35 research outputs found
Overview of experimental critical point search
The existence and location of the QCD critical point is an object of vivid
experimental and theoretical studies. Rich and beautiful data recorded by
experiments at SPS and RHIC allow for a systematic search for the critical
point - the search for a non-monotonic dependence of various correlation and
fluctuation observables on collision energy and size of colliding nuclei.Comment: The 18th International Conference on Strangeness in Quark Matter (SQM
2019) proceedings, 8 pages, 8 figure
Non-invasive characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation
We propose and use a technique to measure the transverse emittance of a
laser-wakefield accelerated beam of relativistic electrons. The technique is
based on the simultaneous measurements of the electron beam divergence given by
, the measured longitudinal spectrum
and the transverse electron bunch size in the bubble
. The latter is obtained via the measurement of the source size of
the x-rays emitted by the accelerating electron bunch in the bubble. We measure
a \textit{normalised} RMS beam transverse emittance mmmrad as
an upper limit for a spatially gaussian, spectrally quasi-monoenergetic
electron beam with 230 MeV energy in agreement with numerical modeling and
analytic theory in the bubble regime.Comment: 4 pages, 5 figure
Asymptotic Regge Trajectories of Non-strange Mesons
We analyze the asymptotic behavior of Regge trajectories of non-strange
mesons. In contrast to an existing belief, it is demonstrated that for the
asymptotically linear Regge trajectories the width of heavy hadrons cannot
linearly depend on their mass. Using the data on masses and widths of rho_J,
omega_J, a_J and f_J mesons for the spin values J \leq 6, we extract the
parameters of the asymptotically linear Regge trajectory predicted by the
finite width model of quark gluon bags. As it is shown the obtained parameters
for the data set B correspond to the cross-over temperature lying in the
interval 170.9-175.3 MeV which is consistent with the kinetic freeze-out
temperature of early hadronizing particles found in relativistic heavy ion
collisions at and above the highest SPS energy.Comment: 14 pages, 3 figure
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Higher order conserved charge fluctuations inside the mixed phase
General formulas are presented for higher order cumulants of the conserved charge statistical fluctuations inside the mixed phase. As a particular example, the van der Waals model in the grand canonical ensemble is used. The higher order measures of the conserved charge fluctuations up to the hyperkurtosis are calculated in a vicinity of the critical point (CP). The analysis includes both the mixed phase region and the pure phases on the phase diagram. It is shown that even-order fluctuation measures, e.g., scaled variance, kurtosis, and hyperkurtosis, have only positive values in the mixed phase and go to infinity at the CP. For odd-order measures, such as skewness and hyperskewness, the regions of positive and negative values are found near the left and right binodals, respectively. The obtained results are discussed in a context of the event-by-event fluctuation measurements in heavy-ion collisions
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Critical point particle number fluctuations from molecular dynamics
We study fluctuations of particle number in the presence of a critical point by utilizing molecular dynamics simulations of the classical Lennard-Jones fluid in a periodic box. The numerical solution of the N-body problem naturally incorporates all correlations, exact conservation laws, and finite size effects, allowing us to study the fluctuation signatures of the critical point in a dynamical setup. We find that large fluctuations associated with the critical point are observed when measurements are performed in coordinate subspace, but, in the absence of collective flow and expansion, are essentially washed out when momentum cuts are imposed instead. We put our findings in the context of event-by-event fluctuations in heavy-ion collisions
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Connecting fluctuation measurements in heavy-ion collisions with the grand-canonical susceptibilities
We derive the relation between cumulants of a conserved charge measured in a subvolume of a thermal system and the corresponding grand-canonical susceptibilities, taking into account exact global conservation of that charge. The derivation is presented for an arbitrary equation of state, with the assumption that the subvolume is sufficiently large to be close to the thermodynamic limit. Our framework – the subensemble acceptance method (SAM) – quantifies the effect of global conservation laws and is an important step toward a direct comparison between cumulants of conserved charges measured in central heavy ion collisions and theoretical calculations of grand-canonical susceptibilities, such as lattice QCD. As an example, we apply our formalism to net-baryon fluctuations at vanishing baryon chemical potentials as encountered in collisions at the LHC and RHIC