654 research outputs found
Measurement of an excess in the yield of J/ at very low in Pb-Pb collisions at = 2.76 TeV
We report on the first measurement of an excess in the yield of J/ at
very low transverse momentum ( GeV/) in peripheral hadronic
Pb-Pb collisions at = 2.76 TeV, performed by ALICE at the
CERN LHC. Remarkably, the measured nuclear modification factor of J/ in
the rapidity range reaches about 7 (2) in the range 0-0.3
GeV/ in the 70-90% (50-70%) centrality class. The J/ production cross
section associated with the observed excess is obtained under the hypothesis
that coherent photoproduction of J/ is the underlying physics mechanism.
If confirmed, the observation of J/ coherent photoproduction in Pb-Pb
collisions at impact parameters smaller than twice the nuclear radius opens new
theoretical and experimental challenges and opportunities. In particular,
coherent photoproduction accompanying hadronic collisions may provide insight
into the dynamics of photoproduction and nuclear reactions, as well as become a
novel probe of the Quark-Gluon Plasma.Comment: 18 pages, 3 captioned figures, 1 table, authors from page 13,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/191
Measurement of pion, kaon and proton production in proton-proton collisions at TeV
The measurement of primary , K, p and
production at mid-rapidity ( 0.5) in proton-proton collisions at
TeV performed with ALICE (A Large Ion Collider Experiment) at
the Large Hadron Collider (LHC) is reported. Particle identification is
performed using the specific ionization energy loss and time-of-flight
information, the ring-imaging Cherenkov technique and the kink-topology
identification of weak decays of charged kaons. Transverse momentum spectra are
measured from 0.1 up to 3 GeV/ for pions, from 0.2 up to 6 GeV/ for kaons
and from 0.3 up to 6 GeV/ for protons. The measured spectra and particle
ratios are compared with QCD-inspired models, tuned to reproduce also the
earlier measurements performed at the LHC. Furthermore, the integrated particle
yields and ratios as well as the average transverse momenta are compared with
results at lower collision energies.Comment: 33 pages, 19 captioned figures, 3 tables, authors from page 28,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/156
First measurement of production in pp collisions at = 7 TeV
The production of the charm-strange baryon is measured for
the first time at the LHC via its semileptonic decay into e
in pp collisions at TeV with the ALICE detector. The transverse
momentum () differential cross section multiplied by the branching
ratio is presented in the interval 1 8 GeV/ at
mid-rapidity, 0.5. The transverse momentum dependence of the
baryon production relative to the D meson production is
compared to predictions of event generators with various tunes of the
hadronisation mechanism, which are found to underestimate the measured
cross-section ratio.Comment: 22 pages, 6 captioned figures, 1 table, authors from page 17,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/412
Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in Pb-Pb collisions at = 2.76$ TeV
In ultrarelativistic heavy-ion collisions, the event-by-event variation of
the elliptic flow reflects fluctuations in the shape of the initial state
of the system. This allows to select events with the same centrality but
different initial geometry. This selection technique, Event Shape Engineering,
has been used in the analysis of charge-dependent two- and three-particle
correlations in Pb-Pb collisions at TeV. The
two-particle correlator ,
calculated for different combinations of charges and , is
almost independent of (for a given centrality), while the three-particle
correlator
scales almost linearly both with the event and charged-particle
pseudorapidity density. The charge dependence of the three-particle correlator
is often interpreted as evidence for the Chiral Magnetic Effect (CME), a parity
violating effect of the strong interaction. However, its measured dependence on
points to a large non-CME contribution to the correlator. Comparing the
results with Monte Carlo calculations including a magnetic field due to the
spectators, the upper limit of the CME signal contribution to the
three-particle correlator in the 10-50% centrality interval is found to be
26-33% at 95% confidence level.Comment: 20 pages, 6 captioned figures, 1 tables, authors from page 15,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/382
Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at = 5.02 TeV
Two-particle angular correlations between unidentified charged trigger and
associated particles are measured by the ALICE detector in p-Pb collisions at a
nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum
range 0.7 5.0 GeV/ is examined,
to include correlations induced by jets originating from low
momen\-tum-transfer scatterings (minijets). The correlations expressed as
associated yield per trigger particle are obtained in the pseudorapidity range
. The near-side long-range pseudorapidity correlations observed in
high-multiplicity p-Pb collisions are subtracted from both near-side
short-range and away-side correlations in order to remove the non-jet-like
components. The yields in the jet-like peaks are found to be invariant with
event multiplicity with the exception of events with low multiplicity. This
invariance is consistent with the particles being produced via the incoherent
fragmentation of multiple parton--parton scatterings, while the yield related
to the previously observed ridge structures is not jet-related. The number of
uncorrelated sources of particle production is found to increase linearly with
multiplicity, suggesting no saturation of the number of multi-parton
interactions even in the highest multiplicity p-Pb collisions. Further, the
number scales in the intermediate multiplicity region with the number of binary
nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/161
Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider
Measurements of multi-particle azimuthal correlations (cumulants) for charged
particles in p-Pb and Pb-Pb collisions are presented. They help address the
question of whether there is evidence for global, flow-like, azimuthal
correlations in the p-Pb system. Comparisons are made to measurements from the
larger Pb-Pb system, where such evidence is established. In particular, the
second harmonic two-particle cumulants are found to decrease with multiplicity,
characteristic of a dominance of few-particle correlations in p-Pb collisions.
However, when a gap is placed to suppress such correlations,
the two-particle cumulants begin to rise at high-multiplicity, indicating the
presence of global azimuthal correlations. The Pb-Pb values are higher than the
p-Pb values at similar multiplicities. In both systems, the second harmonic
four-particle cumulants exhibit a transition from positive to negative values
when the multiplicity increases. The negative values allow for a measurement of
to be made, which is found to be higher in Pb-Pb collisions at
similar multiplicities. The second harmonic six-particle cumulants are also
found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find
which is indicative of a Bessel-Gaussian
function for the distribution. For very high-multiplicity Pb-Pb
collisions, we observe that the four- and six-particle cumulants become
consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and
Pb-Pb are measured. These are found to be similar for overlapping
multiplicities, when a gap is placed.Comment: 25 pages, 11 captioned figures, 3 tables, authors from page 20,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/87
Death and Resurrection of the Human IRGM Gene
Immunity-related GTPases (IRG) play an important role in defense against intracellular pathogens. One member of this gene family in humans, IRGM, has been recently implicated as a risk factor for Crohn's disease. We analyzed the detailed structure of this gene family among primates and showed that most of the IRG gene cluster was deleted early in primate evolution, after the divergence of the anthropoids from prosimians ( about 50 million years ago). Comparative sequence analysis of New World and Old World monkey species shows that the single-copy IRGM gene became pseudogenized as a result of an Alu retrotransposition event in the anthropoid common ancestor that disrupted the open reading frame (ORF). We find that the ORF was reestablished as a part of a polymorphic stop codon in the common ancestor of humans and great apes. Expression analysis suggests that this change occurred in conjunction with the insertion of an endogenous retrovirus, which altered the transcription initiation, splicing, and expression profile of IRGM. These data argue that the gene became pseudogenized and was then resurrected through a series of complex structural events and suggest remarkable functional plasticity where alleles experience diverse evolutionary pressures over time. Such dynamism in structure and evolution may be critical for a gene family locked in an arms race with an ever-changing repertoire of intracellular parasites
Особливості співробітництва України з Міжнародним валютним фондом
Ціль статті - розкрити особливості співпраці України з МВФ, спрямованої на досягнення макроекономічної стабілізації в умовах світової фінансової кризи. Для досягнення мети було поставлено і вирішено коло завдань, у тому числі: дослідити основні проблеми та перспективи співробітництва України з МВФ та розкрити сутність стабілізаційних програм і визначити в них роль МВФ
Вступне слово
Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at 0.9, 2.76 and 7 TeV, and Pb–Pb collisions at 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 emission 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–Pb data exhibit a similar multiplicity dependence as that observed in pp. In central Pb–Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb–Pb are in qualitative agreement with previous measurements in Au–Au at lower collision energies and with expectations from models that incorporate collective phenomena
Ієрархія лексем у польовій структурі
У статті зроблено спробу з’ясувати ієрархічні відношення і структурно-семантичні особливості центральних одиниць, які творять ядро лексико-семантичного поля. Аналіз здійснено на матеріалі лексем, які є членами лексико-семантичного поля звуконайменувань. Зроблено висновки про спільні риси ядерних одиниць, про характер постійних, диференційних і факультативних семантичних ознак, виявлено ієрархію сем у структурі ядерної одиниці.The article is aimed to identify hierarchical relations as well as structural and semantic features of central items, which constitute the core of a lexical-semantic field. The analysis is conducted on the basis of lexemes, which are components of the sound nominations semantic field. The analysis defines common features of core items, a character of permanent, differential and optional semantic features, as well as semes hierarchy in a structure of core item
- …