Particle-yield modification in jet-like azimuthal di-hadron correlations in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV

The yield of charged particles associated with high-$p_{\rm T}$ trigger particles ($8 < p_{\rm T} < 15$ GeV/$c$) is measured with the ALICE detector in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV relative to proton-proton collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jet-like correlation peaks in azimuthal di-hadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta $p_{\rm T}> 3$ GeV/$c$ on the away-side drops to about 60% of that observed in pp collisions, while on the near-side a moderate enhancement of 20-30% is found.Comment: 15 pages, 2 captioned figures, 1 table, authors from page 10, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/350

Sphagnum magellanicum growth and productivity in Chilean anthropogenic peatlands

Sphagnum peatlands are threatened at a global scale, not only by peat extraction, but also by Sphagnum harvesting. In Chile, dry Sphagnum moss is mainly exported for use as substrate for horticulture and orchids. Although the use of Sphagnum within Chile is limited, there are no data about its productivity and growth. These peatlands have a special microtopography with hummocks, hollows and lawns, which vary the distance of moss to the water table level. In these ecosystems, the water table is almost all year near the surface. We measured cumulative and relative growth rates and productivity during approximately one annual cycle in private Sphagnum peatlands that are being yearly harvested for commercial purposes. We evaluated the relationship between Sphagnum magellanicum growth and productivity with microtopography and water table depth. Productivity, cumulative and relative growths were higher in lawns than in hummocks. Overall and relative growth of S. magellanicum showed a negative relationship with depth of the water table. There were also differences between sites, some of them showed high growth rates, but low productivity. Sphagnum extraction in Chile, is now at low scale, but the growing international market demands constitute a real threat to the resource.Las turberas de Sphagnum están amenazadas a escala global, no solo por la extracción de turba, sino también por la cosecha de Sphagnum. En Chile, el musgo seco es importado principalemente para su uso como sustrato para la horticultura y cultivo de orquídeas. Aunque el uso del musgo en Chile es limitado, no existen datos sobre su productividad y crecimiento. Las turberas de Sphagnum tienen una microtopografía especial con cojines, zonas planas y zonas bajas o depresiones en el terreno, las que varían en la distancia del musgo a la napa freática. En estos ecosistemas, el nivel freático se encuentra gran parte del año muy cercano a la superfi cie. Se midieron las tasas de crecimiento acumulado y relativo por aproximadamente un ciclo anual en turberas de Sphagnum que se cosechan periódicamente para fi nes comerciales. Se evaluó la relación entre el crecimiento de Sphagnum magellanicum y la productividad con la microtopografía y la profundidad de la napa freática. La productividad, el crecimiento acumulado y relativo fueron mayores en zonas bajas que en cojines. El crecimiento total y relativo de S. magellanicum mostró una relación negativa con la profundidad de la napa freática. También se encontraron diferencias entre sitios, algunos mostraron mayores tasas de crecimiento en altura, pero menor productividad. La extracción de Sphagnum en Chile aún se realiza a baja escala, pero la creciente demanda del mercado internacional constituye una real amenaza para el musgo

Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions at root s(NN)=2.76 TeV

The centrality dependence of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at root s(NN) = 2: 76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor of 2 from peripheral (70%-80%) to central (0%-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions

Light vector meson production in pp collisions at sqrt(s)= 7 TeV.

The ALICE experiment has measured low-mass dimuon production in pp collisions at root s = 7 TeV in the dimuon rapidity region 2.5 < y < 4. The observed dimuon mass spectrum is described as a superposition of resonance decays (eta, rho, omega, eta', phi) into muons and semi-leptonic decays of charmed mesons. The measured production cross sections for omega and phi are sigma(omega)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 5.28 +/- 0.54(stat) +/- 0.49(syst) mb and sigma(phi)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 0.940 +/- 0.084(stat) +/- 0.076(syst) mb. The differential cross sections d(2)sigma/dy dp(t) are extracted as a function of p(t) for omega and phi. The ratio between the rho and omega cross section is obtained. Results for the phi are compared with other measurements at the same energy and with predictions by models

Harmonic decomposition of two particle angular correlations in Pb\u2013Pb collisions at 1asNN = 2.76 TeV.

Angular correlations between unidentified charged trigger (t) and associated (a) particles are measured by the ALICE experiment in Pb\u2013Pb collisions at 1asNN = 2.76 TeV for transverse momenta 0.25 p(aT) . The shapes of the pair correlation distributions are studied in a variety of collision centrality classes between 0 and 50% of the total hadronic cross section for particles in the pseudorapidity interval |\u3b7| 0.8, and are referred to as \u201clong-range correlations\u201d. Fourier components Vn 61 cos(n\u3c6) are extracted from the long-range azimuthal correlation functions. If particle pairs are correlated to one another through their individual correlation to a common symmetry plane, then the pair anisotropy Vn(p(tT) , p(aT) ) is fully described in terms of single-particle anisotropies vn(pT) as Vn(p(tT), p(aT)) = vn(p(tT)vn(paT). This expectation is tested for 1 64 n 64 5 by applying a global fit of all Vn(p(tT), p(aT) to obtain the best values vn{GF}(pT ). It is found that for 2 64 n 64 5, the fit agrees well with data up to p(aT) ~ 3\u20134 GeV/c, with a trend of increasing deviation as p(tT) and p(aT) are increased or as collisions become more peripheral. This suggests that no pair correlation harmonic can be described over the full 0.25 < pT < 15 GeV/c range using a single vn(pT) curve; such a description is however approximately possible for 2 64 n 64 5 when p(aT) <4 GeV/c. For the n = 1 harmonic, however, a single v1(pT) curve is not obtained even within the reduced range p(aT) <4 GeV/c

J/psi polarization in pp collisions at sqrt(s)=7 TeV

See paper for full list of authors - 3 figures, 1 table, submitted to Phys. Rev. LettInternational audienceThe ALICE Collaboration has studied J/psi production in pp collisions at sqrt(s)=7 TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/psi polarization parameters lambda_theta and lambda_phi were obtained. The study was performed in the kinematic region 2.