57,442 research outputs found
Event by event di-hadron correlations in Pb-Pb 2.76 TeV collisions from the ALICE experiment
The large multiplicities at the LHC may permit flow harmonics to be
determined on an event by event basis in Pb-Pb collisions. We extract these
harmonics from event by event di-hadron correlations. Within a fine centrality
bin, we find the correlation function varies substantially on an event by event
basis, indicating large fluctuations in the initial conditions for a given
impact parameter. Such large fluctuations lead to some events being highly
triangular or highly elliptical, where the angular correlation function is
completely dominated by the respective second and third Fourier harmonics. We
will show unfolded distributions for various centralities, and
implications for our understanding of the initial conditions.Comment: 4 pages, Hot Quarks 201
Untriggered di-hadron correlations in Pb-Pb collisions at 2.76 TeV from ALICE
We present measurements of untriggered di-hadron correlations as a function
of centrality in Pb-Pb \sNN collisions, for charged hadrons with
GeV. These measurements provide a map of the bulk correlation structures in
heavy-ion collisions. Contributions to these structures may come from jets,
initial density fluctuations, elliptic flow, resonances, and/or momentum
conservation. We decompose the measured correlation functions via a
multi-parameter fit in order to extract the nearside Gaussian, the longer range
correlation often referred to as the soft ridge. The effect of
including higher harmonics ( and ) in this procedure will be
discussed. We investigate how the nearside Gaussian scales with the number of
binary collisions. Finally, we show the charge dependence of the nearside
Gaussian.Comment: 4 pages, QM 2011 proceeding
Radial Velocities of Stars with Multiple Co-orbital Planets
To date, well over a thousand planets have been discovered orbiting other
stars, hundreds of them in multi-planet systems. Most of these exoplanets have
been detected by either the transit method or the radial velocity method,
rather than by other methods such as astrometry or direct imaging. Both the
radial velocity and astrometric methods rely upon the reflex motion of the
parent star induced by the gravitational attraction of its planets. However,
this reflex motion is subject to misinterpretation when a star has two or more
planets with the same orbital period. Such co-orbital planets may effectively
"hide" from detection by current algorithms.
In principle, any number of planets can share the same orbit; the case where
they all have the same mass has been studied most. Salo and Yoder (A & A 205,
309--327, 1988) have shown that more than 8 planets of equal mass sharing a
circular orbit must be equally spaced for dynamical stability, while fewer than
7 equal-mass planets are stable only in a configuration where all of the
planets remain on the same side of their parent star. For 7 or 8 equal-mass
planets, both configurations are stable.
By symmetry, it is clear that the equally-spaced systems produce no reflex
motion or radial velocity signal at all in their parent stars. This could lead
to their being overlooked entirely, unless they happen to be detected by the
transit method. It is equally clear that the lopsided systems produce a greater
radial velocity signal than a single such planet would, but a smaller signal
than if all of the planets were combined into one. This could seriously mislead
estimates of exoplanet masses and densities. Transit data and ellipsoidal
(tidal) brightness variations in such systems also are subject to
misinterpretation. This behavior is also representative of more natural
systems, with co-orbital planets of different masses.Comment: 16 pages, 3 figures, 1 tabl
Viscous liquid flow on Martian dune slopes
The observed temporary dark streaks on some dune slopes on Mars may be due to
thin sheets of water (or some other liquid) trickling downhill. This note
corrects conceptual errors in a previous paper (M\"{o}hlmann and Kereszturi
2010, Icarus 207, 654-658) which affect the velocity profile of such flows, and
produce over-estimates of their depths and mass fluxes by factors of almost
two.Comment: 6 pages, 1 figur
The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au sqrt(s_NN) = 200 GeV collisions
Transverse momentum spectra of Lambda and K0Short particles are presented for
Cu+Cu sqrt(s_NN) = 200 GeV collisions observed at STAR, and compared to Au+Au
measurements at the same energy. For both systems, a number of observables are
shown to increase at mid-rapidity (|y| < 0.5) with increasing centrality. These
are the integrated Lambda and K0Short yields, the integrated Lambda and K0Short
yields per participating nucleon, and mid-pT (1 GeV/c -> 4.5 GeV/c)
Lambda/KK0Short ratios. The RCP ratio is found to be higher for the Lambda
yields at mid-pT compared to the K0Short yields for both the Cu+Cu and Au+Au
data. In contrast, when similar numbers of participating nucleons are
considered for the Cu+Cu and Au+Au data, an indication of increased bulk
strangeness production and a higher mid-pT (1 -> 4.5 GeV/c) Lambda/K0Short
ratio are found, for Cu+Cu.Comment: Quark Matter 2006 Proceeding
Ocean acidification in the aftermath of the Marinoan glaciation
Boron isotope patterns preserved in cap carbonates deposited in the aftermath of the younger Cryogenian (Marinoan, ca. 635 Ma) glaciation confirm a temporary ocean acidification event on the continental margin of the southern Congo craton, Namibia. To test the significance of this acidification event and reconstruct Earth’s global seawater pH states at the Cryogenian-Ediacaran transition, we present a new boron isotope data set recorded in cap carbonates deposited on the Yangtze Platform in south China and on the Karatau microcontinent in Kazakhstan. Our compiled δ11B data reveal similar ocean pH patterns for all investigated cratons and confirm the presence of a global and synchronous ocean acidification event during the Marinoan deglacial period, compatible with elevated postglacial pCO2 concentrations. Differences in the details of the ocean acidification event point to regional distinctions in the buffering capacity of Ediacaran seawater
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