461 research outputs found
Physics of the Muon Spectrometer of the ALICE Experiment
The main goal of the Muon spectrometer of the ALICE experiment at LHC is the
measurement of heavy quark production in p+p, p+A and A+A collisions at LHC
energies, via the muonic channel. Physics motivations and expected performances
have been presented in this talk.Comment: 10 pages and 4 figures. Talk presented in the ICPAQGP Conference,
February 8-12, 2005, Salt Lake City, Kolkata, India. Web page of the
conference : http://www.veccal.ernet.in/~icpaqgp
A Cone Jet-Finding Algorithm for Heavy-Ion Collisions at LHC Energies
Standard jet finding techniques used in elementary particle collisions have
not been successful in the high track density of heavy-ion collisions. This
paper describes a modified cone-type jet finding algorithm developed for the
complex environment of heavy-ion collisions. The primary modification to the
algorithm is the evaluation and subtraction of the large background energy,
arising from uncorrelated soft hadrons, in each collision. A detailed analysis
of the background energy and its event-by-event fluctuations has been performed
on simulated data, and a method developed to estimate the background energy
inside the jet cone from the measured energy outside the cone on an
event-by-event basis. The algorithm has been tested using Monte-Carlo
simulations of Pb+Pb collisions at TeV for the ALICE detector at
the LHC. The algorithm can reconstruct jets with a transverse energy of 50 GeV
and above with an energy resolution of .Comment: 13 pages, 7 figure
Proton-Nucleus Collisions at the LHC: Scientific Opportunities and Requirements
Proton-nucleus (p+A) collisions have long been recognized as a crucial
component of the physics programme with nuclear beams at high energies, in
particular for their reference role to interpret and understand nucleus-nucleus
data as well as for their potential to elucidate the partonic structure of
matter at low parton fractional momenta (small-x). Here, we summarize the main
motivations that make a proton-nucleus run a decisive ingredient for a
successful heavy-ion programme at the Large Hadron Collider (LHC) and we
present unique scientific opportunities arising from these collisions. We also
review the status of ongoing discussions about operation plans for the p+A mode
at the LHC.Comment: 33 pages, 15 Figure
Effective Rheology of Bubbles Moving in a Capillary Tube
We calculate the average volumetric flux versus pressure drop of bubbles
moving in a single capillary tube with varying diameter, finding a square-root
relation from mapping the flow equations onto that of a driven overdamped
pendulum. The calculation is based on a derivation of the equation of motion of
a bubble train from considering the capillary forces and the entropy production
associated with the viscous flow. We also calculate the configurational
probability of the positions of the bubbles.Comment: 4 pages, 1 figur
Enhanced production of multi-strange hadrons in high-multiplicity proton-proton collisions
At sufficiently high temperature and energy density, nuclear matter undergoes a transition to a phase in which quarks and gluons are not confined: the quark-gluon plasma (QGP)(1). Such an exotic state of strongly interacting quantum chromodynamics matter is produced in the laboratory in heavy nuclei high-energy collisions, where an enhanced production of strange hadrons is observed(2-6). Strangeness enhancement, originally proposed as a signature of QGP formation in nuclear collisions(7), is more pronounced for multi-strange baryons. Several effects typical of heavy-ion phenomenology have been observed in high-multiplicity proton-proton (pp) collisions(8,9), but the enhanced production of multi-strange particles has not been reported so far. Here we present the first observation of strangeness enhancement in high-multiplicity proton-proton collisions. We find that the integrated yields of strange and multi-strange particles, relative to pions, increases significantly with the event charged-particle multiplicity. The measurements are in remarkable agreement with the p-Pb collision results(10,11), indicating that the phenomenon is related to the final system created in the collision. In high-multiplicity events strangeness production reaches values similar to those observed in Pb-Pb collisions, where a QGP is formed.Peer reviewe
Measurement of azimuthal correlations of D mesons with charged particles in pp collisions at √s=7 TeV and p-Pb collisions at √sNN=5.02 TeV
The azimuthal correlations of D mesons with charged particles were measured with the ALICE apparatus in pp collisions at root s = 7 TeV and p-Pb collisions at root sNN = 5.02 TeV at the Large Hadron Collider. D-0, D+, and D*+ mesons and their charge conjugates with transverse momentum 3 0.3 GeV/c. The yield of charged particles in the correlation peak induced by the jet containing the D meson and the peak width are compatible within uncertainties in the two collision systems. The data are described within uncertainties by Monte-Carlo simulations based on PYTHIA, POWHEG, and EPOS 3 event generators.Peer reviewe
Measurement of D-s(+) product ion and nuclear modification factor in Pb-Pb collisions at root S-NN=2.76 TeV
Peer reviewe
Elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity in Pb-Pb collisions at root s(NN)=2.76 TeV
The elliptic flow of electrons from heavy-flavour hadron decays at mid-rapidity (|y| <0.7) is measured in Pb-Pb collisions at TeV with ALICE at the LHC. The particle azimuthal distribution with respect to the reaction plane can be parametrized with a Fourier expansion, where the second coefficient (v (2)) represents the elliptic flow. The v (2) coefficient of inclusive electrons is measured in three centrality classes (0-10%, 10-20% and 20-40%) with the event plane and the scalar product methods in the transverse momentum (p (T)) intervals 0.5-13 GeV/c and 0.5-8 GeV/c, respectively. After subtracting the background, mainly from photon conversions and Dalitz decays of neutral mesons, a positive v (2) of electrons from heavy-flavour hadron decays is observed in all centrality classes, with a maximum significance of 5.9 sigma in the interval 2 <p (T) <2.5 GeV/c in semi-central collisions (20-40%). The value of v (2) decreases towards more central collisions at low and intermediate p (T) (0.5 <p (T) <3 GeV/c). The v (2) of electrons from heavy-flavour hadron decays at mid-rapidity is found to be similar to the one of muons from heavy-flavour hadron decays at forward rapidity (2.5 <y <4). The results are described within uncertainties by model calculations including substantial elastic interactions of heavy quarks with an expanding strongly-interacting medium.Peer reviewe
One-dimensional pion, kaon, and proton femtoscopy in Pb-Pb collisions at root(NN)-N-S=2.76 TeV
The size of the particle emission region in high-energy collisions can be deduced using the femtoscopic correlations of particle pairs at low relative momentum. Such correlations arise due to quantum statistics and Coulomb and strong final state interactions. In this paper, results are presented from femtoscopic analyses of pi(+/-) pi(+/-), K-+/- K-+/-, K-S(0) K-S(0), pp, and (pp) over bar correlations from Pb-Pb collisions at root s(NN) = 2.76 TeV by the ALICE experiment at the LHC. One-dimensional radii of the system are extracted from correlation functions in terms of the invariant momentum difference of the pair. The comparison of the measured radii with the predictions from a hydrokinetic model is discussed. The pion and kaon source radii display a monotonic decrease with increasing average pair transverse mass m(T) which is consistent with hydrodynamic model predictions for central collisions. The kaon and proton source sizes can be reasonably described by approximate m(T) scaling.Peer reviewe
Charged jet cross sections and properties in proton-proton collisions at root s=7 TeV
The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at center-of-mass energy root s = 7 TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the midrapidity region using the sequential recombination k(T) and anti-k(T) as well as the SISCone jet finding algorithms with several resolution parameters in the range R = 0.2-0.6. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum (p(T)) interval 20 ) of the reconstructed jet p(T). The fragmentation of leading jets with R = 0.4 using scaled p(T) spectra of the jet constituents is studied. The measurements are compared to model calculations from event generators (PYTHIA, PHOJET, HERWIG). The measured radial density distributions and distributions are well described by the PYTHIA model (tune Perugia-2011). The fragmentation distributions are better described by HERWIG.Peer reviewe
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