7,728 research outputs found
Quantum Mechanics as a Framework for Dealing with Uncertainty
Quantum uncertainty is described here in two guises: indeterminacy with its
concomitant indeterminism of measurement outcomes, and fuzziness, or
unsharpness. Both features were long seen as obstructions of experimental
possibilities that were available in the realm of classical physics. The birth
of quantum information science was due to the realization that such
obstructions can be turned into powerful resources. Here we review how the
utilization of quantum fuzziness makes room for a notion of approximate joint
measurement of noncommuting observables. We also show how from a classical
perspective quantum uncertainty is due to a limitation of measurability
reflected in a fuzzy event structure -- all quantum events are fundamentally
unsharp.Comment: Plenary Lecture, Central European Workshop on Quantum Optics, Turku
2009
Observation of electron-antineutrino disappearance at Daya Bay
The Daya Bay Reactor Neutrino Experiment has measured a non-zero value for
the neutrino mixing angle with a significance of 5.2 standard
deviations. Antineutrinos from six 2.9 GW reactors were detected in
six antineutrino detectors deployed in two near (flux-weighted baseline 470 m
and 576 m) and one far (1648 m) underground experimental halls. With a 43,000
ton-GW_{\rm th}-day livetime exposure in 55 days, 10416 (80376) electron
antineutrino candidates were detected at the far hall (near halls). The ratio
of the observed to expected number of antineutrinos at the far hall is
. A rate-only analysis
finds in a
three-neutrino framework.Comment: 5 figures. Version to appear in Phys. Rev. Let
Observation of charge asymmetry dependence of pion elliptic flow and the possible chiral magnetic wave in heavy-ion collisions
We present measurements of and elliptic flow, , at
midrapidity in Au+Au collisions at 200, 62.4, 39, 27,
19.6, 11.5 and 7.7 GeV, as a function of event-by-event charge asymmetry,
, based on data from the STAR experiment at RHIC. We find that
() elliptic flow linearly increases (decreases) with charge asymmetry
for most centrality bins at and higher.
At , the slope of the difference of
between and as a function of exhibits a
centrality dependence, which is qualitatively similar to calculations that
incorporate a chiral magnetic wave effect. Similar centrality dependence is
also observed at lower energies.Comment: 6 pages, 4 figure
Observation of Transverse Spin-Dependent Azimuthal Correlations of Charged Pion Pairs in at GeV
We report the observation of transverse polarization-dependent azimuthal
correlations in charged pion pair production with the STAR experiment in
collisions at RHIC. These correlations directly probe quark
transversity distributions. We measure signals in excess of five standard
deviations at high transverse momenta, at high pseudorapidities eta>0.5, and
for pair masses around the mass of the rho-meson. This is the first direct
transversity measurement in p+p collisions. Comparing the results to data from
lepton-nucleon scattering will test the universality of these spin-dependent
quantities.Comment: 11 pages, 5 figures, 15 tables. Submitted to PR
Azimuthal anisotropy in U+U and Au+Au collisions at RHIC
Collisions between prolate uranium nuclei are used to study how particle
production and azimuthal anisotropies depend on initial geometry in heavy-ion
collisions. We report the two- and four-particle cumulants, and
, for charged hadrons from U+U collisions at =
193 GeV and Au+Au collisions at = 200 GeV. Nearly fully
overlapping collisions are selected based on the amount of energy deposited by
spectators in the STAR Zero Degree Calorimeters (ZDCs). Within this sample, the
observed dependence of on multiplicity demonstrates that ZDC
information combined with multiplicity can preferentially select different
overlap configurations in U+U collisions. An initial-state model with gluon
saturation describes the slope of as a function of multiplicity in
central collisions better than one based on Glauber with a two-component
multiplicity model.Comment: Final paper version accepted for publication in Phys. Rev. Lett. New
version includes comparisons to a constituent quark glauber mode
Centrality and transverse momentum dependence of elliptic flow of multi-strange hadrons and meson in Au+Au collisions at = 200 GeV
We present high precision measurements of elliptic flow near midrapidity
() for multi-strange hadrons and meson as a function of
centrality and transverse momentum in Au+Au collisions at center of mass energy
200 GeV. We observe that the transverse momentum dependence of
and is similar to that of and , respectively,
which may indicate that the heavier strange quark flows as strongly as the
lighter up and down quarks. This observation constitutes a clear piece of
evidence for the development of partonic collectivity in heavy-ion collisions
at the top RHIC energy. Number of constituent quark scaling is found to hold
within statistical uncertainty for both 0-30 and 30-80 collision
centrality. There is an indication of the breakdown of previously observed mass
ordering between and proton at low transverse momentum in the
0-30 centrality range, possibly indicating late hadronic interactions
affecting the proton .Comment: 7 pages and 4 figures, Accepted for publication in Physical Review
Letter
Studies of di-jet survival and surface emission bias in Au+Au collisions via angular correlations with respect to back-to-back leading hadrons
We report first results from an analysis based on a new multi-hadron
correlation technique, exploring jet-medium interactions and di-jet surface
emission bias at RHIC. Pairs of back-to-back high transverse momentum hadrons
are used for triggers to study associated hadron distributions. In contrast
with two- and three-particle correlations with a single trigger with similar
kinematic selections, the associated hadron distribution of both trigger sides
reveals no modification in either relative pseudo-rapidity or relative
azimuthal angle from d+Au to central Au+Au collisions. We determine associated
hadron yields and spectra as well as production rates for such correlated
back-to-back triggers to gain additional insights on medium properties.Comment: By the STAR Collaboration. 6 pages, 2 figure
Measurements of Dihadron Correlations Relative to the Event Plane in Au+Au Collisions at GeV
Dihadron azimuthal correlations containing a high transverse momentum (\pt)
trigger particle are sensitive to the properties of the nuclear medium created
at RHIC through the strong interactions occurring between the traversing parton
and the medium, i.e. jet-quenching. Previous measurements revealed a strong
modification to dihadron azimuthal correlations in Au+Au collisions with
respect to \pp\ and \dAu\ collisions. The modification increases with the
collision centrality, suggesting a path-length dependence to the jet-quenching
effect. This paper reports STAR measurements of dihadron azimuthal correlations
in mid-central (20-60\%) Au+Au collisions at \snn=200~GeV as a function of
the trigger particle's azimuthal angle relative to the event plane,
\phis=|\phit-\psiEP|. The azimuthal correlation is studied as a function of
both the trigger and associated particle \pt. The subtractions of the
combinatorial background and anisotropic flow, assuming Zero Yield At Minimum
(\zyam), are described. The away-side correlation is strongly modified, and the
modification varies with \phis, which is expected to be related to the
path-length that the away-side parton traverses. The pseudo-rapidity (\deta)
dependence of the near-side correlation, sensitive to long range \deta
correlations (the ridge), is also investigated. The ridge and jet-like
components of the near-side correlation are studied as a function of \phis.
The ridge appears to drop with increasing \phis while the jet-like component
remains approximately constant. ...Comment: 50 pages, 39 figures, 6 table
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