7,352 research outputs found
Thermal Dileptons at LHC
We predict dilepton invariant-mass spectra for central 5.5 ATeV Pb-Pb
collisions at LHC. Hadronic emission in the low-mass region is calculated using
in-medium spectral functions of light vector mesons within hadronic many-body
theory. In the intermediate-mass region thermal radiation from the Quark-Gluon
Plasma, evaluated perturbatively with hard-thermal loop corrections, takes
over. An important source over the entire mass range are decays of correlated
open-charm hadrons, rendering the nuclear modification of charm and bottom
spectra a critical ingredient.Comment: 2 pages, 2 figures, contributed to Workshop on Heavy Ion Collisions
at the LHC: Last Call for Predictions, Geneva, Switzerland, 14 May - 8 Jun
2007 v2: acknowledgment include
Measurements of elliptic and triangular flow in high-multiplicity HeAu collisions at GeV
We present the first measurement of elliptic () and triangular ()
flow in high-multiplicity HeAu collisions at
GeV. Two-particle correlations, where the particles have a large separation in
pseudorapidity, are compared in HeAu and in collisions and
indicate that collective effects dominate the second and third Fourier
components for the correlations observed in the HeAu system. The
collective behavior is quantified in terms of elliptic and triangular
anisotropy coefficients measured with respect to their corresponding
event planes. The values are comparable to those previously measured in
Au collisions at the same nucleon-nucleon center-of-mass energy.
Comparison with various theoretical predictions are made, including to models
where the hot spots created by the impact of the three He nucleons on the
Au nucleus expand hydrodynamically to generate the triangular flow. The
agreement of these models with data may indicate the formation of low-viscosity
quark-gluon plasma even in these small collision systems.Comment: 630 authors, 9 pages, 4 figures, 2 tables. v2 is the version accepted
for publication by Physical Review Letters. Plain text data tables for the
points plotted in figures for this and previous PHENIX publications are (or
will be) publicly available at http://www.phenix.bnl.gov/papers.htm
Longitudinal Spin Transfer to and Hyperons in Polarized Proton-Proton Collisions at = 200 GeV
The longitudinal spin transfer, , from high energy polarized protons
to and hyperons has been measured for the first time
in proton-proton collisions at with the STAR
detector at RHIC. The measurements cover pseudorapidity, , in the range
and transverse momenta, , up to . The longitudinal spin transfer is found to be for inclusive
and for
inclusive hyperons with and . The dependence on and is presented.Comment: 5 pages, 4 figure
Parton Ladder Splitting and the Rapidity Dependence of Transverse Momentum Spectra in Deuteron-Gold Collisions at RHIC
We present a phenomenological approach (EPOS), based on the parton model, but
going much beyond, and try to understand proton-proton and deuteron-gold
collisions, in particular the transverse momentum results from all the four
RHIC experiments. It turns out that elastic and inelastic parton ladder
splitting is the key issue. Elastic splitting is in fact related to screening
and saturation, but much more important is the inelastic contribution, being
crucial to understand the data. We investigate in detail the rapidity
dependence of nuclear effects, which is actually relatively weak in the model,
in perfect agreement with the data, if the latter ones are interpreted
correctly.Comment: 39 pages, 28 figure
Measurement of heavy-flavour decay muon production at forward rapidity in pp and Pb-Pb collisions at sqrt(s_NN)=2.76 TeV with the ALICE experiment
The ALICE experiment measured the heavy-flavour production in the semi-muonic
decay channel at forward rapidities () in pp and Pb--Pb collisions at
TeV. We report on the first results on the -differential cross-sections in pp collisions as well as on the nuclear
modification factors as a function of the transverse momentum and centrality.Comment: 4 pages, 3 figures, Proceedings of parallel talk at the 5th
international conference on hard and electromagnetic probes of high-energy
nuclear collisions (Hard Probes 2012), Cagliari, Ital
Effective Lagrangians for (0+1) and (1+1) dimensionally reduced versions of D=4 N=2 SYM theory
We consider dimensionally reduced versions of N=2 four- dimensional
supersymmetric Yang-Mills theory and determine the one-loop effective
Lagrangians associated with the motion over the corresponding moduli spaces. In
the (0+1) case, the effective Lagrangian describes an N=4 supersymmetric
quantum mechanics of the Diaconescu--Entin type. In (1+1) dimensions, the
effective Lagrangian represents a twisted N=4 supesymmetric sigma model due to
Gates, Hull, and Rocek. We discuss the genetic relationship between these two
models and present the explicit results for all gauge groups.Comment: 16 pages, no figures, minor correction
Micro-canonical pentaquark production in \ee annihilations
The existence of pentaquarks, namely baryonic states made up of four quarks
and one antiquark, became questionable, because the candidates, i.e. the
peak, are seen in certain reactions, i.e. p+p collisions, but not in
others, i.e. \ee annihilations. In this paper, we estimate the production of
and in \ee annihilations at different
energies using Fermi statistical model as originally proposed in its
microcanonical form. The results is compared with that from pp collisions at
SPS and RHIC energies. We find that, if pentaquark states exist, the production
is highly possible in \ee annihilations. For example, at LEP energy
=91.2 GeV, both and yield more
than in pp collisions at SPS and RHIC energy.Comment: 7 pages 2 figure
Single Spin Asymmetry in Polarized Proton-Proton Elastic Scattering at GeV
We report a high precision measurement of the transverse single spin
asymmetry at the center of mass energy GeV in elastic
proton-proton scattering by the STAR experiment at RHIC. The was measured
in the four-momentum transfer squared range \GeVcSq, the region of a significant interference between the
electromagnetic and hadronic scattering amplitudes. The measured values of
and its -dependence are consistent with a vanishing hadronic spin-flip
amplitude, thus providing strong constraints on the ratio of the single
spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated
by the Pomeron amplitude at this , we conclude that this measurement
addresses the question about the presence of a hadronic spin flip due to the
Pomeron exchange in polarized proton-proton elastic scattering.Comment: 12 pages, 6 figure
System Size and Energy Dependence of Jet-Induced Hadron Pair Correlation Shapes in Cu+Cu and Au+Au Collisions at sqrt(s_NN) = 200 and 62.4 GeV
We present azimuthal angle correlations of intermediate transverse momentum
(1-4 GeV/c) hadrons from {dijets} in Cu+Cu and Au+Au collisions at sqrt(s_NN) =
62.4 and 200 GeV. The away-side dijet induced azimuthal correlation is
broadened, non-Gaussian, and peaked away from \Delta\phi=\pi in central and
semi-central collisions in all the systems. The broadening and peak location
are found to depend upon the number of participants in the collision, but not
on the collision energy or beam nuclei. These results are consistent with sound
or shock wave models, but pose challenges to Cherenkov gluon radiation models.Comment: 464 authors from 60 institutions, 6 pages, 3 figures, 2 tables.
Submitted to Physical Review Letters. Plain text data tables for the points
plotted in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
Cross sections and double-helicity asymmetries of midrapidity inclusive charged hadrons in p+p collisions at sqrt(s)=62.4 GeV
Unpolarized cross sections and double-helicity asymmetries of
single-inclusive positive and negative charged hadrons at midrapidity from p+p
collisions at sqrt(s)=62.4 GeV are presented. The PHENIX measurements for 1.0 <
p_T < 4.5 GeV/c are consistent with perturbative QCD calculations at
next-to-leading order in the strong coupling constant, alpha_s. Resummed pQCD
calculations including terms with next-to-leading-log accuracy, yielding
reduced theoretical uncertainties, also agree with the data. The
double-helicity asymmetry, sensitive at leading order to the gluon polarization
in a momentum-fraction range of 0.05 ~< x_gluon ~< 0.2, is consistent with
recent global parameterizations disfavoring large gluon polarization.Comment: PHENIX Collaboration. 447 authors, 12 pages, 5 figures, 5 tables.
Submitted to Physical Review
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