119,633 research outputs found
Observation of time-reversal violation in the B0 meson system
The individually named authors work collectively as The BABAR Collaboration. Copyright @ 2012 American Physical Society.Although CP violation in the B meson system has been well established by the B factories, there has been no direct observation of time-reversal violation. The decays of entangled neutral B mesons into definite flavor states (B0 or B¯¯¯0), and J/ψK0L or cc¯K0S final states (referred to as B+ or B−), allow comparisons between the probabilities of four pairs of T-conjugated transitions, for example, B¯¯¯0→B− and B−→B¯¯¯0, as a function of the time difference between the two B decays. Using 468×106 BB¯¯¯ pairs produced in Υ(4S) decays collected by the BABAR detector at SLAC, we measure T-violating parameters in the time evolution of neutral B mesons, yielding ΔS+T=−1.37±0.14(stat)±0.06(syst) and ΔS−T=1.17±0.18(stat)±0.11(syst). These nonzero results represent the first direct observation of T violation through the exchange of initial and final states in transitions that can only be connected by a T-symmetry transformation.DOE and NSF (USA), NSERC (Canada), CEA and CNRS-IN2P3 (France), BMBF and
DFG(Germany), INFN (Italy), FOM (The Netherlands),
NFR (Norway), MES (Russia), MINECO (Spain), STFC
(United Kingdom). Individuals have received support from
the Marie Curie EIF (European Union), the A. P. Sloan
Foundation (USA) and the Binational Science Foundation
(USA-Israel)
Beam energy dependent two-pion interferometry and the freeze-out eccentricity of pions in heavy ion collisions at STAR
We present results of analyses of two-pion interferometry in Au+Au collisions
at = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV measured in the
STAR detector as part of the RHIC Beam Energy Scan program. The extracted
correlation lengths (HBT radii) are studied as a function of beam energy,
azimuthal angle relative to the reaction plane, centrality, and transverse mass
() of the particles. The azimuthal analysis allows extraction of the
eccentricity of the entire fireball at kinetic freeze-out. The energy
dependence of this observable is expected to be sensitive to changes in the
equation of state. A new global fit method is studied as an alternate method to
directly measure the parameters in the azimuthal analysis. The eccentricity
shows a monotonic decrease with beam energy that is qualitatively consistent
with the trend from all model predictions and quantitatively consistent with a
hadronic transport model.Comment: 27 pages; 27 figure
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
Centrality dependence of identified particle elliptic flow in relativistic heavy ion collisions at sqrt(s)= 7.7--62.4 GeV
Elliptic flow (v_2) values for identified particles at midrapidity in Au + Au
collisions measured by the STAR experiment in the Beam Energy Scan at the
Relativistic Heavy Ion Collider at sqrt{s_{NN}}= 7.7--62.4 GeV are presented
for three centrality classes. The centrality dependence and the data at
sqrt{s_{NN}}= 14.5 GeV are new. Except at the lowest beam energies we observe a
similar relative v_2 baryon-meson splitting for all centrality classes which is
in agreement within 15% with the number-of-constituent quark scaling. The
larger v_2 for most particles relative to antiparticles, already observed for
minimum bias collisions, shows a clear centrality dependence, with the largest
difference for the most central collisions. Also, the results are compared with
A Multiphase Transport Model and fit with a Blast Wave model.Comment: 14 pages, 12 figures, Phys. Rev. C, to be published. Data tables
available at
https://drupal.star.bnl.gov/STAR/publications/centrality-dependence-identified-particle-elliptic-flow-relativistic-heavy-ion-collisi
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
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
production at low transverse momentum in p+p and d+Au collisions at = 200 GeV
We report on the measurement of production in the dielectron
channel at mid-rapidity (|y|<1) in p+p and d+Au collisions at =
200 GeV from the STAR experiment at the Relativistic Heavy Ion Collider. The
transverse momentum spectra in p+p for < 4 GeV/c and d+Au
collisions for < 3 GeV/c are presented. These measurements extend the
STAR coverage for production in p+p collisions to low .
The from the measured invariant cross section in
p+p and d+Au collisions are evaluated and compared to similar measurements at
other collision energies. The nuclear modification factor for is
extracted as a function of and collision centrality in d+Au and
compared to model calculations using the modified nuclear Parton Distribution
Function and a final-state nuclear absorption cross section
Observation and study of baryonic B decays: B -> D(*) p pbar, D(*) p pbar pi, and D(*) p pbar pi pi
We present a study of ten B-meson decays to a D(*), a proton-antiproton pair,
and a system of up to two pions using BaBar's data set of 455x10^6 BBbar pairs.
Four of the modes (B0bar -> D0 p anti-p, B0bar -> D*0 p anti-p, B0bar -> D+ p
anti-p pi-, B0bar -> D*+ p anti-p pi-) are studied with improved statistics
compared to previous measurements; six of the modes (B- -> D0 p anti-p pi-, B-
-> D*0 p anti-p pi-, B0bar -> D0 p anti-p pi- pi+, B0bar -> D*0 p anti-p pi-
pi+, B- -> D+ p anti-p pi- pi-, B- -> D*+ p anti-p pi- pi-) are first
observations. The branching fractions for 3- and 5-body decays are suppressed
compared to 4-body decays. Kinematic distributions for 3-body decays show
non-overlapping threshold enhancements in m(p anti-p) and m(D(*)0 p) in the
Dalitz plots. For 4-body decays, m(p pi-) mass projections show a narrow peak
with mass and full width of (1497.4 +- 3.0 +- 0.9) MeV/c2, and (47 +- 12 +- 4)
MeV/c2, respectively, where the first (second) errors are statistical
(systematic). For 5-body decays, mass projections are similar to phase space
expectations. All results are preliminary.Comment: 28 pages, 90 postscript figures, submitted to LP0
Measurements of Weak Decay Asymmetries of , , , and
Using production from a 567 pb
data sample collected by BESIII at 4.6 GeV, a full angular analysis is carried
out simultaneously on the four decay modes of , , , and . For the first time, the
transverse polarization is studied in unpolarized
collisions, where a non-zero effect is observed with a statistical significance
of 2.1. The decay asymmetry parameters of the weak
hadronic decays into , , and
are measured to be ,
,
, and
, respectively. In comparison with
previous results, the measurements for the and
modes are consistent but with improved precision, while the parameters for the
and modes are measured for the first time
Evolution of swelling pressure of cohesive-frictional, rough and elasto-plastic granulates
The subject of this study is the modeling of the evolution of the swell-ing pressure of granulates with cohesive-frictional, rough and elasto-plastic “mi-croscopic” contact properties. The spherical particles are randomly arranged in a periodic cubic space with a fixed volume so that an increase of the particle size – i.e. swelling that can be caused by intake of some fluid – is accompanied by a de-crease of the void space. An analytical function is proposed that properly de-scribes the (macroscopic) void ratio as function of pressure for different micro-scopic contact properties
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