0.5) in pp and centrality differential Pb-Pb collisions at sNN= 2.76 TeV with the ALICE detector at the Large Hadron Collider. The particles have been reconstructed in the ρ(770)0→π+π- decay channel in the transverse-momentum (pT) range 0.5-11 GeV/c. A centrality-dependent suppression of the ratio of the integrated yields 2ρ(770)0/(π++π-) is observed. The ratio decreases by ∼40% from pp to central Pb-Pb collisions. A study of the pT-differential 2ρ(770)0/(π++π-) ratio reveals that the suppression occurs at low transverse momenta, pT<2 GeV/c. At higher momentum, particle ratios measured in heavy-ion and pp collisions are consistent. The observed suppression is very similar to that previously measured for the K∗(892)0/K ratio and is consistent with EPOS3 predictions that may imply that rescattering in the hadronic phase is a dominant mechanism for the observed suppression.
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2013)
        Differential cross sections of charged particles in inelastic pp collisions as a function of pT have been measured at [Formula: see text] at the LHC. The pT spectra are compared to NLO-pQCD calculations. Though the differential cross section for an individual [Formula: see text] cannot be described by NLO-pQCD, the relative increase of cross section with [Formula: see text] is in agreement with NLO-pQCD. Based on these measurements and observations, procedures are discussed to construct pp reference spectra at [Formula: see text] up to pT=50 GeV/c as required for the calculation of the nuclear modification factor in nucleus-nucleus and proton-nucleus collisions.
          Cover page: Energy dependence of the transverse momentum distributions of charged particles in pp collisions measured by ALICE
          • Article
          • Peer Reviewed
          LBL Publications (2019)
          Inclusive ϒ(1S) and ϒ(2S) production have been measured in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair sNN=5.02 TeV, using the ALICE detector at the CERN LHC. The ϒ mesons are reconstructed in the centre-of-mass rapidity interval 2.5
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2017)
            The transverse momentum (pT) spectra and elliptic flow coefficient (v2) of deuterons and anti-deuterons at mid-rapidity (| y| < 0.5) are measured with the ALICE detector at the LHC in Pb–Pb collisions at sNN = 2.76 TeV. The measurement of the pTspectra of (anti-)deuterons is done up to 8 GeV/ c in 0–10% centrality class and up to 6 GeV/ c in 10–20% and 20–40% centrality classes. The v2is measured in the 0.8 < pT<5 GeV/ c interval and in six different centrality intervals (0–5, 5–10, 10–20, 20–30, 30–40 and 40–50%) using the scalar product technique. Measured π±, K± and p+p ¯ transverse-momentum spectra and v2are used to predict the deuteron pTspectra and v2within the Blast-Wave model. The predictions are able to reproduce the v2 coefficient in the measured pTrange and the transverse-momentum spectra for pT> 1.8 GeV/ c within the experimental uncertainties. The measurement of the coalescence parameter B2is performed, showing a pT dependence in contrast with the simplest coalescence model, which fails to reproduce also the measured v2 coefficient. In addition, the coalescence parameter B2 and the elliptic flow coefficient in the 20–40% centrality interval are compared with the AMPT model which is able, in its version without string melting, to reproduce the measured v2(pT) and the B2(pT) trend.
              Cover page: Measurement of deuteron spectra and elliptic flow in Pb–Pb collisions at sNN = 2.76 TeV at the LHC
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2019)
              The measurements of the production of prompt D , D +, D ∗ +, and Ds+ mesons in proton–proton (pp) collisions at s=5.02TeV with the ALICE detector at the Large Hadron Collider (LHC) are reported. D mesons were reconstructed at mid-rapidity (| y| < 0.5) via their hadronic decay channels D → K -π+, D +→ K -π+π+, D ∗ +→ D π+→ K -π+π+, Ds+→ϕπ+→K+K-π+, and their charge conjugates. The production cross sections were measured in the transverse momentum interval 0
                • Article
                • Peer Reviewed
                LBL Publications (2019)
                The first measurement of dielectron (e+e-) production in central (0-10%) Pb-Pb collisions at sNN=2.76TeV at the LHC is presented. The dielectron invariant-mass spectrum is compared to the expected contributions from hadron decays in the invariant-mass range 0
                  • Article
                  • Peer Reviewed
                  UC Berkeley Previously Published Works (2016)
                  We report on results obtained with the event-shape engineering technique applied to Pb-Pb collisions at sNN=2.76 TeV. By selecting events in the same centrality interval, but with very different average flow, different initial-state conditions can be studied. We find the effect of the event-shape selection on the elliptic flow coefficient v2 to be almost independent of transverse momentum pT, which is as expected if this effect is attributable to fluctuations in the initial geometry of the system. Charged-hadron, -pion, -kaon, and -proton transverse momentum distributions are found to be harder in events with higher-than-average elliptic flow, indicating an interplay between radial and elliptic flow.
                    Cover page: Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at sNN=2.76 TeV
                    • Article
                    • Peer Reviewed
                    UC Berkeley Previously Published Works (2020)
                    Midrapidity production of π±, K±, and (p¯)p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at sNN=5.02 TeV, is presented. The invariant yields are measured over a wide transverse momentum (pT) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0-90%. The comparison of the pT-integrated particle ratios, i.e., proton-to-pion (p/π) and kaon-to-pion (K/π) ratios, with similar measurements in Pb-Pb collisions at sNN=2.76 TeV show no significant energy dependence. Blast-wave fits of the pT spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios (p/π, K/π) as a function of pT show pronounced maxima at pT≈3GeV/c in central Pb-Pb collisions. At high pT, particle ratios at 5.02 TeV are similar to those measured in pp collisions at the same energy and in Pb-Pb collisions at sNN=2.76 TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high pT and compatible with measurements at sNN=2.76 TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.
                      Cover page: Production of charged pions, kaons, and (anti-)protons in Pb-Pb and inelastic pp collisions at sNN=5.02 TeV
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