Production of the rho(770)(0) meson in pp and Pb-Pb collisions at root S-NN=2.76 TeV

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

Lambda(+)(c) production in pp collisions at root s=7 TeV and in p-Pb collisions at root s(NN)=5.02 TeV

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOThe p(T)-differential production cross section of prompt Lambda(+)(c) charmed baryons was measured with the ALICE detector at the Large Hadron Collider (LHC) in pp collisions at root s = 7 TeV and in p-Pb collisions at root s(NN) = 5.02 TeV at midrapidity. The Lambda(+)(c) and (Lambda) over bar (-)(c) were reconstructed in the hadronic decay modes Lambda(+)(c) -gt; pK(-)pi(+), Lambda(+)(c)-gt; pK(S)(0)) and in the semileptonic channel Lambda(+ )(c)-gt; e(+)nu(e)Lambda (and charge conjugates). The measured values of the Lambda(+)(c)/D-0 ratio, which is sensitive to the c-quark hadronisation mechanism, and in particular to the production of baryons, are presented and are larger than those measured previously in different colliding systems, centre-of-mass energies, rapidity and p(T) intervals, where the Lambda(+)(c) production process may differ. The results are compared with the expectations obtained from perturbative Quantum Chromodynamics calculations and Monte Carlo event generators. Neither perturbative QCD calculations nor Monte Carlo models reproduce the data, indicating that the fragmentation of heavy-flavour baryons is not well understood. The first measurement at the LHC of the Lambda(+)(c) nuclear modification factor, R-ppb, is also presented. The R-ppb is found to be consistent with unity and with that of D mesons within the uncertainties, and consistent with a theoretical calculation that includes cold nuclear matter effects and a calculation that includes charm quark interactions with a deconfined medium.4147CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOAgências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig

Dielectron and heavy-quark production in inelastic and high-multiplicity proton-proton collisions at root s=13 TeV

The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye|<0.8) in proton\u2013proton (pp) collisions at a centre-of-mass energy 1as = 13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at 1as = 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: d\u3c3cc \u304/dy|y=0 = 974 \ub1 138(stat.) \ub1 140(syst.) \ub1 214(BR) \u3bcb and d\u3c3bb \u304/dy|y=0 =79\ub114(stat.)\ub111(syst.)\ub15(BR) \u3bcb using PYTHIA simulations and d\u3c3cc \u304/dy|y=0 = 1417 \ub1 184(stat.) \ub1 204(syst.) \ub1 312(BR) \u3bcb and d\u3c3bb \u304/dy|y=0 = 48 \ub1 14(stat.) \ub1 7(syst.) \ub1 3(BR) \u3bcb 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

Neutral pion and eta meson production at midrapidity in Pb-Pb collisions at root S-NN=2.76 TeV

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULONeutral pion and eta meson production in the transverse momentum range 1 < p(T) < 20 GeV/c have been measured at midrapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semicentral Pb-Pb collisions at root S-NN = 2.76 TeV. These results were obtained using the photon conversion method as well as the Photon Spectrometer (PHOS) and Electromagnetic Calorimeter detectors. The results extend the upper p(T) reach of the previous ALICE pi(0) measurements from 12 to 20 GeV/c and present the first measurement of eta meson production in heavy-ion collisions at the LHC. The eta/pi(0) ratio is similar for the two centralities and reaches at high p(T) a plateau value of 0.457 +/- 0.013(stat) +/- 0.018(syst) A suppression of similar magnitude for pi(0) and eta meson production is observed in Pb-Pb collisions with respect to their production in pp collisions scaled by the number of binary nucleon-nucleon collisions. We discuss the results in terms of Next to Leading Order (NLO) pQCD predictions and hydrodynamic models. The measurements show a stronger suppression than observed at lower center-of-mass energies in the p T range 6 < p(T) < 10 GeV/c. For p(T) < 3 GeV/c, hadronization models describe the pi(0) results while for the eta some tension is observed.984120CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOAgências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig

Dielectron and heavy-quark production in inelastic and high-multiplicity proton-proton collisions at root s=13 TeV

The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (p T ) at midrapidity (|y e |<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: dσ cc¯ /dy| y=0 =974±138(stat.)±140(syst.)±214(BR)μb and dσ bb¯ /dy| y=0 =79±14(stat.)±11(syst.)±5(BR)μb using PYTHIA simulations and dσ cc¯ /dy| y=0 =1417±184(stat.)±204(syst.)±312(BR)μb and dσ bb¯ /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 p T 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 p T . Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations

Dielectron and heavy-quark production in inelastic and high-multiplicity proton–proton collisions at s=13TeV

The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (p T ) at midrapidity (|y e |<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: dσ cc¯ /dy| y=0 =974±138(stat.)±140(syst.)±214(BR)μb and dσ bb¯ /dy| y=0 =79±14(stat.)±11(syst.)±5(BR)μb using PYTHIA simulations and dσ cc¯ /dy| y=0 =1417±184(stat.)±204(syst.)±312(BR)μb and dσ bb¯ /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 p T 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 p T . Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations