We study a two-species totally asymmetric exclusion process (TASEP) in 1D lattice in which the particles of both species move stochastically in opposite directions (with rate
v
) and switch ...directions stochastically (with rate
α
) while adjacent a particle of either species. We focus on the cluster size distribution
P
(
m
), where a cluster is taken to be a contiguous set of sites occupied by either species, as a function of
Q
=
v
/
α
. For a total density
ρ
of particles, in the limit
Q
→
0
, the cluster size distribution is shown to be
P
(
m
)
=
1
/
ρ
-
1
e
-
m
/
ln
ρ
and the mean cluster size
⟨
m
⟩
=
1
/
(
1
-
ρ
)
, results which are independent of
Q
and are identical to those for the simple exclusion process. By contrast, in the opposite limit,
Q
≫
1
, we find the average cluster size,
⟨
m
⟩
∝
Q
1
/
2
—similar to the that for the persistent exclusion process (PEP), although the cluster size distributions are different in both limits. We further find that, for a finite system with
L
sites, the probability distribution of cluster sizes exhibits a distinct peak which corresponds to the formation of a single cluster of size
m
s
=
ρ
L
. However, this peak vanishes in the thermodynamic limit
L
→
∞
. Interestingly, the probability of this largest size cluster,
P
(
m
s
)
, for different
L
,
ρ
and
Q
exhibits data collapse in terms of the scaled variable
Q
s
≡
Q
/
L
2
ρ
(
1
-
ρ
)
. The statistical features of the clustering observed for this minimal model may be relevant for
active
particle systems in 1D.
Midrapidity production of π±, K±, and (¯p)p measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic pp collisions at √sNN=5.02 TeV, is presented. The invariant ...yields are measured over a wide transverse momentum (pT) range from hundreds of MeV/c up to 20 GeV/c. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range 0–90%. The comparison of the pT-integrated particle ratios, i.e., proton-to-pion (p/π) and kaon-to-pion (K/π) ratios, with similar measurements in Pb-Pb collisions at √sNN=2.76 TeV show no significant energy dependence. Blast-wave fits of the pT spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios (p/π, K/π) as a function of pT show pronounced maxima at pT≈3GeV/c in central Pb-Pb collisions. At high pT, particle ratios at 5.02 TeV are similar to those measured in pp collisions at the same energy and in Pb-Pb collisions at √sNN=2.76 TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high pT and compatible with measurements at √sNN=2.76 TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.
Performance of a new LMRPC prototype for the STAR MTD system Wang, Y.; Chen, H.S.; Ding, W.C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2011, Volume:
640, Issue:
1
Journal Article
Peer reviewed
A new prototype of a Long-Strip Multi-Gap Resistive Plate Chamber (LMRPC) for the STAR Muon Telescope Detector (MTD) at RHIC has been developed. This prototype has an active area of 52×90
cm
2 and ...consists of six 250
μm wide gaps. Each detector has 12 strips, read-out at both ends, which are each 3.8
cm wide and 90
cm long with 0.6
cm intervals. In cosmic-ray tests, the efficiency was larger than 95% and the time resolution was ∼75
ps for the 94% Freon, 5% iso-butane, and 1% SF
6 gas mixture. There was good uniformity in the performance across the different strips. The module was also tested in a proton beam at IHEP in Beijing. The efficiency was close to 100% and the best timing resolution achieved was 55
ps for the 90% Freon, 5% iso-butane, and 5% SF
6 gas mixture. Trigger scans along and across the strip direction were also performed.
Comprehensive results on the production of unidentified charged particles, π±, K±, K$_S^0$, K*(892)0, $p, \bar{p}, ϕ$(1020), Λ, Λ, Ξ-, Ξ+, Ω-, and $\bar{Ω}^+$ hadrons in proton-proton ...(pp) collisions at $ \sqrt{s}$=7 TeV at midrapidity (|y|<0.5) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum (pT) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle-to-pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in p-Pb and Pb-Pb collisions at Large Hadron Collider energies. The obtained pT distributions and yields are compared to expectations from QCD-based pp event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity pp collisions.
This article reports measurements of the pT-differential inclusive jet cross section in pp collisions at s=5.02TeV and the pT-differential inclusive jet yield in Pb-Pb 0-10% central collisions at ...sNN=5.02TeV. Jets were reconstructed at midrapidity with the ALICE tracking detectors and electromagnetic calorimeter using the anti-kT algorithm. For pp collisions, we report jet cross sections for jet resolution parameters R=0.1-0.6 over the range 20<pT,jet<140 GeV/c, as well as the jet cross-section ratios of different R and comparisons to two next-to-leading-order (NLO)-based theoretical predictions. For Pb-Pb collisions, we report the R=0.2 and R=0.4 jet spectra for 40<pT,jet<140 GeV/c and 60<pT,jet<140 GeV/c, respectively. The scaled ratio of jet yields observed in Pb-Pb to pp collisions, RAA, is constructed, and exhibits strong jet quenching and a clear pT dependence for R=0.2. No significant R dependence of the jet RAA is observed within the uncertainties of the measurement. These results are compared to several theoretical predictions.
We report the measurements of correlations between event-by-event fluctuations of amplitudes of anisotropic flow harmonics in nucleus-nucleus collisions, obtained for the first time using a new ...analysis method based on multiparticle cumulants in mixed harmonics. This novel method is robust against systematic biases originating from nonflow effects and by construction any dependence on symmetry planes is eliminated. We demonstrate that correlations of flow harmonics exhibit a better sensitivity to medium properties than the individual flow harmonics. The new measurements are performed in Pb-Pb collisions at the center-of-mass energy per nucleon pair of √ s N N = 2.76 TeV by the ALICE experiment at the Large Hadron Collider. The centrality dependence of correlation between event-by-event fluctuations of the elliptic v2 and quadrangular v4 flow harmonics, as well as of anticorrelation between v2 and triangular v3 flow harmonics are presented. The results cover two different regimes of the initial state configurations: geometry dominated (in midcentral collisions) and fluctuation dominated (in the most central collisions). Comparisons are made to predictions from Monte Carlo Glauber, viscous hydrodynamics, ampt, and hijing models. Together with the existing measurements of the individual flow harmonics the presented results provide further constraints on the initial conditions and the transport properties of the system produced in heavy-ion collisions.
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