Analysis of directed flow from three-particle correlations

We present a new method for analysing directed flow, based on a three-particle azimuthal correlation. It is less biased by nonflow correlations than two-particle methods, and requires less statistics than four-particle methods. It is illustrated on NA49 data.Comment: Contribution to Quark Matter 2002, Nantes, July 18-24, 200

Exsertion, flowering and shedding in Panicum maximum (Poaceae)

La floraison, l'exsertion et la maturation des graines ont été observées sur les panicules de quatre clones de #P. maximum$. Les relations à l'intérieur du clone et les différences entre clones ont été étudiées. Floraison, exsertion et maturation des graines sont des processus rapides (< 10 j). Les dates et les durées sont stables à l'intérieur du clone, et les conséquences sur la récolte semencière ont été soulignées. Deux types de comportement floral et leur interaction avec le "seed-set" ont été décrits. La présence de ce polymorphisme montre que ces deux comportements ont soit une "fitness" similaire, soit une fitness dépendante de l'environnement. L'agencement dans le temps de la floraison, de la maturation des graines et de l'apparition successive de plusieurs panicules sur une même talle semble être contrôlé pour minimiser la compétition. Plusieurs points corroborent cette hypothèse : l'arrêt de cette ramification sur la talle lié à un retard de plus de 10 jours entre 2 panicules évite le recouvrement dans le temps des trois processus ; à l'intérieur d'un plant, les talles les plus vigoureuses ont le plus de panicules ; plus le nombre de panicules par talle d'un clone est petit, plus sa panicule est grande. (Résumé d'auteur

Determination of the reaction plane in ultrarelativistic nuclear collisions

In the particles produced in a nuclear collision undergo collective flow, the reaction plane can in principle be determined through a global event analysis. We show here that collective flow can be identified by evaluating the reaction plane independently in two separate rapidity intervals, and studying the correlation between the two results. We give an analytical expression for the correlation function between the two planes as a function of their relative angle. We also discuss how this correlation function is related to the anisotropy of the transverse momentum distribution. Email contact: [email protected]: Saclay-T93/026 Email: [email protected]

Staggering of heading in Panicum maximum Jacq. : origin and regulation

Chez #Panicum maximum$, l'étalement de l'épiaison sur 2 mois, voire plus est un comportement fréquent. L'initiation des talles sur 1 mois est à l'origine de la première vague d'épiaison. Les vagues suivantes sont le résultat d'un processus de ramification paniculaire. Deux principaux systèmes de régulation interviennent durant l'épiaison : 1. une régulation rapide qui alterne les jours de sous-épiaison et de sur-épiaison; 2. une régulation mensuelle qui diminue ou augmente l'intensité de la troisième vague en fonction de l'intensité de la première vague. Ces régulations dans l'étalement des investissements reproductifs peuvent constituer une adaptation aux variations de pluviométrie en milieu tropical. (Résumé d'auteur

Phenomenology of the little bang

I review recent selected developments in the theory and modeling of ultrarelativistic heavy-ion collisions. I explain why relativistic viscous hydrodynamics is now used to model the expansion of the matter formed in these collisions. I give examples of first quantitative predictions, and I discuss remaining open questions associated with the description of the freeze-out process. I argue that while the expansion process is now well understood, our knowledge of initial conditions is still poor. Recent analyses of two-particle correlations have revealed fine structures known as ridge and shoulder, which extend over a long range in rapidity. These correlations are thought to originate from initial state fluctuations, whose modeling is still crude. I discuss triangular flow, a simple mechanism recently put forward, through which fluctuations generate the observed correlation pattern.Comment: 10 pages, plenary talk at the International Nuclear Physics Conference (INPC 2010), Vancouver, Canada, July 4-9, 2010. (version 2: minor revision.

New method for measuring azimuthal distributions in nucleus-nucleus collisions

The methods currently used to measure azimuthal distributions of particles in heavy ion collisions assume that all azimuthal correlations between particles result from their correlation with the reaction plane. However, other correlations exist, and it is safe to neglect them only if azimuthal anisotropies are much larger than 1/sqrt(N), with N the total number of particles emitted in the collision. This condition is not satisfied at ultrarelativistic energies. We propose a new method, based on a cumulant expansion of multiparticle azimuthal correlations, which allows to measure much smaller values of azimuthal anisotropies, down to 1/N. It is simple to implement and can be used to measure both integrated and differential flow. Furthermore, this method automatically eliminates the major systematic errors, which are due to azimuthal asymmetries in the detector acceptance.Comment: final version (misprints corrected), to be published in Phys.Rev.

Cryopreservation of cell suspensions and embryogenic calluses of Citrus using a simplified freezing process

Une méthode de congélation simplifiée a été expérimentée avec une suspension cellulaire de mandarine commune et des cals embryogènes de six variétés de #citrus$. Son efficacité est comparable à celle du protocole de congélation standard développé précédemment pour ces matériels, qui nécessitait l'emploi d'un congélateur programmable. La suspension cellulaire peut être congelée sans modifier les conditions originales (0,15 M saccharose +5 % DMSO). Les cals embryogènes de 5 variétés sur les 6 expérimentées résistent à la congélation avec le procédé simplifié. Les résultats optimaux sont obtenus en augmentant la concentration en DMSO à 10 ou 15%. (Résumé d'auteur

Relativistic hydrodynamics for heavy-ion collisions

Relativistic hydrodynamics is essential to our current understanding of nucleus-nucleus collisions at ultrarelativistic energies (current experiments at the Relativistic Heavy Ion Collider, forthcoming experiments at the CERN Large Hadron Collider). This is an introduction to relativistic hydrodynamics for graduate students. It includes a detailed derivation of the equations, and a description of the hydrodynamical evolution of a heavy-ion collisions. Some knowledge of thermodynamics and special relativity is assumed.Comment: Lectures given at the Advanced School on Quark-Gluon Plasma, Indian Institute of Technology, Bombay, 3-13 July, 200

Effects of momentum conservation on the analysis of anisotropic flow

We present a general method for taking into account correlations due to momentum conservation in the analysis of anisotropic flow, either by using the two-particle correlation method or the standard flow vector method. In the latter, the correlation between the particle and the flow vector is either corrected through a redefinition (shift) of the flow vector, or subtracted explicitly from the observed flow coefficient. In addition, momentum conservation contributes to the reaction plane resolution. Momentum conservation mostly affects the first harmonic in azimuthal distributions, i.e., directed flow. It also modifies higher harmonics, for instance elliptic flow, when they are measured with respect to a first harmonic event plane such as one determined with the standard transverse momentum method. Our method is illustrated by application to NA49 data on pion directed flow.Comment: RevTeX 4, 10 pages, 1 eps figure. Version accepted for publication in Phys Rev

Elliptic flow at SPS and RHIC: from kinetic transport to hydrodynamics

Anisotropic transverse flow is studied in Pb+Pb and Au+Au collisions at SPS and RHIC energies. The centrality and transverse momentum dependence at midrapidity of the elliptic flow coefficient v_2 is calculated in the hydrodynamic and low density limits. Hydrodynamics is found to agree well with the RHIC data for semicentral collisions up to transverse momenta of 1-1.5 GeV/c, but it considerably overestimates the measured elliptic flow at SPS energies. The low density limit LDL is inconsistent with the measured magnitude of v_2 at RHIC energies and with the shape of its p_t-dependence at both RHIC and SPS energies. The success of the hydrodynamic model points to very rapid thermalization in Au+Au collisions at RHIC and provides a serious challenge for kinetic approaches based on classical scattering of on-shell particles.Comment: 7 pages incl. 5 figures; submitted to Physics Letters B; Ref. 4 and a few typos corrected; no changes in content