667 research outputs found
Dynamical quark recombination in ultrarelativistic heavy-ion collisions and the proton to pion ratio
We study quark thermal recombination as a function of energy density during
the evolution of a heavy-ion collision in a numerical model that reproduces
aspects of QCD phenomenology. We show that starting with a set of free quarks
(or quarks and antiquarks) the probability to form colorless clusters of three
quarks differs from that to form colorless clusters of quark-antiquark and that
the former has a sharp jump at a critical energy density whereas the latter
transits smoothly from the low to the high energy density domains. We interpret
this as a quantitative difference in the production of baryons and mesons with
energy density. We use this approach to compute the proton and pion spectra in
a Bjorken scenario that incorporates the evolution of these probabilities with
energy density, and therefore with proper time. From the spectra, we compute
the proton to pion ratio and compare to data at the highest RHIC energies. We
show that for a standard choice of parameters, this ratio reaches one, though
the maximum is very sensitive to the initial evolution proper time.Comment: 10 pages, 12 figures, version to appear in Phys. Rev.
VHMPID: a new detector for the ALICE experiment at LHC
This article presents the basic idea of VHMPID, an upgrade detector for the
ALICE experiment at LHC, CERN. The main goal of this detector is to extend the
particle identification capabilities of ALICE to give more insight into the
evolution of the hot and dense matter created in Pb-Pb collisions. Starting
from the physics motivations and working principles the challenges and current
status of development is detailed.Comment: 4 pages, 6 figures. To be published in EPJ Web of Conference
Measurement of the proton and deuteron structure functions, F2p and F2d, and of the ratio sigma(L)/sigma(T)
The muon-proton and muon-deuteron inclusive deep inelastic scattering cross
sections were measured in the kinematic range 0.002 < x < 0.60 and 0.5 < Q2 <
75 GeV2 at incident muon energies of 90, 120, 200 and 280 GeV. These results
are based on the full data set collected by the New Muon Collaboration,
including the data taken with a small angle trigger. The extracted values of
the structure functions F2p and F2d are in good agreement with those from other
experiments. The data cover a sufficient range of y to allow the determination
of the ratio of the longitudinally to transversely polarised virtual photon
absorption cross sections, R= sigma(L)/sigma(T), for 0.002 < x < 0.12 . The
values of R are compatible with a perturbative QCD prediction; they agree with
earlier measurements and extend to smaller x.Comment: In this replacement the erroneously quoted R values in tables 3-6 for
x>0.12, and R1990 values in tables 5-6 for all x, have been corrected, and
the cross sections in tables 3-4 have been adapted. Everything else,
including the structure functions F2, remained unchanged. 22 pages, LateX,
including figures, with two .sty files, and three separate f2tab.tex files
for the F2-tables. Accepted for publication in Nucl.Phys.B 199
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