493 research outputs found
Elliptic flow of electrons from heavy-flavor hadron decays in Au+Au collisions at 200, 62.4, and 39 GeV
We present measurements of elliptic flow () of electrons from the decays
of heavy-flavor hadrons () by the STAR experiment. For Au+Au collisions
at 200 GeV we report , for transverse momentum
() between 0.2 and 7 GeV/c using three methods: the event plane method
({EP}), two-particle correlations ({2}), and four-particle
correlations ({4}). For Au+Au collisions at = 62.4 and
39 GeV we report {2} for GeV/c. {2} and {4} are
non-zero at low and intermediate at 200 GeV, and {2} is consistent
with zero at low at other energies. The {2} at the two lower beam
energies is systematically lower than at 200 GeV for
GeV/c. This difference may suggest that charm quarks interact less
strongly with the surrounding nuclear matter at those two lower energies
compared to GeV.Comment: Version accepted by PR
Isolation of Flow and Nonflow Correlations by Two- and Four-Particle Cumulant Measurements of Azimuthal Harmonics in 200 GeV Au+Au Collisions
A data-driven method was applied to measurements of Au+Au collisions at
200 GeV made with the STAR detector at RHIC to isolate
pseudorapidity distance -dependent and -independent
correlations by using two- and four-particle azimuthal cumulant measurements.
We identified a component of the correlation that is -independent,
which is likely dominated by anisotropic flow and flow fluctuations. It was
also found to be independent of within the measured range of
pseudorapidity . The relative flow fluctuation was found to be for particles of transverse momentum
less than GeV/. The -dependent part may be attributed to
nonflow correlations, and is found to be relative to the
flow of the measured second harmonic cumulant at
Charged-to-neutral correlation at forward rapidity in Au+Au collisions at =200 GeV
Event-by-event fluctuations of the ratio of inclusive charged to photon
multiplicities at forward rapidity in Au+Au collision at =200
GeV have been studied. Dominant contribution to such fluctuations is expected
to come from correlated production of charged and neutral pions. We search for
evidences of dynamical fluctuations of different physical origins. Observables
constructed out of moments of multiplicities are used as measures of
fluctuations. Mixed events and model calculations are used as baselines.
Results are compared to the dynamical net-charge fluctuations measured in the
same acceptance. A non-zero statistically significant signal of dynamical
fluctuations is observed in excess to the model prediction when charged
particles and photons are measured in the same acceptance. We find that, unlike
dynamical net-charge fluctuation, charge-neutral fluctuation is not dominated
by correlation due to particle decay. Results are compared to the expectations
based on the generic production mechanism of pions due to isospin symmetry, for
which no significant (<1%) deviation is observed.Comment: 14 pages, 6 figure
Measurement of the mass difference and the binding energy of the hypertriton and antihypertriton
According to the CPT theorem, which states that the combined operation of
charge conjugation, parity transformation and time reversal must be conserved,
particles and their antiparticles should have the same mass and lifetime but
opposite charge and magnetic moment. Here, we test CPT symmetry in a nucleus
containing a strange quark, more specifically in the hypertriton. This
hypernucleus is the lightest one yet discovered and consists of a proton, a
neutron, and a hyperon. With data recorded by the STAR
detector{\cite{TPC,HFT,TOF}} at the Relativistic Heavy Ion Collider, we measure
the hyperon binding energy for the hypertriton, and
find that it differs from the widely used value{\cite{B_1973}} and from
predictions{\cite{2019_weak, 1995_weak, 2002_weak, 2014_weak}}, where the
hypertriton is treated as a weakly bound system. Our results place stringent
constraints on the hyperon-nucleon interaction{\cite{Hammer2002,
STAR-antiH3L}}, and have implications for understanding neutron star interiors,
where strange matter may be present{\cite{Chatterjee2016}}. A precise
comparison of the masses of the hypertriton and the antihypertriton allows us
to test CPT symmetry in a nucleus with strangeness for the first time, and we
observe no deviation from the expected exact symmetry
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