27 research outputs found
Two-pion Bose-Einstein correlations in central Pb-Pb collisions at = 2.76 TeV
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb
collisions at TeV at the Large Hadron Collider is
presented. We observe a growing trend with energy now not only for the
longitudinal and the outward but also for the sideward pion source radius. The
pion homogeneity volume and the decoupling time are significantly larger than
those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/388
Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at TeV
Inclusive transverse momentum spectra of primary charged particles in Pb-Pb
collisions at = 2.76 TeV have been measured by the ALICE
Collaboration at the LHC. The data are presented for central and peripheral
collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross
section. The measured charged particle spectra in and GeV/ are compared to the expectation in pp collisions at the same
, scaled by the number of underlying nucleon-nucleon
collisions. The comparison is expressed in terms of the nuclear modification
factor . The result indicates only weak medium effects ( 0.7) in peripheral collisions. In central collisions,
reaches a minimum of about 0.14 at -7GeV/ and increases
significantly at larger . The measured suppression of high- particles is stronger than that observed at lower collision energies,
indicating that a very dense medium is formed in central Pb-Pb collisions at
the LHC.Comment: 15 pages, 5 captioned figures, 3 tables, authors from page 10,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/98
Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at 2.76 TeV
We report on the first measurement of the triangular , quadrangular
, and pentagonal charged particle flow in Pb-Pb collisions at 2.76
TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show
that the triangular flow can be described in terms of the initial spatial
anisotropy and its fluctuations, which provides strong constraints on its
origin. In the most central events, where the elliptic flow and
have similar magnitude, a double peaked structure in the two-particle azimuthal
correlations is observed, which is often interpreted as a Mach cone response to
fast partons. We show that this structure can be naturally explained from the
measured anisotropic flow Fourier coefficients.Comment: 10 pages, 4 figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/387
Elliptic flow of identified hadrons in Pb-Pb collisions at 1asNN = 2.76 TeV
The elliptic flow coefficient (v2) of identified particles in Pb-Pb collisions at 1asNN = 2.76 TeV was measured with the ALICE detector at the Large Hadron Collider (LHC). The results were obtained with the Scalar Product method, a two-particle corre- lation technique, using a pseudo-rapidity gap of | 06\u3b7| > 0.9 between the identified hadron under study and the reference particles. The v2 is reported for \u3c0\ub1, K\ub1, K0S, p+p, \u3c6, \u39b+\u39b, \u39e 12+\u39e+ and \u3a9 12+\u3a9+ in several collision centralities. In the low transverse momentum (pT) region, pT 3 GeV/c
Centrality dependence of inclusive J/\u3c8 production in p-Pb collisions at 1asNN = 5.02 TeV
We present a measurement of inclusive J/\u3c8 production in p-Pb collisions at 1asNN = 5.02TeV as a function of the centrality of the collision, as estimated from the energy deposited in the Zero Degree Calorimeters. The measurement is performed with the ALICE detector down to zero transverse momentum, pT, in the backward ( 124.46 < ycms < 122.96) and forward (2.03 < ycms < 3.53) rapidity intervals in the dimuon decay channel and in the mid-rapidity region ( 121.37 < ycms < 0.43) in the dielectron decay channel. The backward and forward rapidity intervals correspond to the Pb-going and p-going direction, respectively. The pT-differential J/\u3c8 production cross section at backward and forward rapidity is measured for several centrality classes, together with the corresponding average pT and pT2 values. The nuclear modification factor is presented as a function of centrality for the three rapidity intervals, and as a function of pT for several centrality classes at backward and forward rapidity. At mid- and forward rapidity, the J/\u3c8 yield is suppressed up to 40% compared to that in pp interactions scaled by the number of binary collisions. The degree of suppression increases towards central p-Pb collisions at forward rapidity, and with decreasing pT of the J/\u3c8. At backward rapidity, the nuclear modification factor is compatible with unity within the total uncertainties, with an increasing trend from peripheral to central p-Pb collisions
Centrality dependence of high-pT D meson suppression in Pb-Pb collisions at 1asNN = 2.76 TeV
The nuclear modification factor, RAA, of the prompt charmed mesons D0, D+ and D 17+, and their antiparticles, was measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass energy 1asNN = 2.76 TeV in two transverse momentum intervals, 5 < pT < 8GeV/c and 8 < pT < 16GeV/c, and in six collision centrality classes. The RAA shows a maximum suppression of a factor of 5\u20136 in the 10% most central collisions. The suppression and its centrality dependence are compatible within uncertainties with those of charged pions. A comparison with the RAA of non-prompt J/\u3c8 from B meson decays, measured by the CMS Collaboration, hints at a larger suppression of D mesons in the most central collisions
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
Transverse Momentum Distribution and Nuclear Modification Factor of Charged Particles in p+Pb Collisions at sqrt[s_{NN}]=5.02\u2009\u2009TeV
The transverse momentum (pT) distribution of primary charged particles is measured in minimum bias (non-single-diffractive) p+Pb collisions at 1asNN=5.02 TeV with the ALICE detector at the LHC. The p T spectra measured near central rapidity in the range 0.5<p T<20 GeV/c exhibit a weak pseudorapidity dependence. The nuclear modification factor RpPb is consistent with unity for pT above 2 GeV/c. This measurement indicates that the strong suppression of hadron production at high pT observed in Pb+Pb collisions at the LHC is not due to an initial-state effect. The measurement is compared to theoretical calculations
Event-by-event mean pT \ua0fluctuations in pp and Pb\u2013Pb collisions at the LHC
Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at 1as = 0.9, 2.76 and 7 TeV, and Pb\u2013Pb collisions at 1asNN = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emis- sion are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb\u2013Pb data exhibit a similar multiplicity dependence as that observed in pp. In central Pb\u2013Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb\u2013 Pb are in qualitative agreement with previous measurements in Au\u2013Au at lower collision energies and with expectations from models that incorporate collective phenomena
Relationship between the mineralogical composition of the clay fraction of some andalusian caracteristic soils and theri behaviour in relation to potassium
12 páginas, 7 figuras, 3 tablas, 7 referencias.[ES]: Se estudia la fracción arcilla de los suelos más característicos de nuestra región
y su comportamiento frente al potasio, relacionándolo con la composición mineralógica
de dicha fracción.
Exceptuando el suelo fersialítico, los diferentes horizontes de cada suelo no presentan
variaciones importantes en su comportamiento frente al potasio.
Los suelos vérticos litomorfos y vérticos topomorfos presentan los valores más
altos de Kx, lo que está de acuerdo con una mayor edafización y con altas concentraciones
de montmorillonita e ilita. El suelo calcimorfo, a pesar de poseer composición
mineralógica simlar, está muy poco evolucionado y presenta valores más
bajos de Kx, similares a los del suelo aluvial, que está asimismo poco evolucionado,
con alta proporción de ilita, a la que acompañan pequeñas proporciones de montmorillonita
y caolinita. En el suelo fersialítico lavado disminuye el valor de Kx, al
descender en el perfil, en el mismo sentido en que disminuye la ilita y aumenta la
montmorillonita. Los horizontes C de los suelos de gran desarrollo edafogenético
presentan en relación con los horizontes superiores, a pesar de poseer composición
mineralógica similar, valores muy pequeños de Kx. El grado de desarrollo del suelo
es el que tiene mayor influencia en los valores de Kx.
Los tratamientos de eliminación de materia orgánica y/o geles producen un aumento
muy apreciable de los valores de Kx.[EN]: The clay fractions of soils caracteristic of western Anclalucía and their behaviour
in relation to potassium are studied, and the latter in related to the mineralogical
composition of the former.
Except the "fersialitico soil" (Rhocloxeralfs), the various horizons of each soil
do not present distinct variations in their behaviour in relation to potassium.
The "vertisol litomorfo" (chromoxererts) and «topomorfo» (Pelloxererts) soils
present the highest values of Kx which agrees with the strong weathering of these
soils and their nigh proportions of montmoillonite and illite. The "calcimorfo soil" (Calciorthids) is little weathered and present lower values of Kx, despite its mineralogical
composition, which is analogous to the preceding soils. Similarly low values
of Kx are obtained for the «aluvial soil» (Xerofluvents), also little weathered, which
contains high proportion of illite, with small amounts of montmorillonite and kaolinite.
The value of Kx and the proportion of illite for the leached fersialitico soil
decrease and the proportion of montmorillonite increases as getting down across the
profile.
C horizons of soils with high podogenic development present much lower values
of Kx than upper horizona, despite the analogy of their mineralogical compositions.
The degree of development of soils has the highest influence on Kx, values.
Treatments for removing organic matter and/or gels originate important increases
in Kx values.Peer reviewe