351 research outputs found
Systematic analysis of pT -distributions in p + p collisions
A systematic analysis of transverse momentum distribution of hadrons produced
in ultra-relativistic p + p collisions is presented. We investigate the
effective temperature and the entropic parameter from the non-extensive
thermodynamic theory of strong interaction. We conclude that the existence of a
limiting effective temperature and of a limiting entropic parameter is in
accordance with experimental data.Comment: 9 pages, 5 figure
Measurement of χ c1 and χ c2 production with s√ = 7 TeV pp collisions at ATLAS
The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at s√ = 7 TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → μ + μ −) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured
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
Collins and Sivers transverse-spin asymmetries in inclusive muoproduction of mesons
The production of vector mesons in deep inelastic scattering is an
interesting yet scarsely explored channel to study the transverse spin
structure of the nucleon and the related phenomena. The COMPASS collaboration
has performed the first measurement of the Collins and Sivers asymmetries for
inclusively produced mesons. The analysis is based on the data set
collected in deep inelastic scattering in using a
beam impinging on a transversely polarized target. The
mesons are selected from oppositely charged hadron pairs, and the
asymmetries are extracted as a function of the Bjorken- variable, the
transverse momentum of the pair and the fraction of the energy carried by
the pair. Indications for positive Collins and Sivers asymmetries are observed
Spin Density Matrix Elements in Exclusive Meson Muoproduction
We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard
exclusive meson muoproduction at COMPASS using 160~GeV/ polarised
and beams impinging on a liquid hydrogen target. The
measurement covers the kinematic range 5.0~GeV/ 17.0~GeV/,
1.0 (GeV/) 10.0 (GeV/) and 0.01 (GeV/) 0.5 (GeV/). Here, denotes the mass of the final
hadronic system, the virtuality of the exchanged photon, and
the transverse momentum of the meson with respect to the
virtual-photon direction. The measured non-zero SDMEs for the transitions of
transversely polarised virtual photons to longitudinally polarised vector
mesons () indicate a violation of -channel helicity
conservation. Additionally, we observe a dominant contribution of
natural-parity-exchange transitions and a very small contribution of
unnatural-parity-exchange transitions, which is compatible with zero within
experimental uncertainties. The results provide important input for modelling
Generalised Parton Distributions (GPDs). In particular, they may allow one to
evaluate in a model-dependent way the role of parton helicity-flip GPDs in
exclusive production
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
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
Impact of glucocorticoid receptor density on ligand-independent dimerization, cooperative ligand-binding and basal priming of transactivation: a cell culture model
Glucocorticoid receptor (GR) levels vary between tissues and individuals and are altered by physiological and pharmacological effectors. However, the effects and implications of differences in GR concentration have not been fully elucidated. Using three statistically different GR concentrations in transiently transfected COS-1 cells, we demonstrate, using co-immunoprecipitation (CoIP) and fluorescent resonance energy transfer (FRET), that high levels of wild type GR (wtGR), but not of dimerization deficient GR (GRdim), display ligand-independent dimerization. Whole-cell saturation ligand-binding experiments furthermore establish that positive cooperative ligand-binding, with a concomitant increased ligand-binding affinity, is facilitated by ligand-independent dimerization at high concentrations of wtGR, but not GRdim. The down-stream consequences of ligand-independent dimerization at high concentrations of wtGR, but not GRdim, are shown to include basal priming of the system as witnessed by ligand-independent transactivation of both a GRE-containing promoter-reporter and the endogenous glucocorticoid (GC)-responsive gene, GILZ, as well as ligand-independent loading of GR onto the GILZ promoter. Pursuant to the basal priming of the system, addition of ligand results in a significantly greater modulation of transactivation potency than would be expected solely from the increase in ligand-binding affinity. Thus ligand-independent dimerization of the GR at high concentrations primes the system, through ligand-independent DNA loading and transactivation, which together with positive cooperative ligand-binding increases the potency of GR agonists and shifts the bio-character of partial GR agonists. Clearly GR-levels are a major factor in determining the sensitivity to GCs and a critical factor regulating transcriptional programs
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