487 research outputs found
The "Ridge" in Proton-Proton Scattering at 7 TeV
One of the most important experimental results for proton-proton scattering
at the LHC is the observation of a so-called "ridge" structure in the two
particle correlation function versus the pseudorapidity difference
and the azimuthal angle difference . One finds a strong correlation
around , extended over many units in . We show that a
hydrodynamical expansion based on flux tube initial conditions leads in a
natural way to the observed structure. To get this result, we have to perform
an event-by-event calculation, because the effect is due to statistical
fluctuations of the initial conditions, together with a subsequent collective
expansion. This is a strong point in favour of a fluid-like behavior even in
scattering, where we have to deal with length scales of the order of 0.1
fm.Comment: 5 pages, 4 figure
Hydrodynamic Models for Heavy Ion Collisions
Application of hydrodynamics for modeling of heavy-ion collisions is
reviewed. We consider several physical observables that can be calculated in
this approach and compare them to the experimental measurements.Comment: 42 pages, 15 figures, An invited review for Nov. 2006 edition of
Annual Review of Nuclear and Particle Physic
Formation Time of QGP from Thermal Photon Elliptic Flow
We show that the transverse momentum dependent elliptic flow of
thermal photons is quite sensitive to the initial formation time () of
Quark Gluon Plasma (QGP) for semi-central collision of gold nuclei at RHIC
\cite{tau}. A smaller value of the formation time or a larger initial
temperature leads to a significant increase in the thermal photon radiation
from QGP phase, which has a smaller . The elliptic flow of thermal photon
is dominated by the contribution from the quark matter at intermediate and high
range and as a result sum decreases with smaller for GeV. On the other hand we find that the elliptic flow parameter for
hadrons depends only marginally on the value of .Comment: 4 pages, 3 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee, v2: minor
correction
Dynamical freeze-out condition in ultrarelativistic heavy ion collisions
We determine the decoupling surfaces for the hydrodynamic description of
heavy ion collisions at RHIC and LHC by comparing the local hydrodynamic
expansion rate with the microscopic pion-pion scattering rate. The pion
spectra for nuclear collisions at RHIC and LHC are computed by applying the
Cooper-Frye procedure on the dynamical-decoupling surfaces, and compared with
those obtained from the constant-temperature freeze-out surfaces. Comparison
with RHIC data shows that the system indeed decouples when the expansion rate
becomes comparable with the pion scattering rate. The dynamical decoupling
based on the rates comparison also suggests that the effective decoupling
temperature in central heavy ion collisions remains practically unchanged from
RHIC to LHC.Comment: 7 pages, 9 figure
Elliptic flow in nuclear collisions at the Large Hadron Collider
We use perfect-fluid hydrodynamical model to predict the elliptic flow
coefficients in Pb + Pb collisions at the Large Hadron Collider (LHC). The
initial state for the hydrodynamical calculation for central collisions
is obtained from the perturbative QCD + saturation (EKRT) model. The centrality
dependence of the initial state is modeled by the optical Glauber model. We
show that the baseline results obtained from the framework are in good
agreement with the data from the Relativistic Heavy Ion Collider (RHIC), and
show predictions for the spectra and elliptic flow of pions in Pb + Pb
collisions at the LHC. Also mass and multiplicity effects are discussed.Comment: 11 pages, 10 figure
v4: A small, but sensitive observable for heavy ion collisions
Higher order Fourier coefficients of the azimuthally dependent single
particle spectra resulting from noncentral heavy ion collisions are
investigated. For intermediate to large transverse momenta, these anisotropies
are expected to become as large as 5 %, and should be clearly measurable. The
physics content of these observables is discussed from two different extreme
but complementary viewpoints, hydrodynamics and the geometric limit with
extreme energy loss.Comment: as published: typos corrected, Fig. 3 slightly improved in numerics
and presentatio
Rapid hydrodynamic expansion in relativistic heavy-ion collisions
Hydrodynamic expansion of the hot fireball created in relativistic Au-Au
collisions at 200GeV in 3+1-dimensions is studied. We obtain a simultaneous,
satisfactory description of the transverse momentum spectra, elliptic flow and
pion correlation radii for different collision centralities and different
rapidities. Early initial time of the evolution is required to reproduce the
interferometry data, which provides a strong indication of the early onset of
collectivity. We can also constraint the shape of the initial energy density in
the beam direction, with a relatively high initial energy density at the center
of the fireball.Comment: 10 pages, 13 fig
The effect of ethanol and nicotine on ER stress in human placental villous explants
Pregnant mothers continue smoking and drinking during pregnancy. To clarify the mechanisms of nicotine and ethanol toxicity during development, we have examined their effects on endoplasmic reticulum (ER) stress in human first trimester and term placental explants. First trimester and term human placental explants were treated with ethanol (2 ‰) or nicotine (15 µM), or their combination. The ER stress markers glucose regulated protein 78 (GRP78/BiP) and inositol requiring enzyme 1 α (IRE1α) were analyzed by immunoblotting. A statistically significant increase (p < 0.05) of GRP78/BiP by nicotine was noted in first trimester placental explants at 48 h, and in term placental explants at 24 h. Ethanol did not change protein expression of GRP78/BiP in either first trimester or term placental explants. IRE1α increased, although not statistically significantly, by all treatments in both first trimester and term placental explants. Thus, regardless of the known structural and functional differences in early and late placenta, both responded very similarly to the toxic compounds studied. These data support our earlier results in BeWo cells (Repo et al., 2014) implicating that nicotine induces ER stress in human placenta and may interfere with placental functions potentially disrupting fetal growth and development
Size fluctuations of the initial source and the event-by-event transverse momentum fluctuations in relativistic heavy-ion collisions
We show that the event-by-event fluctuations of the transverse size of the
initial source, which follow directly from the Glauber treatment of the
earliest stage of relativistic heavy-ion collisions, cause, after hydrodynamic
evolution, fluctuations of the transverse flow velocity at hadronic freeze-out.
This in turn leads to event-by-event fluctuations of the average transverse
momentum, p_T. Simulations with GLISSANDO for the Glauber phase, followed by a
realistic hydrodynamic evolution and statistical hadronization carried out with
THERMINATOR, lead to agreement with the RHIC data. In particular, the magnitude
of the effect, its centrality dependence, and the weak dependence on the
incident energy are properly reproduced. Our results show that bulk of the
observed event-by-event p_T fluctuations may be explained by the fluctuations
of the size of the initial source.Comment: 5 pages, 4 figures, version accepted in PR
Chemical freeze-out temperature in hydrodynamical description of Au+Au collisions at sqrt(s_NN) = 200 GeV
We study the effect of separate chemical and kinetic freeze-outs to the ideal
hydrodynamical flow in Au+Au collisions at RHIC (sqrt(s_NN) = 200 GeV energy).
Unlike in earlier studies we explore how these effects can be counteracted by
changes in the initial state of the hydrodynamical evolution. We conclude that
the reproduction of pion, proton and antiproton yields necessitates a chemical
freeze-out temperature of T = 150 MeV instead of T = 160 - 170 MeV motivated by
thermal models. Unlike previously reported, this lower temperature makes it
possible to reproduce the p_T-spectra of hadrons if one assumes very small
initial time, tau_0 = 0.2 fm/c. However, the p_T-differential elliptic flow,
v_2(p_T) remains badly reproduced. This points to the need to include
dissipative effects (viscosity) or some other refinement to the model.Comment: 8 pages, 7 figures; Accepted for publication in European Physical
Journal A; Added discussion about the effect of weak decays to chemical
freeze-out temperature and a figure showing isentropic curves in T-mu plan
- …