427 research outputs found
Exploring the initial stage of high multiplicity proton-proton collisions by determining the initial temperature of the quark-gluon plasma
We have analyzed identified particle transverse momentum spectra in high multiplicity events in
p
p
collisions at LHC energies
√
s
=
0.9
–
13
TeV
published by the CMS Collaboration using the color string percolation model (CSPM). In CSPM color strings are formed after the collision, which decay into new strings through color neutral
q
−
¯
q
pairs production. With the increase in the
p
p
collisions energy number of strings grow and randomly statistically overlap producing higher string tension of the composite strings. The net color in the overlap string area is a vector sum of the randomly oriented strings. The Schwinger color string breaking mechanism produces these color neutral
q
−
¯
q
pairs at time
∼
1
fm
/c, which subsequently hadronize. The initial temperature is extracted both in low and high multiplicity events.The shear viscosity to entropy density ratios
η
/
s
are obtained as a function of temperature. For the higher multiplicity events at
√
s
=
7
and 13 TeV the initial temperature is above the universal hadronization temperature and is consistent with the creation of deconfined matter. The
η
/
s
is similar to that in
Au
+
Au
collisions at
√
s
N
N
=
200
GeV
. The small value of
η
/
s
above the universal hadronization temperature suggested that the matter is a strongly coupled quark gluon plasma. In these small systems it can be argued that the thermalization is a consequence of the quantum tunneling through the event horizon introduced by the quarks confined in the colliding nucleons and their deceleration due to string formation, in analogy to the Hawking-Unruh radiation which provides a stochastic approach to equilibrium. The disk areas cluster on the nucleon transverse collision area. At the
2
D
percolation threshold a macroscopic spanning cluster suddenly occurs at the temperature
T
i
=
T
h
, representing a small connected droplet of
q
−
¯
q
pairs, the quark-gluon plasma (QGP).
T
h
is the universal hadronization temperature
∼
167.7
MeV
. The collision energy dependent buildup of the 2D percolation clusters defines the temperature range
159
±
9
MeV
of the crossover transition between hadrons to the QGP in reasonable agreement with the lattice quantum chromodynamics (LQCD) pseudocritical temperature value of
155
±
9
MeV
. Color string percolation model is the new initial stage paradigm for the study of the high density matter produced in
p
p
and
A
+
A
collisions. With CSPM we can directly explore the thermodynamics of the QGP above the universal hadronization temperature.We express our thanks to N. Armesto for fruitful comments.
C. P. thanks the grant Maria de Maeztu Unit of
excellence MDM-2016-0682 of Spain, the support of
Xunta de Galicia under the Projects No. ED431C 2017
and No. FPA 2017-83814 of Ministerio de Ciencia e
Innovacion of Spain and FEDERS
Recommended from our members
The study of hadronic matter at the highest density; the search for the deconfined quark-gluon phase using 2 TeV anti p -p collisions; and the exclusive study of nuclear fragmentation using the Lawrence Berkeley Laboratory EOS-TPC
This report discusses the: Fermilab experiment 735, a search for the quark-gluon plasma; an exclusive study of nuclear fragmentation using the EOS-TPC; and a study of the central rapidity region at the relativistic heavy ion collider
A Study of One-Pion Exchange in (p,n) Reactions Using PCAC and the Elementary Particle Model
This work was supported by National Science Foundation Grants PHY 76-84033A01, PHY 78-22774, and Indiana Universit
An Ad-Hoc Facility for Forward Angle Neutron Time-of-Flight Experiments: The 12-C(p,n)12-N Reaction
This work was supported by National Science Foundation Grant PHY 75-00289 and Indiana Universit
Scaling in the Lattice Gas Model
A good quality scaling of the cluster size distributions is obtained for the
Lattice Gas Model using the Fisher's ansatz for the scaling function. This
scaling identifies a pseudo-critical line in the phase diagram of the model
that spans the whole (subcritical to supercritical) density range. The
independent cluster hypothesis of the Fisher approach is shown to describe
correctly the thermodynamics of the lattice only far away from the critical
point.Comment: 4 pages, 3 figure
Evidence for hadronic deconfinement in -p collisions at 1.8 TeV
We have measured deconfined hadronic volumes, fm,
produced by a one dimensional (1D) expansion. These volumes are directly
proportional to the charged particle pseudorapidity densities . The hadronization temperature is (syst)
MeV. Using Bjorken's 1D model,the hadronization energy density is (stat) GeV/fm corresponding to an excitation of (stat) quark-gluon degrees of freedom.Comment: 15 pages, 3 figures, 2 table
Isotopic composition of fragments in multifragmentation of very large nuclear systems: effects of the chemical equilibrium
Studies on the isospin of fragments resulting from the disassembly of highly
excited large thermal-like nuclear emitting sources, formed in the ^{197}Au +
^{197}Au reaction at 35 MeV/nucleon beam energy, are presented. Two different
decay systems (the quasiprojectile formed in midperipheral reactions and the
unique source coming from the incomplete fusion of projectile and target in the
most central collisions) were considered; these emitting sources have the same
initial N/Z ratio and excitation energy (E^* ~= 5--6 MeV/nucleon), but
different size. Their charge yields and isotopic content of the fragments show
different distributions. It is observed that the neutron content of
intermediate mass fragments increases with the size of the source. These
evidences are consistent with chemical equilibrium reached in the systems. This
fact is confirmed by the analysis with the statistical multifragmentation
model.Comment: 9 pages, 4 ps figure
Excitation and decay of projectile-like fragments formed in dissipative peripheral collisions at intermediate energies
Projectile-like fragments (PLF:15<=Z<=46) formed in peripheral and
mid-peripheral collisions of 114Cd projectiles with 92Mo nuclei at E/A=50 MeV
have been detected at very forward angles, 2.1 deg.<=theta_lab<=4.2 deg.
Calorimetric analysis of the charged particles observed in coincidence with the
PLF reveals that the excitation of the primary PLF is strongly related to its
velocity damping. Furthermore, for a given V_PLF*, its excitation is not
related to its size, Z_PLF*. For the largest velocity damping, the excitation
energy attained is large, approximately commensurate with a system at the
limiting temperatureComment: 5 pages, 6 figure
Percolation of Color Sources and the Shear Viscosity of the QGP in Central A-A Collisions at RHIC and LHC Energies
The Color String Percolation Model (CSPM) is used to determine the shear
viscosity to entropy ratio () of the Quark-Gluon Plasma (QGP) produced
in Au-Au collisions at = 200 GeV at RHIC and Pb-Pb at
= 2.76 TeV at LHC. The relativistic kinetic theory relation for
is evaluated using CSPM values for the temperature and the mean free
path of the QGP constituents. The experimental charged hadron transverse
momentum spectrum is used to determine the percolation density parameter
in Au-Au collisions (STAR). For Pb-Pb at = 2.76 TeV
values are obtained from the extrapolation at RHIC energy. The value of
is 0.2040.020 and 0.2620.026 at the CSPM initial
temperatures of 193.63 MeV (RHIC) and 262.2 13 MeV (LHC)
respectively. These values are 2.5 and 3.3 times the AdS/CFT conjectured lower
bound . We compare the CSPM analytic expression with weak
coupling (wQGP) and strong coupling (sQGP) calculations. This indicates that
the QGP is a strongly coupled fluid in the phase transition region.Comment: 4 pages, 3 figures Accepted for publication in European Physical
Journal C (Particles & Fields
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
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