95 research outputs found
Center vortices as sources of Abelian dominance in pure SU(2) Yang-Mills theory
We argue that in the infrared regime of continuum Yang-Mills theory, the
possibility of a mass gap in the charged sector is closely associated with the
center vortex sector.
The analysis of the possible consequences of the ensembles of defects is done
by showing that the description of center vortices and monopoles is naturally
unified by means of a careful treatment of Cho decomposition.
If on the one hand confinement is usually associated with monopole
condensation in a compact abelian model, in this scenario, the previous
decoupling of the off-diagonal degrees of freedom, for the abelian model
dominate at large distances, can be understood as induced by a phase where
center vortices become thick objects.
Other important scenarios for correlated monopoles and center vortices,
observed in lattice simulations, are also accomodated in our general
formulation.Comment: 36 pages, improved version containing a more general discussio
Low-Temperature Specific Heat of an Extreme-Type-II Superconductor at High Magnetic Fields
We present a detailed study of the quasiparticle contribution to the
low-temperature specific heat of an extreme type-II superconductor at high
magnetic fields. Within a T-matrix approximation for the self-energies in the
mixed state of a homogeneous superconductor, the electronic specific heat is a
linear function of temperature with a linear- coefficient
being a nonlinear function of magnetic field . In the range of magnetic
fields H\agt (0.15-0.2)H_{c2} where our theory is applicable, the calculated
closely resembles the experimental data for the borocarbide
superconductor YNiBC.Comment: 7 pages, 2 figures, to appear in Physical Review
Free flux flow resistivity in strongly overdoped high-T_c cuprate; purely viscous motion of the vortices in semiclassical d-wave superconductor
We report the free flux flow (FFF) resistivity associated with a purely
viscous motion of the vortices in moderately clean d-wave superconductor
Bi:2201 in the strongly overdoped regime (T_c=16K) for a wide range of the
magnetic field in the vortex state. The FFF resistivity is obtained by
measuring the microwave surface impedance at different microwave frequencies.
It is found that the FFF resistivity is remarkably different from that of
conventional s-wave superconductors. At low fields (H<0.2H_c2) the FFF
resistivity increases linearly with H with a coefficient which is far larger
than that found in conventional s-wave superconductors. At higher fields, the
FFF resistivity increases in proportion to \sqrt H up to H_c2. Based on these
results, the energy dissipation mechanism associated with the viscous vortex
motion in "semiclassical" d-wave superconductors with gap nodes is discussed.
Two possible scenarios are put forth for these field dependence; the
enhancement of the quasiparticle relaxation rate and the reduction of the
number of the quasiparticles participating the energy dissipation in d-wave
vortex state.Comment: 9 pages 7 figures, to appear in Phys. Rev.
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
Improved Measurement of Double Helicity Asymmetry in Inclusive Midrapidity pi^0 Production for Polarized p+p Collisions at sqrt(s)=200 GeV
We present an improved measurement of the double helicity asymmetry for pi^0
production in polarized proton-proton scattering at sqrt(s) = 200 GeV employing
the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The
improvements to our previous measurement come from two main factors: Inclusion
of a new data set from the 2004 RHIC run with higher beam polarizations than
the earlier run and a recalibration of the beam polarization measurements,
which resulted in reduced uncertainties and increased beam polarizations. The
results are compared to a Next to Leading Order (NLO) perturbative Quantum
Chromodynamics (pQCD) calculation with a range of polarized gluon
distributions.Comment: 389 authors, 4 pages, 2 tables, 1 figure. Submitted to Phys. Rev. D,
Rapid Communications. 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
Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration
Extensive experimental data from high-energy nucleus-nucleus collisions were
recorded using the PHENIX detector at the Relativistic Heavy Ion Collider
(RHIC). The comprehensive set of measurements from the first three years of
RHIC operation includes charged particle multiplicities, transverse energy,
yield ratios and spectra of identified hadrons in a wide range of transverse
momenta (p_T), elliptic flow, two-particle correlations, non-statistical
fluctuations, and suppression of particle production at high p_T. The results
are examined with an emphasis on implications for the formation of a new state
of dense matter. We find that the state of matter created at RHIC cannot be
described in terms of ordinary color neutral hadrons.Comment: 510 authors, 127 pages text, 56 figures, 1 tables, LaTeX. Submitted
to Nuclear Physics A as a regular article; v3 has minor changes in response
to referee comments. 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
Scaling properties of azimuthal anisotropy in Au+Au and Cu+Cu collisions at sqrt(s_NN) = 200 GeV
Detailed differential measurements of the elliptic flow for particles
produced in Au+Au and Cu+Cu collisions at sqrt(s_NN) = 200 GeV are presented.
Predictions from perfect fluid hydrodynamics for the scaling of the elliptic
flow coefficient v_2 with eccentricity, system size and transverse energy are
tested and validated. For transverse kinetic energies KE_T ~ m_T-m up to ~1
GeV, scaling compatible with the hydrodynamic expansion of a thermalized fluid
is observed for all produced particles. For large values of KE_T, the mesons
and baryons scale separately. A universal scaling for the flow of both mesons
and baryons is observed for the full transverse kinetic energy range of the
data when quark number scaling is employed. In both cases the scaling is more
pronounced in terms of KE_T rather than transverse momentum.Comment: 422 authors from 58 institutions, 6 pages, 3 figures. 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
Photoproduction of J/psi and of high mass e+e- in ultra-peripheral Au+Au collisions at sqrt(s_NN) = 200 GeV
We present the first measurement of photoproduction of J/psi and of
two-photon production of high-mass e+e- pairs in electromagnetic (or
ultra-peripheral) nucleus-nucleus interactions, using Au+Au data at sqrt(s_NN)
= 200 GeV. The events are tagged with forward neutrons emitted following
Coulomb excitation of one or both Au^{star} nuclei. The event sample consists
of 28 events with m_{e+e-} > 2 GeV/c^2 with zero like-sign background. The
measured cross sections at midrapidity of d\sigma / dy (J/psi + Xn, y=0) = 76
+/- 33 (stat) +/- 11 (syst) micro b and d^2\sigma/dm dy (e^+e^- + Xn, y=0) = 86
+/- 23 (stat) +/- 16 (syst) micro b/(GeV/c^2) for m_{e+e-} \in [2.0,2.8]
GeV/c^2 are consistent with various theoretical predictions.Comment: 345 authors from 52 institutions, 20 pages, 4 figures, 3 tables.
Submitted to Physics Letters B. 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
Saturation of azimuthal anisotropy in Au + Au collisions at sqrt(s_NN) = 62 - 200 GeV
New measurements are presented for charged hadron azimuthal correlations at
mid-rapidity in Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV. They are
compared to earlier measurements obtained at sqrt(s_NN) = 130 GeV and in Pb+Pb
collisions at sqrt(s_NN) = 17.2 GeV. Sizeable anisotropies are observed with
centrality and transverse momentum (p_T) dependence characteristic of elliptic
flow (v_2). For a broad range of centralities, the observed magnitudes and
trends of the differential anisotropy, v_2(p_T), change very little over the
collision energy range sqrt(s_NN) = 62-200 GeV, indicating saturation of the
excitation function for v_2 at these energies. Such a saturation may be
indicative of the dominance of a very soft equation of state for sqrt(s_NN) =
62-200 GeV.Comment: 432 authors, 7 pages text, 4 figures, REVTeX4. To be 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
Correlated Production of p and p^bar in Au+Au Collisions at sqrt(s_NN) = 200 GeV
Correlations between p and pbar's at transverse momenta typical of enhanced
baryon production in Au+Au collisions are reported. The PHENIX experiment
measures same and opposite sign baryon pairs in Au+Au collisions at sqrt(s_NN)
= 200 GeV. Correlated production of p and p^bar with the trigger particle from
the range 2.5 < p_T < 4.0 GeV/c and the associated particle with 1.8 < p_T <
2.5 GeV/c is observed to be nearly independent of the centrality of the
collisions. Same sign pairs show no correlation at any centrality. The
conditional yield of mesons triggered by baryons (and anti-baryons) and mesons
in the same pT range rises with increasing centrality, except for the most
central collisions, where baryons show a significantly smaller number of
associated mesons. These data are consistent with a picture in which hard
scattered partons produce correlated p and p^bar in the p_T region of the
baryon excess.Comment: 420 authors from 58 institutions, 21 pages,5 figures. Submitted to
Physics Letters B. 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
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