565 research outputs found
Evolution of induced axial magnetization in a two-component magnetized plasma
In this paper, the evolution of the induced axial magnetization due to the
propagation of an electromagnetic (em) wave along the static background
magnetic field in a two-component plasma has been investigated using the Block
equation. The evolution process induces a strong magnetic anisotropy in the
plasma medium, depending nonlinearly on the incident wave amplitude. This
induced magnetic anisotropy can modify the dispersion relation of the incident
em wave, which has been obtained in this paper. In the low frequency Alfven
wave limit, this dispersion relation shows that the resulting phase velocity of
the incident wave depends on the square of the incident wave amplitude and on
the static background magnetic field of plasma. The analytical results are in
well agreement with the numerically estimated values in solar corona and
sunspots.Comment: 7 pages, 1 figur
Implementation of a medium-modified parton shower algorithm
We present a Monte Carlo implementation of medium-induced gluon radiation in
the final-state branching process. Medium effects are introduced through an
additive term in the splitting functions. We have implemented such modification
within PYTHIA. We show the medium effects on the hump-backed plateau, and the
transverse momentum and angular distributions with respect to the parent
parton. As expected, with increasing medium densities there is an increase
(decrease) of partons with small (large) momentum fraction, and angular
broadening is observed. The effects on the transverse-momentum distributions
are more involved, with an enhancement of low- and intermediate- partons
and a decrease at large , which is related to energy conservation, and to
the lack of momentum exchange with the medium in our approach.Comment: LaTeX, 6 pages, 2 eps figures; proceedings of the 3rd International
Conference on Hard and Electromagnetic Probes in High-Energy Nuclear
Collisions - Hard Probes 2008 (Illa de A Toxa, Spain, June 8th-14th 2008
Signatures of Nucleon Disappearance in Large Underground Detectors
For neutrons bound inside nuclei, baryon instability can manifest itself as a
decay into undetectable particles (e.g., ), i.e.,
as a disappearance of a neutron from its nuclear state. If electric charge is
conserved, a similar disappearance is impossible for a proton. The existing
experimental lifetime limit for neutron disappearance is 4-7 orders of
magnitude lower than the lifetime limits with detectable nucleon decay products
in the final state [PDG2000]. In this paper we calculated the spectrum of
nuclear de-excitations that would result from the disappearance of a neutron or
two neutrons from C. We found that some de-excitation modes have
signatures that are advantageous for detection in the modern high-mass,
low-background, and low-threshold underground detectors, where neutron
disappearance would result in a characteristic sequence of time- and
space-correlated events. Thus, in the KamLAND detector [Kamland], a
time-correlated triple coincidence of a prompt signal, a captured neutron, and
a decay of the residual nucleus, all originating from the same
point in the detector, will be a unique signal of neutron disappearance
allowing searches for baryon instability with sensitivity 3-4 orders of
magnitude beyond the present experimental limits.Comment: 13 pages including 6 figures, revised version, to be published in
Phys.Rev.
Small Corrections to the Tunneling Phase Time Formulation
After reexamining the above barrier diffusion problem where we notice that
the wave packet collision implies the existence of {\em multiple} reflected and
transmitted wave packets, we analyze the way of obtaining phase times for
tunneling/reflecting particles in a particular colliding configuration where
the idea of multiple peak decomposition is recovered. To partially overcome the
analytical incongruities which frequently rise up when the stationary phase
method is adopted for computing the (tunneling) phase time expressions, we
present a theoretical exercise involving a symmetrical collision between two
identical wave packets and a unidimensional squared potential barrier where the
scattered wave packets can be recomposed by summing the amplitudes of
simultaneously reflected and transmitted wave components so that the conditions
for applying the stationary phase principle are totally recovered. Lessons
concerning the use of the stationary phase method are drawn.Comment: 14 pages, 3 figure
Event-by-Event Fluctuations in Particle Multiplicities and Transverse Energy Produced in 158.A GeV Pb+Pb collisions
Event-by-event fluctuations in the multiplicities of charged particles and
photons, and the total transverse energy in 158 GeV Pb+Pb collisions
are studied for a wide range of centralities. For narrow centrality bins the
multiplicity and transverse energy distributions are found to be near perfect
Gaussians. The effect of detector acceptance on the multiplicity fluctuations
has been studied and demonstrated to follow statistical considerations. The
centrality dependence of the charged particle multiplicity fluctuations in the
measured data has been found to agree reasonably well with those obtained from
a participant model. However for photons the multiplicity fluctuations has been
found to be lower compared to those obtained from a participant model. The
multiplicity and transverse energy fluctuations have also been compared to
those obtained from the VENUS event generator.Comment: To appear in Physical Review C; changes : more detailed discussion on
errors and few figures modifie
Proximity effect at superconducting Sn-Bi2Se3 interface
We have investigated the conductance spectra of Sn-Bi2Se3 interface junctions
down to 250 mK and in different magnetic fields. A number of conductance
anomalies were observed below the superconducting transition temperature of Sn,
including a small gap different from that of Sn, and a zero-bias conductance
peak growing up at lower temperatures. We discussed the possible origins of the
smaller gap and the zero-bias conductance peak. These phenomena support that a
proximity-effect-induced chiral superconducting phase is formed at the
interface between the superconducting Sn and the strong spin-orbit coupling
material Bi2Se3.Comment: 7 pages, 8 figure
Centrality Dependence of the High p_T Charged Hadron Suppression in Au+Au collisions at sqrt(s_NN) = 130 GeV
PHENIX has measured the centrality dependence of charged hadron p_T spectra
from central Au+Au collisions at sqrt(s_NN)=130 GeV. The truncated mean p_T
decreases with centrality for p_T > 2 GeV/c, indicating an apparent reduction
of the contribution from hard scattering to high p_T hadron production. For
central collisions the yield at high p_T is shown to be suppressed compared to
binary nucleon-nucleon collision scaling of p+p data. This suppression is
monotonically increasing with centrality, but most of the change occurs below
30% centrality, i.e. for collisions with less than about 140 participating
nucleons. The observed p_T and centrality dependence is consistent with the
particle production predicted by models including hard scattering and
subsequent energy loss of the scattered partons in the dense matter created in
the collisions.Comment: 7 pages text, LaTeX, 6 figures, 2 tables, 307 authors, resubmitted to
Phys. Lett. B. Revised to address referee concerns. Plain text data tables
for the points plotted in figures for this and previous PHENIX publications
are publicly available at
http://www.phenix.bnl.gov/phenix/WWW/run/phenix/papers.htm
Intensity-dependent dispersion under conditions of electromagnetically induced transparency in coherently prepared multistate atoms
Published versio
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
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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