1,693 research outputs found
Describing transverse dynamics and space-time evolution at RHIC in a hydrodynamic model with statistical hadronization
A hydrodynamic model coupled to the statistical hadronization code
Therminator is used to study a set of observables in the soft sector at RHIC. A
satisfactory description of the pT-spectra and elliptic flow is obtained,
similarly to other hydrodynamic models. With the Gaussian initial conditions
the transverse femtoscopic radii are also reproduced, providing a possible
solution of the RHIC HBT puzzle.Comment: to appear in the conference proceedings for Quark Matter 2009, March
30 - April 4, Knoxville, Tennesse
Measurement of , K, p transverse momentum spectra with ALICE in proton-proton collisions at 0.9 and 7 TeV
Results of the measurement of the , K, p transverse momentum
() spectra at mid-rapidity in proton-proton collisions at
TeV are presented. Particle identification was performed using
the energy loss signal in the Inner Tracking System (ITS) and the Time
Projection Chamber (TPC), while information from the Time-of-Flight (TOF)
detector was used to identify particles at higher transverse momentum. From the
spectra at TeV the mean transverse momentum ()
and particle ratios were extracted and compared to results obtained for
collisions at TeV and lower energies.Comment: Quark Matter 2011 proceeding
Early dynamics of transversally thermalized matter
We argue that the idea that the parton system created in relativistic
heavy-ion collisions is formed in a state with transverse momenta close to
thermodynamic equilibrium and its subsequent dynamics at early times is
dominated by pure transverse hydrodynamics of the perfect fluid is compatible
with the data collected at RHIC. This scenario of early parton dynamics may
help to solve the problem of early equilibration.Comment: 4 pages, 2 figures, Talk given by M. Chojnacki at Quark Matter 2008,
Jaipur, Indi
The Use of an Individualized Levels System and Extinction to Increase Task Compliance and to Decrease Aggressive Behavior with a Child with Autism
In a token economy level system, as an individual progresses from one task level to the next, there is an increase in the demand of tasks and an increase in the magnitude of reinforcers earned. The motivation for the individual in level systems stems from the increasing of value of reinforcers earned at each level. In this study a level system in concordance with an extinction procedure for aggressive behaviors was employed as a behavioral intervention. In this single-subject design study, a 5-year-old boy with autism was observed across a variety of 15 minute teaching sessions, implementing synchronously, the reinforcement for task compliant behaviors and extinction for aggressive behavior. Based upon a prior behavioral function analysis, it was hypothesized that, as a function of the intervention, compliance behaviors would increase, and the frequency of aggressive behaviors will decrease. Overall, the intervention was a success. On-task compliance behaviors increased, response latency for on-task behaviors were faster, and aggressive behaviors decreased to 0 levels. These results are further evidence of theoretical and practical importance for the use of a token economy level system
Instability of Boost-invariant hydrodynamics with a QCD inspired bulk viscosity
We solve the relativistic Navier-Stokes equations with homogeneous
boost-invariant boundary conditions, and perform a stability analysis of the
solution. We show that, if the bulk viscosity has a peak around as
inferred from QCD-based arguments, the background solution "freezes" at
to a nearly constant temperature state. This state is however highly unstable
with respect to certain inhomogeneous modes. Calculations show that these modes
have enough time to blow up and tear the system into droplets. We conjecture
that this is how freeze-out occurs in the QGP created in heavy ion collisions,
and perhaps similar transitions in the early universe.Comment: Accepted for publication, Rapid Communication in Physical Review C
Discussion extended, derivation and conclusions not change
Early dynamics of transversally thermalized matter
We argue that the idea that the parton system created in relativistic
heavy-ion collisions is formed in a state with transverse momenta close to
thermodynamic equilibrium and its subsequent dynamics at early times is
dominated by pure transverse hydrodynamics of the perfect fluid is compatible
with the data collected at RHIC. This scenario of early parton dynamics may
help to solve the problem of early equilibration.Comment: 4 pages, 2 figures, Talk given by M. Chojnacki at Quark Matter 2008,
Jaipur, Indi
Directed flow in ultrarelativistic heavy-ion collisions
We study the generation of directed flow in the hydrodynamic expansion of the
hot matter formed in ultrarelativistic heavy-ion collisions at 200GeV. The
experimentally observed negative directed flow in a wide range of central
pseudorapidities isreproduced assuming that the fireball is tilted away from
the collision axis. The tilt of the source is consistent with a preferential
emission in the forward/backward hemisphere from forward/backward participating
nucleons. The model reproduces the experimentally observed scaling of the
directed flow when going from Au-Au to Cu-Cu systems.Comment: figure adde
Temperature dependent sound velocity in hydrodynamic equations for relativistic heavy-ion collisions
We analyze the effects of different forms of the sound-velocity function
cs(T) on the hydrodynamic evolution of matter formed in the central region of
relativistic heavy-ion collisions. At high temperatures (above the critical
temperature Tc) the sound velocity is calculated from the recent lattice
simulations of QCD, while in the low temperature region it is obtained from the
hadron gas model. In the intermediate region we use different interpolations
characterized by the values of the sound velocity at the local maximum (at T =
0.4 Tc) and local minimum (at T = Tc). In all considered cases the temperature
dependent sound velocity functions yield the entropy density, which is
consistent with the lattice QCD simulations at high temperature. Our
calculations show that the presence of a distinct minimum of the sound velocity
leads to a very long (about 20 fm/c) evolution time of the system, which is not
compatible with the recent estimates based on the HBT interferometry. Hence, we
conclude that the hydrodynamic description is favored in the case where the
cross-over phase transition renders the smooth sound velocity function with a
possible shallow minimum at Tc.Comment: 6 pages, 3 figures, talk given at SQM'07 Levoca, Slovaki
Highly-anisotropic and strongly-dissipative hydrodynamics with transverse expansion
A recently formulated framework of highly-anisotropic and
strongly-dissipative hydrodynamics (ADHYDRO) is used to describe the evolution
of matter created in ultra-relativistic heavy-ion collisions. New developments
of the model contain: the inclusion of asymmetric transverse expansion
(combined with the longitudinal boost-invariant flow) and comparisons of the
model results with the RHIC data, which have become possible after coupling of
ADHYDRO with THERMINATOR. Various soft-hadronic observables (the
transverse-momentum spectra, the elliptic flow coefficient v_2, and the HBT
radii) are calculated for different initial conditions characterized by the
value of the initial pressure asymmetry. We find that as long as the initial
energy density profile is unchanged the calculated observables remain
practically the same. This result indicates the insensitivity of the analyzed
observables to the initial anisotropy of pressure and suggests that the
complete thermalization of the system may be delayed to easily acceptable times
of about 1 fm/c
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